BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a pipe-shaped catalyst
construction for exhaust gas purification used to purify an
exhausted gas discharged from a motorbike or an automobile.
Related Background Art
With increased interest to a recent environmental problem,
measurements to an exhausted gas discharged from an internal
combustion engine of a motorbike or an automobile has attracted much
attention in industrial world. In view of this, the exhausted gas
discharged from the motorbike etc., after having been purified
harmful components such as carbon monoxide (CO), hydrocarbon (HC)
and nitrogen oxide (NOx) contained therein is discharged to an
atmosphere. Various kinds of catalysts for exhaust gas
purification has been known, one sample of which is a pipe-shaped
catalyst construction.
The pipe-shaped catalyst construction used in the motorbike
etc. is comprised by supporting or bearing catalyst on an inner
peripheral surface of a metallic pipe. Although, the pipe-shaped
catalyst construction has simple construction, it can hardly
perform the exhaust gas purification sufficiently due to small
contacting area of the catalyst with the exhaust gas. In view of
this, the catalyst has been supported on a metal foil or a metal
sheet contained within a hollow portion of the pipe to broaden
contacting area of the catalyst with the exhaust gas.
As such kinds of conventional art, a catalyst construction
disclosed in Japanese Patent Publication No. 55-51624 and a catalyst
construction disclosed Patent National Laid-open No. 11-510872 have
been known. The former catalyst construction 50 shown in Fig. 5 is
comprised of a cylindrical pipe 51, a metallic sheet 54 contained
within the pipe 51, and catalysts (only partially shown) coated on
an inner peripheral surface of the pipe 51 and an outer and on inner
surfaces of the metallic sheet 54. The metallic sheet 54 is
continuously formed plural concaved portions 53 circumferentially
by plural section V-shaped portions 52 extending outwardly and
inwardly in radial direction, to resultantly have a star shape.
The pipe 51 and the metallic sheet 54 constructs a pipe-shaped
supporting body.
The latter catalyst construction 60 shown in Fig. 6 is
comprised of a cylindrical pipe 61 made of metal, a metallic film
(foil) 62 contained within the pipe 61, and catalysts (only
partially shown) 64 supported on the metallic film 62. The metallic
film 62 is continuously formed plural concaved portions 63
circumferentially by plural section U-shape portions, constructing
a pipe-shaped supporting body together with the pipe 61.
In the catalyst construction 50 shown in Fig. 5, a circle
defined by connecting opened portions of the section V-shaped
portion 52 ie top portions of the concaved portions 53 has smaller
diameter, so that the opened portions extend radially near to a
central portion of the pipe 51. As a result, a rate of a sectional
area portion where the metallic sheet 54 does not exist to whole
sectional area of the pipe 51 is very small. Increased contacting
area of the catalyst 55 on the metallic sheet 54 with the exhaust gas
improves the purifying ability of the exhaust gas. However, the
exhaust gas flows faster at a central portion of the pipe 5 with
receiving small resistance than at a surrounding portion with
receiving larger resistance. Also, temperature of the exhaust gas
rises higher at the central portion with radiating smaller heat than
the surrounding portion with radiating larger heat. Accordingly,
the opened portions of the section V-shaped portion 52 located near
to the central portion of the pipe 51 have been exposed in the
exhaust gas of high pressure and high temperature. In this way, a
part of the metallic sheet 54 may crack and damaged by pressure and
heat of the exhaust gas.
To the contrary, in the catalyst construction 60 shown in
Fig. 6, the metallic film 63 is disposed only at a surrounding
portion of a pipe 61, not being disposed at a central portion of the
pipe 61. So, the metallic film 63 is hardly damaged by heat and
pressure of the exhaust gas flowing at the central portion of the
pipe 61. However, in this catalyst construction, rate of a
surrounding sectional area where the metallic film 63 existed to a
whole sectional area defined by an inner peripheral surface of the
pipe 61 is very small. Thus, small contacting area of the catalyst
64 of the metallic film 63 with the exhaust gas hinders sufficient
exhaust gas purification.
As mentioned above, a high catalyst ability to purify the
exhaust gas efficiently and a high temperature resisting character
not to be damaged by heat of high temperature, contradicting to each
other, are required for the pipe-shaped catalyst construction.
Whereas, no catalyst construction which can satisfy the both
requirements has not been known.
Summary of the Invention
The present invention has ben made in view of the above
circumstances and intends to provide a pipe-shaped catalyst
construction which has high catalyst ability and which is excellent
in high temperature resisting character.
Inventor of this application has hit on, for realizing such
pipe-shaped catalyst construction to dispose a metal foil or a metal
sheet as small as possible at a central portion of the pipe. This is
because at the central portion, the exhaust gas flows in high speed
with receiving small flowing resistance from the pipe and holds high
temperature with small heat radiation through the pipe. In other
words, the metallic foil etc. is preferably disposed at a
surrounding portion of the pipe along an inner surface thereof. As
a result of eager studying, the inventor has found out the most
suitable rate of the central sectional area portion where the
metallic foil etc. is not disposed to the whole sectional area of
the pipe.
That is, a pipe-shaped catalyst construction for exhaust gas
purification is comprised of (a) a pipe-shaped supporting body
including a metallic pipe and a cylindrical metallic foil or a
metallic sheet contained in the metallic pipe and provided with
concaved portions formed continuously in circumferential direction
to be concaved inwardly and outwardly in radial direction, and (b) a
catalyst material supported at least on the metallic foil or the
metallic sheet of the supporting body. In such catalyst
construction, the metallic foil or the metallic sheet is disposed
along an inner peripheral surface of the metallic pipe except for a
central portion of the metallic pipe in section, and rate of a
central sectional area portion where the metallic foil or the
metallic sheet is not disposed to a whole sectional area of the
metallic pipe defined by the inner peripheral surface of the pipe is
selected to be 20 % to 60 %.
In the pipe-shaped catalyst construction according to the
present invention, the metallic foil etc. is not disposed at the
central portion (a cylindrical space having distance smaller than a
predetermined value from a centre) of the pipe to leave a space at
the central portion. In other words, the metallic foil etc. is
disposed at the surrounding portion of the pipe along the inner
peripheral surface thereof. As a result, the metallic foil etc. is
hardly exposed to the exhaust gas of high speed and high temperature
at the central portion of the pipe, which prevents damage of the
metallic foil etc., and holds shape stability of it.
In addition, the surrounding sectional area has the larger
rate (40 % to 80 %) to the whole sectional area of the pipe.
Accordingly, the exhaust gas flowing at the surrounding portion of
the pipe in relatively low speed is purified by the catalyst
supported on the metallic foil etc. effectively, whereby the
purifying ability of the catalyst construction is maintained.
When the rate of the central sectional area portion to the
whole sectional area defined by the inner peripheral surface of the
pipe decreases under 20 %, there is fear the part of the metallic
foil etc. disposed at the central portion being damaged by high heat
of the exhaust gas. On the other hand, when this rate increases
over 60 %, there is fear the purifying ability by the catalyst on the
metallic foil etc. being insufficient.
Next, embodying modes of the pipe-shaped catalyst
construction for exhaust gas purification of the present invention
will be explained.
The catalyst construction can be used to purify the exhaust
gas discharged from an internal combustion engine of a motorbike or
an automobile.
Various kinds of metals having heat resisting character and
pressure resisting character can be used to construct the pipe of
the pipe-shaped supporting body. For example, a stainless steel is
suitably used. The pipe can have a cylindrical shape, elliptical
shape or polygonal shape.
As metals constructing the metallic foil or the metallic
sheet for the pipe-shaped supporting body, various kinds of metals
excellent in the heat resisting character can be used. For example,
20Cr-5Al is preferably used. Here, the metallic foil and the
metallic foil are distinguished by thickness thereof, but this
distinction is not essential since both of them are included in the
present invention.
Each of concaved portions continuously formed on the
metallic foil or the metallic sheet circumferentially can be
comprised of, for example, two section U-shaped portions being
adjacent and protruding outwardly in radial direction, and a
connecting portion connecting them. Also, concaved portion can be
formed by two adjacent section V-shaped portions protruding
outwardly radially or can be formed by two adjacent section
V-shaped portions protruding outwardly in radial direction and a
connecting portion connecting them.
The rate of the central sectional area portion to the whole
sectional area defined by the inner peripheral surface can be
selected in a range from 20 % to 60 %, more preferably it can be
selected in a range from 31 % to 52 %. In connection with this, a
rate of radius of the pipe central portion where the metallic foil
etc. is not disposed (distance from a center of the cylindrical
space to outer surface thereof) to radius of the pipe, can be
selected in range from 45 % to 77 %, more preferably it can be
selected in range from 55 % to 72 %.
The number of the concaved portions of the metallic foil is
determined depending on circumferential length of the concave
portion. It does not directly affect the rate of the central
sectional area portion to the whole sectional area, and therefore
can be freely selected. The number of the concaved portions changes
size of each concaved portion. However, there is suitable size
(height) of the concave portion to increase the purifying
efficiency of the exhaust gas, to be explained later.
The concaved portions of the metallic foil etc. are joined,
at the opened ends (radially outward ends) thereof, to the inner
peripheral surface of the pipe. In the joined state, cavities of
the concaved portions preferably form together with the pipe
flowing paths (cells) allowing the exhaust gas flow at the
surrounding portion of the pipe. With supporting the catalyst on
the inner peripheral surface of the pipe and on the inner surfaces
of the recessed portions defining the cells, the exhaust gas
flowing through the cells is efficiently purified by the catalyst.
When the cell size is too small due to small height of the concaved
portions, most of the exhaust gas flows in the pipe central portion,
resulting in low purifying ability of the exhaust gas. On the
other hand, when the cells are too large due to large height of the
concaved portions, the cells tend to be expanded by heat and
pressure of the exhaust gas. As a result, the concaved portions may
be deformed, or crack may be generated at a part of the concaved
portion or at connected part between the concaved portion and the
pipe.
Various kinds of catalysts such as a oxidizing catalyst,
reducing catalyst and three-way catalyst can be supported on the
supporting body. As well known, the oxidizing catalyst oxidizes
harmful carbon monoxide and hydrocarbon in the exhaust gas to
harmless carbon dioxide and steam, respectively. The reducing
catalyst reduces harmful nitrogen oxide to nitrogen. The three-way
catalyst oxidizes carbon monoxide and hydrocarbon and reduces
nitrogen oxide. Using catalyst is selected in view of harmful
component(s) required to be purified especially.
The catalyst is sufficiently supported at least on the
metallic foil or the metallic sheet of the pipe-shaped supporting
body, but can be supported on the pipe inner surface as occasion
demands. The catalyst can be supported on the inner surface and/or
the outer surface of the metallic foil etc.. Supporting the
catalyst on broad area of the supporting body surface is preferable
to increase the purifying ability of the catalyst. Part or area of
the supporting body where the catalyst is supported is determined in
view of the rate of the central cross-sections member to the
surrounding sectional area, and the number of the concaved portions.
Above embodying modes of each component of the present
invention can be selectively combined.
Brief Explanation of the Drawings
Fig. 1 is a sectional view of a pipe-shaped catalyst
construction of the first embodiment according to the present
invention;
Fig. 2 is a sectional view along a line 2- 2 in Fig. 1;
Fig. 3 is a sectional view of a pipe-shaped catalyst
construction of the second embodiment according to the present
invention;
Fig. 4 is a sectional view of a pipe-shaped catalyst
construction of the third embodiment according to the present
invention;
Fig. 5 is a sectional view of the first conventional
pipe-shaped catalyst construction; and
Fig. 6 is a sectional view of the second conventional
pipe-shaped catalyst construction.
Preferred Embodiment of the Invention
A preferred embodiment of the present invention will be
explained reference to attached drawings.
<Embodiment 1>
Here, three (embodiment 1, comparative sample 1 and
comparative sample 2) pipe-shaped catalyst construction have been
produced to be tested.
The pipe-shaped catalyst construction 10 of the embodiment 1
is shown in Figs. 1 and 2. It is comprised of a pipe-shaped
supporting body including a metallic pipe 11 and a metallic foil 12,
and a catalyst 19 supported on a surface of the metallic foil 12.
The pipe 11 made of a stainless steel has a cylindrical shape of
which inner diameter is 25.4 mm, thickness is 1.2 mm and length is 170
mm, respectively. Thus, whole sectional area S1 of the pipe 11 is
about 506.5 mm 2.
The metallic foil 12 made of 20Cr-5Al having foil thickness
of about 200 µm is formed plural recessed portion 13
circumferentially and has a cylindrical shape. Each of the
concaved portions 13 includes two section U-shaped potions 16
extending outwardly in radial direction and a connecting portion
connecting them. All of the section U-shaped portions 14 have same
construction, each including a pain of stand-up portions 14a and a
top portion 14b connecting them. The stand-up portion 14a has
height of about 4 mm, which means distance between the connecting
portions 15 opposing in diameter direction, ie diameter of the
central portion 16 where the metallic foil 12 is not disposed is of
about 17.4 mm. As a result, the rate of central portion diameter to
the pipe diameter is of about 69 %. Also, the area of the central
portion (central sectional area) S2 is of about 237.7 mm 2, the rate
to the above whole sectional area S1 of the pipe 11 being of about 47
%. Here, the surrounding sectional area portion S3 is of about
268.8 mm 2, and has the rate to the whole sectional area S1 being of
about 53 %.
The section U-shaped portion 14 has circumferential length
smaller than distance between the adjacent section U-shaped
portions 14. The metallic foil 12 is joined to the inner surface of
the pipe at the opened ends of each concaved portion 13 (joined
portion 17), so that the pipe 11 and the concaved portions 13 form
flowing passages 18 each having section trapezoidal shape at the the
surrounding portion. The three-way catalysts 19 (only partially
shown) are coated on inner and outer surfaces of the concaved
portions 13, and on inner and outer surfaces of the connecting
portions 15.
<Comparative Sample 1>
A pipe-shaped catalyst construction of a comparative sample
1 is comprised of a pipe similar to the pipe 11 of the embodiment 1, a
metallic foil having concaved portions of which size differs from
the metallic foil 12 of the embodiment 1, and a catalyst similar to
the catalyst 19 of the embodiment 1. Each of the concaved portions
has radial height of about 8 mm, resulting in distance between the
connecting portions opposed in diameter direction is of about 9.4 mm.
As a result, the rate of central portion diameter to the pipe
diameter is of about 37 %. Also, the area of the central portion S2
is of about 69.4 mm 2, the rate to the above whole sectional area S1
of the pipe 11 being of about 14 %. So, rate of the surrounding
sectional area portion S3 to the whole sectional area Sl is of about
86 %. Another points such as the metallic foil material, the number
of the concaved portions etc.are similar to the catalyst
construction of the embodiment 1.
<Comparative Sample 2>
A pipe-shaped catalyst construction of a comparative sample
2 is comprised of a pipe similar to the pipe 11 of the embodiment 1, a
metallic foil having concaved portions of which size differs from
the metallic foil 12 of the embodiment 1, and a catalyst similar to
the catalyst 19 of the embodiment 1.
Each of the concaved portions has radial height of about 2 mm,
resulting in distance between the connecting portions opposed in
diameter direction is of about 21.4 mm. As a result, the rate of
central portion diameter to the pipe diameter is of about 84 %.
Also, the area of the central portion S2 is of about 359.5 mm 2, the
rate to the above whole sectional area S1 of the pipe 11 being of
about 71 %. So, rate of the surrounding sectional area portion S3
to the whole sectional area S1 is of about 29 %. Another points such
as the metallic foil material, the number of the concaved portions
etc. are similar to the catalyst construction of the embodiment 1.
An exhaust gas purifying test has been carried out by using
the pipe-shaped catalyst construction of the embodiment 1 and the
comparative samples 1 and 2, result of which are shown in Tables 1
and 2. In the Table 1 showing the purifying character, "HC
purifying rate" is calculated by dividing ((HC density in exhaust
gas not passed thorough catalyst) - (HC density in exhaust gas
passed through catalyst)) by (HC density in exhaust gas not passed
through catalyst), and multiplying 100. Also, "CO purifying rate"
is calculated by dividing ((CO density in exhaust gas not passed
thorough catalyst) - (CO density in exhaust gas passed through
catalyst)) by (CO density in exhaust gas not passed through
catalyst), and multiplying 100.
The Table 2 shows shape stability character of the metallic
foil which is judged by observing deformation visually. Here,
"cool and heat test" is carried out by repeating heating the
catalyst construction at 950 °C in 10 min. and cooling them at room
temperature in 10 min. by using a 2-stroke engine.
| HC purified rate | CO purified rate |
Embodiment 1 | 45 % | 58 % |
Comparative Sample 1 | 50 % | 65 % |
Comparative Sample |
2 | 20 % | 35 % |
As apparent from the Table 1, the catalyst construction of
the comparative sample 1 is excellent in both of the HC purifying
ability and CO purifying ability, the catalyst construction of the
embodiment 1 is secondary excellent, and catalyst construction of
the
comparative sample 2 is most poor. These results can be
expected since the exhaust purifying ability depends on the rate of
the surrounding sectional area portion where the metallic foil is
disposed to the whole sectional area (53 % in the embodiment 1, 86 %
in the comparative sample 1, and 29 % in the comparative sample 2).
| metallic foil deformation after heat-cool test |
Embodiment 1 | no deformation |
Comparative Sample 1 | large deformation, partial crack |
Comparative Sample |
2 | no deformation |
As apparent from Table 2, deformation has not occurred in the
metallic foil of the catalyst construction of the embodiment 1 and
the comparative sample 2, but deformation and partial crack have
occurred in the metallic foil of the catalyst construction of the
comparative sample 2. This may results from large rate (47 % and 71
%) of the central sectional area portion in the catalyst
construction of the embodiment 1 and comparative sample 2, and
small rate (14 %) of the same in the catalyst construction of the
comparative sample 2.
Here, quality of pipe-shaped catalyst construction is
evaluated by the purifying ability and shape stability of the
metallic foil. The catalyst construction of the embodiment 1 is
excellent in the both aspects. To the contrary, the catalyst
construction of the comparative sample 1 excellent in the catalyst
ability is poor in the shape stability, while the catalyst
construction in the comparative sample 2 excellent in the shape
stability is poor in the catalyst ability. Judging them from
totally, the catalyst construction of the embodiment 1 is most
excellent.
Generally speaking, as selecting the rate of the surrounding
sectional area portion to the whole sectional area larger, the
purifying ability by the catalyst becomes higher while the shape
stability of the metallic foil becomes poorer. How they are
balanced is important.
In the catalyst construction in the comparative sample 1,
size of the central portion is set extremely small by selecting the
rate of radius of the central portion to radius of the pipe is 37 %,
that is, by selecting the rate of the central sectional area portion
to the whole sectional area is 14 %. However, it has only the HC
purifying rate and the CO purifying rate corresponding to about 1.1
times that of the catalyst construction in the embodiment 1.
Judging from this fact, excessive heightening of radial height (4
mm) of the concaved portion 13 does not contribute to purifying
ability increase, but deteriorates the shape stability. In view of
the both requirements, the concaved portion having height of about 5
mm seems to have the purifying ability of high level by the catalyst,
and to maintain shape stability of the concaved portion. When the
concaved portion has height of 5 mm, the rate of radius of the
central portion to radius of the pipe is 61 %, which means the rate
of the central sectional area portion to the whole sectional area is
37 %.
On the other hand, in the catalyst construction of the
comparative sample 2, both of the HC purifying rate and the CO
purifying rate have been inferior to that of the catalyst
construction 10 of the embodiment 1. Judging from this fact,
decreasing radial height (4 mm) of the concaved portion 13 greatly
is not preferable. The concaved portion 13 having radial height
down to 3.5 mm seems to perform the equivalent purifying ability to
the concaved portion having radial height of 4 mm. In this case,
the rate of radius of the central portion to radius of the pipe is
72 %, which means g the rate of the central sectional area portion to
the whole sectional area is 52 %.
Value of the rate of the central portion radius to the pipe
radius selected within range of 45 % to 77 %, and the value of the
rate of the central sectional area portion to the whole sectional
area selected within range of 20 % to 60 %, depend on shape and size
of the metallic foil, shape and the number of the concaved portions,
and supported area of the catalyst onto the supporting body.
In the pipe-shaped catalyst construction of the embodiment 1,
different from the conventional catalyst construction 50 shown
in Fig. 5, the metallic foil 12 does not have any part located
radially inside of the connecting portion 13. Therefore, there is
no fear the metallic foil 12 is damaged by the exhaust gas of high
temperature and high pressure flowing through the central portion
of the pipe 11.
<Embodiment 2>
A pipe-shaped catalyst construction 20 of the embodiment 2
shown in Fig. 3 differs from the catalyst construction 10 of the
embodiment 1 in shape of concaved portions of metallic foil.
In the catalyst construction 20, each of concaved portions 23
of metallic foil 22 contained in a pipe 21 is comprised of two
adjacent section V-shaped portions formed continuously in
circumferential direction. Each of the section V-shaped portions
24 is joined to an outer peripheral surface of a cylindrical portion
25 of the metallic foil at opened ends thereof, and joined to an
inner peripheral surface of the pipe 21 at top portion thereof.
Sizes of the catalyst construction 20 such as inner diameter
of the pipe 21 and radial height of the concaved portion 23 of the
metallic foil 22 are selected same as that of the catalyst
construction of the embodiment 1. Accordingly, the rate of radius
of the central portion to radius of the pipe is 69 %, which means the
rate of the central sectional area portion to the whole sectional
area is 47 %.
The pipe-shaped catalyst construction 20 can render the
purifying ability by the catalyst and the shaped stability of the
metallic foil 22, same as the above catalyst construction of the
embodiment 1.
<Embodiment 3>
A pipe-shaped catalyst construction 30 of the embodiment 3
shown in Fig. 4 differs from the catalyst construction of the
embodiment 1 in shape of concaved portions of metallic foil.
In the catalyst construction 30, each of concaved portions 33
of a metallic foil 32 contained in pipe 31 is comprised of two
adjacent section V-shaped portions 34 each protruding outwardly in
radial direction, and a connecting portion 35 disposed
therebetween to connect them. That is, each section V-shaped
portion 34 is comprised of a pair of stand-up portions 34a, so that
the concaved portion 33 is defined by the stand-up portion 34a of the
section V-shaped portion 34, the connecting portion 35 and the
stand-up portion 34a of the adjacent section V-shaped portion 34.
Each concaved portion 33 is joined to the inner peripheral surface
of the pipe at opened ends thereof, ie at a bottom portion of the
section V-shaped portion 34.
Sizes of the catalyst construction 30 such as inner diameter
of the pipe 31 and radial height of the concaved portion 33 of the
metallic foil 32 are selected same as that of the catalyst
construction of the embodiment 1. Accordingly, the rate of radius
of the central portion to radius of the pipe is 69 %, which means the
rate of the central sectional area portion to the whole sectional
area is 47 %.
The pipe-shaped catalyst construction 30 can render the
purifying ability by the catalyst and the shaped stability of the
metallic foil 32, same as the above catalyst construction of the
embodiment 1.
The present invention intends to provide a pipe-shaped
catalyst construction 10 which has high catalyst ability and which
is excellent in high temperature resisting character, in a
pipe-shaped catalyst construction. It is comprised of a
pipe-shaped supporting body including a metallic pipe 11 and a
cylindrical metallic foil 12 contained therein and provided with
plural concaved portions 13 formed circumferentially, and a
catalyst material 19 supported on the metallic foil.
In such catalyst construction, the metallic foil 12 is
disposed along an inner peripheral surface of the pipe 11 except for
a central portion of the metallic pipe in section. Also, rate of a
central sectional area portion where the metallic foil 2 is not
disposed to a whole sectional area of the pipe 11 defined by the
inner peripheral surface of the pipe is selected to be 20 % to 60 %.