U.S. patent application number 12/738414 was filed with the patent office on 2010-09-30 for control unit and control method for reductant supply device.
Invention is credited to Wataru Domon, Hiroyuki Igarashi, Eiji Nakao.
Application Number | 20100242439 12/738414 |
Document ID | / |
Family ID | 40567225 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100242439 |
Kind Code |
A1 |
Domon; Wataru ; et
al. |
September 30, 2010 |
CONTROL UNIT AND CONTROL METHOD FOR REDUCTANT SUPPLY DEVICE
Abstract
There are provided a reductant supply device and a control
method for the reductant supply device, which can prevent heat
damage of a reductant injection valve, and also prevent
crystallization of urea solution due to excessive cooling of the
solution reductant. The reductant supply device which is used in an
exhaust gas purification device that injects and supplies, as a
reductant, a urea solution to an exhaust gas upstream side of a
reduction catalyst disposed in an exhaust gas passage of an
internal combustion engine, and that reduces and purifies nitrogen
oxides contained in exhaust gas using the reduction catalyst, the
reductant supply device having a reductant injection valve that is
fixed to an exhaust pipe on the exhaust gas upstream side of the
reduction catalyst, includes: a cooling water circulation passage
that circulates at least part of cooling water of the internal
combustion engine to cool the reductant injection valve; flow rate
control means for adjusting a flow rate of cooling water flowing
through the cooling water circulation passage; temperature
detection means for detecting a temperature of the reductant
injection valve; and control means for controlling the flow rate
control means based on the temperature of the reductant injection
valve.
Inventors: |
Domon; Wataru; (Saitama,
JP) ; Igarashi; Hiroyuki; (Saitama, JP) ;
Nakao; Eiji; (Saitama, JP) |
Correspondence
Address: |
RONALD E. GREIGG;GREIGG & GREIGG P.L.L.C.
1423 POWHATAN STREET, UNIT ONE
ALEXANDRIA
VA
22314
US
|
Family ID: |
40567225 |
Appl. No.: |
12/738414 |
Filed: |
September 1, 2008 |
PCT Filed: |
September 1, 2008 |
PCT NO: |
PCT/JP2008/065641 |
371 Date: |
April 16, 2010 |
Current U.S.
Class: |
60/274 ;
60/295 |
Current CPC
Class: |
F01N 3/208 20130101;
B01D 53/9431 20130101; F01N 2610/11 20130101; F01N 2610/1473
20130101; F01N 2900/1812 20130101; F01P 3/20 20130101; F01N
2900/1811 20130101; F01P 2060/16 20130101; B01D 2251/2067 20130101;
F01N 2260/024 20130101; F01N 2610/10 20130101; Y02T 10/24 20130101;
Y02T 10/12 20130101; F01N 2610/02 20130101; F01N 2610/1433
20130101 |
Class at
Publication: |
60/274 ;
60/295 |
International
Class: |
F01N 3/20 20060101
F01N003/20 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 19, 2007 |
JP |
2007-272370 |
Claims
1-6. (canceled)
7. A reductant supply device which is used in an exhaust gas
purification device that injects and supplies, as a reductant, a
urea solution to an exhaust gas upstream side of a reduction
catalyst disposed in an exhaust gas passage of an internal
combustion engine, and that reduces and purifies nitrogen oxides
contained in exhaust gas using the reduction catalyst, the
reductant supply device having a reductant injection valve that is
fixed to an exhaust pipe on the exhaust gas upstream side of the
reduction catalyst, the reductant supply device comprising: a
cooling water circulation passage that circulates at least part of
cooling water of the internal combustion engine to cool the
reductant injection valve; flow rate control means for adjusting a
flow rate of cooling water flowing through the cooling water
circulation passage; temperature detection means for detecting a
temperature of the reductant injection valve; and control means for
controlling the flow rate control means based on the temperature of
the reductant injection valve.
8. The reductant supply device according to claim 7, wherein the
control means controls the flow rate control means such that the
temperature of the reductant injection valve is maintained at a
temperature lower than a heat resistance temperature of the
reductant injection valve.
9. The reductant supply device according to claim 7, wherein the
control means controls the flow rate control means such that the
temperature of the reductant injection valve is maintained at a
temperature equal to or higher than a boiling point of the urea
solution.
10. The reductant supply device according to claim 8, wherein the
control means controls the flow rate control means such that the
temperature of the reductant injection valve is maintained at a
temperature equal to or higher than a boiling point of the urea
solution.
11. The reductant supply device according to claim 7, wherein the
temperature detection means calculates a temperature at a tip of
the reductant injection valve based on at least one of a
temperature of the exhaust gas, a flow rate of the exhaust gas, a
temperature of the liquid reductant, a temperature of the cooling
water, an outside air temperature, and an injection supply amount
from the reductant injection valve.
12. The reductant supply device according to claim 8, wherein the
temperature detection means calculates a temperature at a tip of
the reductant injection valve based on at least one of a
temperature of the exhaust gas, a flow rate of the exhaust gas, a
temperature of the liquid reductant, a temperature of the cooling
water, an outside air temperature, and an injection supply amount
from the reductant injection valve.
13. The reductant supply device according to claim 9, wherein the
temperature detection means calculates a temperature at a tip of
the reductant injection valve based on at least one of a
temperature of the exhaust gas, a flow rate of the exhaust gas, a
temperature of the liquid reductant, a temperature of the cooling
water, an outside air temperature, and an injection supply amount
from the reductant injection valve.
14. The reductant supply device according to claim 10, wherein the
temperature detection means calculates a temperature at a tip of
the reductant injection valve based on at least one of a
temperature of the exhaust gas, a flow rate of the exhaust gas, a
temperature of the liquid reductant, a temperature of the cooling
water, an outside air temperature, and an injection supply amount
from the reductant injection valve.
15. The reductant supply device according to claim 7, wherein if
the cooling water circulation passage, the flow rate control means
and the control means are respectively referred to as a first
cooling water circulation passage, first flow rate control means
and first control means, the reductant supply device further
comprising: a second cooling water circulation passage that
circulates at least part of the cooling water of the internal
combustion engine in order to adjust a temperature of the urea
solution in a storage tank that stores the urea solution; second
flow rate control means for adjusting a flow rate of the cooling
water that flows through the second cooling water circulation
passage; and second control means for controlling the second flow
rate control means based on the temperature of the urea solution in
the storage tank.
16. The reductant supply device according to claim 8, wherein if
the cooling water circulation passage, the flow rate control means
and the control means are respectively referred to as a first
cooling water circulation passage, first flow rate control means
and first control means, the reductant supply device further
comprising: a second cooling water circulation passage that
circulates at least part of the cooling water of the internal
combustion engine in order to adjust a temperature of the urea
solution in a storage tank that stores the urea solution; second
flow rate control means for adjusting a flow rate of the cooling
water that flows through the second cooling water circulation
passage; and second control means for controlling the second flow
rate control means based on the temperature of the urea solution in
the storage tank.
17. The reductant supply device according to claim 9, wherein if
the cooling water circulation passage, the flow rate control means
and the control means are respectively referred to as a first
cooling water circulation passage, first flow rate control means
and first control means, the reductant supply device further
comprising: a second cooling water circulation passage that
circulates at least part of the cooling water of the internal
combustion engine in order to adjust a temperature of the urea
solution in a storage tank that stores the urea solution; second
flow rate control means for adjusting a flow rate of the cooling
water that flows through the second cooling water circulation
passage; and second control means for controlling the second flow
rate control means based on the temperature of the urea solution in
the storage tank.
18. The reductant supply device according to claim 10, wherein if
the cooling water circulation passage, the flow rate control means
and the control means are respectively referred to as a first
cooling water circulation passage, first flow rate control means
and first control means, the reductant supply device further
comprising: a second cooling water circulation passage that
circulates at least part of the cooling water of the internal
combustion engine in order to adjust a temperature of the urea
solution in a storage tank that stores the urea solution; second
flow rate control means for adjusting a flow rate of the cooling
water that flows through the second cooling water circulation
passage; and second control means for controlling the second flow
rate control means based on the temperature of the urea solution in
the storage tank.
19. The reductant supply device according to claim 11, wherein if
the cooling water circulation passage, the flow rate control means
and the control means are respectively referred to as a first
cooling water circulation passage, first flow rate control means
and first control means, the reductant supply device further
comprising: a second cooling water circulation passage that
circulates at least part of the cooling water of the internal
combustion engine in order to adjust a temperature of the urea
solution in a storage tank that stores the urea solution; second
flow rate control means for adjusting a flow rate of the cooling
water that flows through the second cooling water circulation
passage; and second control means for controlling the second flow
rate control means based on the temperature of the urea solution in
the storage tank.
20. The reductant supply device according to claim 12, wherein if
the cooling water circulation passage, the flow rate control means
and the control means are respectively referred to as a first
cooling water circulation passage, first flow rate control means
and first control means, the reductant supply device further
comprising: a second cooling water circulation passage that
circulates at least part of the cooling water of the internal
combustion engine in order to adjust a temperature of the urea
solution in a storage tank that stores the urea solution; second
flow rate control means for adjusting a flow rate of the cooling
water that flows through the second cooling water circulation
passage; and second control means for controlling the second flow
rate control means based on the temperature of the urea solution in
the storage tank.
21. The reductant supply device according to claim 13, wherein if
the cooling water circulation passage, the flow rate control means
and the control means are respectively referred to as a first
cooling water circulation passage, first flow rate control means
and first control means, the reductant supply device further
comprising: a second cooling water circulation passage that
circulates at least part of the cooling water of the internal
combustion engine in order to adjust a temperature of the urea
solution in a storage tank that stores the urea solution; second
flow rate control means for adjusting a flow rate of the cooling
water that flows through the second cooling water circulation
passage; and second control means for controlling the second flow
rate control means based on the temperature of the urea solution in
the storage tank.
22. The reductant supply device according to claim 14, wherein if
the cooling water circulation passage, the flow rate control means
and the control means are respectively referred to as a first
cooling water circulation passage, first flow rate control means
and first control means, the reductant supply device further
comprising: a second cooling water circulation passage that
circulates at least part of the cooling water of the internal
combustion engine in order to adjust a temperature of the urea
solution in a storage tank that stores the urea solution; second
flow rate control means for adjusting a flow rate of the cooling
water that flows through the second cooling water circulation
passage; and second control means for controlling the second flow
rate control means based on the temperature of the urea solution in
the storage tank.
23. A control method for a reductant supply device which is used in
an exhaust gas purification device that injects and supplies a
liquid reductant to an exhaust gas upstream side of a reduction
catalyst disposed in an exhaust gas passage of an internal
combustion engine, and that reduces and purifies nitrogen oxides
contained in exhaust gas using the reduction catalyst, the
reductant supply device having a reductant injection valve that is
fixed to an exhaust pipe on the exhaust gas upstream side of the
reduction catalyst, the control method comprising: cooling the
reductant injection valve by circulating at least part of cooling
water of the internal combustion engine; detecting a temperature of
the reductant injection valve; and controlling a flow rate of the
cooling water such that a temperature of a fuel control valve is
maintained in a predetermined range.
Description
TECHNICAL FIELD
[0001] The present invention relates to a reductant supply device
and a control method used in an exhaust gas purification device.
Particularly, the present invention relates to a reductant supply
device that uses a urea solution as a reductant and that cools a
reductant injection valve by circulating cooling water for cooling
an internal combustion engine, and a control method for the
reductant supply device.
BACKGROUND ART
[0002] Generally, exhaust gas discharged from an internal
combustion engine, such as a diesel engine, contains nitrogen
oxides (hereinafter referred to as NO.sub.x) that may have an
impact on the environment. As an exhaust gas purification device
used to purify NO.sub.x, an exhaust gas purification device (an SCR
system) is known which injects and supplies a liquid reductant,
such as a urea solution, into exhaust gas on the upstream side of a
reduction catalyst disposed in an exhaust gas passage, and which
selectively reduces and purifies NO.sub.x using the reduction
catalyst.
[0003] As one form of an exhaust gas purification device structured
like that described above, an exhaust gas purification device of a
type is known that pressure-feeds a liquid reductant toward a
reductant injection valve fixed to an exhaust pipe, and controls
opening and closing of the reductant injection valve, thereby
injecting and supplying the liquid reductant into the exhaust pipe.
In this type of exhaust gas purification device, if a urea solution
is used as a liquid reductant and the temperature of the urea
solution becomes excessively high, urea is hydrolyzed and
crystallized before the urea solution is injected from the
reductant injection valve. As a result, there is a possibility that
a supply system of the liquid reductant will be partially or
completely clogged. In light of this fact, in order to maintain the
urea solution at a sufficiently low temperature, a method for
reducing NO.sub.x discharge has been proposed in which a heat
exchange fluid, such as an engine coolant, is caused to pass
through a line or an injector when heat is exchanged, while
maintaining sufficient supply speed of the urea solution and a heat
exchange fluid channel (see Patent Document 1).
[0004] Further, an electromagnetically controlled valve that is
used as the above-described reductant injection valve is directly
attached to an exhaust pipe, regardless of the fact that a control
part and a plastic part of the valve are relatively weak against
heat. As a result, the electromagnetically controlled valve is
likely to suffer from heat damage caused by heat being transferred
from the exhaust pipe.
[0005] To address this, although a hydrocarbon (HC) fuel is used as
a reductant, an exhaust gas purification device for a diesel engine
has been proposed that is capable of improving durability of an
injector for adding a reductant to a NO.sub.x catalyst. More
specifically, an exhaust gas purification device for a diesel
engine is disclosed that includes a NO.sub.x catalyst arranged in
an exhaust gas passage of the engine, and an injector for adding a
NO.sub.x reductant that is provided in the exhaust gas passage on
the upstream side of the NO.sub.x catalyst. The exhaust gas
purification device includes: a cooling water passage provided in
the injector; a circulation passage that connects the cooling water
passage and an engine cooling water passage; and circulation means
for circulating cooling water between the cooling water passage and
an engine cooling water passage via the circulation passage (see
Patent Document 2).
[0006] Patent Document 1: Published Japanese Translation of PCT
Application No. JP-T-2001-518830 (Claim 11, page 8, lines 7 to
10)
[0007] Patent Document 2: Japanese Patent Application Publication
No. JP-A-9-96212 (full text, all drawings)
DISCLOSURE OF THE INVENTION
Problems that the Invention is to Solve
[0008] When the reductant injection valve is cooled by circulating
engine cooling water, the reductant injection valve is cooled
effectively because a relatively large amount of the engine cooling
water is circulated. However, in some cases, the reductant
injection valve is cooled more than necessary due to a large
circulation amount of the cooling water. As a result, not only
crystallization of urea that is caused because the temperature of
the urea solution becomes high and the urea solution is decomposed
in a reductant supply device as indicated in Patent Document 1, but
also crystallization of urea due to natural evaporation of a
solvent may occur in the vicinity of a nozzle hole of the reductant
injection valve.
[0009] More specifically, because the engine cooling water is
maintained at approximately 70 to 80.degree. C., for example, if
the circulation amount of the cooling water that is circulated in
the reductant injection valve becomes large, the temperature of the
reductant injection valve may be cooled to approximately 80 to
100.degree. C., for example. On the other hand, a urea aqueous
solution that flows into the reductant supply valve is fed to the
nozzle hole while being maintained at a temperature less than
100.degree. C. even if the urea aqueous solution is affected by the
heat of the reductant injection valve. Accordingly, the temperature
of the urea aqueous solution injected from the reductant injection
valve becomes lower than the boiling point in the exhaust gas
passage whose pressure is relatively close to the atmospheric
pressure. Therefore, the urea aqueous solution does not rapidly
evaporate, and is likely to adhere to the vicinity of the nozzle
hole. The urea aqueous solution that is maintained at a temperature
lower than 100.degree. C. is likely to cause precipitation due to
natural evaporation of water acting as a solvent, in an environment
under a pressure relatively close to atmospheric pressure. In
addition, an exhaust gas flow occurs in the vicinity of the nozzle
hole of the reductant invention valve. As a result, natural
evaporation of the water contained in the urea aqueous solution is
more likely to occur, and precipitation of urea is facilitated. If
crystallization of urea occurs in the vicinity of the nozzle hole
of the reductant injection valve in this manner, the atomization of
the urea aqueous solution is adversely affected. At the same time,
clogging of the nozzle hole may occur.
[0010] To address this, the inventors of the present invention have
made strenuous efforts, and have found that the above-described
problems can be solved by providing means for controlling the
circulation amount of cooling water, in a reductant supply device
having a structure in which engine cooling water is circulated to
cool a urea solution. Thus, the present invention has been
achieved. More specifically, it is an object of the present
invention to provide a reductant supply device which can prevent
heat damage of a reductant injection valve by adjusting the
circulation amount of cooling water in accordance with the
temperature of the reductant injection valve, and which can also
prevent crystallization of a urea solution due to excessive cooling
of a liquid reductant, and a control method for the reductant
supply device.
Means for Solving the Problems
[0011] In order to solve the problems described above, according to
the present invention, there is provided a reductant supply device
which is used in an exhaust gas purification device that injects
and supplies, as a reductant, a urea solution to an exhaust gas
upstream side of a reduction catalyst disposed in an exhaust gas
passage of an internal combustion engine, and that reduces and
purifies nitrogen oxides contained in exhaust gas using the
reduction catalyst, the reductant supply device having a reductant
injection valve that is fixed to an exhaust pipe on the exhaust gas
upstream side of the reduction catalyst. The reductant supply
device is characterized by including: a cooling water circulation
passage that circulates at least part of cooling water of the
internal combustion engine to cool the reductant injection valve;
flow rate control means for adjusting a flow rate of cooling water
flowing through the cooling water circulation passage; temperature
detection means for detecting a temperature of the reductant
injection valve; and control means for controlling the flow rate
control means based on the temperature of the reductant injection
valve.
[0012] Further, with the structure of the reductant supply device
of the present invention, it is desirable that the control means
controls the flow rate control means such that the temperature of
the reductant injection valve is maintained at a temperature lower
than a heat resistance temperature of the reductant injection
valve.
[0013] Further, with the structure of the reductant supply device
of the present invention, it is desirable that the control means
controls the flow rate control means such that the temperature of
the reductant injection valve is maintained at a temperature equal
to or higher than a boiling point of the urea solution.
[0014] Further, with the structure of the reductant supply device
of the present invention, it is desirable that the temperature
detection means calculates a temperature at a tip of the reductant
injection valve based on at least one of a temperature of the
exhaust gas, a flow rate of the exhaust gas, a temperature of the
liquid reductant, a temperature of the cooling water, an outside
air temperature, and an injection supply amount from the reductant
injection valve.
[0015] Further, with the structure of the reductant supply device
of the present invention, if the cooling water circulation passage,
the flow rate control means and the control means are respectively
referred to as a first cooling water circulation passage, first
flow rate control means and first control means, it is desirable
that the reductant supply device further includes: a second cooling
water circulation passage that circulates at least part of the
cooling water of the internal combustion engine in order to adjust
a temperature of the urea solution in a storage tank that stores
the urea solution; second flow rate control means for adjusting a
flow rate of the cooling water that flows through the second
cooling water circulation passage; and second control means for
controlling the second flow rate control means based on the
temperature of the urea solution in the storage tank.
[0016] Furthermore, according to another aspect of the present
invention, there is provided a control method for a reductant
supply device which is used in an exhaust gas purification device
that injects and supplies a liquid reductant to an exhaust gas
upstream side of a reduction catalyst disposed in an exhaust gas
passage of an internal combustion engine, and that reduces and
purifies nitrogen oxides contained in exhaust gas using the
reduction catalyst, the reductant supply device having a reductant
injection valve that is fixed to an exhaust pipe on the exhaust gas
upstream side of the reduction catalyst. The control method for the
reductant supply device is characterized in that: the reductant
injection valve is cooled by circulating at least part of cooling
water of the internal combustion engine; a temperature of the
reductant injection valve is detected; and a flow rate of the
cooling water is controlled such that a temperature of the
reductant injection valve is maintained in a predetermined
range.
ADVANTAGE OF THE INVENTION
[0017] According to the reductant supply device of the present
invention, the reductant injection valve is cooled effectively by
using the cooling water of the internal combustion engine. Further,
while the temperature at the tip of the reductant injection valve
is detected, the flow rate of the cooling water is adjusted in
accordance with the detected temperature. As a result, it is
possible to prevent excessive cooling of the reductant injection
valve. Accordingly, heat damage of the reductant injection valve is
prevented, and crystallization of urea in the vicinity of the
reductant injection valve is prevented. Thus, stable atomization of
the reductant is realized.
[0018] Further, in the reductant supply device of the present
invention, the control means performs control such that the
temperature of the reductant injection valve is maintained at a
temperature lower than the heat resistance temperature. Thus, heat
damage of the reductant injection valve is reliably prevented.
[0019] Further, in the reductant supply device of the present
invention, the control means performs control such that the
temperature of the reductant injection valve is maintained at a
temperature equal to or higher than a boiling point of the urea
solution. Thus, the urea solution that is exposed in the exhaust
pipe is also rapidly vaporized due to exhaust heat, and
crystallization of urea in the vicinity of the nozzle hole is
reliably inhibited.
[0020] Further, in the reductant supply device of the present
invention, the temperature detection means is means for calculating
the temperature at the tip of the reductant injection valve.
Therefore, it is possible to estimate the temperature at the tip of
the reductant injection valve by using a known device structure,
without using an additional temperature sensor.
[0021] Further, in the reductant supply device of the present
invention, the cooling water of the internal combustion engine is
used to adjust the temperature of the urea solution in the storage
tank. Therefore, the urea solution having a temperature equal to or
lower than the boiling point is inhibited from being injected
without adjustment from the reductant injection valve. As a result,
crystallization of urea in the vicinity of the nozzle hole is
inhibited more reliably.
[0022] Moreover, according to the control method for the reductant
supply device of the present invention, when the reductant
injection valve is cooled by circulating the cooling water of the
internal combustion engine, the circulation amount of the cooling
water is adjusted based on the temperature of the reductant
injection valve. Thus, heat damage of the reductant injection valve
is prevented, and crystallization of urea due to excessive cooling
of the reductant injection valve is prevented. Accordingly, stable
atomization of the reductant is realized.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a diagram showing an example of the structure of
an exhaust gas purification device.
[0024] FIG. 2 is a block diagram showing an example of the
structure of a control unit (DCU) of a reductant supply device
provided in the exhaust gas purification device.
[0025] FIG. 3 is a flowchart showing an example of temperature
control of a reductant injection valve that uses cooling water of
an internal combustion engine.
[0026] FIG. 4 is a flowchart showing an example of temperature
control of a urea aqueous solution that uses the cooling water of
the internal combustion engine.
BEST MODE FOR CARRYING OUT THE INVENTION
[0027] Hereinafter, an embodiment relating to a reductant supply
device and a control method for the reductant supply device of the
present invention will be described concretely with reference to
the appended drawings. However, the embodiment is just one form of
the present invention and in no way limits the present invention,
and any modification can be made within the scope of the present
invention.
[0028] Note that, in the respective drawings, structural members
that are the same are denoted with the same reference numerals, and
explanation thereof is omitted as appropriate.
1. Exhaust Gas Purification Device
[0029] First, an example of the structure of an exhaust gas
purification device in which a reductant supply device of the
present embodiment is provided will be described with reference to
FIG. 1.
[0030] An exhaust gas purification device 10 shown in FIG. 1
injects and supplies a urea aqueous solution serving as a liquid
reductant to the upstream side of a reduction catalyst 13 disposed
in an exhaust gas passage. The exhaust gas purification device 10
selectively reduces and purifies NO.sub.x contained in exhaust gas
using the reduction catalyst 13. The exhaust gas purification
device 10 includes, as main elements, the reduction catalyst 13 and
a reductant supply device 20. The reduction catalyst 13 is arranged
in the middle of an exhaust pipe 11 that is connected to an
internal combustion engine 5, and selectively reduces NO.sub.x
contained in exhaust gas. The reductant supply device 20 includes a
reductant injection valve 31 that injects and supplies the urea
aqueous solution into the exhaust pipe 11, on the upstream side of
the reduction catalyst 13.
2. Reductant Supply Device
[0031] The reductant supply device 20 provided in the exhaust gas
purification device 10 of the present embodiment includes: the
reductant injection valve 31 that is fixed to the exhaust pipe 11
on the upstream side of the reduction catalyst 13; a storage tank
50 that stores the urea aqueous solution; a pump module 40 having a
pump 41 that pressure-feeds the urea aqueous solution from the
storage tank 50 to the reductant injection valve 31; and a control
unit (hereinafter referred to as a "DCU: dosing control unit") 60
that performs control of the reductant injection valve 31 and the
pump 41 in order to control an injection amount of the reductant
that is injected and supplied into the exhaust pipe 11. Further,
the pump module 40 and the reductant injection valve 31 are
connected by a first supply passage 58. The storage tank 50 and the
pump module 40 are connected by a second supply passage 57.
Furthermore, the pump module 40 and the storage tank 50 are
connected by a circulation passage 59.
[0032] For example, an on-off valve whose on-off positioning is
controlled by duty control is used as the reductant injection valve
31. The urea aqueous solution that is pressure-fed from the pump
module 40 to the reductant injection valve 31 is maintained at a
predetermined pressure. When the reductant injection valve 31 is
opened by a control signal transmitted from the DCU 60, the urea
aqueous solution is injected into the exhaust gas passage.
[0033] Further, a cooling water passage 37 is provided in the
reductant injection valve 31, and the cooling water of the internal
combustion engine 5 is used to cool the reductant injection valve
31. In the example of the reductant supply device 20 of the present
embodiment, a first cooling water circulation passage 85 that
includes the cooling water passage 37 of the reductant injection
valve 31 is provided. The cooling water of the internal combustion
engine 5 is circulated by a cooling water circulation pump 73
through a cooling water passage 75 of the internal combustion
engine 5, and diverges from the cooling water passage 75 and also
flows into the first cooling water circulation passage 85. The
cooling water that has flowed into the first cooling water
circulation passage 85 returns again to the cooling water passage
75 of the internal combustion engine 5, by way of the cooling water
passage 37 provided in the reductant injection valve 31. Thus, the
reductant injection valve 31 is cooled.
[0034] A first cooling water flow rate control valve 81 for
adjusting the flow rate of the cooling water flowing through the
first cooling water circulation passage 85 is provided in the first
cooling water circulation passage 85 on the upstream side of the
reductant injection valve 31. For example, an on-off valve of an
electromagnetically controlled type, an electromagnetic
proportional flow rate control valve or the like is used as the
first cooling water flow rate control valve 81, and is controlled
by the DCU 60 which will be described later. Normally, the first
cooling water flow rate control valve 81 is opened, and the
reductant injection valve 31 is cooled by the cooling water. On the
other hand, when there is a possibility that the reductant
injection valve 31 will be cooled excessively, the first cooling
water flow rate control valve 81 is closed to block the circulation
of the cooling water, or the opening degree of the first cooling
water flow rate control valve 81 is reduced to decrease the flow
rate of the cooling water. The reductant injection valve 31 is
thereby adjusted so as not to be cooled excessively.
[0035] Further, in the first supply passage 58 connected to the
reductant injection valve 31, an inlet portion of the reductant
injection valve 31 is provided with a temperature sensor 33 for
detecting the temperature of the urea aqueous solution that flows
into the reductant injection valve 31. Further, in the first
cooling water circulation passage 85, an inlet portion on the
upstream side of the reductant injection valve 31 is provided with
a temperature sensor 35 for detecting the temperature of the
cooling water that flows into the reductant injection valve 31.
Temperature information detected by the sensors 33 and 35 is
transmitted to the DCU 60.
[0036] Moreover, in the reductant supply device 20 of the present
embodiment, a second cooling water circulation passage 87 is
provided such that it further diverges, on the upstream side of the
first cooling water flow rate control valve 81, from the first
cooling water circulation passage 85 that diverges from the cooling
water passage 75 of the internal combustion engine 5. The second
cooling water circulation passage 87 is arranged such that it
passes through the storage tank 50, and joins again with the first
cooling water circulation passage 85. A second cooling water flow
rate control valve 83 for adjusting the flow rate of the cooling
water flowing through the second cooling water circulation passage
87 is provided in the second cooling water circulation passage 87
on the upstream side of the storage tank 50.
[0037] The cooling water of the internal combustion engine 5 that
circulates through the second cooling water circulation passage 87
is used as heating means for heating the urea aqueous solution in
the storage tank 50. The cooling water of the internal combustion
engine 5 is maintained at a temperature of approximately 70 to
80.degree. C., for example. Therefore, when the temperature of the
urea aqueous solution in the storage tank 50 decreases, the second
cooling water flow rate control valve 83 is opened to circulate the
cooling water in the storage tank 50. Thus, control is performed
such that the temperature of the urea aqueous solution does not
excessively decrease and the urea aqueous solution does not
freeze.
[0038] In the same manner as in the first cooling water flow rate
control valve 81, an on-off valve of an electromagnetically
controlled type, an electromagnetic proportional flow rate control
valve or the like is used as the second cooling water flow rate
control valve 83, and is controlled by the DCU 60. More
specifically, a temperature sensor 51 for detecting the temperature
of the urea aqueous solution in the tank is provided in the storage
tank 50 that stores the urea aqueous solution. The value detected
by the temperature sensor 51 is output to the DCU 60 as a signal,
and the second cooling water flow rate control valve 83 is
controlled based on the temperature information.
[0039] Further, the pump module 40 is provided with the pump 41.
The pump 41 pumps the urea aqueous solution in the storage tank 50
via the second supply passage 57, and pressure-feeds the urea
aqueous solution to the reductant injection valve 31 via the first
supply passage 58. The pump 41 is, for example, an electric gear
pump, and can be designed to be duty-controlled by a signal
transmitted from the DCU 60. Further, a pressure sensor 43 is
provided in the first supply passage 58, and the value detected by
the pressure sensor 43 is output to the DCU 60 as a signal. The
drive duty of the pump 41 is controlled such that the pressure
value in the first supply passage 58 is maintained at a
predetermined value. More specifically, in a state where the
pressure in the first supply passage 58 becomes lower than the
predetermined value, the drive duty of the pump 41 is controlled to
be increased. Conversely, in a state where the pressure in the
first supply passage 58 becomes higher than the predetermined
value, the drive duty of the pump 41 is controlled to be
reduced.
[0040] Note that, the term "drive duty of the pump" means the ratio
of a pump drive time taken in one cycle, in a pulse width
modulation (PWM) control.
[0041] In addition, a main filter 47 is provided in the first
supply passage 58, and foreign matter contained in the urea aqueous
solution that is pressure-fed to the reductant injection valve 31
is caught. Further, the circulation passage 59 is provided such
that it diverges from the first supply passage 58 between the pump
41 and the main filter 47, and the circulation passage 59 is
connected to the storage tank 50. An orifice 45 is provided in the
middle of the circulation passage 59, and a pressure control valve
49 is provided closer to the storage tank 50 than the orifice 45.
With the provision of the circulation passage 59 structured as
described above, when the pressure value in the first supply
passage 58 exceeds the predetermined value in a state where the
urea aqueous solution is pressure-fed by the pump 41 that is
feedback controlled based on the detection value of the pressure
sensor 43, the pressure control valve 49 is opened and a part of
the urea aqueous solution flows back into the storage tank 50. For
example, a known check valve or the like can be used as the
pressure control valve 49.
[0042] Further, a reverting valve 71 is provided in the pump module
40. When the reductant supply device 20 does not perform injection
control of the urea aqueous solution, the urea aqueous solution in
a reductant supply passage, which includes the pump module 40, the
reductant injection valve 31, the first supply passage 58 and the
second supply passage 57, is collected into the storage tank 50.
Therefore, when the internal combustion engine 5 is stopped and the
control of the reductant supply device 20 is not performed in a
cold condition, i.e., under a temperature condition in which the
urea aqueous solution is likely to freeze, freezing of the urea
aqueous solution in the reductant supply passage is prevented. When
the operation of the internal combustion engine is restarted after
that, it is ensured that an injection failure due to clogging does
not occur.
[0043] The reverting valve 71 is, for example, a switching valve
that functions to switch a flow channel of the urea aqueous
solution, from a forward direction, i.e., a direction from the
storage tank 50 toward the pump module 40, to an opposite
direction, i.e., a direction away from the pump module 40 toward
the storage tank 50. When an ignition switch of the internal
combustion engine is turned off, if the flow channel is switched to
the opposite direction, the urea aqueous solution is collected in
the storage tank 50.
[0044] Moreover, heaters 92 to 97 are provided in respective
sections of the reductant supply passage in the reductant supply
device 20. The heaters 92 to 97 are provided in order to prevent a
case where, if the urea aqueous solution is present in the
reductant supply passage in a cold condition, the urea aqueous
solution freezes and clogs the reductant supply passage partially
or completely, thus inhibiting the reductant injection control from
being performed accurately by the reductant injection valve 31.
Further, energization of the heaters 92 to 97 is controlled by the
DCU 60. When it is determined that the reductant supply passage is
under a temperature condition in which freezing of the urea aqueous
solution may occur, based on, for example, the temperature of the
urea aqueous solution, the outside air temperature or the like,
voltage is supplied from a battery and heating is performed.
[0045] The heaters 92 to 97 are not particularly limited, and
heating wires or the like can be used.
3. Control Unit (DCU) for the Reductant Supply Device
[0046] FIG. 2 shows the structure of the DCU 60 for controlling the
reductant supply device of the present embodiment. The DCU 60 is
principally structured by a microcomputer having a known structure.
FIG. 2 shows an example of the structure that is represented by
functional blocks that correspond to portions relating to operation
control of the first cooling water flow rate control valve 81 and
the second cooling water flow rate control valve 83 shown in FIG.
1.
[0047] The DCU 60 of the present embodiment includes, as main
elements, an injection valve temperature detection portion (denoted
by "Injector-Temp Detection") that detects the temperature of the
reductant injection valve, a first control portion (denoted by
"Injector-Cooling Control") that controls the first cooling water
flow rate control valve, and a second control portion (denoted by
"Tank-Heating Control") that controls the second cooling water flow
rate control valve. These portions are specifically realized by the
microcomputer (not shown in the figures) executing a program.
[0048] Among these portions, the injection valve temperature
detection portion detects the temperature of the reductant
injection valve, and transmits temperature information to the first
control portion. A method for detecting the temperature of the
reductant injection valve is not particularly limited. The
temperature may be directly detected by providing a temperature
sensor on the reductant injection valve, or may be estimated by
calculation.
[0049] The injection valve temperature detection portion in the DCU
60 of the present embodiment estimates a temperature Ti at the tip
of the reductant injection valve, based on respective pieces of
information, namely, an exhaust gas temperature Tg and an exhaust
gas flow rate Ve that are estimated from an operation state of the
internal combustion engine, a temperature Tu1 of the urea aqueous
solution in the storage tank, a temperature Tu2 of the urea aqueous
solution that flows into the reductant injection valve, a
temperature Tr of the cooling water that flows into the reductant
injection valve, an outside air temperature To, an injection
command value Qu transmitted from the DCU 60 to the reductant
injection valve, and a vehicle speed S.
[0050] The temperature Ti at the tip of the reductant injection
valve is estimated by the injection valve temperature detection
portion. This is because the flow rate of the cooling water can be
controlled based on a temperature in the vicinity of a nozzle hole
where crystallization of urea is likely to occur due to evaporation
of water contained in the urea aqueous solution. Moreover, the
reductant injection valve is heated by exhaust heat that is
transferred via the exhaust pipe. Therefore, if the temperature at
the tip of the reductant injection valve, at which the temperature
becomes highest, is maintained at a temperature equal to or lower
than a heat resistance temperature, it is possible to maintain the
entire reductant injection valve at a temperature equal to or lower
than the heat resistance temperature.
[0051] Note that, when the temperature Ti at the tip of the
reductant injection valve is estimated, all the information
described above need not necessarily be referred to, and the
estimation may be performed based on only part of the
information.
[0052] The first control portion, which performs control of the
first cooling water flow rate control valve, outputs a control
signal for controlling the opening and closing of the first cooling
water flow rate control valve, based on the temperature Ti at the
tip of the reductant injection valve that is transmitted from the
injection valve temperature detection portion.
[0053] For example, when the internal combustion engine is normally
operated, in order to maintain the temperature Ti at the tip of the
reductant injection valve at a temperature lower than the heat
resistance temperature, the first cooling water flow rate control
valve is opened to circulate a relatively large amount of cooling
water through the first cooling water circulation passage 85. The
temperature Ti at the tip of the reductant injection valve that is
necessary to maintain a plastic portion and an electromagnetically
controlled portion of the reductant injection valve at a
temperature equal to or lower than the heat resistance temperature
varies depending on the type of the reductant injection valve.
However, the cooling water is circulated such that the temperature
Ti at the tip is maintained at a temperature equal to or higher
than 140 and lower than 160.degree. C., for example.
[0054] On the other hand, if the reductant injection valve is
excessively cooled by the cooling water, crystallization of urea
may occur in the vicinity of the nozzle hole. Therefore, the
cooling water is blocked by closing the first cooling water flow
rate control valve, or the opening degree is decreased to reduce
the flow rate of the cooling water. For example, in order to
facilitate rapid evaporation and vaporization of the urea aqueous
solution that is injected through the nozzle hole, the flow rate of
the cooling water is adjusted such that the temperature Ti at the
tip of the reductant injection valve is maintained at a temperature
equal to or higher than the boiling point of the urea aqueous
solution. Although the boiling point of the urea aqueous solution
varies depending on concentration, the flow rate of the cooling
water is adjusted such that the temperature Ti at the tip is
maintained at a temperature equal to or higher than 100 and lower
than 110.degree. C., for example.
[0055] More specifically, based on information about the
temperature Ti at the tip of the reductant injection valve that is
transmitted from the injection valve temperature detection portion,
the first control portion in the DCU 60 of the present embodiment
performs feedback control of the opening and closing of the first
cooling water flow rate control valve so that the temperature Ti at
the tip of the reductant injection valve becomes equal to or higher
than the boiling point of the urea aqueous solution in the exhaust
gas passage and lower than the heat resistance temperature of the
reductant injection valve. As a result, heat damage of the
reductant injection valve is inhibited and durability is thereby
improved. At the same time, crystallization of urea in the vicinity
of the nozzle hole is inhibited, which allows stable atomization of
the urea aqueous solution.
[0056] Note that, in the example of the present embodiment, control
is performed such that the temperature Ti at the tip of the
reductant injection valve is equal to or higher than the boiling
point of the urea aqueous solution. However, as long as the urea
aqueous solution is rapidly vaporized after injection by the
influence of exhaust heat, the temperature Ti at the tip may be
lower than the boiling point of the urea aqueous solution.
[0057] Further, the second control portion outputs a control signal
for controlling the opening and closing of the second cooling water
flow rate control valve, based on the temperature of the urea
aqueous solution that is detected by the temperature sensor
provided in the storage tank.
[0058] For example, when the temperature of the urea aqueous
solution in the storage tank becomes lower than the freezing point,
the urea aqueous solution freezes and cannot be supplied to the
reductant injection valve. In addition, even when the temperature
of the urea aqueous solution exceeds the freezing point, if it is,
for example, 80.degree. C. or higher, the urea aqueous solution may
deteriorate.
[0059] Given this, when the temperature of the urea aqueous
solution in the storage tank is lower than 60.degree. C., the
second control portion in the DCU 60 of the present embodiment
opens the second cooling water flow rate control valve. Thus, the
urea aqueous solution in the storage tank is heated, and freezing
of the urea aqueous solution is prevented. On the other hand, when
the temperature of the urea aqueous solution in the storage tank is
equal to or higher than 60.degree. C., the second cooling water
flow rate control valve is closed. Thus, heating by the cooling
water of the internal combustion engine is stopped, and
deterioration of the urea aqueous solution in the storage tank is
prevented.
4. Reductant Injection Control
[0060] Next, reductant injection control that is performed by the
reductant supply device 20 provided in the exhaust gas purification
device 10 shown in FIG. 1 will be described.
[0061] When the internal combustion engine is operated, the liquid
reductant in the storage tank 50 is pumped by the pump 41, and is
pressure-fed to the reductant injection valve 31. At this time, a
detection value detected by the pressure sensor 43, which is
provided in the first supply passage 58 on the downstream side of
the pump 41, is fed back and controlled to indicate a predetermined
pressure value. For example, when the detection value is less than
the predetermined value, the output of the pump 41 is increased. On
the other hand, when the pressure value exceeds the predetermined
value, the output of the pump 41 is reduced. At the same time, the
fluid reductant is caused to flow back to the storage tank 50 via
the pressure control valve 49, and the pressure is reduced. Thus,
the pressure of the reductant that is pressure-fed to the reductant
injection valve 31 side is maintained at an approximately fixed
value.
[0062] Further, the reductant that is pressure-fed from the pump
module 40 to the reductant injection valve 31 is maintained at an
approximately fixed pressure value, and is injected into the
exhaust gas passage when the reductant injection valve 31 is
opened. The DCU 60 determines an injection supply amount of the
reductant to be injected, based on information about the operation
state of the internal combustion engine, the temperature of the
reduction catalyst 13, and the amount of NO.sub.x that has passed
through the reduction catalyst 13 without being reduced, the amount
of NO.sub.x being measured on the downstream side of the reduction
catalyst 13. The DCU 60 generates a control signal in accordance
with the determined injection supply amount, and outputs it to the
reductant injection valve 31. The reductant injection valve 31 is
duty controlled by the control signal, and an appropriate amount of
reductant is injected and supplied into the exhaust gas passage.
The reductant that has been injected into the exhaust gas passage
flows into the reduction catalyst 13, and is used in reductive
reaction of NO.sub.x contained in exhaust gas.
5. Cooling Water Circulation Control
[0063] Next, an example of the routine of cooling water circulation
control performed by the control unit (DCU) 60 for the reductant
supply device of the present embodiment shown in FIG. 2 will be
described, with reference to the control flow shown in FIG. 3 and
FIG. 4.
[0064] First, as shown in FIG. 3, at step S1 after the start, the
temperature of the reductant injection valve is detected. As
described earlier, in the DCU 60 of the present embodiment, the
temperature Ti at the tip of the reductant injection valve is
calculated based on the respective pieces of information, namely,
the exhaust gas temperature Tg, the exhaust gas flow rate Ve, the
temperature Tu1 of the urea aqueous solution in the storage tank,
the temperature Tu2 of the urea aqueous solution that flows into
the reductant injection valve, the temperature Tr of the cooling
water that flows into the reductant injection valve, the outside
air temperature To, the injection command value Qu transmitted from
the DCU 60 to the reductant injection valve, and the vehicle speed
S.
[0065] Next, at step S2, it is determined whether or not the
detected temperature Ti at the tip of the reductant injection valve
is lower than a lower limit value Ti1. In the present embodiment,
the lower limit value Ti1 is set to the boiling point of the urea
aqueous solution. When the temperature Ti at the tip of the
reductant injection valve is lower than the lower limit value Ti1,
the process proceeds to step S3, and the first cooling water flow
rate control valve is fully closed or its opening degree is
reduced. After that, the process returns to the start. As a result,
the flow rate of the cooling water that flows through the cooling
water passage provided in the reductant injection valve is reduced,
and the temperature Ti at the tip of the reductant injection valve
is raised by the influence of exhaust heat transferred through the
exhaust pipe.
[0066] On the other hand, at step 2, when the temperature Ti at the
tip of the reductant injection valve is equal to or higher than the
lower limit value Ti1, the process proceeds to step S4, and it is
determined whether or not the temperature Ti at the tip of the
reductant injection valve is equal to or higher than an upper limit
value Ti2. In the present embodiment, the upper limit value Ti2 is
set to the heat resistance temperature of the reductant injection
valve. When the temperature Ti at the tip of the reductant
injection valve is lower than the upper limit value Ti2, the
process returns to the start without performing any other
processing. On the other hand, when the temperature Ti at the tip
of the reductant injection valve is equal to or higher than the
upper limit value Ti2, the process proceeds to step S5, and the
first cooling water flow rate control valve is fully opened or its
opening degree is increased. After that, the process returns to the
start. As a result, the flow rate of the cooling water that flows
through the cooling water passage provided in the reductant
injection valve is increased, and the reductant injection valve is
cooled and the temperature Ti at the tip thereof decreases.
[0067] In the control method for the reductant supply device of the
present embodiment, along with the above-described temperature
control of the reductant injection valve that is performed by
controlling the opening and closing of the first cooling water flow
rate control valve, temperature control of the urea aqueous
solution in the storage tank is performed by controlling the
opening and closing of the second cooling water flow rate control
valve.
[0068] FIG. 4 shows the flow of the temperature control of the urea
aqueous solution in the storage tank. First, at step S11, the
temperature Tu1 of the urea aqueous solution in the storage tank is
detected. In the case of the reductant supply device of the present
embodiment, temperature information that is detected by the
temperature sensor provided in the storage tank is read.
[0069] Next, at step S12, it is determined whether or not the
detected temperature Tu1 of the urea aqueous solution is equal to
or lower than a reference value Tu0. The reference value Tu0 at
this time is set to 60.degree. C., for example, using as an
indication the temperature at which the urea aqueous solution in
the storage tank is maintained without deterioration.
[0070] When the temperature Tu1 of the urea aqueous solution is
equal to or lower than the reference value Tu0, the process
proceeds to step S13, and the second cooling water flow rate
control valve is fully opened or its opening degree is increased.
After that, the process returns to the start. As a result, the urea
aqueous solution in the storage tank is heated by the cooling water
of the internal combustion engine that is maintained at 70 to
80.degree. C.
[0071] On the other hand, when the detected temperature Tu1 of the
urea aqueous solution exceeds the reference value Tu0, the
temperature of the urea aqueous solution in the storage tank has
been raised excessively and the urea aqueous solution may
deteriorate. Therefore, the process proceeds to step S14, and the
second cooling water flow rate control valve is fully closed or its
opening degree is reduced. After that, the process returns to the
start.
[0072] In this manner, because the temperature of the urea aqueous
solution in the storage tank is controlled to be maintained, for
example, within a range of 60 to 80.degree. C., freezing and
deterioration of the urea aqueous solution are prevented. At the
same time, because the urea aqueous solution is rapidly vaporized
when it is injected from the reductant injection valve, the urea
aqueous solution is easily dispersed uniformly in exhaust gas.
[0073] Note that, in the example of the opening and closing control
of the second cooling water flow rate control valve according to
the present embodiment, it is only determined whether or not the
temperature Tu1 of the urea aqueous solution exceeds the reference
value Tu0, and then the flow rate control is performed. However,
the second reference value Tu2 that is different from the reference
value Tu0 may be further set, and the temperature range of the urea
aqueous solution in the storage tank may be more finely set. Then,
cooling control of the urea aqueous solution in the storage tank
may be performed using the cooling water of the internal combustion
engine.
* * * * *