Abstract: A method of feedback-controlling the air-fuel ratio of a mixture, supplied to an internal combustion engine, by at least one of proportional control and integral control in dependence upon the results of a comparison between the output of an exhaust gas concentration sensor and a predetermined reference value. The method includes obtaining the ratio of a first time period required for an output value from the exhaust gas concentration sensor to make a transition from a peak value on a rich side to a predetermined reference value with respect to the predetermined reference value, and a second time period required for the output value to make a transition from a peak value on a lean side to the predetermined reference value with respect to the predetermined reference value, and altering, in dependence upon the ratio obtained, at least one predetermined control factor applied to control of the air-fuel ratio.

Abstract: A secondary air intake system is used in an internal combustion engine. The system supplies secondary air through a first and a second secondary air passage. The first secondary air passage includes a first vacuum operated air control valve. A vacuum control which includes an electrically operated vacuum control valve operates the first vacuum operated air control valve to vary the effective area of the first secondary air passage. The second secondary air passage includes a second vacuum operated air control valve and an electrically operated air control valve positioned in series. Intake manifold vacuum operates the second vacuum operated air control valve to vary the effective area of the second secondary air passage.

Abstract: An air-fuel ratio control system for an internal combustion engine having an oxygen concentration sensor disposed in the exhaust system of the engine is provided with means for detecting a high load operation of the engine and an air-fuel ratio control signal is produced by comparing an output signal of the oxygen sensor with a first reference level corresponding to a stoichiometric value of the air-fuel ratio when the engine is operating under medium or low load condition and with a second reference level corresponding to an air-fuel ratio which is on the leaner side of the stoichiometric value when the engine is operating under the high load condition.

Abstract: A secondary air intake system is used in an internal combustion engine. The system supplies secondary air through a first and a second secondary air passage. The first secondary air passage includes a first vacuum operated air control valve. The second secondary air passage includes a second vacuum operated air control valve and an electrically operated air control valve positioned in series. A vacuum control which includes an electrically operated vacuum control valve operates the first and second vacuum operated air control valves to vary the effective area of the two air passages. An air-fuel ratio control which includes an intake air temperature sensor, an exhaust gas oxygen concentration sensor and a throttle plate vacuum sensor determines the engine air-fuel ratio to intermittently open and close the second electrically operated air control valve to open and close the second secondary air passage.

Abstract: The so called air intake side secondary air supply system for an internal combustion engine, having first and second secondary air supply passages leading to an intake air passage on downstream side of a throttle valve is, provided with a delay device in the second secondary air supply passage on upstream side of an open/close valve disposed in the second secondary air supply passage, a pressure supply passage which provides communication between a pressure chamber of an air control valve disposed in the first secondary air supply passage and a part of the second secondary air supply passage between the delay device and the open/close valve, and a pressure control means for supplying a pressure capable of reducing an opening degree of the air control valve into a part of the second secondary air supply passage between the open/close valve and the delay device in response to a predetermined operating condition of the engine.

Abstract: The so called air intake side secondary air supply system for an internal combustion engine, having first and second secondary air supply passages leading to an intake air passage on downstream side of a throttle valve is provided with a delay device in the second secondary air supply passage on upstream side of an open/close valve disposed in the second secondary air supply passage, and a pressure supply passage which provides communication between a pressure chamber of an air control valve disposed in the first secondary air supply passage and a part of the second secondary air supply passage between the delay device and the open/close valve. Thus, one of the secondary air supply passages is utilized as a passage for introducing a vacuum into the pressure chamber of the air control valve and the open/close valve is used as a switch device for switching over between the atmospheric pressure and the vacuum which are to be introduced into the pressure chamber of the air control valve.

Abstract: A fuel supply control system for a vehicle engine carburetor and particularly a carburetor that includes a variable venturi portion and fixed venturi or nozzle portion. The system includes a fuel valve for supplying additional fuel to the nozzle under low speed or high load conditions sensed by elements responsive to those conditions. The system also includes an air valve for controlling the air supplied to the nozzle and a sensor for closing the air valve to thereby also increase the fuel supplied to the nozzle under high load conditions. Other sensors of engine temperature also control the operation of the fuel and air valves.

Abstract: An air intake side secondary air supply system for an internal combustion engine equipped with an automatic choke valve and a fast idle system is provided with a detection means for detecting an operating condition of the engine in which the fast idle system is operated to open the throttle valve. The supply of the secondary air for the feedback control is stopped when a detection signal is produced by the detection means so that the feedback control of the air-fuel ratio is suspended when the throttle valve is opened by means of the fast idle system while the choke valve may be substantially closed. Thus, a hunting of the engine speed which might have occured after the start of the feedback control is prevented.

Abstract: An intake secondary air supply system for adding air to the intake of an internal combustion engine under certain sensed conditions, such as an excessively rich air-fuel ratio detected by an oxygen sensor in the exhaust system, wherein two separate secondary air supply passages are provided and separately controlled by vacuum responsive valves. One of such valves is controlled to open and close over a period of time to provide a changing supply of secondary air while the other valve is connected through a solenoid operated valve to the engine intake to provide an immmediate opening or closing of that secondary air supply. Vacuum controls responsive to engine operating condition serve to operate the vacuum responsive valves although in one embodiment one of such valves is operated by a constant regulated vacuum.

Abstract: A closed-loop air-fuel control system for an internal combustion engine comprising a control circuit having an open-loop mode of operation in which an air-fuel ratio control signal is fixed to a predetermined value determined by a sensed value of the atmospheric pressure and the temperature of the intake air of the engine. In order to shorten the time period for calculating the air-fuel ratio and to simplifying the circuit construction, an output signal of an atmospheric pressure sensor is supplied to an intake air temperature sensor so as to produce an output signal which represents both the temperature of the intake air and the atmospheric pressure at the same time.

Abstract: An improvement in an exhaust gas purification apparatus wherein a detector senses the operation of a device for injecting additional intake air into the intake passage and triggers a timing unit. The timing unit produces a signal for a predetermined amount of time which holds open a control valve for introducing secondary air into the exhaust passage ahead of the catalytic converter. This structure enables the reduction of harmful components of the exhaust gas produced during a gear-change operation of the engine without greatly overheating the catalytic converter.

Abstract: A method of controlling the recirculation of exhaust gases in an internal combustion engine provided with an exhaust-gas recirculation system by which the exhaust gases emitted from the exhaust manifold are partially recirculated into the intake manifold of the engine, comprising cutting off the recirculation of exhaust gases to the intake manifold of the engine when the engine is being warmed up, recirculating exhaust gases to the intake manifold of the engine at a rate variable in a predetermined required exhaust-gas recirculation ratio to the rate at which air is circulated to the intake manifold of the engine after the engine is warmed up, and recirculating exhaust gases to the intake manifold of the engine with a reduced exhaust-gas recirculation ratio lower than said required exhaust-gas recirculation ratio during a transient period of time intervening the conditions in which the engine is being warmed up and the conditions in which the engine has been warmed up.

Abstract: A system is disclosed for preventing overheating of a carburetor of the type which is placed with an intake manifold above an exhaust manifold. A heat insulating plate is disposed substantially horizontally between the intake manifold and the carburetor. This plate extends to substantially cover the area above the exhaust manifold. A substantially vertical plate extends upwardly from the heat insulating plate at an edge thereof most distant from the engine. A path is thereby created for the convection currents from the exhaust manifold to bypass the carburetor.