Catalytic converter monitoring using downstream oxygen sensor

Claim 1

An apparatus for monitoring catalytic converter efficiency in an internal combustion engine including an exhaust path for an engine; an upstream exhaust gas oxygen sensor (EGO); a catalytic converter in the exhaust stream; a downstream exhaust gas oxygen sensor; switching means coupled to both said upstream exhaust gas oxygen sensor and said downstream exhaust gas oxygen sensor; fuel control means coupled to said switch means for causing the switch means to switch between said upstream and downstream exhaust gas oxygen sensor; fuel injectors coupled to said fuel control means and responsive to said control means for injecting a determined amount of fuel; and said fuel control means adapted to switch to said upstream exhaust gas oxygen sensor during normal air/fuel ratio control and switch to said downstream exhaust gas oxygen sensor during air/fuel control when catalytic converter efficiencies being monitored.

Claim 2

An apparatus for monitoring catalytic converter efficiency in an internal combustion engine including an exhaust path for an engine; an upstream exhaust gas oxygen sensor (EGO); a catalytic converter in the exhaust stream; a downstream exhaust gas oxygen sensor; switching means coupled to both said upstream exhaust gas oxygen sensor and said downstream exhaust gas oxygen sensor; fuel control means coupled to said switch means for causing the switch means to switch between said upstream and downstream exhaust gas oxygen sensor; fuel injectors coupled to said fuel control means and responsive to said control means for injecting a determined amount of fuel; and said fuel control means adapted to switch to said upstream exhaust gas oxygen sensor during normal air/fuel ratio control and switch to said downstream exhaust gas oxygen sensor during air/fuel control when catalytic converter efficiencies being monitored.

Claim 6

An apparatus for monitoring catalytic converter efficiency in an internal combustion engine including an exhaust path for an engine; an upstream exhaust gas oxygen sensor; a catalytic converter in the exhaust stream; a downstream exhaust gas oxygen sensor; switching means coupled to both said upstream exhaust gas oxygen sensor and said downstream exhaust gas oxygen sensor; control means coupled to said switch means for causing the switch means to switch between said upstream and downstream exhaust gas oxygen sensor; fuel injectors coupled to said control means and responsive to said control means for injecting a determined amount of fuel; said control means adapted to switch to said upstream exhaust gas oxygen sensor during normal air/fuel ratio control and switch to said downstream exhaust gas oxygen sensor during air/fuel control when catalytic converter efficiencies being monitored; said fuel control means including means for comparing a limit cycle frequency measured during the test to a calculation of the maximum acceptable frequency based upon speed-load conditions encountered during the test; means for rationalizing data by filtering out erroneous EGO switching due to cylinder air/fuel maldistribution; means for ensuring limits on fluctuations of vehicle operating conditions, stabilizing under the downstream EGO control and monitoring to determine whether the measured frequency is within the designated limits; and means for rationalizing data to filter out erroneous gas oxygen sensor switching due to cylinder to cylinder air/fuel maldistribution.

Claim 7

An apparatus for monitoring catalytic converter efficiency in an internal combustion engine including an exhaust path for an engine; an upstream exhaust gas oxygen sensor; a catalytic converter in the exhaust stream; a downstream exhaust gas oxygen sensor; switching means coupled to both said upstream exhaust gas oxygen sensor and said downstream exhaust gas oxygen sensor; control means coupled to said switch means for causing the switch means to switch between said upstream and downstream exhaust gas oxygen sensor; fuel injectors coupled to said control means and responsive to said control means for injecting a determined amount of fuel; said control means adapted to switch to said upstream exhaust gas oxygen sensor during normal air/fuel ratio control and switch to said downstream exhaust gas oxygen sensor during air/fuel control when catalytic converter efficiencies being monitored; said fuel control means including means for comparing a limit cycle frequency measured during the test to a calculation of the maximum acceptable frequency based upon speed-load conditions encountered during the test; means for rationalizing data by filtering out erroneous EGO switching due to cylinder air/fuel maldistribution; means for ensuring limits on fluctuations of vehicle operating conditions, stabilizing under the downstream EGO control and monitoring to determine whether the measured frequency is within the designated limits; and means for rationalizing data to filter out erroneous gas oxygen sensor switching due to cylinder to cylinder air/fuel maldistribution.

Claim 8

A method of monitoring catalytic converter efficiency in an engine. control having an EGO sensor upstream and another exhaust gas oxygen sensor downstream from a catalytic converter in the exhaust path from an engine including the steps of: using a table of speed versus load indicating a threshold limit cycle frequency at each at each speed-load combination for use in accepting or rejecting a catalytic converter; using the downstream exhaust gas oxygen sensor to control the feedback fuel control system during the catalytic converter monitor test; comparing the limit cycle frequency measured during the test to a calculation of the maximum acceptable limit cycle frequency based on the load speed conditions encountered during the test; and rationalizing data to filter out erroneous exhaust gas oxygen sensor switching due to cylinder to cylinder air/fuel maldistribution.

Claim 9

A method of monitoring catalytic converter efficiency in an engine. control having an EGO sensor upstream and another exhaust gas oxygen sensor downstream from a catalytic converter in the exhaust path from an engine including the steps of: using a table of speed versus load indicating a threshold limit cycle frequency at each at each speed-load combination for use in accepting or rejecting a catalytic converter; using the downstream exhaust gas oxygen sensor to control the feedback fuel control system during the catalytic converter monitor test; comparing the limit cycle frequency measured during the test to a calculation of the maximum acceptable limit cycle frequency based on the load speed conditions encountered during the test; and rationalizing data to filter out erroneous exhaust gas oxygen sensor switching due to cylinder to cylinder air/fuel maldistribution.

Claim 11

A method of catalytic converter efficiency monitoring in a system having an exhaust gas oxygen sensor upstream and another gas oxygen sensor downstream from a catalytic converter including the steps of: using the downstream exhaust gas oxygen sensor to control feedback fuel control system during catalytic converter monitoring; and using a stored table of catalytic converter operating parameters for monitoring catalytic converter efficiency.

Claim 12

A method of catalytic converter efficiency monitoring in a system having an exhaust gas oxygen sensor upstream and another gas oxygen sensor downstream from a catalytic converter including the steps of: using the downstream exhaust gas oxygen sensor to control feedback fuel control system during catalytic converter monitoring; and using a stored table of catalytic converter operating parameters for monitoring catalytic converter efficiency.

Claim 15

A method of catalytic converter efficiency monitoring in an engine control system ha exhaust gas oxygen sensor upstream and another exhaust gas oxygen sensor downstream from a catalytic converter including the steps of: using the downstream exhaust gas oxygen sensor to control feedback fuel control system during catalytic converter monitor; using a speed-load table with stored limit cycle frequencies; comparing sensed limit cycle frequency data at engine speed load operating points to the stored limit cycle frequency at the corresponding speed load operating point; determining whether to accept or reject the catalytic converter based upon the comparison of the two limit cycle frequencies; ensuring desired limits on fluctuations of vehicle operating conditions prior to and during monitoring of catalytic converter efficiency; and rationalizing data to filter out erroneous exhaust gas oxygen sensor switching due to cylinder to cylinder air/fuel maldistribution.

Claim 16

A method of catalytic converter efficiency monitoring in an engine control system ha exhaust gas oxygen sensor upstream and another exhaust gas oxygen sensor downstream from a catalytic converter including the steps of: using the downstream exhaust gas oxygen sensor to control feedback fuel control system during catalytic converter monitor; using a speed-load table with stored limit cycle frequencies; comparing sensed limit cycle frequency data at engine speed load operating points to the stored limit cycle frequency at the corresponding speed load operating point; determining whether to accept or reject the catalytic converter based upon the comparison of the two limit cycle frequencies; ensuring desired limits on fluctuations of vehicle operating conditions prior to and during monitoring of catalytic converter efficiency; and rationalizing data to filter out erroneous exhaust gas oxygen sensor switching due to cylinder to cylinder air/fuel maldistribution.