Abstract: An exhaust device in which an exhaust passage wraps around from a front side of an engine to a lower side of the engine and extends to a rear side is provided. The exhaust device includes a catalyst configured to purify exhaust gas in the exhaust passage and disposed in front of the engine, and a gas sensor disposed on a wall surface of the exhaust passage at an upstream side than the catalyst. The gas sensor is disposed in front of the engine so as to be directed toward the engine.

Abstract: Methods and systems are provided for detection of cylinder-to-cylinder air fuel ratio imbalance in engine cylinders. In one example, a method may include indicating air fuel ratio imbalance in an engine cylinder based on a comparison of an estimated cylinder acceleration for the cylinder and a calibrated cylinder acceleration for each of the engine cylinders. The indication of imbalance may be further confirmed based on one or more of an exhaust air-fuel ratio, an exhaust manifold pressure, and an individual cylinder torque weighted by respective confidence factors.

Abstract: A system for regeneration of a particulate filter in a V-pipe exhaust system includes a pair of post-converter universal heated exhaust gas oxygen (UHEGO) sensors disposed at a pair of pipes of the V-pipe exhaust system downstream from a pair of three-way catalytic (TWC) converters and the pair of post-converter UHEGO sensors measure lambda values. The system also includes an engine controller in communication with the pair of post-converter UHEGO sensors. The engine controller is configured to receive and compare measured lambda values from the pair of post-converter UHEGO sensors to a target exhaust gas lambda value for exhaust gas flowing into the particulate filter and provide at least one adjusted target exhaust gas lambda value as a function of a difference between the measured lambda values and the target exhaust gas lambda value.

Abstract: Methods and systems are provided for operating an engine to diagnose and compensate for cylinder imbalance in an engine. In one example, a method may include diagnosing a torque imbalance in a multi-cylinder engine by operating the engine at a lean air-fuel ratio (AFR) while an amount of ammonia stored in an selective catalytic reduction (SCR) system is greater than a threshold amount and a temperature of the engine is greater than a threshold temperature; and responsive to the diagnosed torque imbalance, adjusting fueling and spark timing for each cylinder, the adjustments based on an AFR offset of each cylinder determined while adjusting the lean AFR.

Abstract: An exhaust system for receiving exhaust gas from an engine of a vehicle includes first, second, and third exhaust components, and first and second pipes. The first and second exhaust components are each adapted to receive exhaust gas from the engine. The first pipe has a first inlet, and first and second outlets. The first inlet is adapted to receive exhaust gas from the first exhaust component. The second pipe has a second inlet, and third and fourth outlets. The second inlet is adapted to receive exhaust gas from the second exhaust component. The third exhaust component is disposed downstream of and laterally between the first and second exhaust components. The third exhaust component has third and fourth inlets, and fifth and sixth outlets. The third inlet is fluidly connected to the first outlet. The fourth inlet is fluidly connected to the third outlet.

Abstract: An exhaust system for an off road vehicle includes a main intake pipe running in a generally longitudinal direction on the vehicle, receiving gasses from a first intake pipe for a forward cylinder and from a second intake pipe for a rearward cylinder of an mid-mounted internal combustion engine. A catalytic converter receives gasses from the main intake pipe. Instead of being mounted longitudinally, the catalytic converter extends in a transverse direction, at the rearward end of the exhaust system, behind the axis of the rear wheels. A muffler, located over the axis of the rear wheels, also extends in a transverse direction and receives gasses from the catalytic converter. The muffler outputs the gasses through a tailpipe, which is preferably above and extends wider than the main intake pipe.

Abstract: Systems and methods for monitoring cylinder air/fuel imbalances are provided. In one example approach, a method comprises, identifying a cylinder with a potential air/fuel imbalance based on crankshaft accelerations generated by a series of rich, lean, and stoichiometric conditions in the cylinder while keeping the engine at stoichiometry.

Abstract: A control apparatus controlling a controlled variable of a controlled object having a response lag characteristic using a combination of feedforward control method, response-specifying control method, and disturbance compensation method. An ECU of the apparatus calculates driver demand boost pressure for feedforward-controlling actual boost pressure as controlled variable, and calculates FB target pressure as value on which response lag characteristic of the actual value to the driver demand value is reflected.

Abstract: A system and method for detecting air-fuel ratio rich-lean imbalance in an automotive engine cylinder is provided. The system and the method are configured to receive an oxygen sensor voltage of an oxygen sensor. They also include filtering the oxygen sensor voltage to create a filtered oxygen sensor voltage. An engine speed and load are determined, and an air-fuel ratio imbalance detection threshold is determined based on the engine speed and the engine load. A rich-lean imbalance status is determined, the rich-lean imbalance status being non-normal if any portion of the filtered oxygen sensor voltage exceeds the air-fuel ratio imbalance detection threshold, and the rich-lean imbalance status being normal if none of the filtered oxygen sensor voltage exceeds the air-fuel ratio imbalance detection threshold. An engine control unit having several control logics to execute similar steps is also provided.

Abstract: In a multicylinder internal combustion engine including a turbocharger, the turbocharger employs a twin-entry turbo where a turbine includes two exhaust gas inflow ports. A first exhaust passage guides an exhaust gas discharged from a first cylinder group of the internal combustion engine to one exhaust gas inflow port of the turbocharger. A second exhaust passage guides an exhaust gas discharged from a second cylinder group of the internal combustion engine to the other exhaust gas inflow port of the turbocharger. An exhaust gas collecting portion of the first exhaust passage and an exhaust gas collecting portion of the second exhaust passage each include an air-fuel ratio sensor. This configuration allows efficiently contact of the exhaust gas on an element portion of the air-fuel ratio sensor, thus accurately detecting an air-fuel ratio of the exhaust gas at an upstream side of a catalyst for each cylinder.

Abstract: An inter-cylinder air-fuel ratio imbalance determining apparatus for an internal combustion engine includes an air-fuel ratio sensor; fuel injection valves; an instructed fuel injection amount control unit; and an imbalance determination unit configured: to acquire a time-differential-value corresponding value that is an amount of change per predetermined time in an output value of the sensor or a detected air-fuel ratio represented by the output value; to acquire a positive gradient corresponding value based on a positive value of the time-differential-value corresponding value; to acquire a negative gradient corresponding value based on a negative value of the time-differential-value corresponding value; to determine an imbalance determination threshold based on a magnitude of a ratio of the negative gradient corresponding value to the positive gradient corresponding value; and to determine whether inter-cylinder air-fuel ratio imbalance has occurred by comparing a magnitude of the negative gradient corresp

Abstract: Methods and systems are provided for adjusting cylinder valve timings to enable a group of cylinders to operate and combust while another group of cylinders on a second are selectively deactivated. Valve timing may be adjusted to allow flow of air through the inactive cylinders to be reduced, lowering catalyst regeneration requirements upon reactivation. The valve timing may alternatively be adjusted to enable exhaust gas to be recirculated to the active cylinders via the inactive cylinders, providing cooled EGR benefits.

Abstract: Methods and systems for diagnosing a multiple cylinder engine are provided herein. An exemplary method of diagnosing an internal combustion engine system having a multi-cylinder internal combustion engine is described. In one example, cylinder air-fuel imbalance is determined from the squared value of a difference of two values.

Abstract: An air-fuel ratio imbalance among cylinders determining apparatus according to the present invention comprises an air-fuel ratio sensor having a protective cover and an air-fuel ratio detection element accommodated in the protective cover, and imbalance determining means. The imbalance determining means obtains a detected air-fuel ratio abyfs based on an output Vabyfs of the air-fuel ratio sensor every elapse of a constant sampling time ts, and obtains, as an indicating amount of air-fuel ratio change rate, a difference (detected air-fuel ratio change rate ?AF) between a present detected air-fuel ratio abyfs which is newly detected and a previous air-fuel ratio abyfsold which was detected the sampling time ts ago, an average of the detected air-fuel ratio change rate ?AF, and the like.

Abstract: Method to detect a faulty operating condition during a cylinder cutoff of an internal combustion engine with at least two cylinder banks, wherein the internal combustion engine comprises in each case a separate mechanism to determine the Lambda value of the combustion for each cylinder bank. When the Lambda values of the cylinder banks change in opposite directions, a faulty cylinder cutoff is suggested.

Abstract: An engine having a first and second bank of cylinders is disclosed. The engine may have improved fuel economy and emission as compared to other similar engines. In one example, engine cylinders may be deactivated.

Abstract: Air/fuel imbalance monitoring systems and methods for monitoring air/fuel ratio imbalance of an internal combustion engine are disclosed. In one embodiment, an oxygen sensor is sampled above cylinder firing frequency and a ratio of data from at least one window over a total number of windows is determined. The approach can be used to indicate imbalances between engine cylinders.

Abstract: Various systems and methods are disclosed for carrying out combustion in a fuel-cut operation in some or all of the engine cylinders of a vehicle. Further, various subsystems are considered, such as fuel vapor purging, air-fuel ratio control, engine torque control, catalyst design, and exhaust system design.

Abstract: Disclosed is an internal combustion engine comprising a first and a second cylinder line, each of which is provided with a camshaft for the gas intake valves and the gas discharge valves as well as a mechanism for adjusting a valve overlap between the gas intake valves and the gas discharge vales. A lambda controller whose manipulated variable acts upon an actuator that is allocated to the respective cylinder line is associated with each cylinder line. Values of the manipulated controller variables are detected as non-valve-overlapping values of the two cylinder lines in an operating situation in which the valve overlap is so small that the same does not influence the manipulated controller variables while values of the manipulated controller variables are detected as valve-overlapping values of the two cylinder lines in another operating situation in which the valve overlap is so great that the same influences the manipulated controller variables.

Abstract: Control method for the mixture ratio in a multi-cylinder internal combustion engine, the control method providing for the following: reading a first real value of the mixture ratio via a master lambda sensor associated with a first cylinder group, reading a second real value of the mixture ratio via a slave lambda sensor associated with a second cylinder group, calculating a first amount of fuel to inject into the cylinders of the first cylinder group to track a mixture ratio target value by using the first real value of the mixture ratio as a feedback variable, calculating the mean of the second real value of the mixture ratio in the detection window, calculating a correction value for the amount of fuel to inject based on the difference between a target value and the mean of the second real value of the mixture ratio, and calculating a second amount of fuel to inject into the cylinders of the second cylinder group by applying the correction value to the first amount of fuel to inject into the cylinders of t

Abstract: Methods and systems are provided for monitoring cylinder valve deactivation in an engine operating with a plurality of cylinder valves. One example method comprises, sensing a plurality of cylinder valve positions of a plurality of cylinder valves; and combining the plurality of sensed positions to form a combined cylinder valve signal. The method may further include identifying valve degradation and differentiating valve degradation among the plurality of cylinder valves based on the combined cylinder valve signal and an expected value of the signal, and further based on a crank angle at which the expected value differs from the combined signal.

Abstract: Various systems and methods are disclosed for carrying out combustion in a fuel-cut operation in some or all of the engine cylinders of a vehicle. Further, various subsystems are considered, such as fuel vapor purging, air-fuel ratio control, engine torque control, catalyst design, and exhaust system design.

Abstract: Various systems and methods are disclosed for carrying out combustion in a fuel-cut operation in some or all of the engine cylinders of a vehicle. Further, various subsystems are considered, such as fuel vapor purging, air-fuel ratio control, engine torque control, catalyst design, and exhaust system design.

Abstract: Various systems and methods are disclosed for carrying out combustion in a fuel-cut operation in some or all of the engine cylinders of a vehicle. Further, various subsystems are considered, such as fuel vapor purging, air-fuel ratio control, engine torque control, catalyst design, and exhaust system design.

Abstract: A valve timing correction control apparatus for an internal combustion engine is provided. The engine includes a plurality of banks and variable valve operating mechanisms disposed at the respective banks for variably controlling valve timings of intake valves separately at the respective banks. The valve timing correction control apparatus comprises air/fuel ratio sensors provided to exhaust systems of the respective banks, and a control unit that corrects the valve timings of the intake valves at the respective banks in accordance with deviations of air/fuel ratios detected by the respective air/fuel ratio sensors. A valve timing correction control method is also provided.

Abstract: A system for a vehicle comprising of an engine including a first cylinder group and a second cylinder group; a linear exhaust gas sensor coupled exclusively to the first cylinder group; a switching exhaust gas sensor coupled exclusively to the second cylinder group; and a controller configured to operate the engine in at least a first mode and a second mode, where in the first mode the first and second cylinder groups combust air and fuel, where in the second mode at least one of the first and second cylinder groups combusts air and injected fuel and the other one of the first and second cylinder groups pumps air without injecting fuel, and where the controller is further configured to estimate torque of the engine in each of the first and second modes of operation based on the air-fuel ratio of the first cylinder group and the air-fuel ratio of the second cylinder group independent of the switching sensor and dependent on the linear sensor.

Abstract: A multi-cylinder group engine system operable in at least a first mode and a second mode, where in the first mode a first and second cylinder group combust air and fuel with a lean air-fuel ratio, and where in the second mode at least one of the first and second cylinder groups combusts air and fuel and the other one of the first and second cylinder groups pumps air without injected fuel, the engine system comprising of a fuel injection activity sensor coupled to each cylinder in the first and second cylinder groups; a exhaust gas sensor disposed in an exhaust passage to measure air fuel exhausted from the engine; and a controller configured to transition out of the first mode responsive to detection of exhaust gas sensor degradation and to transition out of the second mode responsive to detection of fuel injection sensor degradation. In one example, the transition out of the second mode may be slower than the transition out of the first mode in response to the respective degradation.

Abstract: A control apparatus, a control method, and an engine control unit are provided for controlling an output of a controlled object which has a relatively large response delay and/or dead time to rapidly and accurately converge to a target value. When the output of the controlled object is chosen to be that of an air/fuel ratio sensor in an internal combustion engine, the output of the air/fuel ratio sensor can be controlled to rapidly and accurately converge to a target value even in an extremely light load operation mode.

Abstract: A method is disclosed for controlling operation of an engine coupled to an exhaust treatment catalyst. Under predetermined conditions, the method operates an engine with a first group of cylinders combusting a lean air/fuel mixture and a second group of cylinders pumping air only (i.e., without fuel injection). In addition, the engine control method also provides the following features in combination with the above-described split air/lean mode: idle speed control, sensor diagnostics, air/fuel ratio control, adaptive learning, fuel vapor purging, catalyst temperature estimation, default operation, and exhaust gas and emission control device temperature control. In addition, the engine control method also changes to combusting in all cylinders under preselected operating conditions such as fuel vapor purging, manifold vacuum control, and purging of stored oxidants in an emission control device.

Abstract: A system for balancing first and second work outputs between first and second cylinder banks of an engine includes a first intake camshaft associated the first cylinder bank and a first fuel injector associated with the first cylinder bank. A controller trims a pulse-width of the first fuel injector until first and second A/F ratios of respective exhaust of the first and second cylinder banks are equivalent. The controller adjusts timing of the first intake camshaft to effect air flow into the first cylinder bank and trims the pulse-width to maintain equivalency of the first and second A/F ratios.

Abstract: A method is disclosed for controlling operation of an engine coupled to an exhaust treatment catalyst. Under predetermined conditions, the method operates an engine with a first group of cylinders combusting a lean air/fuel mixture and a second group of cylinders pumping air only (i.e., without fuel injection). In addition, the engine control method also provides the following features in combination with the above-described split air/lean mode: idle speed control, sensor diagnostics, air/fuel ratio control, adaptive learning, fuel vapor purging, catalyst temperature estimation, default operation, and exhaust gas and emission control device temperature control. In addition, the engine control method also changes to combusting in all cylinders under preselected operating conditions such as fuel vapor purging, manifold vacuum control, and purging of stored oxidants in an emission control device.

Abstract: A method is disclosed for controlling operation of an engine coupled to an exhaust treatment catalyst. Under predetermined conditions, the method operates an engine with a first group of cylinders combusting a lean air/fuel mixture and a second group of cylinders pumping air only (i.e., without fuel injection). In addition, the engine control method also provides the following features in combination with the above-described split air/lean mode: idle speed control, sensor diagnostics, air/fuel ratio control, adaptive learning, fuel vapor purging, catalyst temperature estimation, default operation, and exhaust gas and emission control device temperature control. In addition, the engine control method also changes to combusting in all cylinders under preselected operating conditions such as fuel vapor purging, manifold vacuum control, and purging of stored oxidants in an emission control device.

Abstract: A control system of an internal combustion engine is comprised of an operation angle adjustment mechanism which continuously varies an operation angle of intake valves of the engine, an air-fuel ratio detector which detects an exhaust parameter indicative of air-fuel ratio information, and a control unit which are coupled to the operation angle adjustment mechanism and the air-fuel ratio detector. The control unit feedback-controls an air-fuel ratio of the engine on the basis of the exhaust parameter and corrects the operation angle on the basis of the exhaust parameter.

Abstract: A control method for an internal combustion engine has multiple cylinder groups with at least one control device positioned between an intake manifold and a cylinder group. The engine operates the cylinder groups at different air/fuel ratio and uses the control device to balance torque produced by the different cylinder groups. In one aspect of the invention, one cylinder group is operated rich and another cylinder group is operated lean thereby providing heat to an exhaust system located downstream of the engine.

Abstract: The invention provides a fuel control method and system for an internal combustion engine. The method includes: calculating an initial amount of fuel based on an amount of intake air, calculating a first cylinder bank air/fuel ratio matching coefficient and a second cylinder bank air/fuel ratio matching coefficient based on an engine speed and a volumetric efficiency, and controlling the amounts of fuel in the second and first banks, using the calculated second bank air/fuel ratio matching coefficient and the first bank air/fuel ratio matching coefficient, respectively. The system includes a control unit and a fuel injection system for implementing the method.

Abstract: A method and a device for regulating the fuel/air ratio of an internal combustion engine having a first cylinder group, whose exhaust gases are guided through a first exhaust duct area, and having a second cylinder group, whose exhaust gases are guided through a second exhaust duct area. The first exhaust duct area contains a first catalytic portion and the second exhaust duct area contains a second catalytic portion. An exhaust gas analyzer probe, arranged upstream from the first catalytic portion, influences the fuel/air ratio of both the first and the second cylinder groups. A second exhaust gas analyzer probe, arranged downstream from the first catalytic portion, influences the fuel/air ratio of the first cylinder group, and a third exhaust gas analyzer probe, arranged downstream from the second catalytic portion, influences the fuel/air ratio of the second cylinder group. An additional exhaust gas analyzer probe upstream from the second catalytic portion may be eliminated.

Abstract: The invention provides a fuel control method and system for an internal combustion engine. The method includes: calculating an initial amount of fuel based on an amount of intake air, calculating a first cylinder bank air/fuel ratio matching coefficient and a second cylinder bank air/fuel ratio matching coefficient based on an engine speed and a volumetric efficiency, and controlling the amounts of fuel in the second and first banks, using the calculated second bank air/fuel ratio matching coefficient and the first bank air/fuel ratio matching coefficient, respectively. The system includes a control unit and a fuel injection system for implementing the method.

Abstract: A method for controlling the phasing of first and second air/fuel ratio oscillations in first and second cylinder groups, respectively, of an internal combustion engine is provided. The method includes determining a phase difference between the first air/fuel ratio oscillations and the second air/fuel ratio oscillations. The method further includes adjusting a phase of the first air/fuel ratio oscillations so that both first and second air/fuel ratio oscillations are at a predetermined phase offset with respect to one another, while maintaining an average air/fuel bias in the first cylinder group.

Abstract: A method for selecting one of first and second cylinder groups of an internal combustion engine is provided. The first and second cylinder groups are coupled with first and second catalytic converters, respectively. The method includes identifying one of the first and second catalytic converters by comparing first and second catalyst parameters, associated with the first and second catalytic converters, respectively, to one another. The first and second catalyst parameters indicate which one of the catalytic converters is more capable of maintaining reduced emissions while adjusting an engine operational parameter. The method further includes selecting one of the first and second cylinder groups coupled to the identified catalytic converter for changing an engine operational parameter in the selected cylinder group.

Abstract: A method for controlling first and second air/fuel ratio oscillations in first and second cylinder groups, respectively, of an internal combustion engine is provided. The method includes determining a first frequency of the first air/fuel ratio oscillations in the first cylinder group. The method further includes determining a second frequency of the second air/fuel ratio oscillations in the second cylinder group. Finally, the method includes adjusting the first frequency towards the second frequency responsive to a frequency difference between the first and second frequencies.

Abstract: An internal combustion engine (10) has a plurality of cylinders which are arranged in two cylinder banks. A sensor (131, 132) is assigned to each of the two cylinder banks for determining the composition of the exhaust gas. A control apparatus is provided with which a control factor (fr1, fr2) can be determined for each of the two cylinder banks in dependence upon the output signals generated by the two sensors (131, 132). The fuel mass (ti1, ti2), which is to be injected into the two cylinder banks, can be influenced by the control factors. The two control factors (fr1, fr2) of the two cylinder banks can be compared to each other via the control apparatus. The control apparatus can distinguish between a cylinder-bank independent fault and a cylinder-bank dependent fault in dependence upon the two control factors (fr1, fr2).

Abstract: A control system and method is provided for selecting one of first and second cylinder groups of an internal combustion engine when a frequency of air/fuel ratio oscillations in the selected cylinder group is to be adjusted. The method includes determining which of first and second frequencies of air/fuel ratio oscillations in the first and second cylinder groups, respectively, has a greater frequency. Further, the method includes selecting one of the first and second cylinder groups having the greater frequency of air/fuel ratio oscillations. The selection is made to reduce engine torque fluctuations when changing a frequency of air/fuel ratio oscillations in the selected cylinder group.

Abstract: A control system of an internal combustion engine is comprised of an operation angle adjustment mechanism which continuously varies an operation angle of intake valves of the engine, an air-fuel ratio detector which detects an exhaust parameter indicative of air-fuel ratio information, and a control unit which are coupled to the operation angle adjustment mechanism and the air-fuel ratio detector. The control unit feedback-controls an air-fuel ratio of the engine on the basis of the exhaust parameter and corrects the operation angle on the basis of the exhaust parameter.

Abstract: A method of determining shift points in a step gear transmission system to maximize fuel economy is disclosed. In operation, the method uses fuel economy data from a first gear ratio to determine a first series of constant fuel consumption curves for the first gear ratio. The method then uses fuel economy data from a second gear ratio to determine a second series of constant fuel consumption curves for the second gear ratio. Next, the method determines points of intersection where a respective fuel consumption curve for the first gear ratio intersects its corresponding fuel consumption curve for the second gear ratio. A decision curve is generated from the points of intersection.

Abstract: The characteristics of the output of an exhaust gas sensor with respect to the air-fuel ratio of an engine are expressed by a nonlinear function such as a quadratic function or the like, and the parameters of the nonlinear function are sequentially identified according to a sequential identifying algorithm using the data of the output of the exhaust gas sensor and the data of the output of an air-fuel ratio sensor which detects the air-fuel ratio of the engine. An air-fuel ratio at which the function value of the nonlinear function whose parameters have been identified is used as a target air-fuel ratio, and the air-fuel ratio of the engine is controlled at the target air-fuel ratio.

Abstract: An exhaust system is regarded as being equivalent to a system for generating an output of an O2 sensor or exhaust gas sensor from a combined air-fuel ratio that is produced by combining outputs of air-fuel ratio sensors associated with respective cylinder groups according to a filtering process of the mixed model type. With the equivalent system as an object to be controlled, an exhaust system controller determines a target value for the combined air-fuel ratio, and determines a target air-fuel ratio for the cylinder groups from the target combined air-fuel ratio. The outputs of the air-fuel ratio sensors are converted to the target combined air-fuel ratio under feedback control.

Abstract: A control method for an internal combustion engine has multiple cylinder groups with at least one control device positioned between an intake manifold and a cylinder group. The engine operates the cylinder groups at different air/fuel ratios and uses the control device to balance torque produced by the different cylinder groups. In one aspect of the invention, one cylinder group is operated rich and another cylinder group is operated lean thereby providing heat the an exhaust system located downstream of the engine.

Abstract: An internal combustion engine (10) has a plurality of cylinders which are arranged in two cylinder banks. A sensor (131, 132) is assigned to each of the two cylinder banks for determining the composition of the exhaust gas. A control apparatus is provided with which a control factor (fr1, fr2) can be determined for each of the two cylinder banks in dependence upon the output signals generated by the two sensors (131, 132). The fuel mass (ti1, ti2), which is to be injected into the two cylinder banks, can be influenced by the control factors. The two control factors (fr1, fr2) of the two cylinder banks can be compared to each other via the control apparatus. The control apparatus can distinguish between a cylinder-bank independent fault and a cylinder-bank dependent fault in dependence upon the two control factors (fr1, fr2).

Abstract: In an engine having first and second cylinder groups, a first sensor senses an air-fuel ratio of an exhaust gas mixture into a first catalytic converter for the first cylinder group, a second sensor senses an air-fuel ratio of an exhaust gas mixture into a second catalytic converter for the second cylinder group. A controller normally controls the air fuel ratios of the first and second cylinder groups independently by using first and second air-fuel ratio feedback correction coefficients.

Abstract: An object system is regarded as being equivalent to a system for generating an output of an O2 sensor or exhaust gas sensor from a target combined air-fuel ratio that is produced by combining target air-fuel ratios KCMD for respective cylinder groups according to a filtering process of the mixed model type. With the equivalent system as an object to be controlled, an air-fuel ratio processing controller determines a target combined air-fuel ratio, and determines a target air-fuel ratio KCMD for each of the cylinder groups from the target combined air-fuel ratio. The air-fuel ratios in the cylinder groups are manipulated into the target air-fuel ratio according to a feed-forward control process.