U.S. patent application number 13/499115 was filed with the patent office on 2012-09-27 for exhaust purification system of internal combustion engine.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Takamitsu Asanuma, Daichi Imai, Katsuhiko Oshikawa, Hiroshi Otsuki, Yuichi Sobue, Kou Sugawara.
Application Number | 20120240561 13/499115 |
Document ID | / |
Family ID | 44114727 |
Filed Date | 2012-09-27 |
United States Patent
Application |
20120240561 |
Kind Code |
A1 |
Sobue; Yuichi ; et
al. |
September 27, 2012 |
EXHAUST PURIFICATION SYSTEM OF INTERNAL COMBUSTION ENGINE
Abstract
An exhaust purification system of an internal combustion engine
which is controlled so that a combustion air-fuel ratio becomes
lean at the time of ordinary operation, provided with an adsorption
part which adsorb unburned fuel which is contained in exhaust gas
and an oxidation part which has catalyst particles of a metal which
oxidizes carbon monoxide. The adsorption part includes zeolite
which substantially adsorbs the lower olefins which are contained
in the exhaust gas. The adsorption part and the oxidation part are
arranged so that the exhaust gas contacts the adsorption part, then
contacts the oxidation part.
Inventors: |
Sobue; Yuichi; (Susono-shi,
JP) ; Imai; Daichi; (Susono-shi, JP) ;
Oshikawa; Katsuhiko; (Susono-shi, JP) ; Otsuki;
Hiroshi; (Susono-shi, JP) ; Asanuma; Takamitsu;
(Mishima-shi, JP) ; Sugawara; Kou; (Kakegawa-shi,
JP) |
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi, Aichi
JP
|
Family ID: |
44114727 |
Appl. No.: |
13/499115 |
Filed: |
December 1, 2009 |
PCT Filed: |
December 1, 2009 |
PCT NO: |
PCT/JP2009/070445 |
371 Date: |
March 29, 2012 |
Current U.S.
Class: |
60/297 |
Current CPC
Class: |
F01N 2510/0684 20130101;
F01N 3/0814 20130101; Y02A 50/20 20180101; F01N 3/035 20130101;
B01D 2255/912 20130101; B01D 53/9486 20130101; B01D 2257/702
20130101; F01N 13/0097 20140603; B01D 2255/102 20130101; B01D
2257/404 20130101; B01D 2257/502 20130101; B01D 2253/108 20130101;
B01D 2255/902 20130101; F01N 3/0842 20130101; B01D 53/944 20130101;
F01N 3/103 20130101; Y02A 50/2341 20180101; B01D 2255/91 20130101;
F01N 2370/04 20130101; F01N 3/0835 20130101; B01D 53/9477 20130101;
B01D 2258/01 20130101 |
Class at
Publication: |
60/297 |
International
Class: |
F01N 3/035 20060101
F01N003/035 |
Claims
1. An exhaust purification system of an internal combustion engine
which is controlled so that an air-fuel ratio at the time of
combustion at the time of ordinary operation where an engine body
outputs a torque becomes lean, the exhaust purification system of
an internal combustion engine provided with an adsorption part
which adsorbs unburned fuel which is contained in exhaust gas when
a temperature is less than a release temperature of the unburned
fuel and releases the unburned fuel when the temperature is the
release temperature of the unburned fuel or more and an oxidation
part which has catalyst particles of a metal which oxidizes carbon
monoxide which is contained in the exhaust gas, the adsorption part
being comprised of .beta.-zeolite which adsorbs lower olefins which
are contained in the exhaust gas and does not include a zeolite
other than .beta.-zeolite, the adsorption part and the oxidation
part being arranged so that the exhaust gas contacts the adsorption
part, then contacts the oxidation part.
2. An exhaust purification system of an internal combustion engine
as set forth in claim 1, wherein the adsorption part and the
oxidation part are stacked on the surface of a base member, and the
oxidation part is arranged at the side farther from an engine
exhaust passage than the adsorption part.
3. An exhaust purification system of an internal combustion engine
as set forth in claim 1, wherein the adsorption part and the
oxidation part are arranged along the direction of flow of the
exhaust gas, and the oxidation part is arranged at the downstream
side from the adsorption part in the direction of flow of the
exhaust gas.
4. (canceled)
5. (canceled)
6. An exhaust purification system of an internal combustion engine
as set forth in claim 1, wherein the metal particles of the
oxidation part are mainly comprised of platinum.
7. An exhaust purification system of an internal combustion engine
as set forth in claim 6, wherein the metal particles of the
oxidation part are formed substantially all from platinum.
8. (canceled)
9. An exhaust purification system of an internal combustion engine
as set forth in claim 1, wherein the catalyst particles of the
metal of the oxidation part are comprised of metal particles other
than metal particles which have an oxygen storage ability.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust purification
system of an internal combustion engine.
BACKGROUND ART
[0002] Exhaust gas of a diesel engine, gasoline engine, or other
internal combustion engine, for example, contains carbon monoxide
(CO), unburned fuel (HC), nitrogen oxides (NO.sub.x), particulate
matter (PM), and other constituents. An exhaust purification system
of an internal combustion engine is provided with an exhaust
treatment device for removing these constituents.
[0003] Among the constituents contained in exhaust gas, nitrogen
oxides are removed by an exhaust treatment device which reduces the
nitrogen oxides. The particulate matter is removed by an exhaust
treatment device which traps the particulate matter. On the other
hand, carbon monoxide and unburned fuel are removed by exhaust
treatment devices for oxidizing these substances. For example, the
engine exhaust passage has an oxidation catalyst or three-way
catalyst arranged in it.
[0004] In the WO00/27508 pamphlet, an exhaust gas purification
method is disclosed which brings exhaust gas reduced in
concentration of HC into contact with an oxidation/reduction
catalyst comprised of an oxygen storing material carrying at least
one type of element of rhodium and palladium so as to suppress the
exhaust of HC to a high degree from the low temperature region to
the high temperature region.
[0005] Further, in Japanese Patent Publication (A) No 7-166852, an
exhaust purification device which is provided with zeolite and a
main converter, the zeolite having a maximum pore aperture larger
than 5.6 angstroms, and including non-frame structure anions
selected from copper or other ions is disclosed. It is disclosed
that this exhaust purification device effectively converts the
unburned hydrocarbons contained in the exhaust gas which is
exhausted from the engine, in particular low molecular weight
alkenes.
CITATIONS LIST
Patent Literature
[0006] PLT 1: WO00/27508 pamphlet [0007] PLT 2: Japanese Patent
Publication (A) No. 7-166852
SUMMARY OF INVENTION
Technical Problem
[0008] The above WO00/27508 pamphlet discloses an internal
combustion engine which controls the air-fuel ratio at the time the
fuel is burned to the stoichiometric air-fuel ratio at the time of
ordinary operation. The exhaust purification system includes a
three-way catalyst for oxidizing the unburned fuel or other
substance to be oxidized. A three-way catalyst is a catalyst which
simultaneously performs an oxidation reaction and a reduction
reaction. The three-way catalyst can remove the unburned fuel,
carbon monoxide, and nitrogen oxides by a high purification rate at
the vicinity where the air-fuel ratio of the exhaust gas is the
stoichiometric air-fuel ratio.
[0009] The exhaust purification system which is disclosed in this
publication includes a three-way catalyst which has an oxygen
storage/release material and an HC adsorption material. The
adsorption action and release action of the unburned fuel by the HC
adsorption material and the storage action and release action of
the oxygen by the oxygen storage/release material enable the
surface of the three-way catalyst to be constantly held near the
stoichiometric air-fuel ratio. For this reason, it is disclosed
that a high purification rate can be maintained.
[0010] An internal combustion engine includes a device which
controls the air-fuel ratio at the time of combustion in the
combustion chambers at the time of ordinary operation to be lean.
In this internal combustion engine, at the time of ordinary
operation, the air-fuel ratio of the exhaust gas which flows into
the exhaust purification system becomes lean. The carbon monoxide
is oxidized at the oxidation catalyst and is converted to carbon
dioxide. In this regard, in the exhaust gas, carbon monoxide and
unburned fuel are copresent. Sometimes the unburned fuel obstructed
the oxidation of the carbon monoxide.
[0011] In recent years, the demands on the amount of release of
carbon dioxide have been becoming stricter. To reduce the amount of
release of carbon dioxide, reducing the amount of fuel burned is
being studied. In this regard, if reducing the amount of fuel
burned, the temperature of the exhaust gas will fall. If the
temperature of the exhaust gas falls, there is the problem that the
catalyst temperature will fall and the efficiency of removal of
carbon monoxide will fall.
[0012] The present invention has as its object to provide an
exhaust purification system of an internal combustion engine which
can give a high purification rate of carbon monoxide from the low
temperature region.
Solution to Problem
[0013] The exhaust purification system of an internal combustion
engine of the present invention is an exhaust purification system
of an internal combustion engine which is controlled so that an
air-fuel ratio at the time of combustion at the time of ordinary
operation where an engine body outputs a torque becomes lean, which
includes an adsorption part which adsorbs unburned fuel which is
contained in exhaust gas when a temperature is less than a release
temperature of the unburned fuel and releases the unburned fuel
when the temperature is the release temperature of the unburned
fuel or more and an oxidation part which has catalyst particles of
a metal which oxidizes carbon monoxide which is contained in the
exhaust gas. The adsorption part includes zeolite which
substantially adsorbs lower olefin which is contained in the
exhaust gas. The adsorption part and the oxidation part are
arranged so that the exhaust gas contacts the adsorption part, then
contacts the oxidation part.
[0014] In the above invention, the adsorption part and the
oxidation part can be stacked on the surface of a base member, and
the oxidation part can be arranged at a side farther from an engine
exhaust passage than the adsorption part.
[0015] In the above invention, the adsorption part and the
oxidation part can be arranged along the direction of flow of the
exhaust gas, and the oxidation part can be arranged at a downstream
side from the adsorption part in the direction of flow of the
exhaust gas.
[0016] In the above invention, preferably the adsorption part
includes a higher hydrocarbon adsorption part which adsorbs higher
hydrocarbons and a lower olefin adsorption part which adsorbs lower
olefins, and the higher hydrocarbon adsorption part and lower
olefin adsorption part are arranged so that the exhaust gas
contacts the higher hydrocarbon adsorption part, then contacts the
lower olefin adsorption part.
[0017] In the above invention, preferably the higher hydrocarbon
adsorption part includes .beta.-zeolite, and the lower olefin
adsorption part includes zeolite which has exchanged ions with a
metal.
[0018] In the above invention, the metal particles of the oxidation
part may be mainly comprised of platinum.
[0019] In the above invention, the metal particles of the oxidation
part can be formed substantially all from platinum.
[0020] In the above invention, preferably the zeolite which
substantially adsorbs the lower olefins includes at least one of
ZMS5 which has exchanged ions with iron and ZMS5 which has
exchanged ions with silver.
[0021] In the above invention, the catalyst particles of the metal
of the oxidation part can be comprised of metal particles other
than metal particles which have an oxygen storage ability.
Advantageous Effects of Invention
[0022] According to the present invention, it is possible to
provide an exhaust purification system for obtaining a high carbon
monoxide purification rate from a low temperature region
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 A schematic view of an internal combustion engine in
an embodiment.
[0024] FIG. 2 A schematic cross-sectional view of a first exhaust
treatment device in the embodiment.
[0025] FIG. 3 An enlarged schematic cross-sectional view of the
first exhaust treatment device in the embodiment.
[0026] FIG. 4 A graph showing the relationship between a
temperature of an oxidation catalyst and a purification rate of
carbon monoxide.
[0027] FIG. 5 A graph of a temperature which purifies exhaust of
50% of carbon monoxide in an exhaust treatment device of Example 1
and exhaust treatment devices of comparative examples.
[0028] FIG. 6 An enlarged schematic cross-sectional view of an
exhaust treatment device of Comparative Example 1 in the
embodiment.
[0029] FIG. 7 An enlarged schematic cross-sectional view of an
exhaust treatment device of Comparative Example 2 in the
embodiment.
[0030] FIG. 8 An enlarged schematic cross-sectional view of an
exhaust treatment device of Comparative Example 3 in the
embodiment.
[0031] FIG. 9 An enlarged schematic cross-sectional view of a
second exhaust treatment device in the embodiment.
[0032] FIG. 10 A graph of an amount of exhaust of carbon monoxide
of an exhaust treatment device of Example 1 and an exhaust
treatment device of Example 2 and of exhaust treatment devices of
comparative examples.
[0033] FIG. 11 An enlarged schematic cross-sectional view of an
exhaust treatment device of Comparative Example 4 in the
embodiment.
[0034] FIG. 12 A graph showing the relationship between types of
zeolite and an amount of exhaust of carbon monoxide in the
embodiment.
[0035] FIG. 13 A graph of a temperature which purifies exhaust of
50% of carbon monoxide in an exhaust treatment device of Example 3
and an exhaust treatment device of a comparative example.
[0036] FIG. 14 An enlarged schematic cross-sectional view of a
fourth exhaust treatment device in the embodiment.
[0037] FIG. 15 An enlarged schematic cross-sectional view of a
fifth exhaust treatment device in the embodiment.
[0038] FIG. 16 A graph of an amount of exhaust of carbon monoxide
of exhaust treatment devices of Example 4 and Example 5 and exhaust
treatment devices of comparative examples.
[0039] FIG. 17 An enlarged schematic cross-sectional view of an
exhaust treatment device of Comparative Example 6 in the
embodiment.
[0040] FIG. 18 An enlarged schematic cross-sectional view of a
sixth exhaust treatment device in the embodiment.
DESCRIPTION OF EMBODIMENTS
[0041] Referring to FIG. 1 to FIG. 18, an exhaust purification
system of an internal combustion engine in an embodiment will be
explained. The internal combustion engine in the present embodiment
is mounted in a vehicle. In the present embodiment, the explanation
will be given with reference to the example of a compression
ignition type of diesel engine.
[0042] FIG. 1 shows an overall view of an internal combustion
engine in the present embodiment. The internal combustion engine is
provided with an engine body 1. Further, the internal combustion
engine is provided with an exhaust purification system which
purifies exhaust gas. The engine body 1 includes combustion
chambers 2 as cylinders, electronic control type fuel injectors 3
which inject fuel into the respective combustion chambers 2, an
intake manifold 4, and an exhaust manifold 5.
[0043] The intake manifold 4 is connected through an intake duct 6
to an outlet of a compressor 7a of an exhaust turbocharger 7. The
inlet of the compressor 7a is connected through an intake air
detector 8 to an air cleaner 9. Inside the intake duct 6, a
throttle valve 10 which is driven by a step motor is arranged.
Further, in the intake duct 6, a cooling device 11 for cooling the
intake air which flows through the inside of the intake duct 6 is
arranged. In the example which is shown in FIG. 1, engine cooling
water is led to the cooling device 11. The engine cooling water is
used to cool the intake air.
[0044] The exhaust manifold 5 is connected to an inlet of an
exhaust turbine 7b of the exhaust turbocharger 7. The exhaust
purification system in the present embodiment is provided with an
exhaust treatment device 13 for oxidizing unburned fuel and carbon
monoxide and other substances which should be oxidized. The exhaust
treatment device 13 is connected to an outlet of the exhaust
turbine 7b through an exhaust pipe 12. Inside of the engine exhaust
passage downstream of the exhaust treatment device 13, a
particulate filter 16 for trapping particulate matter in the
exhaust gas is arranged. The exhaust gas flows along the engine
exhaust passage as shown by the arrows 100.
[0045] Between the exhaust manifold 5 and the intake manifold 4, an
exhaust gas recirculation (EGR) passage 18 is arranged for EGR. In
the EGR passage 18, an electronic control type EGR control valve 19
is arranged. Further, in the EGR passage 18, a cooling device 20
for cooling the EGR gas which flows through the inside of the EGR
passage 18 is arranged. In the example which is shown in FIG. 1,
engine cooling water is guided to the inside of the cooling device
20. The engine cooling water is used to cool the EGR gas.
[0046] The respective fuel injectors 3 are connected through fuel
feed pipes 21 to a common rail 22. The common rail 22 is connected
through an electronic control type variable discharge fuel pump 23
to a fuel tank 24. The fuel which is stored in the fuel tank 24 is
fed by the fuel pump 23 to the inside of the common rail 22. The
fuel which is fed into the common rail 22 is fed through the
respective fuel feed pipes 21 to the fuel injectors 3.
[0047] The electronic control unit 30 includes a digital computer.
The electronic control unit 30 in the present embodiment functions
as a control device of the exhaust purification system. The
electronic control unit 30 includes components which are connected
to each other by a bidirectional bus 31 such as a ROM (read only
memory) 32, RAM (random access memory) 33, CPU (microprocessor) 34,
input port 35, and output port 36.
[0048] The ROM 32 is a storage device for read only operations. The
ROM 32 stores maps and other information necessary for control in
advance. The CPU 34 can perform any processing or judgment. The RAM
33 is a storage device for random access operations. The RAM 33 can
store operational history and other information or temporarily
store processing results.
[0049] Downstream of the exhaust treatment device 13, a temperature
sensor 27 for detecting the temperature of the exhaust treatment
device 13 is arranged. Downstream of the particulate filter 16, a
temperature sensor 26 for detecting the temperature of the
particulate filter 16 is arranged. At the particulate filter 16, a
differential pressure sensor 28 for detecting a differential
pressure before and after the particulate filter 16 is attached.
The output signals of these temperature sensors 26 and 27,
differential pressure sensor 28, and intake air detector 8 are
input through corresponding AD converters to the input port 35.
[0050] An accelerator pedal 40 is connected to a load sensor 41
which generates an output voltage which is proportional to an
amount of depression of the accelerator pedal 40. The output signal
of the load sensor 41 is input through a corresponding AD converter
37 to the input port 35. Further, the input port 35 has a crank
angle sensor 42 connected to it which generates an output pulse
every time a crank shaft rotates by for example 15.degree.. From
the output of the crank angle sensor 42, it is possible to detect
the speed of the engine body 1.
[0051] On the other hand, the output port 36 is connected through
corresponding drive circuits 38 to the fuel injectors 3, the step
motor for driving the throttle valve 10, the EGR control valve 19,
and the fuel pump 23. In this way, the fuel injectors 3 and the
throttle valve 10 etc. are controlled by the electronic control
unit 30.
[0052] The particulate filter 16 is a filter which removes fine
carbon particles which are contained in exhaust gas, fine particles
of sulfates and other ions, and other particulate matter. The
particulate filter, for example, has a honeycomb structure and has
a plurality of flow paths which extend in the direction of flow of
the gas. In the plurality of flow paths; flow paths which have
sealed bottom ends and flow paths which have sealed top ends are
alternately formed. The partition walls of the flow paths are
formed by porous materials such as cordierite. Particulate matter
is trapped when exhaust gas passes through the partition walls. The
particulate matter which gradually builds up at the particulate
filter 16 is removed by being oxidized by raising the temperature
up to for example 600.degree. C. in an excess air atmosphere for
example.
[0053] The exhaust purification system of an internal combustion
engine in the present embodiment is provided with not only the
exhaust treatment device 13, but also the particulate filter 13,
but the invention is not limited to this. It is also possible to
arrange another exhaust treatment device in addition to the exhaust
treatment device 13. For example, the exhaust purification system
may also be provided with an NO.sub.x storage reducing catalyst
(NSR) which purifies the exhaust gas of the NO.sub.x which is
contained in it. The NO.sub.x storage reducing catalyst can, for
example, be arranged between the exhaust treatment device 13 and
the particulate filter 16.
[0054] The NO.sub.x storage reducing catalyst temporarily stores
the NO.sub.x which is contained in the exhaust gas which is
exhausted from the engine body and converts it to N.sub.2 when
releasing the stored NO.sub.x. The NO.sub.x storage reducing
catalyst is comprised of a base member on which for example a
catalyst carrier which includes aluminum oxide is carried. On the
surface of the catalyst carrier, catalyst particles formed by a
precious metal are carried dispersed. Further, on the surface of
the catalyst carrier, a layer of an NO.sub.x adsorbent is formed.
As the catalyst particles, for example, platinum Pt is used. As the
constituents forming the NO.sub.x adsorbent, for example, barium Ba
or other such alkali earth is used.
[0055] In the present invention, the ratio of the air and fuel
(hydrocarbons) in the exhaust gas which is supplied to the engine
intake passage, combustion chambers, or engine exhaust passage is
referred to as the "air-fuel ratio of the exhaust gas (A/F)". When
the air-fuel ratio of the exhaust gas is lean (when it is larger
than the stoichiometric air-fuel ratio), the NO which is contained
in the exhaust gas is oxidized and is stored in the NO.sub.x
adsorbent. As opposed to this, when the air-fuel ratio of the
exhaust gas is rich or becomes the stoichiometric air-fuel ratio,
the NO.sub.x which is stored in the NO.sub.x adsorbent is released.
The released NO.sub.x is reduced to N.sub.2 by the unburned fuel or
carbon monoxide etc. which is contained in the exhaust gas.
[0056] FIG. 2 is an enlarged schematic cross-sectional view of a
first exhaust treatment device in the present embodiment. The first
exhaust treatment device 13 in the present embodiment has a
plurality of passages along the direction of flow of the exhaust
gas. The first exhaust treatment device 13 is split in the middle
of the direction of flow of the exhaust gas. The first exhaust
treatment device 13 includes an upstream-side part 13a for
adsorption of unburned fuel and a downstream-side part 13b for
oxidation of the unburned fuel and carbon monoxide.
[0057] FIG. 3 is an enlarged schematic cross-sectional view of the
first exhaust treatment device in the present embodiment. FIG. 3 is
an enlarged schematic cross-sectional view of the part at the
boundary of the upstream-side part 13a and the downstream-side part
13b. The upstream-side part 13a and the downstream-side part 13b
are respectively provided with base members 55. The base members 55
in the present embodiment have pluralities of flow paths and are
formed into honeycomb structures. The base members 55 are, for
example, formed by cordierite or SiC or other monolithic base
members.
[0058] At the surface of the base member 55 of the upstream-side
part 13a, the adsorption part 51 is formed. The adsorption part 51
is formed at the plurality of flow paths of the base member 55. The
adsorption part 51 is formed in a layer shape along the engine
exhaust passage. The adsorption part 51 has the function of
adsorbing unburned fuel. The adsorption part 51 in the first
exhaust treatment device includes the carrier 60 and
.beta.(beta)-zeolite particles 61. The carrier 60 includes, for
example, aluminum oxide (alumina: Al.sub.2O.sub.3) or other porous
oxide powder. The carrier 60 and .beta.-zeolite particles 61 are,
for example, supported at the base member 55 by a binder.
[0059] At the surface of the base member 55 of the downstream-side
part 13b, an oxidation part 52 is formed. The oxidation part 52 is
formed at the plurality of flow paths of the base member 55. The
oxidation part 52 is formed in a layer shape along the engine
exhaust passage. The oxidation part 52 has the function of
oxidizing the unburned fuel and carbon monoxide etc. The oxidation
part 52 of the first exhaust treatment device 13 includes the
carrier 60 and catalyst particles 62. The carrier 60 is fastened to
the base member 55 by a binder. The catalyst particles 62 are
carried at the carrier 60. The catalyst particles 62 are metal
particles for oxidizing the substances to be oxidized contained in
the exhaust gas. The catalyst particles 62 in the present
embodiment are formed from precious metals. As the catalyst
particles 62, platinum group metals (PGM) may be used. The catalyst
particles 62 can, for example, use at least one precious metal
among platinum Pt, palladium Pd, and rhodium Rh.
[0060] In the first exhaust treatment device of the present
embodiment, the adsorption part 51 is arranged at the upstream side
base member 55, while the oxidation part 52 is arranged at the
downstream side base member 55. The first exhaust treatment device
13 is formed by an upstream-side part and a downstream-side part by
the base member 55 being split, but the invention is not limited to
this. The base member may also be integrally formed. That is, the
absorption part may be formed on a single surface of the base
member at the upstream side along the direction of flow of the
exhaust gas, while the oxidation part may be formed at the
downstream side.
[0061] The unburned fuel (HC) which is contained in exhaust gas
includes chain hydrocarbons which have double bond, that is,
olefins, chain hydrocarbons which do not have unsaturated bond,
that is, paraffins, and aromatic hydrocarbons which have benzene
nuclei, that is, aromatics. Exhaust gas contains higher
hydrocarbons with large numbers of carbon atoms. Higher
hydrocarbons include higher olefins, higher paraffins, aromatics,
etc. Olefins include lower olefins and higher olefins with greater
numbers of carbon atoms than lower olefins. Lower olefins, for
example, are hydrocarbons with five or less number of carbon atoms.
Preferably, the lower olefins include hydrocarbons with two or
three carbon atoms, that is, ethylene and propylene.
[0062] The exhaust treatment device 13 which oxidizes the
substances to be oxidized in the present embodiment adsorbs the
unburned fuel at the adsorption part 51 when the exhaust gas is low
in temperature. For example, unburned fuel is adsorbed when the
temperature of the exhaust treatment device 13 is less than the
release temperature of the unburned fuel. If the temperature of the
exhaust gas rises, unburned fuel is released from the adsorption
part 51. For example, if the temperature of the exhaust treatment
device 13 becomes the release temperature of the unburned fuel or
more, unburned fuel is released. The released unburned fuel is
purified from the exhaust by being oxidized at the oxidation part
52. The carbon monoxide which flows into the exhaust treatment
device is oxidized at the oxidation part 52. By having the carbon
monoxide or unburned hydrocarbons which are contained in exhaust
gas be oxidized, it is converted to water and carbon dioxide.
[0063] Referring to FIG. 3, when the exhaust gas flows into the
exhaust treatment device 13, it contacts the adsorption part 51.
When the exhaust gas is a low temperature, the unburned fuel which
is contained in the exhaust gas is adsorbed at the adsorption part
51. At least part of the unburned fuel can be removed from the
exhaust gas. Next, the exhaust gas contacts the oxidation part 52.
At the oxidation part 52, the carbon monoxide can be oxidized.
[0064] In this regard, in the oxidation catalyst, sometimes the
unburned fuel contained in exhaust gas obstructs the oxidation of
carbon monoxide. For example, the unburned fuel is adsorbed at the
surface of the catalyst particles and poisons the catalyst. As a
result, sometimes oxidation of carbon monoxide was obstructed.
[0065] FIG. 4 shows a graph of the relationship between the
temperature of the oxidation catalyst and the purification rate of
carbon monoxide. In the test shown in FIG. 4, an oxidation catalyst
which includes a ceria-zirconia solid solution and catalyst
particles of platinum is used. Further, the air-fuel ratio of the
exhaust gas which flows into the oxidation catalyst is made lean.
The test was run for the case where the exhaust gas includes
unburned fuel HC and the case where unburned fuel HC is not
included. The abscissa indicates the temperature of the oxidation
catalyst, while the ordinate indicates the purification rate of
carbon monoxide.
[0066] It is learned that more the temperature of the oxidation
catalyst rises, the more the purification rate of carbon monoxide
is improved. When comparing the case where unburned fuel is
included and the case where it is not included, it is learned that
at the substantially entire temperature region, the purification
rate of carbon monoxide is higher in the case where no unburned
fuel is included than the case where unburned fuel is included.
Alternatively, it is learned that the temperature of the oxidation
catalyst which is required for obtaining the same purification rate
of carbon monoxide is lower when unburned fuel is not included than
when unburned fuel is included. From the test results, it is
learned that by removing at least part of the unburned fuel before
the exhaust gas contacts the oxidation part, the purification rate
of carbon monoxide is improved.
[0067] In the first exhaust treatment device in the present
embodiment, the adsorption part 51 is arranged at the upstream
side, while the oxidation part 52 is arranged at the downstream
side. The adsorption part 51 and the oxidation part 52 are arranged
so that the exhaust gas contacts the adsorption part 51, then
contacts the oxidation part 52. The exhaust gas which flows into
the adsorption part 51 has at least part of the unburned fuel
removed. For this reason, it is possible to reduce the
concentration of unburned fuel which flows into the oxidation part
52. The oxidation part 52 can effectively cause oxidation of the
carbon monoxide. In particular, when the exhaust treatment device
13 is a low temperature, it is possible to keep unburned fuel from
building up at and poisoning the oxidation part 52.
[0068] In the exhaust gas which is exhausted from the combustion
chambers 2, higher paraffins with a large number of carbon atoms
remain. The olefins include large amounts of higher olefins with
large numbers of carbon atoms and lower olefins with small numbers
of carbon atoms.
[0069] The lower olefins in the unburned fuel which is contained in
the exhaust gas have the property of a strong effect in obstructing
oxidation of carbon monoxide. The adsorption part of the exhaust
treatment device in the present embodiment includes zeolite which
substantially adsorbs the lower olefins. That is, the adsorption
part includes zeolite which adsorbs lower olefins by a
predetermined efficiency or more so that the oxidation of carbon
monoxide is not substantially obstructed at the oxidation part. The
adsorption part of the first exhaust treatment devices includes
.beta.-zeolite. The exhaust treatment device in the present
embodiment can effectively remove lower olefins from the exhaust
gas at the adsorption part. As a result, it is possible to purify
the exhaust of carbon monoxide by a high purification rate at the
oxidation part.
[0070] As the zeolite which substantially adsorbs the lower
olefins, in addition to .beta.-zeolite, zeolite in which a metal is
carried by ion exchange can be used. In particular, ZMS5 which has
exchanged ions with iron and ZMS5 which has exchanged ions with
silver are superior in efficiency of adsorption of lower olefins.
For this reason, the adsorption part preferably includes at least
one of ZMS5 which has exchanged ions with iron and ZMS5 which has
exchanged ions with silver.
[0071] FIG. 5 shows a graph of the 50% purification temperature of
carbon monoxide of Example 1 and comparative examples of the
present embodiment. The ordinate indicates the temperature at which
the purification rate of carbon monoxide contained in the exhaust
gas becomes 50%. In the examples and comparative examples described
below, the volumes or weights of the corresponding parts are made
the same. The exhaust treatment devices are formed so that the
total volume of the base member becomes the same (11), the weight
of the coated layer which is formed on the surface of the base
member is formed to become the same (150 g), and the weight of the
catalyst particles is formed to become the same (1.8 g).
[0072] Example 1 corresponds to the first exhaust treatment device
in the present embodiment. Referring to FIG. 3, in Example 1, as
the base member 55 of the upstream-side part 13a and the base
member 55 of the downstream-side part 13b, a cordierite base member
(0.5 L) is used. The adsorption part 51 is provided with a coated
layer including .beta.-zeolite particles 61 (60 g) and the carrier
60 of aluminum oxide (15 g). The oxidation part 52 is provided with
a coated layer including the carrier 60 of aluminum oxide (75 g).
The catalyst particles 62 include platinum (1.2 g) and palladium
(0.6 g). The catalyst particles 62 of Example 1 are formed so that
the amount of platinum becomes greater than the amount of
palladium.
[0073] FIG. 6 is an enlarged schematic cross-sectional view of an
exhaust treatment device of Comparative Example 1 in the present
embodiment. In the exhaust treatment device of Comparative Example
1, the carrier 60 is arranged at the surface of the base member 55.
The carrier 60 carries catalyst particles 62 of a precious metal.
The base member 55 of Comparative Example 1 is formed integrally
without being split. In Comparative Example 1, a cordierite base
member (1 L) is used as the base member 55. At the surface of the
base member 55, a coated layer including the carrier 60 of aluminum
oxide (150 g) is formed. The carrier 60 carries catalyst particles
62 which are formed from platinum (1.2 g) and palladium (0.6
g).
[0074] FIG. 7 is an enlarged schematic cross-sectional view of an
exhaust treatment device of Comparative Example 2 in the present
embodiment. In the exhaust treatment device of Comparative Example
2, at the surface of the base member 55, a coated layer including
the carrier 60 formed by aluminum oxide and .beta.-zeolite
particles 61 is formed. At the layers of the carrier 60 and
.beta.-zeolite particles 61, catalyst particles 62 are arranged. In
Comparative Example 2, as the base member 55, a cordierite base
member (1 L) is used. The carrier 60 of aluminum oxide (90 g) and
.beta.-zeolite particles 61 (60 g) are used to form the coated
layer. As the catalyst particles 62, platinum (1.2 g) and palladium
(0.6 g) are arranged.
[0075] FIG. 8 is an enlarged schematic cross-sectional view of an
exhaust treatment device of Comparative Example 3 in the present
embodiment. In Comparative Example 3, the base member 55 is split.
The exhaust treatment device includes the adsorption part 51 and
the oxidation part 52. The respective adsorption part 51 and
oxidation part 52 are similar to those in the first exhaust
treatment device in the present embodiment. In Comparative Example
3, the oxidation part 52 is arranged at the upstream side in the
direction of flow of the exhaust gas, while the adsorption part 51
is arranged at the downstream side. In Comparative Example 3,
compared with Example 1, the oxidation part and the adsorption part
are reversed in order.
[0076] In Comparative Example 3, as the base member 55 of the
adsorption part 51 and the base member 55 of the oxidation part 52,
a cordierite base member (0.5 L) was used. At the oxidation part
52, a coated layer of the carrier 60 of aluminum oxide (75 g) is
formed. The carrier 60 carries catalyst particles 62 which are
formed from platinum (1.2 g) and palladium (0.6 g). In the
adsorption part 51, a coated layer of the carrier 60 of aluminum
oxide (15 g) and .beta.-zeolite particles 61 (60 g) is formed.
[0077] Referring to FIG. 5, internal combustion engines provided
with the exhaust treatment device of Example 1 and the exhaust
treatment devices of Comparative Example 1 to Comparative Example 3
were tested. In the tests, an engine bench test apparatus was used.
In the tests shown in FIG. 5, the tests were run in the steady
state with a constant output torque.
[0078] It is learned that the exhaust treatment device of Example 1
has the lowest 50% purification temperature of carbon monoxide
compared with the exhaust treatment devices of Comparative Example
1 to Comparative Example 3. That is, it is learned that when the
exhaust gas is a low temperature, an excellent ability to purify
the exhaust of carbon monoxide can be exhibited. Further, it is
learned that the exhaust treatment device of Example 1 is superior
in the ability to purify the exhaust of carbon monoxide compared
with the exhaust treatment devices of Comparative Example 1 to
Comparative Example 3.
[0079] Comparative Example 1 which is shown in FIG. 6 is an exhaust
treatment device comprised of a coated layer formed by aluminum
oxide in which catalyst particles 62 are arranged. Comparative
Example 2 which is shown in FIG. 7 further has .beta.-zeolite
particles 61 contained in the coated layer. Comparing Comparative
Example 2 and Example 1, it is learned that even when
.beta.-zeolite particles 61 are arranged at the coated layer, by
separating the layer which contains the catalyst particles 62 and
the layer which contains the .beta.-zeolite particles 61, the
ability to purify the exhaust of carbon monoxide is improved. In
particular, by comparing Comparative Example 3 which is shown in
FIG. 8 and Example 1 which is shown in FIG. 3, it is learned that
by arranging the oxidation part 52 at the downstream side from the
adsorption part 51, the ability to purify the exhaust of carbon
monoxide is improved.
[0080] In this way, in the first exhaust treatment device of the
present embodiment, by arranging .beta.-zeolite at the adsorption
part 51 and arranging the oxidation part 52 at the downstream side
of the adsorption part 51, it is possible to obtain a superior
ability to purify exhaust of carbon monoxide. Alternatively, it is
possible to obtain a superior ability to purify exhaust of carbon
monoxide from a low temperature region of the exhaust treatment
device. For example, in the period of a warmup operation of
internal combustion engine after startup, it is possible to
efficiently purify the exhaust of carbon monoxide. Alternatively,
even when the oxidation part is less than the activation
temperature, the exhaust can be efficiently purified of carbon
monoxide. Alternatively, it is possible to efficiently purify the
exhaust of carbon monoxide in an internal combustion engine with a
low temperature of the exhaust gas which flows into the exhaust
treatment device.
[0081] The exhaust purification system in the present embodiment
can make the temperature of the oxidation part quickly rise so as
to enable efficient oxidation of the carbon monoxide. For example,
even during the warmup period of the internal combustion engine, it
is possible to make the temperature of the oxidation part rise to
the activation temperature in a short time. As a result, it is
possible to purify the exhaust of unburned fuel quickly by a high
efficiency. Further, when the exhaust treatment device to be raised
quickly in temperature is arranged downstream of the oxidation
part, it is possible to raise the temperature in a short time. For
example, when an NO.sub.x storage reducing catalyst is arranged
downstream of the oxidation part, it is possible to make the
NO.sub.x storage reducing catalyst rise to the activation
temperature or more in a short time.
[0082] FIG. 9 is an enlarged schematic cross-sectional view of a
second exhaust treatment device in the present embodiment. The
second exhaust treatment device 13 is provided with the base member
55 which is formed by cordierite etc. The base member 55 of the
second exhaust treatment device is formed integrally without being
split in the middle of the direction of flow of the exhaust
gas.
[0083] The second exhaust treatment device 13 is provided with the
adsorption part 51 and the oxidation part 52. The adsorption part
51 and the oxidation part 52 are respectively formed in layer
shapes whereby a coated layer is formed. The adsorption part 51 and
the oxidation part 52 are stacked on the surface of the base member
55. The oxidation part 52 is arranged at the side farther from the
engine exhaust passage than the adsorption part 51. In the example
which is shown in FIG. 9, the oxidation part 52 is arranged at the
surface of the base member 55, while the adsorption part 51 is
arranged at the surface of the oxidation part 52. The adsorption
part 51 includes the carrier 60 and .beta.-zeolite particles 61.
The oxidation part 52 includes the carrier 60 and catalyst
particles 62.
[0084] By forming the adsorption part 51 and the oxidation part 52
in layer shapes and stacking them so that the adsorption part 51
becomes closer to the engine exhaust passage than the oxidation
part 52, it is possible to make the exhaust gas contact the
adsorption part 51, then contact the oxidation part 52. It is
possible to remove at least part of the unburned fuel which is
contained in the exhaust gas at the adsorption part 51. Exhaust gas
reduced in unburned fuel flows into the oxidation part 52. For this
reason, at the oxidation part 52, it is possible to oxidize the
carbon monoxide efficiently. Further, by having the adsorption part
include zeolite which substantially adsorbs the lower olefins, it
is possible to oxidize the carbon monoxide efficiently.
[0085] FIG. 10 shows a graph of the amount of exhaust of carbon
monoxide of Example 2 and comparative examples in the present
embodiment. FIG. 10 shows the results of a transient test
simulating actual operating conditions in an engine bench test
apparatus. That is, the test was run while changing the running
mode and output torque etc. FIG. 10 shows the amount of carbon
monoxide which flows into the exhaust treatment device and the
amount of carbon monoxide which is exhausted from the exhaust
treatment device. Example 2 corresponds to the second exhaust
treatment device. Further, FIG. 10 describes the test results of
Example 1 which corresponds to the first exhaust treatment device
and the test results of Comparative Example 2 shown in FIG. 7.
[0086] Referring to FIG. 9, in Example 2, a cordierite base member
(1 L) is used as the base member 55. The oxidation part 52 includes
the carrier 60 of aluminum oxide (75 g). The carrier 60 carries
platinum (1.2 g) and palladium (0.6 g) as the catalyst particles
62. On the surface of the oxidation part 52, the carrier 60 of
aluminum oxide (15 g) and .beta.-zeolite particles 61 (60 g) are
arranged to form the adsorption part 51.
[0087] FIG. 11 is a schematic cross-sectional view of an exhaust
treatment device of Comparative Example 4 in the present
embodiment. In Comparative Example 4, the absorption part 51 is
arranged at the surface of the base member 55. The oxidation part
52 is arranged at the surface of the adsorption part 51. That is,
compared with the second exhaust treatment device, the adsorption
part 51 and the oxidation part 52 are reversed in position. The
exhaust gas contacts the oxidation part 52, then contacts the
adsorption part 51.
[0088] In Comparative Example 4, a cordierite base member (1 L) is
used as the base member 55. On the surface of the base member 55,
the carrier 60 of aluminum oxide (15 g) and .beta.-zeolite
particles 61 (60 g) are used to form an adsorption part 51. On the
surface of the adsorption part 51, the carrier 60 of aluminum oxide
(75 g) is arranged to form the oxidation part 52. The carrier 60
carries catalyst particles 62 which are formed from platinum (1.2
g) and palladium (0.6 g).
[0089] Referring to FIG. 10, it is learned that in Example 2
corresponding to the second exhaust treatment device as well, the
amount of exhaust of carbon monoxide is smaller compared with the
exhaust treatment device of Comparative Example 2 where catalyst
particles 62 are arranged at a coated layer of a mixture of the
carrier 60 and .beta.-zeolite particles 61 (see FIG. 7).
[0090] Further, it is learned that the exhaust treatment device of
Example 2, compared with the exhaust treatment device of
Comparative Example 4 which arranges the oxidation part 52 at the
side near the engine exhaust passage (see FIG. 11), is superior in
ability to purify exhaust of carbon monoxide. That is, it is
learned that an exhaust treatment device in which the oxidation
part is arranged at the side farther from the engine exhaust
passage compared with the adsorption part is superior. In this way,
even in the second exhaust treatment device, by arranging the
oxidation part and the adsorption part so that the exhaust gas
contacts the adsorption part, then contacts the oxidation part, it
is possible to efficiently purify exhaust of carbon monoxide.
[0091] Further, it is learned that the exhaust treatment device of
Example 2 is superior to the exhaust treatment device of Example 1.
That is, by stacking the oxidation part and the adsorption part on
the surface of the base member in this order, it is possible to
efficiently purify exhaust of carbon monoxide.
[0092] In this regard, the adsorption part which is contained in
the exhaust treatment device preferably includes zeolite for
adsorbing the unburned fuel HC. Next, the type of zeolite was
changed and the purification ability of carbon monoxide was tested.
As the exhaust treatment device, the second exhaust treatment
device in the present embodiment was used (see FIG. 9) for the
tests.
[0093] FIG. 12 is a graph showing the relationship between the type
of zeolite which is contained in the adsorption part and the amount
of exhaust of carbon monoxide. As the zeolite, in addition to
.beta.-zeolite, ZSM5 and rnordenite (MOR) were used for the tests.
By using .beta.-zeolite in the zeolite, it is learned that the
amount of exhaust of carbon monoxide becomes smaller. That is, by
using .beta.-zeolite as the zeolite which is contained in the
adsorption part, it is possible to efficiently adsorb the unburned
fuel and to reduce the exhaust of carbon monoxide more.
[0094] Next, a third exhaust treatment device in the present
embodiment will be explained. In the above exhaust treatment
devices, the catalyst particles contained in the oxidation part
included platinum and palladium, the invention is not limited to
this. The catalyst particles may include any metal which has an
oxidation ability.
[0095] The third exhaust treatment device in the present embodiment
has substantially all of the catalyst particles formed from
platinum. As shown in FIG. 4, the exhaust treatment device in the
present embodiment can efficiently purify the exhaust of carbon
monoxide even if substantially all of the catalyst particles are
formed from platinum.
[0096] FIG. 13 shows a graph of the 50% purification temperature of
carbon monoxide for Example 3 and a comparative example in the
present embodiment. Example 3 corresponds to the third exhaust
treatment device. The exhaust treatment device of Example 3 is
configured in the same way as the second exhaust treatment device
in the present embodiment (see FIG. 9). In the exhaust treatment
device of Example 3, substantially all of the catalyst particles 62
are formed from platinum.
[0097] In Example 3, the oxidation part 52 is formed by arranging
the carrier 60 of aluminum oxide (75 g) on the surface of the
cordierite base member (1 L) used as the base member 55. The
carrier 60 carries platinum (1.8 g) catalyst particles 62. On the
surface of the oxidation part 52, the adsorption part 51 including
the carrier 60 (15 g) of aluminum oxide and .beta.-zeolite (60 g)
is formed.
[0098] Further, as the exhaust treatment device of Comparative
Example 5, a similar constitution as the exhaust treatment device
of Comparative Example 1 is employed (see FIG. 6). The carrier 60
of aluminum oxide (150 g) is arranged on the surface of the
cordierite base member (1 L) used as the base member 55. The
carrier 60 carries platinum (1.8 g) catalyst particles 62.
[0099] Referring to FIG. 13, even when forming substantially all of
the catalyst particles which are arranged at the oxidation part
from platinum, compared with the exhaust treatment device of
Comparative Example 5, the exhaust treatment device of Example 3
has a lower 50% purification temperature of carbon monoxide. That
is, it is learned that compared with the exhaust treatment device
of Comparative Example 5, the exhaust treatment device of Example 3
is superior in ability to purify exhaust of carbon monoxide. In
particular, it is learned that the exhaust treatment device of
Example 3 is superior in ability to purify exhaust of carbon
monoxide even at a low temperature region.
[0100] In this way, the exhaust treatment device in the present
embodiment can employ catalyst particles which are formed
substantially entirely from platinum. Alternatively, it is possible
to employ a precious metal comprised mainly of platinum as the
catalyst particles. For example, when including platinum,
palladium, rhodium, etc. as the catalyst particles of the precious
metal, it is possible to increase the amount of platinum over the
total amount of palladium, rhodium, etc. other than the platinum.
Alternatively, for example, it is possible to make the total amount
of palladium, rhodium, etc. other than the platinum not more than
one-half of the amount of platinum.
[0101] Furthermore, the internal combustion engine of the present
embodiment controls the air-fuel ratio at the time of combustion to
be lean at the time of ordinary operation. The air-fuel ratio of
the exhaust gas which is exhausted from the combustion chambers is
lean. The exhaust gas contains excess oxygen. The oxidation part in
the present embodiment is not provided with an oxygen storing
substance. The catalyst particles of metal of the oxidation part
are comprised of metal particles other than metal particles which
have an oxygen storage ability.
[0102] The exhaust treatment device is not limited to one which
does not contain an oxygen storing substance. It may also contain
an oxygen storing substance. As the oxygen storing substance, ceria
CeO.sub.2 or another co-catalyst which has the ability to store
oxygen may be illustrated. For example, the oxygen storing
substance contains a composite of oxides of cerium and zirconium.
The oxygen storing substance sometimes can suppress deterioration
of other catalyst particles. In such a case, the exhaust treatment
device may also contain an oxygen storing substance.
[0103] FIG. 14 shows a fourth exhaust treatment device in the
present embodiment. In the fourth exhaust treatment device, the
oxidation part 52 and the adsorption part 51 are stacked on the
surface of the base member 55. The oxidation part 52 includes the
carrier 60 on which the catalyst particles 62 are carried. The
adsorption part 51 in the fourth exhaust treatment device includes
zeolite particles exchanging ions with metal in addition to the
carrier 60 and the .beta.-zeolite particles 61. As the zeolite
particles 63 exchanging ions with metal, zeolite particles which
have exchanged ions with iron or silver may be illustrated. At the
adsorption part 51, the carrier 60, .beta.-zeolite particles 61,
and zeolite particles 63 exchanging ions with a metal are arranged
substantially uniformly.
[0104] Lower olefins have a strong effect in obstructing the
oxidation of carbon monoxide. For example, propylene etc. have a
strong effect obstructing the oxidation reaction of carbon
monoxide. On the other hand, zeolite exchanging ions with a metal
has the property of a high efficiency of adsorption of lower
olefins. By arranging zeolite particles 63 exchanging ions with a
metal at the adsorption part 51, it is possible to further
efficiency adsorb the lower olefins. For this reason, it is
possible to raise the efficiency of purification of exhaust of
carbon monoxide at the oxidation part 52. In this way, it is
possible to mix in zeolite with a high ability to adsorb lower
olefins so as to form the adsorption part.
[0105] FIG. 15 is a schematic cross-sectional view of a fifth
exhaust treatment device in the present embodiment. The fifth
exhaust treatment device is comprised of the base member 55 on the
surface of which the oxidation part 52 is arranged. The oxidation
part 52 includes the carrier 60 on which the catalyst particles 62
are carried. At the surface of the oxidation part 52, the
adsorption part 51 is formed.
[0106] The adsorption part 51 at the fifth exhaust treatment device
has a plurality of parts. The adsorption part 51 includes a higher
hydrocarbon adsorption part 51a which adsorbs higher hydrocarbons
and a lower olefin adsorption part 51b which adsorbs lower olefins.
The lower olefin adsorption part 51b is arranged at the surface of
the oxidation part 52. The higher hydrocarbon adsorption part 51a
is arranged at the surface of the lower olefin adsorption part
51b.
[0107] The fifth exhaust treatment device is formed so that the
exhaust gas contacts the higher hydrocarbon adsorption part 51a,
then contacts the lower olefin adsorption part 51b. The higher
hydrocarbon adsorption part 51a includes the carrier 60 of aluminum
oxide and .beta.-zeolite particles 61. The lower olefin adsorption
part 51b includes the carrier 60 of aluminum oxide and the zeolite
particles 63 exchanging ions with a metal.
[0108] As explained above, zeolite which has exchanged ions with a
metal is superior in efficiency of adsorption of lower olefins.
However, if higher hydrocarbons contact zeolite which has exchanged
ions with a metal, the higher hydrocarbons will be adsorbed. At
this time, the adsorption sites for adsorption of lower olefins
will end up being blocked. For example, the acid centers for
adsorption of propylene or ethylene etc. will end up being blocked.
As a result, the efficiency of adsorption of lower olefins will
deteriorate.
[0109] In the fifth exhaust treatment device, the higher
hydrocarbon adsorption part 51a can remove in advance the higher
hydrocarbons with large molecular weights. After that, the lower
olefin adsorption part 51b can remove the lower olefins. For this
reason, it is possible to efficiently adsorb the lower olefins at
the lower olefin adsorption part 51b. It is possible to reduce the
amount of lower olefins which reach the oxidation part 52. As a
result, the purification ability of carbon monoxide can be
improved.
[0110] The higher hydrocarbon adsorption part preferably includes
zeolite which can efficiently adsorb higher hydrocarbons. For
example, the higher hydrocarbon adsorption part preferably includes
.beta.-zeolite. The lower olefin adsorption part preferably
includes zeolite able to efficiently adsorb lower olefins. The
lower olefin adsorption part preferably includes zeolite on which a
metal is carried by ion exchange. For example, it is preferable to
include at least one of ZSM5 which has exchanged ions with iron and
ZSM5 which has exchanged ions with silver.
[0111] FIG. 16 shows a graph of the amount of exhaust of carbon
monoxide of Example 4 and Example 5 and comparative examples in the
present embodiment. Example 4 corresponds to the fourth exhaust
treatment device in the present embodiment. Example 5 corresponds
to the fifth exhaust treatment device in the present embodiment.
FIG. 16 shows the results of a transient test in an engine bench
test apparatus.
[0112] Referring to FIG. 14, in the exhaust treatment device of
Example 4, a cordierite base member (1 L) is used as the base
member 55. The oxidation part 52 includes the carrier 60 of
aluminum oxide (75 g). The carrier 60 carries catalyst particles 62
which contain platinum (1.2 g) and palladium (0.6 g). The
adsorption part 51 contains the carrier 60 of aluminum oxide (15
g), particles of ZSM5 which have exchanged ions with iron (4 wt %)
(30 g) as the zeolite particles 63 which have exchanged ions with a
metal, and .beta.-zeolite particles 61 (30 g).
[0113] Referring to FIG. 15, in the exhaust treatment device of
Example 5, a cordierite base member (1 L) is used as the base
member 55. The oxidation part 52 includes the carrier 60 of
aluminum oxide (75 g) and catalyst particles 62 which are formed
from platinum (1.2 g) and palladium (0.6 g). At the surface of the
oxidation part 52, the lower olefin adsorption part 51b and higher
hydrocarbon adsorption part 51a are arranged. The lower olefin
adsorption part 51b includes the carrier 60 of aluminum oxide (7.5
g) and particles of ZSM5 which have exchanged ions with iron (4 wt
%) (30 g) as the zeolite particles 63 which have exchanged ions
with a metal. The higher hydrocarbon adsorption part 51a includes
the carrier 60 of aluminum oxide (7.5 g) and .beta.-zeolite
particles 61 (30 g).
[0114] FIG. 17 is a schematic cross-sectional view of an exhaust
treatment device of Comparative Example 6 in the present
embodiment. In Comparative Example 6, the adsorption part 51 is
arranged on the surface of the oxidation part 52. The adsorption
part 51 includes the higher hydrocarbon adsorption part 51a and the
lower olefin adsorption part 51b. The higher hydrocarbon adsorption
part 51a includes the carrier 60 of aluminum oxide and
.beta.-zeolite particles 61. The lower olefin adsorption part 51b
includes the carrier 60 of aluminum oxide and particles of ZSM5
which have exchanged ions with iron as the zeolite particles 63
which have exchanged ions with a metal.
[0115] The exhaust treatment device of Comparative Example 6,
compared with the exhaust treatment device of Example 5, has the
higher hydrocarbon adsorption part 51a and the lower olefin
adsorption part 51b stacked in the reverse order. In Comparative
Example 6, the lower olefin adsorption part 51b is arranged at the
surface side contiguous with the engine exhaust passage, while the
higher hydrocarbon adsorption part 51a is arranged at a layer below
that.
[0116] In Comparative Example 6, a cordierite base member (1 L) is
used as the base member 55. The oxidation part 52 includes catalyst
particles which were formed from the carrier 60 of aluminum oxide
(75 g) and platinum (1.2 g) and palladium (0.6 g). At the surface
of the oxidation part 52, the higher hydrocarbon adsorption part
51a and lower olefin adsorption part 51b are arranged. The higher
hydrocarbon adsorption part 51a includes the carrier 60 of aluminum
oxide (7.5 g) and .beta.-zeolite particles 61 (30 g). The lower
olefin adsorption part 51b includes the carrier 60 of aluminum
oxide (7.5 g) and particles of ZSM5 (30 g) which have exchanged
ions with iron (4 wt %) as zeolite particles 63 which have
exchanged ions with a metal.
[0117] Referring to FIG. 16, the exhaust treatment device of
Example 4 and the exhaust treatment device Example 5 have smaller
amounts of exhaust of carbon monoxide compared with the exhaust
treatment device of Comparative Example 2 (see FIG. 7) where the
carrier 60 and .beta.-zeolite particles 61 are uniformly
arranged.
[0118] Furthermore, compared with the exhaust treatment device of
Example 4, the exhaust treatment device of Example 5 has a smaller
amount of exhaust of carbon monoxide. By forming the higher
hydrocarbon adsorption part and lower olefin adsorption part at the
adsorption part, it is possible to more efficiently purify the
exhaust of carbon monoxide.
[0119] Further, when comparing the exhaust treatment device of
Comparative Example 6 and the exhaust treatment device of Example
5, the exhaust treatment device of Example 5 has a smaller amount
of exhaust of carbon monoxide. When the adsorption part includes a
higher hydrocarbon adsorption part and lower olefin adsorption
part, preferably the higher hydrocarbon adsorption part is arranged
at the side near to the engine exhaust passage. By arranging the
higher hydrocarbon adsorption part and lower olefin adsorption part
in this way so that at the adsorption part, the exhaust gas
contacts the higher hydrocarbon adsorption part, then contacts the
lower olefin adsorption part, it is possible to more efficiently
reduce the amount of exhaust of carbon monoxide.
[0120] In the above third exhaust treatment device to fifth exhaust
treatment device, the explanation was given with reference to the
example of an exhaust treatment device comprised of an adsorption
part and an oxidation part stacked on the surface of a base member,
the invention is not limited to this. It is also possible to apply
this to an exhaust treatment device which arranges the adsorption
part and the oxidation part along the direction of flow of the
exhaust gas like in the first exhaust treatment device. For
example, in the first exhaust treatment device, the catalyst
particles 62 of the oxidation part 52 can be formed from a precious
metal such as mainly platinum. Further, in the first exhaust
treatment device, it is possible to mix in zeolite which has
exchanged ions with a metal in the adsorption part 51.
[0121] FIG. 18 is a schematic cross-sectional view of a sixth
exhaust treatment device in the present embodiment. The sixth
exhaust treatment device 13 employs the higher hydrocarbon
adsorption part and the lower olefin adsorption part of the
adsorption part in the fifth exhaust treatment device. The
adsorption part and the oxidation part are arranged along the
direction of flow of the exhaust gas. In the adsorption part, the
higher hydrocarbon adsorption part is arranged at the upstream
side, while the lower olefin adsorption part is arranged at the
downstream side. The exhaust treatment device 13 is provided with
an upstream-side part 13a which includes the adsorption part and a
downstream-side part 13b which includes the oxidation part. The
upstream-side part 13a includes a first part 14a which has the
higher hydrocarbon adsorption part and a second part 14b which has
the lower olefin adsorption part. The exhaust gas contacts the
higher hydrocarbon adsorption part, then contacts the lower olefin
adsorption part. The exhaust gas then flows into the oxidation
part. Due to this configuration as well, the purification
efficiency of carbon monoxide can be improved.
[0122] In the exhaust treatment device of the present embodiment,
the zeolite which is contained in the adsorption part preferably
has many acid centers, so the molar ratio of
SiO.sub.2/Al.sub.2O.sub.3 is preferably small. On the other hand,
in the engine exhaust passage, the temperature of the exhaust gas
sometimes reaches a high temperature of for example over
700.degree. C. The exhaust treatment device requires heat
resistance against such a high temperature. Further, exhaust gas
contains water vapor which is produced by the combustion. The
device is liable to be unable to withstand the usage environment
and to end up breaking. Considering the durability of the exhaust
treatment device, the molar ratio of the SiO.sub.2/Al.sub.2O.sub.3
is for example 20 or more.
[0123] In the present embodiments, an exhaust treatment device in
which the adsorption part and the oxidation part are adjacent is
illustrated, but the invention is not limited to this. The
adsorption part and the oxidation part may also be separated from
each other. Further, another member may be arranged between the
adsorption part and the oxidation part. For example, in the engine
exhaust passage, it is also possible to arrange an exhaust
treatment device which includes an oxidation part downstream of an
exhaust treatment device which includes an adsorption part.
[0124] In the present embodiments, catalyst particles which have an
oxidation function are not arranged at the adsorption part, but the
invention is not limited to this. Catalyst particles which have an
oxidation function may also be arranged at the adsorption part.
[0125] In the present embodiments, the explanation was given with
reference to a diesel engine, but the invention is not limited to
this. The present invention can be applied to an internal
combustion engine which is controlled so that the air-fuel ratio at
the time of combustion becomes lean at the time of ordinary
operation when the engine body outputs torque. For example, in a
gasoline engine, the present invention can be applied to a lean
burn engine which is controlled by a large combustion air-fuel
ratio, an engine which engages in stratified combustion, etc.
Alternatively, the present invention can be applied to an exhaust
purification system of an internal combustion engine which oxidizes
carbon monoxide in an oxygen rich atmosphere.
[0126] The above embodiments can be suitably combined. In the
above-mentioned figures, the same or corresponding parts are
assigned the same reference signs. Note that the above embodiments
are illustrative and do not limit the inventions. Further, in the
embodiments, changes covered by the claims are intended.
REFERENCE SIGNS LIST
[0127] 1 engine body [0128] 2 combustion chamber [0129] 12 exhaust
pipe [0130] 13 exhaust treatment device [0131] 13a upstream-side
part [0132] 13b downstream-side part [0133] 14a first part [0134]
14b second part [0135] 30 electronic control unit [0136] 51
adsorption part [0137] 51a higher hydrocarbon adsorption part
[0138] 51b lower olefin adsorption part [0139] 52 oxidation part
[0140] 55 base member [0141] 60 carrier [0142] 61 .beta.-zeolite
particles [0143] 62 catalyst particles [0144] 63 zeolite
particles
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