WO2004033866A1

WO2004033866A1 - Housing arranged in an exhaust gas system for a combustion engine

Info

Publication number: WO2004033866A1
Application number: PCT/SE2003/001522
Authority: WO
Inventors: Ragnar Glav; Michael Linden; Stefan Jonsson
Original assignee: Scania Cv Ab (Publ)
Priority date: 2002-10-09
Filing date: 2003-10-01
Publication date: 2004-04-22
Also published as: ATE462872T1; EP1576261A1; KR20050061526A; EP1576261B1; AU2003268799A1; SE520350C2; DE60331950D1; BR0315118A; AU2003268799B2; BRPI0315118B1; SE0202966D0; SE0202966L; KR101001349B1

Abstract

The present invention relates to a converter device intended to be arranged in an exhaust system for a combustion engine. The converter device comprises an outer casing (1), a tubular body (4) which is enclosed by said casing (1), and a passage for leading exhaust gases through the converter device. The passage comprises a first portion (17a) situated externally about the tubular body (4), a second portion (17b) situated inside the tubular body (4) and a third portion (17c) which caters for flow of exhaust gases in a radial direction between the first portion (17a) and the second portion (17b) of the passage. The third portion comprises at least one flowpath (13a, b) which provides exhaust gases with a longer flow route than a substantially rectilinear radial flow between the externally situated first portion (17a) and the internally situated second portion (17b) of the passage.

Description

Housing arranged in an exhaust gas system for a combustion engine

BACKGROUND TO THE INVENTION, AND STATE OF THE ART

The invention relates to a converter device intended to be arranged in an exhaust system for a combustion engine.

The years immediately ahead will see increasingly restrictive requirements being introduced, at least in Europe, with regard to emissions from diesel-powered vehicles. Increasingly severe requirements for effective exhaust gas cleaning are also being set for other types of combustion engines than diesel engines. To be able to meet these emission requirements, exhaust systems of vehicles driven by combustion engines are being equipped with catalysts which inter alia reduce the amount of nitrogen oxides, and particle filters which reduce the amount of soot particles, in exhaust gases. Such exhaust gas cleaning components work largely like a low-pass filter. This means that low-frequency sound, which is the predominant element in exhaust noise, passes almost undamped through the exhaust gas cleaning components. This makes it necessary for a further noise-damping volume to be added to the exhaust system to compensate for the volume occupied by the particle filter and the catalyst cleaner in the exhaust system. Such a converter device will therefore be relatively elongate and will thereby occupy a great deal of space in the vehicle.

SUMMARY OF THE INVENTION

The object ofthe present invention is to provide a converter device which has good sonic damping characteristics with respect in particular to low-frequency noise in an exhaust system for a combustion engine while at the same time being attractive from the point of view of space occupied, flexible and easy to service.

The object stated above is achieved with the device mentioned in the introduction which is characterised by what is indicated in the characterising part of claim 1. Achieving good damping of low-frequency engine noise from a combustion engine usually requires an elongate passage which leads the exhaust gases through the converter device. As the passage according to the present invention comprises a first portion external about the tubular body and a second portion internal to the tubular body, the result is a substantially two-way flow ofthe exhaust gases in the converter device. Such a two-way flow provides a relatively long passage for the exhaust gases through the converter device, thereby automatically providing relatively good sonic damping of low-frequency noise. A suitably shaped passage results in two-way flow in the converter device with relatively little flow resistance. With a suitably shaped passage, the flow resistance need not be much greater than in a conventional converter device with a substantially straight-through passage for the exhaust gases. Introducing a flowpath which provides the exhaust gases with a longer distance of flow than a substantially rectilinear radial flow between the outer first portion and the inner second portion further lengthens the passage without having to increase the length ofthe converter device. The converter device according to the present invention thus provides a long passage for exhaust gases within a short and compact structure which effects very good damping of low-frequency engine noise.

According to a preferred embodiment ofthe present invention, the positioning ofthe flowpath is such as to connect a first space and a second space ofthe passage. A basic principle for damping low-frequency noise is to create a long exhaust line between two relatively large spaces. An effective low-frequency noise damper with a conventional straight flowpath between two such spaces for exhaust gases represents a considerable length and thereby occupies a great deal of space. Suitable positioning ofthe flowpath between two such spaces in the converter device results in a converter device with a short and compact structure which at the same time exhibits good sonic damping characteristics.

According to another preferred embodiment ofthe invention, the flowpath has a spiral extent. Such a spiral path may have a relatively large outside diameter resulting in the flowpath being considerably longer than a substantially rectilinear radial flow route between the first portion situated outside the pipe and the second portion arranged inside the pipe. A spiral flowpath can be made very compact and may be given a main extent in the radial plane. Such a spiral flowpath means that the converter device can be made very short and compact despite constituting a passage of considerable length for exhaust gases. A spiral flowpath also provides substantially optimum gentle control ofthe exhaust flow. The flow losses in the flowpath can thus be kept down to a low level.

According to another preferred embodiment ofthe present invention, the flowpath exhibits a spiral extent of 180° to 1080°. A spiral flowpath need for example only extend one turn to cover a considerable length and provide good sonic damping. The flowpath may exhibit at least one portion with a varying cross-sectional area. The cross-sectional area ofthe flowpath may be varied to achieve controlled damping of the exhaust noise and the flow resistance. The cross-sectional area may, for example, comprise an increasing cross-sectional area in the direction of flow ofthe exhaust gases. An increasing cross-sectional area in the direction of flow reduces the velocity ofthe exhaust gases. The flow resistance through the flowpath will thus be low.

According to another preferred embodiment ofthe present invention, the flowpath comprises at least one profiled section which has a spiral extent. Such a profiled section may be elongate and exhibit a length which corresponds to the length ofthe flowpath. The profiled section thus forms a wall surface ofthe flowpath. The third portion may comprise n flowpaths formed by n profiled sections which are offset 360% from one another. With advantage, at least two flowpaths are used to make it easier for the exhaust gases to flow through. The two flowpaths preferably have their respective inlets and outlets offset 180° from one another. The result is a substantially even distribution of exhaust gases between the two flowpaths. To further facilitate the distribution of exhaust gases between different flowpaths, the number of flowpaths may be increased further. Three or more such flowpaths have with advantage their inlets and outlets offset from one another according to the above formula in order to distribute the exhaust gases evenly between the various flowpaths. The length ofthe third portion may also be increased in this way. According to another preferred embodiment ofthe present invention, the exhaust gases are intended to be led through the passage in a direction such that they first flow through the first portion situated radially outside the pipe before they flow through the second portion situated inside the pipe. Such a direction of flow of exhaust gases through the passage has a number of advantages. Inter alia, it makes the constituent parts ofthe converter device relatively easy to assemble, facilitates the design ofthe flowpath such as to achieve effective sonic damping and simplifies the arranging of any possible burner at the passage inlet. Such a burner is intended where necessary to raise the temperature of exhaust gases before they reach the particle filter. For soot particles in exhaust gases to ignite and burn in the particle filter, the exhaust gases need to have reached a specific temperature.

According to another preferred embodiment ofthe present invention, said flowpath comprises a detachable module. Such a module makes it easy for the flowpath to be assembled and dismantled in the converter device. Such modules may with advantage be manufactured in various versions and sizes. Modules may thus comprise flowpaths of different lengths and in different numbers appropriate to combustion engines of different types and sizes. Said detachable module preferably comprises an endwall of the casing. Such a module forms substantially a side cover which is very easy to fit and remove.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment ofthe invention is described below by way of example with reference to the attached drawings, in which:

Fig. 1 depicts a converter device according to the present invention,

Fig. 2 depicts a section along the line A-A in Fig. 1.

Fig.3 depicts a section along the line B-B in Fig. 1. Fig. 4 depicts a section along the line C-C in Fig. 1 and

Fig. 5 depicts only one module comprising a spiral flowpath.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Fig. 1 depicts a converter device intended to be arranged in an exhaust system for a diesel-powered vehicle. The converter device comprises an external casing 1 which has a substantially cylindrical shape. In Fig. 1, the portion ofthe casing 1 which faces the observer has been removed to show the items arranged inside the casing 1. The casing 1 forms a closed external surface apart from the points where an inlet 2 and an outlet 3 are arranged for the exhaust gases. A pipe 4 of circular cross-section is arranged inside the casing 1 so that centrelines through the casing 1 and the pipe 4 coincide. The length ofthe pipe 4 is such that it extends from a first endwall 5 ofthe casing 1 to a module M which comprises a second endwall 6 ofthe casing 1.

The converter device comprises exhaust cleaning components for cleaning the exhaust gases which flow through a passage which extends between the inlet 2 and the outlet 3. A first exhaust cleaning component in the form of a particle filter 7 is arranged externally about the pipe 4. Fig. 2 depicts a section along the line A-A in Fig. 1. It shows a particle filter 7 extending annularly round the pipe 4. The particle filter 7 has a radial extent such that it entirely fills the radial space between the pipe 4 and the casing 1. The particle filter 7 comprises elongate ducts which have an extent in a first direction 8. The elongate ducts are intended to lead the exhaust gases through the particle filter 7. The particle filter 7 has a constant cross-sectional shape in the direction of flow ofthe exhaust gases. The exhaust gases are therefore led substantially in the first direction 8 through the particle filter 7. The particle filter 7 comprises stop surfaces 9 arranged at appropriate points along the extent ofthe elongate ducts. The stop surfaces cause the exhaust gases to be led at 9 into adjacent elongate ducts in the particle filter. Soot particles are thus caught and burn in the particle filter 7. A second exhaust cleaning component in the form of a catalytic cleaner 10 is arranged inside the pipe 4. The catalytic cleaner 10 is arranged radially within the particle filter 7. The catalytic cleaner 10 also comprises elongate ducts intended to lead the exhaust gases in a substantially second direction 11 through the catalytic cleaner 10. The catalytic cleaner 10 has a constant cross-sectional shape in the exhaust gas flow direction 11. The catalytic cleaner 10 is intended to effect catalytic cleaning ofthe exhaust gases, particularly in order to reduce the nitrogen oxides content ofthe exhaust gases passing through. The particle filter 7 has a larger cross-sectional area than the catalytic cleaner 10 in the plane A depicted in Fig. 2. The result is that the exhaust gases have a lower velocity through the particle filter 7 than through the catalytic cleaner 10. The flow resistance of exhaust gases is related to their flow velocity. Owing to the stop surfaces 9, the exhaust gas flow resistance is normally greater in the particle filter 7 than in the catalytic cleaner 10. Lowering the flow velocity through the particle filter 7 can considerably reduce the total flow resistance tlirough the passage. The cross-sectional area ofthe particle cleaner 7 is preferably about double that ofthe catalytic cleaner 10.

A basic principle for damping low-frequency noise is to create a long exhaust route between two spaces. An effective low-frequency noise damper in which such an exhaust route is straight occupies a great deal of space. Low-frequency sound is the predominant element in the noise from a combustion engine. The converter device comprises sonic damping means designed according to its basic principle. The converter device thus comprises two profiled sections 12a, b which extend spirally. In this case, each ofthe profiled sections 12a, b extends about 1.5 turns, i.e. 540°. The two profiled sections 12a, b form wall surfaces for two spiral flowpaths 13 a, b whose inlets and outlets are offset 180° from one another. The spiral paths 13a, b are arranged inside the module M. The exhaust gases are led in radially via a third portion 17c ofthe passage which comprises said spiral flowpaths 13a, b from a first portion 17a ofthe passage which is situated outside the pipe 4 to a second portion 17b ofthe passage which is situated inside the pipe 4. The space in the passage outside the pipe 4 upstream from the flowpaths 13 a, b constitutes a first space and the space downstream from the flowpaths 13 a, b inside the pipe constitutes a second space. Leading the exhaust gases into said spiral flowpaths 13 a, b with a radial extent results in a long exhaust route without the converter device needing to be elongate in shape. The converter device which thus comprises both exhaust cleaning components and sonic damping components can therefore be made very compact and occupy little space while at the same time displaying very good sonic damping characteristics.

A burner 14 may if necessary be arranged in the vicinity ofthe inlet 2 to the converter device. The purpose ofthe burner 14 is to heat the exhaust gases to a temperature such that soot particles can burn in the particle filter 7. Soot particles normally ignite at a temperature of about 600°C, but in most cases it is difficult to guarantee such a high exhaust temperature even with a high-performance burner 14. The ignition temperature of soot particles has therefore usually to be lowered. This may be achieved by converting the various kinds of nitrogen oxides NO_x arising to nitrogen oxide NO . There are basically two methods for achieving this. According to a first method, CRT (Continuous Regeneration Trap), a separate oxidising catalytic cleaner is arranged for the purpose before the particle filter 7 in the exhaust gas flow direction. In this situation, soot particles ignite at about 225°C in the particle filter 7. According to a second method, CSF (Catalytic Soot Filter), the particle filter 7 is lined with a suitable lining material so that the oxidising catalysis from NO_x to NO₂ takes place directly on the surface ofthe particle filter 7. In this case soot particles ignite at about 250°C. It is also possible by means of various additives in the fuel to achieve a lowered ignition temperature of about 350°C in a conventional particle filter 7.

In cases where a catalytic filter 10 which works by SCR (Selective Catalytic Reduction) is used, injection devices 15 are arranged at the periphery ofthe converter 1 to add an ammonia carrier substance, e.g. in the form of urea. When the ammonia carrier has been added, it needs to be properly mixed in if it is to optimise the performance ofthe catalytic filter 10 in reducing to nitrogen gas and water the ammonia and nitrogen oxides content ofthe exhaust gases passing tlirough. With the elongate spiral flowpaths 13 a, 13b, this is no problem.

The exhaust gases are led into the converter device via the inlet 2. Fig. 3 depicts a section B-B through the converter device at the inlet 2. The exhaust gases are led from the inlet 2 to the first portion 17a ofthe passage, which exhibits a substantially annular space extending externally about the pipe 4. The annular space ofthe first portion 17a ofthe passage affords relatively little flow resistance to the exhaust gases flowing in and imparts to the exhaust gases a substantially even distribution before they are led in an axial direction outside the pipe 4 towards the particle filter 7. Before the exhaust gases reach the particle filter 7, they are heated as necessary by the burner 14 to a temperature such as to guarantee ignition and combustion in the particle filter 7 of soot particles in the exhaust gases. The exhaust gases are led in a first direction 8 through the elongate ducts ofthe particle filter 7. The stop surfaces 9 arranged at suitable points along the elongate ducts in the particle filter 7 force the exhaust gases into adjacent elongate ducts. Depending on the regenerating system and the temperature, the soot particles caught at this stage in the particle filter 7 ignite and burn. The exhaust gases are thus forced to deviate a shorter distance sideways but mainly flow in the first direction 8 along a substantially straight line through the particle filter 7. The exhaust gases flowing out of the particle filter 7 have in principle been cleared of soot particles.

The exhaust gases flowing out ofthe particle filter 7 have a substance in the form of an ammonia carrier added to them by injection devices 15 before they reach the module M. The module M is depicted separately in Fig. 5. The module M comprises a wall surface 18 which abuts sealingly against the pipe 4 in a radially inner region. The wall surface 18 comprises a first inlet 19a whereby the exhaust gases are led into the first flowpath 13 a, and a second inlet 19b whereby the exhaust gases are led into the second flowpath 13b. The spiral profiled sections 12a, b which are partly discernable in the diagram form the first and second flowpaths 13 a, b. The module unit M thus also comprises the second endwall 6 and an outer radial region 20 ofthe casing 1. The module unit M is fitted detachably, e.g. by clamp banding, in a suitable manner together with the other parts ofthe converter device. The exhaust gases are led radially into the module M via one ofthe two flowpaths 13a, b which are formed by the spiral profiled sections 12a, b. The inlets 19a, b to the two flowpaths 13a, b are offset 180° from one another, resulting in a substantially even distribution of exhaust gases between the two flowpaths 13a, b. The exhaust gases successively led in radially via the spiral flowpaths 13 a, b ofthe third portion 17c ofthe passage have a considerably longer transport route than a substantially rectilinear radial flow between the passage's first portion 17a situated outside the pipe 4 and its second portion 17b situated inside the pipe 4. The spiral flowpaths 13 a, b constitute an elongate exhaust route connecting two spaces ofthe passage so that effective sonic damping of low- frequency noise from the diesel engine is achieved. The elongate flowpaths 13a, b also provide a necessary mixing distance for the ammonia carrier so that the latter becomes distributed substantially evenly in the exhaust gases. The exhaust gases are subject to relatively slight changes of direction as they pass through the spiral flowpaths 13 a, b, thereby reducing the flow resistance. The result in the spiral flowpaths 13 a, b is flow in a plane which is substantially perpendicular to the first direction of flow 8 and second direction of flow 11 ofthe exhaust gases. The exhaust gases flowing out from the spiral paths are led into the pipe 4. The exhaust gases flowing out from the flowpaths 13 a, b are received in the centrally situated space 21 ofthe module M before being led into the pipe 4 and towards the catalyst cleaner 10. When the exhaust gases flowing inside the pipe 4 reach the catalyst cleaner 10, they flow into the latter' s elongate ducts. The elongate ducts allow the exhaust gases to flow in the second flow direction 11 which is parallel with, but in the opposite direction to, the first flow direction 8. In the catalytic cleaner 10, the nitrogen oxides and ammonia contained in the exhaust gases are reduced to nitrogen gas and water. Thereafter, the exhaust gases substantially clear of soot particles and nitrogen oxides flow out through the outlet 3. The outlet 3 comprises a well-rounded tapering shape which connects the pipe 4 to a narrower pipe ofthe exhaust system. The narrower pipe 4 is not depicted in the drawings. The shape ofthe outlet 3 means that the exhaust gases are here again subject to very little flow resistance.

The flowpaths 13 a, b are thus comprised within a detachable separate module M which is easy to fit and remove. This means that the endwall 6 and the spiral flowpaths 13 a, b can be fitted as a unit. Such modules M can be manufactured in various versions and sizes. Modules M comprising flowpaths differing in number, length and cross- sectional area can thus be fitted in the converter device, depending inter alia on the type and size of combustion engine. The fitting ofthe module can be by clamp banding.

The invention is in no way limited to the embodiment described but may be varied freely within the scopes ofthe claims. For example, the flowpaths need not necessarily have a spiral extent but may have a curved extent of substantially any desired shape such as to result in a longer exhaust gas route than a substantially rectilinear radial flow. The exhaust gases may alternatively be led in an opposite direction so that they first flow through the pipe 4 on the inside before being led radially outwards, via the flowpaths 13a, b, to a final flow outside the pipe 4. In such a case the particle filter 7 is arranged inside the pipe 4 and the catalyst cleaner 10 outside the pipe 4. The casing 1, the exhaust cleaning components 7, 10 and the pipe 4 need not necessarily be circular in cross-section but may be of substantially any desired functional shape. Nor need the pipe 4 be arranged centrally inside the casing 1 but may have substantially any desired functional positioning

Claims

1. A converter device intended to be arranged in an exhaust system of a combustion engine, which converter device comprises an outer casing (1), a tubular body (4) which is enclosed by said casing (1), and a passage for leading exhaust gases through the converter device, said passage comprising a first portion (17a) situated externally about the tubular body (4), a second portion (17b) situated inside the tubular body (4) and a third portion (17c) which caters for flow of exhaust gases in a radial direction between the first portion (17a) and the second portion (17b) ofthe passage, characterised in that the third portion comprises at least one flowpath (13 a, b) which provides exhaust gases with a longer flow route than a substantially rectilinear radial flow between the externally situated first portion (17a) and the internally situated second portion (17b) ofthe passage.

2. A converter device according to claim 1, characterised in that the positioning ofthe flowpath (13a, b) is such as to connect a first space and a second space ofthe passage.

3. A converter device according to claim 1 or 2, characterised in that the flowpath (13a, b) has a spiral extent.

4. A converter device according to claim 3, characterised in that the flowpath (13 a, b) exhibits a spiral extent of 180° to 1080°.

5. A converter device according to any one ofthe foregoing claims, characterised in that the flowpath (13a, b) exhibits at least one portion with a varying cross-sectional area.

6. A converter device according to any one ofthe foregoing claims 3-5, characterised in that the flowpath (13a, b) comprises at least one profiled section (12a, b) which has a spiral extent.

7. A converter device according to any one ofthe foregoing claims, characterised in that said third portion (17a) ofthe passage comprises n flowpaths (13a, b) formed by n profiled sections (12a, b) which are offset 360° n from one another.

8. A converter device according to claim 7, characterised in that n is greater than or equal to 2.

9. A converter device according to any one ofthe foregoing claims, characterised in that the exhaust gases are intended to be led through the passage in a direction such that they first flow through its first portion (17a) before flowing through its second portion (17b).

10. A converter device according to any one ofthe foregoing claims, characterised in that said flowpath (13a, b) is comprised within a detachable separate module (M).

11. A converter device according to claim 10, characterised in that said detachable module (M) comprises at least an endwall (6) ofthe casing (1).