U.S. patent application number 11/271988 was filed with the patent office on 2006-05-18 for engine self-diagnosis system.
This patent application is currently assigned to HITACHI, LTD.. Invention is credited to Kozo Katogi, Shinji Nakagawa, Minoru Ohsuga.
Application Number | 20060101808 11/271988 |
Document ID | / |
Family ID | 35781212 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060101808 |
Kind Code |
A1 |
Nakagawa; Shinji ; et
al. |
May 18, 2006 |
Engine self-diagnosis system
Abstract
An engine self-diagnosis system capable of performing diagnosis
of the light-off performance of a catalyst at a low cost and high
accuracy without requiring addition or improvement of a sensor,
etc. The engine self-diagnosis system comprises a unit for directly
or indirectly detecting performance A of an exhaust cleaning
catalyst when temperature of the catalyst is within a predetermined
temperature range, and a unit for, based on the detected catalyst
performance A, estimating performance B of the catalyst, which is
resulted when the temperature of the catalyst is outside the
predetermined temperature range.
Inventors: |
Nakagawa; Shinji;
(Hitachinaka, JP) ; Katogi; Kozo; (Hitachi,
JP) ; Ohsuga; Minoru; (Hitachinaka, JP) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
HITACHI, LTD.
TOKYO
JP
|
Family ID: |
35781212 |
Appl. No.: |
11/271988 |
Filed: |
November 14, 2005 |
Current U.S.
Class: |
60/277 ;
60/274 |
Current CPC
Class: |
F01N 2550/02 20130101;
F01N 3/0835 20130101; F01N 2550/03 20130101; F01N 11/005 20130101;
F01N 2570/12 20130101; F01N 2560/02 20130101; F01N 3/0814 20130101;
Y02T 10/40 20130101; F01N 2610/03 20130101; F02M 26/13 20160201;
Y02T 10/47 20130101; F01N 11/002 20130101; F01N 11/007
20130101 |
Class at
Publication: |
060/277 ;
060/274 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 7/00 20060101 F01N007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 15, 2004 |
JP |
2004-330119 |
Claims
1. An engine self-diagnosis system comprising: means for directly
or indirectly detecting performance A of an exhaust cleaning
catalyst when temperature of said catalyst or temperature of
exhaust gas flowing into said catalyst is within a predetermined
temperature range; and means for, based on the detected catalyst
performance A, estimating performance B of said catalyst which is
resulted, when the temperature of said catalyst is outside the
predetermined temperature range.
2. The engine self-diagnosis system according to claim 1, wherein
said catalyst has at least three-way performance.
3. The engine self-diagnosis system according to claim 1, wherein
said catalyst is an HC adsorbing combustion catalyst that adsorbs
HC when the catalyst temperature is within a predetermined
temperature range, desorbs the adsorbed HC when the catalyst
temperature exceeds the predetermined temperature range, and cleans
the adsorbed and desorbed HC.
4. The engine self-diagnosis system according to claim 1, wherein
said catalyst is a lean NOx catalyst.
5. The engine self-diagnosis system according to Claim 1, further
comprising: means for directly or indirectly detecting the
temperature of said catalyst; means for directly or indirectly
detecting the catalyst performance A when the catalyst temperature
detected by said detecting means is within a temperature range in
which an exhaust cleaning rate is not smaller than a predetermined
value; and means for, based on the detected catalyst performance A,
estimating the catalyst performance B resulted when the catalyst
temperature detected by said detecting means is within a
temperature range in which the exhaust cleaning rate is smaller
than the predetermined value.
6. The engine self-diagnosis system according to claim 1, wherein
the catalyst performance B is a catalyst temperature T0 at which
the exhaust cleaning rate is not smaller than the predetermined
value.
7. The engine self-diagnosis system according to claim 6, further
comprising catalyst deterioration determining means for determining
that said catalyst has deteriorated, when the catalyst temperature
T0 at which the exhaust cleaning rate is not smaller than the
predetermined value exceeds a predetermined temperature.
8. The engine self-diagnosis system according to claim 7, wherein
said catalyst is an HC adsorbing combustion catalyst, and said
catalyst deterioration determining means determines that said HC
adsorbing combustion catalyst has deteriorated, when the catalyst
temperature T0 at which the exhaust cleaning rate is not smaller
than the predetermined value exceeds a predetermined
temperature.
9. The engine self-diagnosis system according to claim 7, wherein
said catalyst is a lean NOx catalyst, and said catalyst
deterioration determining means determines that said lean NOx
catalyst has deteriorated, when the catalyst temperature T0 at
which the exhaust cleaning rate is not smaller than the
predetermined value exceeds a predetermined temperature.
10. The engine self-diagnosis system according to claim 1, wherein
the catalyst performance A is exhaust cleaning capacity.
11. The engine self-diagnosis system according to claim 1, wherein
the catalyst performance A is oxygen storage capacity.
12. The engine self-diagnosis system according to claim 1, wherein
the catalyst performance A is given as exhaust cleaning capacity,
and the catalyst performance B is given as the catalyst temperature
T0 at which the exhaust cleaning rate is not smaller than the
predetermined value.
13. The engine self-diagnosis system according to claim 1, wherein
the catalyst performance A is given as oxygen storage capacity, and
the catalyst performance B is given as the catalyst temperature T0
at which the exhaust cleaning rate is not smaller than the
predetermined value or the oxygen storage capacity is not smaller
than a predetermined value.
14. The engine self-diagnosis system according to claim 1, further
comprising exhaust component detecting means disposed downstream of
said catalyst.
15. The engine self-diagnosis system according to claim 1, further
comprising an O.sub.2 sensor or an A/F sensor downstream of said
catalyst.
16. The engine self-diagnosis system according to claim 15, further
comprising means for detecting oxygen storage capacity of said
catalyst based on an output signal from said O.sub.2 sensor or said
A/F sensor.
17. The engine self-diagnosis system according to claim 15, further
comprising: means for oscillating an O.sub.2 concentration or an
air/fuel ratio upstream of said catalyst at a predetermined
frequency; means for computing a component at the predetermined
frequency of the output signal from said O.sub.2 sensor or said A/F
sensor; and means for detecting oxygen storage capacity of said
catalyst based on the computed component at the predetermined
frequency.
18. The engine self-diagnosis system according to claim 15, further
comprising: means for changing an O.sub.2 concentration or an
air/fuel ratio upstream of said catalyst by a predetermined value;
response delay time computing means for computing a response delay
time from a time at which the O.sub.2 concentration or the air/fuel
ratio upstream of said catalyst is changed by a predetermined value
to a time at which an output signal from said O.sub.2 sensor
downstream of said catalyst is changed by a predetermined value;
and means for detecting oxygen storage capacity of said catalyst
based on the computed response delay time.
19. The engine self-diagnosis system according to claim 1, further
comprising: means for raising temperature of said catalyst;
catalyst temperature estimating means; an O.sub.2 sensor, an A/F
sensor, or an exhaust sensor disposed downstream of said catalyst;
means for directly detecting, based on an output signal from said
O.sub.2 sensor, said A/F sensor, or said exhaust sensor, whether
the exhaust cleaning rate of said catalyst is not smaller than a
predetermined value and said catalyst is in a light-off state; and
abnormality determining means for determining said catalyst
temperature raising means to be abnormal, when said means for
directly detecting catalyst light-off does not detect that said
catalyst is in the light-off state, in spite of the catalyst
temperature estimated by said catalyst temperature estimating means
reaching an estimated light-off temperature representing the
catalyst performance B.
20. The engine self-diagnosis system according to claim 1, further
comprising means for indicating the catalyst performance A and/or B
or information related to the catalyst performance A and/or B.
21. The engine self-diagnosis system according to claim 1, further
comprising means for modifying an engine control parameter based on
the catalyst performance A and/or B.
22. The engine self-diagnosis system according to claim 21, further
comprising means for modifying a control parameter for said
catalyst temperature raising means based on the catalyst
performance B represented by a catalyst temperature T0 at which an
exhaust cleaning rate is not smaller than the predetermined
value.
23. The engine self-diagnosis system according to claim 21, wherein
the control parameter for said catalyst temperature raising means
is a retard amount of ignition timing and/or a period during which
the ignition timing is retarded.
24. An automobile equipped with the engine self-diagnosis system
according to any one of claims 1 to 23.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an engine self-diagnosis
system, and more particularly to an engine self-diagnosis system
capable of performing diagnosis of an exhaust cleaning catalyst,
which is provided in an exhaust passage, at a low cost and high
accuracy.
[0003] 2. Description of the Related Art
[0004] Recently, higher accuracy in diagnosis of various devices
related to the engine exhaust performance has been demanded with
severer control applied to self-diagnosis of automobile engines in
North America, Europe, Japan, etc. In particular, the diagnosis
accuracy of a catalyst for cleaning specific components (HC, CO and
NOx) in engine exhaust is important. Generally, a catalyst exhibits
the exhaust cleaning function at temperatures not lower than a
predetermined value. A shift into the state where the exhaust
cleaning rate is not lower than a predetermined value is called
catalyst light-off (or catalyst activation). The catalyst diagnosis
has hitherto been made on the cleaning capacity after the catalyst
light-off. On the other hand, with a recent increase in performance
of a catalyst and catalyst control, the amount of the specific
components in engine exhaust has been dominantly occupied by the
amount exhausted during a period from the engine startup to the
catalyst light-off. For that reason, it is important to diagnose
the light-off performance of the catalyst.
SUMMARY OF THE INVENTION
[0005] As one example of a system for diagnosing the catalyst
performance, Patent Document 1 (JP-A-2003-176714) proposes a system
for detecting the exhaust component concentration corresponding to
both the engine run status and the catalyst operating status by an
exhaust component sensor, e.g., an HC sensor, disposed downstream
of the catalyst, and the diagnosing, e.g., the light-off
performance of the catalyst in accordance with the detected
value.
[0006] Also, Patent Document 2 (JP-A-5-248227) proposes a diagnosis
system including an O.sub.2 sensor downstream of a catalyst and a
sensor for detecting the catalyst temperature. Then, when the
catalyst performance is diagnosed in accordance with the O.sub.2
sensor downstream of the catalyst, a reference value for use in
diagnosis of the catalyst performance is changed in accordance with
the detected catalyst temperature.
[0007] However, any of those proposed diagnosis systems requires an
additional new sensor, such as the exhaust component sensor and the
temperature sensor, and increases the system cost.
[0008] Meanwhile, Patent Document 3 (JP-A-2001-317345) proposes a
system for detecting the timing at which the oxygen storage
capacity of a catalyst is activated, based on the correlation
between output signals of O.sub.2 sensors disposed upstream and
downstream of the catalyst, and diagnosing the light-off
performance of the catalyst in accordance with the detected
timing.
[0009] Such a diagnosis system requires the O.sub.2 sensor
downstream of the catalyst to be activated before the catalyst
light-off. In practice, however, to avoid the sensor from causing a
trouble, e.g., cracking due to the presence of water in the
catalyst, the sensor downstream of the catalyst is generally heated
up after the water in the catalyst has been sufficiently
evaporated. Hence, an improvement of the O.sub.2 sensor downstream
of the catalyst is required in order to activate that sensor before
the catalyst light-off as in the above-mentioned diagnosis
system.
[0010] Further, Patent Document 4 (JP-A-9-158713) proposes a system
in which, in consideration of that the O.sub.2 sensor (or the A/F
sensor) downstream of the catalyst is not sufficiently activated
during the catalyst light-off, a diagnosis determination value is
changed depending on the temperature of the O.sub.2 sensor
downstream of the catalyst.
[0011] However, such a diagnosis system also requires the O.sub.2
sensor downstream of the catalyst to be activated to some extent at
the timing of the catalyst light-off, and accompanies a risk of
sensor cracking as in the diagnosis system proposed by Patent
Document 3. Moreover, there is a fear that diagnosis accuracy
lowers because the diagnosis is performed during activation of the
sensor downstream of the catalyst.
[0012] All of the above-mentioned diagnosis systems have still
another problem that, because light-off characteristics are
directly detected, it is difficult to distinctively confirm whether
the light-off performance of the catalyst, i.e., the catalyst
itself, has deteriorated or the performance of means for raising
the temperature of the catalyst has reduced.
[0013] In view of the above-described problems in the related art,
an object of the present invention is to provide an engine
self-diagnosis system capable of performing diagnosis of the
light-off performance of a catalyst at a low cost and high
accuracy.
[0014] To achieve the above object, the present invention provides
an engine self-diagnosis system comprising a unit for directly or
indirectly detecting performance A of an exhaust cleaning catalyst
when temperature of the catalyst or temperature of exhaust gas
flowing into the catalyst is within a predetermined temperature
range; and a unit for, based on the detected catalyst performance
A, estimating performance B of the catalyst which is resulted, when
the temperature of the catalyst is outside the predetermined
temperature range.
[0015] In a first form of the present invention embodying the above
features, diagnosis (detection) of the catalyst performance after
light-off of the catalyst is carried out, and based on the result
of the performance diagnosis, the catalyst performance before or
during the light-off is estimated for diagnosis. In general, static
(steady-state) performance of a catalyst after the light-off is
decided dominantly depending on the specific surface area
(dispersibility) of a precious metal used in the catalyst. On the
other hand, the light-off performance of the catalyst is also
decided dominantly depending on the specific surface area of the
precious metal. Accordingly, by detecting the catalyst performance
after the light-off, the catalyst performance before or during the
light-off can be indirectly estimated (see FIGS. 1 and 17).
[0016] In a second form of the engine self-diagnosis system
according to the present invention, the catalyst has at least
three-way performance.
[0017] In a third form of the engine self-diagnosis system
according to the present invention, the catalyst is an HC adsorbing
combustion catalyst that adsorbs HC when the catalyst temperature
is within a predetermined temperature range, desorbs the adsorbed
HC when the catalyst temperature exceeds the predetermined
temperature range, and cleans the adsorbed and desorbed HC.
[0018] In a fourth form of the engine self-diagnosis system
according to the present invention, the catalyst is a lean NOx
catalyst.
[0019] Thus, because the catalysts used in the second, third and
fourth forms are all ones using precious metals, the diagnosis
principle employed in the first form is also applicable.
[0020] In a fifth form of the engine self-diagnosis system
according to the present invention, the system further comprises a
unit for directly or indirectly detecting the temperature of the
catalyst; a unit for directly or indirectly detecting the catalyst
performance A when the catalyst temperature detected by the
detecting unit is within a temperature range in which an exhaust
cleaning rate is not smaller than a predetermined value; and a unit
for, based on the detected catalyst performance A, estimating the
catalyst performance B resulted when the catalyst temperature
detected by the detecting unit is within a temperature range in
which the exhaust cleaning rate is smaller than the predetermined
value (see FIG. 2).
[0021] Thus, in the fifth form, the temperature ranges after and
before the light-off are defined respectively depending on that the
exhaust cleaning rate is not smaller than or is smaller than the
predetermined value.
[0022] In a sixth form of the engine self-diagnosis system
according to the present invention, the catalyst performance B is a
catalyst temperature T0 at which the exhaust cleaning rate is not
smaller than the predetermined value (see FIG. 3).
[0023] Thus, in the sixth form, the catalyst performance B
estimated from the directly detected catalyst performance after the
light-off is specifically defined as the light-off temperature.
[0024] In a seventh form of the engine self-diagnosis system
according to the present invention, the system further comprises
catalyst deterioration determining unit for determining that the
catalyst has deteriorated, when the catalyst temperature T0 at
which the exhaust cleaning rate is not smaller than the
predetermined value exceeds a predetermined temperature (see FIG.
4).
[0025] Thus, in the seventh form, when the estimated light-off
temperature exceeds the predetermined temperature, a time from the
engine startup to the catalyst light-off is prolonged and
particular components (HC, CO and NOx) in exhaust are increased. In
such a condition, therefore, it is determined that the catalyst has
deteriorated.
[0026] In an eighth form of the engine self-diagnosis system
according to the present invention, the catalyst is an HC adsorbing
combustion catalyst, and the catalyst deterioration determining
unit determines that the HC adsorbing combustion catalyst has
deteriorated, when the catalyst temperature T0 at which the exhaust
cleaning rate is not smaller than the predetermined value exceeds a
predetermined temperature (see FIG. 4).
[0027] The function of the HC adsorbing combustion catalyst is
mainly divided into HC adsorbing performance and adsorbed-HC
cleaning capacity. However, the adsorbed-HC cleaning capacity
developed by a precious metal as a primary component generally
deteriorates in a shorter term. Hence, deterioration diagnosis of
the HC adsorbing combustion catalyst is realized by diagnosing the
light-off performance in the adsorbed-HC cleaning capacity of the
HC adsorbing combustion catalyst.
[0028] In a ninth form of the engine self-diagnosis system
according to the present invention, the catalyst is a lean NOx
catalyst, and the catalyst deterioration determining unit
determines that the lean NOx catalyst has deteriorated, when the
catalyst temperature T0 at which the exhaust cleaning rate is not
smaller than the predetermined value exceeds a predetermined
temperature (see FIG. 4).
[0029] Thus, this ninth form is based on the fact that the
light-off performance in the NOx storage capacity of the lean NOx
catalyst also depends on the precious metal in the catalyst.
[0030] In a tenth form of the engine self-diagnosis system
according to the present invention, the catalyst performance A is
exhaust cleaning capacity (see FIG. 5).
[0031] Thus, in the tenth form, the performance detected after the
catalyst temperature exceeds the predetermined temperature (i.e.,
after the light-off) is defined as the exhaust cleaning capacity of
the catalyst.
[0032] In an eleventh form of the engine self-diagnosis system
according to the present invention, the catalyst performance A is
oxygen storage capacity (see FIG. 6).
[0033] Thus, in the eleventh form, the performance detected after
the catalyst temperature exceeds the predetermined temperature
(i.e., after the light-off) is defined as the oxygen storage
capacity of the catalyst. The oxygen storage capacity (OSC) of a
catalyst is decided depending on both the specific surface area
(dispersibility) of a precious metal used in the catalyst and the
content of an auxiliary catalyst such as ceria (or zirconia).
Because the content of the auxiliary catalyst is hardly changed
from the initial value, the OSC is substantially decided by
sintering (cohesion) of the precious metal. Accordingly, the
light-off performance (catalyst characteristic B) of the catalyst
is estimated in terms of a sintering degree of the precious metal
by diagnosing the OSC.
[0034] In a twelfth form of the engine self-diagnosis system
according to the present invention, the catalyst performance A is
given as exhaust cleaning capacity, and the catalyst performance B
is given as the catalyst temperature T0 at which the exhaust
cleaning rate is not smaller than the predetermined value (see FIG.
7).
[0035] Thus, in the twelfth form, the performance detected after
the catalyst temperature exceeds the predetermined temperature
(i.e., after the light-off) is defined as the exhaust cleaning
capacity of the catalyst, and the catalyst performance B estimated
from the exhaust cleaning capacity after the light-off is
specifically defined as the light-off temperature.
[0036] In a thirteenth form of the engine self-diagnosis system
according to the present invention, the catalyst performance A is
given as oxygen storage capacity, and the catalyst performance B is
given as the catalyst temperature T0 at which the exhaust cleaning
rate is not smaller than the predetermined value or the oxygen
storage capacity is not smaller than a predetermined value (see
FIG. 8).
[0037] Thus, in the thirteenth form, the performance detected after
the catalyst temperature exceeds the predetermined temperature
(i.e., after the light-off) is defined as the oxygen storage
capacity of the catalyst, and the catalyst performance B estimated
from the oxygen storage capacity after the light-off is
specifically defined as the light-off temperature.
[0038] In a fourteenth form of the engine self-diagnosis system
according to the present invention, the system further comprises an
exhaust component detecting unit disposed downstream of the
catalyst (see FIG. 9).
[0039] Thus, in the fourteenth form, exhaust components downstream
of the catalyst are directly detected by the exhaust component
detecting unit, and the exhaust cleaning rate after the light-off
is detected based on the detected exhaust components. Then, the
light-off performance is estimated based on the detected cleaning
capacity.
[0040] In a fifteenth form of the engine self-diagnosis system
according to the present invention, the system further comprises an
O.sub.2 sensor or an A/F sensor downstream of the catalyst (see
FIG. 10).
[0041] Thus, in the fifteenth form, the A/F ratio downstream of the
catalyst is directly detected by the O.sub.2 sensor or the A/F
sensor, and the exhaust cleaning capacity after the light-off is
detected based on the detected A/F ratio. Then, the light-off
performance is estimated based on the detected cleaning
capacity.
[0042] In a sixteenth form of the engine self-diagnosis system
according to the present invention, the system further comprises a
unit for detecting oxygen storage capacity of the catalyst based on
an output signal from the O.sub.2 sensor or the A/F sensor (see
FIG. 11).
[0043] Thus, in the sixteenth form, the A/F ratio downstream of the
catalyst is directly detected by the O.sub.2 sensor or the A/F
sensor, and the oxygen storage capacity of the catalyst after the
light-off is detected based on the detected A/F ratio. Then, the
light-off performance is estimated based on the detected oxygen
storage capacity.
[0044] In a seventeenth form of the engine self-diagnosis system
according to the present invention, the system further comprises a
unit for oscillating an O.sub.2 concentration or an air/fuel ratio
upstream of the catalyst at a predetermined frequency; a unit for
computing a component at the predetermined frequency of the output
signal from the O.sub.2 sensor or the A/F sensor; and a unit for
detecting oxygen storage capacity of the catalyst based on the
computed component at the predetermined frequency (see FIG.
12).
[0045] When the O.sub.2 concentration or the air/fuel ratio
upstream of the catalyst is oscillated at the predetermined
frequency, the oscillation of the O.sub.2 concentration or the
air/fuel ratio downstream of the catalyst exhibits behaviors
differing from those upstream of the catalyst due to the oxygen
storage capacity of the catalyst if the catalyst (oxygen storage
capacity) is in the light-off state. Based on that finding, in the
seventeenth form, the oxygen storage capacity is detected by
executing frequency analysis of the oscillation of the O.sub.2
concentration or the air/fuel ratio downstream of the catalyst, and
the light-off performance is estimated based on the detected oxygen
storage capacity.
[0046] In an eighteenth form of the engine self-diagnosis system
according to the present invention, the system further comprises a
unit for changing an O.sub.2 concentration or an air/fuel ratio
upstream of the catalyst by a predetermined value; a response delay
time computing unit for computing a response delay time from a time
at which the O.sub.2 concentration or the air/fuel ratio upstream
of the catalyst is changed by a predetermined value to a time at
which an output signal from the O.sub.2 sensor downstream of the
catalyst is changed by a predetermined value; and a unit for
detecting oxygen storage capacity of the catalyst based on the
computed response delay time (FIG. 13).
[0047] When the O.sub.2 concentration or the air/fuel ratio
upstream of the catalyst is changed by the predetermined value, the
response delay time until the O.sub.2 concentration or the air/fuel
ratio downstream of the catalyst is changed depends on the oxygen
storage capacity of the catalyst if the catalyst (oxygen storage
capacity) is in the light-off state. Based on that finding, in the
eighteenth form, the oxygen storage capacity is detected by
determining the response delay time until the O.sub.2 concentration
or the air/fuel ratio downstream of the catalyst is changed, and
the light-off performance is estimated based on the detected oxygen
storage capacity.
[0048] In a nineteenth form of the engine self-diagnosis system
according to the present invention, the system further comprises a
unit for raising temperature of the catalyst; a catalyst
temperature estimating unit; an O.sub.2 sensor, an A/F sensor, or
an exhaust sensor disposed downstream of the catalyst; a unit for
directly detecting, based on an output signal from the O.sub.2
sensor, the A/F sensor, or the exhaust sensor, whether the exhaust
cleaning rate of the catalyst is not smaller than a predetermined
value and the catalyst is in the light-off state; and an
abnormality determining unit for determining the catalyst
temperature raising unit to be abnormal, when the unit for directly
detecting the catalyst light-off does not detect that the catalyst
is in the light-off state, in spite of the catalyst temperature
estimated by the catalyst temperature estimating unit reaching an
estimated light-off temperature representing the catalyst
performance B (see FIG. 14).
[0049] Thus, the nineteenth form is intended to distinctly detect
whether the light-off performance of the catalyst has deteriorated
or the unit for activating the catalyst in a shorter time (i.e.,
the catalyst temperature raising unit) has deteriorated.
Specifically, when the estimated catalyst temperature (not actual
temperature) reaches the estimated light-off temperature, the
catalyst should have been (normally) brought into the light-off
state. Taking into account that point, whether the catalyst is in
the light-off state or not is detected by using, e.g., the O.sub.2
sensor, the A/F sensor, or the exhaust sensor. If the detection
result shows that the catalyst is not in the light-off state, this
is determined as indicating that the catalyst temperature does not
reach the light-off temperature. Then, the catalyst temperature
raising unit is determined to be abnormal.
[0050] In a twentieth form of the engine self-diagnosis system
according to the present invention, the system further comprises a
unit for indicating the catalyst performance A and/or B or
information related to the catalyst performance A and/or B.
[0051] In a twenty-first form of the engine self-diagnosis system
according to the present invention, the system further comprises a
unit for modifying an engine control parameter based on the
catalyst performance A and/or B (see FIG. 15).
[0052] Thus, the engine control parameter is modified based on the
catalyst performance determined as described above, to thereby
further reduce particular components (HC, CO and NOx) in engine
exhaust.
[0053] In a twenty-second form of the engine self-diagnosis system
according to the present invention, the system further comprises a
unit for modifying a control parameter for the catalyst temperature
raising unit based on the catalyst performance B represented by a
catalyst temperature T0 at which an exhaust cleaning rate is not
smaller than the predetermined value (see FIG. 16).
[0054] Thus, in the twenty-second form, for example, a control
parameter for engine startup is modified based on the catalyst
light-off performance estimated as described above.
[0055] In a twenty-third form of the engine self-diagnosis system
according to the present invention, the control parameter for the
catalyst temperature raising unit is a retard amount of ignition
timing and/or a period during which the ignition timing is retarded
(see FIG. 16).
[0056] Thus, in the twenty-third form, for example, the retard
amount of ignition timing and/or the period during which the
ignition timing is retarded is modified based on the catalyst
light-off performance estimated as described above, to thereby
activate the catalyst in a shorter time.
[0057] In addition, the present invention also provides an
automobile equipped with the engine self-diagnosis system
constituted as described above.
[0058] With the engine self-diagnosis system according to the
present invention, the catalyst performance A after the light-off
of the catalyst is detected for diagnosis, and the catalyst
performance before or during the light-off (i.e., the catalyst
performance B) is estimated based on the result of the detection
and diagnosis. Therefore, the light-off performance of the catalyst
can be diagnosed at a low cost and high accuracy without requiring
addition or improvement of a sensor, etc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] FIG. 1 is a block diagram showing first through fourth forms
of an engine self-diagnosis system according to the present
invention;
[0060] FIG. 2 is a block diagram showing a fifth form of the engine
self-diagnosis system according to the present invention;
[0061] FIG. 3 is a block diagram showing a sixth form of the engine
self-diagnosis system according to the present invention;
[0062] FIG. 4 is a block diagram showing seventh to ninth forms of
the engine self-diagnosis system according to the present
invention;
[0063] FIG. 5 is a block diagram showing a tenth form of the engine
self-diagnosis system according to the present invention;
[0064] FIG. 6 is a block diagram showing an eleventh form of the
engine self-diagnosis system according to the present
invention;
[0065] FIG. 7 is a block diagram showing a twelfth form of the
engine self-diagnosis system according to the present
invention;
[0066] FIG. 8 is a block diagram showing a thirteenth form of the
engine self-diagnosis system according to the present
invention;
[0067] FIG. 9 is a block diagram showing a fourteenth form of the
engine self-diagnosis system according to the present
invention;
[0068] FIG. 10 is a block diagram showing a fifteenth form of the
engine self-diagnosis system according to the present
invention;
[0069] FIG. 11 is a block diagram showing a sixteenth form of the
engine self-diagnosis system according to the present
invention;
[0070] FIG. 12 is a block diagram showing a seventeenth form of the
engine self-diagnosis system according to the present
invention;
[0071] FIG. 13 is a block diagram showing an eighteenth form of the
engine self-diagnosis system according to the present
invention;
[0072] FIG. 14 is a block diagram showing a nineteenth form of the
engine self-diagnosis system according to the present
invention;
[0073] FIG. 15 is a block diagram showing a twenty-first form of
the engine self-diagnosis system according to the present
invention;
[0074] FIG. 16 is a block diagram showing twenty-second and--third
forms of the engine self-diagnosis system according to the present
invention;
[0075] FIG. 17 is a graph showing the relationship between the
catalyst temperature and the OSC index for explaining the diagnosis
principle in the present invention;
[0076] FIG. 18 is a schematic view showing an engine self-diagnosis
system according to a first embodiment of the present invention,
along with an engine to which the self-diagnosis system is
applied;
[0077] FIG. 19 is a block diagram showing the internal
configuration of a control unit in the first embodiment of the
present invention;
[0078] FIG. 20 is a block diagram showing a control system in the
first embodiment;
[0079] FIG. 21 is a block diagram for explaining a basic fuel
injection amount computing unit in the first embodiment;
[0080] FIG. 22 is a block diagram for explaining a deterioration
diagnosis permission determining unit in the first embodiment;
[0081] FIG. 23 is a block diagram for explaining an air/fuel ratio
modification term computing unit in the first embodiment;
[0082] FIG. 24 is a block diagram for explaining a target air/fuel
ratio computing unit in the first embodiment;
[0083] FIG. 25 is a block diagram for explaining a unit for
detecting the oxygen storage capacity after the light-off in the
first embodiment;
[0084] FIG. 26 is a block diagram for explaining a frequency
component computing unit in the first embodiment;
[0085] FIG. 27 is a block diagram for explaining an oxygen storage
capacity computing unit in the first embodiment;
[0086] FIG. 28 is a block diagram for explaining a light-off
temperature estimating unit in the first embodiment;
[0087] FIG. 29 is a block diagram showing a control system in a
second embodiment;
[0088] FIG. 30 is a block diagram for explaining a target air/fuel
ratio computing unit in the second embodiment;
[0089] FIG. 31 is a block diagram for explaining a unit for
detecting the oxygen storage capacity after the light-off in the
second embodiment;
[0090] FIG. 32 is a block diagram for explaining a response delay
time computing unit in the second embodiment;
[0091] FIG. 33 is a block diagram for explaining an oxygen storage
capacity computing unit in the second embodiment;
[0092] FIG. 34 is a block diagram showing a control system in a
third embodiment;
[0093] FIG. 35 is a block diagram for explaining a light-off
temperature estimating unit in the third embodiment;
[0094] FIG. 36 is a block diagram showing a control system in a
fourth embodiment;
[0095] FIG. 37 is a block diagram for explaining a deterioration
diagnosis permission determining unit in the fourth embodiment;
[0096] FIG. 38 is a block diagram for explaining a light-off
temperature estimating unit in the fourth embodiment; and
[0097] FIG. 39 is a block diagram for explaining an ignition timing
setting unit in the fourth embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0098] Embodiments of the present invention will be described below
with reference to the drawings.
FIRST EMBODIMENT
[0099] FIG. 18 is a schematic view showing an engine self-diagnosis
system according to a first embodiment of the present invention,
along with one example of a vehicle-loaded engine to which the
self-diagnosis system is applied.
[0100] An engine 10 shown in FIG. 18 is a multi-cylinder engine
having four cylinders, for example, and comprises cylinders 12 and
pistons 15 slidably inserted in the cylinders 12 numbered #1, #2,
#3 and #4. A combustion chamber 17 is defined above the piston 15.
An ignition plug 35 is disposed to face the combustion chamber
17.
[0101] Air supplied for combustion of fuel is taken in from an air
cleaner 21 disposed at a start end of an intake passage 20 and
enters a collector 56 through an airflow sensor 24 and an
electronically-controlled throttle valve 25. Then, the intake air
is introduced from the collector 56 to the combustion chamber 17 of
each cylinder numbered #1, #2, #3 or #4 through an intake valve 28
that is disposed at a downstream end of the intake passage 20
(i.e., at an intake port). Further, a fuel injection valve 30 is
disposed at the downstream end of the intake passage 20.
[0102] A gas mixture of the air introduced to the combustion
chamber 17 and fuel injected from the fuel injection valve 30 is
ignited by the ignition plug 35 and is burnt for explosion.
Combustion waste gas (exhaust gas) is discharged through an exhaust
valve 48 from the combustion chamber 17 to each individual passage
portion 40A forming an upstream part of an exhaust passage 40.
Then, the exhaust gas flows from the individual passage portion 40A
into a three-way catalyst 50, which is disposed in the exhaust
passage 40, through an exhaust collecting portion 40B. After
cleaning by the three-way catalyst 50, the exhaust gas is
discharged to the exterior.
[0103] An O.sub.2 sensor 51 is disposed in the exhaust passage 40
downstream of the three-way catalyst 50, and an A/F (air/fuel
ratio) sensor 52 is disposed in the exhaust passage 40 upstream of
the three-way catalyst 50 at a position near the exhaust collecting
portion 40B.
[0104] The A/F sensor 52 has a linear output characteristic for the
concentration of oxygen contained in the exhaust gas. Because the
relationship between the concentration of oxygen in the exhaust gas
and the air/fuel ratio is substantially linear, the air/fuel ratio
in the exhaust collecting portion 40B can be determined based on a
signal from the A/F sensor 52 for detecting the oxygen
concentration. Also, based on a signal from the O.sub.2 sensor 51,
it is possible to detect the oxygen concentration downstream of the
three-way catalyst 50, or whether the exhaust gas is rich or lean
with respect to the stoichiometric air/fuel ratio.
[0105] Further, a part of the exhaust gas discharged from the
combustion chamber 17 to the exhaust passage 40 is introduced to
the intake passage 20 through an EGR passage 41, as required, for
circulation to the combustion chamber 17 of each cylinder through a
branched passage portion of the intake passage 20. An EGR valve 42
for adjusting the EGR rate is disposed in the EGR passage 41.
[0106] A self-diagnosis system 1 of this embodiment comprises a
control unit 100 with a microcomputer incorporated therein for
executing various kinds of control of the engine 10.
[0107] The control unit 100 basically comprises, as shown in FIG.
19, a CPU 101, an input circuit 102, input/output ports 103, a RAM
104, a ROM 105, etc.
[0108] The control unit 100 is supplied with, as input signals, a
signal detected by the airflow sensor 24 and corresponding to the
intake air amount, a signal detected by a throttle sensor 34 and
corresponding to the opening degree of the throttle valve 25, a
signal detected by a crank angle sensor 37 and indicating the
rotation (engine rotation speed)/phase of a crankshaft 18, a signal
detected by the O.sub.2 sensor 51 disposed in the exhaust passage
40 downstream of the three-way catalyst 50 and corresponding to the
oxygen concentration in the exhaust gas, a signal detected by the
A/F sensor 52 disposed in the exhaust collecting portion 40B of the
exhaust passage 40 upstream of the three-way catalyst 50 and
corresponding to the oxygen concentration (air/fuel ratio), a
signal detected by a water temperature sensor 19 disposed in the
cylinder 12 and corresponding to the temperature of the engine
cooling water, a signal detected by an accelerator sensor 36 and
corresponding to the amount of depression of an accelerator pedal
39 (which represents a torque demanded by a driver), and a signal
detected by a vehicle speed sensor 29 and corresponding to the
vehicle speed of an automobile in which the engine 10 is
mounted.
[0109] In the control unit 100, when the signals outputted from the
various sensors, such as the A/F sensor 52, the O.sub.2 sensor 51,
the throttle sensor 34, the airflow sensor 24, the crank angle
sensor 37, the water temperature sensor 16 and the accelerator
sensor 36, are inputted, those signals are subjected to signal
processing, e.g., removal of noise, in the input circuit 102 and
then sent to the input/output ports 103. Respective values at the
input ports are stored in the RAM 104 and are subjected to
arithmetic/logical operations in the CPU 101. A control program
describing the contents of the arithmetic/logical operations is
written in the ROM 105 beforehand. Values computed in accordance
with the control program and representing strokes of various
actuators to be operated are stored in the RAM 104 and are sent to
the output ports 103.
[0110] A signal for operating the ignition plug 35 is set as an
on/off signal such that it is turned on when a current is supplied
to a primary coil in an ignition output circuit 116 and turned off
when a current is not supplied to the primary coil. The ignition
timing is defined as a time at which the signal is shifted from the
on- to off-state. The signal for operating the ignition plug 35,
which has been set at the output port 103, is amplified by an
ignition output circuit 116 to a level of energy sufficient for
ignition and is then supplied to the ignition plug 35. Also, a
signal for driving the fuel injection valve 30 (i.e., an air/fuel
ratio control signal) is set as an on/off signal such that it is
turned on when the fuel injection valve 30 is opened and turned off
when it is closed. The driving signal is amplified by a fuel
injection valve driving circuit 117 to a level of energy sufficient
for opening the fuel injection valve 30 and is then supplied to the
fuel injection valve 30. A driving signal for realizing the target
opening degree of the electronically-controlled throttle valve 25
is sent to the electronically-controlled throttle valve 25 through
an electronically-controlled throttle valve driving circuit
118.
[0111] The control unit 100 computes the air/fuel ratio upstream of
the three-way catalyst 50 based on the signal from the A/F sensor
52, and also computes, based on the signal from the O.sub.2 sensor
51, the oxygen concentration downstream of the three-way catalyst
50, or whether the exhaust gas is rich or lean with respect to the
stoichiometric air/fuel ratio. Further, by using the outputs of
both the sensors 51, 52, the control unit 100 executes feedback
control for sequentially modifying the fuel injection amount or the
intake air amount so that the cleaning efficiency of the three-way
catalyst 50 is optimized.
[0112] Performance diagnosis of the three-way catalyst 50 executed
by the control unit 100 will be described in more detail below.
[0113] FIG. 20 is a functional block diagram showing a control
system in the first embodiment. As shown in the functional block
diagram, the control unit 100 comprises a basic fuel injection
amount computing unit 110, an air/fuel ratio modification term
computing unit 120, a deterioration diagnosis permission
determining unit 130, a catalyst characteristic A (after-light-off
oxygen storage capacity) detecting unit 140, and a catalyst
characteristic B (light-off temperature) estimating unit 150.
[0114] In an ordinary mode, the control unit 100 computes a fuel
injection amount Ti for each of the cylinders #1-#4 based on a
basic fuel injection amount Tp and an air/fuel ratio modification
term Lalpha so that air/fuel ratios of all the cylinders are held
at the stoichiometric air/fuel ratio. Then, when deterioration
diagnosis is permitted, the control unit 100 oscillates the target
air/fuel ratio at a predetermined frequency and estimates the
after-light-off oxygen storage capacity (catalyst performance A) of
the three-way catalyst 50 in accordance with predetermined
frequency components of respective output signals from the A/F
sensor 52 and the O.sub.2 sensor 51. Then, based on the detection
result, the control unit 100 estimates the light-off
temperature.
[0115] Each of the processing units will be described in more
detail below.
<Basic Fuel Injection Amount Computing Unit 110 (FIG.
21)>
[0116] This computing unit 110 computes, based on the engine intake
air amount, the fuel injection amount for realizing the target
torque and the target air/fuel ratio at the same time under
arbitrary operating conditions. Specifically, a basic fuel
injection amount Tp is computed as shown in FIG. 21. In FIG. 21, K
is a constant having a value for making adjustment such that the
stoichiometric air/fuel ratio is always realized with respect to
the intake air amount. Also, Cyl represents the number of engine
cylinders.
<Deterioration Diagnosis Permission Determining Unit 130 (FIG.
22)>
[0117] This permission determining unit 130 determines whether the
deterioration diagnosis of the three-way catalyst 50 is
permitted.
[0118] Specifically, as shown in FIG. 22, when Twn.gtoreq.Twndag,
NedagH.gtoreq.Ne.gtoreq.NedagL, QadagH.gtoreq.Qa.gtoreq.QadagL,
.DELTA.Ne.ltoreq.DNedag, .DELTA.Qa.ltoreq.Dqadag, and
Tcat.gtoreq.Tcatdag are all satisfied, a deterioration diagnosis
permission flag Fpdag=1 is set to permit the deterioration
diagnosis. Otherwise, Fpdag=0 is set to inhibit the deterioration
diagnosis.
[0119] In FIG. 22, Twn is the engine cooling water temperature, Ne
is the engine rotation speed, Qa is the intake air amount,
.DELTA.Ne is the change rate of the engine rotation speed,
.DELTA.Qa is the change rate of the intake air amount, and Tcat is
the estimated catalyst temperature.
[0120] .DELTA.Ne and .DELTA.Qa can be each given as the difference
between a value computed in the preceding job and a value computed
in the current job. Also, because the catalyst temperature depends
on the temperature of the exhaust gas flowing into the catalyst and
the temperature of the exhaust gas depends on the intake air amount
Qa (fuel injection amount), etc., the catalyst temperature can be
estimated based on Twn, Qa, an integrated value of Qa, etc. Further
details are omitted here for the reason that various methods have
already been proposed and are described in many books, papers, etc.
Tcatdag is preferably set to a temperature at which the three-way
catalyst 50 is in the light-off state at a sufficient level.
<Air/Fuel Ratio Modification Term Computing Unit 120 (FIG.
23)>
[0121] This computing unit 120 executes F/B (feedback) control
based on the air/fuel ratio detected by the A/F sensor 52 so that
the air/fuel ratio at an inlet of the three-way catalyst 50 is held
at the target air/fuel ratio under arbitrary operating conditions.
Specifically, as shown in FIG. 23, an air/fuel ratio modification
term Lalpha is computed with PI control from a deviation Dltabf
between a target air/fuel ratio Tabf set by a target air/fuel ratio
computing unit 121 and an air/fuel ratio Rabf detected by the A/F
sensor. The air/fuel ratio modification term Lalpha is multiplied
by the basic fuel injection amount Tp.
<Target Air/Fuel Ratio Computing Unit 121 (Frequency Response)
(FIG. 24)>
[0122] This computing unit 121 computes the target air/fuel ratio
in a frequency response manner. Specifically, this computation is
executed as shown in FIG. 24. When Fpdag=1 holds, a target air/fuel
ratio Tabf1L and a target air/fuel ratio Tab0 are switched over at
a frequency fa [Hz]. Otherwise, an ordinary target air/fuel ratio
Tabf0 is set. In this embodiment, Tabf0 is a value corresponding to
the stoichiometric air/fuel ratio, Tabf1R is a value shifted from
the stoichiometric air/fuel ratio toward the rich side by a
predetermined value, and Tabf1L is a value shifted from the
stoichiometric air/fuel ratio toward the lean side by a
predetermined value. The values of Tabf1R(L) and fa are preferably
decided based on experiments from the viewpoints of diagnosis
accuracy and exhaust performance (emission characteristics).
<After-Light-Off Oxygen Storage capacity Detecting Unit 140
(Frequency Response) (FIG. 25)>
[0123] This detecting unit 140 detects the oxygen storage capacity
after the light-off. Specifically, this detection is executed as
shown in FIG. 25. This detecting unit 140 comprises a frequency
component computing unit 141 for computing respective frequency
components of an output Rabf of the A/F sensor 52 and an output
RVO2 of the O.sub.2 sensor 51, and an oxygen storage capacity
computing unit 142 for computing the oxygen storage capacity of the
three-way catalyst 50 based on the computed frequency
components.
[0124] The frequency component computing unit 141 and the oxygen
storage capacity computing unit 142 will be described below.
<Frequency Component Computing Unit 141 (FIG. 26)>
[0125] This computing unit 141 computes respective frequency
components of the output Rabf of the A/F sensor 52 and the output
RVO2 of the O.sub.2 sensor 51. Specifically, as shown in FIG. 26,
powers (Power1 and Power2) and phases (Phase1 and Phase2) at the
frequency fa [Hz] are computed from both signals Rabf and RVO2 with
processes using DFT (Discrete Fourier Transform).
<Oxygen Storage capacity Computing Unit 142 (FIG. 27)>
[0126] This computing unit 142 computes the oxygen storage capacity
of the three-way catalyst 50. Specifically, as shown in FIG. 27, an
after-light-off performance deterioration index Ind.sub.13det0 is
obtained by referring to a map with (Phase2-Phase1) and
(Power2/Power1) being parameters. The map used in obtaining
Ind.sub.13det0 is preferably decided based on experiments from the
relationship between the oxygen storage capacity of the three-way
catalyst 50 and the exhaust performance. Also, in the state of
(Phase2-Phase1).gtoreq.(predetermined value A) and
(Power2/Power1).gtoreq.(predetermined value B), this is determined
as indicating that the oxygen storage capacity (catalyst
performance) has deteriorated to a limit, whereupon an
after-light-off performance deterioration flag Fdet0=1 is set. Note
that the predetermined value A and the predetermined value B
representing the deterioration limit are decided depending on the
target exhaust performance (diagnosis performance).
<Light-Off Temperature Estimating Unit 150 (FIG. 28)>
[0127] This computing unit 150 computes (estimates) the light-off
temperature of the three-way catalyst 50. Specifically, as shown in
FIG. 28, a (estimated) light-off temperature T0 is obtained, for
example, by using a map with the after-light-off performance
deterioration index Ind_det0 being a parameter. The map used in
obtaining T0 is preferably decided based on experiment results
shown in FIG. 17, by way of example, from the relationship between
a deterioration amount of the oxygen storage capacity after the
light-off and a change (rise) amount of the light-off temperature.
As an alternative, T0 may be estimated using, e.g., a catalyst
model. Also, in the state of T0.gtoreq.(predetermined value C) or
the after-light-off performance deterioration flag Fdet0=1, this is
determined as indicating that the three-way catalyst 50 has
exceeded its performance limit, whereupon a deterioration indicator
lamp illuminating flag Fdet=1 is set, for example, to illuminate a
deterioration indicator lamp 27 for providing an indication to the
exterior. Note that the predetermined value C representing the
deterioration limit (in light-off performance) of the three-way
catalyst 50 is decided depending on the target exhaust performance
(diagnosis performance).
[0128] As understood from the above description, with the
self-diagnosis system 10 of this embodiment, the target air/fuel
ratio is oscillated at the predetermined frequency, and the
after-light-off oxygen storage capacity (catalyst performance A) of
the three-way catalyst 50 is detected in accordance with the
predetermined frequency components of the output signals from the
A/F sensor 52 and the O.sub.2 sensor 51. The light-off temperature
(catalyst performance B) is then estimated based on the detection
result. Therefore, the light-off performance of the catalyst can be
diagnosed at a low cost and high accuracy without requiring
addition or improvement of a sensor, etc.
SECOND EMBODIMENT
[0129] FIG. 29 is a functional block diagram showing a control
system in a second embodiment. As shown in the functional block
diagram, a control unit 100 similar to that in the first embodiment
comprises a basic fuel injection amount computing unit 110, an
air/fuel ratio modification term computing unit 120 including a
target air/fuel ratio computing unit 221, a deterioration diagnosis
permission determining unit 130, (the units 110 and 130 being the
same as those in the first embodiment), a catalyst characteristic A
(after-light-off oxygen storage capacity) detecting unit 240, and a
catalyst characteristic B (light-off temperature) estimating unit
250.
[0130] In an ordinary mode, the control unit 100 computes a fuel
injection amount Ti per cylinder based on a basic fuel injection
amount Tp and an air/fuel ratio modification term Lalpha so that
air/fuel ratios of all the cylinders are held at the stoichiometric
air/fuel ratio. While that process is the same as that in the first
embodiment, this second embodiment differs in the following point.
When the deterioration diagnosis is permitted, the air/fuel ratio
is shifted from the stoichiometric air/fuel ratio by a
predetermined value for a predetermined time, and the
after-light-off oxygen storage capacity (catalyst performance A) of
the three-way catalyst 50 is detected in accordance with a response
delay time between respective output signals from the A/F sensor 52
and the O.sub.2 sensor 51. Then, based on the detection result, the
control unit 100 estimates the light-off temperature (catalyst
characteristic B).
[0131] The units 221, 240 and 250 executing processing in a
different manner from that in the first embodiment will be
described in more detail below.
<Target Air/Fuel Ratio Computing Unit 221 (step response) (FIG.
30)>
[0132] This computing unit 221 is substituted for the target
air/fuel ratio computing unit 121 (see FIG. 24) included in the
air/fuel ratio modification term computing unit 120 (see FIG. 23)
in the first embodiment. Specifically, the target air/fuel ratio
computing unit 221 executes the processing shown in FIG. 30. When
Fpdag=1 holds, the target air/fuel ratio is set to a diagnosis-mode
target air/fuel ratio Tabf1. Otherwise, an ordinary target air/fuel
ratio Tabf0 is set. More specifically, a response delay time occurs
from a time at which the output of the A/F sensor 52 has reached a
level corresponding to Tabf1 to a time at which the output of the
O.sub.2 sensor 51 has reached a level corresponding to Tabf1. This
response delay time depends on the oxygen storage (release)
performance of the three-way catalyst 50. In this embodiment, Tabf0
is a value corresponding to the stoichiometric air/fuel ratio, and
Tabf1 is a value shifted from the stoichiometric air/fuel ratio
toward the lean side by a predetermined value. The value of Tabf1
is preferably decided based on experiments from the viewpoints of
diagnosis accuracy and exhaust performance.
<After-Light-Off Oxygen Storage capacity Detecting Unit 240
(Step Response) (FIG. 31)>
[0133] This detecting unit 240 detects the oxygen storage capacity
after the light-off. Specifically, as shown in FIG. 31, this
detecting unit 240 comprises a response delay time computing unit
241 for computing the response delay time from an output Rabf of
the A/F sensor 52 to an output RVO2 of the O.sub.2 sensor 51, and
an oxygen storage capacity computing unit 242 for computing the
oxygen storage capacity of the three-way catalyst 50 based on the
computed response delay time.
[0134] The response delay time computing unit 241 and the oxygen
storage capacity computing unit 242 will be described in more
detail below.
<Response Delay Time Computing Unit 241 (FIG. 32)>
[0135] This computing unit 241 computes the response delay time
from the output Rabf of the A/F sensor 52 to the output RVO2 of the
O.sub.2 sensor 51. Specifically, as shown in FIG. 32, when Fpdag=1
holds and the target air/fuel ratio computing unit 221 sets the
diagnosis-mode target air/fuel ratio Tabf1, a response delay time
T_det is given as a period from a time at which
Rabf.gtoreq.Tabf1--K_Tabf1 is met to a time at which
RVO2.ltoreq.KRVO2 is met.
<Oxygen Storage capacity Computing Unit 242 (FIG. 33)>
[0136] This computing unit 242 computes the oxygen storage capacity
of the three-way catalyst 50. Specifically, as shown in FIG. 33, an
after-light-off performance deterioration index Ind_det0 is
obtained by referring to a map with the response delay time T_det
and the intake air amount Qa being parameters. The map used in
obtaining Ind_det0 is preferably decided based on experiments from
the relationship between the oxygen storage capacity of the
three-way catalyst 50 and the exhaust performance. Also, in the
state of Ind_det0.gtoreq.Ind_det_NG, this is determined as
indicating that the oxygen storage capacity (catalyst performance)
has deteriorated to a limit, whereupon an after-light-off
performance deterioration flag Fdet0=1 is set. Note that Ind_det_NG
representing the deterioration limit is decided depending on the
target exhaust performance (diagnosis performance).
<Light-Off Temperature Estimating Unit 250>
[0137] This estimating unit 250 is substantially the same as the
estimating unit 150 in the first embodiment, and therefore a
detailed description thereof is omitted here.
THIRD EMBODIMENT
[0138] FIG. 34 is a functional block diagram showing a control
system in a third embodiment. As shown in the functional block
diagram, a control unit 100 similar to that in the first and second
embodiments comprises a basic fuel injection amount computing unit
110, an air/fuel ratio modification term computing unit 120, a
deterioration diagnosis permission determining unit 130, (these
three units being the same as those in the first embodiment), a
catalyst characteristic A (after-light-off exhaust cleaning
capacity) detecting unit 340, and a catalyst characteristic B
(light-off temperature) estimating unit 350. In this third
embodiment, a NOx sensor 53 is disposed downstream of the three-way
catalyst 50 instead of the O.sub.2 sensor. An output signal from
the NOx sensor 53 is also supplied to the control unit 100.
[0139] In an ordinary mode, the control unit 100 computes a fuel
injection amount Ti per cylinder based on a basic fuel injection
amount Tp and an air/fuel ratio modification term Lalpha so that
air/fuel ratios of all the cylinders are held at the stoichiometric
air/fuel ratio. While that process is the same as that in the first
embodiment, this third embodiment differs in the following point.
When the deterioration diagnosis is permitted, the target air/fuel
ratio is oscillated at a predetermined frequency, and the
after-light-off exhaust cleaning capacity (catalyst performance A)
of the three-way catalyst 50 is detected in accordance with an
output signals of the NOx sensor 53 at that time. Then, based on
the detection result, the control unit 100 estimates the light-off
temperature (catalyst characteristic B).
[0140] The units 340 and 350 executing processing in a different
manner from that in the first and second embodiments will be
described in more detail below.
<After-Light-Off Exhaust Cleaning Capacity Detecting Unit 340
(FIG. 35)>
[0141] This detecting unit 340 detects the exhaust cleaning
capacity after the light-off. Specifically, the detection is
executed as shown in FIG. 35. An after-light-off performance
deterioration index Ind_det0 is obtained by referring to a map with
an output value RNOx of the NOx sensor 53 and an intake air amount
Qa being parameters. The map used in obtaining Ind_det0 is
preferably decided based on experiments from the NOx cleaning
capacity of the three-way catalyst 50. Also, in the state of
Ind_det0.gtoreq.Ind_det_NG, this is determined as indicating that
the exhaust cleaning capacity (catalyst performance) has
deteriorated to a limit, whereupon an after-light-off performance
deterioration flag Fdet0=1 is set. Note that Ind_det_NG
representing the deterioration limit is decided depending on the
target exhaust performance (diagnosis performance).
<Light-Off Temperature Estimating Unit 350 (FIG. 34)>
[0142] This estimating unit 350 is substantially the same as the
estimating units in the first and second embodiments, and therefore
a detailed description thereof is omitted here.
[0143] While this third embodiment employs the NOx sensor, similar
processing to that described above can also be executed by using,
for example, an HC sensor or a CO sensor.
FOURTH EMBODIMENT
[0144] FIG. 36 is a functional block diagram showing a control
system in a fourth embodiment. As shown in the functional block
diagram, a control unit 100 similar to that in the first through
third embodiments comprises a basic fuel injection amount computing
unit 110, an air/fuel ratio modification term computing unit 120, a
deterioration diagnosis permission determining unit 430, a catalyst
characteristic A (after-light-off oxygen storage capacity)
detecting unit 440, a catalyst characteristic B (light-off
temperature) estimating unit 450, and an ignition timing setting
unit 160 for, based on the estimated light-off temperature, setting
a retard amount of ignition timing at the startup and a period
during which the ignition timing is retarded. In this fourth
embodiment, the deterioration diagnosis permission determining unit
430 and the catalyst characteristic B (light-off temperature)
estimating unit 450 are constituted respectively as shown in FIGS.
37 and 38. The ignition timing setting unit 160, which is not
disposed in the above-described embodiments, is constituted as
follows.
<Ignition Timing Setting Unit 160 (FIG. 39)>
[0145] This setting unit 160 sets the ignition timing.
Specifically, the setting is executed as shown in FIG. 39. Basic
ignition timing ADVO is decided based on Tp (basic fuel injection
amount) and Ne (engine rotation speed). When the estimated catalyst
temperature does not reach the light-off temperature, i.e., in the
state of Tcat.ltoreq.T0, a value obtained by referring to a map
with the light-off temperature T0 being a parameter is set as a
retard amount ADVRTD of the ignition timing. Then, a value obtained
by subtracting the retard amount ADVRTD of the ignition timing from
the basic ignition timing ADVO is set as ignition timing ADV.
[0146] While the embodiments have been described above in
connection with the case using the three-way catalyst, the present
invention is not limited to the three-way catalyst so long as a
catalyst has the three-way performance, and the present invention
is also applicable to the cases using an HC adsorbing combustion
catalyst, a lean NOx catalyst, etc. In particular, the present
invention can be advantageously applied to the case using the HC
adsorbing combustion catalyst because the light-off temperature is
a very important factor in deciding the performance of that
catalyst.
* * * * *