Abstract: An upstream-side catalyst is provided at a location in close to an exhaust manifold of an engine. An HC absorbent and a downstream-side catalyst are installed in series at the downstream side. With the upstream-side catalyst put in an inactive state, the HC absorbent absorbs HC having passing through the upstream-side catalyst. After the upstream-side catalyst has been activated, HC released from the HC absorbent is refluxed to the upstream side of the upstream-side catalyst through a reflux path to be removed by the upstream-side catalyst. At that time, the ECU executes catalyst-early-warming control right after an engine start in order to raise the temperature of the upstream-side catalyst at an early time so as to shorten the time it takes to activate the upstream-side catalyst.

Abstract: An emission control system has a catalyst and a sensor responding to a component of exhaust gas. In order to speed warming up the catalyst, the emission control system increases the amount of heat dissipated by exhaust gas. A diagnosis of the emission control system is carried out by determining whether the amount of heat dissipated by exhaust gas is sufficient or insufficient. The amount of heat dissipated by exhaust gas is represented by the length of time to an activated state of the sensor. In the diagnosis, the amount of heat generated by a heater provided in the sensor is taken into consideration. The diagnosis can also be carried out before and after the warming up the catalyst. The heater can also be deactivated. Detection of an abnormality of a secondary air control system can be based on a component of exhaust gas. If the amount of heat dissipated by exhaust gas is found insufficient, additional control can be executed.

Abstract: An upstream catalyst and a downstream catalyst are disposed in series in an exhaust pipe, and first through third sensors for detecting the air-fuel ratio or an adsorption amount of hazardous components on the rich/lean side of exhaust gases are disposed on the upstream and downstream sides of the upstream catalyst and the downstream side of the downstream catalyst, respectively. An ECU for controlling an engine controls the air-fuel ratio so that when the adsorption amount of the hazardous components on the rich side of the downstream catalyst is large, that of the hazardous components on the lean side of the upstream catalyst is large. Similarly, the ECU controls the air-fuel ratio so that when the adsorption amount of the hazardous components on the lean side of the downstream catalyst is large, that of the hazardous components on the rich side of the upstream catalyst is large.

Abstract: A plurality of catalysts are installed in an exhaust pipe, air-fuel ratio sensors or oxygen sensors are installed upstream and downstream of each catalyst, and the air-fuel ratio of the exhaust gas is feedback controlled to a target air-fuel ratio based on the output of the air-fuel ratio sensor located upstream of the upstream catalyst. In this the exhaust gas is sufficiently purified with the upstream catalyst alone when the exhaust gas flow rate is small, the oxygen sensor located downstream of the upstream catalyst is used as the downstream sensor for setting a target air-fuel ratio. Furthermore, when the exhaust gas flow rate increases, the amount of exhaust gas components passing through without purification in the upstream catalyst is increased. Therefore, the downstream sensor used for setting the air-fuel ratio is switched to the oxygen sensor located downstream of the downstream catalyst.

Abstract: In a fuel injection control system for an internal combustion engine, a fuel atomization device is provided to atomize fuel injected at the time of engine starting. The fuel atomization device may be a type which increases fuel pressure to a higher value at the time of engine starting than after the engine starting. Alternatively, the fuel atomization device may be a type which supplies assist air to the injected fuel. An intake valve is opened for a longer period at the time of engine starting than after the engine starting, so that more fuel may be supplied to an engine cylinder. A fuel leakage which may occur during engine stop is estimated, and the amount of fuel to be injected at the time of next engine starting after the engine stop is corrected by the estimated amount of fuel leakage. Fuel injection timing at the time of engine starting is retarded relative to that of post-engine starting.

Abstract: An upstream catalyst and a downstream catalyst are disposed in series in an exhaust pipe, and first through third sensors for detecting the air-fuel ratio or an adsorption amount of hazardous components on the rich/lean side of exhaust gases are disposed on the upstream and downstream sides of the upstream catalyst and the downstream side of the downstream catalyst, respectively. An ECU for controlling an engine controls the air-fuel ratio so that when the adsorption amount of the hazardous components on the rich side of the downstream catalyst is large, that of the hazardous components on the lean side of the upstream catalyst is large. Similarly, the ECU controls the air-fuel ratio so that when the adsorption amount of the hazardous components on the lean side of the downstream catalyst is large, that of the hazardous components on the rich side of the upstream catalyst is large.

Abstract: An air-fuel ratio control system has a catalyst and controls the air-fuel ratio properly in accordance with the in-catalyst state. The in-catalyst state amount variation is calculated based on the deviation between the actual excess fuel factor detected by means of an air-fuel ratio sensor on the upstream side of the catalyst and the target excess fuel factor, and then accumulated to obtain the current in-catalyst state amount. At that time, the previous air flow derived earlier by a lag time corresponding to the time period from the time of fuel injection to the time of detection of the excess fuel factor of exhaust gas is used as the air flow. The calculated in-catalyst state amount value is subjected to guard processing, and thereafter the target excess fuel factor on the upstream side of the catalyst is calculated by use of various gains and control parameters.

Abstract: A heater control system is provided for controlling the temperature of a heater used to heat a solid electrolyte-made sensing element of a gas concentration sensor up to a given temperature at which the sensing element is activated to provide a desired gas concentration output for controlling a preselected variable used in a given feedback control system. The heater control system controls an electric power supplied to the heater to bring the temperature of the sensing element into agreement with a target temperature value and determines the target temperature value as a function of the preselected variable used in the feedback control system so that only desired quantity of power may be supplied to the heater, thereby minimizing a consumption of the power.

Abstract: An oxygen concentration detecting apparatus precisely and easily performs diagnosis of a limit current type oxygen sensor. The limit current type oxygen sensor has an oxygen concentration detecting element for outputting limit current proportional to the oxygen concentration and a heater for heating the detecting element. A CPU of a microcomputer controls energization of the heater to activate the oxygen sensor. The CPU calculates element resistance based on the voltage applied to the oxygen sensor and the current detected in the sensor. In a sensor diagnosis routine, the CPU determines whether preconditions for the diagnosis have been met. If all the preconditions have been met, the CPU executes the diagnosis. That is, the CPU determines whether the element resistance is within a predetermined range. If it is below the range, the CPU determines that the sensor has high element temperature abnormality.

Abstract: An air-fuel ratio control apparatus for internal combustion engine includes exhaust gas purifying catalysts mounted on the upstream and downstream sides of an exhaust passage of an internal combustion engine, a fuel injector for injection of a desired quantity of fuel into a cylinder of the internal combustion engine in accordance with an engine operating condition, and an ECU. The ECU changes an air-fuel ratio to lean and rich magnitudes by alternately increasing and decreasing the quantity of fuel injection. The lean/rich changeover of the exhaust air-fuel ratio is performed at an interval including a period during which the lean and rich components in the exhaust gas react with the upstream catalyst and a period thereafter during which an unreacted exhaust gas passes through the upstream catalyst.

Abstract: In an engine exhaust system, an NOx catalyst for occluding NOx in a state of the lean air-fuel ratio and reducing the occluded NOx in the state of the rich air-fuel ration A CPU sets a target air-fuel ratio of a mixture supplied to an engine to the lean side with respect to the stoichiometric air-fuel ratio for the lean mixture combustion. The CPU sets a rich time for a rich mixture combustion in accordance with the engine operating state and the NOx purification rate in the NOx catalyst. In this moment, the shortest rich time is set within a range in which a desired NOx purification rate by the NOx catalyst is obtained. A three-way catalyst may be arranged upstream of the NOx catalyst. The three-way catalyst carries only a noble metal such as platinum having no oxygen storing capability.

Abstract: In a fuel injection control system for an internal combustion engine, a fuel atomization device is provided to atomize fuel injected at the time of engine starting. The fuel atomization device may be a type which increases fuel pressure to a higher value at the time of engine starting than after the engine starting. Alternatively, the fuel atomization device may be a type which supplies assist air to the injected fuel. An intake valve is opened for a longer period at the time of engine starting than after the engine starting, so that more fuel may be supplied to an engine cylinder. A fuel leakage which may occur during engine stop is estimated, and the amount of fuel to be injected at the time of next engine starting after the engine stop is corrected by the estimated amount of fuel leakage. Fuel injection timing at the time of engine starting is retarded relative to that of post-engine starting.

Abstract: A sensor element of an A/F sensor is constructed to laminate and integrate a solid electrolyte and a heater. The A/F sensor outputs a linear A/F detection signal proportional to the oxygen concentration in exhaust gases, when voltage is applied. An ECU controls the heater through heater control circuit to keep the sensor element at a predetermined activation temperature. The ECU detects an element resistance on the basis of the voltage applied to the sensor element and sensor current caused by the applied voltage, and converts the element resistance to an element temperature. During the temperature increasing of the A/F sensor, the current supply to the heater is duty-controlled according to the element temperature changing rate (the temperature increasing rate of the sensor element). Accordingly, the temperature increasing characteristics of the sensor is satisfactorily maintained, and disadvantages such as an element cracking are prevented.

Abstract: A NOx catalyst is attached to an engine exhaust pipe, an A/F sensor is disposed upstream of the NOx catalyst, and an O2 sensor is disposed downstream of the NOx catalyst. A CPU in an ECU executes a lean combustion control so that NOx in exhaust gases discharged at the time of the lean combustion is occluded by the NOx catalyst. The CPU further executes a rich combustion control temporarily, so that the occluded NOx to be discharged from the NOx catalyst. The CPU checks if the NOx catalyst deteriorates. When occurrence of deterioration is detected, the CPU increases the proportion of the rich combustion to the lean combustion, thereby increasing the temperature of the NOx catalyst. After the catalyst temperature increases, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio to regenerate the NOx catalyst.

Abstract: An upstream-side catalyst is provided at a location in close to an exhaust manifold of an engine. An HC absorbent and a downstream-side catalyst are installed in series at the downstream side. With the upstream-side catalyst put in an inactive state, the HC absorbent absorbs HC having passing through the upstream-side catalyst. After the upstream-side catalyst has been activated, HC released from the HC absorbent is refluxed to the upstream side of the upstream-side catalyst through a reflux path to be removed by the upstream-side catalyst. At that time, the ECU executes catalyst-early-warming control right after an engine start in order to raise the temperature of the upstream-side catalyst at an early time so as to shorten the time it takes to activate the upstream-side catalyst.

Abstract: In a fuel injection control system for an internal combustion engine, a fuel atomization device is provided to atomize fuel injected at the time of engine starting. The fuel atomization device may be a type which increases fuel pressure to a higher value at the time of engine starting than after the engine starting. Alternatively, the fuel atomization device may be a type which supplies assist air to the injected fuel. An intake valve is opened for a longer period at the time of engine starting than after the engine starting, so that more fuel may be supplied to an engine cylinder. A fuel leakage which may occur during engine stop is estimated, and the amount of fuel to be injected at the time of next engine starting after the engine stop is corrected by the estimated amount of fuel leakage. Fuel injection timing at the time of engine starting is retarded relative to that of post-engine starting.

Abstract: A gas concentration sensor voltage and current (in both heater on and heater off states) are detected and compared with predetermined thresholds, respectively, by a microcomputer. Based on a combination of the comparison results, the presence or absence of trouble in the system is detected and trouble location in the system is specified. In addition or alternatively, the sensor voltage is compared with thresholds to determine whether it is outside of a normal zone. The voltage may be actually detected or calculated. If the voltage is outside the normal zone, sensor voltage is reduced to zero or restricted to a predetermined limit.

Abstract: In an engine exhaust system, an NOx catalyst for occluding NOx in a state of the lean air-fuel ratio and reducing the occluded NOx in the state of the rich air-fuel ratio. A CPU sets a target air-fuel ratio of a mixture supplied to an engine to the lean side with respect to the stoichiometric air-fuel ratio for the lean mixture combustion. The CPU sets a rich time for a rich mixture combustion in accordance with the engine operating state and the NOx purification rate in the NOx catalyst. In this moment, the shortest rich time is set within a range in which a desired NOx purification rate by the NOx catalyst is obtained. A three-way catalyst may be arranged upstream of the NOx catalyst. The three-way catalyst carries only a noble metal such as platinum having no oxygen storing capability.

Abstract: In a system using a gas concentration sensor such as an A/F sensor having a heater, a microcomputer detects an abnormality in a heater power supply control. After the detection of abnormality, the computer reduces the electric power to the heater to a minimum and determines whether the heater has restored its normal operation. The power supply to the heater is stopped and returned to the normal power supply control when it is determined that the detected abnormality continues and discontinues during the reduced power supply period, respectively.

Abstract: An air-fuel ratio feedback control has an air-fuel ratio sensor and an oxygen sensor at an upstream side and a downstream side of a catalytic converter. A CPU feedback controls an air-fuel ratio detected by the air-fuel ratio sensor to a target air-fuel ratio, with a feedback gain being varied with an output of the oxygen sensor. The CPU further estimates an air-fuel ratio response speed based on a ratio between an exhaust gas flow amount and a capacity of the catalyst and determines a rate of deterioration of the catalyst. The CPU varies further the feedback gain based on the estimated response speed and the determined rate of deterioration.