WO2004079169A1

WO2004079169A1 - A silencer for combustion engine exhaust systems and a method of servicing the exhaust system

Info

Publication number: WO2004079169A1
Application number: PCT/DK2004/000146
Authority: WO
Inventors: Søren Ærendal MIKKELSEN
Original assignee: Chris-Invest A/S
Priority date: 2003-03-05
Filing date: 2004-03-05
Publication date: 2004-09-16
Also published as: DK200300343A; EP1608853A1

Abstract

A silencer (60) has a chamber with one or more first ports (61) and one or more second ports (62) for exhaust gases to flow through the chamber between the first (61) and second ports (62) and a particle filter in the chamber. The silencer (60) is connectable to the exhaust system in a first position with each of the one or more first ports (61) connected to respective ones of corresponding first pipes (67) of the exhaust system for receiving exhaust gases from the engine (66) through the one or more first ports (61), and in a second, reversed position with each of the one or more second ports (62) connected to respective ones of corresponding first pipes (67) of the exhaust system for receiving exhaust gases from the engine (66) through the one or more second ports (62). In both positions the silencer achieves silencing values above a predetermined minimum silencing value, and pressure drop values both below a predetermined maximum pressure drop value.

Description

A silencer for combustion engine exhaust systems and a method of servicing the exhaust system

This invention relates to silencers and purification devices for use with ex- haust systems for combustion engines, in particular for use with heavy-duty diesel engines, and to service of exhaust systems of such engines.

Background

Vehicles driven by a combustion engine produce exhaust gases. Combustion engine exhaust gases contain combustion products, which negatively influence the environment. Motor vehicle exhaust systems may therefore be equipped with a purification device that purifies the exhaust gases. Noise generated by the engine is reduced in silencing devices in the exhaust sys- tern. An exhaust system component for a combustion engine exhaust system, such as a silencer, often includes one or more purification devices and one or more silencing devices and possibly other devices such as a heat recovery device.

Purification devices include catalytic converters and particle filters. Particle filters retain soot particles originating from the engine fuel. Soot particles mainly consist of carbon, which is gradually incinerated in the particle filter. However, particle filters become fouled by retained particles that contain other combustion products, which leave a residue in the particle filter. Typi- cally, such combustion products can be caused by impurities in the engine fuel or by small amounts of engine oil. Additionally, the particle filter also retains metal particles from pistons and cylinder linings, valves and valve seats etc. Such accumulations of deposit in the particle filter degrade the properties of the filter and in particular increase its flow resistance. Consequently, the filter has to be cleaned from time to time. Cleaning of the particle filter can take place at regular, scheduled intervals, e.g. after a predetermined hours of operation, or based on measurements or estimates of the pressure drop over the filter or the silencer.

Today's combustion engine exhaust systems are very complex and comprise one or more exhaust system components in the form of chambers with silencing devices and purification devices. In addition to retaining particles, particle filters often have flow properties and acoustic properties that play an active role in the silencing properties of the exhaust system components.

Cleaning of the fouled particle filter in such complex systems is a time consuming process. The entire exhaust system component must be removed from the vehicle and disassembled in order to get access to the filter. The filter can be removed and cleaned in a separate cleaning facility and reinstalled, or the filter can be turned and reinstalled in a reversed position, so that the flow direction through only the filter is reversed. The exhaust system component must then be reassembled and reinstalled in the exhaust system of the vehicle. If the particle filter has been reversed without cleaning, the engine is set to run for a predetermined period and at predetermined conditions, whereby the accumulated deposit in the filter will be released from the filter and let out of the exhaust system together with the filtered exhaust gases. A service filter is required for collecting the released deposit.

When handling the filter the service people may become exposed to accumulated particles when handling the filter. This is a serious drawback. Further- more, this known method is time consuming, and the exhaust system component must be manufactured with a view to being disassembled and reassembled, which makes the exhaust system unnecessarily complicated.

Exhaust systems exist that have a filter component that contains essentially only a particle filter and that are separate from e.g. the silencer component.

In order to clean the particle filter the filter component is removed from the exhaust system and reinstalled in a reverse position, in which the flow in the filter component and in the particle filter is reversed. This is a relatively simple operation, but the separate filter component requires much space.

Both of the above-mentioned known types of exhaust system suffer from the drawback that when the exhaust systems are handled during service with the purpose of reversing the particle filter, there is a substantial risk that particles accumulated in the particle filter are spilled, and service personnel may be exposed to spilled particles. Great care must therefore be exercised when handling the particle filters.

Summary of the invention

The invention solves this problem by providing a silencer that has a chamber with one or more first ports and one or more second ports for exhaust gases to flow through the chamber between the first and second ports and a particle filter in the chamber. The silencer is connectable to the exhaust system in a first position with each of the one or more first ports connected to respective ones of corresponding first pipes of the exhaust system for receiving exhaust gases from the engine through the one or more first ports, and in a second, reversed position with each of the one or more second ports connected to respective ones of corresponding first pipes of the exhaust system for receiving exhaust gases from the engine through the one or more second ports. In both positions the silencer achieves silencing values above a predetermined minimum silencing value, and pressure drop values both below a predetermined maximum pressure drop value.

This has the advantage that when the particle filter needs cleaning, only the connections of the first and second ports are disassembled, and the entire silencer is removed, reversed and repositioned in its reversed orientation, whereby the flow in the silencer is reversed. The particle filer remains within the chamber of the silencer when the silencer is reversed, and the risk of spilling accumulated particles from the filter is eliminated.

For cleaning the particle filter a service filter or other device for collecting the accumulated deposit in the filter is placed at the end of the final outlet pipe of the exhaust system, and the engine is set to run for the predetermined period and at the predetermined conditions.

In particular, during regular service and maintenance no disassembly and reassembly of the silencer is required, whereby time is saved. Further, since there is no need for disassembling and reassembling the silencer during normal use and service, there is no need for devices that allow such manipulation of the silencer. Fewer components are thereby needed in the silencer, and its manufacture is simpler and less costly.

The internal structure of the silencer of the invention can be symmetrical, but no internal structural symmetry is required; only functional symmetry is required, in particular in relation to flow properties, silencing properties and purification properties. The skilled person is thus given the freedom of con- structing and arranging the internal structure of the silencer to obtain functional symmetry without being limited by requirements for structural symmetry. The skilled person will know how to benefit from this. Here functional symmetry means that the functional properties remain unchanged, when the silencer is reversed. Correspondingly, structural symmetry means that each structure in the component has a symmetrically arranged counterpart.

Preferably, the particle filter is not accessible without destroying the silencer, but, if needed, the particle filter can be accessible e.g. for repair or exchange of the particle filter. The silencer of the invention may have devices for performing several functions related to combustion engine exhaust. Examples are purification devices, silencing devices and heat recovery devices.

Brief description of the drawings

Figures 1-5 show schematically silencers according to the invention,

Figures 6 and 7 illustrate silencers of the invention connected to the exhaust system of a combustion engine, and

Figure 8 is a longitudinal section through a silencer of the invention showing schematically its internal structure.

Detailed description of the invention

In figure 1 is shown a silencer 10 with a main body forming a chamber 13. A first pipe 11 and a second pipe 12 communicate with the interior of the chamber 13 and are arranged at opposite ends of the main body. The first pipe 11 can be used as an inlet pipe for exhaust gases from a combustion engine to receive the exhaust gases within the chamber 13; an arrow at the first pipe 11 indicates this. Likewise, the second pipe 12 can be used as an outlet pipe from the chamber 13; an arrow at the second pipe 12 indicates this. The chamber 13 accommodates a particle filter and a silencer, which are only shown as boxes, since their actual configurations are not part of the invention, but the skilled person knows how to make and arrange such units. In accordance with the invention the functions of the filter and of silencer are symmetrical with respect to flow properties, silencing properties and purification properties, i.e. the same functions are observed when the first pipe 11 is used as inlet pipe for exhaust gases, and the second pipe 12 is used as out- let pipe, and when the second pipe 12 is used as inlet pipe for exhaust gases, and the first pipe 11 is used as outlet pipe from the chamber 13.

The chamber is preferably made as a sealed unit, e.g. by welding, whereby the particle filter and silencer components are inaccessible.

The silencer 10 has an outer configuration that is symmetrical about a vertical axis 14, and the silencer 10 can therefore be reversed by rotating it 180 degrees about the vertical axis of symmetry 14 and thereby be in a function- ally identical configuration. In the reversed position the second pipe 12 can be used as inlet pipe, and the first pipe 11 can be used as outlet pipe.

In figure 2 is shown a second embodiment of a silencer 20 according to the invention. First and second pipes 21 , 22 communicate with a chamber 23 that accommodates a catalytic converter, a filter, a silencer and a heat recovery unit for recovering waste heat in the exhaust gases. Like in the embodiment in figure 1 , the functions of these units in the chamber 23 are symmetrical with respect to flow properties, silencing properties, purification properties and heat recovery properties. The silencer 20 is symmetrical about an axis 24 perpendicular to the plane of the drawing, and by rotating it 180 degrees about the axis of symmetry 24 it will assume a functionally identical configuration. Like in the embodiment in figure 1 , in the thus reversed position the second pipe 22 can be used as inlet pipe, and the first pipe 21 can be used as outlet pipe.

In figure 3 is illustrated a third embodiment of a silencer 30 according to the invention. First and second pipes 31 , 32 communicate with a chamber 33 that may accommodate one or more units of the kind shown in figure 2. The silencer 30 is symmetrical about an axis 34 in a diagonal direction, and by rotating the component about the axis 34 it too will be in a reversed position that is functionally identical to the position shown. In figures 4 and 5 are shown a fourth and a fifth embodiments of silencers 40, 50 that have horizontal axes of symmetry 44, 54, respectively, in the plane of the drawing. The silencers 40, 50 can be reversed by rotation about the re- spective axes 44, 54 to assume a reversed position that is functionally identical to the position shown.

In the embodiments of the invention illustrated in figures 1-5 the first and second pipes may also be referred to as ports.

In figure 6 is shown a combustion engine 66 with an outlet pipe 67 for combustion gases from the engine. An silencer 60, e.g. any one of the embodiments shown in figures 1-5, has a first pipe 61 connected to a first pipe 67 of an exhaust system of the engine 66, and a second pipe 62 connected to a second pipe 68, i.e. the tail pipe, of the exhaust system of the engine 66. The silencer 60 is has a vertical axis of symmetry 64 and can be reversed by rotation about the axis 64 to assume a reversed position that is functionally identical to the position shown.

In figure 6, the second pipe 68 of the exhaust system of the engine 66 may not be present, whereby the second pipe 62 of the silencer is the tailpipe of the exhaust system.

In figure 7 is shown a seventh embodiment of a silencer 70 with two first ports or openings 71 and two second ports 72. The silencer 70 has no protruding pipes and is for inserting into the exhaust system of a combustion engine 75 with two exhaust outlets, such as is common on diesel engines with their cylinders arranged in two rows in a V-form. The two corresponding first pipes 76 are shown each having a flange 77 for being connected to the two first ports 71 of the silencer 70 as indicated in dotted lines. The exhaust system comprises two second pipes 78 each having a flange 79 for being connected to the two second ports 72 of the silencer 70, also as indicated in dotted lines, for receiving exhaust gases from the silencer. Like in figure 6, the silencer 70 can be reversed, whereby its first ports 71 are connected to the flanges 79 of the second pipes 78, and its second ports 72 are connected to the flanges 77 of the first pipes 76.

According to need silencers according to the invention can have any number of first ports and second ports.

In figure 8 is illustrated a silencer 80 in longitudinal section illustrating its internal structure. The silencer 80 has an outer shell 81 that delimits a chamber 82 with a first port 83 and a second port 84. A particle filter 85 is arranged in the chamber 82 and connected to the shell by means of a transversal wall 86 so that exhaust gases can only flow through the particle filter. An intermedi- ate pipe 87 is also connected to the shell by means of a transversal wall 88. The chamber 82 is thus divided into three consecutive sub-chambers. The funnel shape connecting the first and second ports 83 and 84 to the end sub- chambers and the funnel shaped end of the intermediate pipe distribute the flow, and the changes in cross sectional area between sub-chambers and the space between the particle filter and the shell contribute to attenuating the noise in addition to the noise reduction caused solely by the particle filter if contained in a shell sized substantially only big enough to accommodate the particle filter.

The internal structure of the silencer 80 not symmetrical with respect to its two ports, but its flow properties and silencing properties remain substantially unchanged, or the differences are within specified limits, when the silencer is reversed. Naturally, a silencer according to the invention can also have a symmetrical internal structure. In practice both of the pressure drop and the noise attenuation achieved by the silencer in the first position should not be more than a predetermined factor k times 25 % larger, and not more than the factor k times 20 % smaller, than the pressure drop and the noise attenuation, respectively, achieved by the silencer in the second position, where k < 1. For more demanding requirements, smaller values of the factor k can be chosen, e.g. k < 0.5 and k < 0.25, to obtain more uniform performance of the silencer in its two possible positions.

In a silencer according to the invention the interior structure is essentially symmetrical, whereby that the exhaust gas flow through the silencer will meet essentially the same fluid flow boundary geometrical composition in the first position and in the second position, except for such deviations that may be caused, either by manufacturing tolerances and/or by unequal lengths or di- mensions of pipes of the silencer.

A silencer according to the invention can have means for catalytic conversion, either applied to the inner surface(s) of the particle filter, and/or as cata- lytically active surface(s) of one or more additional internal units of the si- lencer. Such catalytically acti ve surfaces can be adapted for catalytic conver- sion of noxious components nto less noxious components of the exhaust gas and / or for promoting oxidat on of oxidizable components of particulate matter accumulated in the one or more filters.

Two methods for determining if silencers are in accordance with the invention will be given in the following.

A non-fouled silencer, e.g. taken as being representative of a series of substantially identical, non-fouled samples of the silencer, is inserted into the exhaust system of e.g. a heavy duty diesel engine, and the pressure drop and insertion loss noise attenuation are measured for both orientations of the silencer. The insertion loss noise attenuation values are determined by comparing measured noise levels outside the exhaust system with the noise level measured when the silencer has been replaced by one or more simple pipes, as it is commonly prescribed in acoustics, to obtain noise attenuation values according to the insertion loss method of determining noise attenuation for silencers.

If it is desired to test silencers in laboratory facilities, or if it is impossible or unpractical to perform measurements involving a real vehicle, the following method can be used. A specimen, taken to be representative of a series of substantially identical non-fouled samples of the silencer, is inserted into one a test rig for measuring the fluid flow resistance and the noise attenuation, where the ports of the silencer are connected to corresponding pipes of the test rig. The silencer is exposed to fluid flow, for determining the pressure drop, and to exhaust gas noise as well. In case that both properties are determined this can be done either in a test rig providing only a gas flow and separately in a test rig equipped with a sound generating device such as a loud speaker for generating noise on the upstream side of the silencer under test, or in a test rig where the properties of the silencer can be determined in the same test rig. Based on recorded values from test rig measurements and using well-known calculation methods pressure drop values and noise reduction values are calculated, and taken as representative of values that would result if the silencer were inserted into the exhaust system. The noise level vs. frequency characteristic of the noise source are also taken into account to establish the noise attenuation in dB(A), where the fluid flow rate is high enough to establish that the aimed noise reduction is not being compromised by regenerated noise. All these features are recorded for both positions of the silencer.

Claims

1. A silencer for insertion into a combustion engine exhaust system, the silencer having an outer shell delimiting a chamber having one or more first ports and one or more second ports for exhaust gases to flow through the chamber between the first and second ports, the silencer having at least one particle filter in the chamber and a silencing structure for causing noise reduction in addition to a noise reduction caused solely by the at least one particle filter if contained in a shell sized substantially only big enough to ac- commodate the at least one particle filter,

the silencer being connectable to the exhaust system in a first position with each of the one or more first ports connected to respective ones of corresponding first pipes of the exhaust system for receiving exhaust gases from the engine through the one or more first ports,

characterized in that the silencer is connectable to the exhaust system in a second position with each of the one or more second ports connected to respective ones of corresponding first pipes of the exhaust system for receiving exhaust gases from the engine through the one or more second ports,

and that

the silencer, in the first position and in the second position, respectively, achieves first and second silencing values both above a predetermined minimum silencing value, and achieves first and second pressure drop values both below a predetermined maximum pressure drop value.

2. A silencer according to claim 1 characterized in that the first and second silencing values and the first and second pressure drop values relate to an unfouled condition of the silencer.

3. A silencer according to any one of claims 1-2 characterized in that each of the first and second ports comprises a pipe with a free end connectable to the corresponding first pipes of the exhaust system.

4. A silencer according to any of claims 2-3 characterized in that the silencer, when inserted into the exhaust system in the first position or in the second position and when the engine is being run at a predetermined engine load, causes a noise attenuation, determined as insertion loss, which is at least 10 dB(A).

5. A silencer according to claim 4 characterized in that the noise attenuation is at least 15 dB(A).

6. A silencer according to any of the preceding claims characterized in that both of the pressure drop and the noise attenuation achieved by the silencer in the first position are not more than a predetermined factor k times 25 % larger, and not more than the factor k times 20 % smaller, than the pressure drop and the noise attenuation, respectively, achieved by the silencer in the second position, where k < 1.

7. A silencer according to claim 6 characterized in that k < 0.5.

8. A silencer according to claim 6 characterized in that k < 0.25.

9. A silencer according to any of claims 2-8 characterized in that its interior structure is essentially symmetrical, whereby that the exhaust gas flow through the silencer will meet essentially the same fluid flow boundary geometrical composition in the first position and in the second position, except for such deviations that may be caused, either by manufacturing tolerances and/or by unequal lengths or dimensions of pipes of the silencer.

10. A silencer according to any of the preceding claims characterized in that the silencer has means for catalytic conversion, either applied to the inner surface(s) of the at least one filter, and/or as catalytically active surface(s) of one or more additional internal units of the silencer, such catalytically active surface(s) being adapted for catalytic conversion of noxious components into less noxious components of the exhaust gas and / or for promoting oxidation of oxidizable components of particulate matter accumulated in the one or more filters.

11. A silencer according to any of the preceding claims characterized in that the silencer has means for heat recovery.

12. A method of servicing an exhaust system of a combustion engine, the exhaust system comprising a silencer having an outer shell delimiting a chamber having one or more first ports and one or more second ports for exhaust gases to flow through the chamber between the first and second ports, the silencer having at least one particle filter in the chamber and a silencing structure for causing noise reduction in addition to a noise reduction caused solely by the al least one particle filler if contained in a shell sized substantially only big enough to accommodate the at least one particle filter,

the silencer being connected to the exhaust system in a first position with each of the one or more first ports connected to respective ones of corre- spending first pipes of the exhaust system for receiving exhaust gases from the engine through the one or more first ports,

the silencer being connectable to the exhaust system in a second position with each of the one or more second ports connected to respective ones of corresponding first pipes of the exhaust system for receiving exhaust gases from the engine through the one or more second ports, the method comprising:

disassembling the silencer form the exhaust system,

reassembling the silencer with the exhaust system in the second position, and

running the engine under predetermined operating conditions for a predeter- mined period of time.

13. A method according to claim 12 characterized in that the silencer is according to any one of claims 1-11.

14. A method according to any one of claims 12-13 characterized by using a service filter for collecting released particles from the at least one particle filter.