Nissan Motor Company Limited

Masatomo Kakuyama

Osamu Matsuno

Shigeaki Kakizaki

Hirofumi Tsuchida

Akira Tayama

Hideaki Kobayashi

Hideaki Takahashi

Ritsuo Sato

An engine exhaust emission control arrangement has a catalytic converter including a three-way catalyst. A first oxygen sensor detects an oxygen concentration of exhaust gas upstream of the catalyst and a second oxygen sensor detects an oxygen concentration of exhaust gas downstream of the catalyst. A microprocessor calculates a specific period oxygen storage amount of a catalyst while the upstream oxygen concentration is higher than the stoichiometric concentration and the downstream oxygen concentration is in a predetermined concentration range which has a value approximately equal to the stoichiometric oxygen concentration. The microprocessor also calculates a specific period oxygen release amount of a catalyst while the upstream oxygen concentration is lower than the stoichiometric concentration and the downstream oxygen concentration produces an indication of a predetermined concentration range. A specific period oxygen storage amount is sampled at a time at which the downstream oxygen concentration becomes greater than the predetermined concentration range as a maximum oxygen storage amount and a specific period oxygen release amount is sampled at a time at which the downstream oxygen concentration becomes smaller than the predetermined concentration range as a maximum oxygen release amount. The engine air-fuel ratio is controlled to cause the oxygen storage amount of the catalyst to coincide with a target value which is set at approximately half of an average value of the maximum oxygen storage amount and the maximum oxygen release amount.

Exhaust emission control for engine

A controller ( ) computes the oxygen storage amount of the catalyst ( ) separately as a high-speed component and a low speed component in accordance with actual characteristic. A target air-fuel ratio of an engine ( ) is computed so that the oxygen storage amount is a predetermined target amount, and air-fuel ratio control of the engine ( ) is performed. The oxygen storage amount is computed using an storage/release rate set according to the exhaust air-fuel ratio and catalyst temperature, etc. In this way, the oxygen storage amount of the catalyst can be precisely computed regardless of the variation in the storage/release rate which accompanies a catalyst temperature variation, and the real oxygen storage amount can therefore be controlled with a higher level of precision.

Engine exhaust purification device

A microprocessor ( ) computes an oxygen storage amount of a catalyst ( ) separately for a high speed component and a low speed component in accordance with real characteristic. A target air-fuel ratio of an engine ( ) is computed and air-fuel ratio control of the engine ( ) it is performed so that the high speed component is constant. The deterioration of the catalyst ( ) is determined by integrating the high speed component of the oxygen storage amount computed during the air-fuel ratio control process for a predetermined number of times, and comparing its average value with a determining value. The oxygen storage amount of the high speed component which is sensitive to catalyst deterioration is integrated so as to obtain a highly precise determining result to determine the deterioration.

A controller ( ) computes an oxygen storage amount of a catalyst ( ) separately as a high speed component/amount and a low speed component/amount according to predetermined release/adsorption characteristics. A target air-fuel ratio of an engine is computed and the air-fuel ratio of the engine is controlled so that the high speed component is maintained constant. The target air-fuel ratio of the engine ( ) is limited by an upper limiter and lower limiter so that the high speed component converges to the target value, an excessively large variation of the air-fuel ratio is prevented, and impairment of drivability and fuel cost-performance is also prevented. Further, after lean running due to fuel cut, etc., the lower limiter is lowered to the rich side, and the oxygen storage amount is rapidly induced to converge on the target value.

Engine exhaust purification arrangement

A controller ( ) controls an air-fuel ratio of an engine ( ) so that an oxygen storage amount of a catalyst ( ) provided in an exhaust passage ( ) is maintained constant. At this time, the controller ( ) computes or estimates the oxygen storage amount separately for a first amount and a second amount, where the first amount is estimated based on a relationship between the first and second amount. The controller ( ) controls the air/fuel ratio based on the estimated first amount.

A catalyst which has oxygen storage performance is installed in an engine exhaust passage an oxygen storage amount is estimated based on the output of an upstream air-fuel ratio sensor installed in the upstream of the catalyst and an air-fuel ratio is controlled so that this oxygen storage amount coincides with a target value. When the output of a downstream air-fuel ratio sensor has become lean or rich for longer than a fixed time, the output of the upstream air-fuel ratio sensor is corrected based on the output of the downstream air-fuel ratio sensor placed in the downstream of the catalyst In this way, the output fluctuation due to deterioration of the air-fuel ratio sensor upstream of the catalyst is corrected, and the catalyst oxygen storage amount is always precisely controlled to the target value.

Engine air-fuel ratio controller

An oxygen storage amount of the catalyst ( ) is estimated using a detection result from a front A/F sensor ( ). An HC storage amount is calculated as a time integral of the product of the storage rate by the catalyst ( ), the air-fuel ratio and the intake air amount, and a target air-fuel ratio is corrected so that a deficiency relative to a target amount of the oxygen storage amount is compensated based on this computation result.

A catalytic converter ( ) having a three-way catalyst which stores oxygen is disposed in the exhaust passage ( ) of an engine ( ). An oxygen storage amount of the catalyst is estimated based on the output of a universal exhaust gas oxygen sensor ( ) provided upstream of the catalytic converter ( ). A control unit ( ) controls an air-fuel ratio of the fuel mixture supplied to the engine ( ) through a fuel injector ( ) so that the oxygen storage amount coincides with a target value. An excess/deficiency oxygen amount in the exhaust gas is accumulated when the output of an oxygen sensor ( ) which detects the oxygen concentration downstream of the catalytic converter ( ) is in an excess oxygen region which is higher than a stoichiometric oxygen concentration region. An average oxygen excess ratio is calculated by dividing the accumulated value by an accumulated intake air amount. The output of the universal exhaust gas oxygen sensor ( ) is corrected based on the average oxygen excess ratio. In the same manner, the output of the universal exhaust gas oxygen sensor ( ) is corrected based on the average oxygen excess ratio when the output of the oxygen sensor ( ) is in an deficiency oxygen region which is lower than the stoichiometric oxygen concentration region. These corrections compensate for fluctuations in the output resulting from deterioration of the universal exhaust gas oxygen sensor ( ) or due to manufacturing errors and the calculation accuracy of the oxygen storage amount of the catalyst is thereby increased.

Air-fuel ratio control of engine

In an automotive vehicle with at least one catalyst located in an exhaust passage for adsorbing oxygen contained within exhaust gases entering the catalyst, and an air/fuel ratio sensor located in the exhaust passage upstream of the catalyst for detecting an air/fuel ratio based on a percentage of oxygen contained within the exhaust gases flowing through the exhaust passage and entering the catalyst, an air/fuel ratio control system controls an air/fuel mixture ratio of the engine at as close to stoichiometric as possible, an air/fuel ratio control system calculates a quantity of oxygen stored in the catalyst on the basis of a deviation of the air/fuel ratio detected by the air/fuel ratio sensor from a stoichiometric air/fuel ratio to produce informational data indicative of a calculated value of the quantity of oxygen stored. The control system controls the air/fuel mixture ratio of the engine so that the calculated value of the quantity of oxygen stored is adjusted to a desired value. The control system has a limiter capable of preventing the calculated value of the quantity of oxygen stored from exceeding a specified level.

Air/fuel ratio control system of internal combustion engine

An air-fuel ratio controller for an internal combustion engine with a catalytic converter in an exhaust passage has an air-fuel ratio sensor, an engine sensor, and a control unit. The air-fuel ratio sensor produces a signal indicative of an air-fuel ratio of an exhaust gas in the exhaust passage on an upstream side of the catalytic converter. The engine sensor produces a signal indicative of misfiring of the engine. The control unit is operatively coupled to the air-fuel ratio sensor and the engine sensor. The control unit computes an estimated quantity of oxygen to be stored in the catalytic converter based on the signal from the air-fuel ratio sensor, and determines if the engine is misfiring based on the signal from the engine sensor. The control unit also produces an estimated adjustment value and adjusts an air-fuel ratio of intake air based on the estimated adjustment value such that the estimated quantity of oxygen to be stored substantially coincides with a predetermined target quantity of oxygen to be stored. However, when misfiring is determined based on the signal from the engine sensor, the computation of the estimated quantity of oxygen to be stored is stopped or not used, and a predetermined value is used to control the air-fuel ratio of intake air. With the air-fuel ratio controller of the present invention, influence of misfiring on air-fuel ratio control can be reduced.

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Yokohama, Japan

Masatomo Kakuyama