TECHNICAL FIELD
[0001] The present invention relates to an exhaust purifying apparatus for purifying exhaust
gas discharged from an internal combustion engine according to the preamble of claim
1.
BACKGROUND ART
[0002] Such a purifying apparatus is known from
US 4,206,177. Various types of exhaust purifying apparatuses for internal combustion engines are
known today, among which are an "exhaust purifying apparatus for an internal combustion
engine" disclosed in
JP-A-3-85316 and an "exhaust purifying apparatus for a motor bicycle or the like" disclosed in
JP-A-4-287821.
[0003] The exhaust purifying apparatus in the
JP-A-3-85316 is shown in Figs. 17 and 18, where an exhaust pipe 100 is coupled to an exhaust port
of a small-size internal combustion engine mounted on a motor bicycle or the like,
and a internal pipe 101 made of a porous sheet is disposed within the exhaust pipe
100 and extending along the inner surface of the pipe 100, with catalyst-bearing layers
102 attached to the inner and outer surfaces of the porous Internal pipe 101.
[0004] The exhaust purifying apparatus in
JP-A-4-287821. is shown in Figs. 19 to 21, where an exhaust muffler (corresponding to the exhaust
pipe) 110 is coupled to an exhaust port of a small-size internal combustion engine
mounted on a motor bicycle or the like, and a catalyst pipe 111 is provided in the
central region of the exhaust muffler 110 with a catalyst-bearing member 112 received
within the pipe 111. The catalyst-bearing member 112 comprises a honeycomb having
catalyst materials attached thereto.
[0005] As known in the art, in order to allow catalysts to perform their exhaust purifying
function to a sufficient degree, it is generally necessary to activate the catalysts
by heating them to a high temperature. But, with a small-size internal combustion
engine, it is not easy to increase the exhaust gas temperature sufficiently to activate
the catalysts, and hence some measure has to be taken to increase the catalyst temperature
as high as possible. To this end, one must take into account the fact that the temperature
of exhaust gas flowing in the exhaust pipe is higher in the central region (i.e.,
the central region as viewed in cross section) of the pipe and lower in the peripheral
region or near the inner wall surface of the pipe remote from the central region.
[0006] However, because the catalyst-attached internal pipe 101 is disposed near and along
the inner wall surface of the exhaust pipe 100, the exhaust purifying apparatus shown
in Figs. 17 and 18 can not easily provide a sufficient purifying capability.
[0007] On the other hand, the exhaust purifying apparatus shown in Figs. 19 to 21 can easily
perform a sufficient purifying capability because the catalyst bearing member 112
is located in the central region of the exhaust muffler 110 and the relatively high
exhaust temperature can keep the catalysts hot. But, the honeycomb catalyst bearing
member 112 in the apparatus in Figs. 19 to 21 tends to cause a greater loss in the
exhaust gas pressure than the porous internal pipe 101 in the apparatus of Figs. 17
and 18. An even greater pressure loss would result in the central region of the muffler
110 where the exhaust gas flows at a higher speed. The performance of the internal
combustion engine would be adversely influenced by the pressure loss to a substantial
degree; in particular, the pressure loss could be a significant adverse factor for
low-power internal combustion engines such as those of motor cycles. Further, the
arrangement that the honeycomb catalyst member 112 is received in the catalyst pipe
111 would require a considerable manufacturing cost as compared to the arrangement
that the catalyst-attached internal pipe 101 is just received in the exhaust pipe
100.
DISCLOSURE OF THE INVENTION
[0008] It is therefore an object of the present invention to provide an exhaust purifying
device for an internal combustion engine which achieves a sufficient purifying function
while minimizing an adverse effect on the performance of the engine and yet can be
manufactured at low cost.
[0009] The present invention provides an exhaust purifying device for an internal combustion
engine according to claim 1. Thus, the catalytic metal of the first steel sheet member
is placed in the region of the exhaust pipe where the temperature of the exhaust gas
from the engine is relatively high. The high-temperature exhaust gas effectively activates
the catalytic metal on the steel sheet member to thereby allow the catalytic metal
to perform its exhaust purifying function to a sufficient degree. The first steel
sheet member is in the form of a hollow cylinder extending in the axial direction
of the exhaust port so that a pressure loss in the exhaust gas flowing through the
steel sheet member can be reduced. The cylinder is made of a porous steel sheet and
preferably closed at its upstream end. In this case, the exhaust gas is directed to
pass through small openings formed through the wall thickness of the cylinder, during
which time the exhaust gas contacts the catalytic metal on the inner and outer catalytic-metal-bearing
surfaces. Thus, the exhaust is acted on by the catalytic metal in a greater area of
the surfaces and accordingly can provide an enhanced exhaust purifying capability.
[0010] Preferably a partition plate is provided within the exhaust pipe to block passage
of the exhaust gas between the cylinder and the exhaust pipe. The partition plate
functions to suppress the pulsating motion of the exhaust gas caused by the engine,
so as to provide a generally smooth steady flow of the exhaust gas. Owing to the provision
of such a partition plate, the purifying capability of the exhaust purifying apparatus
does not significantly vary and hence can be enhanced effectively. Further, because
the steel cylinder is supported via the partition plate suppressing the pulsating
motion of the exhaust gas, no separate support is required.
[0011] The steel cylinder is preferably mounted in such a manner that the cylinder is free
to axially expand or contract relative to the exhaust pipe, and this feature advantageously
accommodates a difference in amounts of axial thermal expansion between the steel
cylinder and exhaust pipe.
[0012] According to the present invention, a first catalytic-metal-bearing member is provided
within the exhaust pipe along an inner wall surface of said pipe and a second catalytic-metal-bearing
member is provided substantially in the central region of the first catalytic-metal-bearing
member. Because the catalytic-metal-bearing members are provided near the inner wall
surface of and in the central region of the exhaust pipe, the exhaust purifying function
can be further enhanced without adversely affecting the performance of the internal
combustion engine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013]
Fig. 1 is a side elevational view showing a motor cycle on which is mounted an exhaust
purifying apparatus for an internal combustion engine according to a first embodiment
of the present invention,
Fig. 2 is a side view showing an embodiment of an exhaust pipe employed in the apparatus
of Fig. 1 and constructed in accordance with the present invention,
Fig. 3 is a sectional view taken along the line A - A of Fig. 2, showing an upstream
exhaust purifier shown in Fig. 2,
Fig. 4 is a sectional view taken along the line B - B of Fig. 3,
Fig. 5 is a perspective view showing an embodiment of a downstream exhaust purifier
shown in Fig. 2,
Fig. 6 is a sectional view taken along the line C - C of Fig. 2,
Fig. 7 is a sectional view taken along the line D - D of Fig. 6,
Fig. 8 is a sectional view taken along the line E - E of Fig. 6,
Figs. 9A to 9E are views showing how a second catalytic-metal-bearing member of the
downstream exhaust purifier of Fig. 5 is assembled,
Figs. 10A to 10D are views showing modifications of the second catalytic-metal-bearing
member,
Figs. 11A to 11H are views showing modifications of a support structure for the second
catalytic-metal-bearing member,
Fig. 12 is a perspective view showing another embodiment of the downstream exhaust
purifier,
Fig. 13 is a sectional view taken along the line F - F of Fig. 12,
Fig. 14 is a view showing a modification of the downstream exhaust purifier of Fig.
12,
Fig. 15 is a sectional view taken along the line G - G of Fig. 14,
Figs. 16A to 16E are views showing still another embodiment of the exhaust purifier
apparatus,
Fig. 17 is a cross-sectional view of an exhaust pipe in a prior art exhaust purifying
apparatus,
Fig. 18 is a side view, partly in vertical section, of the exhaust pipe of Fig. 17,
Fig. 19 is a plan view of an exhaust muffler in another prior art exhaust purifying
apparatus,
Fig. 20 is a perspective view, partly in vertical section, of the exhaust purifying
apparatus of Fig. 19, and
Fig. 21 is a vertical sectional view of a catalyst pipe and peripheral components
in the exhaust purifying apparatus of Fig. 19.
BEST MODE FOR CARRYING OUT THE INVENTION
[0014] Fig. 1 is a side elevational view showing a motor cycle 1 on which is mounted an
exhaust purifying apparatus for an internal combustion engine according to a first
embodiment of the present invention. As shown, the motor cycle 1 includes a two-cycle
internal combustion engine 3 provided near the central part of a vehicle body 2, and
an exhaust pipe 5 connected to an exhaust port 4 of the engine 3. The rear end portion
of the exhaust pipe 5 is coupled to a muffler 6.
[0015] Fig. 2 shows details of the exhaust pipe 5, which is formed of a thin steel sheet
and has a circular sectional shape. The exhaust pipe 5 having an upstream end portion
5a connected by flange coupling to the engine exhaust port 4 of Fig. 1 and having
a downstream end portion 5b connected by flange coupling to the muffler 6 of Fig.
1 (the words "upstream" and "downstream" are used herein in terms of the flow of exhaust
gas from the engine exhaust port 4). Upstream and downstream exhaust purifiers 10
and 20 are provided within the exhaust pipe 5; in other words, the former is a front-stage
exhaust purifier and the latter is a rear-stage exhaust purifier. The portion of the
exhaust pipe 5 in which the downstream exhaust purifier 20 is disposed is greater
in diameter than the other portions of the pipe 5.
[0016] Fig. 3 shows a detailed structure of the upstream exhaust purifier 10 in a sectional
view taken along the line A - A of Fig. 2. The upstream exhaust purifier 10 includes
an internal pipe 11 having numerous small openings 11c formed through the wall thickness
thereof, which is disposed within the exhaust pipe 5 and in the form of a hollow cylinder
made of a thin, porous steel sheet and extending along the inner wall surface of the
exhaust pipe 5. The internal pipe 11 has one or upstream end portion 11a fixed by
welding to the inner wall surface of the exhaust pipe 5 and the other or downstream
end portion 11b supported by a support member 13 in such a manner that the downstream
end portion 11b is free to axially move (expand or contract) relative to the exhaust
pipe 5 so as to accommodate a difference in amounts of axial thermal expansion between
the two pipes 5 and 11.
[0017] The inner wall surface of the internal pipe 11 has a layer of catalytic metal, such
as platinum or rhodium, which is formed by, for example, applying a solution of the
catalytic metal onto the surface. A clearance 5c is formed between the intermediate
portion of the exhaust pipe 5 and the internal pipe 11.
[0018] As shown in Fig. 4, the exhaust pipe 5 comprises a pair of upper and lower hollow
cylinder halves each having a semicircular sectional shape, which are welded together
into a hollow cylinder with the internal pipe 11 received therein.
[0019] The support member 13 comprises a corrugated sheet that is wound around the outer
periphery of the internal pipe 11 with its parallel ridges and grooves extending in
the axial direction of the exhaust pipe 5 (i.e., the ridges and grooves alternating
along the periphery of the pipe 11). Overlapping surfaces of the thus-wound corrugated
sheet are secured together by spot-welding. By means of such a corrugated structure,
the support member 13 can resiliently deform relative to the internal pipe 11 in the
radial direction thereof to allow the downstream end portion 11a of the internal pipe
11 to axially slide along the support member 13, to thereby accommodate a difference
in amounts of axial thermal expansion between the exhaust pipe 5 and internal pipe
11 due to the temperature of the exhaust gas. Note that the above-mentioned corrugated
sheet is just illustrative and the support member 13 may be implemented in any other
suitable manner, such as by a stainless steel wire knitted into a ring disposed around
the outer periphery of the internal pipe 11.
[0020] Protecting members 14 are in the form of a pair of hollow cylinder halves (each having
a substantially semicircular sectional shape) are bolted to nuts 15 welded to the
outer periphery of the exhaust pipe 5, so as to together form a substantially cylindrical
cover for the exhaust pipe 5 that are heated by the exhaust gas flowing therethrough.
[0021] Fig. 5 shows the downstream exhaust purifier 20 of Fig. 2, which includes a first
catalytic-metal-bearing member 21 provided within the exhaust pipe 5 near the inner
wall surface of the pipe 5. The first catalytic-metal-bearing member 21 comprises
a pair of hollow cylinder halves 21 each having a semicircular sectional shape so
as to together form a hollow cylinder within the exhaust pipe 5 as shown in Fig. 5.
A second catalytic-metal-bearing member 22, which is in the form of a straight hollow
cylinder smaller in diameter than the first catalytic-metal-bearing member 21, is
provided substantially in a central region (i.e., central region as viewed in cross
section) of the bearing member (and hence substantially in a central region of the
exhaust pipe 5). It can be said that the exhaust pipe 5 and first and second catalytic-metal-bearing
members 21 and 22 are mounted concentrically. The first and second catalytic-metal-bearing
members 21 and 22 both extend in the axial direction of the exhaust pipe 5.
[0022] Each of the first and second catalytic-metal-bearing members 21 and 22 is made of
a thin, porous steel sheet to have numerous small openings 21a, 22c formed through
the wall thickness thereof. A layer of catalytic metal, such as platinum or rhodium,
is formed on the wall surfaces of the first and second catalytic-metal-bearing members
21 and 22 by, for example, applying a solution of the catalytic metal onto the surfaces.
A clearance is formed between the exhaust pipe 5 and the hollow cylinder halves 21
of the first catalytic-metal-bearing member 21.
[0023] As shown in Fig. 6, a support structure 23 is provided, at one or upstream end portion
(left end portion in the figure) 22a of the second catalytic-metal-bearing member
22, to support the end portion 22a in such a manner that the end portion 22a is free
to axially move (expand or contract) relative to the exhaust pipe 5. The support structure
23 includes a cushion member 24 wound around the upstream end portion 22a of the second
catalytic-metal-bearing member 22, an annular holder 25 receiving and holding the
cushion member 24 in place, and a bracket 26 that secures the annular holder 25 with
the cushion member 24 to the exhaust pipe 5. Because of the cushion member 24, the
support structure 23 accommodates a difference in amounts of axial thermal expansion
between the exhaust pipe 5 and the second catalytic-metal-bearing member 22 by allowing
the upstream end portion 22a to axially move relative to the exhaust pipe 5. Further,
a cap 28 is provided within the second catalytic-metal-bearing member 22 to close
the upstream end portion 22a of the member 22.
[0024] A partition plate 27 is provided, at the downstream end portion (right end portion
in the figure) of the second catalytic-metal-bearing member 22, to support that end
and block passage of the exhaust gas between the second catalytic-metal-bearing member
22 and the exhaust pipe 5. The partition plate 27, which is a dish-shaped end plate
made of a thin steel plate, has a flange along the entire outer periphery thereof
and is fixed in place by the flange being plug-welded to the inner wall surface of
the exhaust pipe 5. The other or downstream end portion 22b is threaded through a
central through-hole 27b and fixed by welding to the entire edge of the plate 27 defining
the through-hole 27b.
[0025] As shown in Fig. 7 which is a sectional view taken along the line D - D of Fig. 6,
the cushion member 24 comprises a corrugated sheet that is wound around the outer
periphery of the second catalytic-metal-bearing member 22 with its parallel ridges
and grooves extending in the axial direction of the exhaust pipe 5 (i.e., the ridges
and grooves alternating along the outer periphery of the member 24). The thus-wound
corrugated sheet is fixed around the second catalytic-metal-bearing member 22 by spot-welding
its overlapping surfaces. Owing to such a corrugated structure, the cushion member
24 can resiliently deform relative to the member 22 in the radial direction thereof,
so as to accommodate a difference in amounts of axial thermal expansion between the
exhaust pipe 5 and second catalytic-metal-bearing member 22.
[0026] As shown in Fig. 8 which is a sectional view taken along the line E - E of Fig. 6,
each of the hollow cylinder halves 21 of the first catalytic-metal-bearing member
21 is spot-welded at its opposite edges to the inner wall surface of the exhaust pipe
5.
[0027] The following paragraphs describe how the above-mentioned second catalytic-metal-bearing
member 22 is assembled, with reference to Figs. 6 and 9A - 9E.
[0028] First, the cap 28 is fit into the upstream end portion 22a of the second catalytic-metal-bearing
member 22 as shown in Fig. 9A, and the outer peripheral edge of the cap 28 and the
inner wall surface of the member 22 are fixed together by spot welding in order to
close the upstream end portion 22a as shown in Fig. 9B. Then, as shown in Fig. 9C,
the downstream end portion 22b of the second catalytic-metal-bearing member 22 is
threaded through the central through-hole 27b of the partition plate 27 and welded
to the edge defining the hole 27b.
[0029] After that, the annular holder 25 receiving the cushion member 25 (Fig. 6) is threaded
on the upstream end portion 22a of the second catalytic-metal-bearing member 22 as
shown in Fig. 9D, and the second catalytic-metal-bearing member 22 is assembled into
a predetermined condition as shown in Fig. 9E. The second catalytic-metal-bearing
member 22 assembled as shown in Fig. 9E is then positioned in the lower half of the
exhaust pipe 5 as shown in Fig. 6, and a part of the outer surface of the annular
holder 25 is welded to the bracket 26 previously fixed to the exhaust pipe 5. Finally,
the upper hollow cylinder half of the exhaust pipe 5 is placed edge to edge on the
lower hollow cylinder half, then the upper and lower hollow cylinder halves are welded
together, and then the flange 27a of the partition plate 27 is plug-welded to the
inner wall surface of the exhaust pipe 5. This completes the required assembly of
the second catalytic-metal-bearing member 22.
[0030] Next, with reference to Figs. 2 and 6, a description will be given as to how the
upstream and downstream exhaust purifiers 10 and 20 behave.
[0031] As shown in Fig. 2, the exhaust gas from the internal combustion engine is introduced
into the exhaust pipe 5 via its upstream end portion 5a. As the introduced exhaust
gas passes through the upstream exhaust purifier 10, the exhaust gas contacts the
catalytic metal layers on the inner and outer surfaces of the internal pipe 11 and
is effectively purified through its chemical reaction with the catalytic metal. The
exhaust gas thus purified by the upstream exhaust purifier 10 is then directed toward
the downstream exhaust purifier 20.
[0032] As shown in Fig. 6, the exhaust gas initially purified by the upstream exhaust purifier
10 is prevented from flowing into the second catalytic-metal-bearing member 22 through
its upstream end portion 22a because the end portion 22a is closed by the cap 28.
[0033] A portion of the exhaust pipe 5 in which the downstream exhaust purifier 20 is disposed
is greater in diameter than the other portions of the pipe 5 as noted earlier, and
this greater-diameter portion is partitioned off by the partition plate 27 so that
an expanding chamber 29 is formed in the greater-diameter portion upstream of the
plate 27. The expanding chamber 29 functions to suppress the pulsating motion of the
exhaust gas caused by the engine 3, so as to provide a generally smooth steady flow
of the exhaust gas. This allows the exhaust gas to flow as indicated by black arrows,
and a portion of the exhaust gas flowing near and along the inner wall surface of
the exhaust pipe 5 comes into contact with the catalytic metal layers on the inner
and outer surfaces of the first catalytic-metal-bearing member 21 to be purified through
its chemical reaction with the catalytic metal.
[0034] In the meantime, another portion of the exhaust gas flows into the second catalytic-metal-bearing
member 22 via the numerous small openings 22c, flows through the member 22 and then
is discharged through the downstream end portion of the exhaust pipe 5 into the atmosphere.
As the exhaust gas flows in the second catalytic-metal-bearing member 22, it comes
into contact with the catalytic metal layer surfaces on the member 22 to be purified
through its chemical reaction with the catalytic metal.
[0035] When passing through the numerous small openings 22c formed in the second catalytic-metal-bearing
member 22, the exhaust gas contacts the catalytic metal layers on the outer and inner
wall surfaces of the member 22. Therefore, the exhaust gas can contact a great area
of the catalytic metal layers, and thus the catalytic metal can perform its exhaust
purifying function to a sufficient degree.
[0036] As previously discussed in relation to the prior art apparatuses, it is necessary
to activate the catalyst metal by heating in order to allow the catalyst metal to
perform its exhaust purifying function to a sufficient degree, and the temperature
of the exhaust gas flowing in the exhaust pipe is higher in the central region of
the pipe and lower near the inner wall surface of the pipe. According to the embodiment
of the present invention, even a relatively hot portion of the exhaust gas flowing
in the central region of the exhaust pipe 5 is caused to flow in the downstream exhaust
purifier 20 in contact with the catalytic metal layer, the catalytic metal can be
sufficiently activated by being heated by the high-temperature exhaust gas and thus
perform its exhaust purifying function to a sufficient degree. In addition, the second
catalytic-metal-bearing member 22, in the form of a hollow cylinder having a porous
wall, effectively reduces a pressure loss of the exhaust gas flowing through the member
22, so that the engine performance will not be significantly influenced by the pressure
loss.
[0037] In the above-mentioned manner, the exhaust gas from the internal combustion engine
3 can be purified efficiently by contacting the catalytic metal layers on the first
and second catalytic-metal-bearing members 21 and 22. Besides, because the exhaust
gas is allowed to flow in a generally smooth steady current, the purifying capability
of the downstream exhaust purifier 20 does not significantly vary, which would result
in uniform and efficient exhaust purification.
[0038] Due to heat of the reaction, the second catalytic-metal-bearing member 22 becomes
much hotter than the exhaust pipe 5. While the downstream end portion 22b is fixed
to the exhaust pipe 5 via the partition plate 27, the upstream end portion 22a is
movably mounted via the support structure 23 on the fixed bracket 26 of the exhaust
pipe 5. Thus, when a difference in amounts of axial thermal expansion occurs between
the exhaust pipe 5 and the member 22, the upstream end portion 22a is allowed to move
relative to the bracket 26, in the upstream direction as indicated by a white arrow,
to thereby accommodate the difference in axial expansion. Specifically, the difference
in axial expansion between the exhaust pipe 5 and the second catalytic-metal-bearing
member 22 is accommodated by the resilient deformation of the cushion member 24.
[0039] The second catalytic-metal-bearing member 22 has been described above as being closed
at the upstream end portion 22a by the straight vertical cap 28, but the closing structure
of the upstream end portion 22a may be modified in various ways as shown in Figs.
10A to 10D.
[0040] In the modification of Fig. 10A, the upstream end portion 22a of the second catalytic-metal-bearing
member 22 is closed by a porous cap 31 that projects upstream in a dome-like shape.
The cap 31 may be made by pressing a porous sheet material. In Fig. 10B, another modified
cap 32 is formed by squeezing or pressing the upstream end portion 22a flat.
[0041] In Fig. 10C, a modified cap 33 comprises a plurality of porous blades that are attached
spirally (i.e., in the shape of a pinwheel) to the upstream end portion 22a of the
second catalytic-metal-bearing member 22. This spiral cap 33 functions to increase
the flowing resistance of the exhaust gas. Finally, in the modification of Fig. 10D,
the upstream end portion 22a of the second catalytic-metal-bearing member 22 is closed
by a cap 34 made of a flat porous plate. In stead of providing the flat porous cap
34, the upstream end portion 22a may itself be folded toward its center along the
entire peripheral edge thereof to form an integral cap.
[0042] Each of the caps 31, 32, 33 and 34 functions in the same way as in the above-described
first embodiment, and additionally, the pressure loss resulting from the provision
of the cap is substantially reduced as compared to the first embodiment by virtue
of its porous nature.
[0043] While the second catalytic-metal-bearing member 22 has been described above being
supported at one end portion supported movably relative to the exhaust pipe 5 and
fixed at the other end portion to the exhaust pipe 5, the mounting mechanism of the
member 22 may be modified in various ways as shown in Figs. 11A to 11H. In each of
these figures, the exhaust gas flows rightward as indicated by black arrows and the
one or upstream end portion 22a of the second catalytic-metal-bearing member 22 is
allowed to move leftward as indicated by a white arrow.
[0044] In the modification of Fig. 11A, the upstream end portion 22a projects upstream beyond
the support structure 23 and is closed by a flat cap 28. In the modification of Fig.
11B, the upstream end of the support structure 23 is closed by a cap 36. Between the
upstream end portion 22a and the cap 36, there is provided a clearance S
1 having an axial length greater than an expected maximum amount of axial thermal expansion
of the second catalytic-metal-bearing member 22. In this case, no cap separate from
the cap 36 needs to be attached to the upstream end portion 22a of the catalytic-metal-bearing
member 22. In the modification of Fig. 11C, the annular holder member 25 of the support
structure 23 is greater in axial length than the bracket 26 and projects upstream
beyond the bracket 26.
[0045] Further, in Fig. 11D, the catalytic-metal-bearing member 22 is supported only at
the downstream end portion 22b by a supporting structure 37 in a so-called "cantilever"
fashion. The support structure 37 includes a cushion member 38 that supports the downstream
end portion 22b in such a manner that the end portion 22a is free to axially move
(expand and contract) relative to the exhaust pipe 5, a holder member 39 receiving
and holding the cushion member 38, and a partition plate 27 fixing the holder member
39 to the exhaust pipe 5. A clearance S
2 is provided between the downstream end portion 22b and a flange 39a of the holder
member 39 so that movement of the downstream end portion 22b relative to the exhaust
pipe 5 is limited within the bound of the clearance S
2. In the modification of Fig. 11E, cushion and holder members 38 and 39 are smaller
in axial length than those of Fig. 11D.
[0046] In the modification of Fig. 11F, the catalytic-metal-bearing member 22 is fixed at
the upstream end portion 22a to the exhaust pipe 5 via a bracket 41 and supported
at the downstream end 22b via a support structure 42 for axial movement relative to
the exhaust pipe 5. The support structure 42 includes a cushion member 43 that supports
the downstream end portion 22b in such a manner that the end portion 22b is free to
axially move (expand or contract) relative to the exhaust pipe 5, a holder member
44 receiving and holding the cushion member 43 in place, and a partition plate 27
fixing the holder member 44 to the exhaust pipe 5. The downstream end portion 22b
projects downstream beyond the support structure 42.
[0047] Further, the modification of Fig. 11G is similar to that of Fig. 11F, except that
the upstream end portion 22a is closed by a cap 45 having a locking projection to
engage or disengage the end portion by a user's snap action. The modification of Fig.
11H employs a pair of front and rear cushion members 48 different from the above-mentioned
cushion members 24, 38, 43, each of which comprises a stainless steel wire knitted
into a ring around the outer periphery of the downstream end portion 22b. Support
structure 46 includes a seat 47 wound around the downstream end portion 22b, the front
and rear cushion members 48 disposed upstream and downstream of the seat 47, respectively,
for supporting the downstream end portion 22b in such a manner that the end portion
22b is axially movable relative to the exhaust pipe 5, a holder member 49 receiving
and holding the cushion members 48, and a partition plate 27 fixing the holder member
49 to the exhaust pipe 5.
[0048] The following paragraphs describe a second embodiment of the downstream exhaust purifier
with reference to Figs. 12 and 13.
[0049] In the downstream exhaust purifier 50 of Fig. 12, a first catalytic-metal-bearing
member 51 is provided near and along the inner wall surface of the exhaust pipe, and
a second catalytic-metal-bearing member 52 is provided substantially in a central
region within the first catalytic-metal-bearing member 51 (and hence in a central
region of the exhaust pipe 5). The first and second catalytic-metal-bearing members
51 and 52 extend in the axial direction of the exhaust pipe 5.
[0050] The first catalytic-metal-bearing member 51 is a hollow cylinder that is made of
a porous steel sheet (having numerous small openings 51c formed through the wall thickness
thereof) and has outwardly-widening conical portions 51a at the axially opposite ends
thereof, and at least one of the conical portions 51a is fixed by welding to the inner
wall surface of the exhaust pipe 5. The second catalytic-metal-bearing member 52 is
a flat porous steel sheet (having numerous small openings 52c formed through the wall
thickness thereof) and welded at at least one of its longitudinal edges to the inner
wall surface of the first catalytic-metal-bearing member 51. On the wall surfaces
of the first and second catalytic-metal-bearing members 51 and 52, a layer of catalytic
metal, such as platinum or rhodium, is formed by, for example, applying a solution
of the catalytic metal onto the surfaces. Fig. 13 is a sectional view taken along
the line F - F of Fig. 12, showing the flat second catalytic-metal-bearing member
52 in an upright position within the first catalytic-metal-bearing member 51.
[0051] The following paragraphs describe how the downstream exhaust purifier 50 of Fig.
12 operates, with reference to Fig. 12.
[0052] The exhaust gas from the internal combustion engine flows as denoted by arrows. More
specifically, a portion of the exhaust gas flowing near and along the inner wall surface
of the exhaust pipe 5 is caused to pass through the numerous small openings 51c formed
in the wall of the catalytic-metal-bearing member 51, and another portion of the exhaust
gas flowing in a generally central region of the exhaust pipe 5 is caused to pass
through the numerous small openings 52a formed in the second second catalytic-metal-bearing
member 52. Thus, the exhaust gas contacts the catalytic metal layers on the inner
and outer surfaces of the first and second catalytic-metal-bearing members 51 and
52 and is effectively purified through its chemical reaction with the catalytic metal.
[0053] When passing through the numerous small openings 52a formed in the second catalytic-metal-bearing
member 52, the exhaust gas contacts the catalytic metal layers on the outer and inner
wall surfaces of the member 52. Therefore, the exhaust gas is brought into contact
with a great area of the catalytic metal layers, and the catalytic metal can perform
its exhaust purifying function to a sufficient degree.
[0054] Further, because the second catalytic-metal-bearing member 52 contacts the relatively
hot portion of the exhaust gas flowing though the central region in the exhaust pipe
5, the catalytic metal can be heated to be sufficiently activated and therefore can
perform its exhaust purifying function to a sufficient degree. In addition, because
the second catalytic-metal-bearing member 52 is just in the form of a flat plate,
a pressure loss of the exhaust gas flowing in the member 52 can be reduced even further
than in the above-described first embodiment of the downstream exhaust purifier.
[0055] The downstream exhaust purifier 50 of Fig. 12 may be modified in such a manner as
shown in Figs. 14 and 15. Namely, in the modification, the first catalytic-metal-bearing
member 51 is in the form of a hollow cylinder having a generally C-shape in section
with a part (bottom part in the example of Fig. 14) cut away along the entire length
thereof. As shown in Fig. 15, the first catalytic-metal-bearing member 51 in the form
of the partly-cut-away hollow cylinder has a pair of flanges 51b integrally formed
with the opposed longitudinal edges, which are in contact with the inner wall surface
of the exhaust pipe 5. In this example, one longitudinal edge portion extends, through
the opening between the opposed longitudinal edges of the second catalytic-metal-bearing
member 52, into contact with the wall surface of the exhaust pipe 5.
[0056] Figs. 16A to 16E schematically shows several other embodiments of the exhaust purifying
apparatus.
[0057] The exhaust purifying apparatus 61 shown in Fig. 16A, which comprises a pair of upstream
(front-stage) and downstream (rear-stage) exhaust purifiers disposed within an exhaust
pipe 5, is characterized by the provision of a control valve (e.g., butterfly valve)
62 between the upstream and downstream exhaust purifiers. The upstream exhaust purifier
is constructed in the same manner as the upstream exhaust purifier 10 of Fig. 3, and
the downstream exhaust purifier is constructed in the same manner as the downstream
exhaust purifier 50 of Fig. 12.
[0058] The exhaust purifying apparatus 63 shown in Fig. 16B comprises three exhaust purifiers
disposed in succession within an exhaust pipe 5. The upstream (front-stage) exhaust
purifier is constructed in the same manner as the upstream exhaust purifier 10 of
Fig. 3, the central (intermediate-stage) exhaust purifier is constructed in the same
manner as the downstream exhaust purifier 50 of Fig. 12, and the downstream (rear-stage)
exhaust purifier is an exhaust discharging conduit 64 partly extending out of the
exhaust pipe 5. The exhaust discharging conduit 64 is made of a porous steel sheet,
and a layer of catalytic metal, such as platinum or rhodium, is formed on the inner
and outer wall surfaces of the conduit 64 by, for example, applying a solution of
the catalytic metal onto the surfaces.
[0059] The exhaust purifying apparatus 65 shown in Fig. 16C comprises a catalytic-metal-bearing
member 66 that is disposed in a central region and extends in the axial direction
of an exhaust pipe 5. The catalytic-metal-bearing member 66 is made of a flat, porous
steel sheet, and a layer of catalytic metal, such as platinum or rhodium, is formed
on the opposite wall surfaces of the member 66 by, for example, applying a solution
of the catalytic metal onto the surfaces. The exhaust purifying apparatus 67 shown
in Fig. 16D is a modification of the exhaust purifying apparatus 65 of Fig. 16C, which
is characterized in that the catalytic-metal-bearing member 66 is made of a corrugated
porous steel sheet rather than the flat, porous steel sheet of Fig. 16C.
[0060] The exhaust purifying apparatus 68 shown in Fig. 16E comprises a catalytic-metal-bearing
member 69 in the form of a hollow semicylinder, which extends in the axial direction
of an exhaust pipe 5 and is closed at opposite ends. The semicylindrical catalytic-metal-bearing
member 69 has a hollow space 69a, opening toward the inner wall surface of the exhaust
pipe 5, between the opposed longitudinal edges thereof. The catalytic-metal-bearing
member 69 is made of a porous steel sheet, and a layer of catalytic metal, such as
platinum or rhodium, is formed on the inner and outer wall surfaces of the member
69 by, for example, applying a solution of the catalytic metal onto the surfaces.
[0061] Note that any of the catalytic-metal-bearing members 66 and 69 shown in Figs. 16C,
16D and 16E may be employed in the plural-stage exhaust purifiers of Figs. 16A and
16B provided within the exhaust pipe 5.
[0062] In the above-described first, second and third embodiments and their modifications,
the "steel sheet" bearing catalytic metal is disposed in the central region of the
exhaust pipe 5 or first catalytic-metal-bearing element 21, 51. More specifically,
in the first embodiment of Figs. 1 to 9 and its modifications of Figs. 11A to 11H,
the "steel sheet" bearing catalytic metal is embodied as the second catalytic-metal-bearing
member 22 in the form of a hollow cylinder made of a porous steel sheet; in the embodiment
of Figs. 12 and 13 and its modifications of Figs. 14 and 15, and in the examples of
the embodiment of Figs. 16A and 16B, the "steel sheet" bearing catalytic metal is
embodied as the second catalytic-metal-bearing member 52 in the form of a flat porous
steel plate; and in the other examples of the third embodiment of Figs. 16C, 16D and
16E, the "steel sheet" bearing catalytic metal is embodied as the catalytic-metal-bearing
members 66 and 69 in the form of a flat or corrugated porous plate, or porous semicylinder.
[0063] The "steel sheet" bearing catalytic metal should be understood as not being limited
to the construction described above in relation to various embodiments and modifications
and also as not being limited to the porous sheet. Also, the small openings in the
porous sheet or plate may be of any desired shape, size and quantity.
INDUSTRIAL APPLICABILITY
[0064] As has been described so far, the exhaust purifying device for an internal combustion
engine according to the present invention is characterized in that a steel sheet member
having inner and outer catalytic-metal-bearing surfaces is disposed substantially
in the central of an exhaust port extending from an exhaust port of the internal combustion
engine. Thus, the catalytic metal is placed in the central region of the exhaust pipe
where the temperature of the exhaust gas from the engine remains relatively high.
The high-temperature exhaust gas effectively activates the catalytic metal on the
steel sheet member, and this achieves the benefit that a sufficient exhaust purifying
function of the catalytic metal can be acquired at low cost.
[0065] In one implementation, the steel sheet member is in the form of a hollow cylinder
extending in the axial direction of the exhaust port, so that a pressure loss in the
exhaust flowing through the steel sheet member can be reduced significantly to avoid
adverse effects on the performance of the internal combustion engine.
[0066] Further, the cylinder is made of a porous steel sheet and closed at its upstream
end. In this case, the exhaust gas is directed to pass through small openings formed
through the wall thickness of the cylinder, during which time the exhaust gas contacts
the catalytic metal on the inner and outer catalytic-metal-bearing surfaces. Thus,
the exhaust is acted on by the catalytic metal in a greater area of the catalytic-metal-bearing
surfaces and hence can provide an further enhanced exhaust purifying capability.
[0067] In another implementation, a hollow cylinder is provided and supported substantially
in the central region of the exhaust pipe substantially along a center axis of said
pipe, and the hollow cylinder is made of a steel sheet having inner and outer catalytic-metal-bearing
surfaces. Also, a partition plate is provided within the exhaust pipe to block passage
of the exhaust gas between the cylinder and the exhaust pipe. Thus, the catalytic
metal is placed in the central region of the exhaust pipe where the temperature of
the exhaust gas from the engine remains relatively high, so that the high-temperature
exhaust gas effectively activates the catalytic metal on the steel sheet member. This
achieves the benefit that a sufficient exhaust purifying function of the catalytic
metal can be acquired at low cost. In addition, the partition plate functions to restrict
the pulsating motion of the exhaust gas caused by the engine, so as to provide a generally
smooth steady flow of the exhaust gas. Owing to the provision of such a partition
plate, the purifying capability of the exhaust purifying apparatus does not significantly
vary and can achieve sufficient exhaust purification. Further, because the steel cylinder
is supported via the partition plate restricting the pulsating motion of the exhaust
gas, no separate support is required, which simplifies the supporting mechanism for
the cylinder.
[0068] Besides, the steel cylinder is mounted in such a manner that the cylinder is free
to axially expand and contract relative to the exhaust pipe, and this feature easily
accommodates a difference in axial thermal expansion between the steel cylinder and
exhaust pipe.
[0069] In still another implementation, a first catalytic-metal-bearing member is provided
within the exhaust pipe along an inner wall surface of said pipe and a second catalytic-metal-bearing
member is provided substantially in the central of the first catalytic-metal-bearing
member. Thus, the catalytic-metal-bearing members are provided near the inner wall
surface of and in the central region of the exhaust pipe, and the exhaust purifying
function can be further enhanced without adversely affecting the performance of the
internal combustion engine and yet at low cost.
[0070] Particularly, since the first catalytic-metal-bearing member extending along the
inner wall surface of the exhaust pipe is disposed coaxially with the second catalytic-metal-bearing
member, the first catalytic-metal-bearing member is subjected to a high temperature,
whereby the catalytic purification function is enhanced still further.
1. An exhaust purifying apparatus (10; 20; 50; 61; 63) for an internal combustion engine
(3), comprising:
an exhaust pipe (5) adapted to extend from an exhaust port (4) of the internal combustion
engine (3) and having at least one exhaust purifier for purifying exhaust gas from
the engine (3), the exhaust pipe (5) having a greater-diameter portion, wherein the
exhaust pipe (5) has an expanding chamber (29) defined at the greater-diameter portion
thereof,
a first, upstream exhaust purifier (10) and a second, downstream exhaust purifier
(20; 50) which are arranged successively but separated from each other in the exhaust
pipe (5),
wherein the downstream exhaust purifier (20; 50) is arranged in a central region of
the expanding chamber (29),
characterized in that
the upstream exhaust purifier (10) and the downstream exhaust purifier (20; 50) comprise
a respective first thin, porous steel sheet member (11; 21; 51) taking the form of
a hollow cylinder, extending axially of the exhaust pipe (5), and bearing catalytic
metal,
that a respective clearance is formed between each first thin, porous steel sheet
member (11, 21) and the exhaust pipe (5), and
that the downstream purifier (20; 50) further comprises a second thin, porous steel
sheet member (22; 52) provided in a central region of the corresponding first thin,
porous steel sheet member (21; 51) and bearing catalytic metal thereon.
2. The exhaust purifying apparatus of claim 1, wherein said second steel sheet member
(22) takes the form of a straight hollow cylinder.
3. The exhaust purifying apparatus according to claim 2, wherein said second steel sheet
member (22) is mounted in such a manner that it can freely expand or contract axially
relative to the exhaust pipe (5).
4. The exhaust purifying apparatus according to claim 2 or 3, wherein said second steel
sheet member (22) is fixed by welding to the exhaust pipe (5) at only a part in an
axial direction thereof.
5. The exhaust purifying apparatus according to any of claims 2 to 4, characterized in that a cap (28) is provided within the second steel sheet member (22) to close its upstream
end portion, wherein a partition plate (27) is provided at the downstream end portion
of the second steel sheet member (22) to block the passage of the exhaust gas between
the second steel sheet member (22) and the exhaust pipe (5).
6. The exhaust purifying apparatus according to any of claims 2 to 5, wherein the hollow
cylinder (22) is mounted to the exhaust pipe (5) at its upstream end portion (22a).
7. The exhaust purifying apparatus according to any of the preceding claims, wherein
the first steel sheet member (21) comprises two halves welded together to form the
cylinder.
8. The exhaust purifying apparatus according to claim 1, further comprising a third exhaust
purifier (64) disposed in succession to the second exhaust purifier (50), having a
corresponding first steel sheet member (5) taking the form of a hollow cylinder and
bearing catalytic metal thereon.
9. The exhaust purifying apparatus according to claim 8, wherein the second steel sheet
member (52) takes the form of a flat plate.
10. The exhaust purifying apparatus according to any one of claims 1 to 9, wherein each
of the first and second steel sheet members (11; 22, 52; 21, 51; 64) has a multiplicity
of openings (11c; 21a, 22c; 51c, 52a) formed through a wall thickness thereof.
1. Abgasreinigungsvorrichtung (10; 20; 50; 61; 63) für einen Verbrennungsmotor (3), umfassend:
ein Abgasrohr (5), welches dazu ausgebildet ist, sich von einer Auslassöffnung (4)
des Verbrennungsmotors (3) aus zu erstrecken und wenigstens einen Abgasreiniger hat,
um Abgas von dem Motor (3) zu reinigen, wobei das Abgasrohr (5) einen Abschnitt mit
größerem Durchmesser hat, wobei das Abgasrohr (5) eine Expansionskammer (29) hat,
welche an dessen Abschnitt mit größerem Durchmesser definiert ist,
einen ersten stromaufwärtigen Abgasreiniger (10) und einen zweiten stromabwärtigen
Abgasreiniger (20; 50), welche hintereinander, aber getrennt voneinander in dem Abgasrohr
(5) angeordnet sind,
wobei der stromabwärtige Abgasreiniger (20; 50) in einem zentralen Bereich der Expansionskammer
(29) angeordnet ist,
dadurch gekennzeichnet,
dass der stromaufwärtige Abgasreiniger (10) und der stromabwärtige Abgasreiniger (20;
50) ein jeweiliges erstes dünnes, poröses Stahlblechelement (11; 21; 51) umfassen,
welches die Form eines Hohlzylinders annimmt, welches sich in Achsrichtung des Abgasrohrs
(5) erstreckt und ein katalytisches Metall trägt,
dass ein jeweiliger Zwischenraum zwischen jedem ersten dünnen, porösen Stahlblechelement
(11,21) und dem Abgasrohr (5) ausgebildet ist, und
dass der stromabwärtige Reiniger (20; 50) ferner ein zweites dünnes, poröses Stahlblechelement
(22; 52) umfasst, welches in einem zentralen Bereich des entsprechenden ersten dünnen,
porösen Stahlblechelements (21; 51) vorgesehen ist, und katalytisches Metall darauf
trägt.
2. Auspuffreinigungsvorrichtung nach Anspruch 1, wobei das zweite Stahlblechelement (22)
die Form eines geraden Hohlzylinders annimmt.
3. Auspuffreinigungsvorrichtung nach Anspruch 2, wobei das zweite Stahlblechelement (22)
in einer solchen Weise montiert ist, dass es sich frei axial relativ zu dem Abgasrohr
(5) ausdehnen oder zusammenziehen kann.
4. Auspuffreinigungsvorrichtung nach Anspruch 2 oder 3, wobei das zweite Stahlblechelement
(22) durch Schweißen an dem Abgasrohr (5) nur an einem Teil in einer axialen Richtung
desselben befestigt ist.
5. Auspuffreinigungsvorrichtung nach einem der Ansprüche 2 bis 4, dadurch gekennzeichnet, dass eine Kappe (28) im Inneren des zweiten Stahlblechelements (22) vorgesehen ist, um
dessen stromaufwärtigen Endabschnitt zu schließen, wobei eine Trennplatte (27) an
dem stromabwärtigen Endabschnitt von dem zweiten Stahlblechelement (22) vorgesehen
ist, um den Durchgang des Abgases zwischen dem zweiten Stahlblechelement (22) und
dem Abgasrohr (5) zu blockieren.
6. Abgasreinigungsvorrichtung nach einem der Ansprüche 2 bis 5, wobei der Hohlzylinder
(22) an dem stromaufwärtigen Endabschnitt (22a) des Abgasrohrs (5) angebracht ist.
7. Auspuffreinigungsvorrichtung nach einem der vorhergehenden Ansprüche, wobei das erste
Stahlblechelement (21) zwei Hälften umfasst, welche aneinander geschweißt sind, um
den Zylinder auszubilden.
8. Abgasreinigungsvorrichtung nach Anspruch 1, ferner umfassend einen dritten Abgasreiniger
(64), welcher in Folge zu dem zweiten Abgasreiniger (50) angeordnet ist, welcher ein
entsprechendes erstes Stahlblechelement (5) hat, das die Form eines Hohlzylinders
annimmt und ein katalytisches Metall darauf trägt.
9. Abgasreinigungsvorrichtung nach Anspruch 8, wobei das zweite Stahlblechelement (52)
die Form einer flachen Platte annimmt.
10. Abgasreinigungsvorrichtung nach einem der Ansprüche 1 bis 9, wobei jedes von den ersten
und zweiten Stahlblechelementen (11; 22, 52; 21, 51; 64) eine Mehrzahl von Öffnungen
(11c; 21a, 22c; 51c, 52a) hat, welche durch eine Wanddicke davon ausgebildet sind.
1. Appareil d'épuration des gaz d'échappement (10 ; 20 ; 50 ; 61 ; 63) pour un moteur
à combustion interne (3), comprenant :
un tuyau d'échappement (5) adapté pour s'étendre à partir d'un orifice d'échappement
(4) du moteur à combustion interne (3) et ayant au moins un épurateur des gaz d'échappement
pour épurer les gaz d'échappement du moteur (3), le tuyau d'échappement (5) ayant
une partie de plus grand diamètre, dans lequel le tuyau d'échappement (5) a une chambre
d'expansion (29) définie au niveau de sa partie de plus grand diamètre ,
un premier épurateur des gaz d'échappement en amont (10) et un second épurateur des
gaz d'échappement en aval (20 ; 50) qui sont agencés successivement, mais séparés
l'un de l'autre dans le tuyau d'échappement (5),
dans lequel l'épurateur des gaz d'échappement en aval (20 ; 50) est agencé dans une
région centrale de la chambre d'expansion (29) ;
caractérisé en ce que :
l'épurateur des gaz d'échappement en amont (10) et l'épurateur des gaz d'échappement
en aval (20 ; 50) comprennent un premier élément de tôle d'acier poreux fin (11 ;
21 ; 51) respectif prenant la forme d'un cylindre creux, s'étendant de manière axiale
par rapport au tuyau d'échappement (5) et supportant un métal catalytique,
en ce qu'un jeu respectif est formé entre le premier élément de tôle d'acier poreux fin (11,
21) et le tuyau d'échappement (5), et
en ce que l'épurateur en aval (20 ; 50) comprend en outre un second élément de tôle d'acier
poreux fin (22 ; 52) prévu dans une région centrale du premier élément de tôle d'acier
poreux fin (21 ; 51) correspondant et supportant un métal catalytique sur celui-ci.
2. Appareil d'épuration des gaz d'échappement selon la revendication 1, dans lequel ledit
second élément de tôle d'acier (22) prend la forme d'un cylindre droit creux.
3. Appareil d'épuration des gaz d'échappement selon la revendication 2, dans lequel ledit
second élément de tôle d'acier (22) est monté de sorte qu'il peut s'expanser ou se
contracter librement de manière axiale par rapport au tuyau d'échappement (5).
4. Appareil d'épuration des gaz d'échappement selon la revendication 2 ou 3, dans lequel
ledit second élément de tôle d'acier (22) est fixé par soudage au tuyau d'échappement
(5) uniquement sur une partie dans sa direction axiale.
5. Appareil d'épuration des gaz d'échappement selon l'une quelconque des revendications
2 à 4, caractérisé en ce qu'un capuchon (28) est prévu à l'intérieur de l'élément de tôle d'acier (22) pour fermer
sa partie d'extrémité en amont, dans lequel une plaque de séparation (27) est prévue
au niveau de la partie d'extrémité en aval du second élément de tôle d'acier (22)
pour bloquer le passage des gaz d'échappement entre le second élément de tôle d'acier
(22) et le tuyau d'échappement (5).
6. Appareil d'épuration des gaz d'échappement selon l'une quelconque des revendications
2 à 5, dans lequel le cylindre creux (22) est monté sur le tuyau d'échappement (5)
au niveau de sa partie d'extrémité en amont (22a).
7. Appareil d'épuration des gaz d'échappement selon l'une quelconque des revendications
précédentes, dans lequel le premier élément de tôle d'acier (21) comprend deux moitiés
soudées ensemble afin de former le cylindre.
8. Appareil d'épuration des gaz d'échappement selon la revendication 1, comprenant en
outre un troisième épurateur des gaz d'échappement (64) disposé à la suite du deuxième
épurateur des gaz d'échappement (50), ayant un premier élément de tôle d'acier (5)
correspondant prenant la forme d'un cylindre creux et supportant un métal catalytique
sur celui-ci.
9. Appareil d'épuration des gaz d'échappement selon la revendication 8, dans lequel le
second élément de tôle d'acier (52) prend la forme d'une plaque plate.
10. Appareil d'épuration des gaz d'échappement selon l'une quelconque des revendications
1 à 9, dans lequel chacun des premier et deuxième éléments de tôle d'acier (11 ; 22,
52 ; 21, 51 ; 64) a plusieurs ouvertures (11c ; 21a, 22c ; 51c, 52a) formées à travers
son épaisseur de paroi.