On-board catalytic converter efficiency monitoring

Claim 1

An apparatus for monitoring catalytic converter efficiency in treating exhaust gas from an internal combustion engine, comprising: a catalytic converter; an exhaust conduit means for passing downstream exhaust gas from the catalytic converter; a downstream EGO sensor mounted for exposure to the downstream exhaust gas in the exhaust conduit means for generating a downstream output signal corresponding to the oxygen content level of the downstream exhaust gas; an air/fuel ratio perturbation means for perturbing the air/fuel ratio at which fuel is supplied to the engine during a perturbation period, each cylinder air/fuel ratios being perturbed individually above and below a mean air/fuel ratio; comparison means for performing a comparison of the downstream output signal for exhaust gas from the engine during the perturbation period to the downstream output signal for exhaust gas from the engine during an adjacent non-perturbation time period; and test result signal means for generating a signal at least when the comparison indicates catalytic converter efficiency below the minimum acceptable efficiency.

Claim 2

An apparatus for monitoring catalytic converter efficiency in treating exhaust gas from an internal combustion engine, comprising: a catalytic converter; an exhaust conduit means for passing downstream exhaust gas from the catalytic converter; a downstream EGO sensor mounted for exposure to the downstream exhaust gas in the exhaust conduit means for generating a downstream output signal corresponding to the oxygen content level of the downstream exhaust gas; an air/fuel ratio perturbation means for perturbing the air/fuel ratio at which fuel is supplied to the engine during a perturbation period, each cylinder air/fuel ratios being perturbed individually above and below a mean air/fuel ratio; comparison means for performing a comparison of the downstream output signal for exhaust gas from the engine during the perturbation period to the downstream output signal for exhaust gas from the engine during an adjacent non-perturbation time period; and test result signal means for generating a signal at least when the comparison indicates catalytic converter efficiency below the minimum acceptable efficiency.

Claim 9

A method of monitoring efficiency of a catalytic converter in treating exhaust gas from an internal combustion engine having multiple cylinders and fuel control means for generating fuel control signals in response to input signals for individually controlling electronically actuated fuel injectors coupled to each cylinder to maintain a mean air/fuel ratio among the cylinders, the method comprising: perturbing the air/fuel ratio at which air and fuel are supplied to the engine during a perturbation period, each cylinder air/fuel ratio being perturbed individually, alternating above and below the mean air/fuel ratio; performing a comparison of an output signal of an EGO sensor exposed to the exhaust gas downstream of the catalytic converter for the perturbation period to the output signal of said EGO sensor for an adjacent non-perturbation time period; and generating a test result signal at least when the comparison indicates catalytic efficiency below a minimum acceptable catalytic converter efficiency level.

Claim 10

A method of monitoring efficiency of a catalytic converter in treating exhaust gas from an internal combustion engine having multiple cylinders and fuel control means for generating fuel control signals in response to input signals for individually controlling electronically actuated fuel injectors coupled to each cylinder to maintain a mean air/fuel ratio among the cylinders, the method comprising: perturbing the air/fuel ratio at which air and fuel are supplied to the engine during a perturbation period, each cylinder air/fuel ratio being perturbed individually, alternating above and below the mean air/fuel ratio; performing a comparison of an output signal of an EGO sensor exposed to the exhaust gas downstream of the catalytic converter for the perturbation period to the output signal of said EGO sensor for an adjacent non-perturbation time period; and generating a test result signal at least when the comparison indicates catalytic efficiency below a minimum acceptable catalytic converter efficiency level.

Claim 13

A method for controlling the air/fuel ratio of an air and fuel mixture fed to an internal combustion engine and for periodically monitoring the efficiency of a catalytic converter treating exhaust gas exposed to a first EGO sensor means for generating a first EGO signal having a value corresponding to oxygen content level therein as it is passed from the engine to the catalytic converter through first exhaust gas conduit means, and thereafter exposed to a second EGO sensor means for generating a second EGO signal having a value corresponding to oxygen content level therein as it is passed from the catalytic converter through a second exhaust gas conduit means, the engine having multiple cylinders and fuel control means for generating individual injector control signals for individually controlling corresponding electronically actuated fuel injectors coupled, one each, to a corresponding one of said cylinders, the method comprising the steps of: A) operating the fuel control means during a normal operating mode for controlling the air/fuel ratio based, at least in part, on (a) a first feedback control loop generating an input signal to the fuel control means based, at least in part, on the first EGO signal, and (b) a second feedback control loop generating an input signal to the fuel control means based, at least in part, on the second EGO signal, to maintain a mean air/fuel ratio among the cylinders, the mean air/fuel ratio having a value which cycles at a limit cycle frequency generally within limits defining a range about a stoichiometric value; B) switching to a test mode, comprising (a) initiating a test interval, (b) opening the first feedback control loop and generating an A/F modulation signal as an input signal to the fuel control means simulating the limit cycle frequency immediately prior to initiating the test interval, (c) measuring a first test value based on the second EGO signal corresponding to exhaust gas from the engine during a non-perturbation period of the test interval, (d) generating, during a perturbation period of the test interval, a perturbation signal as an input signal to the fuel control means to perturb the air/fuel ratio of each cylinder individually alternating above and below the mean air/fuel ratio of the non-perturbation period, and measuring a second test value based on the second EGO signal corresponding to exhaust gas from the engine during the perturbation period, (e) performing a comparison of the first test value and the second test value, and (f) generating a test result signal at least when the comparison indicates catalytic converter efficiency below a minimum acceptable catalytic converter efficiency; and C) returning to normal operating mode.

Claim 14

A method for controlling the air/fuel ratio of an air and fuel mixture fed to an internal combustion engine and for periodically monitoring the efficiency of a catalytic converter treating exhaust gas exposed to a first EGO sensor means for generating a first EGO signal having a value corresponding to oxygen content level therein as it is passed from the engine to the catalytic converter through first exhaust gas conduit means, and thereafter exposed to a second EGO sensor means for generating a second EGO signal having a value corresponding to oxygen content level therein as it is passed from the catalytic converter through a second exhaust gas conduit means, the engine having multiple cylinders and fuel control means for generating individual injector control signals for individually controlling corresponding electronically actuated fuel injectors coupled, one each, to a corresponding one of said cylinders, the method comprising the steps of: A) operating the fuel control means during a normal operating mode for controlling the air/fuel ratio based, at least in part, on (a) a first feedback control loop generating an input signal to the fuel control means based, at least in part, on the first EGO signal, and (b) a second feedback control loop generating an input signal to the fuel control means based, at least in part, on the second EGO signal, to maintain a mean air/fuel ratio among the cylinders, the mean air/fuel ratio having a value which cycles at a limit cycle frequency generally within limits defining a range about a stoichiometric value; B) switching to a test mode, comprising (a) initiating a test interval, (b) opening the first feedback control loop and generating an A/F modulation signal as an input signal to the fuel control means simulating the limit cycle frequency immediately prior to initiating the test interval, (c) measuring a first test value based on the second EGO signal corresponding to exhaust gas from the engine during a non-perturbation period of the test interval, (d) generating, during a perturbation period of the test interval, a perturbation signal as an input signal to the fuel control means to perturb the air/fuel ratio of each cylinder individually alternating above and below the mean air/fuel ratio of the non-perturbation period, and measuring a second test value based on the second EGO signal corresponding to exhaust gas from the engine during the perturbation period, (e) performing a comparison of the first test value and the second test value, and (f) generating a test result signal at least when the comparison indicates catalytic converter efficiency below a minimum acceptable catalytic converter efficiency; and C) returning to normal operating mode.