Abstract: In a heater control of an oxygen sensor, a heater control circuit is rendered fully conductive at 100% duty initially to supply full power to a heater until the resistance value of the heater reaches a predetermined initial value corresponding to a predetermined temperature. Then, the duty of the heater control circuit is feedback controlled so that the heater temperature becomes a target value until the internal resistance of the oxygen sensor reaches a target temperature, and further, after the internal resistance of the oxygen sensor S reaches the target temperature, the duty of the heater control circuit is feedback controlled so that the element temperature of the sensor becomes a target value.

Abstract: An air-fuel ratio control system for an internal combustion engine includes a pair of cylinder banks, a pair of exhaust passages connected to the cylinder banks, respectively, a common exhaust pipe where the exhaust passages join each other at their downstream ends, a pair of catalytic converters provided in the exhaust passages, respectively, a pair of main air-fuel ratio sensors provided in the exhaust passages upstream of the catalytic converters, respectively, a pair of auxiliary air-fuel ratio sensors provided in the exhaust passages downstream of the catalytic converters, respectively, and a catalytic converter provided in the common exhaust pipe. The system derives an air-fuel ratio feedback control correction value for each of the cylinder banks based on outputs of the auxiliary air-fuel ratio sensors.

Abstract: An assist air control system for an internal combustion engine introduces, via an assist air passage bypassing a throttle valve, a portion of intake air flowing in an intake pipe upstream of the throttle valve to an area where fuel is injected from a fuel injection valve, so as to facilitate atomization of the injected fuel. The assist air passage includes a flow control unit for opening and closing the assist air passage. The degree of opening of the assist air passage is limited to a value that is reduced as an engine temperature increases, while increased as an engine load increases. The opening degree of the flow control unit may be controlled electrically, mechanically, or both. In this case, the electrically controlled opening degree value is set smaller than the mechanically controlled opening degree value.

Abstract: For stable air-fuel ratio control without hunting, an output condition of an air-fuel ratio sensor is monitored to decide whether or not a modern or advanced control using a dynamic model may be performed. The appropriateness of using the dynamic model may be determined by monitoring whether the output value of an air-fuel ratio sensor exists in a predetermined range or whether the air-fuel ratio sensor is maintained stably in an air-fuel ratio detectable state. When the sensor output condition is out of the predetermined range suitable for the modern control, an optimum feedback gain for performing the modern control is switched over to a lowered gain or the modern control is switched over into normal feedback control by proportional-and-integral control. By this control mode switch-over, most appropriate air-fuel ratio feedback control may be performed.

Abstract: In a fuel injection system for an internal combustion engine, engine cylinders are divided into a plurality of cylinder groups. An air passage is provided for supplying mixing air to areas near injection holes of fuel injection valves so as to facilitate atomization of fuel injected from the respective fuel injection valves. The air passage is opened synchronously with a fuel injection of each fuel injection valve such that the mixing air is selectively distributed to the above-noted areas per cylinder group. The mixing air is distributed for such a cylinder group that includes the engine cylinder being injected with the fuel from the corresponding fuel injection valve. The air passage includes a branch portion for the distribution of the mixing air to the above-noted areas. Capacities of the air passage from the branch portion to the respective fuel injection valves may be set substantially equal to each other so as to further facilitate the atomization of the injected fuel.

Abstract: An oxygen concentration measuring device capable of significantly shortening the period of time during which oxygen concentration cannot be measured. When measuring the temperature of a sensor main body, a microcomputer determines the temperature of the sensor main body by estimating a saturation current starting from a current detected by a current detecting circuit in a period of time before current flowing through the sensor main body finishes rising, after the sensor main body has been negatively biased by a bias control circuit. The sensor main body is positively biased by the bias control circuit directly after the period of time has lapsed. The microcomputer determines an air fuel ratio by using current in a period of time before current flowing through the sensor main body due to the positive bias finishes decreasing.

Abstract: The present invention pertains to a method for producing a mixture including an injected engine fuel from an injector, a combustion engine intake-air and an evaporative gas from the engine fuel. The method includes the steps of measuring a characteristic of the evaporative gas and changing step for changing a mixing ratio of the evaporative gas to at least one of the injected engine fuel and the combustion engine intake-air, according to the measured characteristic of the evaporative gas, by changing a flow rate of the combustion engine intake-air.

Abstract: An ignition timing control system for an internal combustion engine which can perform fast catalyst warm-up operation and prevent stalling at the restart of the internal combustion engine at a low temperature is disclosed. This control system judges whether the engine is in the start state or not, whether the cooling water temperature is lower than the specified temperature or not, and whether the intake air temperature is higher than the preset temperature or not. When these judgments are all affirmative, the system further judges whether the time after the start has reached the control starting time or not, and then whether the engine is in the idle operation state or not. When these judgments are both affirmative, the system sets the target ignition timing retard amount and the ignition timing gradual change time according to the intake air temperature, and then actually performs the ignition timing control according to the target retard amount and gradual retard time.

Abstract: A fuel injection system for a multi-cylinder internal combustion engine is provided. This fuel injection system includes a plurality of fuel injection valves each arranged to inject fuel into an intake port of each cylinder of the engine, an air passage connected to a portion of an air intake passage leading to the intake ports, a plurality of branch air passages each communicating with a preselected portion around an injection nozzle of each fuel injection valve, an air control valve, connecting between the air passage and the plurality of branch air passages, for selectively introducing a portion of intake air in the air intake passage to the preselected portions around the injection nozzles of the fuel injection valves.

Abstract: A fuel vapor purging control system for an internal combustion engine is provided. This purging control system incorporates an air/fuel ratio compensating system which includes a purge control valve for controlling a purge flow rate of an air-fuel vapor mixture flowing into an induction system of the engine through a purge passage according to a preselected engine operating condition parameter, a sensor disposed in the purge passage for determining an amount of fuel in the air-fuel vapor mixture, an air/fuel ratio controller for modifying an amount of fuel in an air/fuel mixture injected through a fuel injection system of the engine based on the amount of fuel in the air-fuel vapor mixture determined by the sensor for assuring a desired air/fuel ratio of the air/fuel mixture entering a combustion chamber of the engine.

Abstract: An apparatus for detecting an abnormality of a fuel transpiration prevention system which includes a canister with an absorbing device and a control valve provided in a passage between a fuel tank and an intake pipe of an internal combustion engine so that a fuel gas generated within the fuel tank is absorbed by the absorbing device of the canister and introduced into the intake pipe by opening and closing the control valve in accordance with an operating state of said internal combustion engine. The apparatus includes a pressure detecting device for detecting a pressure within the fuel tank and a deviation calculating unit responsive to the output of the pressure detecting device for calculating a deviation between the pressure detected when the control valve opens the passage and the pressure detected when the control valve closes the passage. The apparatus decides an abnormality of the fuel gas supply system on the basis of the deviation calculated by the deviation calculating unit.

Abstract: There is disclosed a self-diagnosis apparatus in which when detecting a supply abnormally (i.e., failure to lead fuel evaporation gas into an intake passage), the abnormality can be accurately detected, taking into consideration variations in the fuel gas density (variations in the ambient temperature, variations in the volatility of the fuel, and etc.) due to the residual air in a fuel tank. In the apparatus, the amount of flow of the gas from the fuel tank to a canister can be detected, and a control circuit controls a purge valve to close a fuel gas discharge passage, and in this condition the control circuit detects the amount of flow of the gas from the fuel tank to the canister. When this flow amount exceeds a set value, the control circuit controls the purge valve to close and open the discharge passage, and judges in accordance with a change in an air-fuel ratio detected at this time by an O.sub.2 sensor whether or not any abnormality exists.