U.S. patent application number 11/812871 was filed with the patent office on 2007-11-22 for exhaust emission purifying apparatus for engine.
This patent application is currently assigned to NISSAN DIESEL MOTOR CO., LTD.. Invention is credited to Toshikazu Katou, Mitsuhiro Nishina.
Application Number | 20070266697 11/812871 |
Document ID | / |
Family ID | 35004100 |
Filed Date | 2007-11-22 |
United States Patent
Application |
20070266697 |
Kind Code |
A1 |
Nishina; Mitsuhiro ; et
al. |
November 22, 2007 |
Exhaust emission purifying apparatus for engine
Abstract
A technology for purifying an exhaust emission from an engine is
provided, in which a misjudgment caused by a time lag between the
abnormality detection and an abnormality judgment is avoided, in
the case where a plurality of abnormalities is judged on the
aqueous solution of a reducing agent or the like. After a first
abnormality judgment (Femp=1: the time t2) is made, when a second
abnormality is detected as a result that the concentration Dn as a
state parameter is directly shifted from a first region A to a
second region C (the time t3), the first abnormality judgment is
maintained for a predetermined period of time PRD after the second
abnormality detection.
Inventors: |
Nishina; Mitsuhiro; (Ageo,
JP) ; Katou; Toshikazu; (Ageo, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
18191 VON KARMAN AVE.
SUITE 500
IRVINE
CA
92612-7108
US
|
Assignee: |
NISSAN DIESEL MOTOR CO.,
LTD.
Ageo-shi
JP
|
Family ID: |
35004100 |
Appl. No.: |
11/812871 |
Filed: |
June 22, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP05/17244 |
Sep 20, 2005 |
|
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11812871 |
Jun 22, 2007 |
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Current U.S.
Class: |
60/277 ; 60/286;
60/295 |
Current CPC
Class: |
Y02T 10/40 20130101;
F01N 2900/0422 20130101; B01D 53/9431 20130101; B01D 53/90
20130101; F01N 11/00 20130101; F01N 2610/10 20130101; F01N 2550/05
20130101; F01N 2610/02 20130101; Y02T 10/12 20130101; Y02T 10/47
20130101; F01N 13/0097 20140603; F02B 37/00 20130101; F01N
2900/1818 20130101; B01D 2251/20 20130101; F01N 2610/1406 20130101;
F01N 13/009 20140601; B01D 53/9495 20130101; F01N 2900/0421
20130101; F01N 3/208 20130101; Y02T 10/24 20130101 |
Class at
Publication: |
060/277 ;
060/286; 060/295 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 7/00 20060101 F01N007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 2004 |
JP |
2004-373889 |
Claims
1. An exhaust emission purifying apparatus for an engine, operable
to add a reducing agent for NO.sub.x to an exhaust gas of the
engine thereby reducing the NO.sub.x in the exhaust gas,
comprising: a tank for storing the reducing agent to be added to
the exhaust gas or a precursor thereof, in an aqueous solution
state; a detecting unit for detecting a predetermined state
parameter on the aqueous solution based on a thermal characteristic
of the aqueous solution stored in the tank; and a calculating unit
for performing a predetermined calculation on abnormalities of the
aqueous solution based on the detected state parameter, wherein the
calculating unit includes: an abnormality detecting section which
detects a predetermined abnormality on the aqueous solution when
the detected state parameter is within an abnormal region other
than a predetermined region defined as a normal region; and an
abnormality judging section which makes an abnormality judgment
upon an establishment of a predetermined determinate condition
after the abnormality is detected, the abnormality detecting scion
detects a first abnormality when the detected state parameter is
within a first region in the abnormal region, and also detects a
second abnormality when the detected state parameter is within a
second region defined as a different region from the first region
in the abnormal region, and the abnormality judging section makes a
first abnormality judgment in association with the first
abnormality detection, and also makes a second abnormality judgment
in association with the second abnormality detection, and after the
first abnormality judgment is made, when the second abnormality is
detected as a result that the detected state parameter is directly
shifted from the first region to the second region, maintains the
first abnormality judgment for a predetermined period of time from
the detection of the second abnormality concerned.
2. The apparatus according to claim 1, wherein the abnormality
detecting section detects, as the first abnormality, one
abnormality that is selected from a group containing a residual
amount deficiency of the aqueous solution, a dilution of the
aqueous solution and a mixing of a different kind of aqueous
solution in the tank, based on the detected state parameter, and
also detects, as the second abnormality, another one selected from
the group.
3. The apparatus according to claim 1, wherein the abnormality
judging section performs setting of a counter therein, which is
increased by a predetermined value at every time when the first or
second abnormality is detected, and makes the first or second
abnormality judgment based on a value counted by the counter.
4. The apparatus according to claim 3, wherein the abnormality
judging section judges whether or not the aqueous solution is in a
stable state in the tank, and varies the predetermined value
between a first case where it is judged that the aqueous solution
is in the stable state and a second case where it is judged that
the aqueous solution is not in the stable state.
5. The apparatus according to claim 3, wherein the abnormality
judging section performs setting of the counter on conducting of at
least the second abnormality judgment, and makes the second
abnormality judgment when the counter reaches a predetermined
abnormality judgment value, and the predetermined period of time is
determined as being a period of time elapsing from a detection of
the second abnormality by the detecting unit until the counter
reaches the predetermined abnormality judgment value.
6. The apparatus according to claim 1, wherein the abnormality
judging section makes the second abnormality judgment, when the
detected state parameter remaining inside the second region becomes
a predetermined proportion with respect to a predetermined number
of detection of frequencies after the detected state parameter has
been shifted to the second region from the outside thereof.
7. The apparatus according to claim 1, wherein the calculating unit
generates a signal indicating that the addition of the reducing
agent to the exhaust gas should be stopped, when one of the first
and second abnormality judgments is made.
8. The apparatus according to claim 7, wherein the calculating unit
generates, when one of the first or second abnormality judgments is
made, a signal indicating that an amount of NO.sub.x emission from
the engine should be reduced to a level below that encountered when
one of the first and second abnormality judgments is not made.
9. The apparatus according to claim 7, wherein the calculating unit
generates, when one of the first and second abnormality judgments
is made, a signal indicating that an output characteristic of the
engine should be varied relative to an accelerator control
operation from that taken when one of the first and second
abnormality judgments is not made, to thereby restrict an output of
the engine.
10. The apparatus according to claim 7, wherein the calculating
unit further includes an addition control section which controls an
adding amount of the reducing agent to the exhaust gas based on the
detected state parameter.
11. The apparatus according to claim 1, further comprising a
warning unit capable of urging a driver to recognize an occurrence
of abnormality when one of the first and second abnormality
judgments is made.
12. The apparatus according to claim 1, wherein the state parameter
is a concentration of the reducing agent or the precursor thereof
contained in the aqueous solution.
13. The apparatus according to claim 12, wherein the detecting unit
comprises: a sensor element part arranged inside of the tank; and a
circuit section connected to the sensor element part to execute a
predetermined calculation to calculate the concentration of the
reducing agent or the precursor thereof, wherein the sensor element
part includes: a heater; and a temperature sensing element having a
property in which an electrical characteristic value thereof is
changed according to the temperature, which is directly or
indirectly in contact with the aqueous solution and also is heated
by the heater, and wherein the circuit section drives the heater,
detects the electrical characteristic value of the heated
temperature sensing element, and calculates the concentration of
the reducing agent or the precursor thereof based on the detected
electrical characteristic value.
14. The apparatus according to claim 1, wherein the reducing agent
is ammonia.
15. An exhaust emission purifying apparatus for an engine, for
adding a reducing agent for NO.sub.x to an exhaust gas of the
engine to reduce NO.sub.x in the exhaust gas, comprising: a tank
for storing the reducing agent to be added to the exhaust gas or a
precursor thereof, in an aqueous solution state; means for
detecting a concentration of the reducing agent or the precursor
thereof contained in the aqueous solution stored in the tank; means
for detecting a predetermined abnormality on the aqueous solution
when the detected concentration is within an abnormal region other
than a predetermined region defined as a normal region; and means
for making an abnormality judgment upon the establishment of a
predetermined determinate condition after the abnormality is
detected, wherein the means for detecting the predetermined
abnormality detects a first abnormality when the detected
concentration remains within a first region in the abnormal region,
and also detects a second abnormality when the detected
concentration remains within a second region defined as a different
region from the first region in the abnormal region, and the means
for making an abnormality judgment makes a first abnormality
judgment in association with the first abnormality detection, and
also makes a second abnormality judgment in association with the
second abnormality detection, and after the first abnormality
judgment is made, when the second abnormality is detected as a
result that the detected concentration is directly shifted from the
first region to the second region, maintains the first abnormality
judgment for a predetermined period of time from the detection of
the second abnormality concerned.
Description
[0001] This application is a continuation of PCT/JP2005/017244,
filed on Sep. 20, 2005.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an exhaust emission
purifying apparatus for an engine, and in particular, to a
technology for purifying nitrogen oxides emitted from the engine by
using ammonia as a reducing agent.
[0004] 2. Description of the Related Art
[0005] There has been known the following SCR (Selective Catalytic
Reduction) apparatus, as an apparatus for purifying, by the
post-treatment, the air pollution offender emitted from an engine,
in particular, nitrogen oxides (to be referred to as "NO.sub.x") in
the exhaust gas. In this apparatus, an injection device for an
aqueous solution of ammonia or a precursor thereof is disposed in
an exhaust passage of the engine, and injected ammonia is used as a
reducing agent to be reacted with NO.sub.x on a catalyst, to
thereby reduce and purify NO.sub.x. Further, there has also been
known a SCR apparatus in which, taking the ammonia storability on a
vehicle into consideration, urea being the ammonia precursor is
stored in a tank in an aqueous solution state, and in actual
operations, the urea water supplied from the tank is injected into
an exhaust passage, to thereby generate ammonia by the urea
hydrolysis utilizing the exhaust heat (refer to Japanese Unexamined
Patent Publication No. 2000-027627, paragraph number 0013).
[0006] The applicant of this invention has reviewed the application
of the SCR apparatus to the exhaust gas purification in an
on-vehicle engine. In order to inject the urea water of amount
precise for a NO.sub.x emission amount from the engine and to
satisfactorily perform the NO.sub.x reduction-reaction, it is
important from a practical view point that a urea sensor is
disposed in a urea water tank, and the actual urea concentration
(hereunder, the simply called "concentration" indicates the urea
concentration) is reflected onto controlling of the engine and the
SCR apparatus. At the present day, there has been developed a urea
sensor in which a heater and a resistance temperature sensor are
disposed in an insulation state, and focusing attention on a heat
transfer characteristic of the urea water according to the urea
concentration, the actual urea concentration is detected based on
an electric resistance value of the resistance temperature sensor
(refer to Japanese Unexamined Patent Publication No.
2001-228004).
[0007] The applicant of this invention has already disclosed an
exhaust emission purifying apparatus for an engine which adopts a
temperature sensitive urea sensor in the past filed Japanese Patent
Application No. 2003-366737. In this apparatus, the urea
concentration is detected by the urea sensor, and also, when a high
concentration above a normal region is detected, a judgment is made
that a residual amount of the urea water is deficient, whereas when
a low concentration below the normal region is detected, a judgment
is made that the urea water is in a dilute state equal to or near
the water, and accordingly, the urea concentration is abnormal.
When either one of the judgments is made, measures are taken to
stop the urea water injection and the like. Further, in this
apparatus, particularly in the latter case where the low
concentration is detected, when this low concentration is
repetitively detected for the predetermined number of frequencies,
this low concentration is adopted as an established value so that
the reliability of the detected concentration is ensured (refer to
FIGS. 7 and 9 of the above prior application).
[0008] However, there is the following problem in such an exhaust
emission purifying apparatus in which the detection of the
concentration higher or lower than the normal region and the
abnormality judgment corresponding to this detection are not
performed simultaneously, and consequently, there appears a time
lag between the former detection and the latter judgment. Namely,
in the case where a driver inadvertently or intentionally
replenishes the water or the diluted urea water after it is judged
that the residual amount of the urea water is deficient, the
judgment of the residual amount deficiency is cancelled, but the
judgment of the abnormal concentration is made belatedly by a
period of time corresponding to the above time lag, after the
replenishment. Therefore, it is impossible to take the measures to
the abnormal concentration during the time lag, and accordingly,
there is a possibility that unpurified NO.sub.x is discharged into
the atmosphere.
SUMMARY OF THE INVENTION
[0009] The present invention has an object to provide a technology
for judging a plurality of abnormalities on the aqueous solution of
a reducing agent or the precursor thereof, and also, in the case
where there exists a time lag between the abnormality detection and
the abnormality judgment, for avoiding a misjudgment caused by this
time lag.
[0010] The present invention provides an exhaust emission purifying
apparatus for an engine. The exhaust emission purifying apparatus
for the engine according to the present invention, which adds a
reducing agent for NO.sub.x to the exhaust gas of the engine to
reduce NO.sub.x in the exhaust gas, is configured to include a tank
for storing the reducing agent to be added to the exhaust gas or
the precursor thereof, in an aqueous solution state. In this
apparatus, a predetermined state parameter on the aqueous solution
is detected based on a thermal characteristic of the aqueous
solution stored in the tank, and when the detected state parameter
is within an abnormal region other than a predetermined region
defined as a normal region, a predetermined abnormality on the
aqueous solution is detected, and also, after the abnormality is
detected, an abnormality judgment is made upon an establishment of
a predetermined determinate condition. Further, a first abnormality
is detected when the detected state parameter is within a first
region in the abnormal region, whereas a second abnormality is
detected when the detected state parameter is within a second
region defined as a different region from the first region in the
abnormal region, and further, a first abnormality judgment is made
in association with the first abnormality detection, and also, a
second abnormality judgment is made in association with the second
abnormality detection. Further, after the first abnormality
judgment is made, when the second abnormality is detected as a
result that the detected state parameter is directly shifted from
the first region to the second region, the first abnormality
judgment is maintained for a predetermined period of time from the
detection of the second abnormality concerned.
[0011] In the present invention, there exists a time lag necessary
for establishing the predetermined determinate condition from the
detection of the state parameter within the abnormal region to the
performance of the abnormality judgment that is determined in
association within this detection. Here, in the present invention,
after the first abnormality judgment is made, when the second
abnormality is detected as a result that the detected state
parameter is directly shifted from the first region to the second
region, the first abnormality judgment is maintained for the
predetermined period of time from the second abnormality detection.
Therefore, despite of existence of the time lag, it is possible to
avoid a misjudgment of normality on the aqueous solution of the
reducing agent.
[0012] The other objects, features, advantages and various aspects
of the present invention will become more apparent from the ensuing
description of preferred embodiments with reference to the
accompanying drawings.
[0013] It should be appreciated that the entire contents of
Japanese Patent Application No. 2004-373889, a priority of which is
claimed, is incorporated herein by reference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a diagram showing a configuration of an engine
according to one embodiment of the present invention;
[0015] FIG. 2 is a diagram showing a configuration of a urea
sensor;
[0016] FIG. 3 is a graphical view showing the principle of
concentration detection using the urea sensor;
[0017] FIG. 4 is a flowchart of detection permission routine;
[0018] FIG. 5 is a sub-routine of stability judgment process in the
above routine,
[0019] FIG. 6 is a flowchart of concentration detection and
abnormality judgment routine;
[0020] FIG. 7 is a flowchart of stop control routine;
[0021] FIG. 8 is a flowchart of urea water injection control
routine; and
[0022] FIG. 9 is a time chart showing an operation of a
SCR-C/U.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] Hereunder, there will be described preferred embodiments of
the present invention, referring to the accompanying drawings.
[0024] FIG. 1 shows a configuration of an automobile engine (to be
referred to as "engine" hereunder) 1 according to one embodiment of
the present invention. In the present embodiment, a direct
injection type diesel engine is adopted as the engine 1.
[0025] In an intake passage 11, an air cleaner (not shown in the
figure) is attached to an introduction thereof, and dust in an
intake air is removed by this air cleaner. In the intake passage
11, a compressor 12a of a variable nozzle type turbocharger 12 is
disposed, and the intake air is compressed by the compressor 12a to
be sent out. The compressed intake air is flown into a surge tank
13, and is distributed to each cylinder in a manifold.
[0026] In an engine body, to a cylinder head, an injector 21 is
disposed for each cylinder. The injector 21 operates in response to
a signal from an engine control unit (to be referred to as "engine
C/U", hereunder) 51. Fuel sent out by a fuel pump (not shown in the
figure) is supplied to the injector 21 via a common rail 22, to be
injected to the inside of a combustion chamber by the injector
21.
[0027] In an exhaust passage 31, a turbine 12b of the turbocharger
12 is disposed on the downstream of a manifold. The turbine 12b is
driven by the exhaust gas, so that the compressor 12a is rotated. A
movable vane 121 of the turbine 12b is connected to an actuator
122, and accordingly, an angle of the movable vane 12 is controlled
by the actuator 122.
[0028] On the downstream of the turbine 12b, an oxidation catalyst
32, a NO.sub.x purification catalyst 33 and an ammonia catalyst 34
are disposed in this order from the upstream side. The oxidation
catalyst 32 oxidizes hydrocarbon and carbon monoxides in the
exhaust gas, and converts nitrogen monoxides (to be referred to as
"NO", hereunder) into NO.sub.x mainly containing nitrogen dioxides
(to be referred to as "NO.sub.2" hereunder) to perform the function
of adjusting a ratio between NO and NO.sub.2 contained in the
exhaust gas to a ratio appropriate for the NO.sub.x reduction
reaction described later. The NO.sub.x purification catalyst 33
reductively purifies NO.sub.x. For the reduction of NO.sub.x, in
the present embodiment, ammonia as a reducing agent is added to the
exhaust gas on the upstream of the NO.sub.x purification catalyst
33.
[0029] In the present embodiment, considering the storability of
ammonia, urea being the ammonia precursor is stored in an aqueous
solution state. It is possible to ensure the safety by storing
ammonia in a urea state.
[0030] To a tank 41 storing the urea water, a urea water supply
pipe 42 is connected. To a tip end of the urea water supply pipe
42, an injection nozzle 43 for the urea water is attached. To the
urea water supply pipe 42, a feed pump 44 and a filter 45 are
disposed in this order from the upstream side. The feed pump 44 is
driven by an electric motor 441. The number of revolutions of the
electric motor 441 is controlled based on a signal from a SCR
control unit (to be referred to as "SCR-C/U, hereunder) 61, so that
a discharge amount of the feed pump 44 is adjusted. Further, on the
downstream of the filter 45, a urea water return pipe 46 is
connected to the urea water supply pipe 42. To the urea water
return pipe 46, a pressure control valve 47 is disposed, and
configured so that the surplus urea water of amount exceeding a
specified pressure is returned to the tank 41.
[0031] The injection nozzle 43 is an air-assist type injection
nozzle, and includes a body 431 and a nozzle portion 432. To the
body 431, the urea water supply pipe 42 is connected, and also, an
air supply pipe 48 for supplying the assist air is connected. The
air supply pipe 48 is connected to an air tank (not shown in the
figure), and the assist air is supplied from this air tank. The
nozzle portion 432 is disposed on the upstream of the NO.sub.x
purification catalyst 33, so as to pass through a case of the
NO.sub.x purification catalyst 33 and the ammonia catalyst 34 from
a side surface of the case. An injection direction of the nozzle
portion 432 is set in parallel to the exhaust gas flow, and toward
an end surface of the NO.sub.x purification catalyst 33.
[0032] When the urea water is injected, urea in the injected urea
water is hydrolyzed by the exhaust heat, so that ammonia is
generated. Generated ammonia functions as a reducing agent for
NO.sub.x on the NO.sub.x purification catalyst 33, to reduce
NO.sub.x. The ammonia catalyst 34 is for purifying slip ammonia
which passed through the NO.sub.x purification catalyst 33 without
contributing to the NO.sub.x reduction. Since ammonia has an
irritating odor, it is not preferable to discharge ammonia without
purification. The oxidation reaction of NO on the oxidation
catalyst 32, the hydrolysis reaction of urea, the NO.sub.x
reduction reaction on the NO.sub.x purification catalyst 33, and
the oxidation reaction of slip ammonia on the ammonia catalyst 34
are expressed by the following formulas (1) to (4). Incidentally,
in the present embodiment, the NO.sub.x purification catalyst 33
and the ammonia catalyst 34 are integrated in a single case.
However, these catalysts 33, 34 may be respectively contained in
separate cases. NO+1/2O.sub.2.fwdarw.NO.sub.2 (1)
(NH.sub.2).sub.2CO+H.sub.2O.fwdarw.2NH.sub.3CO.sub.2 (2)
NO+NO.sub.2+2NH.sub.3.fwdarw.2N.sub.2+3H.sub.2O (3)
4NH.sub.3+3O.sub.2.fwdarw.2N.sub.2+6H.sub.2O (4)
[0033] Further, the exhaust page 31 is connected to the intake
passage 11 via an EGR pipe 35. To the EGR pipe 35, an EGR valve 36
is disposed. To the EGR valve 36, an actuator 361 is connected, so
that an opening degree of the EGR valve 36 is controlled by the
actuator 361.
[0034] In the exhaust passage 31, a temperature sensor 71 for
detecting the temperature of the exhaust gas which is not yet added
with the urea water, is disposed between the oxidation catalyst 32
and the NO.sub.x purification catalyst 33. On the downstream of the
ammonia catalyst 34, there are disposed a temperature sensor 72 for
detecting the temperature of the exhaust gas after the reduction,
and a NO.sub.x sensor 73 for detecting the concentration of
NO.sub.x contained in the exhaust gas after the reduction. Further,
in the tank 41, a urea sensor 74 for detecting the concentration
(corresponding to "a state parameter") of urea contained in the
urea water is disposed.
[0035] Detection signals from the temperature sensors 71 and 72,
the NO.sub.x sensor 73 and the urea sensor 74 are output to the
SCR-C/U 61. The SCR-C/U 61 calculates and sets an optimum urea
water injection amount based on the input signals, and outputs a
command signal according to the set urea water injection amount to
the injection nozzle 43. Further, the SCR-C/U 61 is connected to
the engine C/U 51 so as to be communicable with each other in
bi-directions, and outputs the detected urea concentration to the
engine C/U 51. On the other hand, on the engine 1 side, an ignition
switch, a start switch, a crank angle sensor, a vehicle speed
sensor, an accelerator sensor and the like are disposed, and
detection signals from them are input to the engine C/U 51. The
engine C/U 51 calculates an engine rotating number NE based on the
signal input from the crank angle sensor. The engine C/U 51 outputs
information such as a fuel injection amount and the like, which is
necessary for the injection control of the urea water, to the
SCR-C/U 61.
[0036] FIG. 2 shows a configuration of the urea sensor 74.
[0037] The urea sensor 74 has a configuration similar to that of a
flow meter disclosed in Japanese Unexamined Patent Publication No.
2001-228004, and detects the urea concentration based on electrical
characteristic values of two temperature sensing elements.
[0038] The flow meter disclosed in the above Unexamined Patent
Publication No. 2001-228004 includes a first sensor element with a
heater function and a second sensor element without a heater
function. The former first sensor element has a heater layer and a
resistance temperature sensing layer (to be referred to as "first
sensing layer", hereunder) as the temperature sensing element,
formed on the heater layer in an insulating state. The latter
second sensor element has a resistance temperature sensing layer
(to be referred to as "second sensing layer", hereunder) as the
temperature sensing element, but does not have a heater layer. The
respective sensor elements are integrated within a resin case and
are connected to one ends of fin plates serving as heat transfer
bodies.
[0039] In the present embodiment, a sensor element part 741 of the
urea sensor 74 is configured to include the above first and second
sensor elements. The sensor element part 741 is disposed in the
vicinity of a bottom of the tank 41, and is used in a state of
being dipped into the urea water, at the detection of the urea
concentration. Further, respective fin plates 7414 and 7415 pass
through a case 7413 to expose to the inside of the tank 41.
[0040] A circuit section 742 is connected to the heater layer and
the resistance temperature sensing layer (or first sensing layer)
of the first sensor element 7411, and also to the resistance
temperature sensing layer (or second sensing layer) of the second
sensor element 7412. The circuit section 742 supplies the electric
current to the heater layer to heat the first sensing layer, and
also detects a resistance value Rn1 of the heated first sensing
layer and a resistance value Rn2 of the second sensing layer which
is not directly heated. The resistance temperature sensing layer
has a characteristic in which a resistance value thereof is changed
in proportion to the temperature. The circuit section 742
calculates the concentration Dn as follows, based on the detected
Rn1 and Rn2. Incidentally, the urea sensor 74 has both of a
function of detecting the urea concentration and a function of
judging a residual amount of the urea water.
[0041] FIG. 3 shows the principle of concentration detection and
residual amount judgment.
[0042] The heating by the heater layer is performed by supplying a
heater drive current in to the heater layer for a predetermined
period of time .DELTA.t01. The circuit section 742 detects the
resistance values Rn1 and Rn2 of the respective resistance
temperature sensing layers at a time point t1 at which the electric
power supply to the heater layer is shut off, and also, calculates
a temperature difference .DELTA.Tmp12 (=Tn1-Tn2) between the
resistance temperature sensing layers at the time point. The
temperature difference between the resistance temperature sensing
layers is changed according to a characteristic of heat transfer
via the urea water as a medium, and accordingly, this heat transfer
characteristic is changed according to the urea concentration.
Therefore, it is possible to convert the calculated .alpha.Tmp12 to
calculate the concentration Dn. Further, based on the calculated
.alpha.Tmp12, it is possible to judge whether or not an amount of
the urea water retained in the tank 41 is deficient.
[0043] Incidentally, in the present embodiment, the configuration
is such that the first sensing layer is in contact with the urea
water via the fin plate 7414 in the first sensor element 7411.
However, the configuration may be such that a measuring chamber, to
which the urea water in the tank 41 is introduced, is formed in the
sensor element part 741, and the first sensing layer is heated by
the heater via the urea water in the measuring chamber. In this
case, the first sensing layer and the urea water are directly in
contact with each other.
[0044] Next, there will be described an operation of the SCR-C/U 61
with reference to flowcharts.
[0045] The operation of the SCR-C/U 61 according to the present
embodiment will be described roughly as follows. Namely, the
SCR-C/U 61 performs a detection permission judgment (FIG. 4;
detection permission routine), and only when the concentration
detection is permitted by this judgment, actually conducts a
detection of the concentration Dn. When the detected concentration
Dn is within a predetermined range defined as a normal region, the
SCR-C/U 61 judges that a predetermined abnormality on the urea
water does not occur, and outputs the concentration Dn. On the
other hand, when the detected concentration Dn is without the
predetermined range, the SCR-C/U 61 outputs the concentration Dn,
but judges that an abnormality on the residual amount of the urea
water or the concentration thereof occurs as the predetermined
abnormality. In the present embodiment, the abnormality judgment on
the residual amount of the urea water (to be referred to as
"residual amount abnormality judgment", hereunder) is made when the
concentration Dn is within a region above the predetermined range,
whereas the abnormality judgment on the concentration of the urea
water (to be referred to as "concentration abnormality judgment",
hereunder) is made when the concentration Dn is within a region
below the predetermined range. Further, in the present embodiment,
in making the respective abnormality judgments, the SCR-C/U61 adds
up, as "determinate condition", error counters CNTc and CNTe by
each predetermined value at every time when each of the
abnormalities is detected, and actually makes the abnormality
judgments on condition that the error counters CNTc and CNTe reach
predetermined values CNTclim and CNTelim (FIG. 6; concentration
detection and abnormality judgment routine). When either the
residual amount abnormality judgment or the concentration
abnormality judgment is made, the SCR-C/U 61 outputs a signal for
stopping the urea water injection to the injection nozzle 43 (FIG.
8; urea water injection control routine).
[0046] FIG. 4 is a flowchart of the detection permission routine.
This routine is activated when the ignition switch is turned on,
and thereafter, is repetitively executed at each predetermined
time. By this routine, the detection of the concentration Dn is
permitted or prohibited.
[0047] In S101, an ignition switch signal SWign is read in, and it
is judged whether or not the signal SWign is 1. When the signal
SWign is 1 it is judged that the ignition switch is turned on, and
the routine proceeds to S102.
[0048] In S102, a start switch signal SWstr is read in, and it is
judged whether or not the signal SWstr is 1. When the signal SWstr
is 1, it is judged that the start switch is turned on, and
accordingly the engine 1 starts to operate, and the routine
proceeds to S103 in order to make the permission judgment. This is
because, at the start of the engine 1, there is high probability
that a considerable time has elapsed after occurrence of the
previous stopping of the engine 1, and therefore the urea water is
stable in the tank 41. On the other hand, when the signal SWstr is
not 1, the routine proceeds to S105.
[0049] In S103, a detection interval INT is reset to 0.
[0050] In S104, a permission judgment flag Fdtc is set to 1, and
the permission judgment is made.
[0051] In S105, the detection interval INT is counted up by 1
(INT=INT+1).
[0052] In S106, it is judged whether or not the detection interval
INT after counted up reaches a predetermined value INT1. When the
detection interval INT reaches the predetermined value INT1, it is
judged that the detection interval necessary for the concentration
Dn detection is ensured, and the routine proceeds to S103. On the
other hand, when the detection interval INT does not reach the
predetermined value INT1, it is judged that the necessary detection
interval is not ensured, and the routine proceeds to S107 in order
to make a prohibition judgment.
[0053] In S107, the permission judgment flag Fdtc is set to 0, and
the prohibition judgment is made.
[0054] FIG. 5 is a flowchart of the stability judgment routine.
This routine is repetitively executed at each predetermined time.
By this routine, it is judged whether or not the urea water is
stable in the tank 41, and a stability judgment flag Fstb according
to the judgment result is set. The set flag Fstb is reflected to
the concentration detection and abnormality judgment routine (FIG.
6).
[0055] In S201, the engine rotating number NE is read in.
[0056] In S202, it is judged whether or not the read NE is
decreased to a predetermined idle judgment rotating number NEidle
or less. When the read NE is decreased to NEidle or less, the
routine proceeds to S203, whereas when the read NE is not decreased
to NEidle or less, the routine proceeds to S206.
[0057] In S203, the vehicle speed VSP is read in.
[0058] In S204, it is judged whether or not the read VSP is
decreased to a predetermined value VSP1 (for example, 0) or less.
When the read VSP is decreased to VSP1 or less, the routine
proceeds to S207, whereas when the read VSP is not decreased to
VSP1 or less, the routine proceeds to S205. The predetermined value
VSP1 is not limited to 0, and can be set to be larger than 0, as a
vehicle speed maximum value capable of judging that the vehicle
substantially stops. This is because, even though the vehicle does
not completely stop, when the vehicle speed is low to some extent,
and accordingly it is ensured that the large deceleration does not
occur, the swaying of the urea water in the tank 41 is attenuated
so that the state of the urea water is shifted to be stable.
[0059] In S205, an elapsed time TIM is reset to 0.
[0060] In S206, it is judged that the urea water is not in the
stable state, the stability judgment flag Fstb is set to 0.
[0061] In S207, the elapsed time TIM is counted up by 1
(TIM=TIM+1).
[0062] In S208, it is judged whether or not the time TIM after
counted up reaches a stabilization time TIM1. When the time TIM
roaches the time TIM1, the routine proceeds to S209, whereas when
the time TIM does not reach the time TIM1, the routine proceeds to
S206. Incidentally, it is preferable that the stabilization time
TIM1 is set to have a large value as the deceleration is large,
provided that the stabilization time TIM1 is changed according to
the deceleration at the vehicle stop. This is because, when the
vehicle suddenly stops, the swaying of the urea water is increased
just after the vehicle stop, and consequently, a long period of
time is required until the urea water is stabilized.
[0063] In S209, the stability judgment flag Fstb is set to 1, and
it is judged that the urea water is in the stable state.
[0064] FIG. 6 is a flowchart of the concentration detection and
abnormality judgment routine. This routine is executed by the
SCR-C/U 61 and the circuit section 742 when the permission judgment
flag Fdtc is set to 1. S302 and S303 are processing performed by
the circuit section 742. By this routine, the concentration Dn is
detected, and also, predetermined abnormalities on the urea water
are detected and judged.
[0065] In S301, the permission judgment flag Fdtc is read in, and
it is judged whether or not the read flag Fdtc is 1. Only when the
flag Fdtc is 1, the routine proceeds to S302.
[0066] In S302, in order to detect the concentration Dn, the
electric current is supplied to the heater layer of the urea sensor
74, so that the first sensing layer is directly heated, and also,
the second sensing layer is indirectly heated using the urea water
as the medium.
[0067] In S303, the concentration Dn is detected. The detection of
the concentration Dn is performed such that the resistance values
Rn1 and Rn2 of the heated resistance temperature sensing layers are
detected, and also the temperature difference .DELTA.Tmp12 between
the resistance temperature sensing layers according to a difference
between the detected resistance values Rn1 and Rn2 is calculated,
and the calculated .alpha.Tmp12 is converted into the concentration
Dn.
[0068] In S304, it is judged whether or not the detected
concentration Dn is within the predetermined range (corresponding
to "normal region") having a lower limit value of a first value D1
and an upper limit value of a second value D2 which is larger than
the first value D1. When the detected concentration Dn is within
the predetermined range, the routine proceeds to S316, whereas when
the detected concentration Dn is not within the predetermined
range, the routine proceeds to S305.
[0069] In S305, it is judged whether or not the concentration Dn is
larger than a predetermined third value D3. When the concentration
Dn is larger than the value D3, the routine proceeds to S311,
whereas when the concentration Dn is equal to or smaller than the
value D3, the routine proceeds to S306. The predetermined value D3
is set to an intermediate value between an output Dn obtained in
the state where the urea sensor 74 is in the urea water and an
output Dn obtained in the state where the urea sensor 74 is in the
air. Incidentally, in the present embodiment, the predetermined
value D3 is set to a different value from the value D2 (namely,
larger than D2), but may be set to an equal value to the value
D2.
[0070] In S306, a point "a" or "b" of a value according to the
stability judgment flag Fstb is added to a concentration error
counter CNTc. Namely, when it is judged that the flag Fstb is 1 and
the urea water is stable in the tank 41, the point "a" which has a
relatively large value is added (CNTc=CNTC+"a"), whereas when it is
judged that the flag Fstb is 0 and the urea water is not stable,
the point "b" which is smaller than the point "a" is added
(CNTc=CNTc+"b":"b"<"a"). This is because when the urea water is
left stable, variation in the heat transfer characteristic due to
the urea water agitation is small, and accordingly, the high
reliability of the concentration Dn obtained is to be reflected
onto the abnormality judgment.
[0071] In S307, it is judged whether or not the counter CNTc after
counted up reaches a predetermined value CNTclim. When the counter
CNTc reaches the value CNTclim, the routine proceeds to S308,
whereas when the counter CNTc does not reach the value CNTclim, the
routine is returned.
[0072] In S308, a residual amount abnormality judgment flag Femp is
set to 0.
[0073] In S309, a residual amount error counter CNTe is reset to
0.
[0074] In S310, the concentration abnormality judgment that the
urea water is a dilute state equal to or near the water, or that a
different kind of aqueous solution from the urea water is stored in
the tank 41 is made, and a concentration abnormality judgment flag
Fcnc is set to 1. Incidentally, in the present embodiment, simple
one concentration abnormality judgment is made when the
concentration less than the first value D1 is detected. However,
the configuration may be such that different concentration
abnormality judgment flags are set for the case where the water is
filled in the tank 41 and for the case where the urea water is
diluted, and the concentration Dn and a fourth value D4 (for
example, 0) smaller than D1 are compared with each other, to
thereby distinguish between the abnormalities for the respective
cases.
[0075] In S311, a point "c" or "d" of a value according to the
stability judgment flag Fstb is added to the residual amount error
counter CNTe. Namely, when it is judged that the flag Fstb is 1,
and the urea water is stable in the tank 41, the point "c" which
has a relatively large value is added (CNTe=CNTe+"c"), where when
it is judged that the urea water is not stable, the point "d" which
is smaller than the point "c" is added (CNTe=CNTe+"d":"d"<"c").
This is because, the high reliability of the concentration Dn
obtained when the urea water is stable is to be reflected,
similarly to the case of the concentration error counter CNTc.
[0076] In S312, it is judged whether or not the counter CNTe after
counted up reaches a predetermined value CNTelim. When the counter
CNTe reaches the value CNTelim, the routine proceeds to S313,
whereas when the counter CNTe does not reach the value CNTelim,
this routine is returned.
[0077] In S313, the concentration abnormality judgment flag Fcnc is
set to 0.
[0078] In S314, the concentration error counter CNTc is reset to
0.
[0079] In S315, the residual amount abnormality judgment that the
amount of the urea water retained in the tank 41 is less than a
predetermined amount (for example, the tank 41 is empty) is made,
and the residual amount abnormality judgment flag Femp is set to
1.
[0080] In S316, the normality judgment is made, and the respective
abnormality judgment flags Fcnc and Femp are set to 0.
[0081] In S317, the respective error counters CNTc and CNTe are
reset to 0.
[0082] FIG. 7 is a flowchart of the stop control routine. This
routine is executed when the Ignition switch is turned off.
[0083] In S401, the ignition switch signal SWign is read in, and it
is judged whether or not the signal SWign is 0. When the signal
SWign is 0, it is judged that the ignition switch is turned off,
and the routine proceeds to S402.
[0084] In S402, various types of calculation information are
written into a backup memory. The calculation information written
into this memory are stored even after the ignition switch is
turned off and the power supply is shut off, and in the next
operation, are read in the concentration detection and abnormality
judgment routine and the urea water injection control routine
(S306, S503 and the like) described in the followings. In the
present embodiment, as the calculation information, the respective
error counters CNTc and CNTe and the respective abnormality
judgment flags Fcnc and Femp are read in.
[0085] Next, there will be described one example of the urea water
injection control adopting the concentration Dn, with reference to
a flowchart shown in FIG. 8. This routine is executed at each
predetermined time.
[0086] In S501, the concentration Dn is read in.
[0087] In S502, it is judged whether or not the residual amount
abnormality judgment flag Femp is 0. When the flag Femp is 0, the
routine proceeds to S503, whereas when the flag Femp is not 0, it
is judged that the residual amount abnormality judgment is made,
and the routine proceeds to S506.
[0088] In S503, it is judged whether or not a concentration
abnormality judgment flag Fcon is 0. When the flag Fcon is 0, the
routine proceeds to S504, whereas when the flag Fcon is not 0, it
is judged that the concentration abnormality judgment is made, and
the routine proceeds to S507.
[0089] In S504, the urea water injection amount is set. The setting
of the urea water injection amount is performed such that a basic
injection amount according to the fuel injection amount of the
engine 1 and the output from the NO.sub.x sensor 73 is calculated,
and also, be calculated basic injection amount is corrected with
the concentration Dn. When the concentration Dn is high and the
urea content per unit injection amount is high, the basic injection
amount is corrected to be decreased. On the other hand, when the
concentration Dn is low and the urea content per unit injection
amount is low, the basic injection amount is corrected to be
increased.
[0090] In S505, an operation signal according to the set urea water
injection amount is output to the injection nozzle 43.
[0091] In S506, a residual amount warning lamp disposed on a
control panel of a driver's seat is elevated, so as to make a
driver recognize that the residual amount of the urea water is
deficient.
[0092] In S507, a concentration warning lamp disposed on the
control panel is activated, so as to make the driver recognize that
the urea concentration is excessively low.
[0093] In S508, the injection of the urea water is stopped. This is
because the urea water of amount necessary for adding ammonia
cannot be injected, not only when the residual amount of the urea
water is deficient, but also when the urea concentration is
excessively low and when not the urea water but the water or the
like is stored in the tank 41. Incidentally, in the present
embodiment, the injection of the urea water is stopped when the
respective abnormality judgments are made. However, in addition to
or in place of this control, a signal for decreasing the NO.sub.x
emission amount itself from the engine 1 or a signal for
restricting the output of the engine 1 may be output to the engine
C/U 51. As a control of the former NO.sub.x emission amount
decreasing, the exhaust gas amount to be flown back via the EGR
pipe 35 is changed to be larger than that at a normal time other
than the abnormality judgment time. Further, as a control of the
latter engine 1 output restriction, an output characteristic of the
engine 1 relative to an accelerator control is differed from that
at the normal time, for example, the fuel injection amount relative
to an accelerator opening is changed to be smaller than that at the
normal time.
[0094] In the present embodiment, the urea sensor 74 constitutes "a
detecting unit" and the SCR-C/U 61 constitutes a calculating unit.
Further, in "the calculating unit" according to the present
embodiment, the processing of S304 and S305 in the flowchart shown
in FIG. 6 realizes a function as "an abnormality detecting
section", the processing of S306, S307, S311 and S312 in the
flowchart shown in FIG. 6 and the processing of S201 to S205, S207
and S208 in the flowchart shown in FIG. 5 realize a function as "an
abnormality judging section", and further, the processing of S504
in the flowchart shown in FIG. 8 realizes a function as "an
addition control section".
[0095] According to the present embodiment, the following effects
can be achieved.
[0096] FIG. 9 is a time chart showing the operation of the SCR-C/U
61, and shows transitions of the error counters CNTc and CNTe, and
the abnormality judgment flags Fcnc and Femp, for the case where,
after the residual amount abnormality judgment (corresponding to
"the first abnormality judgment") is made (the time t2), the water
or Me like is inadvertently or intentionally replenished so that
the concentration Dn is directly shifted from a region A above a
predetermined range B to another region C below the predetermined
range B (the time t3).
[0097] In the present embodiment, in such a case, the residual
amount abnormality judgment is maintained (CNTe=CNTelim, Femp=1;
S307 in FIG. 6) for a period of time PRD until the concentration
error counter CNTc is increased to reach the predetermined value
CNTclim and the concentration abnormality judgment (corresponding
to "the second abnormality judgment) is made, after the abnormal
concentration Dn in the region C is detected (the time t3).
Therefore, it is possible to avoid that, although the concentration
Dn is excessively low and the NO.sub.x reduction is not
sufficiently performed, the engine 1 is operated as per usual and
also the injection is performed since the concentration error
counter CNTc does not reach the predetermined value CNTclim, and
consequently, avoid discharging unpurified NO.sub.x into the
atmosphere.
[0098] Further, by making the stability judgment and by making the
predetermined values "a" to "d" to be added to the error counters
CNTc and CNTe different from each other according to the judgment
results, it is possible to reduce an influence on the abnormality
judgment of the concentration Dn which is variably detected as a
result that the urea water is agitated due to the vibration during
the vehicle running or the shock at the vehicle stop.
[0099] Further, by stopping the injection of the urea water when
the respective abnormality judgments are made, and also, by
decreasing the NO.sub.x emission amount from the engine 1, it is
possible to prevent the NO.sub.x discharge as a result that the
urea water of appropriate amount is not injected.
[0100] Furthermore, by restricting the output to the engine 1 when
the respective abnormality judgments are made, it is possible to
promote the appropriate replenishment of the urea water by the
driver.
[0101] Moreover, by setting the urea water injection amount based
on the concentration Dn, it is possible to inject the urea water in
just proportion.
[0102] Incidentally, in the above description, the error counters
CNTc and CNTe are adopted for both of the concentration abnormality
judgment and the residual amount abnormality judgment. However, an
error counter may be adopted for only one of the abnormality
judgments (for example, the concentration abnormality judgment
which is relatively susceptible to a misjudgment), and the other
abnormality judgment (namely the residual amount abnormality
judgment) may be made just after the concentration Dn within the
region A above the predetermined range B is detected.
[0103] Further, in the above description, the abnormality judgment
precision is ensured by adopting me error counters CNTc and CNTe
which are added with the predetermined values "a" to "d" at each
abnormality detection time of the concentration or the residual
amount. However, the configuration may be such that, by simply
adopting the frequencies in place of the error counter, the
abnormality judgment is made in the case where, after the detected
concentration Dn is shifted from the outside of the region A or C
to the region A or C, a predetermined proportion of the
concentrations Dn detected for the predetermined number of
frequencies are within the region A or C (for example, in the case
where the concentrations Dn within the region A or C are
repetitively detected for the predetermined number of
frequencies).
[0104] Furthermore, in the above description, ammonia is generated
by the urea hydrolysis. However, a catalyst for this hydrolysis is
not especially specified. In order to enhance the hydrolysis
efficiency, a hydrolysis catalyst may be disposed on the upstream
of the NO.sub.x purification catalyst.
[0105] In the above description, the present invention has been
described based on the preferred embodiment. However, the scope of
the present invention is not limited to this description, and is
determined based on the disclosure in the scope of claims in
accordance with applied articles.
* * * * *