System and method for measuring hydrocarbon conversion efficiency of a catalytic converter

• US 5,941,928 A
• Filed: 07/31/1997
• Issued: 08/24/1999
• Est. Priority Date: 07/31/1997
• Status: Expired due to Fees

• Current Assignee: Temic Automotive of North America, Incorporated (Continental AG)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Naber, Jeffrey D., Young, Daniel A., Adams, Neil J., Remboski, Donald J. Jr.
• Primary Examiner(s): DOMBROSKE, GEORGE M
• Application Number:
  US08/903,848
• Time in Patent Office: 754 Days
• Field of Search: 73/23.31, 73/23.32, 73/116, 73/118.1, 60/277, 123/688, 701/103, 701/109
• US Class Current: 701/109
• CPC Class Codes: F01N 11/00 Monitoring or diagnostic devices for exhaust-gas treatment apparatus , e.g. for catalytic activity safety, indicating or supervising devices for internal combustion engines F02B77/08; testing of machines G01M13/00
• CPC Class Codes: F01N 11/002 the diagnostic devices measuring or estimating temperature or pressure in, or downstream of the exhaust apparatus
• CPC Class Codes: F01N 11/007 the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
• CPC Class Codes: F01N 2550/02 Catalytic activity of catalytic converters
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A system and method measures hydrocarbon conversion efficiency of a catalytic converter (501). Total-combustible sensors (511, 521) are positioned to measure exhaust gas on both sides of the catalytic converter (501). Signals from these sensors (511, 521) have a magnitude comprised of a first portion, dependent on a concentration of the hydrocarbon gas in the gas stream, and a second portion, dependent on a concentration of the other combustible gasses in the gas stream, where a magnitude relationship between the first portion and the second portion is variable when the gas stream transitions into a region on the rich side of stoichiometry. The signals from these sensors (511, 521) are filtered so that a magnitude relationship between a first and second portion of the filtered signals is constant when the gas stream (506) transitions into the region on the rich-side of stoichiometry. Hydrocarbon conversion efficiency (529) is computed dependent on the filtered signals (515, 525).

Claims

1. A method for measuring hydrocarbon conversion efficiency of a catalytic converter coupled to an engine exhausting a combusted gas stream comprised of hydrocarbon gas and other combustible gasses to the catalytic converter, the catalytic converter exhausting a catalyzed gas stream dependent thereon, the method comprising steps of:

sensing the combusted gas stream and providing a total-combustible gas input signal dependent thereon, the total-combustible gas input signal having a magnitude comprised of a first portion, dependent on a concentration of the hydrocarbon gas in the combusted gas stream, and a second portion, dependent on a concentration of the other combustible gasses in the combusted gas stream, where a magnitude relationship between the first portion and the second portion is variable when the combusted gas stream transitions into a region on the rich side of stoichiometry;

filtering the total-combustible input gas signal and providing a filtered total-combustible gas input signal dependent thereon, the filtered total-combustible gas input signal having a magnitude comprised of a first portion, dependent on the first portion of the total-combustible gas input signal, and a second portion, dependent on the second portion of the total-combustible gas signal, wherein a magnitude relationship between the first portion and the second portion of the filtered total-combustible gas input signal is substantially constant when the combusted gas stream transitions into the region on the rich-side of stoichiometry;

sensing the catalyzed gas stream and providing a total-combustible gas output signal dependent thereon, the total-combustible gas output signal having a magnitude comprised of a first portion, dependent on a concentration of the hydrocarbon gas in the catalyzed gas stream, and a second portion, dependent on a concentration of the other combustible gasses in the catalyzed gas stream, where a magnitude relationship between the first portion and the second portion is variable when the catalyzed gas stream transitions into a region on the rich side of stoichiometry;

filtering the total-combustible gas output signal and providing a filtered total-combustible gas output signal dependent thereon, the filtered total-combustible gas output signal having a magnitude comprised of a first portion, dependent on the first portion of the total-combustible gas output signal, and a second portion, dependent on the second portion of the total-combustible gas output signal, wherein a magnitude relationship between the first portion and the second portion of the filtered total-combustible gas output signal is substantially constant when the catalyzed gas stream transitions into the region on the rich-side of stoichiometry; and

computing an instantaneous catalyst efficiency metric dependent on the filtered total-combustible gas input signal and the filtered total-combustible gas output signal.

2. A method in accordance with claim 1 further comprising the steps of:

measuring the combusted gas stream using a switching-type exhaust gas oxygen sensor and providing a gate signal having a rich-state and a lean-state;

integrating the instantaneous catalyst efficiency metric and providing an integrated catalyst efficiency metric, when the gate signal is indicating the lean-state; and

comparing the integrated catalyst efficiency metric to a threshold and indicating an out-of-compliance signal when the integrated catalyst efficiency metric exceeds the threshold.

3. A method in accordance with claim 1 wherein both steps of filtering comprise steps of median filtering.

4. A method in accordance with claim 1 wherein both steps of filtering comprise steps trimmed-mean filtering.

5. A method in accordance with claim 2 further comprising the step of:

measuring at least one powertrain characteristic selected from the group of;

engine speed, engine load, fuel flow rate, exhaust gas temperature, and engine temperature; and

wherein the threshold is established dependent on the measured at least one powertrain characteristic.

6. A method in accordance with claim 1 wherein the step of computing a catalyst efficiency metric comprises computing a catalyst efficiency metric using the following deterministic equation:

efficiency=1-(filtered total-combustible gas output signal/filtered total-combustible gas input signal.

7. A method for measuring hydrocarbon conversion efficiency of a catalytic converter coupled to an engine exhausting a combusted gas stream comprised of hydrocarbon gas and other combustible gasses to the catalytic converter, the catalytic converter exhausting a catalyzed gas stream dependent thereon, the method comprising steps of:

sensing the combusted gas stream and providing a total-combustible gas input signal dependent thereon, the total-combustible gas input signal having a magnitude comprised of a first portion, dependent on a concentration of the hydrocarbon gas in the combusted gas stream, and a second portion, dependent on a concentration of the other combustible gasses in the combusted gas stream, where a magnitude relationship between the first portion and the second portion is variable when the combusted gas stream transitions into a region on the rich side of stoichiometry;

filtering the total-combustible input gas signal and providing a filtered total-combustible gas input signal dependent thereon, the filtered total-combustible gas input signal having a magnitude comprised of a first portion, dependent on the first portion of the total-combustible gas input signal, and a second portion, dependent on the second portion of the total-combustible gas signal, wherein a magnitude relationship between the first portion and the second portion of the filtered total-combustible gas input signal is substantially constant when the combusted gas stream transitions into the region on the rich-side of stoichiometry;

sensing the catalyzed gas stream and providing a total-combustible gas output signal dependent thereon, the total-combustible gas output signal having a magnitude comprised of a first portion, dependent on a concentration of the hydrocarbon gas in the catalyzed gas stream, and a second portion, dependent on a concentration of the other combustible gasses in the catalyzed gas stream, where a magnitude relationship between the first portion and the second portion is variable when the catalyzed gas stream transitions into a region on the rich side of stoichiometry;

filtering the total-combustible gas output signal and providing a filtered total-combustible gas output signal dependent thereon, the filtered total-combustible gas output signal having a magnitude comprised of a first portion, dependent on the first portion of the total-combustible gas output signal, and a second portion, dependent on the second portion of the total-combustible gas output signal, wherein a magnitude relationship between the first portion and the second portion of the filtered total-combustible gas output signal is substantially constant when the catalyzed gas stream transitions into the region on the rich-side of stoichiometry; and

computing an instantaneous catalyst efficiency metric dependent on the filtered hydrocarbon gas input signal and the filtered hydrocarbon gas output signal using the following deterministic equation;

efficiency=1-(filtered total-combustible gas output signal/filtered total-combustible gas input signal;

measuring the combusted gas stream using a switching-type exhaust gas oxygen sensor and providing a gate signal having a rich-state and a lean-state;

integrating the instantaneous catalyst efficiency metric and providing an integrated catalyst efficiency metric, when the gate signal is indicating the lean-state; and

comparing the integrated catalyst efficiency metric to a threshold and indicating an out-of-compliance signal when the integrated catalyst efficiency metric exceeds the threshold.

8. A method in accordance with claim 7 wherein both steps of filtering comprise steps of median filtering.

9. A method in accordance with claim 7 wherein both steps of filtering comprise steps of trimmed-mean filtering.

10. A method in accordance with claim 8 further comprising the step of:

measuring at least one powertrain characteristic selected from the group of;

engine speed, engine load, fuel flow rate, exhaust gas temperature, and engine temperature; and

wherein the threshold is established dependent on the measured at least one powertrain characteristic.

11. A method in accordance with claim 9 further comprising the step of:

measuring at least one powertrain characteristic selected from the group of;

engine speed, engine load, fuel flow rate, exhaust gas temperature, and engine temperature; and

wherein the threshold is established dependent on the measured at least one powertrain characteristic.

12. A system for measuring hydrocarbon conversion efficiency of a catalytic converter, the system having an engine exhausting a combusted gas stream to the catalytic converter, the catalytic converter exhausting a catalyzed gas stream comprised of hydrocarbon gas and other combustible gasses, the system comprising:

a first sensor coupled between the engine and the catalytic converter, the first sensor having an output terminal for providing a total-combustible gas input signal having a magnitude comprised of a first portion, dependent on a concentration of the hydrocarbon gas in the combusted gas stream, and a second portion, dependent on a concentration of the other combustible gasses in the combusted gas stream, where a magnitude relationship between the first portion and the second portion is variable when the combusted gas stream transitions into a region on the rich side of stoichiometry; and

a first filter, operatively coupled to the output terminal of the first sensor, for providing a filtered total-combustible gas input signal dependent on the total-combustible gas input signal, the filtered total-combustible gas input signal having a magnitude comprised of a first portion, dependent on the first portion of the total-combustible gas input signal, and a second portion, dependent on the second portion of the total-combustible gas signal, wherein a magnitude relationship between the first portion and the second portion of the filtered total-combustible gas input signal is substantially constant when the combusted gas stream transitions into the region on the rich-side of stoichiometry;

a second sensor coupled to the catalytic converter, the second sensor having an output terminal for providing a total-combustible gas output signal, the total-combustible gas output signal having a magnitude comprised of a first portion, dependent on a concentration of the hydrocarbon gas in the catalyzed gas stream, and a second portion, dependent on a concentration of the other combustible gasses in the catalyzed gas stream, where a magnitude relationship between the first portion and the second portion is variable when the catalyzed gas stream transitions into a region on the rich side of stoichiometry; and

a second filter, operatively coupled to the output terminal of the second sensor, for providing a filtered total-combustible gas output signal dependent on the total-combustible gas output signal, the filtered total-combustible gas output signal having a magnitude comprised of a first portion, dependent on the first portion of the total-combustible gas output signal, and a second portion, dependent on the second portion of the total-combustible gas output signal, wherein a magnitude relationship between the first portion and the second portion of the filtered total-combustible gas output signal is substantially constant when the catalyzed gas stream transitions into the region on the rich-side of stoichiometry; and

a computing element coupled to both the first and second filters, the computing element providing an instantaneous catalyst efficiency metric dependent on the filtered hydrocarbon gas input signal and the filtered hydrocarbon gas output signal.

13. A system in accordance with claim 12 further comprising:

a switching-type exhaust gas oxygen sensor coupled between the engine and the catalytic converter, the switching-type exhaust gas oxygen sensor having an output terminal providing a gate signal having a rich-state and a lean-state, dependent on fuel and oxygen content of the catalyzed gas stream;

a gate coupled between the output terminal of the switching-type exhaust gas oxygen sensor and the computing element, the gate providing the instantaneous catalyst efficiency metric when the gate signal indicates the lean-state;

an averager coupled to the gate, the averager providing an average catalyst efficiency metric, dependent on the instantaneous catalyst efficiency metric provided by the gate; and

a comparator for comparing the integrated catalyst efficiency metric to a threshold and indicating an out-of-compliance signal when the integrated catalyst efficiency metric exceeds the threshold.

14. A system in accordance with claim 12 wherein both the first and second sensors are total-combustible sensors.

15. A system in accordance with claim 12 wherein both the first and second filters are median filters.

16. A system in accordance with claim 12 wherein both the first and second filters are trimmed-mean filters.

17. A system in accordance with claim 13 further comprising:

a measurement device for measuring at least one powertrain characteristic selected from the group of;

engine speed, engine load, fuel flow rate, exhaust gas temperature, and engine temperature; and

wherein the threshold is established dependent on the measured at least one powertrain characteristic.

18. A system for measuring hydrocarbon conversion efficiency of a catalytic converter, the system having an engine exhausting a combusted gas stream to the catalytic converter, the catalytic converter exhausting a catalyzed gas stream comprised of hydrocarbon gas and other combustible gasses, the system comprising:

a first sensor coupled between the engine and the catalytic converter, the first sensor having an output terminal for providing a total-combustible gas input signal having a magnitude comprised of a first portion, dependent on a concentration of the hydrocarbon gas in the combusted gas stream, and a second portion, dependent on a concentration of the other combustible gasses in the combusted gas stream, where a magnitude relationship between the first portion and the second portion is variable when the combusted gas stream transitions into a region on the rich side of stoichiometry; and

a first filter, operatively coupled to the output terminal of the first sensor, for providing a filtered total-combustible gas input signal dependent on the total-combustible gas input signal, the filtered total-combustible gas input signal having a magnitude comprised of a first portion, dependent on the first portion of the total-combustible gas input signal, and a second portion, dependent on the second portion of the total-combustible gas signal, wherein a magnitude relationship between the first portion and the second portion of the filtered total-combustible gas input signal is substantially constant when the combusted gas stream transitions into the region on the rich-side of stoichiometry;

a second sensor coupled to the catalytic converter, the second sensor having an output terminal for providing a total-combustible gas output signal, the total-combustible gas output signal having a magnitude comprised of a first portion, dependent on a concentration of the hydrocarbon gas in the catalyzed gas stream, and a second portion, dependent on a concentration of the other combustible gasses in the catalyzed gas stream, where a magnitude relationship between the first portion and the second portion is variable when the catalyzed gas stream transitions into a region on the rich side of stoichiometry; and

a second filter, operatively coupled to the output terminal of the second sensor, for providing a filtered total-combustible gas output signal dependent on the total-combustible gas output signal, the filtered total-combustible gas output signal having a magnitude comprised of a first portion, dependent on the first portion of the total-combustible gas output signal, and a second portion, dependent on the second portion of the total-combustible gas output signal, wherein a magnitude relationship between the first portion and the second portion of the filtered total-combustible gas output signal is substantially constant when the catalyzed gas stream transitions into the region on the rich-side of stoichiometry;

a computing element coupled to both the first and second filters, the computing element providing an instantaneous catalyst efficiency metric dependent on the filtered hydrocarbon gas input signal and the filtered hydrocarbon gas output signal;

a switching-type exhaust gas oxygen sensor coupled between the engine and the catalytic converter, the switching-type exhaust gas oxygen sensor having an output terminal providing a gate signal having a rich-state and a lean-state, dependent on fuel and oxygen content of the catalyzed gas stream;

a gate coupled between the output terminal of the switching-type exhaust gas oxygen sensor and the computing element, the gate providing the instantaneous catalyst efficiency metric when the gate signal indicates the lean-state; and

an integrator coupled to the gate, the integrator providing an integrated catalyst efficiency metric, dependent on the instantaneous catalyst efficiency metric provided by the gate;

a measurement device for measuring at least one powertrain characteristic selected from the group of;

engine speed, engine load, fuel flow rate, exhaust gas temperature, and engine temperature and for establishing a threshold dependent thereon; and

a comparator for comparing the integrated catalyst efficiency metric to the threshold and indicating an out-of-compliance signal when the integrated catalyst efficiency metric exceeds the threshold.

19. A system in accordance with claim 18 wherein both the first and second sensors are total-combustible sensors.

20. A system in accordance with claim 19 wherein both the first and second filters are median filters.

21. A system in accordance with claim 19 wherein both the first and second filters are trimmed-mean filters.