Exhaust gas cleaning device for internal combustion engine

Abstract: An exhaust gas cleaning device is disposed in an exhaust pipe (3) connected to an exhaust port (2) of an internal combustion engine (1) . The exhaust gas cleaning device comprises an inner pipe (5) disposed coaxially in the exhaust pipe (3) with a space (4), the inner pipe (5) being provided with a number of perforations (6), and layer structures disposed on inner and outer surfaces of the inner pipe (5) and including a catalyst (8) for cleaning an unburnt component of the exhaust gas flowing in the exhaust pipe (3), each of the layer structures being formed of a meterial having a property nonpoisonous to the catalyst. The layer structure includes a catalyst carrier layer (8) formed by, in one method, fuse injecting a catalyst including solution (8) on an intermediate layer (7) formed on the inner and outer surfaces of the inner pipe (5) and drying the same to remove the liquid compponent. The layer structure (7,8) may be formed on the inner surface of the exhaust pipe (3) to improve the exhaust gas cleaning effect.

Description: The present invention relates to an exhaust gas cleaning device for an internal combustion engine according to the pre-characterizing part of claim 1 and to a method of making such cleaning device. An internal combustion engine mounted to an automobile, for example, is provided with an exhaust port to which an exhaust manifold is connected. The exhaust gas from the combustion chamber of the internal combustion engine generally includes unburnt component. A catalyst member formed by sticking catalyst to a ceramic carrier having a honeycomb shape is attached to the manifold. The exhaust gas flows in the manifold and, during the flowing, the exhaust gas is subjected to an oxidation reaction in contact to the catalyst member to clean the unburnt component in the exhaust gas. In an internal combustion engine having a small size and mounted to a vehicle such as motorcycle, an exhaust pipe is connected to an exhaust port of the engine and a catalyst member of honeycomb shape, for example, formed by sticking a catalyst to a cloth material such as glass wool is disposed to an inner surface of the exhaust pipe by utilizing a press plate, for example. The unburnt component of the exhaust gas from the combustion chamber of the engine is contacted to the catalyst member to thereby clean the unburnt component of the exhaust gas through the oxidation reaction. These conventional techniques are disclosed in, for example, Japanese Patent Publication No. 59-1324 and Japanese Patent Laid-open Publication No. 61-96120. However, with respect to the catalyst of honeycomb shape, since the exhaust gas passes a number of perforations of the honeycomb-shaped catalyst member, the flow area of the exhaust gas is reduced and the exhaust gas flow is influenced with the resistance of the catalyst member of honeycomb shape. This fact results in the lowering of an output of the engine and, particularly, with respect to the small sized engine, the lowering of the outpout adversely affects on the engine performance Moreover, the location of sucu honeycomb shape catalyst member in the manifold makes enlarge the total size of the manifold, this being inconvenient in the construction and the manufacturing cost. Furthermore, the sticking of the catalyst member made of cloth material to the inner surface of the exhaust pipe involves a problem of the sticking thereof as well as cost increasing in addition to problem of performance or durability of the engine itself. In accordance with the pre-characterizing part of claim 1 and 2, DE-A 2 942 728 discloses an exhaust gas cleaning device and a method for making same. The specific composition of the layer structures is not disclosed in the reference. It is to be assumed that the material of the layer structures have a property nonpoisonous to the catalyst. WO-A 89 03 720 discloses a gas cleaning device which may or may not be a multi-layer structure. The purpose of the multi-layer structure is to remove particles from the gas and to remove further poisonous components of the gas. These layer structures are self-supporting elements without specific supporting means on which the layer structures are disposed. EP-A-238 831 discloses a process and an apparatus for making a catalyst core. Spray guns are used to spray a slurry onto the surface of a carrier material which is in the form of a continuous metal strip. The document does not disclose how to form the inner pipe of an exhaust gas cleaning device having the structure defined in the pre-characterizing part of claim 1. EP-A 246 413 discloses to improve the sticking property between a metal carrier and a catalyst material by applying an intermediate layer to the metal carrier plate prior to applying the catalyst material. Prior to applying the catalyst material to the intermediate layer, the intermediate layer is partially solved by an acid, e.g. H₂SO₄. The object of the present invention is to provide an exhaust gas cleaning device having a simple structure and capable of effectively cleaning the exhaust gas in contact to a catalyst means and improving durabililty and performance of the engine. In addition, the object of the invention is to provide a method for making an exhaust gas cleaning device. This object can be achieved according to the characterizing part of claim 2 and claim 1, respectively. The layer structures include first layers formed of a material having a property nonpoisonous to the catalyst on the inner and outer surfaces of the inner pipe and second layers formed on outer surfaces of the first layers as catalyst carrier layers formed by fuse injecting a slurry composed of a catalyst solution and a catalyst carrier and drying the injected slurry to remove a liquid component. The cuter surface of the first layer is formed to exhibit an irregular surface provided with recessed and protruded portions. According to the present invention, the inner pipe as catalyst support means is provided with a number of perforations for ventilation, so that the exhaust gas flowing in the exhaust pipe passes into the inner pipe through the perforations in contact to the catalyst layer formed on the outer and inner surfaces of the inner pipe. The catalyst layer is formed not to directly contact to the inner pipe through a metallic intermediate layer, for example, having nonpoisonous property to the catalyst. In contact to the catalyst, the unburnt component of the exhaust gas is subjected to the oxidization reaction to clean the same. The inner pipe is coaxially disposed in the exhaust pipe with space and the catalyst layer is formed thereon, so that the flow of the exhaust gas is not substantially influenced, thus improving the durability and performance of the engine itself in comparison with a conventional engine provided with an exhaust gas cleaning means. The location of the intermediate layer between the catalyst carrier layer and the outer surface of the inner pipe may weaken the thermal shock and thermal strain due to the heat cycle. In addition, the fuse injection process may form holes in the catalyst carrier layer and the density of the density of the catalyst can be optionally selected by preparing the catalyst including solution. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view of an engine unit and associated members including an exhaust pipe of an motorcycle to which the present invention is applied; Fig. 2 is an enlarged view of an exhaust pipe, partially in section, shown in Fig. 1; Fig. 3 is a sectional view of the exhaust pipe provided with an exhaust gas cleaning device according to the present invention; Fig. 4 is a view showing a fuse injection condition for forming a layer structure of the exhaust gas cleaning device; Figs. 5 to 8 are brief sectional views showing a part of the exhaust gas cleaning device, in which in Fig. 5, one intermediate layer having an irregular surface is formed, in Fig. 6, two intermediate layers are formed, in Fig. 7, a catalyst carrier layer, before treatment, is formed on the intermediate layer and in Fig. 8, the catalyst carrier layer, after treatment, is formed on the intermediate layer; and Figs. 9 and 10 are views similar to those of Figs. 7 and 8, according to a further embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS First, referring to Fig. 1, showing an engine unit and associated elements including an exhaust pipe provided with an exhaust gas cleaning device, an internal combustion engine 1 is provided with an exhuast port 2 for exhausting an exhaust gas from a combustion chamber of the engine 1. To the exhaust port 2 is coupled an exhaust pipe 3, in which an inner pipe 5 is coaxially disposed with a space 4 between the inner surface of the exhaust pipe 3 and the outer surace of the inner pipe 5 as shown in Fig. 2. The inner pipe 5 acts as a support member for supporting a catalyst carrier layer which will be described hereinlater. The rear end portion of the exhaust pipe 3 is connected to an expansion chamber 12 of tubular structure to which a muffler 13 is connected. The exhaust gas from the exhaust pipe 3 is expanded in the expansion chamber 12, silenced in the muffler 13 and thereafter exhausted from the rear end of the muffler 13. The exhaust pipe 3 and the inner pipe 5 are made of steel plate or stainless plate, in a preferred embodiment, and as shown in Fig. 3, the exhaust pipe 3 and the inner pipe 5 are formed by two pipe members 3a, 3b and 5a, 5b respectively, each having a semi-circular cross section with a pair of jointing flanges 3c, 3d and 5c, 5d extending outwardly from both longitudinal sides of the pipe members. These two pipe members 3a, 3b and 5a, 5b are mated and fused together to form the exhaust pipe 3 and the inner pipe 5, in a manner to put the jointing flanges 5c, 5d between the jointing ranges 3c, 3d so as to dispose the inner pipe 5 coaxially in the exhaust pipe 3. A number of perforations 6 are punched to the inner pipe 5 for the purpose of ventilation. As shown in Figs, 4 to 6, one or two intermediate metal layers such as alumina, ceramic or cermet having a nonpoisonous property to a catalyst is fuse injected to the inner and outer surfaces of the inner pipe 5 to form intermediate irregular surface layers 7 including fine recesses and protrusions. The outer surface of each of the intermediate irregular surface layers 7 may be formed to exhibit a coarse surface by grit blusting technique or rubbing the surface by a sand paper, for example. A slurry composed of a catalyst solution and a catalyst carrier made of porous material such as silica aluminum is sticked to the outer surface of the irregular layer 7 by coating technique, for example, as shown in Fig. 7 and when the thus formed layer is burnt to dry the same and remove the liquid component, a catalyst carrier layer 8 including the catalyst is formed to the outer surface of the intermediate layer 7 as shown in Fig 8. According to the method described above, since the catalyst is not directly contacted to the outer surface of the inner pipe 5, the degradation of the catalyst due to the poisonous material can be prevented. In addition, the irregular intermediate layer 7 is heat insulated and, hence, the active temperature of the catalyst can be effectively maintained. The location of the intermediate layer 7 can prevent chemical reaction of the inner pipe and prevent the fusing-out of metallic ions to thereby improve the durability of the inner pipe 5. In addition, the intermediate layer 7 serves to weaken thermal shock and thermal stress due to a heat cycle and thereby to maintain firm adhered state of the catalyst carrier layer 8. For this purpose, it is desired to select the material for the intermediate layer having a coefficient of thermal expansion having a value between those of the inner pipe 5 and the catalyst carrier layer 8b. The exhaust gas contacts to the catalyst carrier layer 8 during the flowing in the exhaust pipe 3 and carries out the oxidation reaction to thereby clean the unburnt component of the exhaust gas. This effect may be further improved by applying the intermediate irregular layer and the catalyst carrier layer of the characters described above to the inner surface of the exhaust pipe 3. Moreover, the inner pipe 5 has the tubular structure, so that the resistance to the exhaust gas flow is effectively reduced and, hence, the lowering of the output of the engine can be minimized. In another embodiment of the present invention in which intermediate film layers are- also formed on the inner and outer surfaces of the inner pipe 5 disposed inside the exhaust pipe 3 as shown in Fig. 2 and catlyst carrier layers are further formed on the outer surface of the intermediate layers. Namely, as shown in Figs. 9 and 10, intermediate film layers 7b are formed by coating metal such as alumina having a nonpoisonous property to the catalyst by an aluminizing method on the inner and outer surfaces of the inner pipe 5. Thereafter, a metallic oxide such as alumina is fuse injected on the outer surfaces of the intermediate film layers 7b to form carrier layers 8b including a number of holes 11 due to the fuse injection procss. The carrier layer 8b is then dipped into a catalyst solution 9 as briefly shown in Fig. 9 to impregnate the catalyst particles 10 into the carryer layer 8b. The thus formed inner pipe 5 is burnt to dry the catalyst including solution layer to thereby form the catalyst carrier layer 8b as shown in Fig. 10. The intermediate film layer 7b and the catalyst carrier layer 8b may be formed on the inner surface of the exhaust pipe 3 to increase the exhaust gas cleaning effect. The location of the intermediate film layer 7b may attain or achieve substantially the same effects and functions as those described herinbefore with reference to the intermediate irregular layer 7.

Claims: A method of making an exhaust gas cleaning device of an internal combustion engine (1), wherein an inner pipe (5) having a number of perforations (6) is disposed coaxially in the exhaust pipe (3) with a space (4) between an outer surface of the inner pipe (5) and an inner surface of the exhaust pipe (3), layer structures (7, 7b, 8, 8b) being disposed on inner and outer surfaces of the inner pipe (5), said layer structures including a catalyst for cleaning an unburnt component of an exhaust gas flowing in the exhaust pipe (3); characterized in that the exhaust pipe (3) and the inner pipe (5) are manufactured by the following steps: A) two plate members are prepared to assemble the exhaust pipe (3); B) said two plate members are formed so as to provide two exhaust pipe members each having a semi-circular cross-section with a pair of jointing flanges extending outwardly from both longitudinal sides of said exhaust pipe members; C) another two plate members are prepared to assemble the inner pipe (5); D) the perforations (6) are punched through the plate material of said another two plate members; E) the another two plate members are formed so as to provide two inner pipe members each having a semi-circular cross-section with a pair of jointing flanges extending outwardly from both longitudinal edges of the two inner pipe members; F) first layers (7, 7b,) of a material having a property nonpoisonous to the catalyst are fuse injected on the inner and outer surfaces of the two inner pipe members (5a, 5b); G) second layers (8, 8b) are formed on outer surfaces of the first layers (7, 7b) as catalyst carrier layers by fuse injecting a slurry composed of a catalyst solution and a catalyst carrier; H) the injected slurry is dried to remove a liquid component, and I) said two exhaust pipe members (3a, 3b) and said two inner pipe members (5a, 5b) are mated and fused together to form the exhaust pipe (3) and inner pipe (5), in a manner to put the jointing flanges of the inner pipe members between the jointing flanges of the exhaust pipe members so as to dispose the inner pipe (5) coaxially in the exhaust pipe (3). An exhaust gas cleaning device of an internal combustion engine (1), which comprises: an exhaust pipe (3) extending from an exhaust port (2) of the internal combustion engine (1), an inner pipe (5) disposed coaxially in the exhaust pipe (3) with a space (4) between an outer surface of the inner pipe (5) and an inner surface of the exhaust pipe (3), said inner pipe (5) being provided with a number Qf perforations (6), and layer structures (7, 7b; 8, 8b) disposed on inner and outer surfaces of the inner pipe (5) and including a catalyst for cleaning an unburnt components of an exhaust gas flowing in the exhaust pipe (3), each of said layer structures being formed of a material having a property nonpoisonous to the catalyst, characterized in that said exhaust pipe (3) and the inner pipe (5) are each assembled by a pair of plate-like members having semi-circular cross-section with a pair of joining flanges extending outwardly from both longitudinal sides of the plate-like members, said layer structures include first layers (7, 7b) consisting of a material having a property nonpoisonous to the catalyst on the inner and outer surfaces of the plate-like members of the inner pipe and second layers (8, 8b) on outer surfaces of the first layers (7, 7b) as catalyst carrier layers consisting of a dried fuse injected slurry containing a catalyst solution wherein said first and second layers (7, 7b; 8, 8b) are provided on the inner and outer surfaces of each of said pair of plate-like members of the inner pipe, the plate-like members are mated and fused together to form said exhaust pipe (3) and inner pipe (5), in a manner to put the jointing flanges of said inner pipe members between the jointing flanges of said exhaust pipe members so as to dispose the inner pipe (5) coaxially in exhaust pipe (3).

Inventors: ARAI HIDEKI, KAWAI MAKOTO, MIYAI KENJI, ARAI, HIDEKI, KAWAI, MAKOTO, MIYAI, KENJI
Applicants: SUZUKI CO LTD, SUZUKI KABUSHIKI KAISHA
Application year: 1990
Main classification: F01N3
IPC codes: F01N3, F01N13