Nissan Motor Company Limited

Hideki Uema

Masaaki Uchida

Yuki Nakajima

Yoshihisa Kawamura

Kunifumi Sawamoto

Hiromichi Miwa

Naoki Nakada

Fumio Yukawa

Toyaki Nakagawa

Kohei Mitsuhashi

A catalyst deterioration diagnosis system for an internal combustion engine having an exhaust gas passageway in which a catalytic converter having a catalyst is disposed. The diagnosis system comprises a first air-fuel ratio sensor disposed in the exhaust gas passageway upstream of the catalytic converter, and a second air-fuel ratio sensor disposed in the exhaust gas passageway downstream of the catalytic converter. The diagnosis system further comprises a control unit connected to the air-fuel ratio sensors and arranged to make an air-fuel ratio feedback control mainly in response to an output signal of the first air-fuel ratio sensor. The control unit includes means for calculating an inversion ratio value relating to an inversion ratio of output signals from the first and second air-fuel ratio sensors when the engine operating condition is within a diagnosis region requiring a diagnosis of deterioration of the catalyst, means for detecting an inversion state value relating to a state of inversion of the output signal of the first air-fuel ratio sensor, means for setting a decision standard value in accordance with the inversion state value from the inversion state value detecting means, and means for judging the deterioration of the catalyst by comparing the inversion ratio value from the inversion ratio value calculating means with the decision standard value from the decision standard value setting means.

Catalyst deterioration diagnosis system for internal combustion engine

To reliably diagnose catalyst degradation in an air fuel ratio control system without being subjected to the influence of engine operating conditions, a front O.sub.2 sensor output VFO and a rear O.sub.2 sensor output VRO are detected on both the upstream and downstream sides of catalytic converter; air fuel ratio feedback correction coefficients .alpha. are determined on the basis of basic feedback control constants P.sub.R,L or i.sub.R,L and correction values PHOS according to rich and lean air fuel ratio conditions; periods T and amplitudes .alpha..sub.R -.alpha..sub.L of the air fuel ratio feedback correction coefficient .alpha. are measured; a rich discriminating catalyst diagnosing slice level RSLH2 is set higher than a rich discriminating air fuel ratio feedback controlling slice level RSH1 and a lean discriminating catalyst diagnosing slice level RSLL2 is set lower than a lean discriminating air fuel ratio feedback controlling slice level RSLL1 in such a way that RSLH2 increases and RSLL2 decreases with increasing product of the period and amplitude of .alpha.; the number j.sub.F of times when the front sensor output VFO changes across a stoichiometric mixture ratio SL.sub.F is connected; the number j.sub.R of times when the rear sensor output VRO changes across the slice levels RSLH2 and RSLL2 is counted; and the catalyst is determined to be degraded if j.sub.R /j.sub.F .gtoreq.k, where k&lt;1.

Catalyst degradation diagnosing apparatus for air fuel ratio control

A system and method for controlling an air/fuel mixture for an internal combustion engine are disclosed in which an integration constant used for a calculation of an integration portion included in a feedback correction coefficient (.alpha.) of the air/fuel mixture ratio after a relationship between an actual air/fuel mixture raito and target (stoichiometric) air/fuel mixture ratio has been inverted is set and varied according to an engine driving condition, so that the integration constant meets requirements of a stability during an engine steady driving condition and a favorable responsive characteristic during an engine transient condition. In a preferred embodiement, a fuzzy control is applicable to the calculation of the integration constant.

System and method for controlling air/fuel mixture ratio for internal

An air/fuel ratio control system detects transition of air/fuel ratio changing between rich and lean for checking if updating condition is satisfied. Updating value is derived based on a feedback correction value which is derived for adjusting air/fuel ratio toward a stoichiometric value. With the updating value thus derived, one of a plurality of learnt correction value which are set with respect to various engine driving range.

Growing community of inventors

Kanagawa, Japan

Hideki Uema