Failure detecting apparatus for exhaust secondary air supply system

Abstract

In a V-type engine in which two air supply pipes are connected to banks thereof, respectively, two air-fuel ratio sensors are provided at positions downstream of the air supply pipes for producing outputs corresponding to the density of oxygen in exhaust emissions. When exhaust secondary air is supplied, differences between air-fuel ratio feedback correction factors calculated based on outputs of two air-fuel ratio sensors at a time and air-fuel feedback correction factors calculated at a time that is a time that results after a predetermined period of time has elapsed since the time are calculated. The differences so calculated are compared with a predetermined value, and, when the calculated differences do not exceed the predetermined value, the exhaust secondary air supply system is detected to fail.

What is claimed is:  
     
         1 . A failure detecting apparatus for an exhaust secondary air supply system for supplying exhaust secondary air to a position upstream of a catalytic converter disposed along an exhaust system of an internal combustion engine, the failure detecting apparatus comprising: 
 an air-fuel ratio sensor for producing an output corresponding to a density of oxygen contained in exhaust gas flowing through the exhaust system; and    a failure detecting section for comparing values obtained at different times based on outputs of the air-fuel ratio sensor when the exhaust secondary air is supplied so as to detect a failure of the exhaust secondary air supply system.    
     
     
         2 . A failure detecting apparatus for an exhaust secondary air supply system as set forth in  claim 1 , wherein the failure detecting section comprises a correction factor difference calculating section for calculating a difference between an air-fuel feedback correction factor calculated based on an output of the air-fuel ratio sensor at a time tn and an air-fuel feedback correction factor calculated at a time tn+m that is a time that results after a predetermined period of time m has elapsed since the time tn and a comparing section for comparing the difference so calculated with a predetermined value, so as to determine that the exhaust secondary air supply system fails when the calculated difference does not exceed the predetermined value.  
     
     
         3 . A failure detecting apparatus for an exhaust secondary air supply system as set forth in  claim 2 , wherein the predetermined period of time is set based on a time needed for a change in operating conditions of the internal combustion engine caused by an activation of the exhaust secondary air supply system to come to an end.  
     
     
         4 . A failure detecting apparatus for an exhaust secondary air supply system for supplying exhaust secondary air to a position upstream of a catalytic converter disposed along an exhaust system of an internal combustion engine, the failure detecting apparatus comprising: 
 a plurality of air supply pipes connected to the exhaust system of the internal combustion engine for supplying the exhaust secondary air, respectively;    a plurality of air-fuel ratio sensors disposed along the exhaust system at positions downstream of the plurality of air supply pipes for producing an output corresponding to a density of oxygen contained in exhaust emissions flowing through the exhaust system, respectively; and    a failure detecting section for comparing values with each other which are obtained based on the outputs of the plurality of air-fuel ratio sensors so as to detect a failure of the exhaust secondary air supply system.    
     
     
         5 . A failure detecting apparatus for an exhaust secondary air supply system as set forth in  claim 4 , wherein the failure detecting section comprises a correction factor difference calculating section for calculating a difference between air-fuel ratio feedback correction factors calculated, respectively, based on the outputs of the plurality of air-fuel ratio sensors, and a comparing section for comparing the difference so calculated with a predetermined value, so as to determine that the exhaust secondary air supply system fails when the calculated difference exceeds the predetermined value.  
     
     
         6 . A failure detecting apparatus for an exhaust secondary air supply system as set forth in  claim 4 , wherein the internal combustion engine is a V-type engine, wherein the failure detecting apparatus comprises an air pump, and wherein the air supply pipe is connected to the air pump and is branched at an intermediate position along its length so as to be connected to banks of the V-type engine, respectively.  
     
     
         7 . A failure detecting apparatus for an exhaust secondary air supply system as set forth in  claim 5 , wherein the correction factor difference calculating section calculates a difference between maximum values of air-fuel ratio feedback correction factors calculated, respectively, based on the outputs of the plurality of air-fuel ratio sensors.