Title of Invention	" A MONITORING SYSTEM AND A METHOD OF DIAGNOSING A CATALYTIC CONVERTER"
Abstract	This invention relates to a monitoring system for a catalytic converter, comprising a fuel determination module that determines a fuel composition of fuel in a fuel system using a learned shift in fuel trim calculated based on a signal from an oxygen sensor located at an inlet of the catalytic converter; a fuel/air (F/A) determination module that selectively determines a stoichioemetric F/A ratio based on the fuel composition; and an oxygen storage capacity (OSC) diagnostic module that computes a target OSC based on the stoichiometric F/A ratio, that compares the target OSC to a reference value, and that diagnosis the catalytic converter based on the comparison.

Title of Invention

" A MONITORING SYSTEM AND A METHOD OF DIAGNOSING A CATALYTIC CONVERTER"

Abstract

This invention relates to a monitoring system for a catalytic converter, comprising a fuel determination module that determines a fuel composition of fuel in a fuel system using a learned shift in fuel trim calculated based on a signal from an oxygen sensor located at an inlet of the catalytic converter; a fuel/air (F/A) determination module that selectively determines a stoichioemetric F/A ratio based on the fuel composition; and an oxygen storage capacity (OSC) diagnostic module that computes a target OSC based on the stoichiometric F/A ratio, that compares the target OSC to a reference value, and that diagnosis the catalytic converter based on the comparison.

Full Text	FIELD The present disclosure relates to diagnostic systems for vehicles, and more particularly to methods and systems for monitoring catalytic converter efficiency. BACKGROUND The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. Ethanol, also know as ethyl alcohol, is a flammable, colorless chemical compound that can be mixed with gasoline to fuel an internal combustion engine. Flexible fuel vehicles include adaptations that allow the vehicle to run on various blends of gasoline and ethanol. For example, E85 fuel contains a mixture of 85% ethanol and 15% gasoline. A virtual flex fuel sensor and method detects the concentration of ethanol in the fuel. Based on the concentration level, the air/fuel ratio is adjusted and the engine operation is controlled accordingly. During the combustion process, gasoline and ethanol are oxidized and hydrogen (H) and carbon (C) combine with air. Various chemical compounds are formed and released in an exhaust stream including carbon dioxide (CO2), water (H20), carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), sulfur oxides (SOx), and other compounds. However, the use of ethanol in the fuel reduces the amount of carbon dioxide (CO) and nitrogen oxides (NOx) in the exhaust. Automobile exhaust systems include a catalytic converter that further reduces the levels of CO, HC, and NOx in the exhaust gas by chemically converting these gasses into carbon dioxide, nitrogen, and water. Diagnostic regulations require periodic monitoring of the catalytic converter for proper conversion capability. Typical monitoring methods employ two exhaust gas oxygen sensors and infer the conversion capability of the catalytic converter using the sensor signals. One sensor monitors the oxygen level associated with an inlet exhaust stream of the catalytic converter. This inlet O2 sensor is also the primary feedback mechanism that maintains the fuel-to-air (F/A) ratio of the engine at the chemically correct, or stoichiometric F/A ratio needed to support the catalytic conversion processes. A second or outlet O2 sensor monitors the oxygen level concentration of the exhaust stream exiting the catalytic converter. Excess O2 concentration in the exiting exhaust stream induces a "lean" sensor signal. A deficit or absence of O2 in the exiting exhaust stream induces a "rich" sensor signal. Traditional catalytic converter monitoring methods relate the empirical relationships that exist between the inlet and outlet O2 sensor to quantify catalyst conversion capability. These methods compare sensor amplitude, response time, response rate, and/or frequency content data. All of these measurements are affected by a property of a catalytic converter known as Oxygen Storage Capacity (OSC). OSC refers to the ability of a catalytic converter to store excess oxygen under lean conditions and to release oxygen under rich conditions. The amount of oxygen storage and release decreases as the conversion capability of the catalytic converter is reduced. Therefore, the loss in OSC is related to the loss in conversion capability. Methods and systems for monitoring a catalytic converter based on the OSC are described in commonly assigned U.S. patent no. 6,874,313. The methods and systems relate to various types of hydrocarbon fuels. As implemented, the methods and systems may not properly diagnose a catalytic converter for engine systems running alternative fuels such as E85 or diesel. SUMMARY Accordingly, a monitoring system for a catalytic converter is provided. The system includes: a fuel determination module that determines a fuel type based on a composition of fuel in a fuel system; a fuel/air (F/A) determination module that selectively determines a stoichiometric F/A ratio based on the fuel type; and an oxygen storage capacity (OSC) diagnostic module that computes a target OSC based on the stoichiometric F/A ratio, that compares the target OSC to a reference value and diagnosis the catalytic converter based on the comparison. In other features, a method of diagnosing a catalytic converter is provided. The method includes: selectively determining a stoichiometric fuel/air ratio based on a fuel type; computing a target oxygen storage capacity (OSC) of the catalytic converter based on the stoichiometric fuel/air ratio; and diagnosing the catalytic converter based on the oxygen storage capacity. Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. Figure 1 is a functional block diagram of a vehicle including a control module that performs a flexible fuel tolerant catalytic converter diagnostic method according to the present disclosure. Figure 2 is a dataflow diagram illustrating a flexible fuel tolerant catalytic converter diagnostic system. Figure 3 is a flowchart illustrating a flexible fuel tolerant catalytic converter diagnostic method. Figure 4 is a graph illustrating a simplified chemical combustion model for fuel. Figure 5 is a graph illustrating inlet and outlet O2 sensor responses during a data collection period. Figure 6 is a graph illustrating an oxygen storage capacity (OSC) calculation. Figure 7 is a flowchart illustrating an oxygen storage capacity (OSC) diagnostic method. DETAILED DESCRIPTION The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. Referring now to Figure 1, a vehicle 10 includes an engine 12, an exhaust system 14, and a control module 16. The engine 12 includes an intake manifold 17, a throttle position sensor (TPS) 18, and a mass air flow (MAF) sensor 20. The throttle position sensor 18 and the MAF sensor 20 communicate with the control module 16. The exhaust system 14 includes a catalytic converter 22, a pre-catalyst or inlet oxygen sensor 24, and a post- catalyst or outlet oxygen sensor 26. The inlet and outlet oxygen sensors 24, 26 communicate with the control module 16 to provide inlet and outlet F/A ratio signals, respectfully. The control module 16 communicates with a fuel system 28 to regulate fuel flow to the engine 12. The fuel system includes a flex fuel sensor 29. The flex fuel sensor 29 generates a fuel signal to the control module 16 indicating a composition of the fuel in the fuel system 28. Alternatively, the vehicle may employ a virtual flex fuel sensor method in the control module 16 that utilizes a learned shift in fuel trim calculated from the inlet oxygen sensor 24 to estimate the fuel composition. In this manner, the control module 16 determines or estimates the stoichiometric F/A ratio of the engine 12. In addition, the control module 16 diagnoses the catalytic converter 22 of the exhaust system 14 based on a flexible fuel tolerant catalytic converter diagnostic method described herein. Referring now to Figure 2, a dataflow diagram illustrates various embodiments of a flexible fuel tolerant catalytic converter diagnostic system that may be embedded within the control module 16. Various embodiments of catalytic converter diagnostic systems according to the present disclosure may include any number of sub-modules embedded within the control module 16. The sub-modules shown may be combined and/or further partitioned to similarly monitor a catalytic converter 22. Inputs to the system may be received from sensors within the vehicle 10, received from other control modules (not shown) within the vehicle 10, and/or determined by other sub-modules (not shown) within the control module 16. In various embodiments, the control module 16 of Figure 2 includes an enable module 40, a fuel determination module 42, a fuel/air (F/A) ratio module 44, and an oxygen storage capacity (OSC) diagnostic module 46. The enable module 40 receives as input a fuel event signal 48. The fuel event signal 48 indicates a status of the remaining fuel in the fuel system 28 (Figure 1). The enable module 40 determines when a refuel event has occurred based on the fuel event signal 48 and sets a refuel event flag 50 accordingly. In various embodiments, the fuel event signal 48 indicates a current fuel level of the fuel system 28 (Figure 1). The enable module 40 compares the current fuel level to a previous fuel level to determine when a refuel event occurs. It is appreciated, that other methods may be used to detect a refuel event. The fuel determination module 42 receives as input the refuel event flag 50 and a fuel sensor signal 52 indicating a composition of the fuel in the fuel system 28 (Figure 1). The fuel determination module 42 determines a fuel composition 54 of the fuel in the fuel system 28 (Figure 1) after a refuel event has occurred and based on the fuel sensor signal 52. In various embodiments, the fuel determination module 42 estimates a composition of fuel based on engine operating parameters (i.e., fuel trim shift values) and determines the fuel composition 54 based on the estimated composition. These methods eliminate the need for the fuel sensor signal 52. The F/A ratio module 44 receives as input the fuel composition 54. Based on the fuel composition 54, the F/A ratio module 44 determines the ideal stoichiometric F/A ratio 56. The OSC diagnostic module 46 receives as input the stoichiometric F/A ratio 56, mass airflow (MAF) 58, throttle position (TPS) 60, inlet O2 sensor signal 62 and the outlet O2 sensor signal 64. Based on the received signals, the OSC diagnostic module 46 determines an oxygen storage capacity for the catalytic converter 22 (Figure 1) and diagnosis the catalytic converter 22 (Figure 1) based on a comparison of the determined OSC and a reference value. Based on the diagnosis, the OSC diagnostic module 46 sets a failure code 66. Wherein the failure code 66 is set to TRUE or "test fail" if a malfunction is diagnosed. Referring now to Figure 3, a flowchart illustrates a flexible fuel tolerant catalytic converter diagnostic method performed by the control module 16. The method may be run periodically during engine operation. Control evaluates whether a refuel event has occurred at 90. If a refuel event has occurred, the diagnosis is delayed until an accurate determination of the fuel composition is made at 92. Otherwise control proceeds to evaluate the current fuel composition at 94. If the fuel composition is of a typical fixed hydrocarbon mixture at 94, the stoichiometric F/A ratio is set based on a predetermined value at 96. If the fuel composition is of an alternative fuel mixture of more than one typical hydrocarbon, such as E85 (85% ethyl alcohol blended with 15% gasoline), the stoichiometric F/A ratio is computed based on the composition of the fuel mixture at 98. After setting the F/A ratio, control proceeds to perform the OSC diagnostic at 99. More particularly, the details of the OSC diagnostic module 46 of Figure 2 and the process step 99 of Figure 3 will be discussed in the context of Figures 4-7. Referring to Figure 4, a simplified chemical combustion model for hydrocarbon and alternative fuels will be described in detail. The combustion model is based on an equivalence ratio (FR) that is defined as the actual F/A ratio (F/AACT) divided by the determined stoichiometric F/A ratio (F/ASTOICH). During periods of O2 release (i.e. rich engine operation), the chemical combustion model is provided as: During periods of O2 storage, the chemical combustion model is provided as: Where a, u, v, x are coefficients. The coefficient a represents a simplification contsant determined from the following equation: The coefficient u represents the ratio of the alcohol in the fuel mixture of the total fuel mixture. The coefficient v represents the number of carbon atoms in a molecule of the alcohol fuel. The coefficient x represents the number of carbon atoms in a molecule of the non-alcohol hydrocarbon fuel. The coefficient y represents the hydrogen atoms in a molecule of the non-alcohol hydrocarbon fuel. Periods of 02 release require the catalyst to release 1/2 Mole of 02 for each Mole of excess CO in the exhaust to completely convert the CO. Periods of 02 storage require the catalyst to store one mole of 02 for each mole of excess 02 in the exhaust. The ratio of 02 released by the catalyst to the mass of inlet 02 in the F/A charge mixture is given as: A positive term indicates 02 release and a negative term indicates 02 storage. As seen in the graph of Figure 4, when FR is greater than 1 (i.e. rich engine operation), stored 02 within the catalytic converter 22 is released. When FR is less than 1 (i.e. lean engine operation), excess 02 is stored. The rate of 02 released to the mass air rate associated with the F/A mixture is provided as: grams per sec/ Air grams per sec M02 is the mass of 02 in a mole of air. MAIR is the average molar mass of air. The molar ratio of 02 to that of air is assumed to be a constant. The OSC diagnostic is executed during a fuel cut-off mode of the engine 12. The fuel cut-off mode occurs during a vehicle overrun condition, such as when the vehicle 10 is coasting downhill. The fuel cutoff mode can be determined from the throttle position 60 and intake manifold pressure. While in the fuel cut-off mode, the F/A ratio of the exhaust stream from the engine 12 is equal to zero. The OSC diagnostic is initiated after the engine 12 has operated in the fuel cut-off mode for a predetermined period of time and is signaled to return to normal operation (or non fuel cut-off mode). More specifically, the predetermined time period is calibrated to completely saturate the catalytic converter 22 with oxygen. Referring now to Figures 5 and 6, time t=0 indicates the beginning of the OSC diagnostic. Initially, FR is commanded to a fixed percentage rich. Commanding the equivalence ratio a fixed percentage rich results in F/AACT being greater than F/ASTOICH- AS the engine 12 operates rich, the inlet oxygen sensor 24 detects the transition to rich and correspondingly signals the control module 16. The delay time required for the inlet oxygen sensor 24 to achieve a reference signal is indicated as tinlet delay. The reference signal indicates when the exhaust from the engine 12 achieves F/ASTOICH- The outlet oxygen sensor 26 detects the transition to rich and correspondingly signals the control module 16. The outlet oxygen sensor signal 64 is delayed relative to the inlet oxygen sensor signal 62. The transition time required for the outlet oxygen sensor 26 to achieve the reference signal is indicated as toulet delay The lag time required for a predetermined amount of air (such as approximately 1.5g) to flow through an inert catalytic converter 22 (Figure 1) is indicated as tlag. The OSC diagnostic module 46 (Figure 2) determines a target time over which a target OSC of the catalytic converter 22 (Figure 1) is calculated. The target time, indicated as target, is based on tinlet delay, toutlet delay, and tlag. More specifically, the OSC diagnostic module 46 monitors the inlet and outlet sensor signals 62, 64 to determine tinlet delay and toutlet delay The OSC diagnostic module 46 estimates tlag as the interval of time required to pass a fixed mass of air between the oxygen sensors as: tlag= K air_mass_grams/ MAF(tend-of-test) This process assumes that exhaust flow conditions toward the end-of-test are known. Referring to Figure 4, the end-of-test time can be estimated as: This instant in time will vary with the OSC of the catalyst and cannot be determined until after the test conditions have passed. Also, the mass flow rate of air is transient in nature during the diagnostic and cannot be assumed to be constant. For these reasons, MAF 58 is averaged over fixed duration subintervals of the transition period and stored. The estimated lag period is then calculated by a backwards integration of the stored MAF 58 terms beginning at t= tend-of-test and ending when the summation equals K air_mass_grams. By definition, this occurs at t= tend-of-test- tlag . The target time is provided as: The target time is the time period immediately after F/A becoming greater than the stoichiometric F/A 56. In addition to monitoring the above-described times, the OSC diagnostic module 46 stores subinterval averages of the mass air flow (MAF) into the engine 12 and an FR compensated MAF term (see Figure 6). The subinterval is defined as an integer multiple of the data sample rate associated with the MAF and FR terms. This method does not preclude having the subinterval equal the sample rate and subinterval average based on a single value. However, a more efficient use of control module memory can be obtained without significantly affecting the accuracy of the OSC calculation by specifying a larger subinterval. The MAF 58 is provided as a signal to the control module 16 from the MAF sensor 20. The incremental OSC, derived from the simplified O2 release model, is represented by the following relationship: where the incremental OSC is measured in terms of grams of stored oxygen per unit time, a is the mass of oxygen in a mole of air divided by the mass of a mole of air, and p is the mass air flow fraction per catalytic converter. Preferably, for an exhaust system having a single catalytic converter 22 as shown in Figure 1, β is equal to 1. For an exhaust system having a catalytic converter for each N/2 cylinders, β is equal to 0.5. The OSC at ttarget is represented by the numerical integration, or summation, of the incremental OSC over the target period: where T represents the sampled data period, MAF(nT) represents the MAF at time nT, and FR(nT) represents the fuel equivalence ratio at time nT. A prefered equivalent form of this relationship is represented by: This form is less prone to numerical accumulation of small round-off errors. Once the outlet oxygen sensor 26 achieves the reference signal (i.e. detects F/ASTOICH of the exhaust gases from the catalytic converter), the OSC diagnostic module 46 determines the target OSC. Referring again to Figure 6, to determine the target OSC, the OSC diagnostic module 46 calculates the OSC according to the prefered OSC relationship stated previously. The OSC diagnostic module 46 integrates both the stored FR compensated MAF and stored MAF measurements over the target time. This corresponds to the area under each of their respective curves. The difference between these areas, graphically represented by the area between the two curves, is then multiplied by the constant term, α x β x T to obtain the OSC over the target period. The constant term acts as a scalar that optionally could be omitted if an unscaled result was desirable. The calculated OSC is compared to a reference OSC value to determine if the catalytic converter 22 passes or fails. Referring to Figure 7, a flowchart illustrates an OSC diagnostic method performed by the OSC diagnostic module 46 of Figure 2 and shown in process step 99 of Figure 3. Control determines whether a fuel cut-off mode is present at 100. If a fuel cut-off mode is not present, control loops back. Otherwise, control checks particular conditions at 102, 104, and 106 prior to initiating monitoring. At 102, control determines whether the engine 12 has been operating under closed loop fuel control (CLFC) for a sufficient time. If not, control loops back to monitor for a fuel cut-off mode at 100. If the engine 12 has been operating under CLFC for a sufficient time, control determines whether the catalytic converter 22 has achieved an operating temperature at 104. If the temperature has not been achieved at 104, control loops back to 100. If the temperature has been achieved, control continues at 106. At 106, control determines whether the catalytic converter 22 has been exposed to air flow for a time sufficient to achieve oxygen saturation. If the catalytic converter 22 has not been sufficiently exposed, control loops back to 100. If the catalytic converter 22 has been sufficiently exposed, control initiates the OSC diagnostic upon the engine 12 exiting the fuel cut-off mode at 108. Upon exiting the fuel cut-off mode, control commands FR to a fixed percentage rich at 110. At 112, control continually records subinterval measurements of the MAF and FR compensated MAF using the MAF sensor 20 as explained above. At 114, control tracks the signals of the inlet and outlet oxygen sensors 24, 26. At 116, control determines whether the outlet oxygen sensor 26 has achieved the reference signal. If the outlet oxygen sensor 26 has achieved the reference signal, control continues at 118. If not, control loops back to 112. At 118, control determines toutlet delay, tinlet delay, tlag and ttarget therefrom. At 124, control integrates the stored OSC related quantities over the target time and obtains the target OSC value using the preferred difference equation provided above. At 126, control evaluates the target OSC value. If the target OSC is not above a reference value, test failure is indicated at 128. If the target OSC is above the reference value, test pass is indicated at 122. Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and the following claims. WE CLAIM 1. A monitoring system for a catalytic converter, comprising: a fuel determination module that determines a fuel composition of fuel in a fuel system using a learned shift in fuel trim calculated based on a signal frorn an oxygen sensor located at an inlet of the catalytic converter; a fuel/air (F/A) determination module that selectively determines a stoichioemetric F/A ratio based on the fuel composition; and an oxygen storage capacity (OSC) diagnostic module that computes a target OSC based on the stoichiometric F/A ratio, that compares the target OSC to a reference value, and that diagnosis the catalytic converter based on the comparison. 2. The \|system as claimed in claim 1 comprising an enable module that generates an enable signal after detecting a refuel event and wherein the fuel determination module postpones estimating the fuel composition until after (the enable signal is received. 3. The system as claimed in claim 2 wherein the enable module detects the refuel event based on a current and a previous fuel level. 4. The system as claimed in claim 1 wherein the F/A determination module sets the stoichiometric F/A ratio to a predetermined value when the fuel composition is a single specified hydrocarbon fuel. 5. The system as claimed in claim 1 wherein the F/A determination module determines the stoichiometric F/A ratio when the fuel composition is composed of a blend of more than one hydrocarbon fuel. 6. The system as claimed in claim 1 wherein the OSC diagnostic module initiates a rich condition based on the stoichiometric F/A ratio after a fuel cut-off period, computes a mass of oxygen released by the catalytic converter, and computes the target OSC over a target time period based on the mass of oxygen. 7. The system as claimed in claim 6 wherein the OSC diagnostic module determines the target time period based on an inlet delay time to detect a first F/A ratio and an outlet delay time to detect the first F/A ratio. 8. The system as claimed in claim 7 comprising an inlet sensor that generates an inlet sensor signal indicating a first oxygen level of exhaust gases entering the catalytic converter and wherein the inlet delay time is determined based on the inlet sensor signal. 9. The system as claimed in claim 7 comprising an outlet sensor that generates an outlet sensor signal indicating a second oxygen level of exhaust gases exiting the catalytic converter and wherein the outlet delay time is determined based on the outlet sensor signal. 10. A method of diagnosing a catalytic converter, comprising: estimating a fuel composition using a learned shift in fuel trim calculated based on a signal from an oxygen sensor located at an inlet of the catalytic converter; selectively determining a stoichiometric fuel/air (F/A) ratio based on the fuel composition; computing a target oxygen storage capacity (OSC) of the catalytic converter based on the stoichiometric F/A ratio; and diagnosing the catalytic converter based on the target OSC. 11.The method as claimed in claim 10, comprising receiving a fuel event signal indicating an occurrence of a refuel event and postponing the estimating the fuel composition until the fuel event signal is received. 12.The method as claimed in claim 11 wherein the selectively determining comprises determining the stoichiometric F/A ratio to be a predetermined value when the fuel composition indicates a single specified hydrocarbon fuel. 13.The method as claimed in claim 10 wherein the selectively determining comprises computing a stoichiometric F/A ratio when the fuel composition indicates a blend of more than one hydrocarbon fuel. 14.The method as claimed in claim 10 comprising: saturating the catalytic converter with oxygen during a fuel cut-off period; operating an engine in a rich condition based on the stoichiometric F/A ratio after the fuel cut-off period; computing a mass of oxygen released by the catalytic converter based on mass air flow into the engine; and wherein the computing the target OSC is further based on the mass of oxygen released over a target time period. 15.The method as claimed in claim 16 wherein the computing comprises: determining a first delay time for an inlet oxygen sensor to detect a first F/A ratio; determining a second delay time for an outlet oxygen sensor to detect the first F/A ratio; and computing the target time period based on the first and the second delay times. 16.The method as claimed in claim 15 comprising: determining a transport lag time required for a mass of air to flow through an inert catalytic converter; and calculating the target time period based on the transport lag time. 17. The method as claimed in claim 10 wherein the diagnosing comprises diagnosing the catalytic converter based on a comparison of the target OSC and a reference value. 18. The method as claimed in claim 11 comprising setting a malfunction code based on the diagnosing of the catalytic converter. ABSTRACT "A MONITORING SYSTEM AND A METHOD OF DIAGNOSING A CATALYTIC CONVERTER" This invention relates to a monitoring system for a catalytic converter, comprising a fuel determination module that determines a fuel composition of fuel in a fuel system using a learned shift in fuel trim calculated based on a signal from an oxygen sensor located at an inlet of the catalytic converter; a fuel/air (F/A) determination module that selectively determines a stoichioemetric F/A ratio based on the fuel composition; and an oxygen storage capacity (OSC) diagnostic module that computes a target OSC based on the stoichiometric F/A ratio, that compares the target OSC to a reference value, and that diagnosis the catalytic converter based on the comparison.

Full Text

FIELD
The present disclosure relates to diagnostic systems for
vehicles, and more particularly to methods and systems for monitoring
catalytic converter efficiency.
BACKGROUND
The statements in this section merely provide background
information related to the present disclosure and may not constitute prior art.
Ethanol, also know as ethyl alcohol, is a flammable, colorless
chemical compound that can be mixed with gasoline to fuel an internal
combustion engine. Flexible fuel vehicles include adaptations that allow the
vehicle to run on various blends of gasoline and ethanol. For example, E85
fuel contains a mixture of 85% ethanol and 15% gasoline. A virtual flex fuel
sensor and method detects the concentration of ethanol in the fuel. Based on
the concentration level, the air/fuel ratio is adjusted and the engine operation
is controlled accordingly.
During the combustion process, gasoline and ethanol are
oxidized and hydrogen (H) and carbon (C) combine with air. Various
chemical compounds are formed and released in an exhaust stream including
carbon dioxide (CO2), water (H20), carbon monoxide (CO), nitrogen oxides
(NOx), unburned hydrocarbons (HC), sulfur oxides (SOx), and other
compounds. However, the use of ethanol in the fuel reduces the amount of
carbon dioxide (CO) and nitrogen oxides (NOx) in the exhaust.

Automobile exhaust systems include a catalytic converter
that further reduces the levels of CO, HC, and NOx in the exhaust gas by
chemically converting these gasses into carbon dioxide, nitrogen, and water.
Diagnostic regulations require periodic monitoring of the catalytic converter for
proper conversion capability. Typical monitoring methods employ two
exhaust gas oxygen sensors and infer the conversion capability of the
catalytic converter using the sensor signals. One sensor monitors the oxygen
level associated with an inlet exhaust stream of the catalytic converter. This
inlet O2 sensor is also the primary feedback mechanism that maintains the
fuel-to-air (F/A) ratio of the engine at the chemically correct, or stoichiometric
F/A ratio needed to support the catalytic conversion processes. A second or
outlet O2 sensor monitors the oxygen level concentration of the exhaust
stream exiting the catalytic converter. Excess O2 concentration in the exiting
exhaust stream induces a "lean" sensor signal. A deficit or absence of O2 in
the exiting exhaust stream induces a "rich" sensor signal.
Traditional catalytic converter monitoring methods relate the
empirical relationships that exist between the inlet and outlet O2 sensor to
quantify catalyst conversion capability. These methods compare sensor
amplitude, response time, response rate, and/or frequency content data. All
of these measurements are affected by a property of a catalytic converter
known as Oxygen Storage Capacity (OSC). OSC refers to the ability of a
catalytic converter to store excess oxygen under lean conditions and to
release oxygen under rich conditions. The amount of oxygen storage and
release decreases as the conversion capability of the catalytic converter is
reduced. Therefore, the loss in OSC is related to the loss in conversion
capability.

Methods and systems for monitoring a catalytic converter
based on the OSC are described in commonly assigned U.S. patent no.
6,874,313. The methods and systems relate to various types of hydrocarbon
fuels. As implemented, the methods and systems may not properly diagnose
a catalytic converter for engine systems running alternative fuels such as E85
or diesel.
SUMMARY
Accordingly, a monitoring system for a catalytic converter is
provided. The system includes: a fuel determination module that determines
a fuel type based on a composition of fuel in a fuel system; a fuel/air (F/A)
determination module that selectively determines a stoichiometric F/A ratio
based on the fuel type; and an oxygen storage capacity (OSC) diagnostic
module that computes a target OSC based on the stoichiometric F/A ratio,
that compares the target OSC to a reference value and diagnosis the catalytic
converter based on the comparison.
In other features, a method of diagnosing a catalytic
converter is provided. The method includes: selectively determining a
stoichiometric fuel/air ratio based on a fuel type; computing a target oxygen
storage capacity (OSC) of the catalytic converter based on the stoichiometric
fuel/air ratio; and diagnosing the catalytic converter based on the oxygen
storage capacity.
Further areas of applicability will become apparent from the
description provided herein. It should be understood that the description and
specific examples are intended for purposes of illustration only and are not
intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The drawings described herein are for illustration purposes
only and are not intended to limit the scope of the present disclosure in any
way.
Figure 1 is a functional block diagram of a vehicle including a
control module that performs a flexible fuel tolerant catalytic converter
diagnostic method according to the present disclosure.
Figure 2 is a dataflow diagram illustrating a flexible fuel
tolerant catalytic converter diagnostic system.
Figure 3 is a flowchart illustrating a flexible fuel tolerant
catalytic converter diagnostic method.
Figure 4 is a graph illustrating a simplified chemical
combustion model for fuel.
Figure 5 is a graph illustrating inlet and outlet O2 sensor
responses during a data collection period.
Figure 6 is a graph illustrating an oxygen storage capacity
(OSC) calculation.
Figure 7 is a flowchart illustrating an oxygen storage capacity
(OSC) diagnostic method.
DETAILED DESCRIPTION
The following description is merely exemplary in nature and
is not intended to limit the present disclosure, application, or uses. It should
be understood that throughout the drawings, corresponding reference
numerals indicate like or corresponding parts and features. As used herein,
the term module refers to an application specific integrated circuit (ASIC), an
electronic circuit, a processor (shared, dedicated, or group) and memory that
executes one or more software or firmware programs, a combinational logic
circuit, and/or other suitable components that provide the described
functionality.

Referring now to Figure 1, a vehicle 10 includes an engine
12, an exhaust system 14, and a control module 16. The engine 12 includes
an intake manifold 17, a throttle position sensor (TPS) 18, and a mass air flow
(MAF) sensor 20. The throttle position sensor 18 and the MAF sensor 20
communicate with the control module 16. The exhaust system 14 includes a
catalytic converter 22, a pre-catalyst or inlet oxygen sensor 24, and a post-
catalyst or outlet oxygen sensor 26. The inlet and outlet oxygen sensors 24,
26 communicate with the control module 16 to provide inlet and outlet F/A
ratio signals, respectfully. The control module 16 communicates with a fuel
system 28 to regulate fuel flow to the engine 12. The fuel system includes a
flex fuel sensor 29. The flex fuel sensor 29 generates a fuel signal to the
control module 16 indicating a composition of the fuel in the fuel system 28.
Alternatively, the vehicle may employ a virtual flex fuel sensor method in the
control module 16 that utilizes a learned shift in fuel trim calculated from the
inlet oxygen sensor 24 to estimate the fuel composition. In this manner, the
control module 16 determines or estimates the stoichiometric F/A ratio of the
engine 12. In addition, the control module 16 diagnoses the catalytic
converter 22 of the exhaust system 14 based on a flexible fuel tolerant
catalytic converter diagnostic method described herein.
Referring now to Figure 2, a dataflow diagram illustrates
various embodiments of a flexible fuel tolerant catalytic converter diagnostic
system that may be embedded within the control module 16. Various
embodiments of catalytic converter diagnostic systems according to the
present disclosure may include any number of sub-modules embedded within
the control module 16. The sub-modules shown may be combined and/or
further partitioned to similarly monitor a catalytic converter 22. Inputs to the
system may be received from sensors within the vehicle 10, received from
other control modules (not shown) within the vehicle 10, and/or determined by
other sub-modules (not shown) within the control module 16. In various
embodiments, the control module 16 of Figure 2 includes an enable module

40, a fuel determination module 42, a fuel/air (F/A) ratio module 44, and an
oxygen storage capacity (OSC) diagnostic module 46.
The enable module 40 receives as input a fuel event signal
48. The fuel event signal 48 indicates a status of the remaining fuel in the fuel
system 28 (Figure 1). The enable module 40 determines when a refuel event
has occurred based on the fuel event signal 48 and sets a refuel event flag 50
accordingly. In various embodiments, the fuel event signal 48 indicates a
current fuel level of the fuel system 28 (Figure 1). The enable module 40
compares the current fuel level to a previous fuel level to determine when a
refuel event occurs. It is appreciated, that other methods may be used to
detect a refuel event. The fuel determination module 42 receives as input the
refuel event flag 50 and a fuel sensor signal 52 indicating a composition of the
fuel in the fuel system 28 (Figure 1). The fuel determination module 42
determines a fuel composition 54 of the fuel in the fuel system 28 (Figure 1)
after a refuel event has occurred and based on the fuel sensor signal 52. In
various embodiments, the fuel determination module 42 estimates a
composition of fuel based on engine operating parameters (i.e., fuel trim shift
values) and determines the fuel composition 54 based on the estimated
composition. These methods eliminate the need for the fuel sensor signal 52. The F/A ratio module 44 receives as input the fuel
composition 54. Based on the fuel composition 54, the F/A ratio module 44
determines the ideal stoichiometric F/A ratio 56. The OSC diagnostic module
46 receives as input the stoichiometric F/A ratio 56, mass airflow (MAF) 58,
throttle position (TPS) 60, inlet O2 sensor signal 62 and the outlet O2 sensor
signal 64. Based on the received signals, the OSC diagnostic module 46
determines an oxygen storage capacity for the catalytic converter 22 (Figure
1) and diagnosis the catalytic converter 22 (Figure 1) based on a comparison
of the determined OSC and a reference value. Based on the diagnosis, the
OSC diagnostic module 46 sets a failure code 66. Wherein the failure code
66 is set to TRUE or "test fail" if a malfunction is diagnosed.

Referring now to Figure 3, a flowchart illustrates a flexible
fuel tolerant catalytic converter diagnostic method performed by the control
module 16. The method may be run periodically during engine operation.
Control evaluates whether a refuel event has occurred at 90. If a refuel event
has occurred, the diagnosis is delayed until an accurate determination of the
fuel composition is made at 92. Otherwise control proceeds to evaluate the
current fuel composition at 94. If the fuel composition is of a typical fixed
hydrocarbon mixture at 94, the stoichiometric F/A ratio is set based on a
predetermined value at 96. If the fuel composition is of an alternative fuel
mixture of more than one typical hydrocarbon, such as E85 (85% ethyl alcohol
blended with 15% gasoline), the stoichiometric F/A ratio is computed based
on the composition of the fuel mixture at 98. After setting the F/A ratio, control
proceeds to perform the OSC diagnostic at 99.
More particularly, the details of the OSC diagnostic module
46 of Figure 2 and the process step 99 of Figure 3 will be discussed in the
context of Figures 4-7. Referring to Figure 4, a simplified chemical
combustion model for hydrocarbon and alternative fuels will be described in
detail. The combustion model is based on an equivalence ratio (FR) that is
defined as the actual F/A ratio (F/AACT) divided by the determined
stoichiometric F/A ratio (F/ASTOICH). During periods of O2 release (i.e. rich
engine operation), the chemical combustion model is provided as:

During periods of O2 storage, the chemical combustion model is provided as:

Where a, u, v, x are coefficients. The coefficient a represents a simplification
contsant determined from the following equation:

The coefficient u represents the ratio of the alcohol in the fuel mixture of the
total fuel mixture. The coefficient v represents the number of carbon atoms in
a molecule of the alcohol fuel. The coefficient x represents the number of
carbon atoms in a molecule of the non-alcohol hydrocarbon fuel. The
coefficient y represents the hydrogen atoms in a molecule of the non-alcohol
hydrocarbon fuel.
Periods of 02 release require the catalyst to release 1/2 Mole
of 02 for each Mole of excess CO in the exhaust to completely convert the
CO. Periods of 02 storage require the catalyst to store one mole of 02 for
each mole of excess 02 in the exhaust. The ratio of 02 released by the
catalyst to the mass of inlet 02 in the F/A charge mixture is given as:

A positive term indicates 02 release and a negative term indicates 02 storage. As seen in the graph of Figure 4, when FR is greater than 1
(i.e. rich engine operation), stored 02 within the catalytic converter 22 is
released. When FR is less than 1 (i.e. lean engine operation), excess 02 is
stored. The rate of 02 released to the mass air rate associated with the F/A
mixture is provided as:
grams per sec/ Air grams per sec
M02 is the mass of 02 in a mole of air. MAIR is the average molar mass of air.
The molar ratio of 02 to that of air is assumed to be a constant.

The OSC diagnostic is executed during a fuel cut-off mode of
the engine 12. The fuel cut-off mode occurs during a vehicle overrun
condition, such as when the vehicle 10 is coasting downhill. The fuel cutoff
mode can be determined from the throttle position 60 and intake manifold
pressure. While in the fuel cut-off mode, the F/A ratio of the exhaust stream
from the engine 12 is equal to zero. The OSC diagnostic is initiated after the
engine 12 has operated in the fuel cut-off mode for a predetermined period of
time and is signaled to return to normal operation (or non fuel cut-off mode).
More specifically, the predetermined time period is calibrated to completely
saturate the catalytic converter 22 with oxygen.
Referring now to Figures 5 and 6, time t=0 indicates the
beginning of the OSC diagnostic. Initially, FR is commanded to a fixed
percentage rich. Commanding the equivalence ratio a fixed percentage rich
results in F/AACT being greater than F/ASTOICH- AS the engine 12 operates rich,
the inlet oxygen sensor 24 detects the transition to rich and correspondingly
signals the control module 16. The delay time required for the inlet oxygen
sensor 24 to achieve a reference signal is indicated as tinlet delay. The
reference signal indicates when the exhaust from the engine 12 achieves
F/ASTOICH- The outlet oxygen sensor 26 detects the transition to rich and
correspondingly signals the control module 16. The outlet oxygen sensor
signal 64 is delayed relative to the inlet oxygen sensor signal 62. The
transition time required for the outlet oxygen sensor 26 to achieve the
reference signal is indicated as toulet delay The lag time required for a
predetermined amount of air (such as approximately 1.5g) to flow through an
inert catalytic converter 22 (Figure 1) is indicated as tlag.

The OSC diagnostic module 46 (Figure 2) determines a
target time over which a target OSC of the catalytic converter 22 (Figure 1) is
calculated. The target time, indicated as target, is based on tinlet delay, toutlet delay,
and tlag. More specifically, the OSC diagnostic module 46 monitors the inlet
and outlet sensor signals 62, 64 to determine tinlet delay and toutlet delay The OSC
diagnostic module 46 estimates tlag as the interval of time required to pass a
fixed mass of air between the oxygen sensors as:
tlag= K air_mass_grams/ MAF(tend-of-test)
This process assumes that exhaust flow conditions toward the end-of-test are
known. Referring to Figure 4, the end-of-test time can be estimated as:

This instant in time will vary with the OSC of the catalyst and cannot be
determined until after the test conditions have passed. Also, the mass flow
rate of air is transient in nature during the diagnostic and cannot be assumed
to be constant. For these reasons, MAF 58 is averaged over fixed duration
subintervals of the transition period and stored. The estimated lag period is
then calculated by a backwards integration of the stored MAF 58 terms
beginning at t= tend-of-test and ending when the summation equals K
air_mass_grams. By definition, this occurs at t= tend-of-test- tlag . The target
time is provided as:

The target time is the time period immediately after F/A becoming greater
than the stoichiometric F/A 56.
In addition to monitoring the above-described times, the OSC
diagnostic module 46 stores subinterval averages of the mass air flow (MAF)
into the engine 12 and an FR compensated MAF term (see Figure 6). The
subinterval is defined as an integer multiple of the data sample rate
associated with the MAF and FR terms. This method does not preclude
having the subinterval equal the sample rate and subinterval average based

on a single value. However, a more efficient use of control module memory
can be obtained without significantly affecting the accuracy of the OSC
calculation by specifying a larger subinterval. The MAF 58 is provided as a
signal to the control module 16 from the MAF sensor 20. The incremental
OSC, derived from the simplified O2 release model, is represented by the
following relationship:

where the incremental OSC is measured in terms of grams of stored oxygen
per unit time, a is the mass of oxygen in a mole of air divided by the mass of a
mole of air, and p is the mass air flow fraction per catalytic converter.
Preferably, for an exhaust system having a single catalytic converter 22 as
shown in Figure 1, β is equal to 1. For an exhaust system having a catalytic
converter for each N/2 cylinders, β is equal to 0.5. The OSC at ttarget is
represented by the numerical integration, or summation, of the incremental
OSC over the target period:

where T represents the sampled data period, MAF(nT) represents the MAF at
time nT, and FR(nT) represents the fuel equivalence ratio at time nT. A
prefered equivalent form of this relationship is represented by:

This form is less prone to numerical accumulation of small round-off errors.
Once the outlet oxygen sensor 26 achieves the reference
signal (i.e. detects F/ASTOICH of the exhaust gases from the catalytic
converter), the OSC diagnostic module 46 determines the target OSC.
Referring again to Figure 6, to determine the target OSC, the OSC diagnostic
module 46 calculates the OSC according to the prefered OSC relationship
stated previously. The OSC diagnostic module 46 integrates both the stored
FR compensated MAF and stored MAF measurements over the target time.
This corresponds to the area under each of their respective curves. The
difference between these areas, graphically represented by the area between

the two curves, is then multiplied by the constant term, α x β x T to obtain the
OSC over the target period. The constant term acts as a scalar that optionally
could be omitted if an unscaled result was desirable. The calculated OSC is
compared to a reference OSC value to determine if the catalytic converter 22
passes or fails.
Referring to Figure 7, a flowchart illustrates an OSC
diagnostic method performed by the OSC diagnostic module 46 of Figure 2
and shown in process step 99 of Figure 3. Control determines whether a fuel
cut-off mode is present at 100. If a fuel cut-off mode is not present, control
loops back. Otherwise, control checks particular conditions at 102, 104, and
106 prior to initiating monitoring. At 102, control determines whether the
engine 12 has been operating under closed loop fuel control (CLFC) for a
sufficient time. If not, control loops back to monitor for a fuel cut-off mode at
100. If the engine 12 has been operating under CLFC for a sufficient time,
control determines whether the catalytic converter 22 has achieved an
operating temperature at 104. If the temperature has not been achieved at
104, control loops back to 100. If the temperature has been achieved, control
continues at 106. At 106, control determines whether the catalytic converter
22 has been exposed to air flow for a time sufficient to achieve oxygen
saturation. If the catalytic converter 22 has not been sufficiently exposed,
control loops back to 100. If the catalytic converter 22 has been sufficiently
exposed, control initiates the OSC diagnostic upon the engine 12 exiting the
fuel cut-off mode at 108.
Upon exiting the fuel cut-off mode, control commands FR to a
fixed percentage rich at 110. At 112, control continually records subinterval
measurements of the MAF and FR compensated MAF using the MAF sensor
20 as explained above. At 114, control tracks the signals of the inlet and
outlet oxygen sensors 24, 26. At 116, control determines whether the outlet
oxygen sensor 26 has achieved the reference signal. If the outlet oxygen
sensor 26 has achieved the reference signal, control continues at 118. If not,
control loops back to 112. At 118, control determines toutlet delay, tinlet delay, tlag

and ttarget therefrom. At 124, control integrates the stored OSC related
quantities over the target time and obtains the target OSC value using the
preferred difference equation provided above. At 126, control evaluates the
target OSC value. If the target OSC is not above a reference value, test
failure is indicated at 128. If the target OSC is above the reference value, test
pass is indicated at 122.
Those skilled in the art can now appreciate from the
foregoing description that the broad teachings of the present disclosure can
be implemented in a variety of forms. Therefore, while this disclosure has
been described in connection with particular examples thereof, the true scope
of the disclosure should not be so limited since other modifications will
become apparent to the skilled practitioner upon a study of the drawings,
specification, and the following claims.

WE CLAIM
1. A monitoring system for a catalytic converter, comprising:
a fuel determination module that determines a fuel composition of fuel in
a fuel system using a learned shift in fuel trim calculated based on a signal
frorn an oxygen sensor located at an inlet of the catalytic converter;
a fuel/air (F/A) determination module that selectively determines a
stoichioemetric F/A ratio based on the fuel composition; and
an oxygen storage capacity (OSC) diagnostic module that computes a
target OSC based on the stoichiometric F/A ratio, that compares the
target OSC to a reference value, and that diagnosis the catalytic converter
based on the comparison.
2. The |system as claimed in claim 1 comprising an enable module that
generates an enable signal after detecting a refuel event and wherein the
fuel determination module postpones estimating the fuel composition until
after (the enable signal is received.
3. The system as claimed in claim 2 wherein the enable module detects the
refuel event based on a current and a previous fuel level.
4. The system as claimed in claim 1 wherein the F/A determination module
sets the stoichiometric F/A ratio to a predetermined value when the fuel
composition is a single specified hydrocarbon fuel.

5. The system as claimed in claim 1 wherein the F/A determination module
determines the stoichiometric F/A ratio when the fuel composition is
composed of a blend of more than one hydrocarbon fuel.
6. The system as claimed in claim 1 wherein the OSC diagnostic module
initiates a rich condition based on the stoichiometric F/A ratio after a fuel
cut-off period, computes a mass of oxygen released by the catalytic
converter, and computes the target OSC over a target time period based
on the mass of oxygen.
7. The system as claimed in claim 6 wherein the OSC diagnostic module
determines the target time period based on an inlet delay time to detect a
first F/A ratio and an outlet delay time to detect the first F/A ratio.
8. The system as claimed in claim 7 comprising an inlet sensor that
generates an inlet sensor signal indicating a first oxygen level of exhaust
gases entering the catalytic converter and wherein the inlet delay time is
determined based on the inlet sensor signal.
9. The system as claimed in claim 7 comprising an outlet sensor that
generates an outlet sensor signal indicating a second oxygen level of
exhaust gases exiting the catalytic converter and wherein the outlet delay
time is determined based on the outlet sensor signal.
10. A method of diagnosing a catalytic converter, comprising:

estimating a fuel composition using a learned shift in fuel trim calculated
based on a signal from an oxygen sensor located at an inlet of the
catalytic converter;
selectively determining a stoichiometric fuel/air (F/A) ratio based on the
fuel composition;
computing a target oxygen storage capacity (OSC) of the catalytic
converter based on the stoichiometric F/A ratio; and
diagnosing the catalytic converter based on the target OSC.
11.The method as claimed in claim 10, comprising receiving a fuel event
signal indicating an occurrence of a refuel event and postponing the
estimating the fuel composition until the fuel event signal is received.
12.The method as claimed in claim 11 wherein the selectively determining
comprises determining the stoichiometric F/A ratio to be a predetermined
value when the fuel composition indicates a single specified hydrocarbon
fuel.
13.The method as claimed in claim 10 wherein the selectively determining
comprises computing a stoichiometric F/A ratio when the fuel composition
indicates a blend of more than one hydrocarbon fuel.

14.The method as claimed in claim 10 comprising:
saturating the catalytic converter with oxygen during a fuel cut-off period;
operating an engine in a rich condition based on the stoichiometric F/A
ratio after the fuel cut-off period;
computing a mass of oxygen released by the catalytic converter based on
mass air flow into the engine; and
wherein the computing the target OSC is further based on the mass of
oxygen released over a target time period.
15.The method as claimed in claim 16 wherein the computing comprises:
determining a first delay time for an inlet oxygen sensor to detect a first
F/A ratio;
determining a second delay time for an outlet oxygen sensor to detect the
first F/A ratio; and
computing the target time period based on the first and the second delay
times.
16.The method as claimed in claim 15 comprising:

determining a transport lag time required for a mass of air to flow through
an inert catalytic converter; and
calculating the target time period based on the transport lag time.
17. The method as claimed in claim 10 wherein the diagnosing comprises
diagnosing the catalytic converter based on a comparison of the target
OSC and a reference value.
18. The method as claimed in claim 11 comprising setting a malfunction code
based on the diagnosing of the catalytic converter.

ABSTRACT

"A MONITORING SYSTEM AND A METHOD OF DIAGNOSING A
CATALYTIC CONVERTER"
This invention relates to a monitoring system for a catalytic converter,
comprising a fuel determination module that determines a fuel composition of
fuel in a fuel system using a learned shift in fuel trim calculated based on a
signal from an oxygen sensor located at an inlet of the catalytic converter; a
fuel/air (F/A) determination module that selectively determines a stoichioemetric
F/A ratio based on the fuel composition; and an oxygen storage capacity (OSC)
diagnostic module that computes a target OSC based on the stoichiometric F/A
ratio, that compares the target OSC to a reference value, and that diagnosis the
catalytic converter based on the comparison.

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Patent Number

259450

Indian Patent Application Number

1513/KOL/2007

PG Journal Number

11/2014

Publication Date

14-Mar-2014

Grant Date

12-Mar-2014

Date of Filing

02-Nov-2007

Name of Patentee

GM GLOBAL TECHNOLOGY OPERATIONS, INC

Applicant Address

300 GM RENAISSANCE CENTER DETROIT, MICHIGAN

Inventors:

#	Inventor's Name	Inventor's Address
1	JAMES R. YURGIL	18435 BAINBRIDGE COURT LIVONIA, MICHIGAN 48152

PCT International Classification Number

B60K13/04; B60K13/00;G01M15/10; B60T7/12

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	11/561,487	2006-11-20	U.S.A.