Catalyst warm-up assessment method for a motor vehicle catalytic converter

• US 6,668,545 B2
• Filed: 03/30/2001
• Issued: 12/30/2003
• Est. Priority Date: 03/30/2001
• Status: Expired due to Fees

• Current Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Brown, David Brian
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): NGUYEN, TU MINH
• Application Number:
  US09/820,597
• Publication Number:
  US 20020139110A1
• Time in Patent Office: 1,005 Days
• Field of Search: 602/74, 602/76, 602/77, 602/84, 602/85, 731/181, 73/233.1, 73/233.2, 123/691, 123/697
• US Class Current: 60/284
• 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: F01N 2900/0421 using an increment counter when a predetermined event occurs
• CPC Class Codes: F01N 2900/0422 measuring the elapsed time
• 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: F02D 2200/0816 Oxygen storage capacity
• CPC Class Codes: F02D 41/0255 to accelerate the warming-up of the exhaust gas treating apparatus at engine start
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An improved method of assessing the catalyst warm-up rate of a motor vehicle catalytic converter is based on the response rates of fast warm-up exhaust gas sensors located in the exhaust gas upstream and downstream of the catalytic converter. The method essentially measures an oxygen storage characteristic of the catalyst that increases as the catalyst temperature rises to its ideal operating temperature. In one method, a ratio of switching frequency between the upstream and downstream exhaust gas sensors is periodically computed and compared to a threshold during catalyst warm-up. In another method, the response times of the exhaust gas sensors to a known air/fuel ratio transition are detected to form a measure of the oxygen storage characteristic that is compared to a threshold. In each method, the threshold varies as a function of cumulative airflow through the engine to compensate for different engine airflow levels.

Claims

1. A method of assessing a catalyst warm up rate of a catalytic converter connected in an exhaust system of a motor vehicle internal combustion engine downstream of a first exhaust gas sensor and upstream of a second exhaust gas sensor, the method comprising the steps of:

specifying a warm-up rate of said first and second exhaust gas sensors that is faster than a nominal warm-up rate of said catalytic converter;

periodically measuring a first response rate of said first exhaust gas sensor and a second response rate of said second exhaust gas sensor during a warm-up period of said catalytic converter, and computing an oxygen storage characteristic of said catalytic converter based on a ratio of switching frequencies between said first and second exhaust gas sensors;

determining an oxygen storage threshold corresponding to a minimum desired catalyst warm-up rate; and

indicating that the catalyst warm-up rate is good if the computed oxygen storage characteristics is greater than the oxygen storage threshold, and that the catalyst warm-up rate is bad if the computed oxygen storage characteristic is less than the oxygen storage threshold.

5. The method of claim 1, wherein the step of computing the oxygen storage characteristic of said catalytic converter includes the step of:

computing a ratio of said first and second response rates.

6. The method of claim 1, including the steps of:

commanding a transition of an air/fuel ratio of said engine from a first level to a second level;

measuring a first time for said first exhaust gas sensor to respond to the air/fuel ratio transition, and a second time for said second exhaust gas sensor to respond to the air/fuel ratio transition; and

computing the oxygen storage characteristic of said catalytic converter based on a difference between said first and second times.

7. The method of claim 6, wherein the step of computing the oxygen storage characteristic comprises the steps of:

computing a fuel rate based on an air flow rate through said exhaust system and a difference between said first and second air/fuel ratio levels;

computing a quantity of fuel consumed in said catalytic converter based on said fuel rate and said difference between said first and second times; and

computing the oxygen storage characteristic of said catalytic converter based on said quantity of fuel consumed and a ratio of oxygen to fuel for an air/fuel ratio between said first and second air/fuel ratio levels.

2. A method of assessing a catalyst warm up rate of a catalytic converter connected in an exhaust system of a motor vehicle internal combustion engine downstream of a first exhaust gas sensor and upstream of a second exhaust gas sensor, the method comprising the steps of:

specifying a warm-up rate of said first and second exhaust gas sensors that is faster than a nominal warm-up rate of said catalytic converter;

periodically measuring a first response rate of said first exhaust gas sensor and a second response raw of said second exhaust gas sensor during a warm-up period of said catalytic converter, and computing an oxygen storage characteristic of said catalytic converter based on a ratio of switching frequencies between said first and second exhaust gas sensors calculated over a predefined interval;

determining an oxygen storage threshold corresponding to a minimum desired catalyst warm-up rate; and

indicating that the catalyst warm-up rate is good if the computed oxygen storage characteristics is greater than the oxygen storage threshold, and that the catalyst warm-up rate is bad if the computed oxygen storage characteristic is less than the oxygen storage threshold.

3. A method of assessing a catalyst warm-up rate of a catalytic converter connected in an exhaust system of a motor vehicle internal combustion engine downstream of a first exhaust gas sensor and upstream of a second exhaust gas sensor, the method comprising the steps of:

specifying a warm-up rate of said first and second exhaust gas sensors that is faster than a nominal warm-up rate of said catalytic converter;

periodically measuring a first response rate of said first exhaust gas sensor and a second response rate of said second exhaust gas sensor during a warm-up period of said catalytic converter, and computing an oxygen storage characteristic of said catalytic converter based on said first and second response rates;

determining an oxygen storage threshold corresponding to a minimum desired catalyst warm-up rate;

indicating that the catalyst warm-up rate is good if the computed oxygen storage characteristic is greater than oxygen storage threshold, and that the catalyst warm-up rate is bad if the computed oxygen storage characteristic is less than the oxygen storage threshold;

wherein an air/fuel ratio of said engine is controlled by a closed-loop control, and said first and second response rates correspond to output signal frequencies of said first and second exhaust gas sensors, respectively; and

wherein said first and second exhaust gas sensors have respective first and second output signals that switch between high and low states in response to air/fuel ratios upstream and downstream of said catalytic converter, and said first and second response rates are measured by counting switching transitions of said first and second output signals over a predefined time interval.

4. The method of claim 3, wherein the oxygen storage threshold is determined as a function of a cumulative air flow rate through said exhaust system during said warm-up period.