Abstract: An electronic concentration control system in which a first exhaust gas composition sensor located in an exhaust pipe downstream from a catalytic converter is connected to an input to a P.I. circuit which generates a control output signal comprising a succession of opposing triangular ramps. The system includes a second exhaust gas composition sensor located in the exhaust pipe upstream from the catalytic converter generating a signal which is fed to a proportional integral circuit whose integrating and multiplying coefficients are altered on the basis of the control signal. The system includes a diagnostic circuit which checks the efficiency of the first and second sensors.

Abstract: An air-fuel ratio sensor deterioration-detecting system is provided for an internal combustion engine having first and second air-fuel ratio sensors arranged in the exhaust system upstream and downstream of a catalytic converter therein. An ECU calculates a control parameter, based on an output from the second air-fuel ratio sensor, calculates an air-fuel ratio correction amount, based on an output from the first air-fuel ratio sensor and the calculated control parameter, and executes air-fuel ratio feedback control, based on the calculated air-fuel ratio correction amount.

Abstract: A feedback control system for an internal combustion engine that employs a combustion condition sensor for feedback control. The output of the sensor is checked periodically, either by changing the fuel-air ratio and determining if the output changes or by seeing if the output is constant during periods of constant running conditions; and if the sensor is determined to be inaccurate, another control method is employed.

Abstract: An O.sub.2 -sensor fault diagnosis method and apparatus for detecting a fault of an O.sub.2 -sensor when a feedback control of a fuel supply to an engine is performed by making use of the output of an O.sub.2 -sensor and detecting and identifying a fault of the O.sub.2 -sensor even in the case where the feedback control is invalidated. A microcomputer (24) receives an output of an O.sub.2 -sensor (19) for detecting concentration of oxygen contained in an exhaust gas of an internal combustion engine (1). An ECU (20) controls a quantity of fuel supplied to the internal combustion engine (1) through feedback control in dependence on an output signal of the O.sub.2 -sensor (19). A first decision circuit is provided for deciding whether or not the O.sub.2 -sensor (19) exhibits abnormality on the basis of the output signal state of the O.sub.

Abstract: An air-fuel ratio control system for an internal combustion engine has an exhaust gas component concentration sensor having a sensor element and arranged in the exhaust system of the engine, for detecting concentration of a predetermined component present in exhaust gases emitted from the engine. An ECU controls the air-fuel ratio of an air-fuel mixture supplied to the engine, based on results of comparison between an output value from the sensor and a predetermined reference value, and detects deterioration of the exhaust gas component concentration sensor, based on the output value from the sensor. Engine operating condition sensors detect operating conditions of the engine. It is determined whether or not the engine is in a predetermined engine operating condition in which the sensor element temperature of the exhaust gas component concentration sensor lowers, based on outputs from the engine operating condition sensors.

Abstract: An apparatus to determine whether or not an air-fuel ratio sensor is fully activated is provided. In the apparatus according to the present invention, first, the point of the start of the fluctuation of the output voltage of the air-fuel ratio sensor is detected, and thereafter the fully activated state of the air-fuel ratio sensor is determined by detecting the point when the accumulated value of the difference between the present heater resistance and the standard heater resistance after the above point of the start of the fluctuation of the output voltage of the air-fuel ratio sensor, exceeds a predetermined threshold.

Abstract: A self-diagnostic apparatus of an air-fuel ratio control system of an internal combustion engine performs processes of starting the diagnostic process as the fuel-cut is started, reading and storing a sensor output at the start of the fuel-cut and counting an elapsed time after the start of the fuel-cut by actuating a timer, reading a time until when the sensor output rises from the start of the fuel-cut from the count value of the timer, calculating a rate of change of the sensor output and comparing the calculated rate of change with an abnormality determining value. When the rate of change is large, the response characteristic of the sensor is normal. When it is small, the response characteristic of the sensor is abnormal (degraded), so that the abnormality of the sensor is stored in a memory and an alarm lamp is lighted to inform a driver of the abnormality of the sensor.

Abstract: A feedback fuel control circuit for an engine to maintain a stoichiometric fuel/air ratio through adjustment of the fuel supply system. The system operates with a sensor that does not output a signal until the engine temperature is more than a predetermined temperature. Therefore, during the times when the output engine combustion sensor is not at its operating temperature the feedback control is disabled and a lean fuel air mixture is supplied to the engine. This mixture is temporarily enriching during the warmup cycle to determine if the combustion sensor outputs a signal and when it does the system switches to feedback control.

Abstract: An air-fuel ratio sensor deterioration-detecting system for an internal combustion engine includes a catalytic converter arranged in the exhaust system, first and second air-fuel ratio sensors arranged in the exhaust system at respective locations upstream and downstream of the catalytic converter, and an ECU which calculates a value of a first control parameter, based on an output from the second air-fuel ratio sensor, and executes air-fuel ratio feedback control, based on the calculated value of the first control parameter. A value of a second control parameter to be used for calculating the value of the first control parameter is calculated based on the output from the second air-fuel ratio sensor. Whether the second air-fuel ratio sensor is deteriorated is determined based on the output from the second air-fuel ratio sensor.

Abstract: A gaseous fueled engine and method for controlling the gaseous fuel supply using a feedback control to maintain a stoichiometric mixture under all normal running conditions. The feedback control is discontinued under certain running conditions and control is provided in another method so as to accommodate situations such as starting, conditions when the catalyst associated with the engine is overheated, conditions when the engine is running at wide open throttle to avoid the possibility of catalyst overheating and conditions of rapid deceleration so as to reduce the fuel supply and avoid overly rich exhaust gases when the engine is operating as a pump under extreme deceleration.

Abstract: Internal combustion engine control apparatus determines activation status of the O.sub.2 sensor and feasibility of feedback control. If the O.sub.2 sensor is activated and the feedback control is feasible, the apparatus computes a corrected fuel injection duration TAU based on feedback control using detected O.sub.2 concentration. For EGR control, the apparatus selects one of the two maps to retrieve EGR valve opening data based on the feasibility of feedback control, thus achieving an EGR flow in accordance with the selected air-fuel ratio control mode. The combination of the air-fuel ratio control and the EGR control achieves reduction of harmful exhaust gas components and stabilization of engine operation during an initial period after the start of engine operation.

Abstract: In an internal combustion engine with oxygen sensors provided respectively upstream and downstream of an exhaust purification catalytic converter, the air-fuel ratio is feedback controlled based on an output of the second oxygen sensor only. When in this control situation, an output period of the first oxygen sensor becomes longer than that of the second oxygen sensor, response deterioration of the first oxygen sensor is judged to have occurred. Once the occurrence of response deterioration is determined, a proportional operating amount used in a proportional control of an air-fuel ratio feedback correction coefficient LMD for air-fuel ratio feedback control using the first oxygen sensor, is corrected in proportion to the response deterioration to thereby correct a deviation of the air-fuel ratio control point.

Abstract: With an air-fuel ratio control apparatus for an internal combustion engine wherein oxygen sensors are respectively arranged upstream and downstream of an exhaust gas purification catalytic converter, air-fuel ratio feedback control is carried out for diagnosis using only the downstream oxygen sensor. When during diagnostic air-fuel ratio feedback control, phase differences of output fluctuations of the two oxygen sensors are below a predetermined value, deterioration of the catalytic converter is judged. A judgment level is variably set based on the results of the deterioration diagnosis of the catalytic converter, and deterioration of response of the downstream oxygen sensor is diagnosed by comparing the output-period of the downstream oxygen sensor with the set judgment level.

Abstract: Several embodiments of engines and systems for fueling engines to reduce the emission of unwanted exhaust gas constituents and to improve the fuel economy of the engine. A catalytic converter is provided in the exhaust system and a gaseous fuel is used at least during starting so as to bring the catalytic converter up to its operating temperature rapidly without necessitating the provision of an enriched fuel/air mixture. An oxygen sensor is employed in the exhaust system and a feedback control system varies the fuel/air ratio of the engine during its running in response to the output of the oxygen sensor. In order to test that the oxygen sensor is at its operating condition before feedback control is initiated, a rich fuel mixture is supplied and this rich fuel mixture is discontinued immediately upon the receipt of a signal from the oxygen sensor indicating that a rich mixture exits. Applications of the principal to both air valve type of carburetors and conventional carburetors are disclosed.

Abstract: A process for indicating abnormal conditions in a motor vehicle by inducing misfires through the absence of fuel supply. The fuel supply is interrupted cylinder by cylinder in such a manner that the supply is interrupted during a proportion of the total number of injection cycles of the respective cylinders during a first fuel supply sequence, after which the next cylinder interrupts the fuel supply for a proportion of the total number of injection cycles of that cylinder during a subsequent fuel supply sequence. The interruptions of the fuel supply take place preferably as a predetermined number of injection cycles during a fuel supply sequence, and when each injection supply sequence is of equal length or includes a certain number of injection cycles. This can give rise to a distinct signal quality from the engine, in the form of irregular, uncomfortable engine running, while each individual cylinder is subjected to the least possible disturbance, apart from an ideal operating condition.

Abstract: An air-fuel ratio control system for an internal combustion engine comprises an exhaust gas component concentration sensor arranged in the exhaust system of the engine, for detecting concentration of oxygen present in exhaust gases emitted from the engine, and an ECU which controls the air-fuel ratio of an air-fuel mixture to be supplied to the engine, based on the difference between an output value from the exhaust gas component concentration sensor and a predetermined reference value, and detects deterioration of the exhaust gas component concentration sensor, based on the output value from the exhaust gas component concentration sensor. When the deterioration of the exhaust gas component concentration sensor is detected, a deterioration display signal is outputted, while whether execution of air-fuel ratio control is to be inhibited or to be continued is determined based on the deterioration degree of the exhaust gas component concentration sensor.

Abstract: A method and system for reducing emissions from an engine during periods of partial or total heated exhaust gas oxygen (HEGO) sensor failure. A switch point is stored in an electronic engine control for use in controlling the fuel delivered to the engine based on the value of the signal generated by the oxygen sensor relative to the switch point. The method includes the step of sensing the current of the heater element of the HEGO sensor. The sensed current is compared to a first predetermined current threshold which indicates a degradation of the HEGO sensor. A degradation of the HEGO sensor introduces a bias signal to the electronic engine control. If the current of the heater element is below the first predetermined current threshold but not below a second predetermined current threshold, the switch point is changed so as to compensate for degradation of the oxygen sensor.

Abstract: Air/fuel and ignition control of engine (28) are used to more rapidly heat-up a catalytic converter (52). A control system (8) generates a fuel command (100) for fuel delivery to the engine (28) based upon at least an amount of air inducted into the engine. The fuel command is offset by a predetermined amount in a lean direction during a period after engine start to shift the engine exhaust gas mixture towards a preselected air/fuel ratio lean of stoichiometry (106-122). In addition, the fuel command is corrected by a correction value so that the exhaust gas mixture is shifted ore closely to the preselected air/fuel ratio (126-140). Correction values are adaptively learned (300-324) during a portion of the warm-up period from a feedback signal derived from an exhaust gas oxygen sensor (44). Ignition timing and engine idle are also controlled (350-374) to further achieve more rapid warm-up of the catalytic converter (52).

Abstract: An oxygen sensor deterioration-detecting system for an internal combustion engine having a plurality of groups of cylinders groups, an exhaust system having a plurality of exhaust passages extending, respectively, from the cylinder groups, and catalytic converters arranged in the exhaust system, and a plurality of upstream oxygen sensors arranged, respectively, in the exhaust passages at locations upstream of the catalytic converters, includes a single downstream oxygen sensor arranged in a confluent portion of the exhaust passages at a location downstream of the catalytic converters, for detecting the mixed air-fuel ratio of exhaust gases emitted from the cylinder groups.

Abstract: A feedback fuel control circuit for a gaseous fuel engine to maintain a stoichiometric fuel/air ratio through adjustment of an air bleed in the fuel supply circuit. The system operates with a sensor that does not output a signal until the engine temperature is more than a predetermined temperature. Therefore, during the times when the output engine combustion sensor is not at its operating temperature the feedback control is disabled and a lean fuel air mixture is supplied to the engine. This mixture is temporarily enriching during the warmup cycle to determine if the combustion sensor outputs a signal and when it does the system switches to feedback control.

Abstract: A method for distinguishing sources of error in a mixture formation or mixture regulating system of an internal combustion engine having an exhaust system with a lambda regulator and a heated lambda sensor is disclosed. A value of a sensor voltage is continuously measured. The value of the sensor voltage is compared with a lower diagnostic limit value and an upper diagnostic limit value. A lambda regulator value of the lambda regulator is varied in an enriching direction to a maximum lambda regulation limit if the lower diagnostic limit value fails to be attained, and the lambda regulator value is varied in a leaning down direction to a minimum lambda regulation limit if the upper diagnostic limit value is exceeded.

Abstract: An air-fuel ratio control system for an internal combustion engine in which an exhaust sensor is located in an exhaust path of the internal combustion engine. A control means provides feedback control to match an air-fuel ratio with a target value in accordance with a detection signal from the exhaust sensor. The control means is provided with a correction section which, upon fulfillment of predetermined implementation conditions of correction determination, detects a response time that elapses from the occurrence of a change in an operating state of the internal combustion engine until the detection signal from the exhaust sensor issues a determination signal value. The correction section governing the feedback control of the air-fuel ratio corrects the feedback control in accordance with the detected response time.

Abstract: An engine monitoring system and/or emission reduction system is provided for use in conjunction with an internal combustion engine. The system includes a plurality of sensors which detect various engine operating conditions and in which each sensor generates an output signal representative of its particular engine operating condition. At least one of these sensors is a gas sensor associated with the exhaust system which produces an output signal indicative of the concentration of nitric oxides in the exhaust emissions and which has an output which varies as a function of the concentration of such nitric oxides. A central processing unit receives inputs from the various engine sensors and, in accordance with preprogrammed algorithms, monitors the engine for failure and/or deterioration of various components in the emission reduction system as well as the various engine sensors.

Abstract: A failure determination method for an O.sub.2 sensor is provided wherein the air-fuel ratio of a mixture is maintained at a value which produces a leaner or richer air-fuel ratio than a stoichiometric ratio by a predetermined value, for a predetermined time after an engine starts operating in an idle region, to thereby make the oxygen concentration of exhaust gas surrounding the O.sub.2 sensor uniform. Subsequently, the air-fuel ratio is forcibly subjected to an oscillatory change with a predetermined amplitude of .+-.10 to 15% of the stoichiometric ratio with respect to the stoichiometric ratio at a predetermined frequency of several Hz, to determine abnormality of the O.sub.2 sensor based on the change of the output voltage of the O.sub.2 sensor.

Abstract: A failure detection system for an air-to-fuel ratio control system includes a exhaust gas monitor positioned upstream of a catalytic converter for monitoring an emission content of exhaust gas based on which an air-to-fuel ratio is feedback controlled so as to be maintained at a desired ratio. The system has another exhaust gas monitor positioned downstream of the catalytic converter for monitoring an emission content of exhaust gas passed through the catalytic converter. Functional failures of the exhaust gas monitor of the air-to-fuel ratio control system is judged to be present on the basis of detected emission contents only when a predetermined threshold amount of intake air is detected.

Abstract: An apparatus and method for controlling an air/fuel mixture ratio for an internal combustion engine which can start the air/fuel mixture ratio at a earlier timing than the conventional air/fuel mixture ratio controlling apparatus. For example, a control unit determines whether the engine is revolved and, thereafter, accumulates an intake air quantity. When the accumulated value exceeds the predetermined value SQ.sub.ST and the control unit determines that the activation of an oxygen sensor sufficiently occurs, the start of the air/fuel mixture ratio feedback control is determined. At this time, a fuel supply quantity T.sub.I is corrected so that the air/fuel mixture ratio which tends to be inclined to a lean side is shifted to the rich side.

Abstract: A system for controlling the supply of fuel to a multiple cylinder, two cycle, crankcase compression, internal combustion engine wherein air flow is normally measured by a pressure sensor in the crankcase chamber of only one of the cylinders. When an abnormal condition is sensed, the supply of fuel to the cylinder associated with the pressure sensor is discontinued and in some embodiments, the control of the fuel to the other cylinders is accomplished by means other than pressure sensing.

Abstract: The invention relates to an arrangement for monitoring the performance loss of an oxygen probe arranged forward of a catalytic converter. The oxygen probe supplies an actual voltage U.sub.-- ACT for a lambda controller for an internal combustion engine and the arrangement includes: a computation unit for computing the time-dependent mean value .vertline.U.sub.-- ACT-U.sub.-- DES .vertline. of the actual voltage U.sub.-- ACT from a desired voltage U.sub.-- DES; and, an evaluation unit for determining the performance loss of the oxygen probe on the basis of the time-dependent mean value. A simple method sequence which can be carried out with the above arrangement includes the step of deeming the probe to have an impermissibly high performance loss when the above-mentioned mean value drops below a threshold value. However, the quotient is preferably formed between the above-mentioned mean value and the mean value .vertline.FR.sub.-- ACT-FR.sub.-- DES.vertline.

Abstract: The air-furl ratio of an air-fuel mixture supplied to an internal combustion engine is controlled in response to an output from at least one oxygen sensor arranged in an exhaust passage for detecting concentration of oxygen present in exhaust gases. The deterioration of the at least one oxygen sensor is detected based on the output therefrom. When the engine is detected to be in a predetermined abnormal operating state, it is not permitted to monitor the output from the oxygen sensor for detecting deterioration thereof.

Abstract: A system for detecting a fault in an exhaust gas oxygen (EGO) sensor includes generating a first signal with a first voltage if the EGO sensor output signal is approaching an unacceptable voltage and a second voltage if the EGO sensor output signal has an unacceptable voltage. The system further includes setting a first flag if the first signal has the first voltage and a second flag, indicating an EGO sensor fault, if the first signal has the second voltage and the first flag is set.

Abstract: A fuel control system operating under closed-loop control senses the oxygen content of the combustion products of an internal combustion engine along with the engine angular velocity and air flow through the intake manifold. The fuel control system supplies an air/fuel modulation signal to modify a fueling value which is calculated as a function of the engine angular velocity and air flow. An oxygen sensor monitoring test is performed periodically to determine the efficacy of the oxygen sensor. The total switching time of the oxygen sensor, comprising the lean-to-rich and rich-to-lean switching times, is determined and checked against a range. If the total switching time is within the range then the difference between the lean-to-rich and rich-to-lean switching times, is determined and checked against a second range. If the difference is within the second range the oxygen sensor is determined to be operating effectively and the test is terminated.

Abstract: An air-fuel ratio sensor comprises an oxygen concentration cell device, an oxygen pump device, a heater for heating the oxygen concentration cell device and the oxygen pump device, a pump current cut means for stopping the supply of the pump current, first and second timers for controlling the condition of stopping the pump current, and a controller for starting the heating of the heater under the condition of stopping the pump current, to the pump device and for removing the stopping of the pump current for a predetermined time at predetermined intervals from the starting of supplying power to the heater, by means of the first timer, wherein when the pump current shows a predetermined value or higher, the pump current is stopped and the second timer is started, and when the operation of the second timer is finished, the judgment of the activation of the sensor is made, and at the same time, the stopping of the pump current is removed.

Abstract: An engine exhaust purification system is provided with a catalyst in an exhaust line, and oxygen sensors disposed in the exhaust line upstream and downstream from the catalyst, respectively. Deterioration of the catalyst is judged based on a frequency ratio of reversal of an output from the downstream oxygen sensor with respect to a threshold value to an output from the upstream oxygen sensor with respect to a threshold value. The threshold value of the deteriorated oxygen sensor is changed so as to vary the frequency ratio of reversal.

Abstract: A failure detection system for an air-to-fuel ratio control system includes a exhaust gas monitor positioned upstream of a catalytic converter for monitoring an emission content of exhaust gas based on which an air-to-fuel ratio is feedback controlled so as to be maintained at a desired ratio. The system has another exhaust gas monitor positioned downstream of the catalytic converter for monitoring an emission content of exhaust gas passed through the catalytic converter. Functional failures of the exhaust gas monitor of the air-to-fuel ratio control system is judged to be present on the basis of detected emission contents only when a predetermined threshold amount of intake air is detected.

Abstract: An oxygen-sensor abnormality detecting device for detecting abnormalities in an Oz sensor for air-fuel ratio detection in an internal combustion engine. In exhaust passage 9, a converter 10 is installed which contains a three-way catalyst for removing three harmful components HC, CO, and NOx of automotive emission. In the catalytic converter 10, a catalyst temperature sensor 11 is installed which detects catalyst temperature of the converter. O.sub.2 sensors 12 and 13 are provided along the exhaust passage on the upstream side and the downstream side of the catalytic converter 10. For the O.sub.2 sensors 12 and 13, the heaters 12a and 13a are provided for promoting the activity of the O.sub.2 sensors 12 and 13. Control circuit 15 checks the catalyst temperature and compares output voltages of the Oz sensors with reference levels under an inactive temperature state of the catalytic converter.

Abstract: A control device for an internal combustion engine detects the air fuel ratio of the internal combustion engine at a condition with high accuracy and responsibility. Accordingly, improvement of the fuel consumption of the engine, improvement of the power of the engine, and improvement of the exhaust gas are achieved. The control device for an internal combustion engine calculates, in turn, a first air fuel ratio based on the fuel injection suction, a second air fuel ratio at the time when the gas is reached to the large area air fuel ratio sensor, and a third air fuel ratio at the time when the large area air fuel ratio sensor detects the air fuel ratio, according to the fuel amount calculated with respect to the difference between the sensed air fuel ratio and the objective air fuel ratio, to judge a jam of the large area air fuel ratio sensor by comparing the third air fuel ratio with the sensed air fuel ratio.

Abstract: This invention relates to an air-fuel ratio control system for an engine which can continuously detect the air-fuel ratio of the air-fuel mixture supplied to the engine using an air-fuel ratio sensor within a wide range including the theoretical air-fuel ratio, and can then, based on the sensor output, perform feedback correction of the air-fuel ratio to the theoretical air-fuel ratio or to another air-fuel ratio. The deterioration of the air-fuel ratio sensor is judged based on the difference between the feedback correction coefficient when feedback control is performed to the theoretical air-fuel ratio, and the feedback correction coefficient when it is performed to another air-fuel ratio. Deterioration of the sensor is thereby detected completely separate from scatter or deterioration of performance of the fuel injector or other components.

Abstract: An exhaust purification apparatus for an engine uses a catalytic converter provided in an exhaust system of the engine. First and second exhaust sensors are provided on upstream and downstream sides, respectively, of the catalyst converter in the exhaust system. Detected values from the first and second exhaust sensors are used for feed back control of air fuel ratio and judging deterioration of the catalyst of the catalytic converter, respectively. A control constant of the air fuel ratio of the feed back control is changed so that the second exhaust sensor detects in accordance with a condition of the catalyst.

Abstract: An on-board oxygen sensor monitoring system includes measuring a first limit cycle of air/fuel controller operation, changing operating parameters of the air/fuel controller and measuring a second limit cycle with the new calibration of the controller. A time constant of the oxygen sensor is calculated as a function of the first and second limit cycle periods and compared to a maximum response rate.

Abstract: A fuel injection control system for a two cycle crankcase compression internal combustion engine wherein two sensors are provided for sensing air flow by measuring different engine running conditions. One sensor has a greater accuracy in a certain range of operation than the other and the system primarily sets the fuel injection based upon the output of the more sensitive sensor for the running condition. In the event of failure of the more sensitive sensor, the system defaults to control by the other sensor. The system bases the control on average readings over a number of cycles and also senses fault by determining when a sensor outputs a number of erroneous signals that are greater than a predetermined percentage.

Abstract: An air fuel ratio control system for an internal combustion engine having an electronic engine control module and an upstream and a downstream exhaust gas oxygen sensor positioned in the engine exhaust gas stream. A first feedback loop includes the upstream EGO sensor and an air fuel bias table. A second feedback loop includes a downstream EGO sensor and a trim signal to change the stored values in the air fuel bias table.

Abstract: A feedback type air-fuel ratio control system controls the air-fuel ratio of air-fuel mixture fed to an internal combustion engine in accordance with an information signal issued from a first oxygen sensor installed in an exhaust line of the engine. The exhaust line has a catalytic converter at a position downstream of the first oxygen sensor. There is further provided a system in the control system, which detects deterioration of the first oxygen sensor. The system comprises a computer and a second oxygen sensor of delayed response type installed in the exhaust line at a position upstream of the converter. The computer defines higher and lower slice levels with respect to the output of the second oxygen sensor and compares the output of the second oxygen sensor with the higher and lower slice levels.

Abstract: An exhaust purification system has an upstream exhaust gas sensor and a downstream exhaust gas sensor disposed downstream of a catalytic device. Each sensor detects an oxygen concentration in exhaust gases and provides an output which inverts between a lean state, representative of a lean air/fuel ratio, and a rich state, representative of a rich air/fuel ratio, according to oxygen concentrations. The upstream exhaust sensor is determined to have deteriorated when an output from the upstream exhaust sensor is kept in a predetermined correlation with an output from the downstream exhaust sensor while the output from the downstream exhaust sensor remains the same.

Abstract: A control unit for controlling an injection amount of a fuel injection valve and performing an air-fuel ratio control of an engine has an oxygen sensor for detecting an air-fuel ratio in an exhaust outlet and an electrode plug for measuring a flame resistance value in a combustion chamber. The control unit calculates a reference air-fuel ratio from an average value of the minimum values of the flame resistance measured by the electrode plug, obtains a correction coefficient from the air-fuel ratio detected by the oxygen sensor and the reference air-fuel ratio, and then corrects the air-fuel ratio detected by the oxygen sensor. The control unit performs the air-fuel ratio control of the engine based on the corrected air-fuel ratio.

Abstract: Oxygen sensor deterioration is detected by initially counting the number of fuel units required to change the output voltage of a nondeteriorated sensor between first and second voltages, and subsequently counting the number of fuel units required to change the output voltage of the sensor between the first and second voltages, as the sensor ages, until a subsequent count exceeds the initial count by a given amount. The method detects when the air/fuel ratio desired for normal engine operation drifts outside acceptable tolerance. The method detects and stores a first difference between air/fuel ratios, corresponding to first and second sensor output voltages, and then subsequently detects a second difference between air/fuel ratios, corresponding respectively to the first and second sensor output voltages. When the second difference exceeds the first difference by a given amount, deterioration is indicated.

Abstract: An air/fuel control system for use with an internal combustion engine which is adapted to burn fuels having different combustion characteristics. The control system compensates for errors in the fuel-type signal produced by a sensor and provides a failure mode of operation when the sensor fails. A closed-loop air/fuel mixture controller responds to sensed exhaust oxygen levels to maintain combustion near stoichiometry. When the errors from the fuel type sensor predominate, at high engine speed and load, a selected one of two fuel-type variables, is adaptively modified. The first variable is modified in response to the control system's inability to achieve stoichiometry during high speed/high load operation, a condition which causes the first variable to correct the fuel type signal from the sensor. The second variable assumes control when the first variable is unable to achieve stoichiometry, indicating sensor failure, and is updated in accordance with a more vigorous strategy.

Abstract: In a device for feedback control of an air/fuel ratio using an oxygen sensor for detecting oxygen concentration in exhaust gas, two different reference levels for diagnosis are set according to a detection signal level of the above oxygen sensor. And a response time with which the detection signal of the oxygen sensor crosses the above reference levels for diagnosis is measured so as to diagnose deterioration of the oxygen sensor based on comparison between the above measured response time and a predetermined response time.

Abstract: A self diagnosing apparatus and method for a fuel supply control system in an internal comustion engine are disclosed in which since an air/fuel mixture ratio feedback controlled variable is set so that an actual air/fuel mixture ratio is approached to a target (stoichiometric) air/fuel mixture ratio and movement (incremental or decremental change width) of the air/fuel mixture ratio feedback-controlled variable indicates a deviation of the actual air/fuel mixture ratio from the target air/fuel mixture ratio, a diagnosis of the air/fuel mixture ratio controlled state by means of the fuel supply control system is carried out on the basis of at least one of either a total sum of each magnitude by which the air/fuel mixture ratio feedback controlled variable is changed to enrich or enlean the air/fuel mixture ratio so as to approach it to the target air/fuel mixture ratio or a control duration of time during which the air/fuel mixture ratio feedback control variable is set to control the air/fuel mixture ratio.

Abstract: A system for controlling the air/fuel ratio input to a small engine measures the oxygen level in the engine's exhaust and compares it with a reference level. A stepper motor controls the air/fuel ratio and it is advanced one step each time a clock pulse is produced in a direction determined by the level of exhaust oxygen. A fault detector circuit stops the engine if the sensed oxygen level is outside a preset range for more than a preset time interval.

Abstract: A system for detecting deterioration of at least one HC sensor arranged in the exhaust passage of an internal combustion engine. There is calculated a difference between an actual value of output from the HC sensor and a predetermined reference value set in accordance with at least one parameter indicative of operating conditions of the engine, while the engine is in a predetermined operating condition. The difference is compared with a predetermined value. It is judged that there is deterioration in the HC sensor when the difference exceeds the predetermined value. In another aspect of the invention, the actual value of output from the HC sensor is corrected by a value of output from the HC sensor detected and stored when the fuel supply to the engine is cut off. Then, there is calculated a difference between the corrected actual value and the predetermined reference value.