JP2009024498A - Flexible joint structure of exhaust system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a flexible joint structure of an exhaust system with high heat retainability, and introduce it into a post-processing device without lowering the temperature of the exhaust gas discharged from an engine. <P>SOLUTION: A bellows pipe 4 for absorbing the vibration of the engine is interposed in an exhaust pipe 1. A ceramic blade 5 (ceramic nonwoven fabric is possible) cylindrically knitted with heat insulating ceramic fibers is installed on the outer peripheral part of the bellows pipe 4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a flexible joint structure for an exhaust system.

  Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of a soot fraction composed of carbon and a SOF fraction (Soluble Organic Fraction) composed of a high-boiling hydrocarbon component. Furthermore, the composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. Has been performed conventionally.

  The particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the respective channels partitioned in a lattice shape are alternately sealed, and the channels are not sealed. The outlet is sealed, and only the exhaust gas that has permeated through the porous thin wall that defines each flow path is discharged downstream.

  Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate, but in normal diesel engine operation conditions, there are few opportunities to obtain exhaust temperatures that are high enough for particulates to self-combust, so a catalyst regeneration type that integrally supports an oxidation catalyst. Adoption of a particulate filter is being studied.

  That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible.

  However, even when such a catalyst regeneration type particulate filter is used, the trapped amount exceeds the particulate processing amount in the operation region where the exhaust temperature is low, so such a low exhaust gas. If the operation state at the temperature continues, there is a possibility that the particulate filter will fall into an over trapped state without the regeneration of the particulate filter proceeding well.

  Therefore, a flow-through type oxidation catalyst is separately arranged on the inlet side of the particulate filter, and fuel is added to the exhaust gas on the upstream side of the oxidation catalyst when the amount of particulate accumulation increases. It is considered to perform forced regeneration of the filter.

  That is, the fuel (HC) added upstream from the particulate filter undergoes an oxidation reaction while passing through the oxidation catalyst on the inlet side, and the particulate filter catalyst immediately after the inflow of exhaust gas heated by the reaction heat. The bed temperature is raised, the particulates are burned out, and the particulate filter is regenerated.

  In addition to the particulate filter described above, it has also been proposed to equip the exhaust pipe with a NOx selective reduction catalyst, a NOx occlusion reduction catalyst or the like for the purpose of removing NOx in the exhaust gas as a post-treatment device, Particularly in recent years, an aftertreatment device in which a particulate filter is combined with a NOx storage reduction catalyst has been developed.

  However, even if any of these after-treatment devices is adopted, it is common that a relatively high exhaust temperature above a predetermined temperature is required in order to reliably remove particulates and obtain sufficient catalytic activity. Therefore, it is extremely important to introduce the exhaust gas into the aftertreatment device before the temperature of the exhaust gas discharged from the diesel engine is lowered as much as possible.

  On the other hand, as shown in FIG. 4, in the exhaust pipe 1 to be equipped with the aftertreatment device, the vehicle body 3 (example shown in the figure) by the clamp 2 is used to prevent the breaking stress from acting due to vibration from an engine (not shown). In this case, an elastic bellows tube 4 having a bellows structure is interposed between the portion fixed to the frame) side and the engine side. In such a bellows tube 4, the surface area of the bellows is interposed. Is extremely large and extremely thin, and heat release is large. Therefore, this portion may become a heat release point for exhaust heat and may adversely affect the temperature conditions of the downstream aftertreatment device.

Incidentally, as prior art document information related to this type of exhaust joint flexible joint structure, there is the following Patent Document 1 and the like.
JP-A-10-259716

  However, conventionally, a sheet metal outer cover (not shown in FIG. 4) as disclosed in the above-mentioned Patent Document 1 is arranged on the outer periphery of the snake tube 4 so as not to restrict the expansion and contraction operation of the snake tube 4. Although measures have been taken to increase the heat retaining property of the serpentine tube 4 with this sheet metal outer cover, heat radiation from the serpentine tube 4 cannot be sufficiently prevented simply by arranging the sheet metal outer cover on the outer periphery of the serpentine tube 4. From the viewpoint of enhancing the activity of the aftertreatment device in the operating state where the exhaust temperature is low, it is desired to further improve the heat retention.

  The present invention has been made in view of the above-described circumstances, and realizes an exhaust joint flexible joint structure having higher heat retention than before, and an aftertreatment device without reducing the temperature of exhaust gas discharged from the engine as much as possible. The purpose is to be able to be introduced to.

  The present invention provides a cylindrical ceramic blade or ceramic comprising a serpentine tube in the middle of an exhaust pipe so as to absorb engine vibration, and at least one of an outer peripheral portion and an inner peripheral portion of the serpentine tube made of a heat insulating ceramic fiber. The present invention relates to a flexible joint structure of an exhaust system characterized by comprising a nonwoven fabric.

  Thus, since effective heat insulation is achieved by the ceramic blade or the ceramic nonwoven fabric at least one of the outer peripheral portion and the inner peripheral portion of the serpentine tube, the heat release from the serpentine tube is remarkably suppressed. The above high heat retention is ensured.

  Furthermore, when carrying out the present invention more specifically, a metal blade knitted in a cylindrical shape with a heat-resistant metal wire is attached to the outer peripheral portion of the serpentine tube so that excessive extension of the serpentine tube can be constrained. It is possible to provide a ceramic blade or a ceramic nonwoven fabric between the blade and the serpentine tube.

  Also, a metal blade knitted in a cylindrical shape with a heat-resistant metal wire is attached to the outer periphery of the snake tube so that excessive extension of the snake tube can be constrained, and a ceramic blade or a ceramic nonwoven fabric is provided on the inner periphery of the snake tube. May be.

  According to the above-described flexible joint structure of the exhaust system of the present invention, it is possible to remarkably suppress the heat release from the serpentine tube and to ensure higher heat retention than before, so that the exhaust gas discharged from the engine Can be introduced into the aftertreatment device in the middle of the exhaust pipe without reducing the temperature of the exhaust pipe as much as possible, and it is possible to increase the activity of the aftertreatment device in the operation state where the exhaust temperature is low and to achieve a significant performance improvement. Can be played.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment for carrying out the present invention, and parts denoted by the same reference numerals as those in FIG. 4 represent the same items.

  As shown in FIG. 1, in this embodiment, a ceramic blade 5 knitted in a cylindrical shape with a heat insulating ceramic fiber is provided on the outer periphery of a serpentine tube 4 interposed in the exhaust pipe 1 so as to absorb engine vibration. The ceramic blade 5 is arranged between the metal blade 6 mounted on the outer side and the snake tube 4.

  Here, the ceramic blade 5 has a very low thermal conductivity using a heat insulating ceramic fiber made of silicon, titanium or zirconium, carbon, oxygen, and has an upstream end in the flow direction of the exhaust gas 7. The metal blade 6 is fixed together with the upstream end by a fixture 8 and the downstream end is an unfixed free end.

  On the other hand, the metal blade 6 is knitted in a cylindrical shape with a heat-resistant metal wire, and both the upstream end and the downstream end thereof are fixed at the positions of the upstream end and the downstream end of the serpentine tube 4. , 9 and allows the telescopic operation of the serpentine tube 4 within a predetermined range, while restraining excessive expansion beyond the predetermined range of the serpentine tube 4 and applying an unreasonable damage stress to the serpentine tube 4. Can be avoided.

  Thus, if the flexible joint structure of the exhaust system is configured in this way, effective heat insulation is achieved by the ceramic blade 5 at the outer peripheral portion of the serpentine tube 4, so that heat release from the serpentine tube 4 is remarkably suppressed. The above high heat retention is ensured.

  As a result, the heat release from the serpentine tube 4 can be remarkably suppressed, and a higher heat retention than the conventional one can be ensured. Therefore, the exhaust pipe 1 can be produced without reducing the temperature of the exhaust gas 7 discharged from the engine as much as possible. It can be introduced into the post-treatment device on the way, and the activity of the post-treatment device in the operation state where the exhaust temperature is low can be enhanced to greatly improve performance.

  FIG. 2 shows another embodiment of the present invention. A further metal blade 10 is provided between the ceramic blade 5 and the serpentine tube 4 in the embodiment shown in FIG. Thus, the ceramic blade 5 is sandwiched and protected, and even if configured in this manner, the same operational effects as those of the embodiment of FIG. 1 described above can be obtained.

  FIG. 3 shows still another embodiment of the present invention, in which the metal blade 6 is mounted on the outer peripheral portion of the snake tube 4 and the ceramic blade 5 is provided on the inner peripheral portion of the snake tube 4. Yes, in the example shown here, the upstream end in the flow direction of the exhaust gas 7 is fixed by a dedicated fixing tool 11 and the downstream end is set as a non-fixed free end. The same effects as those of the embodiment shown in FIG.

  In addition, the flexible joint structure of the exhaust system of the present invention is not limited to the above-described embodiment example, and the illustrated example describes the case of a ceramic blade, but it may be a ceramic nonwoven fabric. Of course, the metal blade can be used in combination, and various modifications can be made without departing from the scope of the present invention.

It is sectional drawing which shows an example of the form which implements this invention. It is sectional drawing which shows another example of a form of this invention. It is sectional drawing which shows another example of a form of this invention. It is a side view which shows an example of the flexible joint structure of the conventional exhaust system.

Explanation of symbols

1 Exhaust pipe 4 Snake pipe 5 Ceramic blade 6 Metal blade 7 Exhaust gas 10 Metal blade

Claims (3)

  A serpentine tube is interposed in the middle of the exhaust pipe so as to absorb engine vibration, and a cylindrical ceramic blade or a ceramic nonwoven fabric made of a heat insulating ceramic fiber is provided on at least one of the outer peripheral portion and the inner peripheral portion of the serpentine tube. A flexible joint structure for an exhaust system.   A metal blade knitted in a cylindrical shape with a heat-resistant metal wire was attached to the outer periphery of the snake tube so as to restrain excessive extension of the snake tube, and a ceramic blade or a ceramic nonwoven fabric was provided between the metal blade and the snake tube. The exhaust joint flexible joint structure according to claim 1.   A metal blade knitted in a cylindrical shape with a heat-resistant metal wire is attached to the outer periphery of the snake tube so as to restrain excessive extension of the snake tube, and the ceramic blade or ceramic nonwoven fabric is provided on the inner periphery of the snake tube. The exhaust joint flexible joint structure according to claim 1.

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