U.S. patent application number 12/733177 was filed with the patent office on 2011-04-14 for catalyst passing component determining apparatus and exhaust purification apparatus for internal combustion engine.
Invention is credited to Shinya Asaura, Tomihisa Oda, Masaaki Sato, Shunsuke Toshioka.
Application Number | 20110083429 12/733177 |
Document ID | / |
Family ID | 42316399 |
Filed Date | 2011-04-14 |
United States Patent
Application |
20110083429 |
Kind Code |
A1 |
Sato; Masaaki ; et
al. |
April 14, 2011 |
CATALYST PASSING COMPONENT DETERMINING APPARATUS AND EXHAUST
PURIFICATION APPARATUS FOR INTERNAL COMBUSTION ENGINE
Abstract
The present invention comprises a selective reduction type NOx
catalyst located in an exhaust passage and being capable of
purifying NOx with ammonia, an oxidation catalyst located
downstream of the selective reduction type NOx catalyst, an
upstream sensor located between the selective reduction type NOx
catalyst and the oxidation catalyst and having ability to detect
both ammonia and NOx, a downstream sensor located downstream of the
oxidation catalyst and having ability to detect both ammonia and
NOx, and determining means for determining a component passing
through the selective reduction type NOx catalyst, based upon a
relation between output of the upstream sensor and output of the
downstream sensor.
Inventors: |
Sato; Masaaki; (Susono-shi,
JP) ; Oda; Tomihisa; (Numazu-shi, JP) ;
Asaura; Shinya; (Mishima-shi, JP) ; Toshioka;
Shunsuke; (Susono-shi, JP) |
Family ID: |
42316399 |
Appl. No.: |
12/733177 |
Filed: |
January 9, 2009 |
PCT Filed: |
January 9, 2009 |
PCT NO: |
PCT/JP2009/050257 |
371 Date: |
February 16, 2010 |
Current U.S.
Class: |
60/299 |
Current CPC
Class: |
Y02T 10/24 20130101;
F01N 2560/026 20130101; F01N 2610/02 20130101; F01N 3/021 20130101;
F01N 2560/14 20130101; F01N 2560/021 20130101; F01N 2560/06
20130101; Y02T 10/12 20130101; F01N 13/009 20140601; F01N 3/106
20130101; F01N 3/208 20130101; F01N 2610/146 20130101 |
Class at
Publication: |
60/299 |
International
Class: |
F01N 3/18 20060101
F01N003/18 |
Claims
1-5. (canceled)
6. A catalyst passing component determining apparatus comprising: a
selective reduction type NOx catalyst located in an exhaust passage
and being capable of purifying NOx with ammonia; an oxidation
catalyst located downstream of the selective reduction type NOx
catalyst; an upstream sensor located between the selective
reduction type NOx catalyst and the oxidation catalyst and having
ability to detect both ammonia and NOx; a downstream sensor located
downstream of the oxidation catalyst and having ability to detect
both ammonia and NOx; and determining means for determining a
component passing through the selective reduction type NOx
catalyst, based upon a relation between output of the upstream
sensor and output of the downstream sensor.
7. A catalyst passing component determining apparatus according to
claim 6, wherein the determining means determines that the NOx
passes when the output of the upstream sensor and the output of the
downstream sensor change in a similar manner from target outputs
thereof.
8. A catalyst passing component determining apparatus according to
claim 6, wherein the determining means determines that the ammonia
passes when an output change of the upstream sensor from the target
output and an output change of the downstream sensor from the
target output each have a different tendency.
9. A catalyst passing component determining apparatus according to
claim 7, wherein the determining means determines that the ammonia
passes when an output change of the upstream sensor from the target
output and an output change of the downstream sensor from the
target output each have a different tendency.
10. An exhaust purification apparatus for an internal combustion
engine comprising: the catalyst passing component determining
apparatus according to claim 6.
11. An exhaust purification apparatus for an internal combustion
engine according to claim 10 comprising: reducing agent supplying
means for supplying a reducing agent to the selective reduction
type NOx catalyst, wherein the reducing agent supplying means
controls an addition reducing agent amount to the selective
reduction type NOx catalyst based upon a determination result of
the catalyst passing component determining apparatus.
Description
TECHNICAL FIELD
[0001] The present invention relates to a catalyst passing
component determining apparatus for determining a component passing
through a selective reduction type NOx catalyst and an exhaust
purification apparatus for an internal combustion engine equipped
with the catalyst passing component determining apparatus.
BACKGROUND ART
[0002] There is generally known an exhaust purification apparatus
including a NOx catalyst for purifying nitrogen oxides (NOx)
contained in an exhaust gas, as the exhaust purification apparatus
arranged in an exhaust system for an internal combustion engine
such as a diesel engine. Various types of the NOx catalysts are
known, but among them, there is well known a selective reduction
type NOx catalyst (SCR: Selective Catalytic Reduction)
(hereinafter, referred to as SCR catalyst) for reducing and
removing NOx by addition of a reducing agent. Urea is known as the
reducing agent and urea water (urea solution) is usually injected
and supplied in an exhaust gas upstream of the catalyst. When the
urea water receives heat from the exhaust gas or the catalyst,
ammonia is generated therefrom, thereby reducing NOx on the SCR
catalyst. In a case of using the urea as the reducing agent in the
SCR catalyst, a purifying performance of NOx therein varies in
correspondence to an addition amount of the urea water, and the
addition amount of the urea water has an appropriate range
depending on an engine operating state. When the addition amount of
the urea water is less than the appropriate amount, in the SCR
catalyst the NOx can be not purified sufficiently and the NOx
passes through the SCR catalyst as it is (NOx slip). On the other
hand, when the addition amount of the urea water exceeds the
appropriate range and the urea water is excessive, the extra
ammonia passes through the SCR catalyst as it is (ammonia slip).
Therefore, it is important to appropriately check generation of the
NOx slip and the ammonia slip in the SCR catalyst.
[0003] For example, Patent Document 1 discloses an exhaust
purification apparatus for an internal combustion engine provided
with a SCR catalyst located in an exhaust passage for selectively
reducing NOx in the exhaust gas by adding urea water thereto and a
NOx sensor located downstream of the SCR catalyst to detect NOx and
ammonia and outputting a value in accordance with each
concentration thereof. The exhaust purification apparatus is
configured so that, when a deviation between an output value of the
NOx sensor and an appropriate NOx concentration exceeds a
predetermined value, the addition amount of the urea water is
reduced to check a change of the NOx concentration deviation due to
reduction of the addition amount of the urea water, thus making
determination of the NOx slip and the ammonia slip.
[0004] Patent Document 1: Japanese Patent Laid-Open No.
2008-157136
DISCLOSURE OF THE INVENTION
[0005] In order to determine the NOx slip or the ammonia slip with
the exhaust purification apparatus described in Patent Document 1,
it is required that the addition amount of the urea water is
changed and a change of the output value of the NOx sensor due to
the change is observed. Therefore, making such a determination
raises a problem of possibly promoting the NOx slip intentionally.
Further, since the change of the output value of the NOx sensor is
thus observed by changing the addition amount of the urea water,
the NOx slip or the ammonia slip can not be determined quickly and
at an appropriate time.
[0006] Therefore, the present invention is made in view of the
foregoing problem and an object of the present invention is to
appropriately determine the NOx slip and the ammonia slip.
[0007] In order to accomplish the above object, the present
invention provides a catalyst passing component determining
apparatus comprising a selective reduction type NOx catalyst
located in an exhaust passage and being capable of purifying NOx
with ammonia, an oxidation catalyst located downstream of the
selective reduction type NOx catalyst, an upstream sensor located
between the selective reduction type NOx catalyst and the oxidation
catalyst and having ability to detect both ammonia and NOx, a
downstream sensor located downstream of the oxidation catalyst and
having ability to detect both ammonia and NOx, and determining
means for determining a component passing through the selective
reduction type NOx catalyst based upon a relation between output of
the upstream sensor and output of the downstream sensor.
[0008] For example, the determining means may determine that the
NOx passes when the output of the upstream sensor and the output of
the downstream sensor change in a similar manner from target
outputs thereof. In addition, the determining means may determine
that the ammonia passes when an output change of the upstream
sensor from the target output and an output change of the
downstream sensor from the target output each have a different
tendency.
[0009] It should be noted that the present invention relates to an
exhaust purification apparatus for an internal combustion engine
equipped with any of various types of catalyst passing component
determining apparatuses. The exhaust purification apparatus for the
internal combustion engine is preferably provided with reducing
agent supplying means for supplying reducing agent to the selective
reduction type NOx catalyst, wherein the reducing agent supplying
means may control an addition reducing agent amount to the
selective reduction type NOx catalyst based upon a determination
result of the catalyst passing component determining apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a schematic diagram showing a catalyst passing
component determining apparatus according to an embodiment of the
present invention;
[0011] FIG. 2A is a graph in regard to a state when NOx passes
through a SCR catalyst and the graph showing an example of a change
in time of output of an upstream NOx sensor;
[0012] FIG. 2B is a graph in regard to a state when NOx passes
through the SCR catalyst and the graph showing an example of a
change in time of output of a downstream NOx sensor;
[0013] FIG. 3 A is a graph in regard to s state when ammonia passes
through the SCR catalyst and the graph showing an example of a
change in time of output of the upstream NOx sensor;
[0014] FIG. 3B is a graph in regard to a state when ammonia passes
through the SCR catalyst and the graph showing an example of a
change in time of output of the downstream NOx sensor;
[0015] FIG. 4 is a flow chart for determining a leak component from
the SCR catalyst;
[0016] FIG. 5 is a schematic system diagram for an internal
combustion engine to which an exhaust purification apparatus for an
internal combustion engine equipped with a determining apparatus
similar to the apparatus in FIG. 1 according to an embodiment in
the present invention is applied;
[0017] FIG. 6 is a flow chart for controlling addition and supply
of urea water; and
[0018] FIG. 7 is a schematic system diagram for an internal
combustion engine to which an exhaust purification apparatus for an
internal combustion engine equipped with a determining apparatus
similar to the apparatus in FIG. 1 according to another embodiment
in the present invention is applied.
BEST MODES FOR CARRYING OUT THE INVENTION
[0019] First, a catalyst passing component determining apparatus
(hereinafter, referred to as determining apparatus) D according to
an embodiment in the present invention will be explained with
reference to FIG. 1. In a schematic diagram in FIG. 1, a SCR
catalyst C1 located in a catalytic converter and an oxidation
catalyst C2 located in the catalytic converter are arranged in an
exhaust passage P in that order (in series) from upstream to
downstream. In addition, a NOx sensor S1 is arranged between the
SCR catalyst C1 and the oxidation catalyst C2 and a NOx sensor S2
is arranged downstream of the oxidation catalyst C2. Since the NOx
sensor S1 is positioned upstream of the NOx sensor S2, it may be
called an upstream sensor, and on the other hand, the NOx sensor S2
may be called a downstream sensor. The NOx sensors S1 and S2 each
are connected electrically to control means or calculation means
such as ECU (not shown in FIG. 1). In addition, the control means
or the calculation means, as described later, determines leak of
NOx or leak of ammonia from the SCR catalyst C1. That is, the
control means or the calculation means each has a function of the
determining means. It should be noted that in FIG. 1, a direction
of an exhaust gas flow is expressed in an arrow.
[0020] The NOx sensors S1 and S2 each have ability for detecting
NOx and ammonia. The NOx sensors S1 and S2 each have a detecting
part provided with a catalyst component (for example, zirconia),
where an O.sub.2 component is first removed from NOx (for example,
NO.sub.2) in the exhaust gas by a function of the catalyst
component and the remaining NO component is decomposed into N.sub.2
and O.sub.2, allowing detection of NOx concentration by measuring
this O.sub.2 amount. Because of such a construction, when ammonia
exists in the NOx sensors S1 and S2, an ammonia component is
oxidized in the detecting part to generate a NO component
(4NH.sub.3+5O.sub.2.fwdarw.4NO+6H.sub.2O), whereby the NOx sensors
S1 and S2 each have the characteristic of detecting also an O.sub.2
amount decomposed from the NOx component. That is, the NOx sensors
S1 and S2 each have the characteristic of detecting also the
ammonia in the exhaust gas similarly to the NOx. It should be noted
that the NOx sensors S1 and S2 may be equipped with the other
construction or each may be equipped with a different construction
as long as the NOx sensors S1 and S2 can respond to both of NOx and
ammonia.
[0021] The control means or the calculation means in the
determining apparatus D determines (detects) leak of NOx or leak of
ammonia from the SCR catalyst C1 based upon a relation between
output of the NOx sensor S1 and output of the NOx sensor S2 as
described below. Here, FIG. 2 (FIG. 2A and FIG. 2B) shows graphs in
regard to a state when NOx passes through the SCR catalyst C1. FIG.
2A shows an example of a change in time of output of the upstream
NOx sensor S1 and FIG. 2B shows an example of a change in time of
output of the downstream NOx sensor S2. On the other hand, FIG. 3
(FIG. 3A and FIG. 3B) shows graphs in regard to a state when
ammonia passes through the SCR catalyst C1. FIG. 3A corresponds to
FIG. 2A and shows an example of a change in time of output of the
upstream NOx sensor S1. FIG. 3B corresponds to FIG. 2B and shows an
example of a change in time of output of the downstream NOx sensor
S2. However, each graph of FIGS. 2 and 3 shows an example of
continuous electrical output (for example, output current or output
voltage) for a predetermined time from the NOx sensors S1 and S2.
In addition, in FIG. 2A or in FIG. 3A, the target output, that is,
the output in a state where the leak of the NOx or the ammonia from
the SCR catalyst does not substantially occur is indicated in an
arrow. It should be noted that the output of each graph in FIG. 2
and FIG. 3 may be a value found by converting the electrical output
from each of the sensors S1 and S2. That is, the control means or
the calculation means in the determining apparatus D may use, at
the time of determining the leak of the NOx or the leak of the
ammonia from the SCR catalyst C1, numerical values found by
calculation on the basis of output signals from the NOx sensor S1
and S2, for example, a NOx concentration, as the output of the NOx
sensor S1 or the output of the NOx sensor S2. This NOx
concentration reflects the existence of both of the NOx and the
ammonia.
[0022] As understood from FIG. 2 and FIG. 3, in a case where NOx
passes through the SCR catalyst C1 and leaks therefrom (in a case
where the NOx slip occurs), the output from the upstream NOx sensor
S1 increases and exceeds the target output, and the output from the
downstream NOx sensor S2 likewise increases. This is because, when
the component leaked from the SCR catalyst C1 is NOx, the NOx is
not processed to be purified in the oxidation catalyst and is led
to the downstream NOx sensor S2. On the other hand, when ammonia
passes through the SCR catalyst C1 and leaks therefrom (in a case
where the ammonia slip occurs), the output from the upstream NOx
sensor S1 increases and exceeds the target output, but the output
of the downstream NOx sensor S2 does not increase. This is because,
in a case where the component leaked from the SCR catalyst C1 is
ammonia, the ammonia is processed to be purified in the oxidation
catalyst C2. It should be noted that, as shown in FIG. 3B, in a
case where the component leaked from the SCR catalyst C1 is
ammonia, the output from the downstream NOx sensor S2 continues to
be substantially in conformity to the target output as shown in a
solid line or possibly changes reversely to an output change
tendency from the upstream NOx sensor S1 as shown in a dotted
line.
[0023] In a case where the NOx slip thus occurs, the output of the
upstream NOx sensor S1 changes in accordance with a NOx amount
leaked and such output change likewise occurs in the downstream NOx
sensor S2. On the other hand, in a case where the ammonia slip thus
occurs, the output of the upstream NOx sensor S1 changes in
accordance with an ammonia amount leaked, but such output change
does not approximately occur in the downstream NOx sensor S2. That
is, when the output of the upstream NOx sensor S1 and the output of
the downstream NOx sensor S2 change similarly from target outputs,
it is determined that NOx passes through the SCR catalyst C1, and
on the other hand, when the output change of the upstream NOx
sensor S1 from the target output thereof differs in tendency from
the output change of the downstream NOx sensor S2 from the target
output thereof, it is determined that ammonia passes through the
SCR catalyst C1. The present invention can determine whether the
component which passes through the SCR catalyst C1 is NOx or
ammonia by using a relation between outputs of the NOx sensors S1
and S2. It should be noted that the target output of the upstream
NOx sensor S1 may be the same as or different from the target
output of the downstream NOx sensor S2.
[0024] An example of the procedure of this determination will be
explained on the basis of a flow chart in FIG. 4. At step S401, the
control means or the calculation means determines whether or not
the output of the upstream NOx sensor S1 is larger than the target
output thereof. When a negative determination is made at step S401,
the process goes to step S403, wherein it is determined that it is
normal as a result. It should be noted that "normal" means a state
where either NOx or ammonia does not leak from the SCR catalyst C1
or the leak amount is within an allowance range.
[0025] On the other hand, when a positive determination is made at
step S401, it is determined at step S405 whether or not the output
of the downstream NOx sensor S2 is larger than the target output
thereof. When a negative determination is made at step S405, the
process goes to step S407, wherein it is determined that ammonia is
leaked (ammonia slip) as a result. On the other hand, when a
positive determination is made at step S405, the process goes to
step S409, wherein it is determined that NOx is leaked (NOx slip)
as a result.
[0026] Such determination control for the SCR catalyst passing
component based upon the flow chart in FIG. 4 can be repeated each
predetermined time when the control means or the calculation means
makes a determination of NOx or ammonia. It should be noted that
such determination control can be performed under various
conditions, for example, may continue to be performed all the way
when an internal combustion engine is operating or may be performed
in a restricted manner only when the internal combustion engine is
in a predetermined operating state.
[0027] It should be noted that it is here determined simply whether
the NOx is leaked or the ammonia is leaked based upon the relation
between output of the upstream NOx sensor S1 and output of the
downstream NOx sensor S2. However, the leak of the NOx or the leak
of the ammonia may be configured to be step by step or continuously
determined by retrieving data in advance defined by experiments
based upon the outputs of both the sensors S1 and S2 at some point
or at plural points. In addition, here NOx sensors are used as the
upstream NOx sensor S1 and the downstream NOx sensor S2, but
instead of them, there may be used various types of sensors which
can respond to NOx and ammonia, that is, produce output in
accordance with the existence thereof.
[0028] Next, an exhaust purification apparatus for an internal
combustion engine (hereinafter, referred to as exhaust purification
apparatus) 5 equipped with the determining apparatus 1 similar to
the above determining apparatus D according to an embodiment of the
present invention will be explained. FIG. 5 is a schematic system
diagram of an internal combustion engine 10 to which the exhaust
purification apparatus 5 is applied. The internal combustion engine
10 is a compression ignition type internal combustion engine for an
automobile, that is, a diesel engine, and in FIG. 5, a part of the
exhaust system extending from an engine body 10' is expressed in a
magnified manner (an intake system, engine internal mechanisms and
the like are omitted). A first catalytic converter 16, a second
catalytic converter 18 and a third catalytic converter 20 are
serially located in the order from the upstream in an exhaust
passage 14 defined by an exhaust pipe 12 in the internal combustion
engine 10. An oxidation catalyst 22 for oxidizing and purifying
unburned components (particularly HC) in the exhaust gas and a DPR
(diesel particulate reduction) catalyst 24 for trapping and burning
particulate matters (PM) in the exhaust gas for removal are
arranged in the first catalytic converter 16 in the order from the
upstream. In addition, a SCR catalyst 26 as a catalyst having a NOx
purification ability for reducing and purifying NOx in the exhaust
gas is located in the second catalytic converter 18. An oxidation
catalyst 28 for processing ammonia passing through the SCR catalyst
26 is located in the third catalytic converter 20. It should be
noted that the SCR catalyst 26 corresponds to the above SCR
catalyst C1 and the oxidation catalyst 28 corresponds to the above
oxidation catalyst C2.
[0029] A urea adding valve 30 is located between the SCR catalyst
26 and the DPR catalyst 24, that is, in an exhaust passage 14m
downstream of the DPR catalyst 24 and upstream of the SCR catalyst
26 for selectively adding urea as a reducing agent to be capable of
adding ammonia to the SCR catalyst 26. The urea is used as the form
of urea water and is injected and supplied in the exhaust passage
14 toward the SCR catalyst 26 downstream of the urea adding valve
30. A urea water tank 36 for reserving the urea water therein is
connected to the urea adding valve 30 through a urea water
supplying passage 34 defined by a urea water supplying pipe 32 for
supplying the urea water to the urea adding valve 30. In addition,
a pump 38 is provided for supplying the urea water under pressure
toward the urea adding valve 30 from the urea water tank 36.
However, a urea concentration of the urea water as the reducing
agent may be 32.5% by weight for restricting freeze of the urea
water in a cold region or the like.
[0030] It should be noted that here, a urea supplying apparatus 40
is configured to include the urea adding valve 30, the urea water
supplying passage 34, the urea water tank 36 and the pump 38.
However, the urea water added from the urea adding valve 30 is here
substantially and directly added to the SCR catalyst 26 through the
exhaust passage 14, but a dispersion plate or the like for
dispersing and directing in a wide range the addition urea to
appropriately supply the addition urea all over the SCR catalyst 26
may be located at an inlet opening of the second catalytic
converter 18 having the SCR catalyst 26 or near it.
[0031] The selective reduction type NOx catalyst, that is, the SCR
catalyst 26 is here configured to have zeolite having Si, O, and Al
as main components and containing Fe ions. The SCR catalyst 26
reduces and purifies NOx (under existence of ammonia generated due
to chemical reaction of addition urea (urea water)) when the
catalyst temperature is within an active temperature region (NOx
purifying temperature region) and the urea is added from the urea
supplying apparatus 40. The urea is supplied as urea water as
described above, and is hydrolyzed and thermally decomposed with
heat in the exhaust passage 14
(CO(NH.sub.2).sub.2.fwdarw.NH.sub.3+HOCN,
HOCN+H.sub.2O.fwdarw.NH.sub.3+CO.sub.2). As a result, ammonia is
generated. That is, when the urea (urea water) is added to the SCR
catalyst 26, the ammonia is supplied on the SCR catalyst 26. This
ammonia reacts to NOx on the SCR catalyst 26 to reduce the NOx. It
should be noted that as an alternative of the SCR catalyst 26,
there may be adopted a catalyst formed by carrying a vanadium
catalyst (V.sub.2O.sub.5) on a surface of a substrate composed of
alumina or the like. The present invention may allow various types
of SCR catalysts.
[0032] The DPR catalyst 24 as one kind of a diesel particulate
filter (DPF) is of a filter structure and carries noble metals on
its surface. That is, the DPR catalyst 24 is a continuously
regenerating type catalyst which uses a catalyst function of the
noble metal to continuously oxidize (burn) particulate matters (PM)
trapped by the filter.
[0033] The oxidation catalyst 22 here has the same construction as
that of the oxidation catalyst 28. The oxidation catalysts 22 and
28 each are formed by carrying noble metals such as platinum (Pt)
in the honeycomb structure. It should be noted that the oxidation
catalyst 22 and the oxidation catalyst 28 each may be configured to
be different from the above construction or the oxidation catalyst
22 may be configured to be different in construction from the
oxidation catalyst 28. The oxidation catalyst 28 may be, as
described above, provided to oxidize the ammonia leaked in the SCR
catalyst 28 for purification processing.
[0034] Here, the oxidation catalyst 22, the DPR catalyst 24 and the
SCR catalyst 26 are arranged in the exhaust passage 14 in that
order from the upstream, but the arrangement order is not limited
thereto. However, the oxidation catalyst 28 is arranged downstream
of the SCR catalyst 26, preferably as in the case of the present
embodiment, downstream of the SCR catalyst 26 and adjacent thereto.
Further, the DPF is not limited to adopt the DPR catalyst 24, but
other types of DPFs may be used. Specially the DPF may be
configured only as a filter structure and may be structured so that
at a point where a continuous operating time of the internal
combustion engine exceeds a predetermined time or a pressure
difference across the DPF is greater than or equal to a
predetermined value, for example, fuel injection timing is delayed
to generate later burning, as a result oxidizing and burning the
trapped particulate matters for regeneration. However, the
regeneration in the predetermined timing of the DPF can be applied
also to the DPR catalyst 24.
[0035] An electronic control unit (ECU) 50 is provided as control
means for managing control of the entire internal combustion engine
10 equipped with the urea supplying apparatus 40. The ECU 50
includes a CPU, a ROM, a RAM, input and output ports, a memory
apparatus and the like. The ECU 50 controls a fuel injection valve
(not shown) or the like so that a desired internal combustion
engine control is performed based upon detection values obtained by
using various sensors or the like. In addition, the ECU 50 controls
the adding valve 30 and the pump 38 so as to control an addition
amount of the urea water and addition timing of the urea water.
[0036] Sensors connected to the ECU 50 include a rotational speed
sensor 52 for detecting an engine rotational speed of the internal
combustion engine 10, a load sensor 54 for detecting an engine
load, further an exhaust temperature sensor 56 for detecting a
temperature of an exhaust gas, and first, second and third NOx
sensors 58, 60 and 62 for detecting a NOx concentration in the
exhaust gas. The rotational speed sensor 52 may be a crank angle
sensor for detecting a crank angle of the internal combustion
engine 10. The load sensor 54 may be an air flow meter sensor or an
accelerator opening sensor. The exhaust temperature sensor 56 is
here located in the exhaust passage 14u upstream of the oxidation
catalyst 22, but may be located in other places. In addition, the
first NOx sensor 58 is located in the exhaust passage 14m
downstream of the DPR catalyst 24 and upstream of the SCR catalyst
26. The second NOx sensor 60 is located in the exhaust passage 14m
downstream of the SCR catalyst 26 and upstream of the oxidation
catalyst 28. The third NOx sensor 62 is located downstream of the
oxidation catalyst 28. However, the first NOx sensor 58 may be
omitted. It should be noted that the second NOx sensor 60
corresponds to the above upstream sensor S1 and the third NOx
sensor 62 corresponds to the above downstream sensor S2. In
addition, each construction of the NOx sensors 58, 60 and 62 is the
same as that of each of the above NOx sensors S1 and S2.
[0037] The reducing agent supplying means included in the ammonia
supplying means is configured to include the urea supplying
apparatus 40, particularly a part of the ECU 50 as the control
means thereof. In addition, the determining means for determining a
component which has passed through the SCR catalyst 26 is
configured to include a part of the ECU 50. The temperature
determining means is configured to include both of temperature
detecting means configured to include the exhaust temperature
sensor 56 and a part of the ECU 50 for detecting or estimating a
temperature of the SCR catalyst 26 and means configured to include
a part of the ECU 50 for determining the temperature based upon the
temperature of the SCR catalyst 26 detected or estimated by the
temperature detecting means. However, the temperature detecting
means may be configured to include the rotational speed sensor 52,
the load sensor 54, and apart of the ECU 50 or may be configured to
include a temperature sensor mounted directly to the SCR catalyst
26 and a part of the ECU 50.
[0038] Here, first, addition and supply control of the urea water
will be explained with reference to a flow chart in FIG. 6.
Execution and suspension of the addition of the urea water in the
addition and supply control of the urea water is controlled in
accordance with a temperature (here, estimated value) of the SCR
catalyst 26. Specially, when the SCR catalyst temperature is within
a predetermined temperature region, the urea water addition is
executed and when the SCR catalyst temperature is not within the
predetermined temperature region, the urea water addition is
suspended.
[0039] The temperature of the SCR catalyst 26 is here found by its
estimation. Specially, the ECU 50 retrieves data which are in
advance defined by experiments and stored therein, based upon an
exhaust temperature detected based upon an output signal from the
exhaust temperature sensor 56, thus estimating the SCR catalyst
temperature. It should be noted that the estimation method is not
limited to the above example. The temperature of the SCR catalyst
26 may be directly detected by using a temperature sensor embedded
in the SCR catalyst 26. Or the temperature of the SCR catalyst 26
may be estimated based upon an engine operating state defined based
upon output signals of the rotational speed sensor 52 and the load
sensor 54.
[0040] At step S601 it is determined whether or not the temperature
of the SCR catalyst 26 is within a predetermined temperature
region. When a negative determination is here made, the process
goes to step S603, wherein the addition of the urea water is
suspended. On the other hand, when a positive determination is made
at step S601, the process goes to step S605, wherein the addition
of the urea water is executed. The predetermined temperature region
at step S601 is here a temperature region (temperature region equal
to or more than a lower limit temperature) where only the lower
limit temperature is defined. This lower limit temperature is, for
example, 200.degree. C. and can be called the minimum active
temperature. The reason for thus defining the predetermined
temperature region is that even if the addition of the urea water
is executed before the SCR catalyst temperature reaches the minimum
active temperature, NOx can not be efficiently reduced. It should
be noted that an upper limit temperature may be defined to the
predetermined temperature region.
[0041] When the positive determination is made at step S601 by
determining that the temperature of the SCR catalyst 26 is within
the predetermined temperature region, that is, when the addition of
the urea water is executed, an addition amount or an addition
timing of the urea water is controlled based mainly upon output
from the first, second, third NOx sensors 58, 60 and 62. Here, the
addition amount or the addition timing of the urea water is
controlled based upon a NOx concentration (or NOx amount relating
to this NOx concentration) in the exhaust gas detected based upon
an output signal from the first NOx sensor 58. A basic addition
amount or a basic addition timing of the urea water thereof is
corrected based upon a NOx slip or an ammonia slip determined based
upon an output signal from the second NOx sensor 60 or the third
NOx sensor 62. Specially by retrieving data which is in advance
defined by experiments and stored therein, with the NOx
concentration detected based upon the output signal from the first
NOx sensor 58, the basic addition amount or the basic addition
timing of the urea water is defined, and based upon them, the pump
38 or the urea adding valve 30 is controlled. When it is, as
described above, determined that the NOx slip occurs, based upon
the output signals from the second NOx sensor 60 and the third NOx
sensor 62, both or one of the basic addition amount or the basic
addition timing of the urea water are corrected so that the
addition amount of the urea water increases. On the other hand,
when it is, as described above, determined that the ammonia slip
occurs, based upon the output signals from the second NOx sensor 60
and the third NOx sensor 62, both or one of the basic addition
amount and the basic addition timing of the urea water are
corrected so that the addition amount of the urea water
decreases.
[0042] It should be noted that the addition control of the urea
water may be controlled so that the NOx concentration downstream of
the SCR catalyst 26 becomes zero and the NOx slip or the ammonia
slip does not occur, and the calculation or the control for it is
not limited to the above embodiment. However, the NOx slip or the
ammonia slip may be determined based upon a relation between
outputs of the two sensors 60 and 62 which are located to interpose
the oxidation catalyst 28 downstream of the SCR catalyst 26
therebetween. It should be noted that in a case where the first NOx
sensor 58 is not provided, for example, a basic urea injection
amount based upon an engine operating state (for example, engine
rotational speed and engine load) may be feedback-corrected based
upon the determination result based upon output signals from the
two sensors 60 and 62 so that the NOx slip or the ammonia slip does
not occur. Since the SCR catalyst 26 can reduce NOx only under
existence of ammonia, the urea water may be added all the time.
[0043] Next, an exhaust purification apparatus 5A in another
embodiment in the present invention equipped with the above
determining apparatus 1 will be explained. The exhaust purification
apparatus 5A is configured so that the ammonia supplying means
includes a catalyst having a generation capability of ammonia. That
is, the exhaust purification apparatus 5A, which is different from
the exhaust purification apparatus 5, is not equipped with the urea
adding valve and the urea water tank for adding the urea water.
Hereinafter, the exhaust purification apparatus 5A will be
explained. It should be noted that FIG. 7 is a schematic diagram of
an internal combustion engine 10A to which the exhaust purification
apparatus 5A is applied. However, hereinafter, components identical
or similar to those explained in the above embodiment are referred
to as identical codes and the overlap explanation is omitted.
[0044] A eleventh catalytic converter 100, a twelfth catalytic
converter 102, a thirteenth catalytic converter 104, a fourteenth
catalytic converter 18, and a fifteenth catalytic converter 20 are
serially provided in the exhaust passage 14 for the internal
combustion engine 10 in that order from the upstream. In addition,
the oxidation catalyst 22 is located in the eleventh catalytic
converter 100, and the DPR catalyst 24 is located in the thirteenth
catalytic converter 104. In addition, the SCR catalyst 26 is
located in the fourteenth catalytic converter 18, and the oxidation
catalyst 28 is located in the fifteenth catalytic converter 20. It
should be noted that the fourteenth catalytic converter 18
corresponds to the above second catalytic converter, the fifteenth
catalytic converter corresponds to the above third catalytic
converter, and the sensors 60 and 62 are located to interpose the
oxidation catalyst 28 in the fifteenth catalytic converter 20
therebetween.
[0045] Here, a catalyst 106 having ability for generating ammonia
is located in the twelfth catalytic converter. The catalyst 106 in
the twelfth catalytic converter functions to generate ammonia from
a specific component in the exhaust gas. Here, since the catalyst
106 functions to generate ammonia from NOx, the catalyst 106 can be
called a NOx removal catalyst. The catalyst 106 functions, for
example, in such a manner as to trap NO.sub.2 ions in the exhaust
gas in an operating state where fuel burns in a combustion chamber
under a lean environment and facilitate reaction between the
NO.sub.2 ions and H.sub.2 in the exhaust gas for generating ammonia
in an engine operating state where fuel burns in the combustion
chamber under a rich environment. It should be noted that the ECU
50 may control a fuel injection amount or the like in such a manner
as to generate such ammonia generating reaction. However, the
catalyst 106 is not limited to this construction and may be
configured to have various constructions.
[0046] As described above, the present invention is explained with
reference to the embodiment or the like, but various aspects of the
above embodiment may be partially or entirely combined unless it is
contradictory.
[0047] In addition, the present invention is applicable also to an
internal combustion engine other than a compression ignition type
internal combustion engine, for example, a spark ignition type
internal combustion engine. It should be noted that the present
invention is applicable to an apparatus emitting an exhaust gas
containing NOx, which is other than the internal combustion
engine.
[0048] As described above, the present invention is explained with
reference to the various kinds of embodiments, but the present
invention is not limited thereto. The present invention can include
all variations and applications contained in the spirit of the
present invention as claimed in claims and its equivalents.
Accordingly, the present invention should not be interpreted in a
limited way and can be applied to any other technology within the
concept of the present invention.
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