U.S. patent application number 10/063955 was filed with the patent office on 2003-12-04 for system and method for diagnosing egr performance using nox sensor.
This patent application is currently assigned to Ford Global Technologies, Inc.. Invention is credited to Mazur, Christopher John.
Application Number | 20030225503 10/063955 |
Document ID | / |
Family ID | 22052577 |
Filed Date | 2003-12-04 |
United States Patent
Application |
20030225503 |
Kind Code |
A1 |
Mazur, Christopher John |
December 4, 2003 |
SYSTEM AND METHOD FOR DIAGNOSING EGR PERFORMANCE USING NOX
SENSOR
Abstract
A method and system for diagnosing a condition of an EGR valve
used in an engine system. The EGR valve controls the portion
exhaust gases produced by such engine system and fed back to an
intake of such engine system. The engine system includes a NOx
sensor for measuring NOx in such exhaust. The method includes:
determining a time rate of change in NOx measured by the NOx
sensor; comparing the determined time rate of change in the
measured NOx with a predetermined expected time rate of change in
measured NOx; and determining the condition of the EGR valve as a
function of such comparison. The method also includes: determining
from NOx measured by the NOx sensor and engine operating conditions
indications of instances when samples of such measured NOx are
greater than an expected maximum NOx level for such engine
condition and less than an expected minimum NOx level for such
engine condition; and determining the condition of the EGR valve as
a function of a statistical analysis of such indications. The
method includes determining whether the NOx sensor is faulty and
wherein the EGR condition determining includes determining whether
the NOx sensor is faulty.
Inventors: |
Mazur, Christopher John;
(Canton, MI) |
Correspondence
Address: |
FORD GLOBAL TECHNOLOGIES, LLC.
SUITE 600 - PARKLANE TOWERS EAST
ONE PARKLANE BLVD.
DEARBORN
MI
48126
US
|
Assignee: |
Ford Global Technologies,
Inc.
One Parklane Boulevard Parklane Towers East, Suite 600
Dearborn
MI
48126
|
Family ID: |
22052577 |
Appl. No.: |
10/063955 |
Filed: |
May 29, 2002 |
Current U.S.
Class: |
701/108 ;
123/690 |
Current CPC
Class: |
Y02T 10/47 20130101;
F02D 41/222 20130101; F02D 41/146 20130101; F02D 41/0055 20130101;
F02M 26/49 20160201; F01N 2560/026 20130101; Y02T 10/40 20130101;
F02M 26/46 20160201 |
Class at
Publication: |
701/108 ;
123/690 |
International
Class: |
G05D 001/00 |
Goverment Interests
[0001] This invention was made with Government support under
Cooperative Agreement DE-FC26-01NT41103 awarded by the Department
of Energy. The Government has certain rights in the invention.
Claims
1. A method for diagnosing a condition of an EGR valve used in an
engine system, such EGR valve controlling a portion of exhaust
gases fed back to an intake of such engine system, such engine
system including an NOx sensor for measuring NOx in such exhaust,
such method comprising: determining a time rate of change in NOx
measured by the NOx sensor; comparing the determined time rate of
change in the measured NOx with a predetermined expected time rate
of change in measured NOx; and determining the condition of the EGR
valve as a function of such comparison.
2. The method recited in claim 1 including determining the
condition of the EGR valve as a function of a statistical analysis
of such comparison.
3. A method for diagnosing a condition of an EGR valve used in an
engine system, such EGR valve controlling a portion of exhaust
gases fed back to an intake of such engine system, such engine
system including an NOx sensor for measuring NOx in such exhaust,
such method comprising: determining from NOx measured by the NOx
sensor and engine operating conditions indications of instances
when samples of such measured NOx are greater than an expected
maximum NOx level for such engine condition and less than an
expected minimum NOx level for such engine condition; and
determining the condition of the EGR valve as a function of a
statistical analysis of such indications.
4. A method for diagnosing a condition of an EGR valve used in an
engine system, such EGR valve controlling a portion of exhaust
gases fed back to an intake of such engine system, such engine
system including an NOx sensor for measuring NOx in such exhaust,
such method comprising: determining a time rate of change in NOx
measured by the NOx sensor; comparing the determined time rate of
change in the measured NOx with a predetermined expected time rate
of change in measured NOx; and determining from the NOx measured by
the NOx sensor and engine operating conditions indications of
instances when samples of such measured NOx are greater than an
expected maximum NOx level for such engine condition and less than
an expected minimum NOx level for such engine condition.
5. The method recited in claim 4 including determining the
condition of the EGR valve as a function of a statistical analysis
of such indications.
6. The method recited in claim 5 including determining the
condition of the EGR valve as a function of a statistical analysis
of such comparison.
7. The method recited in claim 1 including determining whether the
NOx sensor is faulty and wherein the EGR condition determining
includes determining whether the NOx sensor is faulty.
8. The method recited in claim 3 including determining whether the
NOx sensor is faulty and wherein the EGR condition determining
includes determining whether the NOx sensor is faulty.
9. The method recited in claim 4 including determining whether the
NOx sensor is faulty and wherein the EGR condition determining
includes determining whether the NOx sensor is faulty.
10. The method recited in claim 7 including determining whether the
NOx sensor is faulty and wherein the EGR condition determining
includes determining whether the NOx sensor is faulty.
11. A system for diagnosis a condition of an EGR valve used in an
engine system, such engine system comprising: a NOx sensor for
measuring NOx in exhaust gases from such engine system; an EGR
valve for controlling a portion of the exhaust gases fed back to an
intake of such engine system; and a controller for: determining a
time rate of change in NOx measured by the NOx sensor; comparing
the determined time rate of change in the measured NOx with a
predetermined expected time rate of change in measured NOx; and
determining the condition of the EGR valve as a function of such
comparison.
12. The system recited in claim 11, wherein the controller
determines the condition of the EGR valve as a function of a
statistical analysis of such comparison.
13. A system for diagnosing a condition of an EGR valve used in an
engine system, such engine system comprising: a NOx sensor for
measuring NOx in exhaust gases from such engine system; an EGR
valve for controlling a portion the exhaust gases produced by such
engine system and fed back to an intake of such engine system; and
a controller for: determining from NOx measured by the NOx sensor
and engine operating conditions indications of instances when
samples of such measured NOx are greater than an expected maximum
NOx level for such engine condition and less than an expected
minimum NOx level for such engine condition; and determining the
condition of the EGR valve as a function of a statistical analysis
of such indications.
14. A system for diagnosing a condition of an EGR valve used in an
engine system, such engine system comprising: a NOx sensor for
measuring NOx in exhaust gases from such engine system; an EGR
valve for controlling a portion the exhaust gases produced by such
engine system and fed back to an intake of such engine system; and
a controller for: determining a time rate of change in NOx measured
by the NOx sensor; comparing the determined time rate of change in
the measured NOx with a predetermined expected time rate of change
in measured NOx; and determining from the NOx measured by the NOx
sensor and engine operating conditions indications of instances
when samples of such measured NOx are greater than an expected
maximum NOx level for such engine condition and less than an
expected minimum NOx level for such engine condition.
15. The system recited in claim 14, wherein the controller
determines the condition of the EGR valve as a function of a
statistical analysis of such indications.
16. The system recited in claim 15, wherein the controller
determines the condition of the EGR valve as a function of a
statistical analysis of such indications.
17. The system recited in claim 11, wherein the controller
determines the condition of the EGR valve as a function of a
statistical analysis of such indications.
18. The system recited in claim 13, wherein the controller
determines the condition of the EGR valve as a function of a
statistical analysis of such indications.
19. The system recited in claim 14, wherein the controller
determines the condition of the EGR valve as a function of a
statistical analysis of such indications.
20. The system recited in claim 17, wherein the controller
determines the condition of the EGR valve as a function of a
statistical analysis of such indications.
21. An article of manufacture, comprising: a computer storage
medium having a computer program encoded therein for method for
diagnosing a condition of an EGR valve used in an engine system,
such EGR valve controlling a portion of exhaust gases fed back to
an intake of such engine system, such engine system including an
NOx sensor for measuring NOx in such exhaust, such computer storage
medium comprising: code for determining a time rate of change in
NOx measured by the NOx sensor; code for comparing the determined
time rate of change in the measured NOx with a predetermined
expected time rate of change in measured NOx; and code determining
the condition of the EGR valve as a function of such
comparison.
22. The article recited in claim 1 including code for determining
the condition of the EGR valve as a function of a statistical
analysis of such comparison.
23. An article of manufacture, comprising: a computer storage
medium having a computer program encoded therein for diagnosing a
condition of an EGR valve used in an engine system, such EGR valve
controlling a portion exhaust gases produced by such engine system
and fed back to an intake of such engine system, such engine system
including an NOx sensor for measuring NOx in such exhaust, such
computer storage medium comprising: code for determining from NOx
measured by the NOx sensor and engine operating conditions
indications of instances when samples of such measured NOx are
greater than an expected maximum NOx level for such engine
condition and less than an expected minimum NOx level for such
engine condition; and code for determining the condition of the EGR
valve as a function of a statistical analysis of such
indications.
24. An article of manufacture, comprising: a computer storage
medium having a computer program encoded therein for diagnosing a
condition of an EGR valve used in an engine system, such EGR valve
controlling a portion of exhaust gases fed back to an intake of
such engine system, such engine system including an NOx sensor for
measuring NOx in such exhaust, such computer storage medium
comprising: code for determining a time rate of change in NOx
measured by the NOx sensor; code for comparing the determined time
rate of change in the measured NOx with a predetermined expected
time rate of change in measured NOx; and code for determining from
the NOx measured by the NOx sensor and engine operating conditions
indications of instances when samples of such measured NOx are
greater than an expected maximum NOx level for such engine
condition and less than an expected minimum NOx level for such
engine condition.
25. The article recited in claim 24 including code for determining
the condition of the EGR valve as a function of a statistical
analysis of such indications.
26. The article recited in claim 25 including code for determining
the condition of the EGR valve as a function of a statistical
analysis of such comparison.
27. The article recited in claim 21 including code for determining
whether the NOx sensor is faulty and wherein the EGR condition
determining includes in such determination the determination as to
whether the NOx sensor is faulty.
28. The article recited in claim 23 including code for determining
whether the NOx sensor is faulty and wherein the EGR condition
determining includes in such determination the determination as to
whether the NOx sensor is faulty.
29. The article recited in claim 24 including code for determining
whether the NOx sensor is faulty and wherein the EGR condition
determining includes in such determination the determination as to
whether the NOx sensor is faulty.
30. The article recited in claim 27 including code for determining
whether the NOx sensor is faulty and wherein the EGR valve
condition determining includes in such determination the
determination as to whether the NOx sensor is faulty.
Description
BACKGROUND OF INVENTION
[0002] 1. Technical Field
[0003] This invention relates to systems and methods for diagnosing
Exhaust Gas Recirculation (EGR) valve performance.
[0004] 2. Background and Summary
[0005] As is known in the art, internal combustion engines and more
particularly internal combustion engines used on most passenger and
truck vehicles use exhaust gas recirculation (EGR) systems to
reduce exhaust pollution. As is also known in the art, diesel
engines typically incorporate EGR to reduce combustion temperature
and the formation of NOx. Several techniques have been suggested to
diagnose trouble within the EGR system. One such suggested method
is in U.S. Pat. No. 5,239,971 entitled "Trouble Diagnosis Device
for Exhaust Gas Recirculation System" inventor Uchinami issued Aug.
31, 1993. In such suggested system, a diagnostic device receives
the output detected by one of the engine sensors and compares the
output with a predetermined value of the same kind as the output a
normal state of the EGR system corresponding to the engine
condition detected by the sensors. Specifically, one of the sensors
detects NOx in exhaust gas or exhaust gas temperature. More
particularly, the suggested method diagnoses whether an EGR valve
is stuck open or stuck closed. The diagnosis is based on an
instantaneous NOx sensor reading compared with a predetermined high
or low limit. If the instantaneous difference is greater/less than
the limit, a malfunction illumination light (MIL) is triggered.
[0006] I have discovered that a more robust method for diagnosing
the EGR valve is to process the NOx sensor readings using a
statistical model. The use of such a statistical model reduces
false indications of a faulty EGR valve. Further, my method enables
determination of whether a sticky or loose EGR valve condition
exists. Still further, my method enables determination of whether
it is the EGR valve that is faulty rather than the NOx sensor being
faulty.
[0007] In accordance with the invention, a method and system are
provided for diagnosing a condition of an EGR valve used in an
engine system. The EGR valve controls the portion of exhaust gases
fed back to an intake of such engine system. The engine system
includes a NOx sensor for measuring NOx in such exhaust. The method
includes: determining a time rate of change in NOx measured by the
NOx sensor; comparing the determined time rate of change in the
measured NOx with a predetermined expected time rate of change in
measured NOx; and determining the condition of the EGR valve as a
function of such comparison.
[0008] In accordance with another feature of the invention, a
method and system are provided for diagnosing a condition of an EGR
valve used in an engine system. The EGR valve controls the portion
of exhaust gases fed back to an intake of such engine system. The
engine system includes a NOx sensor for measuring NOx in such
exhaust. The method includes: determining from NOx measured by the
NOx sensor and engine operating conditions indications of instances
when samples of such measured NOx are greater than an expected
maximum NOx level for such engine condition and less than an
expected minimum NOx level for such engine condition; and
determining the condition of the EGR valve as a function of a
statistical analysis of such indications.
[0009] In accordance with yet another feature of the invention, a
method and system are provided for diagnosing a condition of an EGR
valve used in an engine system. The EGR valve controls the portion
of exhaust gases fed back to an intake of such engine system. The
engine system includes a NOx sensor for measuring NOx in such
exhaust. The method includes: determining a time rate of change in
NOx measured by the NOx sensor; comparing the determined time rate
of change in the measured NOx with a predetermined expected time
rate of change in measured NOx; and determining from the NOx
measured by the NOx sensor and engine operating conditions
indications of instances when samples of such measured NOx are
greater than an expected maximum NOx level for such engine
condition and less than an expected minimum NOx level for such
engine condition.
[0010] In one embodiment, the method includes determining whether
the NOx sensor is faulty and wherein the EGR condition determining
includes in such determination the determination as to whether the
NOx sensor is faulty.
[0011] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is block diagram of an engine system 10 according to
the invention;
[0013] FIG. 2 is a flow diagram of a process performed computer
code stored on a computer media in a controller of the system of
FIG. 1, such controller when executing such code determining
whether a EGR valve in the engine system of FIG. 1 is potentially
faulty;
[0014] FIG. 3 is a flow diagram of a process performed computer
code stored on a computer media in a controller of the system of
FIG. 1, such controller when executing such code determining
whether a NOx sensor in the engine system of FIG. 1 is potentially
faulty;
[0015] FIG. 4 is a flow diagram of a performed computer code stored
on a computer media in a controller of the system of FIG. 1, such
controller when executing such code activating an EGR valve fault
MIL and/or a NOx sensor MIL in accordance with the invention;
and
[0016] FIG. 5 is a flow diagram of a process performed computer
code stored on a computer media in a controller of the system of
FIG. 1 to perform a statistical model used by the controller of the
engine of FIG. 1 to determine whether an EGR valve in the engine
system of FIG. 1 is potentially faulty in accordance with the
process in FIG. 3 and whether the NOx sensor in the engine system
of FIG. 1 is potentially faulty and whether the EGR valve in the
engine system of FIG. 1 is potentially faulty in accordance with
the process in FIG. 4.
[0017] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0018] Referring now to FIG. 1, an engine system 10 is shown to
include an internal combustion engine 12, here a diesel engine,
having an intake manifold 14 for receiving external air and exhaust
recirculated gas. More particularly, the engine system 10 includes
an EGR valve 16. The EGR valve 16 controls, in response to a
control signal on line 17 fed thereby by a controller, here a
powertrain control unit (PCU) 18 the portion of exhaust gases in
exhaust manifold 22 produced by such engine 12 which are fed back
to an intake manifold of such engine 12, as indicated by the arrows
23.
[0019] The engine system 10 includes a NOx sensor 24 for measuring
NOx in such exhaust gases produced by the engine 12. The exhaust
gases are passed to any conventional exhaust after-treatment system
26.
[0020] As will be described in more detail hereinafter, the PCU 26
has a storage medium 27 for storing a program (i.e., computer code)
to analyze the NOx measured by the NOx sensor 24 and thereby
provides a diagnosis of a condition of an EGR valve 16. The method
includes: determining a time rate of change in NOx measured by the
NOx sensor 24; comparing the determined time rate of change in the
measured NOx with a predetermined expected time rate of change in
measured NOx; and determining the condition of the EGR valve 16 as
a function of such comparison. Also, the PCU 26 is programmed to
determine, from NOx measured by the NOx sensor 24 and engine
operating conditions indications of instances when samples of such
measured NOx are greater than an expected maximum NOx level for
such engine condition and less than an expected minimum NOx level
for such engine condition. These indications are used to determine
the condition of the EGR valve 16 as a function of a statistical
analysis of such indications. Still further, the PCU 16 has a
storage media 21 for storing a program. The program when executed
determines whether the NOx sensor 24 is faulty and whether the EGR
valve 16 is faulty.
[0021] If the PCU 26 determines that the EGR valve 16 is faulty,
but the NOx sensor 24 has not been determined to be faulty, an EGR
valve MIL 30 is activated. If the EGR 16 is not determined to be
faulty, but the NOx sensor 24 is determined to be faulty, the NOx
sensor MIL 32 is activated.
[0022] Process for Detection of a "Loose" or "Sticky" EGR
Valve:
[0023] Referring now to FIG. 2, the method for determining whether
the EGR valve 16 is defective (e.g., "loose" or "sticky") will be
described.
[0024] The processor first determines whether there is an
accelerator pedal position (app) change and if so, whether the
operator commands a wide-open throttle position. More particularly,
in step 90 a change is accelerator position is made between a
sample App_(t) at time t and a time of a previous sample at time
(t-1) App_(t-1). This difference thereby provides a measure of the
rate of change in accelerator position or accelerator position slew
(App_SLEW_RATE). If, in Step 92, App_SLEW_RATE is determined to be
greater than a predetermined lower threshold value (LOW THRESHOLD
VALUE) and less than a predetermined upper threshold value, then a
test is made as to whether the EGR valve is faulty (e.g., sticky or
loose). The reason for this test in accelerator position slew is
that if the accelerator position does not change from t to (t-1)
then the EGR valve position should, in most cases, not change. The
difference in readings would then equal 0, which would be less than
our NOx_min_slew, and results in an erroneous fault. Another,
scenario is if the customer goes from app=0 to app=100% (wide open
throttle). Here app_slew would be greater than NOx_max_slew and
again result in an erroneous fault.
[0025] If the condition described in Step 92 is determined to be
"yes", the process proceeds to Step 94 where a NOx_SLEW_RATE test
is performed. More particularly, in Step 100, a comparison, here a
difference, is made between a current sample of the measured NOx
(i.e., NOx_RAW_(t)) and a previous NOx sample, (i.e.,
NOx_RAW_(t-1). The difference between NOx_RAW_(t) and NOx_RAW_(t-1)
is NOx_SLEW_RATE (i.e., NOx_SLEW_RATE=I NOx_RAW_(t)-
NOx_RAW_(t-1)I). NOx_SLEW_RATE is therefore a measure of the time
rate of change in measured NOx. NOx_SLEW_RATE is compared with a
predetermined maximum allowed NOx_SLEW_RATE (i.e.,
NOx_MAX_SLEW_RATE), Step 102. If NOx_SLEW_RATE is greater than
NOx_SLEW_MAX, such event indicates the potentially "loose" EGR
valve 16 (FIG. 1) because a properly operating, in this case
non-loose EGR valve would not have resulted in such a large time
rate of change in NOx (i.e., slew rate). In Step 104, a statistical
analysis of these events is performed in order to reject spurious
events (i.e., noise). Here, for example, the statistical analysis,
or model, described in connection with FIG. 5, tests the
differences for statistical significance. The model is familiar to
one in the art and may be described as follows:
[0026] A one-sided t-distribution is used. If a standard normal
random variable is divided by the square root of an independent
random variable, then the resulting random variable is said to have
a t-distribution. Thus, the method we use to infer a population
mean is referred to as a t-procedure and is used to infer a
population mean via hypothesis testing. See for example,
Probability and Statistics for Engineers and Scientists, by A.
Hayter, published by PWS Publishing Co., Boston, Mass. 1996.
[0027] Test Statistic: 1 Test Statistic : t = n ( x _ - 0 ) s ; X =
t n - 1
[0028] X=t.sub.n-1
[0029] p-value=P(X>=t)
[0030] where X is the variable being tested, here slew rates
exceeding NOx_MAX_SLEW_RATE
[0031] Reject H.sub.o condition: p-value<0.01
[0032] With regard to the NOx sensor diagnostic strategy:
[0033] Hi_limit_test: .mu..sub.0=NOx_Hi_lim or
.mu..sub.0=NOx_MAX_SLEW_RAT- E
[0034] Low_limit_test: .mu..sub.0=NOx_lo_lim or
.mu..sub.0=NOx_MIN_SLEW_RA- TE n is the number of samples to be
taken.
[0035] It is a predetermined number that is stored in the PCU
(Powertrain Control Unit). Testing is used to determine the value
of n. In a production vehicle, n is a set value.
[0036] t=test statistic="the equation above"
[0037] H.sub.o is the null hypothesis.
[0038] A null hypothesis (H.sub.o) for a population mean (.mu.) is
a statement which designates possible values for the population
mean. It is associated with an alternative hypothesis (H.sub.A),
which is the "opposite" of the null hypothesis.
[0039] For a Hi_limit_test: H.sub.o: .mu..sub.<=.mu..sub.0;
H.sub.A: .mu..sub.>.mu..sub.0 For a Low_limit_test:
[0040] H.sub.o: .mu..sub.>=.mu..sub.0; H.sub.A:
.mu..sub.<.mu..sub.0
[0041] Example calculation:
[0042] (A) .mu..sub.0=NO.sub.x_Hi_lim=100. The actual required
value is a predetermined constant that is stored in a memory in the
PCU 18.
[0043] (B) Desired confidence=99%. The actual required value is a
predetermined constant that is stored in the memory in the PCU
18.
[0044] (C) The number of samples=n=50. The actual required value is
a predetermined constant that is stored in the memory in the PCU
18. However, it must be greater than 30 unless a smaller sample is
known to be normally distributed.
[0045] (D) 2 The sample average = x _ = 106.
[0046] The actual value is calculated real-time from the values in
the stored samples.
[0047] (E) The sample standard deviation=s=16.9. The actual value
is calculated real-time from the values in the stored samples.
Thus, in this example, the process is:
[0048] 1.Calculate t: 3 t = n ( x _ - 0 ) s = { 50 1 / 2 ( 106 100
) / 16.9 } = 2.5
[0049] 2.Generate p-value:
p-value=P(X>=t)=P(X>=2.5)==p-value=0.005
[0050] 3.Decide to reject or accept Ho:
p-value=0.005<0.01==Reject Ho
[0051] Such statistical model is here implemented as follows:
[0052] A previously set a counter 19 is started to count clock
pulses and a high limit test (i.e., Hi_Lim_Test) is initiated. The
Hi_Lim_Test is initiated by taking n samples of NOx_SLEW_RATE. The
mean and standard deviation of NOx_SLEW_RATE is determined. The
processor then determines .mu..sub.O, H.sub.o, H.sub.A and
calculates 4 t = n ( x _ - 0 ) s
[0053] The process then calculates p-values=p (X.gtoreq.t).
[0054] The process then determines if the p-value is less than a
predetermined threshold, here for example, 0.01. If it is, the
process rejects H.sub.o and triggers an EGR_SLEW_FAULT
condition.
[0055] The EGR is also tested to determine whether it is "sticky".
NOx_SLEW_RATE is compared with a predetermined minimum allowed
NOx_SLEW_RATE (i.e., NOx_MIN_SLEW_RATE), Step 103. If NOx_SLEW_RATE
is less than NOx_SLEW_MIN, such event indicates the potentially
"STICKY" EGR valve 16 (FIG. 1) because a properly operating, in
this case non-STICKY EGR valve would have resulted in such a
smaller time rate of change in NOx (i.e., slew rate). In Step 105 a
statistical analysis of these events is performed in order to
reject spurious events (i.e., noise). Here, for example, the
statistical analysis, or model, described in connection with FIG.
5, and in Step 104, tests the differences for statistical
significance.
[0056] If the statistical model used in Step 104 or the statistical
model used in Step 105 indicts either a sticky EGR or a loose EGR,
a defective EGR (i.e., EGR_SLEW_FAULT) is indicated in Step
107.
[0057] Process for Detecting a Stuck Open/Closed EGR valve:
[0058] Referring again to FIG. 2, engine-operating parameters such
as engine speed (RPM), engine load, and measured NOx (NOx_RAW (t))
are fed to a Look-Up Table 1 (Step 106). From these inputs, and a
priori data stored in the Look-Up Table 1, the Look-Up Table 1
produces an output signal NO.sub.x_Hi_LIM if the NOx exceeds a high
or maximum limit and an output signal NO.sub.x_Lo_LIM if the NOx is
less than a low or minimum limit.
[0059] In Step 108, if NOx_RAW_(t) is less than the low or minimum
limit, NOx_Lo_LIM, a statistical analysis is initiated (Step 109).
Thus, the analysis is performed (Step 116) in statistical model
116, here using the same analysis as described in connection with
FIG. 5 except here X is events where NOx_RAW_(t) is less than the
low or minimum limit, NOx_Lo_LIM. As in the case of model 104,
model 116 is used to reject spurious readings (i.e., noise).
[0060] Likewise, in Step 110 if NOx_RAW_(t) is greater than a high
or maximum limit NOx_Hi_LIM, a statistical analysis is initiated
(Step 111). Thus, the analysis is performed in statistical model
116 (Step 116), here using the same analysis as described in
connection with FIG. 5 except here X represents events where
NOx_RAW_(t) is less than the low or minimum limit, NOx_Lo_LIM. As
in the case of models 104 and 105, model 116 is used to reject
spurious readings (i.e., noise).
[0061] It is noted that the analysis is performed on samples of
NOx_RAW_(t) at the same engine speed and load that resulted in
either NOx_Lo_LIM being less than a low or minimum limit or
NOx_Hi_LIM being greater than a high or maximum limit. If the
statistical analysis verifies that there is a fault disregarding
any spurious detentions, a trigger EGR_RANGE_FAULT signal is
produced in Step 116.
[0062] If either an EGR_SLEW_FAULT or EGR_RANGE_FAULT is produced.
An "EGR_FAULT_INTERMEDIATE" is triggered (Step 118).
[0063] Detection of NOx Sensor Fault
[0064] Referring now to FIG. 3, the process used to detect a NOx
sensor fault is described. In Step 200, engine speed and engine
load are fed to a second look-up table to determine an expected NOx
level, i.e., NOx_STORED. In Step 202, the measured NOx (i.e.,
NOx_RAW_(t)) is compared with NOx_STORED, here by forming the ratio
(NOx_RAW_(t)/NOx_STORED)=NOx_D- RIFT. In Step 204, NOx_DRIFT is
compared with predetermined maximum NOx drift limit,
NOx_DRIFT_HI_LIM. If NOx_DRIFT is greater than NOx_DRIFT_HI_LIM, a
statistical analysis is initiated (Step 206) for these events in
statistical model in Step 208. Here the statistical analysis is
performed on any of these NOx_DRIFT exceeding the limit and the
model is the same as that described in connection with FIG. 5 where
X is the events these NOx_DRIFT exceeding the limit. If the
statistical analysis indicates that there is a valid indication of
a faulty NOx sensor, a "NOx_SENSOR_FAULT_INTERMEDIATE" signal is
triggered.
[0065] In like manner, in Step 206, NOx_DRIFT is compared with
predetermined minimum NOx drift limit, NOx_DRIFT_Lo_LIM. If
NOx_DRIFT is less than NOx_DRIFT_Lo_LIM, a statistical analysis is
initiated (Step 210) for these events in statistical model in Step
208. Here the statistical analysis is performed on any of these
NOx_DRIFT less than the limit and the model is the same as that
described in connection with FIG. 5 where X is the events these
NOx_DRIFT are less than the limit. If the statistical analysis
indicates that there is a valid indication of a faulty NOx sensor,
a "NOx_SENSOR_FAULT_INTERMEDIATE" signal is triggered.
[0066] Malfunction Light Indicator (MIL) Activation
[0067] Referring to FIG. 4, if in Step 300, an
EGR_FAULT_INTERMEDIATE is triggered and a NOx_SENSOR_INTERMEDIATE
signal is triggered (Step 302), the NOx_SENSOR_FAULT MIL 32 (FIG.
1) is activated (Step 304). If, in Step 300, an
EGR_FAULT_INTERMEDIATE is triggered but a NOx_SENSOR_INTERMEDIATE
signal is not triggered (Step 304), an EGR_VALVE_FAULT MIL 30 (FIG.
1) is activated (Step 303).
[0068] If an EGR_FAULT_INTERMEDIATE is not triggered (Step 300) but
a NOx_SENSOR_INTERMEDIATE signal is triggered (Step 306), the
NOx_SENSOR_FAULT MIL is activated (Step 304).
[0069] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. Accordingly, other embodiments are within
the scope of the following claims.
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