A/F ratio estimator for multicylinder internal combustion engine

Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means

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123694, F02D 4114

Patent

active

054620376

ABSTRACT:
An air/fuel ratio estimator for estimating an air/fuel ratio of a mixture supplied to each cylinder of a multicylinder internal combustion engine through an output of an air/fuel ratio sensor installed at a confluence point of an exhaust system of the engine. The estimator includes first device for assuming the output of the air/fuel ratio sensor as an average value made up of a sum of products of past firing histories of each cylinder weighted by a predetermined value, and establishing a model using the air/fuel ratio as a state variable, a second device for obtaining a state equation with respect to the state variable. An observer is provided to estimate the unmeasured state variable indicative of the air/fuel ratio and the air/fuel ratio at each cylinder is estimated from an output of the observer. In the configuration upper and lower limit is established for the state variable such that it is replaced with its initial value if it exceeds either limit. As a result, a range of change of the variable is decreased so that the estimator can be realized on a low-performance microcomputer mounted on a vehicle.

REFERENCES:
patent: 4869222 (1989-09-01), Klassen
patent: 4962741 (1990-10-01), Cook et al.

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