Air-fuel ratio control system for automotive vehicle engine

Claim 2

An air-fuel ratio control system for and engine system which include: a three-way catalytic converter disposed in an exhaust conduit; a source of secondary air which is arranged to introduce secondary air into the exhaust conduit at a location upstream of the catalytic converter under predetermine engine operating conditions, the air-fuel ratio control system comprising: a first air-fuel ratio sensor which is arranged to sense the air-fuel ratio of the exhaust gases at a location upstream of the location at which the source of secondary air introduces air into the exhaust conduit; a second air-fuel ratio sensor which is arranged to sense the air-fuel ratio of the exhaust gases at a location downstream of the catalytic converter; and circuit means operatively connected with said first and second air-fuel ratio sensors for controlling the supply of fuel to the engine, said circuit means including circuitry which: bases the fuel supply control on the output of the first air-fuel ratio sensor, corrects the control based on the output of the second air-fuel ratio sensor, and inhibits the correction control based on the output of the second air-fuel ratio sensor for a predetermined time following the supply of secondary air into the exhaust conduit being stopped.

Claim 3

An air-fuel ratio control system as claimed in claim 1 wherein the predetermined time is variable in accordance with the capacity of the catalytic converter to retain residual air.

Claim 4

An air-fuel ratio control system as claimed in claim 2 wherein said circuit means includes circuitry for monitoring the outputs of said first and second air-fuel ratio sensors for a predetermined period of time during the supply of air into the exhaust conduit and for determining a factor which varies inversely with the capacity and the inverse of which is used to determine said predetermined time.

Claim 5

An air-fuel ratio control system as claimed in claim 1 wherein the inhibition of the correction based on the output of the second air-fuel ratio sensor is additionally implemented during the time the secondary air is being supplied into the exhaust conduit.

Claim 6

An internal combustion engine system comprising: sensor means for sensing engine speed and engine load; a catalytic converter disposed in an exhaust gas conduit; a first air-fuel ratio sensor disposed in the exhaust gas conduit upstream of the catalytic converter; a second air-fuel ratio sensor disposed in the exhaust gas conduit downstream of said catalytic converter; fuel injection means for supplying fuel into the engine; secondary air supply means for introducing air into the exhaust conduit at a location between said first air-fuel ratio sensor and said catalytic converter when the engine is indicated as operating in a predetermined mode by said sensor means; a control circuit operatively connected with said sensor means and said fuel injector means, said control circuit including circuitry for; using the output of said sensor means to determine a basic injection pulse width; determining an air-fuel ratio feedback control factor value based on the output of said first air-fuel ratio sensor; determining an actual pulse width by correcting the basic pulse width using air-fuel ratio feedback control factor; modifying the air-fuel ratio feedback control factor based on the output of said second air-fuel ratio sensor; and inhibiting the air-fuel ratio feedback control factor based on the output of said second air-fuel ratio sensor during the time secondary air is supplied into the exhaust conduit by the secondary air supply means and for continuing the inhibition for a predetermined period from the time the supply of secondary air is stopped.

Claim 7

An internal combustion engine system comprising: sensor means for sensing engine speed and engine load; a catalytic converter disposed in an exhaust gas conduit; a first air-fuel ratio sensor disposed in the exhaust gas conduit upstream of the catalytic converter; a second air-fuel ratio sensor disposed in the exhaust gas conduit downstream of said catalytic converter; fuel injection means for supplying fuel into the engine; secondary air supply means for introducing air into the exhaust conduit at a location between said first air-fuel ratio sensor and said catalytic converter when the engine is indicated as operating in a predetermined mode by said sensor means; a control circuit operatively connected with said sensor means and said fuel injector means, said control circuit including circuitry for; using the output of said sensor means to determine a basic injection pulse width; determining an air-fuel ratio feedback control factor value based on the output of said first air-fuel ratio sensor; determining an actual pulse width by correcting the basic pulse width using air-fuel ratio feedback control factor; modifying the air-fuel ratio feedback control factor based on the output of said second air-fuel ratio sensor; and inhibiting the air-fuel ratio feedback control factor based on the output of said second air-fuel ratio sensor during the time secondary air is supplied into the exhaust conduit by the secondary air supply means and for continuing the inhibition for a predetermined period from the time the supply of secondary air is stopped.