U.S. patent application number 12/619044 was filed with the patent office on 2010-05-20 for exhaust purification control device and exhaust purification system of internal combustion engine.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Tatsuya FUJITA, Masatoshi Maruyama.
Application Number | 20100122525 12/619044 |
Document ID | / |
Family ID | 42105346 |
Filed Date | 2010-05-20 |
United States Patent
Application |
20100122525 |
Kind Code |
A1 |
FUJITA; Tatsuya ; et
al. |
May 20, 2010 |
EXHAUST PURIFICATION CONTROL DEVICE AND EXHAUST PURIFICATION SYSTEM
OF INTERNAL COMBUSTION ENGINE
Abstract
If it is determined that accumulation quantity of deposit on an
inner wall of an exhaust passage is equal to or larger than a
predetermined value, addition quantity of urea solution from a urea
solution addition valve is decreased. Thereafter, exhaust gas
temperature is increased rapidly when request torque of a diesel
engine increases. Thus, the deposit having accumulated on the inner
wall of the exhaust passage is decomposed at once and is supplied
to a urea SCR as ammonia.
Inventors: |
FUJITA; Tatsuya; (Obu-city,
JP) ; Maruyama; Masatoshi; (Nagoya-city, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
DENSO CORPORATION
Kariya-city
JP
|
Family ID: |
42105346 |
Appl. No.: |
12/619044 |
Filed: |
November 16, 2009 |
Current U.S.
Class: |
60/285 ; 60/286;
60/287 |
Current CPC
Class: |
F01N 3/208 20130101;
F02D 41/405 20130101; F01N 13/009 20140601; F01N 2560/026 20130101;
F02D 41/027 20130101; F02D 41/0245 20130101; F01N 2900/1402
20130101; F02D 41/08 20130101; F01N 2560/06 20130101; F01N 2560/14
20130101; F02D 2041/1433 20130101; F02D 41/1446 20130101; F01N
2610/02 20130101; Y02A 50/20 20180101; F01N 2610/146 20130101; F01N
2900/1622 20130101; Y02T 10/12 20130101; Y02A 50/2325 20180101;
F01N 3/106 20130101; Y02T 10/24 20130101 |
Class at
Publication: |
60/285 ; 60/287;
60/286 |
International
Class: |
F01N 9/00 20060101
F01N009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 18, 2008 |
JP |
2008-294029 |
Claims
1. An exhaust purification control device of an internal combustion
engine that is applied to an exhaust purification device having a
purification device provided in an exhaust passage of the internal
combustion engine for purifying nitrogen oxides in exhaust gas and
an addition device for adding a reducing agent into the exhaust gas
upstream of the purification device and that performs purification
control of the nitrogen oxides with the purification device while
adjusting addition quantity of the reducing agent based on
operation of the addition device, the exhaust purification control
device comprising: an estimating means for estimating accumulation
quantity of deposit on an inner wall of the exhaust passage
resulting from the addition of the reducing agent; and a decreasing
means for compulsorily decreasing the addition quantity of the
reducing agent when at least one of a condition that the estimated
accumulation quantity is equal to or larger than a specified value
and a condition that increase speed of the accumulation quantity is
equal to or higher than specified speed is established.
2. The exhaust purification control device as in claim 1, further
comprising: an exhaust gas temperature increasing means for
increasing exhaust gas temperature of the internal combustion
engine to temperature capable of removing the deposit when the
estimated accumulation quantity is equal to or larger than a
predetermined value.
3. The exhaust purification control device as in claim 2, wherein
the increase processing of the exhaust gas temperature is stopped
when it is determined that the accumulation quantity has become
equal to or smaller than a predetermined value.
4. The exhaust purification control device as in claim 1, further
comprising: a torque increase timing temperature increasing means
for increasing the exhaust gas temperature of the internal
combustion engine to temperature capable of removing the deposit at
higher speed than speed of exhaust gas temperature increase
accompanying increase of torque of the internal combustion engine
when request torque of the internal combustion engine
increases.
5. The exhaust purification control device as in claim 2, wherein
the addition quantity of the reducing agent added by the addition
device is decreased when the exhaust gas temperature increasing
means performs the increase processing of the exhaust gas
temperature.
6. The exhaust purification control device as in claim 2, wherein
the exhaust gas temperature increasing means performs at least one
of delaying processing of fuel injection timing of the internal
combustion engine, fuel supplying processing to the exhaust passage
of the internal combustion engine and increasing processing of
exhaust gas recirculation quantity of the internal combustion
engine.
7. The exhaust purification control device as in claim 2, wherein
the internal combustion engine is an in-vehicle internal combustion
engine, an output shaft of which is connected to a drive wheel
through a transmission, and the exhaust gas temperature increasing
means operates a change gear ratio of the transmission to decrease
rotation speed of the output shaft of the internal combustion
engine, while inhibiting fall of running speed of a vehicle.
8. The exhaust purification control device as in claim 1, wherein
the estimating means estimates the accumulation quantity based on a
parameter correlated with temperature of an exhaust system of the
internal combustion engine and the addition quantity.
9. The exhaust purification control device as in claim 1, wherein
the estimating means estimates the accumulation quantity based on a
time, in which idling of the internal combustion engine is
performed, during the idling.
10. The exhaust purification control device as in claim 1, wherein
the reducing agent is urea solution.
11. An exhaust purification system of the internal combustion
engine comprising: the exhaust purification control device as in
claim 1; and the purification device.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese Patent Application No. 2008-294029 filed on Nov.
18, 2008.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an exhaust purification
control device of an internal combustion engine and to an exhaust
purification system having the exhaust purification control device,
wherein the exhaust purification control device is applied to an
exhaust purification device having a purification device provided
in an exhaust passage of the internal combustion engine for
purifying nitrogen oxides in exhaust gas and an addition device for
adding a reducing agent into the exhaust gas upstream of the
purification device and performs purification control of the
nitrogen oxides with the purification device while adjusting
addition quantity of the reducing agent based on operation of the
addition device.
[0004] 2. Description of Related Art
[0005] In recent years, development of an exhaust purification
system (urea SCR system) using a selective reduction catalyst (SCR:
selective catalytic reduction), which selectively purifies NOx
(nitrogen oxides) in exhaust gas by using urea solution as a
reducing agent in an in-vehicle internal combustion engine
(specifically, diesel engine), has been advanced, and such the
exhaust purification system (urea SCR system) has been partly put
into practical use. In the urea SCR system, a selective reduction
NOx catalyst is provided in an exhaust pipe connected to an engine
main body, and a urea solution addition valve for adding the urea
solution (urea aqueous solution) as a NOx reducing agent into the
exhaust pipe is provided upstream of the NOx catalyst.
[0006] In the above-described system, the urea solution is added by
the urea solution addition valve into the exhaust pipe and thus NOx
in the exhaust gas is selectively reduced and removed on the NOx
catalyst. More specifically, ammonia (NH3) is generated when the
urea solution is hydrolyzed with exhaust heat and is adsorbed to
the NOx catalyst, thereby causing a reduction reaction on the NOx
catalyst using the ammonia. Thus, NOx is reduced and purified.
[0007] When exhaust gas temperature of the internal combustion
engine is low, there is a possibility that an efficiency of the
hydrolysis from the urea solution to the ammonia lowers and urea
pyrolysates such as a cyanuric acid deposit in an exhaust passage.
The deposit turns into the ammonia if the exhaust gas temperature
increases. Therefore, when the deposit has accumulated in the
exhaust passage, there is a possibility that the ammonia supplied
to the SCR becomes excessive with the increase of the exhaust gas
temperature and controllability of the ammonia supply quantity to
the SCR lowers.
[0008] Therefore, conventionally, there has been proposed a scheme
that provides a bypass passage to the exhaust passage for passing
small quantity of exhaust gas and provides a hydrolysis catalyst of
urea solution and a heater in the bypass passage, e.g., as
described in Patent document 1 (JPA-2007-327377). Thus, when the
exhaust gas temperature is low, the ammonia is extracted from the
urea solution through the bypass passage and is supplied to the NOx
catalyst, thereby suitably inhibiting or avoiding the deposition of
the urea pyrolysate in the exhaust passage.
[0009] Patent document 2 (JP-A-2007-239500) describes another
conventional exhaust purification control device.
[0010] The above-described conventional technology employs the
additional hardware such as the bypass passage, the hydrolysis
catalyst and the heater for the NOx purification control in the low
exhaust gas temperature range. Accordingly, lowering of cost
performance is not ignorable. Furthermore, there is also a problem
of increase in energy consumption since the heater is used.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide an
exhaust purification control device of an internal combustion
engine and an exhaust purification system having the exhaust
purification control device, wherein the exhaust purification
control device performs purification control of nitrogen oxides
with a purification device by operating an addition device adding a
reducing agent into exhaust gas upstream of the purification device
and is capable of suitably inhibiting accumulation of deposit in an
exhaust passage due to the addition of the reducing agent, while
inhibiting increase in the number of parts.
[0012] According to a first example aspect of the present
invention, an exhaust purification control device of an internal
combustion engine is applied to an exhaust purification device
having a purification device provided in an exhaust passage of the
internal combustion engine for purifying nitrogen oxides in exhaust
gas and an addition device for adding a reducing agent into the
exhaust gas upstream of the purification device and performs
purification control of the nitrogen oxides with the purification
device while adjusting addition quantity of the reducing agent
based on operation of the addition device. The exhaust purification
control device has an estimating section for estimating
accumulation quantity of deposit on an inner wall of the exhaust
passage resulting from the addition of the reducing agent and a
decreasing section for compulsorily decreasing the addition
quantity of the reducing agent when at least one of a condition
that the estimated accumulation quantity is equal to or larger than
a specified value and a condition that increase speed of the
accumulation quantity is equal to or higher than specified speed is
established.
[0013] The addition of the reducing agent by the addition device is
performed to purify the nitrogen oxides. Therefore, if the addition
quantity of the reducing agent is decreased, there is a possibility
that a purification rate of the nitrogen oxides lowers. However,
the inventors of the present invention found that a degree of the
lowering of the purification rate of the nitrogen oxides is small
or negligible even if the addition quantity is decreased under a
situation where the accumulation quantity of the deposit onto the
inner wall of the exhaust passage is large or under a situation
where the increase speed of the accumulation quantity is high. That
is, under the situation where the accumulation quantity of the
deposit is large, adsorption quantity of the reducing substance to
the purification device is large. Therefore, even if the addition
quantity of the reducing agent is decreased, the shortfall of the
addition quantity for the purification of the nitrogen oxides is
compensated by the reducing substance having been adsorbed to the
purification device. Under the situation where the increase speed
of the accumulation of the deposit is high, the exhaust gas
temperature is low and therefore the quantity of the nitrogen
oxides in the exhaust gas is small.
[0014] In view of this point, according to the above-described
first example aspect of the present invention, the addition
quantity of the reducing agent is compulsorily decreased when at
least one of the above-described conditions is established.
Accordingly, the accumulation of the deposit on the inner waif of
the exhaust passage can be suitably inhibited.
[0015] According to a second example aspect of the present
invention, the exhaust purification control device further has an
exhaust gas temperature increasing section for increasing exhaust
gas temperature of the internal combustion engine to temperature
capable of removing the deposit when the estimated accumulation
quantity is equal to or larger than a predetermined value.
[0016] For example, when request torque of the internal combustion
engine increases, the deposit on the inner wall of the exhaust
passage decomposes and is supplied to the purification device since
the exhaust gas temperature increases. If the quantity of the
deposit on the inner wall of the exhaust passage is excessively
large, excessive quantity of the reducing substance is supplied to
the purification device, e.g., when the request torque increases.
In such the case, there is a possibility that the large quantity of
the reducing substance flows out to a downstream side of the
purification device.
[0017] In view of this point, according to the above-described
second example aspect of the present invention, the exhaust gas
temperature is increased when the accumulation quantity on the
inner wall of the exhaust passage is equal to or larger than the
predetermined value. Thus, the excessive increase of the
accumulation quantity of the deposit on the inner wall of the
exhaust passage can be inhibited suitably, Moreover, since the
temperature is increased to the temperature capable of removing the
deposit, the supply quantity of the reducing substance to the
purification device resulting from the decomposition of the deposit
can be determined relatively easily. Therefore, the supply control
of the reducing substance to the purification device can be
performed appropriately.
[0018] According to a third example aspect of the present
invention, the increase processing of the exhaust gas temperature
is stopped when it is determined that the accumulation quantity has
become equal to or smaller than a predetermined value.
[0019] When the processing for increasing the exhaust gas
temperature is performed, there is a possibility that the fuel
consumption of the internal combustion engine increases. Regarding
this point, according to the above-described third example aspect
of the present invention, the increase of the fuel consumption can
be inhibited to the minimum by stopping the increase processing of
the exhaust gas temperature when the accumulation quantity becomes
equal to or smaller than the predetermined value.
[0020] According to a fourth example aspect of the present
invention, the exhaust purification control device further has a
torque increase timing temperature increasing section for
increasing the exhaust gas temperature of the internal combustion
engine to temperature capable of removing the deposit at higher
speed than speed of exhaust gas temperature increase accompanying
increase of torque of the internal combustion engine when request
torque of the internal combustion engine increases.
[0021] When the request torque of the internal combustion engine
increases, the exhaust gas temperature of the internal combustion
engine normally increases. Therefore, the deposit on the inner wall
of the exhaust passage decomposes and is supplied to the
purification device. However, since components of the deposit start
to decompose at different temperatures respectively, it is
difficult to determine the quantity of the reducing substance
supplied to the purification device with the increase of the
exhaust gas temperature.
[0022] In view of this point, according to the above-described
fourth example aspect of the present invention, the exhaust gas
temperature is increased rapidly when the request torque of the
internal combustion engine increases. Accordingly, the lowering of
the determination accuracy of the quantity of the reducing
substance due to the difference in the temperatures, at which the
respective components of the deposit start to decompose, can be
suitably inhibited.
[0023] According to a fifth example aspect of the present
invention, the addition quantity of the reducing agent added by the
addition device is decreased when the exhaust gas temperature
increasing section performs the increase processing of the exhaust
gas temperature.
[0024] If the increase processing of the exhaust gas temperature is
performed, the deposit on the inner wall of the exhaust passage
decomposes and eventually the reducing substance is supplied to the
purification device. Therefore, in this case, the reducing
substance supplied to the purification device contains both of the
reducing substance supplied by the addition device and the reducing
substance resulting from the decomposition. Therefore, if the
addition quantity of the addition device is set without taking the
quantity resulting from the decomposition into account, there is a
possibility that the quantity of the reducing substance actually
supplied to the purification device becomes excessive.
[0025] In view of this point, according to the above-described
fifth example aspect of the present invention, the addition
quantity of the reducing agent added by the addition device is
decreased when the increase processing of the exhaust gas
temperature is performed. Thus, the increase of the supply quantity
of the reducing substance to the purification device resulting from
the decomposition can be compensated suitably. Eventually, desired
quantity of the reducing substance can be supplied to the
purification device.
[0026] According to a sixth example aspect of the present
invention, the exhaust gas temperature increasing section performs
at least one of delaying processing of fuel injection timing of the
internal combustion engine, fuel supplying processing to the
exhaust passage of the internal combustion engine and increasing
processing of exhaust gas recirculation quantity of the internal
combustion engine.
[0027] According to a seventh example aspect of the present
invention, the internal combustion engine is an in-vehicle internal
combustion engine, an output shaft of which is connected to a drive
wheel through a transmission. The exhaust gas temperature
increasing section operates a change gear ratio of the transmission
to decrease rotation speed of the output shaft of the internal
combustion engine, while inhibiting fall of running speed of a
vehicle.
[0028] If the rotation speed of the internal combustion engine is
lowered, the air quantity charged into a combustion chamber of the
internal combustion engine decreases. Therefore, the exhaust gas
temperature can be increased.
[0029] According to an eighth example aspect of the present
invention, the estimating section estimates the accumulation
quantity based on a parameter correlated with temperature of an
exhaust system of the internal combustion engine and the addition
quantity.
[0030] With the above construction, the parameter correlated with
the temperature of the exhaust system, which is a parameter
correlated with the accumulation quantity, and the addition
quantity are used. Thus, the accumulation quantity can be estimated
appropriately.
[0031] According to a ninth example aspect of the present
invention, the estimating section estimates the accumulation
quantity based on a time, in which idling of the internal
combustion engine is performed, during the idling.
[0032] Since the exhaust gas temperature is low during the idling
of the internal combustion engine, the deposit tends to accumulate
on the inner wall of the exhaust passage during the idling. The
accumulation quantity of the deposit increases as an engine idling
time (idling time) lengthens. In view of this point, according to
the above-described ninth example aspect of the present invention,
the accumulation quantity can be suitably estimated by using the
idling time as the parameter correlated with the accumulation
quantity.
[0033] According to a tenth example aspect of the present
invention, the reducing agent is urea solution.
[0034] In the case where the urea solution is used as the reducing
agent, the urea pyrolysate deposits on the inner wall of the
exhaust passage under a situation where heating is insufficient.
Moreover, the deposit contains various components and decomposition
start temperatures differ among the components. Therefore, the
increase of the supply quantity of the reducing substance to the
purification device due to the decomposition of the deposit causes
lowering of controllability of the supply control of the reducing
substance. Therefore, according to the tenth example aspect of the
present invention, utility values of the decreasing section and the
exhaust gas temperature increasing section are specifically
high.
[0035] According to an eleventh example aspect of the present
invention, an exhaust purification system of the internal
combustion engine has the exhaust purification control device and
the purification device.
[0036] The above-described eleventh example aspect of the present
invention has the decreasing device and the exhaust gas temperature
increasing device, thereby realizing a system with high
reliability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] Features and advantages of embodiments will be appreciated,
as well as methods of operation and the function of the related
parts, from a study of the following detailed description, the
appended claims, and the drawings, all of which form a part of this
application. In the drawings:
[0038] FIG. 1 is a system configuration diagram according to a
first embodiment of the present invention;
[0039] FIG. 2 is a diagram showing melting points of urea
pyrolysates according to the first embodiment;
[0040] FIG. 3 is a diagram showing a measurement result of temporal
changes of the urea pyrolysate according to the first
embodiment;
[0041] FIG. 4 is a time chart showing a decrease control mode of
urea solution addition quantity according to the first
embodiment;
[0042] FIG. 5 is a time chart showing an increasing processing mode
of exhaust gas temperature according to the first embodiment;
[0043] FIG. 6 is a time chart showing an increasing processing mode
of the exhaust gas temperature at request torque increasing timing
according to the first embodiment;
[0044] FIG. 7 is a flowchart showing a processing procedure of
exhaust purification control according to the first embodiment;
and
[0045] FIG. 8 is a flowchart showing a processing procedure of
exhaust purification control according to a second embodiment of
the present invention.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
First Embodiment
[0046] Hereafter, an exhaust purification control device of an
internal combustion engine according to a first embodiment of the
present invention will be explained with reference to the
drawings.
[0047] A diesel engine 10 is an internal combustion engine having a
reciprocating engine structure. An air cleaner 14 is provided
upstream of an intake passage 12 of the diesel engine 10. An intake
temperature sensor 16 for sensing intake air temperature and an
airflow meter 18 for sensing an intake air flow rate are provided
to the air cleaner 14. A turbocharger 20 is provided downstream of
the air cleaner 14. An air supercharged by the turbocharger 20 is
cooled by an intercooler 22 and then supplied to a downstream side
of the intake passage 12. The air is supplied to a combustion
chamber 28 of the diesel engine 10 through a throttle valve 24,
which adjusts a flow passage area of the intake passage 12, and an
intake valve 26, which opens and closes communication between the
combustion chamber 28 and the intake passage 12.
[0048] The air thus supplied to the combustion chamber 28 is
compressed with high-pressure fuel (e.g., fuel at tens to 200 MPa)
such as light oil injected by an injector 30, whose tip portion
protrudes into the combustion chamber 28, and is used for
combustion. An energy generated by the combustion is converted into
a rotational energy of a crankshaft 34 via a piston 32. The
rotational energy of the crankshaft 34 is transmitted to drive
wheels via a continuously variable transmission 35 (CVT). A crank
angle sensor 36 that senses a rotation angle of the crankshaft 34
is provided near the crankshaft 34.
[0049] The air and fuel used for the combustion in the combustion
chamber 28 are discharged to an exhaust passage 40 as an exhaust
gas in connection with an opening action of an exhaust valve 38. A
part of the exhaust passage 40 upstream of the turbocharger 20 is
connected to the intake passage 12 through an exhaust gas
recirculation passage 42. A part of the exhaust gas discharged into
the exhaust passage 40 is cooled by an EGR cooler 44 and then
supplied to the intake passage 12 according to an opening degree of
an exhaust gas recirculation valve 46 (EGR valve) that adjusts a
flow passage area of the exhaust gas recirculation passage 42.
[0050] An after treatment device is provided downstream of the
turbocharger 20 in the exhaust passage 40. The after treatment
device includes an oxidation catalyst 50, a urea selective
reduction catalyst 52 (referred to as urea SCR, hereafter) and an
ammonia slip catalyst 54 in this order from the upstream side of
the exhaust passage 40. The ammonia slip catalyst 54 removes
surplus ammonia, which is not consumed in a reaction with NOx in
the urea SCR 52 and is discharged downstream of the urea SCR 52.
The ammonia slip catalyst 54 is constituted by an oxidation
catalyst, for example.
[0051] An upstream NOx sensor 56 that senses a NOx concentration in
the exhaust gas and an exhaust temperature sensor 58 that senses
exhaust gas temperature are provided between the oxidation catalyst
50 and the urea SCR 52. A downstream NOx sensor 60 that senses the
NOx concentration is provided between the urea SCR 52 and the
ammonia slip catalyst 54. The after treatment device further
includes a diesel particulate filter (DPF) that collects
particulate matters in the exhaust gas. The DPF may be provided to
be integrated with the oxidation catalyst 50 or may be provided
downstream of the oxidation catalyst 50.
[0052] A urea solution addition valve 62 is further provided
between the oxidation catalyst 50 and the urea SCR 52. An injection
hole of the urea solution addition valve 62 is directed to a
downstream side of the exhaust passage 40. The urea solution
addition valve 62 is an electronically-controlled valve member that
injects a urea solution, which is supplied from a urea solution
tank 64, into the exhaust passage 40, thereby adding the urea
solution to the exhaust gas. The urea solution tank 64 is
constituted by a hermetic container having a supplying cap. The
urea solution tank 64 stores a urea solution of a prescribed
concentration (for example, 32.5%) therein. The urea solution tank
64 is connected to the urea solution addition valve 62 through a
urea solution pipe 66. An electronically-controlled urea solution
pump 68 is provided in the urea solution pipe 66. The urea solution
pump 68 draws the urea solution in the urea solution tank 64 and
pressure-feeds (pumps) the urea solution to the urea solution
addition valve 62. A pressure sensor 70 that senses pressure of the
pumped urea solution is provided downstream of the urea solution
pump 68.
[0053] A swirl flow generating member 72 is provided upstream of
the urea solution addition valve 62. The swirl flow generating
member 72 generates a swirl flow in the exhaust gas flowing through
the exhaust passage 40 by changing a cross-sectional structure of a
flow passage inside the exhaust passage 40.
[0054] In the urea SCR system constituted by the urea SCR 52, the
urea solution addition valve 62 and the like, the urea solution is
added and supplied into the exhaust passage 40 by the urea solution
addition valve 62, thereby supplying the urea solution to the urea
SCR 52 together with the exhaust gas in the exhaust passage 40.
Thus, in the urea SCR 52, the exhaust gas is purified through a
reduction reaction of NOx.
[0055] More specifically, the urea solution injected from the urea
solution addition valve 62 is hydrolyzed by exhaust heat. At that
time, the ammonia (NH3) as a reducing substance is generated by a
chemical reaction expressed by a following expression (c1).
(NH2)2CO+H2O.fwdarw.2NH3+CO2 (c1)
[0056] NOx in the exhaust gas is selectively reduced and purified
by the ammonia when the exhaust gas passes through the urea SCR 52.
More specifically, NOx is reduced and purified through reduction
reactions shown by following expressions (c2) to (c4).
4NO+4NH3+O2.fwdarw.4N2+6H2O (c2)
6NO2+8NH3.fwdarw.7N2+12H2O (c3)
NO+NO2+2NH3.fwdarw.2N2+3H2O (c4)
[0057] An electronic control unit 80 (ECU) controls the diesel
engine 10 and operates various actuators such as the injector 30.
Sensing signals of the above-described various sensors that sense
the operation states of the diesel engine 10, a sensing signal of
an accelerator sensor 82 that senses accelerator operation amount
ACCP by a user, a sensing signal of a vehicle speed sensor 84 that
sensing running speed Vc of a vehicle and the like are successively
inputted to the ECU 80, and the ECU 80 controls control amounts of
the diesel engine 10 (torque, exhaust characteristic and the like)
based on the sensing signals.
[0058] In order to control the characteristic of the exhaust gas
discharged from the exhaust passage 40 as the above-described
control amount, the ECU 80 operates the urea solution addition
valve 62 and the urea solution pump 68 to perform NOx purification
control using the urea SCR 52. First, urea solution addition
quantity is calculated based on the NOx concentration in the
exhaust gas sensed with the upstream NOx sensor 56. Then, a valve
opening command pulse having a predetermined cycle is outputted to
the urea solution addition valve 62 based on the calculated urea
solution addition quantity. When a driving current flows to a drive
section (solenoid section) of the urea solution addition valve 62
in connection with the output of the pulse, valve opening of the
urea solution addition valve 62 is performed and the urea solution
is added (injected).
[0059] When temperature of an exhaust system of the diesel engine
10 is low, there is a possibility that an efficiency of the
hydrolysis from the urea solution to the ammonia lowers and urea
pyrolysates such as a cyanuric acid deposit and accumulate on an
inner wall surface of the exhaust passage 40. The deposit having
accumulated on the inner wall of the exhaust passage 40 decomposes
with increase of the exhaust temperature, thereby generating the
ammonia. Thus, the deposit having accumulated on the inner wall of
the exhaust passage 40 decomposes and the ammonia is supplied to
the urea SCR 52 irrespective of the operation of the urea solution
addition valve 62. The deposit contains various components having
different decomposition start temperatures. FIG. 2 shows
decomposition start temperatures (melting points) of biuret and the
cyanuric acid among the components constituting the above deposit.
FIG. 2 shows measurement results of the decomposition start
temperatures of the biuret and the cyanuric acid under oxygen
environment. The decomposition start temperatures of the biuret and
the cyanuric acid are different from each other by 100 degrees C.
as shown in FIG. 2. Therefore, it is quite difficult to anticipate
how much deposit on the inner wall of the exhaust passage 40
decomposes with the increase of the exhaust gas temperature and how
much ammonia is supplied to the urea SCR 52 as the result of the
decomposition.
[0060] Furthermore, component concentrations of the above-described
deposit can change with elapse of time. FIG. 3 shows temporal
changes of the composition ratios of the biuret, ammelide and the
cyanuric acid among the components constituting the above deposit.
FIG. 3 shows a measurement result of a relationship between a
heating time of heating treatment applied to a solid urea at 180
degrees C. and the composition ratios of the components remaining
as solids. As shown in FIG. 3, the composition ratio of the
cyanuric acid increases as the heating time lengthens. That is, the
composition ratio of the component having high decomposition start
temperature increases as the heating time lengthens. Such the
phenomenon makes it more difficult to anticipate how much deposit
on the inner wall of the exhaust passage 40 decomposes with the
increase of the exhaust gas temperature and how much ammonia is
supplied to the urea SCR 52 as the result of the decomposition.
[0061] Therefore, in the present embodiment, excessive increase of
the ammonia supply quantity to the urea SCR 52 is suitably avoided
by processing shown in FIGS. 4 to 6.
[0062] FIG. 4 shows a first processing mode according to the
present embodiment. Parts (a), (b), (c), (d) and (e) of FIG. 4
respectively show transitions of the vehicle running speed Vc, the
exhaust gas temperature Tex, the urea solution addition quantity
Qur, the urea deposit accumulation quantity Dur on the inner wall
of the exhaust passage 40 and the NOx purification rate Rnox. The
NOx purification rate Rnox is quantified with a value calculated by
dividing a difference between the NOx concentration upstream of the
urea SCR 52 and the NOx concentration downstream of the urea SCR 52
by the NOx concentration upstream of the urea SCR 52.
[0063] The first processing shown in FIG. 4 is to decrease the urea
addition quantity when the urea deposit accumulation quantity on
the inner wall of the exhaust passage 40 increases. More
specifically, in the present embodiment, the urea addition quantity
Qur is decreased when the urea deposit accumulation quantity Dur
(explained later) becomes equal to or larger than a threshold value
.beta. and the exhaust gas temperature Tex is equal to or lower
than threshold temperature .gamma.. The condition that the exhaust
gas temperature Tex is equal to or lower than the threshold
temperature .gamma. is used in order to accurately determine the
situation where the urea deposit accumulation quantity Dur
increases. In FIG. 4, the decrease control of the urea solution
addition quantity Qur is performed at time t3 when the exhaust gas
temperature Tex becomes equal to or lower than the threshold
temperature y. By performing the decrease control of the urea
solution addition quantity Qur in this way, the increase of the
accumulation quantity Dur of the urea deposit onto the inner wall
of the exhaust passage 40 can be inhibited suitably.
[0064] Originally, the urea solution addition quantity Qur is set
at quantity necessary to purify NOx. Therefore, if the urea
solution addition quantity Qur is decreased unnecessarily, it can
cause the increase of the NOx concentration in the exhaust gas
discharged to the downstream side of the after treatment
device.
[0065] However, the inventors of the present invention found that
the ammonia adsorbed to the urea SCR 52 also increases under the
situation where the deposit accumulation quantity Dur onto the
inner wall of the exhaust passage 40 increases and that the
decrease of the ammonia supply quantity to the urea SCR 52 due to
the decrease of the urea solution addition quantity Qur can be
compensated with the ammonia having been adsorbed to the urea SCR
52.
[0066] The quantity of the adsorbed ammonia increases because the
NOx purification rate Rnox decreases due to the decrease of the
exhaust gas temperature Tex after time t2 shown in FIG. 4. In the
present embodiment, the decrease control of the urea solution
addition quantity Qur is performed based on these findings. In
fact, in the example shown in FIG. 4, the NOx purification rate
Rnox does not fall even when the decrease control of the urea
solution addition quantity Qur is performed.
[0067] FIG. 5 shows a second processing mode according to the
present embodiment. Parts (a) to (e) of FIG. 5 correspond to parts
(a) to (e) of FIG. 4, respectively.
[0068] The second processing shown in FIG. 5 is to perform
processing for increasing the exhaust gas temperature Tex
(temperature increase processing) when the urea deposit
accumulation quantity Dur on the inner wall of the exhaust passage
40 becomes equal to or larger than a threshold value a. In FIG. 5,
the temperature increase control is performed at time t3 when the
accumulation quantity Dur becomes equal to or larger than the
threshold value .alpha.. Then, the temperature increase control is
stopped when the accumulation quantity Dur becomes equal to or
smaller than the threshold value .beta.. Similarly, the temperature
increase control is performed also in a period t5 to t6 and a
period t7 to t8. Marks A in FIG. 5 indicate the periods for
performing the temperature increase control.
[0069] The temperature increase control is processing for rapidly
increasing the exhaust gas temperature Tex to or over the highest
value of the decomposition start temperature of the deposit
accumulating on the inner wall of the exhaust passage 40. More
specifically, the temperature increase control is processing for
increasing the exhaust gas temperature Tex stepwise to 300 degrees
C. The stepwise increase is defined as increase at speed higher
than average increase speed of the exhaust gas temperature Tex
caused by normal increase of request torque of the diesel engine 10
or the like. Thus, the quantity of the ammonia supplied to the urea
SCR 52 due to the decomposition of the deposit can be estimated
easily. Accordingly, the decrease quantity of the urea solution
addition quantity Qur from the urea solution addition valve 62 can
be set based on the estimated ammonia supply quantity resulting
from the decomposition of the deposit, In FIG. 5, as an example
compulsorily decreasing the urea solution addition quantity Qur,
the urea solution addition quantity Qur is decreased gradually with
the start of the temperature increase control and fixed when the
urea solution addition quantity Qur becomes predetermined
quantity.
[0070] The above-described temperature increase control may be
performed by at least one of post-injection, increase processing of
EGR quantity and increase processing of a change gear ratio of the
CVT 35. The post-injection is to inject the fuel to the combustion
chamber 28 at timing largely delayed from a compression top dead
center of the diesel engine 10. Thus, the injected fuel is
combusted not in the combustion chamber 28 but in the exhaust
passage 40. The increase processing of the EGR quantity can be
performed by increase operation of the opening degree of the EGR
valve 46. If the EGR quantity increases, temperature of the gas
supplied from the intake passage 12 to the combustion chamber 28
increases. Therefore, the exhaust gas temperature Tex can be
increased. The increase processing of the change gear ratio of the
CVT 35 is performed to decrease the rotation speed of the diesel
engine 10 without decreasing the running speed Vc of the vehicle.
If the rotation speed of the diesel engine 10 decreases, charging
quantity of the gas supplied to the combustion chamber 28
decreases. Accordingly, the air quantity per unit quantity of the
fuel decreases and eventually the exhaust gas temperature Tex
increases.
[0071] FIG. 6 shows a third processing mode according to the
present embodiment. Parts (a) to (d) of FIG. 6 correspond to parts
(a) to (d) of FIG. 4 respectively.
[0072] The third processing shown in FIG. 6 is to increase the
exhaust gas temperature Tex to or over the maximum value of the
decomposition start temperature of the above-described deposit at
higher speed than the increase speed of the exhaust gas temperature
Tex accompanying the acceleration request of the diesel engine 10
when the acceleration of the diesel engine 10 is requested. More
specifically, the processing is to increase the exhaust gas
temperature Tex stepwise to 300 degrees C. Since the exhaust gas
temperature Tex increases when the acceleration request occurs, the
deposit having accumulated on the inner wall of the exhaust passage
40 decomposes. However, since the decomposition start temperature
differs among the components of the deposit, it is difficult to
determine timing and amount of emergence of the ammonia. Therefore,
the exhaust gas temperature Tex is increased stepwise (as shown by
mark B in FIG. 6) to facilitate anticipation of the amount of
emergence of the ammonia resulting from the decomposition of the
deposit. Thus, it can be facilitated to adjust the urea solution
addition quantity Qur, which is added from the urea solution
addition valve 62, to suitable quantity.
[0073] The temperature increase control according to the present
embodiment may be performed by means of the post-injection.
[0074] FIG. 7 shows a procedure of purification processing of the
nitrogen oxides according to the present embodiment. The ECU 80
repeatedly performs the processing, for example, in a predetermined
cycle.
[0075] In a series of the processing, first in S10 (S means
"Step"), it is determined whether a present operation range of the
diesel engine 10 is a range for performing the urea solution
addition processing. For example, the range for performing the urea
solution addition processing may be a temperature range equal to or
higher than activation temperature of the urea SCR 52. When the
present operation range is the range for performing the addition
processing of the urea solution, the accumulation quantity Dur of
the urea deposit is estimated based on the temperature of the inner
wall of the exhaust passage 40 and the urea solution addition
quantity Qur in S12. It is estimated that the accumulation quantity
Dur increases as the inner wall temperature decreases and that the
accumulation quantity Dur increases as the urea solution addition
quantity Qur increases.
[0076] The temperature of the inner wall of the exhaust passage 40
is estimated based on the vehicle speed Vc sensed with the vehicle
speed sensor 84, the exhaust gas temperature Tex and ambient
temperature. It is thought that a wall surface of the exhaust
passage 40 receives more heat from the exhaust gas as the exhaust
gas temperature Tex increases. Therefore, the inner wall
temperature is estimated to be higher as the exhaust gas
temperature Tex increases. It is thought that more heat amount
flows out of a wall surface of the exhaust passage 40 to an
exterior as the ambient temperature decreases. Therefore, the inner
wall temperature is estimated to be lower as the ambient
temperature decreases. Furthermore, it is thought that a flow rate
of an ambient air blowing against the wall surface of the exhaust
passage 40 increases as the vehicle speed Vc increases. Therefore,
the inner wall temperature is estimated to be lower as the vehicle
speed Vc increases. For example, the estimation may be performed
using a model of heat transfer based on a specific heat of the wall
surface of the exhaust passage 40 and the like. In the present
embodiment, the intake air temperature sensed with the intake
temperature sensor 16 is used as the ambient temperature.
[0077] In following S14, it is determined whether the acceleration
is being performed. More specifically, in S14, it is determined
whether the request torque of the diesel engine 10 is increased
based on the sensing value of the accelerator sensor 82 and the
like. When it is determined that the request torque is increased,
the temperature increase control is performed in S16 in the mode
shown in FIG. 6.
[0078] When the determination result in S14 is negative, it is
determined in S18 whether an idling state is present. This
processing is provided because the urea solution addition quantity
decrease control and the temperature increase control are performed
based on the urea deposit accumulation quantity Dur estimated by a
method different from the processing of S12 during the idling.
[0079] When it is determined in S18 that the idling is not
performed, it is determined in S20 whether the temperature increase
control of the exhaust gas temperature Tex shown in FIG. 5 is in
execution. When the determination result in S20 is negative, the
process proceeds to 322. It is determined in S22 whether the
accumulation quantity Dur estimated by the processing of S12 is
"equal to or larger than" the threshold value .alpha.. This
processing is to determine whether to perform the temperature
increase control shown in FIG. 5. When the determination result of
S22 is negative, it is determined in S24 whether the accumulation
quantity Dur estimated by the processing of S12 is "equal to or
larger than" the threshold value .beta.. The threshold value .beta.
is set as a value smaller than the above-described threshold value
.alpha.. This processing is to determine whether to perform the
decrease control of the urea solution addition quantity Qur shown
in FIG. 4. When the determination result of S24 is affirmative, it
is determined in S26 whether the exhaust gas temperature Tex is
"equal to or lower than" the threshold temperature v. This
processing is also for determining whether to perform the decrease
control of the urea solution addition quantity Qur shown in FIG. 4.
When the determination result of S26 is affirmative, the decrease
control of the urea solution addition quantity Qur is performed in
S28 in the mode shown in FIG. 4.
[0080] When the determination result in S22 is affirmative, the
temperature increase control shown in FIG. 5 is performed in S30.
When the processing of S30 completes or the determination result in
S20 is affirmative, the process proceeds to S32. In S32, as shown
in FIG. 5, the processing for decreasing the urea solution addition
quantity Qur based on the temperature increase control is
performed. More specifically, the quantity Qur of the urea solution
added from the urea solution addition valve 62 is decreased
according to the amount of emergence of the ammonia resulting from
the decomposition of the deposit due to the temperature increase
control based on the accumulation quantity Dur estimated in S12. In
order to perform such the processing easily, it is desirable to
quantify the deposition quantity as the estimation object of S12 as
the amount of emergence of the ammonia in the case where the
deposit is decomposed.
[0081] When the processing of S32 completes, the process proceeds
to S34. In S34, it is determined whether the accumulation quantity
Dur estimated in S12 is "equal to or smaller than" a threshold
value c. This processing is to determine whether to stop the
temperature increase control. The threshold value .epsilon. is set
as a value larger than the threshold value .beta.. When the
determination result of S34 is affirmative, the temperature
increase control and the processing of S32 are stopped in S36, and
the usual urea solution addition control is resumed.
[0082] When the determination result of S18 is affirmative, an
engine idling time (idling time) is counted in S38. The idling time
is a parameter for quantifying the accumulation quantity Our of the
deposit on the inner wall of the exhaust passage 40. In following
S40, it is determined whether the idling time is longer than a
threshold time T1. This processing is to determine whether to
perform the temperature increase control shown in FIG. 5. The
threshold time T1 is set to a certain time, during which the
accumulation quantity Dur of the deposit on the inner wall of the
exhaust passage 40 is assumed to reach approximately the threshold
value a.
[0083] When the determination result of S40 is negative, it is
determined that the accumulation quantity Dur is not large to such
an extent that the temperature increase control should be
performed. In this case, the process proceeds to S42. In S42, it is
determined whether the idling time is longer than a threshold time
T0. This processing is to determine whether to perform the decrease
control of the urea solution addition quantity Qur. The threshold
time T0 is set to a certain time, during which the accumulation
quantity Dur of the deposit on the inner wall of the exhaust
passage 40 is assumed to reach approximately the threshold value
.beta.. When the determination result of S42 is affirmative, the
decrease control of the urea solution addition quantity Qur is
performed in S44.
[0084] When the determination result in S40 is affirmative, the
temperature increase control is performed in S46. In following S48,
processing similar to S32 is performed. In S50, it is determined
whether a temperature increase control time is "equal to or longer
than" a threshold time T2. This processing is to determine whether
to stop the temperature increase control. The threshold time T2 is
set to a certain time, during which the accumulation quantity Dur
of the deposit on the inner wall of the exhaust passage 40 is
assumed to decrease approximately to the threshold value e due to
the temperature increase control. When the determination result of
S50 is affirmative, the temperature increase control and the
processing of S48 are stopped in S52, and the usual urea solution
addition control is resumed. Further, the idling time is
initialized.
[0085] The series of the processing is once ended when the
determination result is negative in S10, S24, S26, S34, S42 or 550
or when the processing of S16, S28, S36, S44 or S52 completes.
[0086] The present embodiment described above exerts following
effects.
[0087] (1) When the estimated accumulation quantity is equal to or
larger than the specified value, the urea solution addition
quantity is decreased compulsorily. Thus, the accumulation of the
deposit onto the inner wall of the exhaust passage 40 can be
inhibited suitably.
[0088] (2) When the estimated accumulation quantity is equal to or
larger than the predetermined value, the exhaust gas temperature of
the diesel engine 10 is increased stepwise to the temperature
capable of removing the deposit. Thus, the excessive increase of
the accumulation quantity of the deposit on the inner wall of the
exhaust passage 40 can be inhibited suitably.
[0089] (3) When it is determined that the accumulation quantity has
become equal to or smaller than the predetermined value, the
increase processing of the exhaust gas temperature is stopped.
Thus, the increase of fuel consumption can be inhibited to the
minimum.
[0090] (4) When the request torque of the diesel engine 10
increases, the exhaust gas temperature of the diesel engine 10 is
increased stepwise to the temperature capable of removing the
deposit. Thus, lowering of the accuracy of the determination of the
ammonia supply quantity to the urea SCR 52 due to the difference in
the decomposition start temperatures of the components of the
deposit can be inhibited suitably.
[0091] (5) When the temperature increase control is performed, the
addition quantity of the urea solution added by the urea solution
addition valve 62 is decreased. Thus, the increase of the ammonia
supply quantity to the urea SCR 52 resulting from the decomposition
of the deposit can be compensated suitably. Eventually, desired
quantity of the ammonia can be supplied to the urea SCR 52.
[0092] (6) The accumulation quantity is estimated based on the
parameter (exhaust gas temperature) correlated with the temperature
of the exhaust system of the diesel engine 10 and the addition
quantity. Thus, the accumulation quantity can be estimated
suitably.
[0093] (7) The vehicle running speed and the ambient temperature
are also used when estimating the accumulation quantity. Thus, a
diffusion mode of the heat from the exhaust passage 40 to the
exterior can be grasped with high accuracy. Accordingly, the inner
wall temperature of the exhaust passage 40 can be determined with
high accuracy and eventually the accumulation quantity can be
estimated with high accuracy.
[0094] (8) The accumulation quantity is estimated based on the
time, in which the idling is performed, when the idling of the
diesel engine 10 is performed. Thus, the accumulation quantity can
be suitably estimated by using the idling time as the parameter
correlated with the accumulation quantity.
Second Embodiment
[0095] Next, a second embodiment of the present invention will be
described with reference to the drawings, focusing on the
differences from the first embodiment.
[0096] In the present embodiment, the addition quantity of the urea
solution added by the urea solution addition valve 62 is calculated
based on the NOx purification rate Rnox. The NOx purification rate
Rnox is calculated based on the both sensing values of the upstream
NOx sensor 56 and the downstream NOx sensor 60.
[0097] FIG. 8 shows a procedure of purification processing of the
nitrogen oxides according to the present embodiment. The ECU 80
repeatedly performs the processing, for example, in a predetermined
cycle. Processing in FIG. 8 corresponding to the processing in FIG.
7 is indicated with the same step number as in FIG. 7.
[0098] As shown in FIG. 8, in the present embodiment, as the
execution condition of the decrease control of the urea solution
addition quantity Qur in the case where the idling is not performed
presently, a condition that increase speed of the accumulation
quantity Dur is equal to or higher than threshold speed Sth is used
(refer to S24a) in place of the condition that the accumulation
quantity Dur is equal to or larger than the threshold value .beta..
Thus, the excessive increase of the accumulation quantity of the
deposit on the inner wall of the exhaust passage 40 can be surely
avoided. When the increase speed of the accumulation quantity is
very high, the NOx concentration in the exhaust gas lowers.
Therefore, even if the decrease control of the urea solution
addition quantity Qur is performed, the NOx purification rate Rnox
does not fall.
[0099] In the present embodiment, the urea solution addition
quantity Qur is set based on the NOx purification rate Rnox.
Therefore, even if there is a situation where the NOx concentration
in the exhaust gas falls, it does not necessarily lead directly to
decrease of the set urea solution addition quantity Qur. Therefore,
as in the present embodiment, it is specifically effective to
perform the processing for decreasing the urea solution addition
quantity Qur when the increase speed of the accumulation quantity
Dur is high.
Modified Embodiments
[0100] The above described embodiments may be modified and
implemented as follows, for example.
[0101] In the above embodiments, the exhaust temperature sensor 58
is provided to sense the exhaust gas temperature. Alternatively,
the exhaust gas temperature may be estimated by using a parameter
indicating an operation state of the diesel engine 10 as an input.
Such the parameter may be fuel injection quantity, the rotation
speed or the like, for example.
[0102] In the above-described second embodiment, a condition that
the accumulation quantity is equal to or larger than the threshold
value .beta. may be used as the start condition of the decrease
control of the urea solution addition quantity in addition to the
condition that the increase speed of the accumulation quantity is
equal to or higher than the threshold speed Sth.
[0103] In the above-described first embodiment, the urea solution
addition quantity is set based on the NOx concentration in the
exhaust gas. Alternatively, the urea solution addition quantity may
be set based on the NOx purification rate in the urea SCR 52 as in
the second embodiment, for example. Alternatively, a device or a
section for estimating ammonia adsorption quantity in the urea SCR
52 may be provided, and the urea solution addition quantity may be
set based on the estimated adsorption quantity.
[0104] In the above-described second embodiment, the urea solution
addition quantity is set based on the NOx purification rate in the
urea SCR 52. Alternatively, for example, a device or a section for
estimating the ammonia adsorption quantity in the urea SCR 52 may
be provided, and the urea solution addition quantity may be set
based on the estimated adsorption quantity. Alternatively, for
example, as in the above-described first embodiment, the urea
solution addition quantity may be set based on the NOx
concentration in the exhaust gas.
[0105] As mentioned above, it is thought that the case where the
increase speed of the accumulation quantity is equal to or higher
than the threshold speed Sth is a situation where the exhaust gas
temperature is low and the NOx concentration in the exhaust gas is
low. However, in the case where the urea solution addition quantity
is set based on the NOx purification rate or the ammonia adsorption
quantity in the urea SCR 52, there is a possibility that decrease
of the urea solution addition quantity delays as compared to the
case where the urea solution addition quantity is set based on the
NOx concentration in the exhaust gas. Therefore, in the case where
the NOx concentration of the exhaust gas discharged from the
combustion chamber 28 of the diesel engine 10 is not used as the
direct input parameter of the estimation of the urea solution
addition quantity, it is specifically effective to perform the
decrease control of the urea addition quantity when the increase
speed of the accumulation quantity is equal to or higher than the
threshold speed Sth in order to promptly perform the decrease
control of the urea addition quantity.
[0106] In the above-described embodiments, the decrease control of
the urea solution addition quantity is performed when a condition
of the conjunction between the condition that the accumulation
quantity is equal to or larger than the threshold value .beta. and
the condition that the exhaust gas temperature is equal to or lower
than the threshold temperature .gamma. is established in the range
of the operation other than the idling. Alternatively, for example,
the decrease control of the urea solution addition quantity may be
performed when the condition that the accumulation quantity is
equal to or larger than the threshold value .beta. is established,
irrespective of the exhaust gas temperature.
[0107] In the above-described embodiments, the threshold value
.epsilon. for the determination of the stop of the temperature
increase control in the range of the operation other than the
idling is set larger than the threshold value .beta. for the
determination of the start of the decrease control of the urea
solution addition quantity. Alternatively, for example, the
threshold value .epsilon. may be set equal to or smaller than the
threshold value .beta.. With such the configuration, the deposit
accumulation quantity on the inner wall surface of the exhaust
passage 40 can be sufficiently decreased even before the request
torque of the diesel engine 10 increases.
[0108] In the above embodiments, the idling time is used as the
estimate of the accumulation quantity of the urea pyrolysate during
the idling. Alternatively, for example, accumulation quantity
estimated based on a parameter correlated with the temperature of
the exhaust system and the urea solution addition quantity may be
used also during the idling. In the case where the accumulation
quantity is estimated based on the parameter correlated with the
temperature of the exhaust system and the urea solution addition
quantity, the accumulation quantity may be estimated in accordance
with the idling time during the idling such that the accumulation
quantity increases with the idling time instead of using the above
parameter and the urea solution addition quantity. With such the
modification, the execution conditions of the temperature increase
control of the exhaust gas temperature and the addition quantity
decrease control can be equalized between the case where the idling
is performed and the case where the idling is not performed.
[0109] The scheme of the estimation of the accumulation quantity of
the deposit is not limited to those illustrated in the
above-described embodiments and the modifications thereof. For
example, estimation processing of the accumulation quantity in each
estimation processing cycle may be performed based on the idling
time and at least one of a parameter correlated with the
temperature of the exhaust system and the urea solution addition
quantity during the idling.
[0110] In the above-described embodiments, the temperature increase
control of the exhaust gas temperature is stopped when the estimate
of the accumulation quantity of the deposit becomes equal to or
smaller than the threshold value .beta. in the range of the
operation other than the idling. Alternatively, for example, the
temperature increase control may be stopped on a condition that the
temperature increase control time reaches a predetermined time. In
this case, the temperature increase control time serves as the
parameter indicating the accumulation quantity of the deposit. That
is, it is meant that the accumulation quantity decreases as the
temperature increase control time lengthens.
[0111] in the above-described embodiments, the temperature increase
control of the exhaust gas temperature is stopped when the
temperature increase control time reaches the threshold time T2 in
the idling range. Alternatively, for example, the temperature
increase control may be stopped when the estimate of the
accumulation quantity of the deposit becomes equal to or smaller
than the threshold value .beta..
[0112] The fuel supply processing to the exhaust passage 40
performed to increase the exhaust gas temperature is not limited to
the processing for performing the post-injection. For example, in
the case where another injector for injecting the fuel into the
exhaust passage 40 is provided separately, processing for injecting
the fuel into the exhaust passage 40 with the another injector may
be performed.
[0113] The transmission used for increasing the exhaust gas
temperature is not limited to the above-described CVT 35. For
example, a transmission with discrete gear ratios may be used.
[0114] The control for increasing the exhaust gas temperature is
not limited to the control that increases the exhaust gas
temperature to approximately 300 degrees C. For example, control
that increases the exhaust gas temperature over 300 degrees C. may
be used. In this case, it is thought that the deposit in the
exhaust passage 40 decomposes at once into the ammonia. Therefore,
it is thought that the estimation of the ammonia supply quantity to
the urea SCR 52 is made much easier.
[0115] The purification device for purifying the nitrogen oxides in
the exhaust gas is not limited to the above-described urea SCR 52.
For example, a selective reduction catalyst that uses a reducing
agent, which is different from the urea solution and is added to
the exhaust gas upstream of the catalyst, may be used. The present
invention can be effectively applied to such the case if there is a
possibility that deposit containing multiple components having
different decomposition start temperatures accumulates because of
the reducing agent when the inner wall surface temperature of the
exhaust passage 40 is low. In this case, it is desirable to set the
target temperature of the temperature increase processing of the
exhaust gas temperature to or over the maximum value among the
decomposition start temperatures of the components of the
deposit.
[0116] The internal combustion engine is not limited to the
compression ignition internal combustion engine such as the diesel
engine. Alternatively, for example, even if the internal combustion
engine is a spark ignition internal combustion engine such as a
direct injection gasoline engine, the present invention can be
effectively applied to the engine if a selective reduction catalyst
is used for the purification of NOx.
[0117] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiments, it is to be understood that the invention is not to be
limited to the disclosed embodiments, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *