U.S. patent application number 12/340152 was filed with the patent office on 2010-06-24 for abnormality detection device for reductant addition valve.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Satoru MAEDA, Hiroshi SAWADA, Daisuke SHIBATA.
Application Number | 20100154387 12/340152 |
Document ID | / |
Family ID | 42264086 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100154387 |
Kind Code |
A1 |
SHIBATA; Daisuke ; et
al. |
June 24, 2010 |
ABNORMALITY DETECTION DEVICE FOR REDUCTANT ADDITION VALVE
Abstract
An addition valve is instructed to add a reductant (step 122). A
cumulative specified addition amount is then determined (step 124).
An air-fuel ratio A/Fcal is estimated in accordance with the
operating status of an internal combustion engine (step 126). An
estimated air-fuel ratio A/Fcal and air-fuel ratio sensor output
A/Fs are used to determine a measured addition amount (.DELTA.t) at
the current moment (step 128). A cumulative measured addition
amount is then determined (step 130). The error between the
measured addition amount and specified addition amount are compared
against a reference value (step 134) to detect an abnormality in
the addition valve.
Inventors: |
SHIBATA; Daisuke;
(Numazu-shi, JP) ; SAWADA; Hiroshi; (Gotemba-shi,
JP) ; MAEDA; Satoru; (Kariya-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
42264086 |
Appl. No.: |
12/340152 |
Filed: |
December 19, 2008 |
Current U.S.
Class: |
60/285 |
Current CPC
Class: |
F01N 3/023 20130101;
F01N 3/0871 20130101; F01N 3/103 20130101; F01N 2560/14 20130101;
F01N 2900/1806 20130101; F01N 11/007 20130101; Y02T 10/12 20130101;
F01N 2560/025 20130101; Y02T 10/20 20130101; Y02T 10/47 20130101;
F01N 2550/05 20130101; Y02T 10/40 20130101; F02B 37/00 20130101;
F01N 3/035 20130101; F01N 2610/03 20130101; F01N 13/009
20140601 |
Class at
Publication: |
60/285 |
International
Class: |
F01N 9/00 20060101
F01N009/00 |
Claims
1. A reductant addition valve abnormality detection device for
detecting an abnormality in a reductant addition valve that adds a
reductant to upstream of a catalyst to recover the purification
capability of the catalyst, the reductant addition valve
abnormality detection device comprising: addition amount
designation means for designating the amount of reductant to be
added by said reductant addition valve; first air-fuel ratio
detection means for detecting a first air-fuel ratio, which is an
exhaust air-fuel ratio prevailing downstream of said reductant
addition valve; second air-fuel ratio acquisition means for
acquiring a second air-fuel ratio, which is an exhaust air-fuel
ratio of an internal combustion engine, during reductant addition
by said reductant addition valve; addition amount measurement means
for measuring the amount of reductant added by said reductant
addition valve in accordance with the second air-fuel ratio, which
is acquired by said second air-fuel ratio acquisition means, and
the first air-fuel ratio, which is detected by said first air-fuel
ratio detection means; and abnormality detection means for
detecting an abnormality in said reductant addition valve by
comparing an addition amount measured by said addition amount
measurement means against an addition amount designated by said
addition amount designation means.
2. The reductant addition valve abnormality detection device
according to claim 1, further comprising: difference calculation
means for calculating the difference between the first air-fuel
ratio detected by said first air-fuel ratio detection means, and
the second air-fuel ratio acquired by said second air-fuel ratio
acquisition means, before said reductant addition valve adds the
reductant; and correction means for correcting said first air-fuel
ratio or said second air-fuel ratio in accordance with the
difference calculated by said difference calculation means.
3. The reductant addition valve abnormality detection device
according to claim 1, wherein said second air-fuel ratio
acquisition means includes at least either second air-fuel ratio
estimation means, which estimates said second air-fuel ratio in
accordance with an operating state of said internal combustion
engine, or second air-fuel ratio detection means, which detects
said second air-fuel ratio prevailing upstream of said reductant
addition valve.
4. A reductant addition valve abnormality detection device for
detecting an abnormality in a reductant addition valve that adds a
reductant to upstream of a catalyst to recover the purification
capability of the catalyst, the reductant addition valve
abnormality detection device comprising: addition amount
designation device for designating the amount of reductant to be
added by said reductant addition valve; first air-fuel ratio
detection device for detecting a first air-fuel ratio, which is an
exhaust air-fuel ratio prevailing downstream of said reductant
addition valve; second air-fuel ratio acquisition device for
acquiring a second air-fuel ratio, which is an exhaust air-fuel
ratio of an internal combustion engine, during reductant addition
by said reductant addition valve; addition amount measurement
device for measuring the amount of reductant added by said
reductant addition valve in accordance with the second air-fuel
ratio, which is acquired by said second air-fuel ratio acquisition
device, and the first air-fuel ratio, which is detected by said
first air-fuel ratio detection device; and abnormality detection
device for detecting an abnormality in said reductant addition
valve by comparing an addition amount measured by said addition
amount measurement device against an addition amount designated by
said addition amount designation device.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an abnormality detection
device for a reductant addition valve that adds a reductant to an
exhaust path.
[0003] 2. Background Art
[0004] A known device disclosed, for instance, in Patent Document 1
estimates, in accordance with an air-fuel ratio sensor output, the
amount of reductant to be added from a reductant addition valve
(hereinafter may be abbreviated to the "addition valve") and
compares the estimated reductant addition amount against a
specified addition amount to judge whether the addition valve is
abnormal.
[0005] [Patent Document 1] JP-A-2005-54723
[0006] [Patent Document 1] JP-A-2002-38928
[0007] The reductant addition amount is estimated in accordance
with the difference between a reference value, which is an air-fuel
ratio detected before a rich spike, and the air-fuel ratio detected
during the rich spike. However, if the combustion air-fuel ratio
changes during the rich spike, a discrepancy arises between the
reference value and actual air-fuel ratio. When such a discrepancy
exists, the reductant addition amount cannot accurately be
estimated. It is therefore conceivable that an addition valve
abnormality may not accurately be detected. It means that
conventional methods achieve addition value abnormality detection
in a steady state only.
SUMMARY OF THE INVENTION
[0008] The present invention has been made in view of the above
circumstances. An object of the present invention is to provide a
reductant addition valve abnormality detection device that is
capable of accurately detecting an abnormality in a reductant
addition valve even when the combustion air-fuel ratio changes
during a rich spike.
[0009] According to one aspect of the present invention, a
reductant addition valve abnormality detection device comprises an
addition amount designation means, first air-fuel ratio detection
means, second air-fuel ratio acquisition means, addition amount
measurement means, and abnormality detection means.
[0010] The addition amount designation means designates the amount
of reductant to be added by the reductant addition valve that adds
a reductant to upstream of a catalyst to recover the purification
capability of the catalyst.
[0011] The first air-fuel ratio detection means detects a first
air-fuel ratio, which is an exhaust air-fuel ratio prevailing
downstream of the reductant addition valve.
[0012] The second air-fuel ratio acquisition means acquires a
second air-fuel ratio, which is an exhaust air-fuel ratio of an
internal combustion engine, during reductant addition by the
reductant addition valve.
[0013] The addition amount measurement means measures the amount of
reductant added by the reductant addition valve in accordance with
the second air-fuel ratio, which is acquired by the second air-fuel
ratio acquisition means, and the first air-fuel ratio, which is
detected by the first air-fuel ratio detection means.
[0014] The abnormality detection means detects an abnormality in
the reductant addition valve by comparing an addition amount
measured by the addition amount measurement means against an
addition amount designated by the addition amount designation
means.
[0015] According to another aspect of the present invention, the
reductant addition valve abnormality detection means further
comprises a difference calculation means, and correction means.
[0016] The difference calculation means calculates the difference
between the first air-fuel ratio detected by the first air-fuel
ratio detection means, and the second air-fuel ratio acquired by
the second air-fuel ratio acquisition means, before the reductant
addition valve adds the reductant.
[0017] The correction means corrects the first air-fuel ratio or
the second air-fuel ratio in accordance with the difference
calculated by the difference calculation means.
[0018] According to another aspect of the present invention, the
second air-fuel ratio acquisition means may include at least either
second air-fuel ratio estimation means, which estimates the second
air-fuel ratio in accordance with an operating state of the
internal combustion engine, or second air-fuel ratio detection
means, which detects the second air-fuel ratio prevailing upstream
of the reductant addition valve.
[0019] Other objects and further features of the present invention
will be apparent from the following detailed description when read
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a diagram illustrating the configuration of a
system according to a first embodiment of the present
invention;
[0021] FIG. 2 shows an example of a method for judging an
abnormality in the addition valve 44;
[0022] FIG. 3 shows how the output from the first air-fuel ratio
sensor 46 changes during a rich spike operation (this output is
hereinafter referred to as the "air-fuel ratio sensor output"
A/Fs);
[0023] FIG. 4 illustrates a method for measuring the amount of fuel
added from the addition valve 44;
[0024] FIG. 5 shows a discrepancy between the reference value
A/Fbase and actual exhaust air-fuel ratio A/Fact that arises when
the combustion air-fuel ratio varies during a rich spike
operation;
[0025] FIG. 6 shows the reference value A/Fbase for determining the
measured addition amount in accordance with the first
embodiment;
[0026] FIG. 7 shows how the first embodiment offset-corrects the
air-fuel ratio A/Fcal;
[0027] FIG. 8 is a flowchart illustrating a routine that the ECU 60
executes in accordance with the first embodiment;
[0028] FIG. 9 is a flowchart illustrating the addition valve
abnormality detection routine that the ECU 60 executes in
accordance with the first embodiment;
[0029] FIG. 10 is a flowchart illustrating an addition valve
abnormality detection routine that the ECU 60 executes in
accordance with a modification of the first embodiment;
[0030] FIG. 11 is a diagram illustrating the configuration of a
system according to the second embodiment of the present
invention;
[0031] FIG. 12 is a flowchart illustrating a routine that the ECU
60 executes in accordance with the second embodiment; and
[0032] FIG. 13 is a flowchart illustrating the addition valve
abnormality detection routine that the ECU 60 executes in
accordance with the second embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0033] Embodiments of the present invention will now be described
with reference to the accompanying drawings. Like elements in the
drawings are designated by the same reference numerals and will not
be redundantly described.
First Embodiment
[Description of System Configuration]
[0034] FIG. 1 is a diagram illustrating the configuration of a
system according to a first embodiment of the present invention.
The system shown in FIG. 1 includes an internal combustion engine
1, which is a four-cycle diesel engine (compression ignition
internal combustion engine). The diesel engine 1 is mounted in a
vehicle and used as its motive power source. Although the diesel
engine 1 shown in FIG. 1 is of an in-line four-cylinder type, the
present invention is not limited to the use of four cylinders and
in-line cylinder arrangement.
[0035] A piston for each cylinder 2 of the diesel engine 1 is
coupled to a crankshaft 4 via a crank mechanism. A crank angle
sensor 5 is installed near the crankshaft 4 to detect the rotation
angle (crank angle) of the crankshaft 4.
[0036] An injector 6, which directly injects fuel into a cylinder,
is installed in each cylinder 2 of the diesel engine 1. The
injector 6 for each cylinder is connected to a common rail 7. The
fuel in a fuel tank (not shown) is pressurized to a predetermined
fuel pressure by a supply pump 8. The pressurized fuel is stored in
the common rail 7 and supplied from the common rail 7 to each
injector 6. The injector 6 can inject fuel into the cylinder
multiple times per cycle with arbitrary timing.
[0037] An intake port 10 of the diesel engine 1 is provided with an
intake valve 12. The valve opening characteristics (valve opening
timing, lift amount, and operating angle) of the intake valve 12
can be changed by a publicly known variable valve train (not
shown).
[0038] The intake port 10 is connected to an intake path 18 through
an intake manifold 16. An intake throttle valve 20 is installed in
the middle of the intake path 18. The intake throttle valve 20 is
an electronically-controlled valve whose opening is determined in
accordance with an accelerator opening AA detected by an
accelerator opening sensor 21. An inter-cooler 22 is installed
upstream of the intake throttle valve 20. A compressor 24a for a
turbocharger 24 is installed upstream of the inter-cooler 22. A
coupling shaft is used to couple the compressor 24a to a turbine
24b in an exhaust path 38.
[0039] An air flow meter 26 is installed upstream of the compressor
24a to detect an intake air amount Ga. An air cleaner 28 is
installed upstream of the air flow meter 26.
[0040] The employed configuration, which has been described above,
uses the inter-cooler 22 to cool intake air that is compressed by
the compressor 24a of the turbocharger 24. The intake air passing
through the inter-cooler 22 is distributed to the intake port 10 of
each cylinder by the intake manifold 16.
[0041] An exhaust port 30 of the diesel engine 1 is provided with
an exhaust valve 32. The valve opening characteristics (valve
opening timing, lift amount, and operating angle) of the exhaust
valve 32 can be changed by a publicly known variable valve train
(not shown).
[0042] The exhaust port 30 is connected to the exhaust path 38
through an exhaust manifold 36. The turbine 24b for the
turbocharger 24 is installed in the exhaust path 38. An oxidation
catalyst 40, which is a pretreatment catalyst, is installed
downstream of the turbine 24b. The oxidation catalyst 40 is capable
of oxidizing HC and CO.
[0043] A NOx catalyst 42 is installed downstream of the oxidation
catalyst 40. In an atmosphere where the air-fuel ratio is greater
than the stoichiometric air-fuel ratio, that is, in an atmosphere
leaner than the stoichiometric air-fuel ratio, the NOx catalyst 42
is capable of occluding NOx in an exhaust gas. In a rich atmosphere
where the air-fuel ratio is not greater than the stoichiometric
air-fuel ratio, the NOx catalyst 42 is capable of reducing and
purifying occluded NOx and releasing it.
[0044] The NOx catalyst 42 may be either a catalyst capable of
merely occluding and reducing NOx or a DPNR (Diesel Particulate-NOx
Reduction system) or other similar catalyst capable of occluding
and reducing NOx and collecting soot in the exhaust gas. The NOx
catalyst 42 may also be a catalyst capable of occluding and
reducing NOx and having a function other than the soot collection
function. The oxidation catalyst 40 and NOx catalyst 42 may be
housed in a single container.
[0045] An exhaust fuel addition valve (hereinafter abbreviated to
the "addition valve") 44 is installed between the turbine 24b and
oxidation catalyst 40 to add fuel to the exhaust gas. The added gas
serves as a reductant. The addition valve 44 communicates with the
supply pump 8 through a fuel supply pipe (not shown).
[0046] A first air-fuel ratio sensor 46 is installed between the
oxidation catalyst 40 and NOx catalyst 42. A second air-fuel ratio
sensor 48 is installed downstream of the NOx catalyst 42. These
air-fuel ratio sensors 46, 48 are configured to detect exhaust
air-fuel ratios prevailing at their positions, respectively.
[0047] One end of an external EGR path 52 is connected to a section
near the intake manifold 16 in the intake path 18. The other end of
the external EGR path 52 is connected to a section near the exhaust
manifold 36 in the exhaust path 38. The system uses the external
EGR path 52 to provide external EGR (Exhaust Gas Recirculation).
More specifically, the system can flow part of the exhaust gas
(burned gas) back to the intake path 18 through the external EGR
path 52.
[0048] An EGR cooler 54 is installed in the middle of the external
EGR path 52 to cool an external EGR gas. An EGR valve 56 is
installed downstream of the EGR cooler 54 in the external EGR path
52. The amount of exhaust gas flowing in the external EGR path 52
(that is, the external EGR amount or external EGR rate) increases
with an increase in the opening of the EGR valve 56.
[0049] The system according to the first embodiment also includes
an ECU (Electronic Control Unit) 60, which serves as a controller.
The output end of the ECU 60 is connected, for instance, to the
injector 6, supply pump 8, intake throttle valve 20, addition valve
44, and EGR valve 56. The input end of the ECU 60 is connected, for
instance, to the crank angle sensor 5, accelerator opening sensor
21, air flow meter 26, first air-fuel ratio sensor 46, and second
air-fuel ratio sensor 48.
[0050] The ECU 60 calculates an engine speed NE in accordance with
an output from the crank angle sensor 5. The ECU 60 also calculates
an engine load KL in accordance, for instance, with the accelerator
opening AA. The ECU 60 calculates the amount of fuel injection from
the injector 6 (in-cylinder fuel injection amount) Q in accordance
with the engine load KL. In accordance with signals from various
sensors and with a predetermined program, the ECU 60 activates
various actuators to control the operating status of the diesel
engine 1.
Features of First Embodiment
[0051] When the amount of NOx occluded by the NOx catalyst 42 in
the system exceeds a predetermined value, a so-called rich spike
operation is performed to reduce and release NOx. More
specifically, the addition valve 44 adds fuel that serves as a
reductant. The added reductant performs a purification capability
recovery process (regeneration process) on the NOx catalyst 42.
[0052] Meanwhile, it may be demanded that an abnormality in
addition amount (injection amount) control over the addition valve
44 be accurately detected.
[0053] FIG. 2 shows an example of a method for judging an
abnormality in the addition valve 44. In FIG. 2, the horizontal
axis represents a specified addition amount, which is indicated
from the ECU 60 to the addition valve 44, whereas the vertical axis
represents a measured addition amount, which is measured
(estimated) by a method described later.
[0054] As shown in FIG. 2, an abnormality in the addition valve 44
can be detected by comparing the measured addition amount against
the specified addition amount. If the ratio R of the measured
addition amount to the specified addition amount is 1, that is, if
the specified amount of reductant is added by the addition valve
44, it goes without saying that the addition valve 44 is normal.
However, it is necessary to consider variations and aging of the
addition valve 44. Thus, the addition valve 44 can be judged to be
normal when the ratio R is within a reference range shown in FIG.
2, and abnormal (defective) when the ratio R is outside the
reference range. More specifically, if the specified addition
amount is equal to a predetermined amount A and the error (absolute
value) between the specified addition amount A and measured
addition amount is not greater than a reference value Dth, the
addition valve 44 can be judged to be normal; however, if the error
is greater than the reference value Dth, the addition valve 44 can
be judged to be abnormal (defective). The reference range or
reference value Dth can be predefined for each vehicle type.
[0055] FIG. 3 shows how the output from the first air-fuel ratio
sensor 46 changes during a rich spike operation (this output is
hereinafter referred to as the "air-fuel ratio sensor output"
A/Fs).
[0056] While no rich spike operation is performed, that is, no fuel
is added from the addition valve 44, the air-fuel ratio sensor
output A/Fs looks like an output A/F_A indicated by a one-dot chain
line in FIG. 3. During rich spike time t, on the other hand, the
addition valve 44 adds fuel; therefore, the air-fuel ratio sensor
output A/Fs changes to an output A/F_B indicated by a solid line in
FIG. 3.
[0057] Although details will be given later, the amount of fuel
added from the addition valve 44 can be measured (estimated) in
accordance with the difference between a reference value A/Fbase,
which is the air-fuel ratio sensor output A/F_A generated while no
rich spike operation is performed, and the air-fuel ratio sensor
output A/F_B generated while a rich spike operation is performed.
In other words, the aforementioned measured addition amount can be
determined in accordance with the air-fuel ratio sensor outputs
A/Fs (A/F_A, A/F_B).
[0058] FIG. 4 illustrates a method for measuring the amount of fuel
added from the addition valve 44. In FIG. 4, the symbol "A/Fs"
denotes an air-fuel ratio sensor output. The symbol "A/Fs (t0)"
denotes an air-fuel ratio sensor output that is generated while no
rich spike operation is performed, or more specifically, at time
t0, which is immediately before the start of a rich spike
operation.
[0059] The air-fuel ratio sensor output A/Fs (t0) at time t0 can be
expressed by Equation (1) below. In Equation (1), "Ga" is an intake
air amount and "Q" is an in-cylinder fuel injection amount.
A/Fs(t0)=Ga/Q (1)
[0060] Equation (2) below is obtained by modifying Equation (1)
above.
Q=Ga/(A/F(t0)) (2)
[0061] The air-fuel ratio sensor output A/Fs generated during a
rich spike operation can be expressed by Equation (3) below. In
Equation (3), "Qex" is the amount of fuel addition from the
addition valve 44.
A/Fs=Ga/(Q+Qex) (3)
[0062] Equation (4) below is obtained by modifying Equation (3)
above.
Q+Qex=Ga/(A/Fs) (4)
[0063] Equation (5) below is obtained by subtracting Equation (2)
from Equation (4). Further, Equation (6) below is obtained by
modifying Equation (5).
Qex = Ga .times. { 1 / ( A / Fs ) - 1 / ( A / Fs ( t 0 ) ) } ( 5 )
= Ga .times. { ( A / Fs ( t 0 ) ) - ( A / Fs ) } / ( A / Fs ( t 0 )
/ ( A / Fs ) ( 6 ) ##EQU00001##
[0064] The air-fuel ratio sensor output A/Fs (t0) in Equation (6)
above can be acquired at time t0, which is immediately before the
start of a rich spike operation. Therefore, when the intake air
amount Ga and air-fuel ratio sensor output A/Fs are known, the
amount of fuel addition at a certain point of time during a rich
spike operation can be calculated from Equation (6). The amount of
fuel added from the addition valve 44 during a rich spike operation
can be measured by adding up the amounts of fuel addition during
the rich spike time t shown in FIG. 4. In other words, the measured
addition amount is obtained.
[0065] The above method uses the air-fuel ratio sensor output A/Fs
(t0) generated immediately before the start of a rich spike
operation as the reference value A/Fbase and determines the
measured addition amount in accordance with the difference between
the reference value A/Fbase and air-fuel ratio sensor output A/Fs
(see FIGS. 3 and 4).
[0066] However, the combustion air-fuel ratio may vary during a
rich spike operation (due, for instance, to a transient state) as
shown in FIG. 5. If, in such an instance, the air-fuel ratio sensor
output A/Fs (t0) generated immediately before the start of a rich
spike operation is used as the reference value A/Fbase as mentioned
above, a discrepancy arises between the reference value A/Fbase and
actual exhaust air-fuel ratio A/Fact (the air-fuel ratio prevailing
upstream of the addition valve 44). FIG. 5 shows a discrepancy
between the reference value A/Fbase and actual exhaust air-fuel
ratio A/Fact that arises when the combustion air-fuel ratio varies
during a rich spike operation. In this instance, the accuracy of
calculating the measured addition amount decreases because an
inaccurate reference value A/Fbase is used to determine the
measured addition amount.
[0067] As such being the case, the first embodiment estimates the
exhaust air-fuel ratio A/Fcal in accordance with the operating
status (Ga, Ne, and Q) of the internal combustion engine 1 that
prevails during a rich spike operation. In the case, for instance,
of the in-line four-cylinder diesel engine shown in FIG. 1, which
injects fuel two times per revolution, the above-mentioned exhaust
air-fuel ratio A/Fcal can be estimated from Equation (7) below when
the density [g/cm.sup.3] of light oil is 0.833. "q" is a quantity
of each fuel injection that relates to Q here.
A/Fcal=Ga/{(Ne/60).times.2.times.q.times.0.833} (7)
[0068] FIG. 6 shows the reference value A/Fbase for determining the
measured addition amount in accordance with the first
embodiment.
[0069] As shown in FIG. 6, the first embodiment uses the exhaust
air-fuel ratio A/Fcal estimated from Equation (7) as the reference
value A/Fbase. More specifically, the above estimated exhaust
air-fuel ratio A/Fcal is used instead of the air-fuel ratio sensor
output A/Fs (t0) in Equation (6) to calculate the fuel addition
amount Qex. The exhaust air-fuel ratio A/Fcal follows changes in
the combustion air-fuel ratio. Therefore, the reference value
A/Fbase for determining the measured addition amount can follow
combustion air-fuel ratio changes during a rich spike operation.
Consequently, the measured addition amount can be accurately
determined even when the combustion air-fuel ratio changes during a
rich spike operation as if a transient state prevails.
[0070] Further, the air flow meter 26, the injector 6, and the
first air-fuel ratio sensor 46 vary respectively. Therefore, even
when these elements operate normally, the above estimated exhaust
air-fuel ratio A/Fcal may disagree with the air-fuel ratio sensor
output A/Fs as indicated in FIG. 7. In such an instance, the
measured addition amount cannot accurately be determined
either.
[0071] As such being the case, the first embodiment determines the
difference .DELTA.A/F between the exhaust air-fuel ratio A/Fcal and
exhaust air-fuel ratio A/Fs before a rich spike operation as shown
in FIG. 7. Then, during the rich spike operation, the first
embodiment offset-corrects the exhaust air-fuel ratio A/Fcal by the
amount of the difference .DELTA.A/F. FIG. 7 shows how the first
embodiment offset-corrects the air-fuel ratio A/Fcal. The offset
correction shown in FIG. 7 can absorb the influence of variations
in the air flow meter 26, injector 6, and first air-fuel ratio
sensor 46. Since this makes it possible to eliminate the difference
between the air-fuel ratio A/Fcal and air-fuel ratio sensor output
A/Fs, which exists when no reductant is added, the measured
addition amount can be accurately determined.
Details of Process Performed by First Embodiment
[0072] FIG. 8 is a flowchart illustrating a routine that the ECU 60
executes in accordance with the first embodiment. The routine shown
in FIG. 8 is started at predetermined time intervals.
[0073] First of all, the routine shown in FIG. 8 performs step 100
to judge whether an addition valve abnormality detection request
flag is ON. The addition valve abnormality detection request flag
turns ON when the vehicle has traveled over a predetermined
distance or for a predetermined period of time after last
abnormality detection or when a predetermined value is exceeded by
an addition amount specified for the addition valve 44 after last
abnormality detection.
[0074] If the judgment result obtained in step 100 indicates that
the addition valve abnormality detection request flag is ON, step
102 is performed to judge whether an offset calculation completion
flag is ON. The offset calculation completion flag turns ON when
the difference (offset) between the air-fuel ratio sensor output
A/Fs and estimated air-fuel ratio A/Fcal is completely calculated
before addition valve abnormality detection.
[0075] If the judgment result obtained in step 102 indicates that
the offset calculation completion flag is OFF, the flow proceeds to
step 104. In step 104, the intake air amount Ga, in-cylinder fuel
injection amount Q, and engine speed Ne are used to calculate the
air-fuel ratio A/Fcal from Equation (7). In other words, step 104
is performed to estimate the exhaust air-fuel ratio A/Fcal of the
internal combustion engine 1 in accordance with the operating
status (Ga, Q, and Ne) of the internal combustion engine 1.
[0076] Subsequently, step 106 is performed so that a numerical
value obtained by subtracting the air-fuel ratio sensor output A/Fs
(the air-fuel ratio detected by the air-fuel ratio sensor 46) from
the air-fuel ratio A/Fcal estimated in step 104 is set as the
air-fuel ratio difference (offset) .DELTA.A/F. More specifically,
the difference .DELTA.A/F between the estimated air-fuel ratio
A/Fcal and air-fuel ratio sensor output A/Fs is determined. This
difference .DELTA.A/F is used to offset-correct the estimated
air-fuel ratio A/Fcal in step 126, which will be described later
with reference to FIG. 9.
[0077] Next, step 108 is performed to turn ON the offset
calculation completion flag. Subsequently, step 110 is performed to
set the specified addition amount to zero (0). Step 112 is then
performed to set the measured addition amount to zero (0). In other
words, steps 110 and 112 are performed to reset the specified
addition amount and measured addition amount.
[0078] Upon completion of step 112, the routine temporarily
terminates. When the routine is restarted later, step 100 is
performed. If the judgment result obtained in step 100 indicates
that the addition valve abnormality detection request flag is OFF,
that is, the addition valve 44 is not to be checked for an
abnormality, step 114 is performed to turn OFF the offset
calculation completion flag.
[0079] If, on the other hand, the judgment result obtained in step
100 indicates that the addition valve abnormality detection request
flag is ON, step 102 is performed. The offset calculation
completion flag was turned ON in step 108 of the last-executed
routine. Therefore, the query in step 102 is answered "Yes." This
starts an addition valve abnormality detection routine shown in
FIG. 9. FIG. 9 is a flowchart illustrating the addition valve
abnormality detection routine that the ECU 60 executes in
accordance with the first embodiment.
[0080] First of all, the routine shown in FIG. 9 performs step 120
to judge whether the specified addition amount is not smaller than
a predetermined value. The predetermined value denotes a fuel
amount that permits addition valve abnormality detection, that is,
a specified addition amount that permits accurate comparison
between the specified addition amount and measured addition amount.
An appropriate value can be predetermined for each vehicle type. If
the judgment result obtained in step 120 indicates that the
specified addition amount is smaller than the predetermined value,
step 122 is performed to instruct the addition valve 44 to add fuel
that serves as a reductant. Subsequently, step 124 is performed so
that a numerical value obtained by adding the currently specified
addition amount, which is specified in step 122, to the previously
specified addition amount is set as the specified addition amount.
In step 124, the specified addition amounts obtained after a reset
in step 110 are added up.
[0081] Next, step 126 is performed to estimate the air-fuel ratio
A/Fcal, which serves as the reference value A/Fbase (see FIGS. 6
and 7), in accordance with the operating status (Ga, Q, and Ne) of
the internal combustion engine 1. In step 126, the intake air
amount Ga, in-cylinder fuel injection amount Q, and engine speed Ne
are used to calculate the air-fuel ratio A/Fcal from Equation (7).
Further, in step 126, a numerical value obtained by subtracting the
offset .DELTA.A/F calculated in step 106 (FIG. 8) from the exhaust
air-fuel ratio A/Fcal of the internal combustion engine 1, which is
calculated from Equation (7), is set as the air-fuel ratio A/Fcal.
In other words, the estimated air-fuel ratio A/Fcal is
offset-corrected.
[0082] Next, step 128 is performed to calculate the measured
addition amount (.DELTA.t). The measured addition amount (.DELTA.t)
is a measured addition amount at the current moment .DELTA.t. In
step 128, a numerical value obtained by subtracting a numerical
value (Ga/A/Fcal), which is obtained by dividing the intake air
amount Ga by the air-fuel ratio A/Fcal offset-corrected in step
126, from a numerical value (Ga/A/Fs), which is obtained by
dividing the intake air amount Ga by the air-fuel ratio sensor
output A/Fs, is set as the measured addition amount (.DELTA.t).
[0083] Next, step 130 is performed so that a numerical value
obtained by adding the measured addition amount (.DELTA.t), which
is calculated in step 128, to the previously determined measured
addition amount is set as the measured addition amount. In step
130, the measured addition amounts obtained after a reset in step
112 are added up. Upon completion of step 130, the routine
temporarily terminates.
[0084] When the routine is started again, the specified addition
amounts and measured addition amounts are added up by sequentially
performing steps 122 to 130 until the cumulative specified addition
amount reaches the predetermined value.
[0085] Meanwhile, when a supplied fuel amount is not smaller than a
predetermined value, the query in step 120 is answered "Yes." Next,
step 132 is performed to determine an estimated error by
subtracting the specified addition amount from the measured
addition amount. Step 134 is then performed to judge whether the
estimated error determined in step 132 is greater than a reference
value. The reference value represents a permissible estimated error
for judging that the addition valve 44 is normal. This reference
value is an abnormality judgment value for the addition valve 44.
The reference value Dth shown in FIG. 2 is an example of this
reference value.
[0086] If the judgment result obtained in step 134 indicates that
the estimated error is greater than the reference value, it is
concluded that the addition valve 44 is abnormal (defective). In
this instance, step 136 is performed to turn ON an addition valve
abnormality flag. If, on the other hand, the judgment result
obtained in step 134 does not indicate that the estimated error is
greater than the reference value, it is concluded that the addition
valve 44 is normal. In this instance, step 138 is performed to turn
OFF the addition valve abnormality flag. Upon completion of step
136 or 138, step 140 is performed to turn OFF the addition valve
abnormality detection request flag.
[0087] As described above, the routine shown in FIGS. 8 and 9
determines the measured addition amount in accordance with the
air-fuel ratio A/Fcal estimated from the operating status (Ga, Q,
and Ne) of the internal combustion engine 1 during a rich spike
operation and with the air-fuel ratio sensor output A/Fs instead of
the air-fuel ratio sensor output A/Fs (t0) generated immediately
before the rich spike operation (at time t0). The air-fuel ratio
A/Fcal can follow combustion air-fuel ratio changes in the internal
combustion engine 1 during a rich spike operation. Therefore, the
measured addition amount can be accurately determined even when the
combustion air-fuel ratio changes during a rich spike operation
due, for instance, to a transient state. Consequently, an
abnormality in the addition valve 44 can be accurately detected
even when the combustion air-fuel ratio changes.
[0088] Further, an abnormality detection sequence can be performed
with increased frequency because abnormality detection can be
achieved even when the combustion air-fuel ratio changes.
Consequently, injection amount control over the addition valve 44
can be frequently monitored.
[0089] Furthermore, the routine calculates the difference
.DELTA.A/F between the estimated air-fuel ratio A/Fcal and air-fuel
ratio sensor output A/Fs before a rich spike operation. During the
rich spike operation, the routine offset-corrects the air-fuel
ratio A/Fcal by the amount of the calculated difference .DELTA.A/F.
This eliminates the air-fuel ratio difference .DELTA.A/F that
exists when no rich spike operation is performed. As a result, the
measured addition amount can be calculated with increased
accuracy.
[0090] Although it is assumed that the first embodiment
offset-corrects the estimated air-fuel ratio A/Fcal, an alternative
would be to offset-correct the air-fuel ratio sensor output A/Fs by
the amount of the difference .DELTA.A/F. FIG. 10 is a flowchart
illustrating an addition valve abnormality detection routine that
the ECU 60 executes in accordance with a modification of the first
embodiment. The routine shown in FIG. 10 performs step 127 instead
of step 126 of the routine shown in FIG. 9. In step 127, the
air-fuel ratio sensor output A/Fs is offset-corrected by the amount
of the air-fuel ratio difference .DELTA.A/F calculated in step 106
in FIG. 8. This modified embodiment can provide the same advantages
as the first embodiment because the former can eliminate the
air-fuel ratio difference .DELTA.A/F that exists when no rich spike
operation is performed.
[0091] It is also assumed that the first embodiment uses the output
A/Fs of the first air-fuel ratio sensor 46 to determine the
measured addition amount. Alternatively, however, the output of the
second air-fuel ratio sensor 48 may be used to determine the
measured addition amount. It should be noted, however, that the use
of the output of the first air-fuel ratio sensor 46 determines the
measured addition amount with higher accuracy than the use of the
output of the second air-fuel ratio sensor 48.
[0092] Further, the first embodiment assumes that the air-fuel
ratio remains unchanged before and after the oxidation catalyst 40,
and uses the air-fuel ratio sensor output A/Fs without correcting
it. Alternatively, however, a publicly known catalyst model may be
used to correct the air-fuel ratio sensor output A/Fs.
[0093] In the first embodiment, the addition valve 44 is positioned
between the turbine 24b and oxidation catalyst 40. Alternatively,
however, the addition valve 44 may be positioned upstream of the
turbine 24b (e.g., in the exhaust port 30 or exhaust manifold 36).
The use of this alternative also provides the same advantages as
the first embodiment.
[0094] Furthermore, the first embodiment checks for an abnormality
in the addition valve 44 by comparing the estimated error against
the reference value. However, an alternative would be to check for
such an abnormality by comparing the ratio R of the measured
addition amount to the specified addition amount against a
reference value.
[0095] In the first embodiment, the NOx catalyst 42 corresponds to
the "catalyst" according to the first aspect of the present
invention; the addition valve 44 corresponds to the "reductant
addition valve" according to the first aspect of the present
invention; and the first air-fuel ratio sensor 46 corresponds to
the "first air-fuel ratio detection device" according to the first
aspect of the present invention. Further, in the first embodiment,
the "addition amount designation device" according to the first
aspect of the present invention is implemented when the ECU 60
performs step 122; the "second air-fuel ratio acquisition device"
according to the first aspect of the present invention and the
"second air-fuel ratio estimation device" according to the third
aspect of the present invention are implemented when the ECU 60
performs step 126; the "addition amount measurement device"
according to the first aspect of the present invention is
implemented when the ECU 60 performs step 128; and the "abnormality
detection device" according to the first aspect of the present
invention is implemented when the ECU 60 performs steps 132, 134,
136, and 138. In the first embodiment or its modification, the
"difference calculation device" according to the second aspect of
the present invention is implemented when the ECU 60 performs step
106; and the "correction device" according to the second aspect of
the present invention is implemented when the ECU 60 performs step
126 or 127.
Second Embodiment
[0096] A second embodiment of the present invention will now be
described with reference to FIG. 11.
[0097] FIG. 11 is a diagram illustrating the configuration of a
system according to the second embodiment of the present invention.
The system shown in FIG. 11 differs from the system shown in FIG. 1
in that the former additional includes an air-fuel ratio sensor 45,
which is positioned upstream of the addition valve 44. This
air-fuel ratio sensor 45 can detect the exhaust air-fuel ratio of
the internal combustion engine 1 even while fuel is being added by
the addition valve 44. The other elements of the system shown in
FIG. 11 are the same as the counterparts of the system shown in
FIG. 1 and will not be redundantly described.
Features of Second Embodiment
[0098] As indicated in FIG. 4, the output A/Fs generated from the
air-fuel ratio sensor 46 during a rich spike operation differs from
the exhaust air-fuel ratio of the internal combustion engine 1. The
reason is that the air-fuel ratio sensor 46 is positioned
downstream of the addition valve 44. During a rich spike operation,
therefore, the method shown in FIG. 4 uses the air-fuel ratio
sensor output A/Fs (t0) generated immediately before the rich spike
operation as the reference value A/Fbase for determining the
measured addition amount.
[0099] However, the reference value A/Fbase cannot follow
combustion air-fuel ratio changes during a rich spike operation as
described in conjunction with the first embodiment. As such being
the case, the first embodiment uses the air-fuel ratio A/Fcal
estimated in accordance with the operating status (Ga, Q, and Ne)
of the internal combustion engine 1 as the reference value A/Fbase
for determining the measured addition amount. In other words, the
first embodiment determines the measured addition amount in
accordance with the difference between the air-fuel ratio A/Fcal
and air-fuel ratio sensor output A/Fs.
[0100] Meanwhile, the system according to the second embodiment,
which is shown in FIG. 11, includes the air-fuel ratio sensor 45
that is positioned upstream of the addition valve 44. Therefore,
the air-fuel ratio sensor 45 can be used to detect the exhaust
air-fuel ratio of the internal combustion engine 1 even while fuel
is being added from the addition valve 44. In other words, the
output A/Fsu generated from the air-fuel ratio sensor 45 can follow
combustion air-fuel ratio changes during a rich spike
operation.
[0101] As such being the case, the second embodiment uses the
air-fuel ratio sensor output A/Fsu as the reference value A/Fbase
for determining the measured addition amount. More specifically,
the measured addition amount is determined in accordance with the
difference between the air-fuel ratio sensor output A/Fsu and
air-fuel ratio sensor output A/Fs. Consequently, the measured
addition amount can be accurately determined even when the
combustion air-fuel ratio changes during a rich spike operation as
if a transient state prevails.
[0102] Further, the air-fuel ratio sensor 45 and air-fuel ratio
sensor 46 vary respectively. Therefore, even when both of these two
air-fuel ratio sensors 45, 46 operate normally, the air-fuel sensor
output A/Fsu and air-fuel ratio sensor output A/Fs may not agree
with each other while no rich spike operation is being
performed.
[0103] Under the above circumstances, the second embodiment
determines the difference .DELTA.A/Fs between the above two
air-fuel ratio sensor outputs A/Fsu, A/Fs before a rich spike
operation. In addition, the second embodiment offset-corrects
either of the above two air-fuel ratio sensor outputs by the amount
of the difference .DELTA.A/Fs. This offset correction absorbs the
influence of variations in the air-fuel ratio sensors 45, 46.
Consequently, the difference .DELTA.A/Fs between the two air-fuel
ratio sensor outputs A/Fsu, A/Fs, which exists when no reductant is
added, can be eliminated. As a result, the measured addition amount
can be accurately determined.
Details of Process Performed by Second Embodiment
[0104] FIG. 12 is a flowchart illustrating a routine that the ECU
60 executes in accordance with the second embodiment. The routine
shown in FIG. 12 is started at predetermined time intervals. The
routine shown in FIG. 12 performs step 142 instead of steps 104 and
106 of the routine shown in FIG. 8. The process performed in step
142 will be mainly described below.
[0105] If the judgment result obtained in step 102 does not
indicate that the offset calculation completion flag is ON, the
routine shown in FIG. 12 proceeds to step 142. In step 142, a
numerical value obtained by subtracting the output A/Fs of the
air-fuel ratio sensor 46 from the output A/Fsu of the air-fuel
ratio sensor 45 is set as the air-fuel ratio difference (offset)
.DELTA.A/Fs. The difference .DELTA.A/Fs is used to offset-correct
the air-fuel ratio sensor output A/Fsu in step 144, which will be
described later with reference to FIG. 13. After completion of step
142, step 108 is performed to turn ON the offset calculation
completion flag as is the case with the routine shown in FIG.
8.
[0106] If, on the other hand, the judgment result obtained in step
102 indicates that the offset calculation completion flag is ON, an
addition valve abnormality detection routine shown in FIG. 13 is
started. FIG. 13 is a flowchart illustrating the addition valve
abnormality detection routine that the ECU 60 executes in
accordance with the second embodiment. The routine shown in FIG. 13
performs steps 144, 146, and 148 instead of steps 126, 128, and 130
of the routine shown in FIG. 9. The process performed in steps 144,
146, and 148 will be mainly described below.
[0107] After the specified addition amounts are added up in step
124, the routine shown in FIG. 13 proceeds to step 144. In step
144, a numerical value obtained by subtracting the offset
.DELTA.A/Fs calculated in step 142 (FIG. 12) from the air-fuel
ratio sensor output A/Fsu is set as the air-fuel ratio sensor
output A/Fsu. In other words, the air-fuel ratio sensor output
A/Fsu is offset-corrected.
[0108] Subsequently, step 146 is performed to calculate the
measured addition amount (.DELTA.t). The measured addition amount
(.DELTA.t) is a measured addition amount at the current moment
.DELTA.t. In step 146, a numerical value obtained by subtracting a
numerical value (Ga/A/Fs), which is obtained by dividing the intake
air amount Ga by the air-fuel ratio sensor output A/Fs, from a
numerical value (Ga/A/Fsu), which is obtained by dividing the
intake air amount Ga by the air-fuel ratio sensor output A/Fsu, is
set as the measured addition amount (.DELTA.t).
[0109] Next, step 148 is performed so that a numerical value
obtained by adding the measured addition amount (.DELTA.t), which
is calculated in step 146, to the previously determined measured
addition amount is set as the measured addition amount. In step
148, the measured addition amounts obtained after a reset in step
112 (FIG. 12) are added up. Upon completion of step 148, the
routine temporarily terminates.
[0110] When the routine is started again, the specified addition
amounts and measured addition amounts are added up by sequentially
performing steps 122, 124, and 144 to 148 until the cumulative
specified addition amount reaches the predetermined value.
[0111] However, when the specified addition amount is not smaller
than the predetermined value, the query in step 120 is answered
"Yes" as is the case with the routine shown in FIG. 9.
Subsequently, steps 132 to 140 are performed as is the case with
the routine shown in FIG. 9.
[0112] As described above, the routine shown in FIGS. 12 and 13
determines the measured addition amount in accordance with the
air-fuel ratio sensor output A/Fsu and air-fuel ratio sensor output
A/Fs generated during a rich spike operation instead of the
air-fuel ratio sensor output A/Fs (t0) generated immediately before
the rich spike operation (at time t0). This air-fuel ratio sensor
output A/Fsu can follow combustion air-fuel ratio changes of the
internal combustion engine 1 during a rich spike operation.
Therefore, the measured addition amount can be accurately
determined even when the combustion air-fuel ratio changes during a
rich spike operation as if a transient state prevails.
Consequently, an abnormality in the addition valve 44 can be
accurately detected even when the combustion air-fuel ratio
changes.
[0113] Further, the routine calculates the difference .DELTA.A/Fs
between the air-fuel ratio sensor output A/Fsu and air-fuel ratio
sensor output A/Fs before a rich spike operation. In addition, the
routine offset-corrects the air-fuel ratio sensor output A/Fsu by
the amount of the calculated difference .DELTA.A/Fs during the rich
spike operation. This eliminates the air-fuel ratio sensor output
difference .DELTA.A/Fs that exists when no rich spike operation is
performed. As a result, the measured addition amount can be
calculated with increased accuracy.
[0114] It is assumed that the second embodiment offset-corrects the
air-fuel ratio sensor output A/Fsu by the amount of the difference
.DELTA.A/Fs. Alternatively, however, the air-fuel ratio sensor
output A/Fs may be offset-corrected by the amount of the difference
.DELTA.A/Fs. The use of such an alternative also makes it possible
to eliminate the air-fuel ratio sensor output difference
.DELTA.A/Fs that exists when no rich spike operation is
performed.
[0115] Further, the second embodiment, which has been described
above, assumes that the air-fuel ratio sensor output A/Fsu is
greater than the air-fuel ratio sensor output A/Fs by .DELTA.A/Fs.
However, it is obvious that the present invention can also be
applied to a case where the air-fuel ratio sensor output A/Fsu is
smaller than the air-fuel ratio sensor output A/Fs by .DELTA.A/Fs.
In such a case, step 144 should be performed so that a numerical
value obtained by adding the difference .DELTA.A/Fs to the air-fuel
ratio sensor output A/Fsu is set as the air-fuel ratio sensor
output A/Fsu.
[0116] In the second embodiment, the air-fuel ratio sensor 45
corresponds to the "second air-fuel ratio acquisition device"
according to the first aspect of the present invention and the
"second air-fuel ratio detection device" according to the third
aspect of the present invention. Further, in the second embodiment,
the "difference calculation device" according to the second aspect
of the present invention is implemented when the ECU 60 performs
step 142; and the "correction device" according to the second
aspect of the present invention is implemented when the ECU 60
performs step 144.
* * * * *