Combined engine air/fuel control and catalyst monitoring

Claim 2

An engine control means including: a catalyst; a first exhaust gas oxygen sensor upstream of said catalyst; a second exhaust gas oxygen sensor downstream of said catalyst; and a complementary filter set coupled to said first and second exhaust gas oxygen sensors characterized by a crossover frequency and including: a high pass filter coupled to said first EGO sensor; a low pass filter coupled to said second EGO sensor; and a summer means coupled to the output of said high pass filter and said low pass filter for providing a composite output from said high Pass and low pass filters for use by the engine control means.

Claim 3

An engine control means as recited in claim 1 wherein: a first voltage follower is coupled between said first EGO sensor and said high pass filter; and a second voltage follower coupled between said second EGO sensor and said second low pass filter.

Claim 4

An engine control means as recited in claim 2 further comprising: a catalyst monitoring output coupled between the second voltage follower and the low pass filter for providing a signal which is a function of degradation of the catalyst conversion efficiency.

Claim 5

An engine control means as recited in claim 3 further comprising: means for establishing a low crossover frequency; means for sensing the amplitude of the catalyst monitoring signal; means for comparing the sensed amplitude to a predetermined amplitude; and means for determining degradation of the catalyst if the sensed amplitude is less than the predetermined amplitude.

Claim 6

An engine control means as recited in claim 3 further comprising: means for increasing the crossover frequency until the catalyst monitoring signal reaches a predetermined amplitude; means for determining the crossover frequency; frequency to a predetermined frequency; and means for determining degradation of the catalyst if the crossover frequency is greater than the predetermined frequency.

Claim 7

An engine control means as recited in claim 3 further comprising: means for increasing the crossover frequency until the engine control means reaches air/fuel ratio limit cycle operation; means for determining the frequency of the limit cycle operation; means for comparing the limit cycle frequency to a stored frequency; and means for determining degradation of the catalyst if the limit cycle frequency is greater than the stored frequency.

Claim 8

An engine control means for an engine including: a catalyst in an engine exhaust gas stream; a first exhaust gas oxygen (EGO) sensor upstream of said catalyst; a second exhaust gas oxygen sensor downstream of said catalyst; a complementary filter set characterized by a crossover frequency coupled to said first and second exhaust gas oxygen sensors; said complementary filter set including a high pass filter coupled to said first EGO sensor, and a low pass filter coupled to said second EGO sensor, and a summer coupled to output from the high pass and low pass filters; an air/fuel feedback controller coupled to an output from said summer for providing a fuel control signal; a fuel metering system coupled to receive an input from said air/fuel feedback controller for supplying the engine with fuel; a catalyst monitoring output coupled to said second EGO sensor for providing a signal which is a function of catalyst degradation; and said complementary filter set including means for varying the crossover frequency to facilitate determining catalyst malfunction, so as to increase the crossover frequency from a low value until a catalyst monitoring output signal reaches a predetermined characteristic.

Claim 9

An engine control means for an engine including: a catalyst in an engine exhaust gas stream; a first exhaust gas oxygen (EGO) sensor upstream of said catalyst; a second exhaust gas oxygen sensor downstream of said catalyst; a complementary filter set characterized by a crossover frequency coupled to said first and second exhaust gas oxygen sensors; said complementary filter set including a high pass filter coupled to said first EGO sensor, and a low pass filter coupled to said second EGO sensor, and a summer coupled to output from the high pass and low pass filters; an air/fuel feedback controller coupled to an output from said summer for providing a fuel control signal; a fuel metering system coupled to receive an input from said air/fuel feedback controller for supplying the engine with fuel; a catalyst monitoring output coupled to said second EGO sensor for providing a signal which is a function of catalyst degradation; and said complementary filter set including means for varying the crossover frequency to facilitate determining catalyst malfunction, so as to increase the crossover frequency from a low value until a catalyst monitoring output signal reaches a predetermined characteristic.

Claim 12

A method as recited in claim 8 wherein said method further includes the steps of: coupling a first voltage follower between the first EGO sensor and the high pass filter; and coupling a second voltage follower between the second EGO sensor and the second low pass filter.

Claim 13

A method as recited in claim 8 wherein said method further includes: coupling a catalyst monitoring signal output between the second voltage follower and the second low pass filter for providing a catalyst monitoring signal whose amplitude is indicative of degradation of the catalyst conversion efficiency.

Claim 14

A method as recited in claim 10, wherein said method further includes the step of: increasing the crossover frequency from a relatively low value until a predetermined characteristic of the catalyst monitoring signal is achieved.

Claim 15

A method as recited in claim 10 wherein said catalyst monitoring signal indicates a defective catalyst when the amplitude of said catalyst monitoring signal drops below a predetermined value.

Claim 16

A method as recited in claim 11 wherein said catalyst monitoring signal indicates a defective catalyst when a crossover frequency associated with said complementary filter set is greater than a preset frequency, when a predetermined amplitude for the catalyst monitoring signal is reached.

Claim 17

A method as recited in claim 11 wherein said catalyst monitoring signal indicates a defective catalyst when a crossover frequency associated with said complementary filter set is increased until limit cycle operation is reached and the limit cycle frequency is greater than a predetermined frequency.