U.S. patent application number 15/072573 was filed with the patent office on 2016-09-22 for exhaust gas treatment apparatus and exhaust gas treatment method for internal combustion engine.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Kosuke YAMAMOTO.
Application Number | 20160273433 15/072573 |
Document ID | / |
Family ID | 55650080 |
Filed Date | 2016-09-22 |
United States Patent
Application |
20160273433 |
Kind Code |
A1 |
YAMAMOTO; Kosuke |
September 22, 2016 |
EXHAUST GAS TREATMENT APPARATUS AND EXHAUST GAS TREATMENT METHOD
FOR INTERNAL COMBUSTION ENGINE
Abstract
An exhaust gas treatment apparatus for an internal combustion
engine includes: an exhaust gas treatment unit arranged in an
exhaust passage of the internal combustion engine, the exhaust
passage being configured such that i) exhaust gas flowing along a
part of a wall face, which defines the exhaust passage, burbles
away from the part of the wall face in an exhaust gas burble zone
and ii) as a result of burble of exhaust gas away from the part of
the wall face of the exhaust passage in the exhaust gas burble
zone, exhaust gas disproportionately flows into the exhaust gas
treatment unit or the amount of exhaust gas flowing into the
exhaust gas treatment unit reduces. A plasma actuator is also
provided arranged at the part of the wall face of the exhaust
passage in the exhaust gas burble zone, the plasma actuator being
configured to generate air current toward the exhaust gas treatment
unit along the part of the wall face in exhaust gas inside the
exhaust passage.
Inventors: |
YAMAMOTO; Kosuke;
(Gotemba-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA |
Toyota-shi |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
55650080 |
Appl. No.: |
15/072573 |
Filed: |
March 17, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01N 2240/20 20130101;
F01N 3/10 20130101; H05H 1/2406 20130101; F01N 3/021 20130101; F01N
13/143 20130101; Y02T 10/40 20130101; F01N 3/103 20130101; Y02T
10/20 20130101; F01N 3/2892 20130101; Y02T 10/47 20130101; F01P
2025/08 20130101; F01N 11/002 20130101; Y02T 10/16 20130101; F01N
2240/02 20130101; F01N 2560/07 20130101; Y02T 10/12 20130101; F01N
13/1833 20130101; F01N 2330/60 20130101; F01N 2240/28 20130101;
F01N 3/0892 20130101; F01N 9/00 20130101; F01N 2560/06 20130101;
H05H 2001/2412 20130101; F01N 3/2889 20130101; F01N 13/08 20130101;
F01N 2900/1411 20130101; F01N 2550/02 20130101; F01N 5/02 20130101;
F01N 2900/1602 20130101; F01N 2250/02 20130101; F01N 13/0097
20140603 |
International
Class: |
F01N 3/28 20060101
F01N003/28; F01N 9/00 20060101 F01N009/00; F01N 13/14 20060101
F01N013/14; F01N 3/021 20060101 F01N003/021; F01N 11/00 20060101
F01N011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2015 |
JP |
2015-054855 |
Claims
1. An exhaust gas treatment apparatus for an internal combustion
engine, the exhaust gas treatment apparatus comprising: an exhaust
gas treatment unit arranged in an exhaust passage of the internal
combustion engine, the exhaust passage being configured such that
i) exhaust gas flowing along a part of a wall face, which defines
the exhaust passage, burbles away from the part of the wall face in
an exhaust gas burble zone and ii) as a result of burble of exhaust
gas away from the part of the wall face of the exhaust passage in
the exhaust gas burble zone, exhaust gas disproportionately flows
into the exhaust gas treatment unit or an amount of exhaust gas
flowing into the exhaust gas treatment unit reduces; and a plasma
actuator arranged at the part of the wall face of the exhaust
passage in the exhaust gas burble zone, the plasma actuator being
configured to generate air current in exhaust gas toward the
exhaust gas treatment unit along the part of the wall face inside
the exhaust passage.
2. The exhaust gas treatment apparatus according to claim 1,
wherein a sectional shape of the part of the wall face of the
exhaust passage in the exhaust gas burble zone, taken along a flow
direction of exhaust gas, includes a convex curved line.
3. The exhaust gas treatment apparatus according to claim 1,
further comprising: a flow rate acquisition device configured to
acquire a flow rate of exhaust gas flowing through the exhaust
passage; and a controller configured to control an amount of energy
that is input to the plasma actuator, wherein the exhaust gas
treatment unit includes a catalytic converter configured to purify
exhaust gas, and the controller is configured to control the plasma
actuator such that the amount of energy that is input to the plasma
actuator increases as the acquired flow rate of exhaust gas
increases.
4. The exhaust gas treatment apparatus according to claim 3,
further comprising: a temperature acquisition device configured to
acquire a temperature of the catalytic converter, wherein the
controller is configured to, when the acquired temperature of the
catalytic converter is higher than or equal to an activation lower
limit temperature of the catalytic converter, input energy to the
plasma actuator.
5. The exhaust gas treatment apparatus according to claim 1,
wherein the exhaust gas treatment unit includes a catalytic
converter configured to purify exhaust gas, the exhaust gas
treatment apparatus further comprises: a temperature acquisition
device configured to acquire a temperature of the catalytic
converter; and a controller configured to control an amount of
energy that is input to the plasma actuator, and the controller is
configured to, when the acquired temperature of the catalytic
converter is higher than or equal to an activation lower limit
temperature of the catalytic converter, input energy to the plasma
actuator.
6. The exhaust gas treatment apparatus according to claim 4,
wherein the controller is configured to, when the acquired
temperature of the catalytic converter is lower than or equal to an
upper limit temperature of the catalytic converter, input energy to
the plasma actuator.
7. The exhaust gas treatment apparatus according to claim 3,
wherein the catalytic converter includes a cylindrical heat
insulation partition surrounding a zone of part of the catalytic
converter along a flow direction of exhaust gas, and the zone
surrounded by the heat insulation partition includes a zone into
which exhaust gas disproportionately flows as a result of burble of
exhaust gas away from the part of the wall face of the exhaust
passage in the exhaust gas burble zone.
8. The exhaust gas treatment apparatus according to claim 7,
wherein a length of the heat insulation partition along the flow
direction of exhaust gas is shorter than a length of the catalytic
converter along the flow direction of exhaust gas, and an upstream
end of the heat insulation partition along the flow direction of
exhaust gas is located at an upstream end of the catalytic
converter along the flow direction of exhaust gas.
9. The exhaust gas treatment apparatus according to claim 7,
wherein the heat insulation partition is an air layer.
10. The exhaust gas treatment apparatus according to claim 4,
wherein the acquired temperature of the catalytic converter is a
temperature of a zone different from a zone into which exhaust gas
disproportionately flows because of the exhaust gas burble
zone.
11. The exhaust gas treatment apparatus according to claim 3,
further comprising: a particulate filter configured to trap
particulate matter contained in exhaust gas, wherein the
particulate filter is arranged downstream of the catalytic
converter.
12. The exhaust gas treatment apparatus according to claim 1,
wherein the exhaust passage is branched into two by a partition
wall extending along a flow direction of exhaust gas, the exhaust
gas treatment unit includes an exhaust heat recovery device
arranged in one of the branched exhaust passages and configured to
exchange heat between exhaust gas flowing through said one of the
branched exhaust passages and coolant of the internal combustion
engine, the exhaust gas burble zone is located at a portion at
which the exhaust passage is branched, and the exhaust passage is
configured such that the amount of exhaust gas flowing into said
one of the branched exhaust passages reduces as a result of burble
of exhaust gas away from a part of a wall face of the exhaust
passage in the exhaust gas burble zone.
13. The exhaust gas treatment apparatus according to claim 12,
further comprising: a coolant temperature sensor configured to
acquire a temperature of coolant of the internal combustion engine;
and a controller configured to, when the acquired temperature of
coolant is lower than a temperature set in advance, input energy to
the plasma actuator.
14. An exhaust gas treatment method for an internal combustion
engine, an exhaust passage of the internal combustion engine being
configured such that exhaust gas flowing along a part of a wall
face, which defines the exhaust passage at a portion upstream of a
catalytic converter for purifying exhaust gas from the internal
combustion engine, disproportionately flows into an exhaust gas
treatment unit arranged in the exhaust passage as a result of
burble of exhaust gas away from the part of the wall face in an
exhaust gas burble zone, a plasma actuator being arranged at the
part of the wall face of the exhaust passage in the exhaust gas
burble zone, the plasma actuator being configured to generate air
current along the wall face of the exhaust passage in exhaust gas
inside the exhaust passage, the exhaust gas treatment method
comprising: acquiring a temperature of the catalytic converter; and
when the acquired temperature of the catalytic converter is higher
than or equal to an activation lower limit temperature of the
catalytic converter, inputting energy to the plasma actuator.
15. An exhaust gas treatment method for an internal combustion
engine, an exhaust passage of the internal combustion engine being
configured such that exhaust gas flowing along a part of a wall
face, which defines the exhaust passage at a portion upstream of a
catalytic converter for purifying exhaust gas from the internal
combustion engine, disproportionately flows into the catalytic
converter as a result of burble of exhaust gas away from the part
of the wall face in an exhaust gas burble zone, a plasma actuator
being arranged at the part of the wall face of the exhaust passage
in the exhaust gas burble zone, the plasma actuator being
configured to generate air current along the wall face of the
exhaust passage in exhaust gas inside the exhaust passage, the
exhaust gas treatment method comprising: acquiring an exhaust gas
flow rate; and causing exhaust gas to flow into the catalytic
converter in a diffused state by applying larger energy to the
plasma actuator as the acquired exhaust gas flow rate
increases.
16. The exhaust gas treatment method according to claim 14, further
comprising: acquiring a temperature of the catalytic converter; and
when the acquired temperature of the catalytic converter is higher
than or equal to an activation lower limit temperature of the
catalytic converter, causing exhaust gas to flow into the catalytic
converter in a diffused state.
17. The exhaust gas treatment method according to any one of claim
14, wherein a sectional shape of the part of the wall face of the
exhaust passage in the exhaust gas burble zone, taken along a flow
direction of exhaust gas, includes a convex curved line.
18. The exhaust gas treatment method according to claim 14, wherein
a cylindrical heat insulation partition surrounding a zone of part
of the catalytic converter along a flow direction of exhaust gas is
provided in the catalytic converter such that the zone surrounded
by the heat insulation partition includes a zone into which exhaust
gas disproportionately flows as a result of burble of exhaust gas
away from the part of the wall face of the exhaust passage in the
exhaust gas burble zone and, when the acquired temperature of the
catalytic converter is lower than an activation lower limit
temperature of the catalytic converter, a major portion of exhaust
gas is guided to the zone of the catalytic converter, surrounded by
the heat insulation partition.
19. The exhaust gas treatment method according to claim 15, wherein
a sectional shape of the part of the wall face of the exhaust
passage in the exhaust gas burble zone, taken along a flow
direction of exhaust gas, includes a convex curved line.
20. The exhaust gas treatment method according to claim 15, wherein
a cylindrical heat insulation partition surrounding a zone of part
of the catalytic converter along a flow direction of exhaust gas is
provided in the catalytic converter such that the zone surrounded
by the heat insulation partition includes a zone into which exhaust
gas disproportionately flows as a result of burble of exhaust gas
away from the part of the wall face of the exhaust passage in the
exhaust gas burble zone and, when the acquired temperature of the
catalytic converter is lower than an activation lower limit
temperature of the catalytic converter, a major portion of exhaust
gas is guided to the zone of the catalytic converter, surrounded by
the heat insulation partition.
Description
INCORPORATION BY REFERENCE
[0001] The disclosure of Japanese Patent Application No.
2015-054855 filed on Mar. 18, 2015 including the specification,
drawings and abstract is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention relate to an apparatus
and method for treating exhaust gas that is emitted from an
internal combustion engine.
[0004] 2. Description of Related Art
[0005] If a vehicle is intended to be downsized, installation space
for auxiliaries that are mounted on the vehicle is subjected to
constraints, and various piping paths, and the like, should be
significantly bent. For example, an exhaust gas turbine of a
supercharger, a catalytic converter of an exhaust gas control
apparatus, a muffler, and the like, are closely arranged in an
exhaust passage that guides exhaust gas that is emitted from an
internal combustion engine mounted on a vehicle, so an exhaust pipe
that connects these devices needs to be significantly bent.
[0006] Incidentally, the passage sectional area of the catalytic
converter of the exhaust gas control apparatus may be about several
times as large as the passage sectional area of the exhaust pipe
for the purpose of increasing exhaust gas purification efficiency.
In order to maximally utilize the purification performance of such
a catalytic converter, it is required to decrease the space
velocity of exhaust gas by diffusing exhaust gas, which flows into
the catalytic converter, over the entire area of an end face of the
catalytic converter. Therefore, a large-diameter casing that
accommodates the catalytic converter and a small-diameter exhaust
pipe that is connected to the casing are coupled to each other via
a tapered member called a cone for diffusing exhaust gas.
[0007] However, with the above-described downsizing of the vehicle,
the length of the tapered member tends to be extremely short. The
flow direction of exhaust gas that passes through the catalytic
converter often significantly differs from the flow direction of
exhaust gas that flows from the exhaust pipe into the tapered
member. In such a case, exhaust gas that flows along a wall face of
the exhaust passage from the small-diameter exhaust pipe to the
catalytic converter via the tapered member burbles away from the
wall face of the exhaust passage at the connection point at which
the exhaust pipe is connected to the tapered member. As a result,
exhaust gas that passes through the tapered member flows into only
the zone of part of the catalytic converter without diffusing so
much, with the result that it is not possible to maximally utilize
the purification performance of the catalytic converter.
[0008] In order to solve such an inconvenience, a technique for
forcibly distributing the flow direction of exhaust gas by
incorporating a louver in an exhaust pipe on the inlet side of the
catalytic converter has been suggested in Japanese Patent
Application Publication No. 2012-193719 (JP 2012-193719 A).
SUMMARY
[0009] When a louver member as described in JP 2012-193719 A is
incorporated in the exhaust passage, passage resistance increases
and, in addition, the louver member absorbs heat of exhaust gas at
the time of a warm-up of the internal combustion engine, with the
result that the time to complete a warm-up is extended. This leads
to deterioration of fuel economy.
[0010] Embodiments of the present invention provide an exhaust gas
treatment apparatus and exhaust gas treatment method that are able
to diffuse exhaust gas over the entire area of a catalytic
converter without increasing passage resistance as described in JP
2012-193719 A even with a configuration where the flow direction of
exhaust gas from an exhaust pipe to the catalytic converter steeply
bends.
[0011] An embodiment of the present invention also provides an
exhaust gas treatment apparatus and exhaust gas treatment method
that, even when the amount of exhaust gas flowing into an exhaust
gas treatment unit tends to reduce because of steep bending of an
exhaust pipe, is able to prevent at least a reduction in the amount
of exhaust gas flowing into the exhaust gas treatment unit without
increasing passage resistance.
[0012] A first embodiment of the invention provides an exhaust gas
treatment apparatus for an internal combustion engine. The exhaust
gas treatment apparatus includes: an exhaust gas treatment unit
arranged in an exhaust passage of the internal combustion engine,
the exhaust passage being configured such that i) exhaust gas
flowing along a part of a wall face, which defines the exhaust
passage, burbles away from the part of the wall face in an exhaust
gas burble zone and ii) as a result of burble of exhaust gas away
from the part of the wall face of the exhaust passage in the
exhaust gas burble zone, exhaust gas disproportionately flows into
the exhaust gas treatment unit or the amount of exhaust gas flowing
into the exhaust gas treatment unit reduces. A plasma actuator is
provided arranged at the part of the wall face of the exhaust
passage in the exhaust gas burble zone, the plasma actuator being
configured to generate air current toward the exhaust gas treatment
unit along the part of the wall face in exhaust gas inside the
exhaust passage.
[0013] In embodiments of the invention, when the plasma actuator
operates, air current is generated toward the exhaust gas treatment
unit along the part of the wall face of the exhaust passage in the
exhaust gas burble zone. Thus, exhaust gas flowing along the part
of the wall face of the exhaust passage in the exhaust gas burble
zone is dragged by the air current, flows without burbling away
from the part of the wall face of the exhaust passage, and then
flows into the exhaust gas treatment unit in a diffused state or a
reduction in the amount of exhaust gas flowing into the exhaust gas
treatment unit is suppressed.
[0014] In the exhaust gas treatment apparatus according to
embodiments of the invention, a sectional shape of the part of the
wall face of the exhaust passage in the exhaust gas burble zone,
taken along a flow direction of exhaust gas, may include a convex
curved line.
[0015] The exhaust gas treatment apparatus may further include a
flow rate acquisition device configured to acquire a flow rate of
exhaust gas flowing through the exhaust passage; and a controller
configured to control the amount of energy that is input to the
plasma actuator. The exhaust gas treatment unit may include a
catalytic converter configured to purify exhaust gas, and the
controller may be configured to control the plasma actuator such
that the amount of energy that is input to the plasma actuator
increases as the acquired flow rate of exhaust gas increases. In
this case, the exhaust gas treatment apparatus may further include
a temperature acquisition device configured to acquire a
temperature of the catalytic converter, and the controller may be
configured to, when the acquired temperature of the catalytic
converter is higher than or equal to an activation lower limit
temperature of the catalytic converter, input energy to the plasma
actuator. A mode of controlling the amount of energy that is input
to the plasma actuator may include changing an applied voltage or a
driving frequency.
[0016] The exhaust gas treatment unit may include a catalytic
converter configured to purify exhaust gas, the exhaust gas
treatment apparatus may further include a temperature acquisition
device configured to acquire a temperature of the catalytic
converter; and a controller configured to control the amount of
energy that is input to the plasma actuator, and the controller may
be configured to, when the acquired temperature of the catalytic
converter is higher than or equal to an activation lower limit
temperature of the catalytic converter, input energy to the plasma
actuator.
[0017] The controller may be configured to, when the acquired
temperature of the catalytic converter is lower than or equal to an
upper limit temperature of the catalytic converter, input energy to
the plasma actuator. The upper limit temperature of the catalytic
converter means a maximum temperature at or below which
degradation, dissolution loss, or the like, of the catalytic
converter due to heat does not occur. Therefore, it may be
understood that degradation, dissolution loss, or the like, of the
catalytic converter begins when the temperature exceeds the upper
limit temperature.
[0018] A cylindrical heat insulation partition surrounding a zone
of part of the catalytic converter along a flow direction of
exhaust gas may be provided in the catalytic converter. The zone
surrounded by the heat insulation partition may include a zone into
which exhaust gas disproportionately flows as a result of burble of
exhaust gas away from the part of the wall face of the exhaust
passage in the exhaust gas burble zone. When the acquired
temperature of the catalytic converter is lower than an activation
lower limit temperature of the catalytic converter, a major portion
of exhaust gas may be guided to the zone surrounded by the heat
insulation partition. In this case, the length of the heat
insulation partition along the flow direction of exhaust gas may be
shorter than the length of the catalytic converter along the flow
direction of exhaust gas, and an upstream end of the heat
insulation partition along the flow direction of exhaust gas may be
located at an upstream end of the catalytic converter along the
flow direction of exhaust gas.
[0019] In this specification, the word "upstream" or "upstream
side" means a side closer to a combustion chamber of the internal
combustion engine; whereas, the word "downstream" or "downstream
side" means a side away from the combustion chamber of the internal
combustion engine.
[0020] The heat insulation partition may be an air layer.
[0021] The acquired temperature of the catalytic converter may be a
temperature of a zone different from a zone into which exhaust gas
from a small-diameter portion flows because of the exhaust gas
burble zone.
[0022] The exhaust gas treatment apparatus may further include a
particulate filter configured to trap particulate matter contained
in exhaust gas, and the particulate filter may be arranged
downstream of the catalytic converter.
[0023] The exhaust passage may be branched into two by a partition
wall extending along a flow direction of exhaust gas, and the
exhaust gas treatment unit may include an exhaust heat recovery
device arranged in one of the branched exhaust passages and
configured to exchange heat between exhaust gas flowing through
this branched exhaust passages and coolant of the internal
combustion engine. In this case, the exhaust gas burble zone may be
located at a portion at which the exhaust passage is branched, and
the exhaust passage may be configured such that the amount of
exhaust gas flowing into the branched exhaust passage mentioned
above reduces as a result of burble of exhaust gas away from a part
of a wall face of the exhaust passage in the exhaust gas burble
zone. The exhaust gas treatment apparatus may further include a
coolant temperature sensor configured to acquire a temperature of
coolant of the internal combustion engine, and the controller may
be configured to, when the acquired temperature of coolant is lower
than a temperature set in advance, input energy to the plasma
actuator.
[0024] A clearance from a part of the wall face, which defines the
aforementioned branched exhaust passage, to the partition wall
along a direction perpendicular to the partition wall may be set so
as to be shorter than a clearance from the part of the wall face,
which defines this branched exhaust passage, to the wall face that
defines the exhaust passage just before branching along the
direction perpendicular to the partition wall.
[0025] A plurality of the exhaust gas treatment units may be
arranged in series along the exhaust passage, the upstream-side
exhaust gas treatment unit may include the above-described
catalytic converter, and the downstream-side exhaust gas treatment
unit may include the above-described exhaust heat recovery
device.
[0026] A second embodiment of the invention provides an exhaust gas
treatment method for an internal combustion engine. An exhaust
passage of the internal combustion engine is configured such that
exhaust gas flowing along a part of a wall face, which defines the
exhaust passage at a portion upstream of a catalytic converter for
purifying exhaust gas from the internal combustion engine, flows
into an exhaust gas treatment unit arranged in the exhaust passage
as a result of burble of exhaust gas away from the part of the wall
face in an exhaust gas burble zone. A plasma actuator is arranged
at the part of the wall face of the exhaust passage in the exhaust
gas burble zone, and the plasma actuator is configured to generate
air current along the wall face of the exhaust passage in exhaust
gas inside the exhaust passage. The exhaust gas treatment method
includes: acquiring a temperature of the catalytic converter; and,
when the acquired temperature of the catalytic converter is higher
than or equal to an activation lower limit temperature of the
catalytic converter, inputting energy to the plasma actuator.
[0027] A third embodiment of the invention provides an exhaust gas
treatment method for an internal combustion engine. An exhaust
passage of the internal combustion engine is configured such that
exhaust gas flowing along a part of a wall face, which defines the
exhaust passage at a portion upstream of a catalytic converter for
purifying exhaust gas from the internal combustion engine, flows
into the catalytic converter as a result of burble of exhaust gas
away from the part of the wall face in an exhaust gas burble zone.
A plasma actuator is arranged at the part of the wall face of the
exhaust passage in the exhaust gas burble zone, and the plasma
actuator is configured to generate air current along the wall face
of the exhaust passage in exhaust gas inside the exhaust passage.
The exhaust gas treatment method includes: acquiring an exhaust gas
flow rate; and causing exhaust gas to flow into the catalytic
converter in a diffused state by applying larger energy to the
plasma actuator as the acquired exhaust gas flow rate
increases.
[0028] The exhaust gas treatment method according to the third
embodiment of the invention may further include acquiring a
temperature of the catalytic converter; and, when the acquired
temperature of the catalytic converter is higher than or equal to
an activation lower limit temperature of the catalytic converter,
causing exhaust gas to flow into the catalytic converter in a
diffused state.
[0029] A sectional shape of the part of the wall face of the
exhaust passage in the exhaust gas burble zone, taken along a flow
direction of exhaust gas, may include a convex curved line.
[0030] A cylindrical heat insulation partition surrounding a zone
of part of the catalytic converter along a flow direction of
exhaust gas may be provided in the catalytic converter. The zone
surrounded by the heat insulation partition may include a zone into
which exhaust gas disproportionately flows as a result of burble of
exhaust gas away from the part of the wall face of the exhaust
passage in the exhaust gas burble zone.
[0031] A fourth embodiment of the invention provides an exhaust gas
treatment method for an internal combustion engine. The exhaust
passage is branched into two by a partition wall extending along a
flow direction of exhaust gas. An exhaust heat recovery device is
arranged in one of the branched exhaust passages and configured to
exchange heat between exhaust gas flowing through this branched
exhaust passages and coolant of the internal combustion engine. An
exhaust gas burble zone is provided at a portion at which the
exhaust passage is branched. The exhaust passage is configured such
that, at the time when part of exhaust gas flows into the
aforementioned branched exhaust passage, the amount of exhaust gas
flowing into this branched exhaust passage reduces as a result of
burble of exhaust gas, flowing along a part of a wall face, which
defines the exhaust passage, away from the part of the wall face. A
plasma actuator is arranged at the part of the wall face of the
exhaust passage in the exhaust gas burble zone so as to suppress
burble of exhaust gas away from the wall face of the exhaust
passage. The plasma actuator is configured to generate air current
along the wall face of the exhaust passage. The exhaust gas
treatment method includes: acquiring a temperature of coolant of
the internal combustion engine; and, when the acquired temperature
of coolant is lower than a temperature set in advance, facilitating
flow of exhaust gas into the one of the branched exhaust passages
by inputting energy to the plasma actuator.
[0032] In the exhaust gas treatment method according to the fourth
embodiment of the invention, a clearance from a part of the wall
face, which defines the aforementioned branched exhaust passage, to
the partition wall along a direction perpendicular to the partition
wall may be set so as to be shorter than a clearance from the part
of the wall face, which defines this branched exhaust passage, to
the wall face that defines the exhaust passage just before
branching along the direction perpendicular to the partition
wall.
[0033] With the exhaust gas treatment apparatus according to
embodiments of the invention, it is possible to cause exhaust gas
to flow along the part of the wall face of the exhaust passage in
the exhaust gas burble zone with the use of the plasma actuator
without burble of exhaust gas away from the part of the wall face
of the exhaust passage in the exhaust gas burble zone. As a result,
it is possible to diffuse exhaust gas flowing from the exhaust gas
burble zone into the exhaust gas treatment unit and cause the
exhaust gas to flow over the entire area of the exhaust gas
treatment unit without increasing passage resistance.
Alternatively, it is possible to suppress or prevent a reduction in
the amount of exhaust gas flowing into the exhaust gas treatment
unit or increase the amount of exhaust gas flowing into the exhaust
gas treatment unit.
[0034] When the sectional shape of the part of the wall face of the
exhaust passage in the exhaust gas burble zone in which the plasma
actuator is arranged, taken along the flow direction of exhaust
gas, includes a convex curved line, an advantageous effect of
embodiments of the invention may be remarkably obtained.
[0035] When the exhaust gas treatment unit includes the catalytic
converter for purifying exhaust gas, it is possible to cause
exhaust gas to constantly flow over the entire area of the
catalytic converter by controlling the plasma actuator such that
the amount of energy that is input to the plasma actuator increases
as the acquired flow rate of exhaust gas increases.
[0036] By inputting energy to the plasma actuator only when the
acquired temperature of the catalytic converter is higher than or
equal to the activation lower limit temperature of the catalytic
converter, it is possible to avoid unnecessary energy consumption
of the plasma actuator. Moreover, it is possible to facilitate
purification of exhaust gas during a warm-up of the internal
combustion engine by further quickly raising the temperature of
part of the catalytic converter to the activation lower limit
temperature or higher.
[0037] By inputting energy to the plasma actuator only when the
acquired temperature of the catalytic converter is lower than or
equal to the upper limit temperature of the catalytic converter, it
is possible to avoid unnecessary energy consumption of the plasma
actuator.
[0038] By guiding the major portion of exhaust gas to the zone of
the catalytic converter, surrounded by the heat insulation
partition, only when the temperature of the catalytic converter is
lower than the activation lower limit temperature of the catalytic
converter, it is possible to avoid unnecessary energy consumption
of the plasma actuator. Moreover, it is possible to facilitate
purification of exhaust gas during a warm-up of the internal
combustion engine by further quickly raising the temperature of
part of the catalytic converter to the activation lower limit
temperature or higher.
[0039] When the length of the heat insulation partition is set so
as to be shorter than the length of the catalytic converter and the
upstream end of the heat insulation partition is located at the
upstream end of the catalytic converter, it is possible to
facilitate a warm-up of the internal combustion engine by using
only the zone of the catalytic converter, surrounded by the heat
insulation partition, during a warm-up. It is also possible to
effectively use the entire area of the catalytic converter other
than during a warm-up.
[0040] When the heat insulation partition is an air layer, the heat
insulation partition may be a simple air gap, so it is possible to
extremely easily provide the heat insulation partition in the
catalytic converter.
[0041] When the temperature of the zone of the catalytic converter,
different from the zone into which exhaust gas from the
small-diameter portion is caused to flow because of the exhaust gas
burble zone, is acquired, it may be estimated that the temperature
of the entire passage section of the catalytic converter including
that zone is higher than or equal to the activation lower limit
temperature.
[0042] When the particulate filter for trapping particulate matter
contained in exhaust gas is arranged downstream of the catalytic
converter, it is possible to facilitate a warm-up of the catalytic
converter. Moreover, because soot contained in exhaust gas is
oxidized by the operation of the plasma actuator, the amount of
soot contained in exhaust gas that flows into the particulate
filter through the catalytic converter reduces, and it is possible
to reduce the frequency of the process of regenerating the
particulate filter.
[0043] When the exhaust gas treatment unit is arranged in the
aforementioned branched exhaust passage into which the exhaust
passage is branched by the partition wall and the exhaust gas
treatment unit includes the exhaust heat recovery device for
exchanging heat between exhaust gas flowing through this branched
exhaust passage and coolant of the internal combustion engine, it
is possible to shorten a time that is required for a warm-up by
raising the rate of rise in the temperature of coolant of the
internal combustion engine.
[0044] By inputting energy to the plasma actuator when the acquired
temperature of coolant is lower than the temperature set in
advance, it is possible to avoid unnecessary energy consumption of
the plasma actuator.
[0045] When the clearance from a part of the wall face, which
defines the aforementioned branched exhaust passage, to the
partition wall is set so as to be shorter than the clearance from
the part of the wall face, which defines this branched exhaust
passage, to the wall face that defines the exhaust passage just
before branching, it is possible to make part of exhaust gas
difficult to flow into the exhaust heat recovery device side after
completion of a warm-up of the internal combustion engine. Thus, it
is possible to suppress an unnecessary rise in the temperature of
coolant.
[0046] When the plurality of the exhaust gas treatment units are
arranged in series along the exhaust passage, the upstream-side
exhaust gas treatment unit includes the catalytic converter, and
the downstream-side exhaust gas treatment unit includes the exhaust
heat recovery device, so it is possible to achieve both early
activation of the catalytic converter and early completion of a
warm-up during a warm-up of the internal combustion engine.
[0047] With the exhaust gas treatment method according to the
second embodiment of the invention, energy is input to the plasma
actuator when the temperature of the catalytic converter is higher
than or equal to the activation lower limit temperature, so it is
possible to suppress unnecessary energy consumption.
[0048] With the exhaust gas treatment method according to the third
embodiment of the invention, it is possible to cause exhaust gas,
flowing from the exhaust gas burble zone into the catalytic
converter, to flow over the entire area of the exhaust gas
treatment unit by diffusing the exhaust gas without increasing
passage resistance irrespective of the flow rate of the exhaust
gas.
[0049] With the exhaust gas treatment method according to the
fourth embodiment of the invention, energy is input to the plasma
actuator when the temperature of coolant is low, so it is possible
to shorten a time that is required to warm-up the internal
combustion engine by raising the rate of rise in the temperature of
coolant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] Features, advantages, and technical and industrial
significance of exemplary embodiments of the invention will be
described below with reference to the accompanying drawings, in
which like numerals denote like elements, and wherein:
[0051] FIG. 1 is a conceptual view of an embodiment in which the
invention is applied to a vehicle on which a compression-ignition
multi-cylinder internal combustion engine is mounted;
[0052] FIG. 2 is a control block diagram of a main portion in the
embodiment shown in FIG. 1;
[0053] FIG. 3 is an extracted enlarged cross-sectional view of an
exhaust gas treatment unit in the embodiment shown in FIG. 1;
[0054] FIG. 4 is a further extracted enlarged electrical circuit
configuration diagram that schematically shows part of a first
exhaust gas burble zone shown in FIG. 3;
[0055] FIG. 5 is a map that schematically shows the relationship
between an exhaust gas flow rate and a voltage applied to a plasma
actuator;
[0056] FIG. 6 is a graph that schematically shows a change in the
temperature of a catalytic converter;
[0057] FIG. 7 is an extracted enlarged cross-sectional view of an
exhaust gas treatment unit in another embodiment of the
invention;
[0058] FIG. 8 is a flowchart that shows the procedure of
controlling the plasma actuator in the catalytic converter; and
[0059] FIG. 9 is a flowchart that shows the procedure of
controlling the plasma actuator for an exhaust heat recovery
device.
DETAILED DESCRIPTION OF EMBODIMENTS
[0060] An embodiment in which an embodiment of the invention is
applied to a vehicle on which a compression-ignition multi-cylinder
internal combustion engine is mounted will be described in detail
with reference to FIG. 1 to FIG. 9. However, the invention is not
limited to this embodiment. The configuration of the embodiment may
be freely modified in response to a required characteristic. For
example, embodiments of the invention are also effective in a
spark-ignition internal combustion engine that uses gasoline,
alcohol, liquefied natural gas (LNG), or the like, as fuel and
ignites the fuel with the use of an ignition plug.
[0061] FIG. 1 schematically shows a main portion of an engine
system in the present embodiment. FIG. 2 roughly shows control
blocks of the main portion. An exhaust gas turbocharger, an EGR
device, and the like, which are typical auxiliaries of an engine
10, are omitted from FIG. 1. It should be noted that various
sensors that are required to smoothly operate the engine 10 are
also partially omitted for the sake of convenience.
[0062] The engine 10 in the present embodiment is a self-ignition,
that is, compression-ignition multi-cylinder internal combustion
engine that causes light oil, biofuel or composite fuel of them, as
fuel, to naturally ignite by directly injecting the fuel from any
one of fuel injection valves 11 into a corresponding one of
combustion chambers 10a, which is placed in a compression state.
However, in view of the characteristic of the invention, the engine
10 may be a single-cylinder internal combustion engine.
[0063] A cylinder head 12 has intake ports 12a and exhaust ports
12b that face the corresponding combustion chambers 10a. A valve
actuating mechanism is incorporated in the cylinder head 12. The
valve actuating mechanism includes intake valves 13 and exhaust
valves 14. Each of the intake valves 13 opens or closes a
corresponding one of the intake ports 12a. Each of the exhaust
valves 14 opens or closes a corresponding one of the exhaust ports
12b. Each fuel injection valve 11 is provided at the center of the
upper end of a corresponding one of the combustion chambers 10a.
Each fuel injection valve 11 is assembled to the cylinder head 12
so as to be placed between the intake valve 13 and the exhaust
valve 14.
[0064] An intake pipe 15 is connected to the intake ports 12a of
the cylinder head 12. The intake pipe 15 defines an intake passage
15a together with the intake ports 12a. An air flow meter 16 is
installed at the upstream side of the intake pipe 15. Information
about an intake air flow rate detected by the air flow meter 16 is
output to the ECU 17. In the present embodiment, the air flow meter
16 is used as a flow rate acquisition device in the invention.
Instead, an exhaust gas flow rate may be acquired from an
additional air flow meter provided in an exhaust passage 18a
(described later) or may be calculated from an engine rotation
speed, an intake air temperature and an intake air pressure.
Alternatively, an exhaust gas flow velocity may be acquired instead
of an exhaust gas flow rate.
[0065] An ECU 17 that serves as a controller in an embodiment of
the invention includes not only a known microprocessor but also a
CPU, a ROM, a RAM, a nonvolatile memory, input/output interfaces,
and the like, which are connected to one another via a data bus
(not shown). The ECU 17 in the present embodiment includes an
operating state determination unit 17a. The operating state
determination unit 17a determines the operating state of the
vehicle on the basis of information from the air flow meter 16,
various sensors (described later), and the like.
[0066] An exhaust pipe 18 is coupled to the cylinder head 12 such
that the exhaust passage 18a communicates with the exhaust ports
12b. The exhaust pipe 18 defines the exhaust passage 18a. An
exhaust gas control apparatus 19 and an exhaust heat recovery
device 20 are arranged in order from the upstream side of the
exhaust passage 18a in the exhaust passage 18a at a portion
upstream of a muffler (not shown) arranged at the downstream end
side of the exhaust passage 18a.
[0067] FIG. 3 shows an extracted enlarged view of a portion
including the exhaust gas control apparatus 19 and the exhaust heat
recovery device 20. FIG. 4 shows the schematic configuration of a
plasma actuator in the present embodiment.
[0068] The exhaust gas control apparatus 19 in the present
embodiment includes a diesel oxidation catalytic converter (DOC) 21
and a diesel particulate filter (DPF) 22. The DOC 21 serves as a
first exhaust gas treatment unit in an embodiment of the invention.
The DPF 22 is arranged downstream of the DOC 21. The DOC 21 is used
to detoxify toxic substances that are produced through combustion
of air-fuel mixture in the combustion chambers 10a. The DPF 22 is
used to trap particulate matter contained in exhaust gas. A
catalytic converter, other than the DOC 21 or the DPF 22, may be
further incorporated in the exhaust gas control apparatus 19.
[0069] When an embodiment of the invention is applied to a
spark-ignition internal combustion engine, a compact three-way
catalyst is typically used as the first exhaust gas treatment unit
of the invention instead of the DOC 21.
[0070] There is a first exhaust gas burble zone Z.sub.1 in the
exhaust passage 18a just on the upstream side of the DOC 21. The
first exhaust gas burble zone Z.sub.1 is a zone in which exhaust
gas flowing along a part of a wall face 18e, which defines the
exhaust passage 18a, burbles away from the part of the wall face
18e and, as a result, exhaust gas disproportionately flows into an
upstream end face 21a of the DOC 21. Usually, the first exhaust gas
burble zone Z.sub.1 is located at the upstream end side of a cone
portion 18b in which the passage sectional area of the exhaust pipe
18 steeply increases, and the sectional shape of the part of the
wall face 18e of the exhaust passage 18a in the first exhaust gas
burble zone Z.sub.1, taken along the flow direction of exhaust gas,
includes a convex curved line shown in FIG. 3.
[0071] A first plasma actuator 23 is arranged at the part of the
wall face 18e of the exhaust passage 18a in the first exhaust gas
burble zone Z.sub.1. The first plasma actuator 23 is used to
generate air current toward the DOC 21 along the part of the wall
face 18e. The principle, basic configuration, and the like, of the
first plasma actuator 23 are known in Japanese Patent Application
Publication No. 2012-180799 (JP 2012-180799 A), or the like, and
will be simply described below. The first plasma actuator 23 in the
present embodiment is formed of a group of first electrodes 23a, a
group of second electrodes 23b, a dielectric layer 23c and an
insulation layer 23d as main components. The first plasma actuator
23 further includes an inverter 24, a first switch 25, and the
like. The group of first electrodes 23a are arranged at set
intervals on one surface of the thin-film dielectric layer 23c,
facing toward the exhaust passage 18a. The group of second
electrodes 23b are arranged at the set intervals same as the group
of first electrodes 23a on the other surface of the dielectric
layer 23c, facing toward the wall face 18e that defines the exhaust
passage 18a. The insulation layer 23d coats the group of second
electrodes 23b, and is bonded to the wall face 18e that defines the
exhaust passage 18a. In the present embodiment, in order to prevent
degradation and corrosion of the group of first electrodes 23a due
to exhaust gas flowing through the exhaust passage 18a, the group
of first electrodes 23a are coated with a thin-film insulation
protection layer 23e. The group of second electrodes 23b are
arranged slightly offset to the downstream side in relative
position with respect to the group of first electrodes 23a along an
arrangement direction in which the groups of first and second
electrodes 23a, 23b are arranged. The arrangement direction is
parallel to the flow direction of exhaust gas flowing through the
exhaust passage 18a. The group of second electrodes 23b are
connected to the inverter 24 via the first switch 25. The on/off
operation of the first switch 25, that is, the on/off state of
energization to the first plasma actuator 23, is controlled by the
ECU 17.
[0072] It should be noted that, because the thickness of the first
plasma actuator 23 is extremely thin and is about several
micrometers to several hundreds of micrometers, the first plasma
actuator 23 installed on the wall face 18e that defines the exhaust
passage 18a does not substantially interfere with flow of exhaust
gas. The first plasma actuator 23 does not need to be arranged over
the entire circumference of the exhaust passage 18a in the first
exhaust gas burble zone Z.sub.1. The first plasma actuator 23 may
be arranged only at a portion having a particularly large curvature
in the first exhaust gas burble zone Z.sub.1. In an embodiment of
the invention, because the first plasma actuator 23 is arranged in
the high-temperature exhaust passage 18a, the groups of electrodes
23a, 23b, the dielectric layer 23c, the insulation layer 23d, the
insulation protection layer 23e, and the like, are desirably made
of materials having high heat resistance. As such materials, for
example, the electrodes may be made of iron or nickel and the
dielectric layer 23c, the insulation layer 23d and the insulation
protection layer 23e may be made of ceramics, or the like.
[0073] An input energy amount setting unit 17b of the ECU 17 stores
a map shown in FIG. 5. The relationship between a flow rate Q of
exhaust gas flowing through the exhaust passage 18a per unit time
and a voltage V.sub.1 that is applied to the first plasma actuator
23 is set in advance in the map. Basically, the operation of the
first plasma actuator 23 is controlled via the first switch 25 such
that the amount of energy that is input to the first plasma
actuator 23 increases as the exhaust gas flow rate Q increases. In
the present embodiment, the input energy amount setting unit 17b
sets the voltage V.sub.1 that is applied to the first plasma
actuator 23, as the amount of energy that is input to the first
plasma actuator 23, on the basis of information from the
above-described air flow meter 16. The inverter 24 is supplied with
electric power from an in-vehicle secondary battery 26. The
inverter 24 is able to change the output voltage, for example,
within the range of about 1 to 10 kV. The inverter 24 applies the
voltage V.sub.1, set by the input energy amount setting unit 17b,
to the first plasma actuator 23 at a predetermined driving
frequency via the first switch 25, of which the on/off state is
controlled by the ECU 17.
[0074] As a mode of controlling the amount of energy that is input
to the first plasma actuator 23, the amount of input energy is
controlled by changing the voltage V that is applied to the first
plasma actuator 23 in the present embodiment. However, it is also
possible to control the amount of input energy by changing the
driving frequency of the first plasma actuator 23, for example,
within the range of about 1 to 10 kHz. Alternatively, the amount of
input energy may be controlled by changing both the applied voltage
V.sub.1 and the driving frequency or a similar advantageous effect
may be obtained by applying direct-current pulse voltage to the
first plasma actuator 23.
[0075] When the high-frequency high voltage V.sub.1 is applied
between the group of first electrodes 23a and the group of second
electrodes 23b in this way, plasma is generated in a surface zone
of the insulation protection layer 23e just downstream of each
individual first electrode 23a, and air current indicated by the
arrows in FIG. 4 is generated accordingly. Exhaust gas intervening
therearound is dragged by such generated air current and is
prevented from burbling away from the wall face 18e that defines
the exhaust passage 18a, with the result that the exhaust gas flows
into the upstream end face 21a of the DOC 21 in a diffused state.
In this case, the strength of air current that is generated as a
result of generation of plasma is directly proportional to the
amount of energy that is input to the groups of first and second
electrodes 23a, 23b.
[0076] When the DPF 22 is arranged downstream of the DOC 21 as in
the case of the present embodiment, soot contained in exhaust gas
is oxidized by the operation of the first plasma actuator 23, so it
is possible to further reduce the amount of soot contained in
exhaust gas flowing into the DPF 22 through the DOC 21. As a
result, it is possible to reduce the frequency of the process of
regenerating the DPF 22.
[0077] A catalyst temperature sensor 27 is attached to the DOC 21
as a temperature acquisition device configured to acquire the
temperature of a catalytic converter according to an embodiment of
the invention. Information about the temperature of the DOC 21,
acquired by the catalyst temperature sensor 27, is output to the
ECU 17. The ECU 17 applies the high voltage V.sub.1 to the first
plasma actuator 23 by switching the first switch 25 to an energized
state only when the temperature T.sub.C of the DOC 21 is higher
than or equal to an activation lower limit temperature T.sub.CL of
the DOC 21 and the temperature T.sub.C of the DOC 21 is lower than
or equal to an upper limit temperature T.sub.CH of the DOC 21.
[0078] The temperature T.sub.C of the DOC 21, acquired by the
catalyst temperature sensor 27, is desirably the temperature of a
zone different from a zone into which exhaust gas flows because of
the first exhaust gas burble zone Z.sub.1, that is, a zone into
which exhaust gas is difficult to flow. In the present embodiment,
the temperature of an outer peripheral end of the DOC 21 at a
portion downstream of a heat insulation partition 21b (described
later) is acquired. Instead of the catalyst temperature sensor 27,
an exhaust gas temperature sensor for detecting an exhaust gas
temperature may be arranged at at least one of a portion upstream
of the exhaust gas control apparatus 19 and a portion downstream of
the exhaust gas control apparatus 19, and the temperature T.sub.C
of the DOC 21 may be estimated on the basis of detected information
from the exhaust gas temperature sensor. Alternatively, a temporal
change in the temperature T.sub.C of the DOC 21 from the start of a
warm-up may be obtained in advance by an experiment, and the
temperature T.sub.C of the DOC 21 may be estimated on the basis of
a time from the start of the warm-up.
[0079] The cylindrical heat insulation partition 21b made of a
heat-resistant material having a lower thermal conductivity than
air, such as Porextherm WDS (trademark) produced by Kurosaki Harima
Corporation, is provided at the upstream end of the DOC 21 in the
DOC 21 in the present embodiment. Instead of using such a special
material, the heat insulation partition 21b may be an air layer. In
this case, a cylindrical air gap just needs to be provided in the
DOC 21. The zone surrounded by the cylindrical heat insulation
partition 21b is a zone in which exhaust gas disproportionately
flows into the DOC 21 as a result of burble of exhaust gas in the
first exhaust gas burble zone Z.sub.1 in a state where the first
plasma actuator 23 is not operated. Usually, the passage sectional
area of the heat insulation partition 21b is substantially equal to
or slightly larger than the passage sectional area of the exhaust
pipe 18 that is connected to the cone portion 18b in the first
exhaust gas burble zone Z.sub.1, and the outline shape of the heat
insulation partition 21b is similar to the sectional shape of the
exhaust pipe 18. Thus, in a state where the first plasma actuator
23 is not operated, it is possible to guide the major portion of
exhaust gas to the zone of the DOC 21, surrounded by the heat
insulation partition 21b. Thus, it is possible to quickly raise the
temperature of only the zone of the DOC 21, surrounded by the heat
insulation partition 21b, during a warm-up of the engine 10. The
length of the heat insulation partition 21b along the longitudinal
direction of the DOC 21 (the flow direction of exhaust gas) is
desirably smaller than or equal to a half of the DOC 21 and may be
about one-third or one quarter of the DOC 21.
[0080] FIG. 6 schematically shows the temperature rise
characteristic of the DOC 21 according to the present embodiment
during a warm-up of the engine 10. The continuous line in FIG. 6
indicates a temperature change at the center portion of the
upstream end face 21a of the DOC 21, surrounded by the heat
insulation partition 21b, in a state where the first plasma
actuator 23 is not operated. The dashed line in FIG. 6 indicates a
temperature change at the center portion of the upstream end of the
DOC 21 in the case where the heat insulation partition 21b is not
provided in a state where the first plasma actuator 23 is not
operated. The alternate long and two-short dashes line in FIG. 6
indicates a temperature change at the center portion of the
upstream end face 21a in the case where exhaust gas flows into the
DOC 21 in the case where the heat insulation partition 21b is not
provided in a state where exhaust gas is diffused by operating the
first plasma actuator 23. The dotted line in FIG. 6 indicates a
temperature change of a zone of which the temperature is detected
by the catalyst temperature sensor 27 in the present
embodiment.
[0081] According to the graph, when the heat insulation partition
21b is provided in the DOC 21, the temperature of the center
portion of the DOC 21 reaches the catalyst activation lower limit
temperature T.sub.CL at time t.sub.1. It is understood that the
center portion of the DOC 21 is heated to the catalyst activation
lower limit temperature TLC in a period of time shorter than or
equal to half of a time that is taken in the case indicated by the
dashed line where the heat insulation partition 21b is not provided
and the corresponding time is t.sub.2. Therefore, by providing the
heat insulation partition 21b and stopping the operation of the
first plasma actuator 23 during a warm-up, it is possible to
improve purification of exhaust gas during a warm-up of the engine
10 by further quickly activating only the center portion of the DOC
21. It appears that the temperature T.sub.C that is detected by the
catalyst temperature sensor 27, that is, the temperature of the
outer peripheral end of the DOC 21, steeply rises after time
t.sub.3 at which the temperature of the outer peripheral end of the
DOC 21 reaches the catalyst activation lower limit temperature
T.sub.CL from time t.sub.0 at which the engine 10 is started. The
reason is that the first plasma actuator 23 begins to operate at
time t.sub.3 at which the temperature of the outer peripheral end
of the DOC 21 has reached the catalyst activation lower limit
temperature T.sub.CL and exhaust gas flows into the DOC 21 in a
diffused state. That is, by operating the first plasma actuator 23
at time t.sub.3 at which the acquired temperature T.sub.C of the
DOC 21 has reached the catalyst activation lower limit temperature
T.sub.CL, it is possible to further early effectively cause the
whole DOC 21 to function.
[0082] It should be noted that the position of the heat insulation
partition 21b with respect to the DOC 21 may significantly deviate
from the center portion of the DOC 21, which is described in the
case of the present embodiment, because of the shape of the cone
portion 18b, an angle at which the exhaust pipe 18 is connected to
the cone portion 18b, and the like. When the heat insulation
partition 21b is not provided in the catalytic converter, the
temperature T.sub.C of the DOC 21, which is acquired by the
above-described catalyst temperature sensor 27, is desirably the
temperature of the zone at the outer peripheral end of the upstream
end face 21a of the DOC 21. FIG. 7 shows the sectional structure of
such a first exhaust gas treatment unit according to another
embodiment. In the present embodiment, because the heat insulation
partition 21b is not provided in the DOC 21, the catalyst
temperature sensor 27 is attached to the outer peripheral end of
the upstream end face 21a of the DOC 21 at a portion farthest from
the exhaust pipe 18 that is connected to the cone portion 18b. The
first plasma actuator 23 is installed in the first exhaust gas
burble zone Z.sub.1 having a convex curved face of a zone in which
the exhaust pipe 18 is connected to the cone portion 18b. When the
heat insulation partition 21b is provided in the DOC 21, the heat
insulation partition 21b may be provided at a portion indicated by
the alternate long and two-short dashes line in FIG. 7, and may be
provided as an air gap as described above.
[0083] The procedure of operating the above-described first plasma
actuator 23 will be described with reference to the flowchart of
FIG. 8. Initially, in step S11, it is determined whether the
catalyst temperature T.sub.C is higher than or equal to the
catalyst activation lower limit temperature T.sub.CL. When it is
determined that the catalyst temperature T.sub.C is higher than or
equal to the catalyst activation lower limit temperature T.sub.CL,
that is, when it is determined that the catalyst temperature
T.sub.C is a temperature at which there is a possibility that the
first plasma actuator 23 is allowed to be operated, the process
proceeds to step S12. In step S12, it is determined whether the
catalyst temperature T.sub.C is lower than or equal to the upper
limit temperature T.sub.CH. When it is determined that the catalyst
temperature T.sub.C is lower than or equal to the upper limit
temperature T.sub.CH, that is, when it is desirable to diffuse
exhaust gas over the entire area of the DOC 21 by operating the
first plasma actuator 23, the process proceeds to step S13. In step
S13, the exhaust gas flow rate Q is acquired. Subsequently, in step
S14, the applied voltage V.sub.1 corresponding to the acquired
exhaust gas flow rate Q is set. Then, in step S15, the first plasma
actuator 23 is driven at the set applied voltage V.sub.1.
[0084] Thus, air current commensurate with the exhaust gas flow
rate Q is generated toward the first exhaust gas treatment unit
along the part of the wall face 18e of the exhaust passage 18a in
the first exhaust gas burble zone Z.sub.1. As a result, exhaust gas
flowing along the part of the wall face 18e of the exhaust passage
18a in the first exhaust gas burble zone Z.sub.1 is dragged by the
air current, flows without burbling away from the part of the wall
face 18e of the exhaust passage 18a, and then flows over the entire
area of the DOC 21 in a diffused state. Thus, it is possible to
effectively utilize the DOC 21 at a maximum.
[0085] After that, it is determined in step S16 whether a first
flag is set. However, because the first flag is not set at first,
the process proceeds to step S17. In step S17, the first flag is
set, and then the process returns to step S11 again.
[0086] On the other hand, when it is determined in step S11 that
the catalyst temperature T.sub.C is lower than the catalyst
activation lower limit temperature T.sub.CL, that is, when it is
desirable to quickly raise the temperature of the zone of the DOC
21, surrounded by the heat insulation partition 21b, the process
proceeds to step S18. As in the case where it is determined in step
S12 that the catalyst temperature T.sub.C is higher than the upper
limit temperature T.sub.CH, the process proceeds to step S18. In
step S18, it is determined whether the first flag is set. When it
is determined that the first flag is set, the operation of the
first plasma actuator 23 is stopped by setting the applied voltage
V.sub.1 to zero in step S19, the first flag is reset in step S20,
and then the process returns to step S11 again. Thus, it is
possible to avoid supplying unnecessary electric power to the first
plasma actuator 23.
[0087] When it is determined in step S11 that the catalyst
temperature T.sub.C is lower than the catalyst activation lower
limit temperature T.sub.CL, the operation of the first plasma
actuator 23 is stopped. Thus, exhaust gas disproportionately flows
from the first exhaust gas burble zone Z.sub.1 into the zone
surrounded by the heat insulation partition 21b of the DOC 21. As a
result, it is possible to further quickly raise the temperature of
the zone surrounded by the heat insulation partition 21b of the DOC
21 to the activation lower limit temperature T.sub.CL or higher, so
it is possible to facilitate purification of exhaust gas during a
warm-up of the engine 10.
[0088] A swelled portion 28 is provided in the exhaust pipe 18
downstream of the exhaust gas control apparatus 19. The swelled
portion 28 has an increased passage sectional area. A partition
wall 29 is arranged in the exhaust passage 18a. The partition wall
29 extends along the flow direction of exhaust gas so as to
partition off a space in the swelled portion 28. An inlet portion
28a is provided between the upstream end of the partition wall 29
and the wall face 18e that defines the swelled portion 28 of the
exhaust pipe 18. An outlet portion 28b is provided between the
downstream end of the partition wall 29 and the wall face 18e that
defines the swelled portion 28 of the exhaust pipe 18. The inlet
portion 28a is used to cause exhaust gas to flow into the swelled
portion 28 side. The outlet portion 28b is used to cause exhaust
gas in the swelled portion 28 to flow out. Thus, the exhaust
passage 18a downstream of the exhaust gas control apparatus 19 is
branched into a main exhaust passage 18c and an auxiliary exhaust
passage 18d. The main exhaust passage 18c is not bypassed to the
swelled portion 28. The auxiliary exhaust passage 18d is bypassed
to the swelled portion 28. The exhaust heat recovery device 20
communicates with a water jacket 30a provided in a cylinder block
30. The exhaust heat recovery device 20 is arranged in the
auxiliary exhaust passage 18d, and exchanges heat between exhaust
gas flowing through the auxiliary exhaust passage 18d and coolant
of the engine 10. The exhaust heat recovery device 20 serves as a
second exhaust gas treatment unit of the invention. The exhaust
heat recovery device 20 is used to achieve an early warm-up of the
engine 10 by raising the temperature of coolant by the use of heat
of exhaust gas. For this purpose, the above-described DPF 22 may be
arranged in the exhaust passage 18a at a portion downstream of the
exhaust heat recovery device 20. In this case, it is possible to
further efficiently recover exhaust heat.
[0089] In the case of the embodiment shown in FIG. 3, there is a
second exhaust gas burble zone Z.sub.2 in which exhaust gas flowing
along a part of the wall face 18e, which defines an upstream
branching zone of the swelled portion 28, burbles away from the
part of the wall face 18e and, as a result, the amount of exhaust
gas flowing into the swelled portion 28 is reduced. A second plasma
actuator 31 is arranged at the part of the wall face 18e of the
exhaust passage 18a in the second exhaust gas burble zone Z.sub.2.
The sectional shape of the second exhaust gas burble zone Z.sub.2,
taken along the flow direction of exhaust gas, includes a convex
curved line. The second plasma actuator 31 is used to generate air
current toward the exhaust heat recovery device 20 along the part
of the wall face 18e. The second plasma actuator 31 basically has
the same configuration as the above-described first plasma actuator
23, and is connected to the inverter 24 via a second switch 32. The
on/off state of the second switch 32 is controlled by the ECU 17.
However, an applied voltage V.sub.2, a driving frequency, and the
like, to the second plasma actuator 31 by the inverter 24 are
constant values set in advance in response to the curvature of the
second exhaust gas burble zone Z.sub.2.
[0090] A clearance W.sub.1 from a part of a wall face 28c of the
swelled portion 28, which defines the auxiliary exhaust passage
18d, to the partition wall 29 along a direction perpendicular to
the partition wall 29 is set so as to be shorter than a clearance
W.sub.2 from the same wall face 28c to a part of the wall face 28e,
which defines the exhaust passage 18a just before branching along
the direction perpendicular to the partition wall 29. In other
words, a distance from the center of the main exhaust passage 18c
to the wall face 18e that defines the exhaust passage 18a just
before branching is set so as to be shorter than a distance from
the center of the main exhaust passage 18c to the partition wall
29. Thus, it is possible to suppress an unnecessary rise in the
temperature of coolant by making part of exhaust gas difficult to
flow into the exhaust heat recovery device 20 side after completion
of a warm-up of the engine 10. In order to reliably suppress an
unnecessary rise in the temperature of coolant after completion of
a warm-up, a mechanical shutter mechanism for opening or closing
the outlet portion 28b may be incorporated. However, it should be
noted that component cost, maintenance, and the like, are required
for incorporating a mechanical shutter mechanism. In the present
embodiment, because there is no movable portion for opening or
closing the inlet portion 28a or the outlet portion 28b,
reliability is high, and it is possible to reduce component cost
and pressure loss.
[0091] A coolant temperature sensor 33 is arranged in the cylinder
block 30. The coolant temperature sensor 33 acquires the
temperature T.sub.W of coolant of the engine 10 and outputs the
detected information to the ECU 17. The coolant of the engine 10
flows through the water jacket 30a. The ECU 17 operates the second
plasma actuator 31 by switching the second switch 32 to the
energized state only when the acquired temperature T.sub.W of
coolant is lower than a temperature T.sub.WL set in advance.
[0092] The procedure of operating the second plasma actuator 31
will be described with reference to the flowchart shown in FIG. 9.
Initially, in step S21, it is determined whether the coolant
temperature T.sub.W is lower than the lower limit coolant
temperature T.sub.WL. When the coolant temperature T.sub.W is lower
than the lower limit coolant temperature T.sub.WL, that is, when it
is determined that a warm-up of the engine 10 is required, the
second plasma actuator 31 is driven in step S22. Thus, it is
possible to efficiently guide part of exhaust gas, which has passed
through the exhaust gas control apparatus 19, to the auxiliary
exhaust passage 18d via the inlet portion 28a. Exhaust gas guided
to the auxiliary exhaust passage 18d exchanges heat with coolant
while passing through the exhaust heat recovery device 20, raises
the temperature of coolant, flows out from the auxiliary exhaust
passage 18d via the outlet portion 28b, merges into exhaust gas
flowing through the main exhaust passage 18c, and then flows down
to the muffler side. Subsequently, in step S23, it is determined
whether a second flag is set. Because the second flag is not set at
first, the process proceeds to step S24. In step S24, the second
flag is set, and then the process returns to step S21 again.
[0093] In this way, electric power is supplied to the second plasma
actuator 31 until the coolant temperature T.sub.W becomes higher
than or equal to the lower limit coolant temperature T.sub.WL, and
the coolant temperature is raised by guiding part of exhaust gas to
the exhaust heat recovery device 20. Thus, a warm-up is
facilitated.
[0094] When it is determined in step S21 that the coolant
temperature T.sub.W is higher than or equal to the lower limit
coolant temperature T.sub.WL, that is, when a warm-up of the engine
10 has completed, the process proceeds to step S25. In step S25, it
is determined whether the second flag is set. When it is determined
that the second flag is set, that is, when electric power is being
supplied to the second plasma actuator 31, the process proceeds to
step S26. The operation of the second plasma actuator 31 is stopped
by setting the voltage V.sub.2, applied to the second plasma
actuator 31, to zero in step S26. After that, the process proceeds
to step S27, the second flag is reset, and the process returns to
step S21 again.
[0095] In this state, part of exhaust gas is difficult to flow into
the auxiliary exhaust passage 18d via the inlet portion 28a because
of a step between the partition wall 29 and the wall face 18e that
defines the exhaust passage 18a just before branching, so it is
possible to suppress an unnecessary rise in the coolant
temperature. It is also possible to prevent supply of unnecessary
electric power to the second plasma actuator 31 after completion of
a warm-up of the engine 10.
[0096] The invention should be interpreted from only matters
described in the appended claims, and any modifications and changes
of the above-described embodiment, included in the concept of the
invention are possible other than the described matters. That is,
all the matters in the above-described embodiment are not intended
to limit the invention, but they can be arbitrarily modified in
response to an application, a purpose, and the like, including a
configuration that is not directly relevant to the invention.
* * * * *