U.S. patent application number 12/274724 was filed with the patent office on 2009-05-28 for exhaust emission control device.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Ataru Ichikawa, Osamu Shimomura.
Application Number | 20090133389 12/274724 |
Document ID | / |
Family ID | 40577250 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090133389 |
Kind Code |
A1 |
Shimomura; Osamu ; et
al. |
May 28, 2009 |
EXHAUST EMISSION CONTROL DEVICE
Abstract
An exhaust emission control device includes an exhaust pipe, a
catalyst in the pipe promoting reduction reaction of nitrogen oxide
in exhaust air, a supply device for supplying an additive agent to
an upstream side of the catalyst, a temperature detecting device
for detecting exhaust air temperature, and a control device for
controlling the supply device to regulate the additive agent amount
supplied into the pipe. The control device stops supply of the
additive agent when exhaust air temperature is lower than
generation temperature needed to generate the reducing agent from
the additive agent, and supplies the additive agent when exhaust
air temperature is equal to or higher than generation temperature.
When a predetermined time has elapsed after a start of supply of
the additive agent, the control device reduces the additive agent
amount supplied, compared to the additive agent amount supplied
before the predetermined time has elapsed.
Inventors: |
Shimomura; Osamu;
(Okazaki-city, JP) ; Ichikawa; Ataru;
(Kariya-city, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
DENSO CORPORATION
Kariya-city
JP
NIPPON SOKEN, INC.
Nishio-city
JP
|
Family ID: |
40577250 |
Appl. No.: |
12/274724 |
Filed: |
November 20, 2008 |
Current U.S.
Class: |
60/295 ;
60/297 |
Current CPC
Class: |
F01N 9/00 20130101; Y02T
10/24 20130101; Y02T 10/12 20130101; F01N 2250/02 20130101; F01N
2560/06 20130101; F01N 3/035 20130101; F01N 2560/026 20130101; F01N
3/208 20130101; Y02T 10/47 20130101; F01N 2610/02 20130101; Y02T
10/40 20130101 |
Class at
Publication: |
60/295 ;
60/297 |
International
Class: |
F01N 3/035 20060101
F01N003/035 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 21, 2007 |
JP |
2007-301757 |
Claims
1. An exhaust emission control device for generating a reducing
agent from an additive agent by use of heat of exhaust air
discharged from an internal combustion engine and for reducing
nitrogen oxide included in the exhaust air by the reducing agent,
the device comprising: an exhaust pipe defining a passage for the
exhaust air; a catalyst disposed in the exhaust pipe, the catalyst
being capable of promoting reduction reaction of the nitrogen oxide
in the exhaust air; a supply means for supplying the additive agent
to an upstream side of the catalyst in a flow direction of the
exhaust air; a temperature detecting means for detecting
temperature of the exhaust air flowing through the exhaust pipe;
and a control means for controlling the supply means so as to
regulate an amount of the additive agent supplied into the exhaust
pipe, wherein: the control means stops the supply of the additive
agent when the temperature of the exhaust air detected by the
temperature detecting means is lower than a generation temperature
that is needed to generate the reducing agent from the additive
agent, and supplies the additive agent when the temperature of the
exhaust air is equal to or higher than the generation temperature;
and when a predetermined time has elapsed after a start of the
supply of the additive agent, the control means reduces the amount
of the additive agent supplied, as compared to the amount of the
additive agent supplied before the predetermined time has
elapsed.
2. An exhaust emission control device for generating a reducing
agent from an additive agent by use of heat of exhaust air
discharged from an internal combustion engine and for reducing
nitrogen oxide included in the exhaust air by the reducing agent,
the device comprising: an exhaust pipe defining a passage for the
exhaust air; a catalyst disposed in the exhaust pipe, the catalyst
being capable of promoting reduction reaction of the nitrogen oxide
in the exhaust air; a supply means for supplying the additive agent
to an upstream side of the catalyst in a flow direction of the
exhaust air; a temperature detecting means for detecting
temperature of the exhaust air flowing through the exhaust pipe; a
reducing agent detecting means disposed on a downstream side of the
catalyst in the flow direction of the exhaust air for detecting the
reducing agent; and a control means for controlling the supply
means so as to regulate an amount of the additive agent supplied
into the exhaust pipe, wherein: the control means stops the supply
of the additive agent when the temperature of the exhaust air
detected by the temperature detecting means is lower than a
generation temperature that is needed to generate the reducing
agent from the additive agent, and supplies the additive agent when
the temperature of the exhaust air is equal to or higher than the
generation temperature; and when the reducing agent that is equal
to or larger than a predetermined value is detected by the reducing
agent detecting means after a start of the supply of the additive
agent, the control means reduces the amount of the additive agent
supplied, as compared to the amount of the additive agent supplied
before the reducing agent that is equal to or larger than the
predetermined value is detected.
3. An exhaust emission control device for generating a reducing
agent from an additive agent by use of heat of exhaust air
discharged from an internal combustion engine and for reducing
nitrogen oxide included in the exhaust air by the reducing agent,
the device comprising: an exhaust pipe defining a passage for the
exhaust air; a catalyst disposed in the exhaust pipe, the catalyst
being capable of promoting reduction reaction of the nitrogen oxide
in the exhaust air; a supply means for supplying the additive agent
to an upstream side of the catalyst in a flow direction of the
exhaust air; a temperature detecting means for detecting
temperature of the exhaust air flowing through the exhaust pipe;
and a control means for controlling the supply means so as to
regulate an amount of the additive agent supplied into the exhaust
pipe, wherein: the control means stops the supply of the additive
agent when the temperature of the exhaust air detected by the
temperature detecting means is lower than a generation temperature
that is needed to generate the reducing agent from the additive
agent, and supplies the additive agent when the temperature of the
exhaust air is equal to or higher than the generation temperature;
and when the temperature of the exhaust air is equal to or higher
than a predetermined temperature that is higher than the generation
temperature, the control means reduces the amount of the additive
agent supplied, as compared to the amount of the additive agent
supplied when the temperature of the exhaust air is equal to or
higher than the generation temperature and is lower than the
predetermined temperature.
4. An exhaust emission control device for generating a reducing
agent from an additive agent by use of heat of exhaust air
discharged from an internal combustion engine and for reducing
nitrogen oxide included in the exhaust air by the reducing agent,
the device comprising: an exhaust pipe defining a passage for the
exhaust air; a catalyst disposed in the exhaust pipe, the catalyst
being capable of promoting reduction reaction of the nitrogen oxide
in the exhaust air; a supply means for supplying the additive agent
to an upstream side of the catalyst in a flow direction of the
exhaust air; a temperature detecting means for detecting
temperature of the exhaust air flowing through the exhaust pipe;
and a control means for controlling the supply means so as to
regulate an amount of the additive agent supplied into the exhaust
pipe, wherein: the control means stops the supply of the additive
agent when the temperature of the exhaust air detected by the
temperature detecting means is lower than a generation temperature
that is needed to generate the reducing agent from the additive
agent, and supplies the additive agent when the temperature of the
exhaust air is equal to or higher than the generation temperature;
and when at least one of the following conditions is satisfied, the
control means reduces the amount of the additive agent supplied, as
compared to the amount of the additive agent supplied before the
one of the following conditions is satisfied: the temperature of
the exhaust air is equal to or higher than a predetermined
temperature that is higher than the generation temperature; and a
predetermined time has elapsed after a start of the supply of the
additive agent.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on and incorporates herein by
reference Japanese Patent Application No. 2007-301757 filed on Nov.
21, 2007.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an exhaust emission control
device for reducing nitrogen oxide in exhaust air of an internal
combustion engine such as a diesel engine. The invention is
effectively applied to a vehicle.
[0004] 2. Description of Related Art
[0005] According to an exhaust emission control device for reducing
a nitrogen oxide (NOx) included in exhaust air of an internal
combustion engine such as a diesel engine, the nitrogen oxide is
purified (reduced) by providing in an exhaust pipe a catalyst that
promotes a reduction reaction and by injecting an additive agent
such as a urea water solution into exhaust air flowing into the
catalyst (see, for example, JP2003-293739A).
[0006] More specifically, Urea (CO(NH2)2) injected into exhaust air
is hydrolyzed by exhaust heat (CO(NH2)2+H2O.fwdarw.2NH3+CO2) to
generate ammonia (NH3), which is a reducing agent. Then, the
nitrogen oxide is reduced by reaction between the nitrogen oxide
and the ammonia through the catalyst.
[0007] Exhaust-gas temperature needs to be equal to or higher than
a temperature of 170.degree. C. to 175.degree. C. (hereinafter
referred to as ammonia generation temperature) in order to
hydrolyze urea by exhaust heat. Therefore, even if urea is added to
the exhaust air when the exhaust-gas temperature is lower than the
ammonia generation temperature, the nitrogen oxide cannot be
reduced by the ammonia, and moreover, the urea is released into the
atmosphere without being hydrolyzed, so that the urea is wastefully
consumed.
SUMMARY OF THE INVENTION
[0008] The present invention addresses the above disadvantages.
Thus, it is an objective of the present invention to prevent an
additive agent, such as urea, from being consumed wastefully, and
to reliably reduce (purify) nitrogen oxide.
[0009] To achieve the objective of the present invention, there is
provided an exhaust emission control device for generating a
reducing agent from an additive agent by use of heat of exhaust air
discharged from an internal combustion engine and for reducing
nitrogen oxide included in the exhaust air by the reducing agent.
The device includes an exhaust pipe, a catalyst, a supply means, a
temperature detecting means, and a control means. The exhaust pipe
defines a passage for the exhaust air. The catalyst is disposed in
the exhaust pipe. The catalyst is capable of promoting reduction
reaction of the nitrogen oxide in the exhaust air. The supply means
is for supplying the additive agent to an upstream side of the
catalyst in a flow direction of the exhaust air. The temperature
detecting means is for detecting temperature of the exhaust air
flowing through the exhaust pipe. The control means is for
controlling the supply means so as to regulate an amount of the
additive agent supplied into the exhaust pipe. The control means
stops the supply of the additive agent when the temperature of the
exhaust air detected by the temperature detecting means is lower
than a generation temperature that is needed to generate the
reducing agent from the additive agent, and supplies the additive
agent when the temperature of the exhaust air is equal to or higher
than the generation temperature. When a predetermined time has
elapsed after a start of the supply of the additive agent, the
control means reduces the amount of the additive agent supplied, as
compared to the amount of the additive agent supplied before the
predetermined time has elapsed. The "predetermined time" may be a
"time that is equal to or shorter than a time in which an amount of
the reducing agent generated exceeds an amount that is able to be
adsorbed to the catalyst 3".
[0010] To achieve the objective of the present invention, there is
also provided an exhaust emission control device for generating a
reducing agent from an additive agent by use of heat of exhaust air
discharged from an internal combustion engine and for reducing
nitrogen oxide included in the exhaust air by the reducing agent.
The device includes an exhaust pipe, a catalyst, a supply means, a
temperature detecting means, a reducing agent detecting means, and
a control means. The exhaust pipe defines a passage for the exhaust
air. The catalyst is disposed in the exhaust pipe. The catalyst is
capable of promoting reduction reaction of the nitrogen oxide in
the exhaust air. The supply means is for supplying the additive
agent to an upstream side of the catalyst in a flow direction of
the exhaust air. The temperature detecting means is for detecting
temperature of the exhaust air flowing through the exhaust pipe.
The reducing agent detecting means is disposed on a downstream side
of the catalyst in the flow direction of the exhaust air for
detecting the reducing agent. The control means is for controlling
the supply means so as to regulate an amount of the additive agent
supplied into the exhaust pipe. The control means stops the supply
of the additive agent when the temperature of the exhaust air
detected by the temperature detecting means is lower than a
generation temperature that is needed to generate the reducing
agent from the additive agent, and supplies the additive agent when
the temperature of the exhaust air is equal to or higher than the
generation temperature. When the reducing agent that is equal to or
larger than a predetermined value is detected by the reducing agent
detecting means after a start of the supply of the additive agent,
the control means reduces the amount of the additive agent
supplied, as compared to the amount of the additive agent supplied
before the reducing agent that is equal to or larger than the
predetermined value is detected.
[0011] Furthermore, to achieve the objective of the present
invention, there is provided an exhaust emission control device for
generating a reducing agent from an additive agent by use of heat
of exhaust air discharged from an internal combustion engine and
for reducing nitrogen oxide included in the exhaust air by the
reducing agent. The device includes an exhaust pipe, a catalyst, a
supply means, a temperature detecting means, and a control means.
The exhaust pipe defines a passage for the exhaust air. The
catalyst is disposed in the exhaust pipe. The catalyst is capable
of promoting reduction reaction of the nitrogen oxide in the
exhaust air. The supply means is for supplying the additive agent
to an upstream side of the catalyst in a flow direction of the
exhaust air. The temperature detecting means is for detecting
temperature of the exhaust air flowing through the exhaust pipe.
The control means is for controlling the supply means so as to
regulate an amount of the additive agent supplied into the exhaust
pipe. The control means stops the supply of the additive agent when
the temperature of the exhaust air detected by the temperature
detecting means is lower than a generation temperature that is
needed to generate the reducing agent from the additive agent, and
supplies the additive agent when the temperature of the exhaust air
is equal to or higher than the generation temperature. When the
temperature of the exhaust air is equal to or higher than a
predetermined temperature that is higher than the generation
temperature, the control means reduces the amount of the additive
agent supplied, as compared to the amount of the additive agent
supplied when the temperature of the exhaust air is equal to or
higher than the generation temperature and is lower than the
predetermined temperature.
[0012] In addition, to achieve the objective of the present
invention, there is provided an exhaust emission control device for
generating a reducing agent from an additive agent by use of heat
of exhaust air discharged from an internal combustion engine and
for reducing nitrogen oxide included in the exhaust air by the
reducing agent. The device includes an exhaust pipe, a catalyst, a
supply means, a temperature detecting means, and a control means.
The exhaust pipe defines a passage for the exhaust air. The
catalyst is disposed in the exhaust pipe. The catalyst is capable
of promoting reduction reaction of the nitrogen oxide in the
exhaust air. The supply means is for supplying the additive agent
to an upstream side of the catalyst in a flow direction of the
exhaust air. The temperature detecting means is for detecting
temperature of the exhaust air flowing through the exhaust pipe.
The control means is for controlling the supply means so as to
regulate an amount of the additive agent supplied into the exhaust
pipe. The control means stops the supply of the additive agent when
the temperature of the exhaust air detected by the temperature
detecting means is lower than a generation temperature that is
needed to generate the reducing agent from the additive agent, and
supplies the additive agent when the temperature of the exhaust air
is equal to or higher than the generation temperature. When at
least one of the following conditions is satisfied, the control
means reduces the amount of the additive agent supplied, as
compared to the amount of the additive agent supplied before the
one of the following conditions is satisfied: the temperature of
the exhaust air is equal to or higher than a predetermined
temperature that is higher than the generation temperature; and a
predetermined time has elapsed after a start of the supply of the
additive agent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The invention, together with additional objectives, features
and advantages thereof, will be best understood from the following
description, the appended claims and the accompanying drawings in
which:
[0014] FIG. 1 is a schematic diagram illustrating an exhaust
emission control device according to a first embodiment of the
invention;
[0015] FIG. 2 is a flow chart illustrating characteristic workings
of the exhaust emission control device according to the first
embodiment;
[0016] FIG. 3 is a graph illustrating a relationship among an
injection amount of an additive agent (urea), an exhaust-gas
temperature, and time according to the first embodiment;
[0017] FIG. 4 is a diagram illustrating a relationship between the
injection amount of the additive agent (urea) and the exhaust-gas
temperature according to the first embodiment;
[0018] FIG. 5 is a schematic diagram illustrating an exhaust
emission control device according to a second embodiment of the
invention; and
[0019] FIG. 6 is a flow chart illustrating characteristic workings
of the exhaust emission control device according to the second
embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Embodiments are applications of an exhaust emission control
device of the invention to a urea SCR (Selective Catalytic
Reduction) system of a diesel engine for vehicles. The embodiments
are described below with reference to the drawings.
First Embodiment
Configuration of an Exhaust Emission Control Device
[0021] As shown in FIG. 1, an exhaust pipe 2 defines a passage for
exhaust air discharged from a diesel internal combustion engine 1.
An SCR catalyst 3 (hereinafter referred to as catalyst 3), which
promotes reduction reaction of nitrogen oxide in exhaust air, and a
DPF (Diesel Particulate Filter) 4 for capturing particulate matter
such as soot contained in exhaust air are provided in the exhaust
pipe 2. The DPF 4 is located on an upstream side (engine side) of
the catalyst 3 in an exhaust flow direction.
[0022] A supply valve 5 is a supply means for supplying an additive
agent (urea water solution in a first embodiment) used for
reduction reaction into the exhaust pipe 2 on an upstream side of
the catalyst 3 in a flow direction of the exhaust air. An
additive-agent tank 6 is a tank means for storing the additive
agent supplied to the exhaust pipe 2.
[0023] An additive-agent pump 7 is a pump means for pumping the
additive agent stored in the additive-agent tank 6 to the supply
valve 5. An exhaust temperature sensor 8 is a temperature detecting
means for detecting the temperature of exhaust air discharged from
the internal combustion engine 1 A NOx sensor 9 is a NOx detecting
means for detecting the nitrogen oxide included in exhaust air
which has passed through the catalyst 3.
[0024] In the first embodiment, the exhaust-air temperature is
detected near the inlet of the catalyst 3, and the nitrogen oxide
is detected near the outlet of the catalyst 3. Detection signals of
the exhaust temperature sensor 8 and the NOx sensor 9 are inputted
into an electronic control unit (hereinafter referred to as ECU)
10. The ECU 10 controls workings of the supply valve 5 and the
additive-agent pump 7 based on these detection signals of the
exhaust temperature sensor 8 and the NOx sensor 9 and the like.
[0025] The ECU 10 is a widely-known microcomputer including a
central processing unit (CPU) 10A, a random access memory (RAM)
10B, a read-only memory (ROM) 10C, and a timer 10D, which keeps
time. A program for controlling the supply valve 5 and the like is
stored in the ROM 10C.
(Basic Workings of the Exhaust Emission Control Device)
[0026] The exhaust emission control device hydrolyzes
(CO(NH2)2+H2O.fwdarw.2NH3+CO2) urea (CO(NH2)2), which is the
additive agent injected into exhaust air, using exhaust heat so as
to generate ammonia (NH3), which is a reducing agent. Then, the
exhaust emission control device causes reaction between the
nitrogen oxide and the ammonia through the catalyst 3 so as to
purify (reduce) the nitrogen oxide.
[0027] Meanwhile, when exhaust-gas temperature is equal to or
larger than a temperature of 170.degree. C. to 175.degree. C.
(hereinafter referred to as ammonia generation temperature), urea
is hydrolyzed to generate ammonia. However, when the exhaust-gas
temperature is lower than the ammonia generation temperature, urea
is released into the atmosphere without being hydrolyzed, and
accordingly urea is consumed wastefully.
(Characteristic Workings of the Exhaust Emission Control
Device)
[0028] As shown in FIG. 2, the exhaust emission control device (the
supply valve 5 and the additive-agent pump 7) is started at the
same time as starting of the internal combustion engine 1. The
amount of the additive agent supplied is controlled (hereinafter
referred to as normal control) normally, based on the temperature
of exhaust air (detection temperature of the exhaust temperature
sensor 8) discharged from the internal combustion engine 1, the
amount of the nitrogen oxide (detection value of the NOx sensor 9)
contained in the exhaust air, and the like.
[0029] The control (hereinafter referred to as reducing agent slip
inhibitory control) shown in FIG. 2 is started at the same time as
the normal control and performed independently of the normal
control. The reducing agent slip inhibitory control is performed as
follows.
[0030] That is, when the exhaust-gas temperature which the exhaust
temperature sensor 8 has detected is smaller than the ammonia
generation temperature, supply of the additive agent (urea) to the
exhaust pipe 2 is stopped. On the other hand, when the exhaust-gas
temperature is equal to or larger than the ammonia generation
temperature, the additive agent is supplied to the exhaust pipe
2.
[0031] An amount of the additive agent supplied into the exhaust
pipe 2 is such that a larger amount of the reducing agent than an
amount of the reducing agent needed to reduce all the nitrogen
oxide contained in the exhaust air discharged from the internal
combustion engine 1 is generated.
[0032] Meanwhile, the reducing agent generated through the
hydrolysis is adsorbed to the catalyst 3, and then produces
reduction reaction with nitrogen oxide through the catalyst 3. An
excessively generated reducing agent is kept adsorbed to the
catalyst 3, and when the exhaust-gas temperature lowers to less
than the ammonia generation temperature and thereby a supply of the
additive agent stops, the reducing agent, which is excessively
generated and adsorbed to the catalyst 3, is consumed on the
reduction reaction and accordingly the nitrogen oxide is
purified.
[0033] However, if the exhaust-gas temperature continues being
equal to or larger than the ammonia generation temperature over a
long time, a total amount of the generated reducing agent exceeds a
threshold limit of the adsorption by the catalyst 3, and
accordingly, the generated reducing agent is released without being
used for the reduction reaction.
[0034] In the first embodiment, on at least one of a condition that
the exhaust-gas temperature is equal to or higher than a
predetermined temperature (hereinafter referred to as supply stop
temperature) that is higher than the ammonia generation
temperature, and a condition that a predetermined time (hereinafter
referred to as a supply stop time) has elapsed since a start of
supply of the additive agent, the supply amount of the additive
agent is reduced compared to an amount of the additive agent that
has been supplied into the exhaust pipe 2 before one of the two
conditions is satisfied.
[0035] "Before one of the two conditions is satisfied" is "when the
exhaust-gas temperature is equal to or higher than the ammonia
generation temperature and lower than the supply stop temperature"
or "before the supply stop time elapses after the exhaust-gas
temperature becomes equal to or higher than the ammonia generation
temperature". Therefore, the "amount of the additive agent that has
been supplied into the exhaust pipe 2 before one of the two
conditions is satisfied" is such that, as described above, a larger
amount of the reducing agent than an amount of the reducing agent
needed to reduce all the nitrogen oxide contained in the exhaust
air discharged from the internal combustion engine 1 is
generated.
[0036] A supply amount of the additive agent, which can generate an
amount of the reducing agent needed to reduce all the nitrogen
oxide contained in the exhaust air is hereinafter referred to as a
normal amount, and a supply amount of the additive agent supplied
before one of the two conditions is satisfied is hereinafter
referred to as more than the normal amount.
[0037] Details of the above-described workings are explained below
with reference to a flow chart in FIG. 2. When the reducing agent
slip inhibitory control is started, whether the detection
temperature (hereinafter referred to as exhaust-gas temperature) of
the exhaust temperature sensor 8 is lower than the ammonia
generation temperature T1 is determined (S1).
[0038] If it is determined that the exhaust-gas temperature is
lower than the ammonia generation temperature T1 (S1: YES), the
time keeping by the timer 10D is started or continued (S7) after
the supply (injection) of the reducing agent is stopped and time
that is kept by the timer 10D is initialized (S2).
[0039] If it is determined that the exhaust-gas temperature is not
lower than the ammonia generation temperature T1, i.e., the
exhaust-gas temperature is equal to or higher than the ammonia
generation temperature T1 (S1:NO), whether the time kept by the
timer 10D is equal to or longer than the supply stop time is
determined (S3). If it is determined that the kept time is equal to
or longer than the supply stop time (S3: YES), the time keeping by
the timer 10D is started or continued (S7) after the normal amount
of the additive agent is supplied into the exhaust pipe 2 (S5).
[0040] If it is determined that the kept time is not equal to or
longer than the supply stop time (S3: NO), it is determined whether
the exhaust-gas temperature is equal to or higher than the supply
stop temperature T2 (S4). If it is determined that the exhaust-gas
temperature is equal to or higher than the supply stop temperature
T2 (S4: YES), the time keeping by the timer 10D is started or
continued (S7) after the normal amount of the additive agent is
supplied into the exhaust pipe 2 (S5).
[0041] If it is determined that the exhaust-gas temperature is not
equal to or higher than the supply stop temperature T2 (S4: NO),
the time keeping by the timer 10D is started or continued (S7)
after the additive agent more than the normal amount is supplied
into the exhaust pipe 2 (S6). Then, after the processing S7 is
performed, the processing S1 is performed again.
(Characteristics of the Exhaust Emission Control Device)
[0042] In the first embodiment, if the exhaust-gas temperature is
lower than the ammonia generation temperature T1, the supply of the
additive agent is stopped as shown in FIG. 3 and FIG. 4.
Accordingly, the additive agent is prevented from being consumed
wastefully.
[0043] If the exhaust-gas temperature is equal to or higher than
the ammonia generation temperature T1, the additive agent more than
the normal amount is supplied. Accordingly, the nitrogen oxide is
reduced (purified) by the reducing agent generated from the
additive agent, and a part of the generated reducing agent is
adsorbed to the catalyst 3. If the exhaust-gas temperature is lower
than the ammonia generation temperature T1 and thereby the supply
of the additive agent stops, the nitrogen oxide is reduced by the
reducing agent adsorbed to the catalyst 3.
[0044] If the exhaust-gas temperature is equal to or higher than
the ammonia generation temperature T1, as described above, a part
of the generated reducing agent is adsorbed to the catalyst 3
without being used for the reductive reaction, and then used for
the reductive reaction when the exhaust-gas temperature is lower
than the ammonia generation temperature T1. However, when the
amount of the generated reducing agent exceeds an amount that is
able to be adsorbed to the catalyst 3, the generated reducing agent
is discharged without being used for the reduction of the nitrogen
oxide. Accordingly, the additive agent is consumed wastefully.
[0045] In the first embodiment, as shown in FIG. 3, if the supply
stop time has elapsed after the start of supply of the additive
agent, the supply amount of the additive agent is reduced compared
to a supply amount before the predetermined time has elapsed.
Accordingly, the amount of the reducing agent generated is
prevented from exceeding the amount that is able to be adsorbed to
the catalyst 3.
[0046] Moreover, when the reducing agent continues being generated
from the additive agent, the exhaust-gas temperature gradually
increases over time. Accordingly, by reducing the supply amount of
the additive agent when the exhaust-gas temperature becomes equal
to or higher than the supply stop temperature T2, the amount of the
generated reducing agent is prevented from exceeding the amount
that is able to be adsorbed to the catalyst 3.
[0047] In addition, as is obvious from the above description, the
supply stop temperature T2 is a temperature corresponding to, for
example, an exhaust-gas temperature at the time the supply stop
time elapses after the ammonia generation temperature T1. The
supply stop time and the supply stop temperature T2 are determined
appropriately based on specifications of the catalyst 3 or
specifications of the internal combustion engine 1.
[0048] As described above, in the first embodiment, the additive
agent is prevented from being consumed wastefully, and the nitrogen
oxide is reliably reduced (purified). In the first embodiment, the
supply valve 5 corresponds to the "supply means", the exhaust
temperature sensor 8 corresponds to the "temperature detecting
means", and the ECU 10 corresponds to a "control means".
Second Embodiment
General Description of an Exhaust Emission Control Device According
to a Second Embodiment
[0049] In the second embodiment, as shown in FIG. 5, an ammonia
sensor 11 for detecting ammonia, which is a reducing agent, is
disposed on a downstream side of a catalyst 3 in a flow direction
of the exhaust air. A larger amount of an additive agent than a
normal amount is supplied until the ammonia sensor 11 detects
ammonia of a predetermined value or above after an exhaust-gas
temperature becomes equal to or higher than an ammonia generation
temperature T1. The normal amount of the additive agent is supplied
until the exhaust-gas temperature becomes lower than the ammonia
generation temperature T1 after the ammonia sensor 11 detects
ammonia.
[0050] The above-described workings are explained in detail with
reference to FIG. 6.
(Characteristic Workings of the Exhaust Emission Control Device of
the Second Embodiment)
[0051] When reducing agent slip inhibitory control is started, it
is first determined whether the exhaust-gas temperature is lower
than the ammonia generation temperature T1 (S11).
[0052] If it is determined that the exhaust-gas temperature is
lower than the ammonia generation temperature T1 (S11: YES), a
supply (injection) of the reducing agent is stopped and time that
is kept by a timer 10D is initialized (S12). Then, when a
predetermined time has elapsed after the time keeping by the timer
10D is started or continued (S16), the processing S11 is performed
again.
[0053] On the other hand, if it is determined that the exhaust-gas
temperature is not lower than the ammonia generation temperature
T1, i.e., the exhaust-gas temperature is equal to or higher than
the ammonia generation temperature T1 (S11: NO), whether the
ammonia sensor 11 detects ammonia of the predetermined value or
above is determined (S13). If it is determined that ammonia of the
predetermined value or above is detected (S13: YES), the normal
amount of the additive agent is supplied into the exhaust pipe 2
(S14). Then, the processing S11 is performed again when the
predetermined time has elapsed (S16).
[0054] If it is determined that ammonia of the predetermined value
or above is not detected (S13: NO), the additive agent more than
the normal amount is supplied into the exhaust pipe 2 (S15). Then,
the processing S11 is performed again when the predetermined time
has elapsed (S16).
(Characteristics of the Exhaust Emission Control Device of the
Second Embodiment)
[0055] In the second embodiment as well, similar to the
above-described embodiment, if the exhaust-gas temperature is lower
than the ammonia generation temperature T1, the supply of the
additive agent is stopped and the nitrogen oxide is reduced by the
reducing agent adsorbed to the catalyst 3. Therefore, the additive
agent is prevented from being consumed wastefully.
[0056] If the exhaust-gas temperature is equal to or higher than
the ammonia generation temperature T1, the additive agent is
supplied and the nitrogen oxide is reduced (purified) by the
reducing agent generated from the additive agent. Furthermore, a
part of the generated reducing agent is adsorbed to the catalyst
3.
[0057] When ammonia (reducing agent) of the predetermined value or
above is detected by the ammonia sensor 11 after the supply of the
additive agent is started, the supply amount of the additive agent
is reduced as compared to the supply amount before the reducing
agent has been detected. Thus, the amount of the generated reducing
agent is prevented from exceeding the amount that is able to be
adsorbed to the catalyst 3.
[0058] Therefore, in the second embodiment as well, the additive
agent is prevented from being consumed wastefully, and the nitrogen
oxide is reliably reduced (purified). In the second embodiment, the
ammonia sensor 11 corresponds to a "reducing agent detecting
means".
Other Embodiments
[0059] In the above embodiments, urea is used as an additive agent
However, the invention is not limited to the above. That is, a
reducing agent other than ammonia, or an additive agent that
generates this reducing agent may be used.
[0060] According to the invention, the first embodiment and the
second embodiment may be combined.
[0061] Additional advantages and modifications will readily occur
to those skilled in the art. The invention in its broader terms is
therefore not limited to the specific details, representative
apparatus, and illustrative examples shown and described.
* * * * *