Silencer combined with catalytic converter for internal combustion engines and modular diaphragm elements for said silencer

Abstract: The silencer combined with a catalytic converter consists of a housing (12) including an inner tubular element (30) in which a catalytic converter is fitted. The engine exhaust gases enter into the silencer through a venturi nozzle (20), flowing through a series of diaphragms (50,70,80) made of porous ceramic material treated with catalytic materials, and flow out from an exhaust outlet (38) of the silencer depleted of pollutants. The ceramic diaphragms may be cup shaped and provided with through-holes or ogive shaped (72) with perforated walls and they may consist of elements formed by a plate (82) provided with lateral flanges forming opposite cavities (90,100). The elements (50,70,80) may be combined with one another in different manners to form a sequence of chambers(V₀,V₁,V₂...) with shape and volume best suited for each type of engine.

Description: This invention relates to a silencer combined with a catalytic converter apt to convert the exhaust gases originating from internal combustion engines of any type into less harmful gases. The harmful effects of exhaust gases discharged into the atmosphere by internal combustion engines has been evidenced since many years and the rapid increase in the number of motor vehicles in circulation has compelled the more industrialized countries to issue restrictive measures aimed at minimizing the emission of carbon monoxide, unburnt hydrocarbons and nitrogen oxide. As a consequence,catalysts have been developed which, when distributed over a large surface in contact with the exhaust gas stream, are suitable for converting these very polluting agents into substantially harmless gases, such as carbon dioxide, water vapour and nitrogen. On grounds of this knowledge, various kinds of catalytic converters to be fitted upstream of the conventional silencers have been developed and marketed. These converters,however,present various problems such as the duration of their chemical efficiency related to the mechanical lifetime of their structure and to the complexity of the structure itself which lead to very high costs as well as to installation difficulties. Whilst, in future, as a rule, vehicles will have to be factory-fitted with exhaust cleaners, the cost of the latter hampers both the installation of new vehicles and the conversion of the enormous number of already existing vehicles. Catalytic converter-mufflers are already known in the art. Swiss patent 334071 to Mastropaolo et al. discloses a series of bell shaped metallic diaphragms (4) arranged in continuation with a short tubular portion (3). Each diaphragm is provided only with a central aperture (5) with the aim of diminishing the noise of the exhaust gas. This patent relates merely to a silencer and does not provide any teaching on cleaning the exhaust gases by means of porous ceramic diaphragms, as disclosed in the presente application. For instance, US 3.649.213 to De Palma describes a catalytic converter-muffler device having a V-shaped bed configuration providing optimum gas flow characteristics and minimization of differential expansion problems from high-temperature conditions. A preferred unit has an oval outer chamber, a catalyst reservoir section, and curved sidewalls for the internal catalyst retaining screens so as to preclude buckling which occurs with flat plate members. A combination muffler and catalytic converter having low back pressure is disclosed in US 4.094.645 to Bayley. The device incorporates a venturi in the exhaust gas inlet path to add secondary air. The efficiency of the venturi is quite high since back pressures introduced downstream of the venturi are kept low by providing an extremely long outlet cone for the venturi which reverses the flow direction while preventing wall separation and turbulence. Sound attenuation is provided upstream of the venturi where the back pressures produced have a minimum effect in reducing venturi efficiency. A housing for a catalytic medium supported on a metal foil and a catalytic converter containing such supported catalytic medium is described in EP-A-0263893 to Grace. The catalytic converters are said to be especially useful for internal combustion engines whether spark ignited or compression ignited and especially for automotive vehicles. An apparatus only for catalytic purposes or other purification of exhaust gases of internal combustion engines, with two exhaust gas treating bodies and a protection ring between them, is disclosed in EP-A-0387422 to Eberspächer. None of these prior art devices anticipate the specific design of a catalytic silencer of the instant invention. Object of the presente invention is that of providing a silencer including a catalytic converter of low manufacturing cost and long life, for cleaning the exhaust gases whereby the catalytic silencer can be replaced to the existing silencers without any installation problems, thereby performing both functions, viz. silencing and exhaust cleaning in one. According to the invention, the combined silencer catalytic converter consists of an outer housing, fitted in a known manner at the exhaust gas inlet end with a fitting to the engine exhaust manifold said housing containing the catalytic converter, mounted inside an inner tubular element. The latter is provided, upstream of the exhaust gas flow, with an open end into which extends the fitting, forming a venturi nozzle, while the opposite end of said tubular element is closed by an end wall to which the silencer exhaust is connected. In the part of said tubular element comprised between the end of the venturi nozzle and said end wall are inserted a plurality of diaphragms made of porous ceramic material processed with catalytic material for depleting the exhaust gas of the pollutants. Each transversal wall of said diaphragms is provided with suitable ports for the passage of the exhaust gases. Successive expansion chambers for the gases are formed between one diaphragm and the next, so that said gases may be discharged from the end diffuser not only depleted of the pollutants but also at a temperature and pressure close to ambient so that the assembly acts also as an efficient silencer, thereby being easily replaceable as a single unit in like manner as the conventional silencer of any type of vehicle, with minimum installation cost. The form of the porous ceramic diaphragms is conceived so that said diaphragms may be inserted in succession with matching joints of fittings, maintaining intervals and distances predetermined in the laboratory and optimized for each of the numerous vehicle models in circulation, considering that the invention is not dedicated exclusively, although mainly, to replacements on the numerous types of vehicles in circulation. In other words, the catalytic silencer may be manufactured in a short time, without tying up capital and utilizing excessive space, in an assortment of heterogeneous silencers readily available for the great variety of existing vehicles. Evident advantage offered by the catalytic silencer according to the invention is the possibility of keeping in stock a limited quantity of internal and external components of predetermined size which can be assembled according to specifications based on laboratory tests whereby to offer the most suitable type of silencer-catalytic converter depending on the cubic capacity, the power and the type of vehicle. As it will be apparent from the description and the appended claims, the presente invention is not directed to the specific chemical nature of physical properties of the ceramic materials suitable for making the filtering elements of the instant invention, nor is the invention directed to the selection of a specific catalytic material or class of materials. In fact, both ceramic materials and catalytic media for converting CO, HC and NO x are well known in the art. Just by way of example, typical useful ceramic materials are represented by inorganic refractory oxides such as alumina, gamma-alumina, alumina-zirconia, zirconia, silica, cordierite, mullite, carbides such as silicium carbide, nitrides and the like. Examples of suitable catalytic materials are platinum, palladium, silver, oxides such as iron oxide, vanadium oxide, chromium oxide, and in general suitable catalytic media may well include other metals of groups I, V, VI and VIII of the Periodic Table, as it is well known to those skilled in the art. Known is also the fact that these catalytic materials may be used singly or in combination with two or more of them. Also the way of treating the porous ceramic materials with the catalytic media is well known in the art and is outside the scope of the present invention. The invention will now be described with reference to the attached drawings which are illustrative of the inventive idea but which shall not be construed restrictively. In the drawings: Fig. 1 illustrates schematically, in axial cross-section, the housing of the combined silencer-catalytic converter according to the invention, provided with an engine exhaust gas inlet nozzle, with a rear exhaust diffuser and with the tubular element into which the ceramic diaphragms have to be inserted; Fig. 2 is a schematic detailed view of the arrangement of the ceramic diaphragms inside the tubular element of the silencer; Fig. 3 is a cross-section of a first type of the porous ceramic diaphragm; Figures 4 to 6 are rear elevation views of the inventive perforated transversal walls of the diaphragms; Fig. 7 shows, in particular, in cross-section, one of the diverging holes of the transversal wall of a diaphragm; Fig. 8 is a cross-section of a second embodiment of the inventive porous ceramic diaphragm; Fig. 9 is a detailed schematic view of the arrangement of porous ceramic diaphragms shown in Fig. 8; Fig. 10 shows the cross-section of a third embodiment of the inventive porous ceramic diaphragm, and Fig. 11 is a front view of the transversal wall of the diaphragm of Fig. 10, along direction XI; Fig. 1 shows the body of the catalytic silencer, identified, in its entirety, by number 10 and consisting of an outer housing 12 terminating at one end with a substantially semispherical head 14, provided with a conical fitting 15, partly surrounded by a sleeve 16, which fitting engages the exhaust manifold of the engine. Within housing 12 is located a tubular element 30 containing, as it will be seen hereinafter, the porous ceramic diaphragms suitably arranged. The tubular element has one end 32 open towards chamber 34 formed by the semispherical head 14, while at the opposite end, is closed by an end wall 36, to which a convergent exhaust tube 38 is connected, housed in an ogive 40, which acts as a diffuser for the exhaust of the gas into the atmosphere and which terminates substantially in line with the outer housing 12. The fitting 15 of length M has preferably a taper of 13% starring from its inlet section 17, of diameter A, up to section 18 which coincides with the entry of the semispherical chamber 34 and in which diameter B has the following value: B = 2(A/2 - M x 0.13). The fitting 15, located inside chamber 34, is gradually tapered to form a convergent duct or venturi nozzle 20, the end diameter C of which has the following value: C = B / 3.5 developing inside the chamber itself for a length N equal to: The venturi nozzle 20 is provided with at least four transversal holes 19 cut out in the proximity of its connection zone with the semispherical head 14 and from which part of the gas is discharged into the catalytic converter, while the remaining part is discharged from the end hole,leading to an internal decompression. Diameter K of holes 19 has the following value: The average length P of the front chamber, including partially semispherical chamber 34,up to the wall of the first diaphragm, is: where HP is the engine horsepower. K = 2.6 for 4 cylinder engines = 6.8 for 4 cylinder engines = 12.5 for 12 cylinder engines. For Diesel engines the indicated K values must be further multiplied by a factor of 4.25. The end diffuser 38 has,towards the inside of tube 30, the following diameter: where S F represents the overall area of the holes in the terminal diaphragm facing the last chamber formed in the tube 30, as will be described hereinafter. Starting from the end of the venturi nozzle 20, a set of porous ceramic modular diaphragms 50 is positioned in the tube 30, as shown schematically in Fig;2. The average distance d of the diaphragms is very closely equal to: d = ( 0.6 to 2) A passing from small piston displacement engine to large displacement engines. However, said distance d is subject to variations which can be defined only experimentally in the laboratory by checking the pressure in the different chambers,with the engine running. According to Fig.3, the diaphragms 50, cup-shaped, have an external cylindrical form with a diameter strictly commensurate to the inside diameter of the metal tubular element 30, a substantially plane outer surface 51 and a concave inner surface 52, preferably with a parabolic profile so that the gas, flowing from the venturi nozzle, always comes into contact with chambers having rounded surfaces without sharp corners so as to avoid the formation of vortexes and unwanted back pressure phenomena, to ensure proper engine performance. Each transversal wall 53 has, in its depth, a series of through-holes of various types, forms and dimensions, as shown by way of example in Figures 4, 5, 6, made with a circular section 54 or buttonhole shaped 56 or polygonally shaped 58 respectively, or in any mixed configuration whatsoever. Lengthwise, the holes have a frustum trend with the smaller base oriented towards the gas inlet so as to constitute in the gas flow direction a plurality of diverging ducts, as shown in Fig. 7, apt to improve in succession, the expansion of said exhaust gases flowing from one chamber to the other. The angle of divergence alpha lies between 8° and 15°. The ratio of the through-holes in each transversal wall of the diaphragms over the total area may vary and is well defined; transversal walls with a greater ratio value, i.e. with more void spaces, will be fitted progressively toward outlet 38 of the catalytic silencer where the exhaust gases are more expanded. Length H in each diaphragm may also vary to allow to empirically define the volume of each successive chamber according to the volume of the exhaust gases produced by the engine, depending on the cubic capacity and the power of the engine. Fig. 2 shows, by way of example, different possible arrangements for diaphragms 50. From left to right a diaphragm 50a is located with its concave part oriented towards the venturi nozzle 20 to form chamber V₀; then follows a pair of diaphragms 50b and 50c of the same type, opposite to each other and having a length H not necessarily equal to that of diaphragm 50a, to forma a chamber V₁. In this case, the pair of diaphragms 50b and 50c is spaced from diaphragm 50a by a ceramic ring 59 with concave inner surface. Further diaphragms 50d, 50e, 50f, all pointing in the same direction, form a succession of chambers V₂, V₃, V₄, ..... up to chamber V n just before the outlet of the catalytic silencer device. The diaphragms 50, prepared with different perforated surfaces in their transversal wall and of different lengths H, are subjected to imbibition with known catalytic materials in order to cover both the surfaces of their porous structures and the surfaces of through-holes 54, 56 and 58. The exhaust gases flowing in contact with said processed surfaces and porous body of the diaphragms are depurated to conform to the purpose foreseen and they flow out, depleted of the unwanted harmful pollutants, at low temperature and silenced. The periferic walls of the diaphragms form an insulating barrier on the inside of the metal tube 30 surrounding it, which tube however is spaced by an interspace 60 from the outer housing 12, which interspace can also be filled in known manner with fiberglass or rock wool. Fig. 8 shows a second alternative embodiment of the ceramic porous diaphragms which is meant to reduce the number of catalytic elements to be introduced into tubular element 30 to permit a more rapid installation of the silencer. Diaphragm 70 may consist of an ogive body 72 combined with a disc or plate 74 provided with holes of the type shown, by way of example, in Figures 4, 5 and 6 for diaphragm 50 (i.e. 54, 56 or 58). The two elements 72 and 74, are moulded separately and processed with catalytic materials. In order to be securely connected to each other, the body 72 and plate 74 are provided with a suitable joint, as shown, by way of example, in said Fig. 8, and moreover they are securely joined with other suitable means. The ogive body 72 is provided with a plurality of holes 76, 76', 76'' ..., of any form, which allow the gases coming from the chamber V₀ (see Fig. 9) and flowing through plate 74 inside chamber V₁ (formed by ogive 72) to come into contact with the inner wall 73 of the ogive, undergoing a first depletion of the harmful chemicals. On flowing out from chamber V₁, the gases pass into chamber V₂, then into a further chamber V₃ inside ogive 72' and so on, into chambers V₄, V₅, V₆, .... as it can be taken from said Fig. 9. A third advantageous variant of the diaphragm which can be used in combination with a plurality of units is shown in Fig. 10. Within the instant invention, the porous ceramic diaphragm consists of a body, identified as 80, the outer surface 81 of which is preferably cylindrical, and provided internally with a transversal wall 82 to which two flanges 84 and 86 are integrally moulded forming two cavities 90, 100, having opposite apertures 92, 102. The adjacent bottoms of cavities 90 and 100, which delimit the transversal wall 82, are preferably concave and connected to their respective flanges, as shown by the dotted lines in Fig. 10, so as to prevent the formation of a sharp peripheral edge which may at times reduce the performance. The cavities 90 and 100 communicate with each other by means of a plurality of cylindrical and/or conical holes 85, passing through the transversal wall 82 and which can be made in any form, number and dimensions, according to the specific needs and uses, and arranged according to the longitudinal axis x-x of diaphragm 80. Flanges 84 and 86 of the diaphragm 80 can be of different heights s and t and they can afford a wide range of application possibilities allowing to conveniently attain, with just a few elements, a very vast range of volumes V₀, V₁, V₂, .... of the successive chambers. Moreover, by using diaphragms of the type indicated as 80 in Fig. 10, the chambers obtained by opposing the elements to each other always have bottoms connected yet without sharp edges on any part.

Claims: A silencer comprising a housing (12) provided, at its exhaust gas inlet end, with a substantially semispherical head (14) upstream of which is secured a tapered fitting (15) for connection to the exhaust manifold of an internal combustion engine, the silencer further including a tubular element (30) located in said housing (12), said tubular element being open at the end upstream the exhaust gas flow, and into which open end extends said fitting (15) which crosses a chamber (34) formed by said semispherical head (14), said fitting forming a venturi nozzle (20) ending inside the open end of the tubular element (30), while the opposite end of the tubular element (30) is closed by an end wall (36) to which is connected an exhaust tube (38) converging towards the outlet of the silencer, characterized in that in the portion of the inner tubular element (30) between the end of the venturi nozzle (20) and the end wall (36) of said tubular element is inserted a plurality of modular diaphragms (50, 70, 80) made of porous ceramic material processed with catalytic materials for depleting the exhaust gas of its pollutants. A catalytic silencer according to Claim 1, characterized in that the porous ceramic modular diaphragms (50) are cup-shaped, preferably externally cylindrical and provided with a transversal wall (53), the outer surface (51) of which is substantially plane, while the inside surface (52) is concave, preferably with parabolic profile, the transversal wall (53) of said diaphragms being provided with through-holes (54, 56 or 58), of any form, number and area suitable for preventing unwanted harmful back pressure phenomena. A catalytic silencer according to Claim 1, characterized in that the porous ceramic modular diaphragms (70) are formed by an ogive shaped body (72), the wall of which is provided with a plurality of holes (76, 76', 76''....) arranged in various manner, of any form, number and area, depending upon the type of engine, in order to prevent harmful back pressure phenomena, the ogive shaped body being joined to a plate (74) provided with through-holes (54, 56 or 58) diverging towards the inner space of said ogive body. A catalytic silencer according to Claim 1, characterized in that the porous ceramic modular diaphragms (80) are formed by a transversal wall (82) provided peripherally with two lateral flanges (84, 86) which form two opposite cavities (90, 100), said cavities communicating with each other by means of a plurality of through-holes (85) in axial direction through said transversal wall (82). A catalytic silencer according to Claim 2, 3 or 4, characterized in that the form and number of through-holes (54, 56, 58, 76, 85) provided in the transversal walls (53, 82) or in the plate (74) may vary both from one ceramic diaphragm to another and in one and the same of said diaphragms so as to form a total area of through-holes varying from a minimum of 1.5 times up to 4 times the area of the holes of the venturi nozzle (20), preferably 3 times said area. A catalytic silencer according to one or more of Claims 1 to 5, characterized in that the length of the porous ceramic diaphragms and/or of their flanges may vary in order to allow the formation in a modular way of successive chambers (V₀, V₁, V₂ ...), generally of increasing volumes, in the direction of the exhaust tube (38) of the catalytic silencer. A catalytic silencer according to Claim 2, characterized in that the cup shaped porous ceramic modular diaphragms (50) housed in the tubular element (30) are in contact one with the other or they may have ceramic rings (59) interposed between each other.

Inventors: GAVONI ALBINO, GAVONI, ALBINO
Applicants: GAVONI BGM SILENZIATORI SAS, GAVONI B.G.M., SILENZIATORI DI ALBINO GAVONI & C. S.A.S.
Application year: 1992
Main classification: F01N3
IPC codes: F01N3, F01N1