Method and system for estimating a midbed temperature of a catalytic converter

• US 5,956,941 A
• Filed: 10/15/1996
• Issued: 09/28/1999
• Est. Priority Date: 10/15/1996
• Status: Expired due to Fees

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Baskins, Robert Sarow, Cullen, Michael John, Davey, Christopher K., Zaghati, Ziad, Nader, David R.
• Primary Examiner(s): ARGENBRIGHT, TONY MICHAEL
• Application Number:
  US08/731,421
• Time in Patent Office: 1,078 Days
• Field of Search: 60/274, 60/276, 60/277, 73/118.1, 701/103
• US Class Current: 60/274
• CPC Class Codes: B01D 53/9495 Controlling the catalytic process
• 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 11/005 the temperature or pressure being estimated, e.g. by means of a theoretical model
• CPC Class Codes: F01N 11/007 the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 2250/12 absorption or adsorption, and catalytic conversion
• CPC Class Codes: F01N 2410/00 By-passing, at least partially, exhaust from inlet to outlet of apparatus, to atmosphere or to other device
• CPC Class Codes: F01N 2550/02 Catalytic activity of catalytic converters
• CPC Class Codes: F01N 2570/12 Hydrocarbons
• CPC Class Codes: F01N 2570/14 Nitrogen oxides
• CPC Class Codes: F01N 3/05 by means of air, e.g. by mixing exhaust with air silencers working by addition of air to exhaust F01N1/14; arrangements for the supply of additional air for the thermal or catalytic conversion of noxious components of exhaust F01N3/30 ; in tailpipes F01N13/082
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/0871 Regulation of absorbents or adsorbents, e.g. purging by electrically controlling the supply of combustible mixture or its constituents only F02D41/0235
• CPC Class Codes: F01N 3/2006 Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating by electrically controlling the supply of combustible mixture or its constituents only F02D41/0235
• CPC Class Codes: F01N 9/00 Electrical control of exhaust gas treating apparatus monitoring or diagnostic devices for exhaust-gas treatment apparatus F01N11/00; conjoint electrical control of two or more combustion engine functions F02D43/00
• CPC Class Codes: F01N 9/005 using models instead of sensors to determine operating characteristics of exhaust systems, e.g. calculating catalyst temperature instead of measuring it directly
• CPC Class Codes: F02D 2041/1433 using a model or simulation of the system
• CPC Class Codes: F02D 2200/0804 Estimation of the temperature of the exhaust gas treatment apparatus
• CPC Class Codes: F02D 2200/1015 Engines misfires
• CPC Class Codes: F02D 41/0047 Controlling exhaust gas recirculation [EGR] temperature control with cooler in recirculation circuit F02M26/33
• CPC Class Codes: F02D 41/1401 : characterised by the control or regulation method F02D41/1473, F02D41/1477 take precedence
• CPC Class Codes: F02D 41/1402 : Adaptive control
• CPC Class Codes: F02D 41/1408 : Dithering techniques
• CPC Class Codes: F02D 41/1441 : Plural sensors
• CPC Class Codes: F02D 41/1446 : the characteristics being exhaust temperatures
• CPC Class Codes: F02D 41/1498 : measuring engine roughness
• CPC Class Codes: G01M 15/11 : by detecting misfire
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 : Engine management systems

Abstract

A method and system for estimating the midbed temperature of a catalytic converter in an exhaust system of an internal combustion engine. A rate of change in the speed of the engine is sensed and an estimated number of misfires occurring in the engine over a predetermined number of cylinder filling events is determined based on the sensed rate of change in engine speed. An instantaneous temperature of exhaust gas at the exhaust flange is determined based on the estimated rate of misfires. An instantaneous temperature at the midbed point of the catalytic converter is then determined based on the instantaneous temperature of exhaust gas at the exhaust flange. The instantaneous temperature at the midbed point is compared to a predetermined temperature threshold and the estimate rate of misfires is compared to a predetermined misfire rate threshold. A malfunction signal is then generated if both the instantaneous temperature at the midbed point exceeds the predetermined temperature threshold and the estimated rate of misfires exceeds the predetermined misfire rate threshold. A method for monitoring catalyst degradation is also disclosed.

Claims

1. A method for estimating the midbed temperature of a catalytic converter in an exhaust system of an internal combustion engine having at least one cylinder, the exhaust system including an exhaust pipe for transporting exhaust gas from the engine to the catalytic converter, the method comprising:

sensing a rate of change of the speed of the engine and generating a corresponding speed signal;

estimating a rate of misfires occurring in the engine over a predetermined number of cylinder filling events based on the speed signal;

determining an instantaneous temperature of exhaust gas at a first point on the exhaust pipe based on the estimated rate of misfires;

determining an instantaneous temperature at a midbed point of the catalytic converter based on the instantaneous temperature of exhaust gas at the first point on the exhaust pipe;

comparing the instantaneous temperature at the midbed point to a first temperature threshold indicative of the temperature at which the catalytic converter is damaged;

comparing the estimated rate of misfires to a misfire rate threshold indicative of the maximum misfires allowed for a given engine speed; and

generating a failure signal if the instantaneous temperature at the midbed point exceeds the first temperature threshold and the estimated rate of misfires exceeds the misfire rate threshold.

2. The method as recited in claim 1 further comprising illuminating a display upon receiving the failure signal.

3. The method as recited in claim 1 wherein estimating the rate of misfires comprises the steps of:

determining a first value indicative of the incremental number of misfires since a last update based on the speed signal;

determining a second value indicative of the incremental number of cylinder filling events since a last update; and

determining a filter constant which is progressively weighted by the total number of cylinder events.

4. The method as recited in claim 3 wherein estimating the rate of misfires is estimated according to the following equation:

space="preserve" listing-type="equation"> FK*B*(A/B-MISFIRE.sub.-- RATE(old)!+MISFIRE.sub.-- RATE(old),

where A corresponds to the first value, B corresponds to the second value, MISFIRE_-- RATE(old) is a value indicative of the average misfire rate estimated during a last update, and FK is the filter constant equal to the reciprocal of the number of cylinder filling events since engine start.

5. The method as recited in claim 1 wherein determining the instantaneous temperature of exhaust gas at the first point comprises:

determining a steady state temperature of exhaust gas at the first point when the engine is firing as a function of a base steady state temperature at the first point at a particular engine speed and aircharge, air/fuel modulation, engine spark timing, exhaust gas recirculation, and engine coolant temperature; and

determining a steady state temperature of exhaust gas at the first point when the engine is not firing as a function of a temperature of airflow into the engine and engine coolant temperature.

6. The method as recited in claim 1 wherein determining the instantaneous temperature at the midbed point of the catalytic converter comprises:

determining an instantaneous temperature of exhaust gas at an exhaust gas inlet of the catalytic converter based on the instantaneous temperature at the first point;

determining an instantaneous temperature of exhaust gas at the catalytic converter due to an exothermic reaction of the exhaust gas based on the estimated rate of misfires; and

determining a stoichiometric instantaneous temperature at the midbed point at a stoichiometric air/fuel ratio.

7. The method as recited in claim 6 wherein determining the instantaneous temperature of exhaust gas at the catalytic converter due to an exothermic reaction of the exhaust gas comprises:

comparing the instantaneous temperature at the midbed point to a second and third temperature threshold;

if the instantaneous temperature at the midbed point is less than the second temperature threshold, setting the instantaneous temperature of exhaust gas at the catalytic converter equal to zero; and

if the instantaneous temperature at the midbed point exceeds the third temperature threshold, determining the instantaneous temperature of exhaust gas at the catalytic converter as a function of a steady state increase in the temperature of exhaust gas in the catalytic converter, the estimated rate of misfires, an increase in the exothermic reaction of the exhaust gas per estimated rate of misfires, and an exothermic reaction at an equivalence ratio of one corresponding to stoichiometric air/fuel ratio.

8. The method as recited in claim 7 wherein determining the stoichiometric instantaneous temperature at the midbed point in the catalytic converter at stoichiometric air/fuel ratio comprises the steps of:

comparing the instantaneous temperature at the midbed point to the second and third temperature threshold;

if the instantaneous temperature at the midbed point is less than the second temperature threshold, setting the stoichiometric instantaneous temperature at the midbed point in the catalytic converter equal to the instantaneous temperature of exhaust gas at the exhaust gas inlet of the catalytic converter; and

if the instantaneous temperature at the midbed point exceeds the third temperature threshold, determining the stoichiometric instantaneous temperature at the midbed point in the catalytic converter as a function of the exothermic reaction at an equivalence ratio of one corresponding to stoichiometric air/fuel ratio and the instantaneous temperature of exhaust gas at the exhaust gas inlet.

9. A method for estimating the midbed temperature of a catalytic converter in an exhaust system of an internal combustion engine having at least one cylinder, the exhaust system including an exhaust pipe for transporting exhaust gas from the engine to the catalytic converter, the method comprising:

sensing a rate of change of the speed of the engine and generating a corresponding speed signal;

estimating a rate of misfires occurring in the engine over a predetermined number of cylinder filling events based on the speed signal;

determining an instantaneous temperature of exhaust gas at a first point on the exhaust pipe based on the estimated rate of misfires; and

determining an instantaneous temperature at a midbed point of the catalytic converter based on the instantaneous temperature of exhaust gas at the first point on the exhaust pipe.

10. The method as recited in claim 9 wherein estimating the rate of misfires comprises:

determining a first value indicative of the incremental number of misfires since a last update based on the speed signal;

determining a second value indicative of the incremental number of cylinder filling events since a last update; and

determining a filter constant which is progressively weighted by the total number of cylinder events.

11. The method as recited in claim 10 wherein estimating the rate of misfires is determined according to the following equation:

space="preserve" listing-type="equation"> FK*B*(A/B-MISFIRE.sub.-- RATE(old)!+MISFIRE.sub.-- RATE(old),

where A corresponds to the first value, B corresponds to the second value, MISFIRE_-- RATE(old) is a value indicative of the average misfire rate estimated during a last update, and FK is the filter constant equal to the reciprocal of the number of cylinder filling events since engine start.

12. The method as recited in claim 9 wherein determining the instantaneous temperature of exhaust gas at the first point comprises:

determining a steady state temperature of exhaust gas at the first point when the engine is firing as a function of a steady state temperature at the first point at a particular engine speed and aircharge, air/fuel modulation, engine spark timing, exhaust gas recirculation, and engine coolant temperature; and

determining a steady state temperature of exhaust gas at the first point when the engine is not firing as a function of a temperature of airflow into the engine and engine coolant temperature.

13. The method as recited in claim 9 wherein determining the instantaneous temperature at the midbed point comprises:

determining an instantaneous temperature of exhaust gas at an exhaust gas inlet of the catalytic converter based on the instantaneous temperature at the first point;

determining an instantaneous temperature of exhaust gas at the catalytic converter due to an exothermic reaction of the exhaust gas based on the estimated rate of misfires; and

determining a stoichiometric instantaneous temperature at the midbed point at a stoichiometric air/fuel ratio.

14. The method as recited in claim 13 wherein determining the instantaneous temperature of exhaust gas at the catalytic converter due to an exothermic reaction of the exhaust gas comprises:

comparing the instantaneous temperature at the midbed point to a second and third temperature threshold;

if the instantaneous temperature at the midbed point is less than the second temperature threshold, setting the instantaneous temperature of exhaust gas at the catalytic converter equal to zero; and

if the instantaneous temperature at the midbed point exceeds the third temperature threshold, determining the instantaneous temperature of exhaust gas at the catalytic converter as a function of a steady state increase in the temperature of exhaust gas in the catalytic converter, the estimated rate of misfires, an increase in the exothermic reaction of the exhaust gas per estimated rate of misfires, and an exothermic reaction at an equivalence ratio of one corresponding to stoichiometric air/fuel ratio.

15. The method as recited in claim 14 wherein determining the stoichiometric instantaneous temperature at the midbed point in the catalytic converter at stoichiometric air/fuel ratio comprises:

comparing the instantaneous temperature at the midbed point to the second and third temperature threshold;

if the instantaneous temperature at the midbed point is less than the second temperature threshold, setting the stoichiometric instantaneous temperature at the midbed point equal to the instantaneous temperature of exhaust gas at the exhaust gas inlet of the catalytic converter; and

if the instantaneous temperature at the midbed point exceeds the third temperature threshold, determining the stoichiometric instantaneous temperature at the midbed point as a function of an exothermic reaction at an equivalence ratio of one corresponding to stoichiometric air/fuel ratio and the instantaneous temperature of exhaust gas at the exhaust gas inlet.

16. A system for estimating the midbed temperature of a catalytic converter in an exhaust system of an internal combustion engine, the exhaust system including an exhaust pipe for transporting exhaust gas from the engine to the catalytic converter, the system comprising:

a sensor for sensing a rate of change of the speed of the engine and generating a corresponding speed signal; and

a controller for performing the following;

estimating a rate of misfires occurring in the engine over a predetermined number of cylinder filling events based on the speed signal;

determining an instantaneous temperature of exhaust gas at a first point on the exhaust pipe based on the estimated rate of misfires; and

determining an instantaneous temperature at a midbed point of the catalytic converter based on the instantaneous temperature of exhaust gas at the first point on the exhaust pipe.

17. The system as recited in claim 16 wherein the controller further performs:

determining a steady state temperature of exhaust gas at the first point when the engine is firing as a function of a base steady state temperature at the first point at a particular engine speed and aircharge, air/fuel modulation, engine spark timing, exhaust gas recirculation, and engine coolant temperature; and

determining a steady state temperature of exhaust gas at the first point when the engine is not firing as a function of a temperature of airflow into the engine and engine coolant temperature.

18. The system as recited in claim 16 wherein the controller further performs:

comparing the instantaneous temperature at the midbed point to a first temperature threshold indicative of the temperature at which the catalytic converter is damaged;

comparing the estimated rate of misfires to a misfire rate threshold indicative of the maximum misfires allowed for a given engine speed; and

generating a failure signal if the instantaneous temperature at the midbed point exceeds the first temperature threshold and the estimated rate of misfires exceeds the misfire rate threshold.

19. The system as recited in claim 18 further comprising a display for displaying the failure signal.

20. A method for monitoring degradation of a catalytic converter in fluid communication with an internal combustion engine, comprising:

detecting engine misfires;

estimating catalyst temperature based in part on said detected misfires; and

providing an indication of catalyst degradation when both a number of said detected misfires and said estimated temperature exceed respective preselected values during a predetermined test interval.

21. The method recited in claim 20 wherein said misfire detection is based on a number of misfires occurring during said test interval.

22. The method recited in claim 21 wherein said catalyst temperature estimate is in part derived from an approximation of temperature increase caused by an exothermic reaction of the exhaust gas due to said misfires.

23. The method recited in claim 20 wherein said estimated temperature is estimated by first estimating temperature at an inlet of the catalyst based on engine operating parameters and then approximating temperature gradient from said inlet to a midpoint of the catalyst.

24. The method recited in claim 23 wherein said operating parameters comprise engine speed, ignition timing, inducted airflow, and engine coolant temperature.

25. The method recited in claim 20 wherein said misfire detection further comprises a step of detecting engine crankshaft acceleration.