U.S. patent application number 13/314888 was filed with the patent office on 2012-04-05 for exhaust gas purification apparatus of engine and exhaust gas purification method of engine.
This patent application is currently assigned to UD TRUCKS CORPORATION. Invention is credited to Nobuhiko MASAKI.
Application Number | 20120079812 13/314888 |
Document ID | / |
Family ID | 43356425 |
Filed Date | 2012-04-05 |
United States Patent
Application |
20120079812 |
Kind Code |
A1 |
MASAKI; Nobuhiko |
April 5, 2012 |
EXHAUST GAS PURIFICATION APPARATUS OF ENGINE AND EXHAUST GAS
PURIFICATION METHOD OF ENGINE
Abstract
A control unit calculates an amount of produced ammonia from an
amount of a dosed urea aqueous solution according to an engine
operation state, and calculates a NOx purification ratio in the
case of dosing the amount of the dosed urea aqueous solution
according to the operation state to exhaust gas on an exhaust
upstream side of an SCR catalyst. Moreover, the control unit
estimates an amount of adsorbed ammonia to the SCR catalyst based
on the produced ammonia amount and the NOx purification ratio.
Then, the control unit subtracts the amount of the urea aqueous
solution corresponding to the amount of the adsorbed ammonia from
the amount of the dosed urea aqueous solution according to the
operation state to correct the amount of the dosed urea aqueous
solution, and controls the dosing of the urea aqueous solution
based on the corrected amount of the dosed urea aqueous
solution.
Inventors: |
MASAKI; Nobuhiko; (Ageo-shi,
JP) |
Assignee: |
UD TRUCKS CORPORATION
|
Family ID: |
43356425 |
Appl. No.: |
13/314888 |
Filed: |
December 8, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2010/060092 |
Jun 15, 2010 |
|
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|
13314888 |
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Current U.S.
Class: |
60/274 ;
60/287 |
Current CPC
Class: |
F01N 2610/02 20130101;
B01D 53/90 20130101; B01D 2255/911 20130101; F01N 13/0097 20140603;
B01D 2251/2067 20130101; F01N 2900/1402 20130101; Y02T 10/24
20130101; F01N 3/208 20130101; F01N 2900/1616 20130101; B01D
53/9495 20130101; B01D 53/9431 20130101; Y02T 10/12 20130101; F01N
2900/1622 20130101; B01D 53/9436 20130101 |
Class at
Publication: |
60/274 ;
60/287 |
International
Class: |
F01N 3/18 20060101
F01N003/18; F01N 3/24 20060101 F01N003/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 18, 2009 |
JP |
2009-145276 |
Claims
1. An exhaust gas purification apparatus of an engine, comprising:
a selective reduction catalyst disposed in an exhaust pipe of the
engine to selectively reduce a nitrogen oxide by use of ammonia
produced from an urea aqueous solution; a dosing unit which doses
the urea aqueous solution to exhaust gas on an exhaust upstream
side of the selective reduction catalyst; and a control unit having
a built-in computer, wherein the control unit calculates an amount
of the produced ammonia from an amount of the dosed urea aqueous
solution in accordance with an engine operation state, calculates a
purification ratio of the nitrogen oxide by the selective reduction
catalyst on the basis of a first nitrogen oxide concentration in
the exhaust gas discharged from the engine and a second nitrogen
oxide concentration in the exhaust gas passed through the selective
reduction catalyst, performs calculation to estimate an amount of
the ammonia to be adsorbed to the selective reduction catalyst on
the basis of the amount of the produced ammonia and the
purification ratio of the nitrogen oxide, corrects the amount of
the urea aqueous solution to be dosed in accordance with the engine
operation state on the basis of the amount of the adsorbed ammonia,
and controls an operation of the dosing unit on the basis of the
corrected amount of the urea aqueous solution to be dosed.
2. The exhaust gas purification apparatus of the engine according
to claim 1, wherein the control unit subtracts an amount of the
adsorbed urea aqueous solution corresponding to the amount of the
adsorbed ammonia from the amount of the urea aqueous solution to be
dosed in accordance with the engine operation state, to correct the
amount of the urea aqueous solution to be dosed in accordance with
the engine operation state.
3. The exhaust gas purification apparatus of the engine according
to claim 1, wherein the control unit further corrects the amount of
the adsorbed ammonia on the basis of an ammonia concentration in
the exhaust gas passed through the selective reduction
catalyst.
4. The exhaust gas purification apparatus of the engine according
to claim 1, wherein the amount of the urea aqueous solution to be
dosed in accordance with the engine operation state is calculated
from an exhaust temperature, a rotation speed and a load of the
engine.
5. An exhaust gas purification apparatus of an engine comprising: a
selective reduction catalyst disposed in an exhaust pipe of the
engine to selectively reduce a nitrogen oxide by use of ammonia
produced from an urea aqueous solution; a dosing unit which doses
the urea aqueous solution to exhaust gas on an exhaust upstream
side of the selective reduction catalyst; and a control unit having
a built-in computer, wherein the control unit calculates a
purification ratio of the nitrogen oxide by the selective reduction
catalyst on the basis of a first nitrogen oxide concentration in
the exhaust gas discharged from the engine and a second nitrogen
oxide concentration in the exhaust gas passed through the selective
reduction catalyst, perform calculation to estimate an amount of
the adsorbed urea aqueous solution corresponding to the ammonia to
be adsorbed to the selective reduction catalyst on the basis of an
amount of the urea aqueous solution to be dosed in accordance with
an engine operation state and the purification ratio of the
nitrogen oxide, corrects the amount of the urea aqueous solution to
be dosed in accordance with the engine operation state on the basis
of the amount of the adsorbed urea aqueous solution, and controls
an operation of the dosing unit on the basis of the corrected
amount of the urea aqueous solution to be dosed.
6. The exhaust gas purification apparatus of the engine according
to claim 5, wherein the control unit subtracts the amount of the
adsorbed urea aqueous solution from the amount of the urea aqueous
solution to be dosed in accordance with the engine operation state,
to correct the amount of the urea aqueous solution to be dosed in
accordance with the engine operation state.
7. The exhaust gas purification apparatus of the engine according
to claim 5, wherein the control unit further corrects the amount of
the adsorbed urea aqueous solution on the basis of an ammonia
concentration in the exhaust gas passed through the selective
reduction catalyst.
8. The exhaust gas purification apparatus of the engine according
to claim 5, wherein the amount of the urea aqueous solution to be
dosed in accordance with the engine operation state is calculated
based on an exhaust temperature, a rotation speed and a load of the
engine.
9. An exhaust gas purification apparatus of an engine which
corrects an amount of an urea aqueous solution to be dosed in
accordance with an engine operation state on the basis of a
purification ratio of a nitrogen oxide by a selective reduction
catalyst, and doses the corrected amount of the urea aqueous
solution to be dosed to exhaust gas on an exhaust upstream side of
the selective reduction catalyst.
10. An exhaust gas purification method of an engine, in which a
control unit having a built-in computer corrects an amount of an
urea aqueous solution to be dosed in accordance with an engine
operation state on the basis of a purification ratio of a nitrogen
oxide by a selective reduction catalyst, and doses the corrected
amount of the urea aqueous solution to be dosed to exhaust gas on
an exhaust upstream side of the selective reduction catalyst.
Description
[0001] This application is a continuation of PCT/JP2010/060092,
filed on Jun. 15, 2010.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an exhaust gas purification
apparatus of an engine, which selectively reduces a nitrogen oxide
(NOx) in exhaust gas by use of ammonia produced from a urea aqueous
solution, and an exhaust gas purification method of an engine.
[0004] 2. Description of Related Art
[0005] As a catalytic purification system which removes NOx
included in exhaust gas of an engine, there has been proposed an
exhaust gas purification apparatus as disclosed in Japanese
Laid-open Patent Application Publication No. 2008-261253. This
exhaust gas purification apparatus injection-supplies an ammonia
solution with a flow rate in accordance with an engine operation
state to the exhaust gas on an exhaust upstream side of a selective
catalytic reduction (SCR) catalyst disposed in an engine exhaust
pipe, and selectively reduces NOx in the exhaust gas by the SCR
catalyst, to convert NOx into harmless components.
[0006] Meanwhile, ammonia which does not reduce NOx in exhaust gas
but is adsorbed to an SCR catalyst and ammonia which does not
reduce NOx in the exhaust gas but passes through the SCR catalyst
and is discharged to the atmosphere are present, depending on an
engine operation state. The ammonia which has passed through the
SCR catalyst is oxidized by an oxidation catalyst disposed on an
exhaust downstream side of the the SCR catalyst, whereby it is
possible to suppress the discharging the ammpnia into the
atmosphere. However, in a conventional proposed technology, the
ammonia adsorbed to the SCR catalyst is not taken into
consideration, but a flow rate of a urea aqueous solution to be
injection-supplied to the exhaust gas on an exhaust upstream side
of the SCR catalyst is controlled. Therefore, when an amount of the
ammonia adsorbed to the SCR catalyst has a saturated state, the
ammonia to be oxidized by the oxidation catalyst increases.
Consequently, in the conventional proposed technology, an amount of
ammonia which does not contribute to NOx purification is large, and
it has not been easily considered that the urea aqueous solution is
effectively utilized.
[0007] Therefore, taking into consideration the above problems up
to now, an object of one aspect of the present invention is to
provide an exhaust gas purification apparatus of an engine which
estimates an amount of ammonia adsorbed to an SCR catalyst to
control the dosing of a urea aqueous solution in accordance with
the estimation result, to achieve the effective utilization of the
urea aqueous solution, and an exhaust gas purification method of an
engine.
SUMMARY OF THE INVENTION
[0008] In consequence, an exhaust gas purification apparatus of an
engine according to an embodiment of the present invention includes
a selective reduction catalyst disposed in an exhaust pipe of the
engine to selectively reduce NOx by use of ammonia produced from a
urea aqueous solution, an dosing unit which doses the urea aqueous
solution to an exhaust gas on an exhaust upstream side of the
selective reduction catalyst, and a control unit having a built-in
computer.
[0009] Moreover, in the exhaust gas purification apparatus of the
engine according to a first embodiment, the control unit calculates
an amount of the produced ammonia from an amount of the dosed urea
aqueous solution in accordance with an engine operation state, and
calculates a purification ratio of NOx by the selective reduction
catalyst on the basis of a first NOx concentration in the exhaust
gas discharged from the engine and a second NOx concentration in
the exhaust gas passed through the selective reduction catalyst.
Moreover, the control unit performs calculation to estimate an
amount of the ammonia to be adsorbed to the selective reduction
catalyst on the basis of the amount of the produced ammonia and the
purification ratio of NOx, and corrects the amount of the urea
aqueous solution to be dosed in accordance with the engine
operation state on the basis of the amount of the adsorbed ammonia.
Afterward, the control unit controls an operation of the dosing
unit on the basis of the corrected amount of the urea aqueous
solution to be dosed.
[0010] Moreover, in the exhaust gas purification apparatus of the
engine according to a second embodiment, the control unit
calculates a purification ratio of NOx by the selective reduction
catalyst on the basis of a first NOx concentration in the exhaust
gas discharged from the engine and a second NOx concentration in
the exhaust gas passed through the selective reduction catalyst,
and performs calculation to estimate an amount of the adsorbed urea
aqueous solution corresponding to ammonia to be adsorbed to the
selective reduction catalyst on the basis of an amount of the urea
aqueous solution to be dosed in accordance with an engine operation
state and the purification ratio of NOx. Moreover, the control unit
corrects the amount of the urea aqueous solution to be dosed in
accordance with the engine operation state on the basis of the
amount of the adsorbed urea aqueous solution, and then controls an
operation of the dosing unit on the basis of the corrected amount
of the urea aqueous solution to be dosed.
[0011] On the other hand, in an exhaust gas purification method of
an engine according to an embodiment of the present invention, a
control unit corrects an amount of an urea aqueous solution to be
dosed in accordance with an engine operation state on the basis of
a purification ratio of NOx by a selective reduction catalyst, and
doses the corrected amount of the urea aqueous solution to be dosed
to an exhaust upstream side of the selective reduction
catalyst.
[0012] According to an embodiment of the present invention, in the
case in which ammonia is adsorbed to a selective reduction
catalyst, an amount of an urea aqueous solution to be dosed in
accordance with an engine operation state is thus corrected, so
that it is possible to suppress the ammonia passed through the
selective reduction catalyst and discharged to the atmosphere,
while acquiring the ammonia required for NOx purification by the
selective reduction catalyst. In consequence, it is possible to
achieve the effective utilization of the urea aqueous solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is an overall block diagram showing an example of an
exhaust gas purification apparatus which embodies the present
invention;
[0014] FIG. 2 is a flowchart showing an example of a control
program; and
[0015] FIG. 3 is a flowchart showing another example of the control
program.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Hereinafter, the present invention will be described in
detail with reference to the accompanying drawings.
[0017] FIG. 1 shows an embodiment of an exhaust gas purification
apparatus which embodies the present invention.
[0018] In an exhaust pipe 14 connected to an exhaust manifold 12 of
an engine 10, a nitrogen oxidation catalyst 16 which oxidizes
nitrogen monoxide (NO) into nitrogen dioxide (NO.sub.2), an
injection nozzle 18 which injection-supplies a urea aqueous
solution, an SCR catalyst 20 which selectively reduces NOx by use
of ammonia produced from the urea aqueous solution and an ammonia
oxidation catalyst 22 which oxidizes the ammonia passed through the
SCR catalyst 20 are arranged in this order along an exhaust
flow-through direction. Moreover, the urea aqueous solution stored
in a reducing agent tank 24 is supplied to the injection nozzle 18
through a reducing agent dosing unit 26 having a built-in pump and
a built-in flow rate control valve therein. It is to be noted that
the injection nozzle 18, the reducing agent tank 24 and the
reducing agent dosing unit 26 are included to constitute an example
of a dosing unit.
[0019] Here, the reducing agent dosing unit 26 may have a
constitution which is divided into a pump module having the
built-in pump, and a dosing module having the built-in flow rate
control valve.
[0020] To the exhaust pipe 14 positioned on an exhaust upstream
side of the nitrogen oxidation catalyst 16, a NOx sensor 28 which
measures a NOx concentration Cu in exhaust gas discharged from the
engine 10 is attached. On the other hand, to the exhaust pipe 14
positioned on an exhaust downstream side of the ammonia oxidation
catalyst 22, a NOx sensor 30 which measures a NOx concentration Cd
in the exhaust gas passed through the ammonia oxidation catalyst 22
is attached. Moreover, on the exhaust upstream side of the SCR
catalyst 20, specifically, to the exhaust pipe 14 positioned
between the injection nozzle 18 and the SCR catalyst 20, an exhaust
temperature sensor 32 which measures a temperature (an exhaust
temperature) T of the exhaust gas flowing into the SCR catalyst 20
is attached to. It is to be noted that in an exhaust gas
purification apparatus in which the ammonia oxidation catalyst 22
is not disposed, the NOx sensor 30 measures the NOx concentration
Cd in the exhaust gas passed through the SCR catalyst 20.
[0021] Each measurement signal of the NOx sensors 28 and 30 and the
exhaust temperature sensor 32 is input into a reducing agent dosing
control unit 34 having a built-in computer. Moreover, the reducing
agent dosing control unit 34 is connected to an engine control unit
36 which electronically controls the engine 10 via a controller
area network (CAN) and the like so that a rotation speed Ne and a
load Q can appropriately be read as an engine operation state.
[0022] Here, as the load Q of the engine 10, for example, a fuel
injection amount, an intake air flow, an intake air pressure, a
supercharging pressure, an accelerator open degree, a throttle open
degree or the like can be applied. Moreover, the rotation speed Ne
and load Q of the engine 10 are not limited to a constitution to be
read from the engine control unit 36, but may directly be measured
by a known sensor.
[0023] Moreover, the reducing agent dosing control unit 34 executes
a control program stored in a read only memory (ROM) or the like,
to electronically control the reducing agent dosing unit 26 so that
the ammonia is supplied to the SCR catalyst 20 in accordance with
the engine operation state.
[0024] In such an exhaust gas purification apparatus, the urea
aqueous solution injection-supplied (dosed) through the injection
nozzle 18 is hydrolyzed by using exhaust heat and vapor in the
exhaust gas, and is converted into ammonia which functions as a
reducing agent. It is known that this ammonia selectively reduces
NOx in the exhaust gas in the SCR catalyst 20, and is converted
into harmless water (H.sub.2O) and nitrogen (N.sub.2). At this
time, NO is oxidized to NO.sub.2 in the nitrogen oxidation catalyst
16 to enhance a NOx purification ratio by the SCR catalyst 20,
whereby a ratio between NO and NO.sub.2 in the exhaust gas is
improved to be suitable for the selective reductive reaction. On
the other hand, the ammonia passed through the SCR catalyst 20 is
oxidized through the ammonia oxidation catalyst 22 disposed on the
exhaust downstream side the SCR catalyst 20, so that the ammonia is
prevented from being discharged as it is to the atmosphere.
[0025] FIG. 2 shows an example of a control program to be executed
by the reducing agent dosing control unit 34 with the start of the
engine 10 as an opportunity.
[0026] In step 1 (abbreviated as "S1" in the drawings. This also
applies to the following description.), the reducing agent dosing
control unit 34 reads, as the engine operation state, the exhaust
temperature T from the exhaust temperature sensor 32 and the
rotation speed Ne and the load Q from the engine control unit
36.
[0027] In step 2, the reducing agent dosing control unit 34
calculates an amount of the urea aqueous solution to be dosed in
accordance with the engine operation state. Specifically, the
reducing agent dosing control unit 34 refers to a control map in
which the amount of the dosed urea aqueous solution adapted to the
exhaust temperature, the rotation speed and the load is set, to
obtain the amount of the urea aqueous solution to be dosed in
accordance with the exhaust temperature T, the rotation speed Ne
and the load Q.
[0028] In step 3, the reducing agent dosing control unit 34
electronically controls each of the pump and flow rate control
valve of the reducing agent dosing unit 26, in accordance with the
amount of the urea aqueous solution to be dosed so that the urea
aqueous solution is injection-supplied through the injection nozzle
18 in accordance with the engine operation state.
[0029] In step 4, the reducing agent dosing control unit 34
calculates an amount of the produced ammonia from the amount of the
dosed urea aqueous solution, by use of a condition that two mols of
ammonia is produced from one mol of urea.
[0030] In step 5, the reducing agent dosing control unit 34 reads
the NOx concentrations Cu and Cd from the NOx sensors 28 and 30,
respectively.
[0031] In step 6, the reducing agent dosing control unit 34
calculates the NOx purification ratio by the SCR catalyst 20 by use
of an equation "NOx purification ratio equals NOx concentration Cu
minus NOx concentration Cd divided by NOx concentration Cu".
[0032] In step 7, the reducing agent dosing control unit 34 perform
calculation to estimate an amount of the ammonia to be adsorbed to
the SCR catalyst 20 by use of an equation "the amount of the
adsorbed ammonia equals the amount of the produced ammonia
multiplied by 1 minus NOx purification ratio, both terms in the
parentheses". In short, the reducing agent dosing control unit 34
presumes that the urea aqueous solution which does not contribute
to the NOx purification in the urea aqueous solution
injection-supplied through the injection nozzle 18 has been
adsorbed to the SCR catalyst 20 in ammonia state.
[0033] In step 8, the reducing agent dosing control unit 34 reads,
as the engine operation state, the exhaust temperature T from the
exhaust temperature sensor 32 and the rotation speed Ne and the
load Q from the engine control unit 36.
[0034] In step 9, the reducing agent dosing control unit 34
calculates the amount of the urea aqueous solution to be dosed in
accordance with the engine operation state by a method similar to
the step 2.
[0035] In step 10, the reducing agent dosing control unit 34
calculates the amount of the urea aqueous solution corresponding to
the amount of the adsorbed ammonia estimated in the step 7, by use
of a condition that one mol of ammonia is produced from 1/2 mol of
urea.
[0036] In step 11, the reducing agent dosing control unit 34
subtracts the amount of the urea aqueous solution from the amount
of the dosed urea aqueous solution, to correct the amount of the
urea aqueous solution to be dosed. That is, it is noted that the
ammonia adsorbed to the SCR catalyst 20 is utilized for the
purification of NOx in the exhaust gas, and thus, the reducing
agent dosing control unit 34 decreases the amount of the urea
aqueous solution to be dosed. Then, upon the completion of the
correction of the amount of the urea aqueous solution to be dosed,
the reducing agent dosing control unit 34 returns the processing to
the step 3.
[0037] According to such an exhaust gas purification apparatus, the
amount of the urea aqueous solution to be dosed in accordance with
the engine operation state is dosed to the exhaust upstream of the
SCR catalyst 20. Afterward, the purification ratio of NOx to be
selectively reduced by the SCR catalyst 20 is obtained on the basis
of the NOx concentration in the exhaust gas discharged from the
engine 10 and the NOx concentration in the exhaust gas passed
through the ammonia oxidation catalyst 22. Moreover, it is
considered that in the amount of the produced ammonia obtained from
the amount of the dosed urea aqueous solution in accordance with
the engine operation state, an amount represented by "1-NOx
purification ratio" is the amount of the ammonia to be adsorbed to
the SCR catalyst 20. Then, the amount of the urea aqueous solution
corresponding to the amount of the adsorbed ammonia is subtracted
from the amount of the urea aqueous solution to be dosed in
accordance with the engine operation state to correct the amount of
the urea aqueous solution to be dosed, and on the basis of the
corrected amount of the urea aqueous solution to be dosed, the
dosing of the urea aqueous solution is controlled. In short, the
amount of the urea aqueous solution to be dosed in accordance with
the engine operation state is corrected on the basis of the NOx
purification ratio by the SCR catalyst 20, and the corrected amount
of the urea aqueous solution to be dosed is dosed to the exhaust
gas on the exhaust upstream side of the SCR catalyst 20.
[0038] Therefore, in the case in which the ammonia is adsorbed to
the SCR catalyst 20, the amount of the urea aqueous solution to be
dosed in accordance with the engine operation state is thus
decreased and corrected. Therefore, the ammonia passed through the
SCR catalyst 20 and discharged to the atmosphere can be suppressed,
while acquiring the ammonia required for the NOx purification by
the SCR catalyst 20. In consequence, the effective utilization of
the urea aqueous solution can be achieved. Moreover, the amount of
the ammonia which is not adsorbed to the SCR catalyst 20 but is
introduced into the ammonia oxidation catalyst 22 decreases.
Therefore, the ammonia oxidation catalyst 22 can be miniaturized,
and the decrease of a weight and cost thereof can be expected.
[0039] FIG. 3 shows another example of the control program to be
executed by the reducing agent dosing control unit 34 with the
start of the engine 10 as the opportunity. Here, the description of
the processing which is common to the control program shown in FIG.
2 is simplified for a purpose of excluding redundant
description.
[0040] In step 21, the reducing agent dosing control unit 34 reads,
as the engine operation state, the exhaust temperature T from the
exhaust temperature sensor 32 and the rotation speed Ne and the
load Q from the engine control unit 36.
[0041] In step 22, the reducing agent dosing control unit 34
calculates the amount of the urea aqueous solution to be dosed in
accordance with the engine operation state.
[0042] In step 23, the reducing agent dosing control unit 34
electronically controls each of the pump and flow rate control
valve of the reducing agent dosing unit 26, in accordance with the
amount of the urea aqueous solution to be dosed.
[0043] In step 24, the reducing agent dosing control unit 34 reads
the NOx concentrations Cu and Cd from the NOx sensors 28 and 30,
respectively.
[0044] In step 25, the reducing agent dosing control unit 34
calculates the NOx purification ratio by the SCR catalyst 20 by use
of the equation "NOx purification ratio equals NOx concentration Cu
minus NOx concentration Cd divided by NOx concentration Cu".
[0045] In step 26, the reducing agent dosing control unit 34
perform calculation to estimate the amount of the adsorbed urea
aqueous solution corresponding to the amount of the ammonia to be
adsorbed to the SCR catalyst 20 by use of an equation "the amount
of the adsorbed urea aqueous solution equals the amount of the
dosed urea aqueous solution multiplied by 1-NOx purification ratio,
both terms in the parentheses".
[0046] In step 27, the reducing agent dosing control unit 34 reads,
as the engine operation state, the exhaust temperature T from the
exhaust temperature sensor 32 and the rotation speed Ne and the
load Q from the engine control unit 36.
[0047] In step 28, the reducing agent dosing control unit 34
calculates the amount of the urea aqueous solution to be dosed in
accordance with the engine operation state.
[0048] In step 29, the reducing agent dosing control unit 34
subtracts the amount of the adsorbed urea aqueous solution from the
amount of the dosed urea aqueous solution, to correct the amount of
the urea aqueous solution to be dosed. Afterward, the unit returns
the processing to the step 23.
[0049] According to such an exhaust gas purification apparatus, in
addition to the function and effect of the above example, the
amount of the urea aqueous solution to be dosed is corrected on the
basis of the urea aqueous solution, so that the control can be
simplified.
[0050] It is to be noted that, in the case in which the amount of
the adsorbed ammonia or the amount of the adsorbed urea aqueous
solution corresponding thereto are calculated in the steps 7 and
26, the amount of the adsorbed ammonia or the amount of the
adsorbed urea aqueous solution may be corrected on the basis of an
ammonia concentration measured by an ammonia sensor attached to the
exhaust pipe 14 positioned on the exhaust downstream side of the
ammonia oxidation catalyst 22. In this case, the amount of the
adsorbed ammonia or the amount of the adsorbed urea aqueous
solution is obtained in consideration of the amount of the ammonia
passed through the ammonia oxidation catalyst 22, and hence control
accuracy can be enhanced. Moreover, the effective utilization of
the urea aqueous solution can further be promoted through the
enhancement of the control accuracy. Here, in an exhaust gas
purification apparatus in which the ammonia oxidation catalyst 22
is not disposed, the ammonia sensor measures the concentration of
the ammonia in the exhaust gas passed through the SCR catalyst
20.
[0051] Moreover, the present invention can be applied to an exhaust
gas purification apparatus including the exhaust pipe 14 further
provided with a diesel particulate filter (DPF) which collects and
removes a particulate matter (PM), an exhaust gas purification
apparatus including the DPF coated with a catalyst component which
functions as an SCR catalyst, and the like.
[0052] It should be noted that the entire contents of Japanese
Patent Application No. 2009-145276, filed on Jun. 18, 2009, on
which the convention priority is claimed is incorporated herein by
reference.
[0053] It should also be understood that many modifications and
variations of the described embodiments of the invention will occur
to a person having an ordinary skill in the art without departing
from the spirit and scope of the present invention as claimed in
the appended claims.
* * * * *