JP4982162B2 - Exhaust purification device - Google Patents

Description

  The present invention relates to an exhaust emission control device.

  Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of soot made of carbonaceous matter and SOF content (Soluble Organic Fraction) made of high-boiling hydrocarbon components. 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. It has been done conventionally.

  This type of particulate filter has a porous honeycomb structure made of ceramics such as cordierite, and the inlets of the flow paths partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. The outlet of the passage is sealed, and only the exhaust gas that has permeated through the porous thin wall defining each flow passage is discharged downstream, while the particulates in the exhaust gas are porous. It is collected on the inner surface of the thin wall.

  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 operating conditions, there are few opportunities to obtain exhaust temperatures that are high enough to cause the particulates to self-combust. The curate filter is integrally supported.

  That is, if such a particulate filter carrying an oxidation catalyst is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates are burned and removed even at a lower exhaust temperature than in the past. It becomes possible.

  However, even when such a particulate filter is adopted, the trapped amount exceeds the processing amount of particulates in the operation region where the exhaust temperature is low, so operation at such a low exhaust temperature is required. If the state 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 attached on the inlet side of the particulate filter, and fuel is added upstream from the particulate filter when the amount of particulate accumulation increases, forcing the particulate filter to regenerate. It is considered to do.

  In other words, in this way, the hydrocarbon generated by the fuel addition undergoes an oxidation reaction while passing through the oxidation catalyst, and the inflow of exhaust gas heated by the reaction heat raises the bed temperature of the particulate filter immediately after. Thus, the particulates are burned out, and the particulate filter is regenerated (see, for example, Patent Document 1 below).

  As a specific means for executing this type of fuel addition, post injection is performed at a non-ignition timing later than the compression top dead center following the main injection of fuel performed near the compression top dead center. It is common to add fuel to the exhaust gas.

  On the other hand, when purifying exhaust gas from a diesel engine, it is not sufficient to remove particulates in the exhaust gas as described above, but it is also necessary to remove NOx (nitrogen oxide) contained in the exhaust gas. Therefore, the present inventors have come up with the idea of providing a NOx adsorption catalyst in front of the particulate filter to simultaneously reduce particulates and NOx.

The NOx adsorption catalyst referred to here is an NOx occlusion reduction catalyst that has already been put into practical use (when exhaust air-fuel ratio is lean, the NOx in the exhaust gas is oxidized and temporarily occluded in the form of nitrate, and the exhaust gas are of quite different nature from the O ₂ concentration to have the property of reducing and purifying by decomposing release NOx by intervention, such as hydrocarbons and CO unburned when lowered) in, Ya NOx in the exhaust gas It means a flow-through type catalyst composed of zeolite with excellent ability to physically adsorb hydrocarbons.

  Zeolite is an alumina silicate porous crystal material, characterized by having uniform molecular level pores oriented regularly in the crystal, through which various molecules are inserted into cavities or channels. In addition to these properties, it has a molecular sieving action based on the uniform pores (only adsorbs molecules smaller than the pore diameter), It also has a property of strongly adsorbing polar substances by the action of cations and anions, and a property of catalysis.

  In addition, this type of zeolite is classified into many types based on the type of its skeletal structure, but it has the ability to adsorb NOx and hydrocarbons into the pores under low exhaust temperature conditions, and the adsorbed hydrocarbons are low exhaust. What is necessary is just to select the thing which was excellent in the ability to make it react with oxygen in exhaust gas slowly under temperature conditions, and to make it a sub-oxide hydrocarbon, and high heat resistance and high durability. It is also possible to select from zeolite-related compounds.

If such a NOx adsorption catalyst is installed in the front stage of the particulate filter, NOx and hydrocarbons in the exhaust gas will become NOx adsorption catalyst in an operating state where the exhaust temperature is low so that the existing NOx storage reduction catalyst does not function effectively. Simultaneously adsorbed, the adsorbed hydrocarbons slowly react with oxygen in the exhaust gas under low exhaust temperature conditions to become sub-oxide hydrocarbons, and NO _{2 in} NOx adsorbed on the NOx adsorption catalyst is It will be reduced and purified by reacting with sub-oxidized hydrocarbons.

Moreover, since the oxidation reaction from NO to NO ₂ is also promoted locally by the heat of oxidation reaction of hydrocarbons to sub-oxide hydrocarbons during adsorption, it is newly changed from NO to NO ₂ during adsorption. As a result, it is reduced and purified by reacting with sub-oxidized hydrocarbons, and about 30% of the NOx adsorbed on the NOx adsorption catalyst is reduced and reduced.
JP 2003-193824 A

  However, when the particulate filter is forcibly regenerated by adding fuel, if the NOx adsorption catalyst is arranged in the previous stage of the particulate filter, most of the hydrocarbons generated from the added fuel are adsorbed by the previous NOx adsorption catalyst. As a result, the generation of reaction heat in the oxidation catalyst is delayed, and the NOx adsorption catalyst becomes a heat accumulator, which increases the heat mass and makes it difficult for the exhaust gas temperature to rise, hindering the forced regeneration of the particulate filter. There was a fear.

  Moreover, when the bed temperature of the NOx adsorption catalyst rises to the hydrocarbon release temperature, a large amount of light hydrocarbons that slowly react with oxygen while adsorbed until then is generated. There is a possibility that a rapid increase in temperature may occur due to the active reaction of the hydrocarbons in the subsequent oxidation catalyst, and it is technically difficult to control the addition of fuel to avoid such a rapid increase in temperature. there were.

  Therefore, the present inventors provide a bypass flow path for directing exhaust gas to the oxidation catalyst by bypassing the NOx adsorption catalyst, and providing flow path switching means for switching the flow of exhaust gas to the bypass flow path during forced regeneration. Has been filed as Japanese Patent Application No. 2006-304959.

  However, since the flow path switching means for switching the exhaust gas flow to the bypass flow path itself can also be a heat storage body, the advantage of diverting the NOx adsorption catalyst by reducing the heat mass by the additional amount of the flow path switching means is reduced. There is a concern.

  As a countermeasure, it is considered to divide the flow path switching means with thin sheet metal parts having a small heat mass. However, when the flow path switching means is manufactured with such thin sheet metal parts, the sheet metal parts are divided into sheet metal parts. Since internal distortion due to rolling at the time of manufacture is latent, when the internal distortion appears due to heating in an environment where high-temperature exhaust gas flows, the housing of the flow path switching means is thermally deformed and malfunctions. There was a risk of it happening.

  More specifically, when the flow path switching means is of a type that switches the flow path using a general butterfly valve, when the housing is thermally deformed, the bearing position of the tilting shaft of the butterfly valve is the original design position. There is a possibility that the butterfly valve cannot be normally opened and closed due to the tilting axis deviating from the center position where it should be.

  The present invention has been made in view of the above circumstances, and provides an exhaust emission control device that can perform forced regeneration of a particulate filter satisfactorily without hindrance even if a NOx adsorption catalyst is provided in the previous stage of the particulate filter. The purpose is that.

The present invention includes a particulate filter provided in the middle of an exhaust pipe with an oxidation catalyst attached to the inlet side, and NOx and hydrocarbons in the exhaust gas at a low exhaust temperature condition provided in the front stage of the particulate filter. and a co-adsorbed and the adsorbed NOx adsorbing catalyst the NO ₂ is reacted with nitrous oxide hydrocarbons is an oxidation product of said hydrocarbon reduced purify in NOx, fuel addition upstream of the said NOx adsorbing catalyst Exhaust purification device that forcibly regenerates the particulate filter by adding fuel to the exhaust gas by means and burning the collected particulates by reaction heat when the hydrocarbons generated from the added fuel undergo oxidation reaction with the oxidation catalyst In addition, the bypass passage bypasses the NOx adsorption catalyst and directly leads to the oxidation catalyst, and the exhaust gas flow is switched to the bypass passage during forced regeneration. The flow path switching means is configured to switch the flow path using a butterfly valve, and a bearing member that pivotally supports both ends of the tilting shaft of the butterfly valve is integrally formed with a cast part. The remaining portion of the flow path switching means excluding the cast parts of the bearing member is divided and configured with thin sheet metal parts.

  Thus, when the exhaust emission control device is configured in this way, when the tilting position of the butterfly valve is switched to the side where the bypass passage is opened during forced regeneration of the particulate filter, the exhaust gas passes through the bypass passage and is adsorbed with NOx. Since the catalyst bypasses the catalyst and is directly guided to the oxidation catalyst, it is possible to guide the hydrocarbon generated from the added fuel to the oxidation catalyst without delay and immediately generate heat of reaction. As a result, it becomes difficult for the exhaust gas temperature to rise or the NOx adsorption catalyst generates a large amount of light hydrocarbons at the release temperature, which may cause a rapid increase in the temperature of the subsequent oxidation catalyst. Can be avoided in advance.

  Further, since the tilting shaft of the butterfly valve in the flow path switching means is supported by the bearing member of the cast part, since this type of cast part does not include internal distortion, the bearing member is not thermally deformed (casting). The parts are simply formed by cooling and hardening the melt in the mold, and they contain almost no internal distortion like rolled parts and forged parts, so they are heated in an environment where high-temperature exhaust gas flows. However, there is no fear of thermal deformation), and the possibility that the butterfly valve may malfunction due to the tilting axis of the butterfly valve deviating from the center position should be eliminated.

Further, since the remaining part of the flow path switching means excluding the cast parts of the bearing member is divided by thin sheet metal parts having a small heat mass, it is possible to keep the heat mass of the flow path switching means as a whole small. In addition, the temperature of the exhaust gas during forced regeneration of the particulate filter is likely to increase.

  Furthermore, in the present invention, it is preferable that an inlet flange of the housing of the flow path switching means is also integrally formed with the cast part forming the bearing member. It is possible to perform the assembly at the same time as the assembly of the inlet flange.

  Further, in the present invention, it is preferable that the outer peripheral portion of the housing of the flow path switching means is encapsulated by a heat insulating material, and in this way, the heat retaining property of the flow path switching means is enhanced and the flow path switching means. It is possible to reduce heat loss due to heat radiation of the exhaust gas passing through to the outside air.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

(I) According to the first aspect of the present invention, when the particulate filter is forcibly regenerated by adding fuel, the flow path switching is performed even if a NOx adsorption catalyst is provided in the preceding stage of the particulate filter. By switching the exhaust gas flow to the bypass flow path by the means and bypassing the NOx adsorption catalyst, the hydrocarbon generated from the added fuel can be led to the oxidation catalyst without delay, and the reaction heat can be immediately generated. The adsorption catalyst becomes a heat accumulator, making it difficult for the exhaust gas temperature to rise, or the NOx adsorption catalyst generates a large amount of light hydrocarbons at the release temperature, causing a rapid increase in the temperature of the subsequent oxidation catalyst. It is possible to avoid the possibility of incurring the failure, and furthermore, the malfunction of the butterfly valve due to thermal deformation by integrally forming the bearing member with cast parts Since the remaining portion of the flow path switching means excluding the cast parts of the bearing member is divided into thin sheet metal parts, the overall heat mass of the flow path switching means can be kept small. The forced regeneration of the curate filter can be performed satisfactorily without any trouble.

  (II) According to the invention described in claim 2 of the present invention, the assembly of the bearing member to the flow path switching means can be performed at the same time as the assembly of the inlet flange. Save time and effort.

  (III) According to the invention described in claim 3 of the present invention, it is possible to improve the heat retaining property of the flow path switching means and reduce heat loss due to heat radiation of the exhaust gas passing through the flow path switching means to the outside air. Therefore, the temperature of the exhaust gas during forced regeneration of the particulate filter can be further increased.

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

  1 to 8 show an example of an embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine equipped with a turbocharger 2, and intake air 4 guided from an air cleaner 3 is connected to an intake pipe 5. Through the compressor 2a of the turbocharger 2, the intake air 4 pressurized by the compressor 2a is further sent to the intercooler 6 to be cooled, and the intake air 4 is guided from the intercooler 6 to an intake manifold (not shown). Thus, it is introduced into each cylinder of the diesel engine 1.

  The exhaust gas 7 discharged from each cylinder of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 8, and the exhaust gas 7 driving the turbine 2b passes through the exhaust pipe 9 to the outside of the vehicle. Particulate filter 11 carrying an oxidation catalyst having an enhanced function of assisting the oxidation reaction of the collected particulates in a casing 10 interposed in the middle of the exhaust pipe 9 Is housed.

  As schematically shown in FIG. 2, this particulate filter 11 has a porous honeycomb structure made of ceramic, and the inlets of the respective flow paths 12 partitioned in a lattice pattern are alternately arranged by plug bodies 13. For the flow path 12 that is sealed by the inlet and the inlet is not sealed, the outlet is sealed by the plug 14 and passes through the porous thin wall 15 that partitions each flow path 12. Thus, only the exhaust gas 7 in which the particulates have been collected is discharged downstream.

  Further, a flow-through type oxidation catalyst 16 having a honeycomb structure as schematically shown in FIG. 3 with a part cut away in FIG. 3 is provided in the preceding stage of the particulate filter 11 in the casing 10. No. 16 has an enhanced function to assist the oxidation reaction of hydrocarbons in the exhaust gas 7, and the amount of active species such as Pt and Pd is higher than that of the oxidation catalyst supported on the particulate filter 11 at the subsequent stage. Has become a lot.

Then, wherein the exhaust pipe 9 upstream of the casing 10, a low exhaust temperature conditions of NOx and hydrocarbons in the exhaust gas 7 simultaneously adsorbing and oxidation products of the NO ₂ in the adsorbed in NOx said hydrocarbon A NOx adsorption catalyst 17 that is reduced and purified by reacting with nitrous oxide hydrocarbon is held in a casing 18 and is equipped.

  The NOx adsorption catalyst 17 is a flow-through type made of zeolite having an excellent ability to physically adsorb NOx and hydrocarbons in the exhaust gas 7 as shown schematically in FIG. Although it has a honeycomb structure, it may be made of a zeolite-related compound having similar properties.

  In addition, the exhaust pipe 9 is provided with a bypass passage 19 that guides the exhaust gas 7 directly to the oxidation catalyst 16 by bypassing the NOx adsorption catalyst 17, and branches from the exhaust pipe 9 upstream of the bypass passage 19. A flow path switching means 20 that switches the flow of the exhaust gas 7 from the flow toward the NOx adsorption catalyst 17 to the flow toward the bypass flow path 19 is provided at the place where the exhaust gas 7 is to be performed.

  That is, as shown in FIG. 5, the flow path switching means 20 has a structure in which a butterfly valve 26 is tiltably held through a tilt shaft 27 in a housing 25 interposed in the middle of the exhaust pipe 9. In the forced regeneration, the butterfly valve 26 is tilted from the position indicated by the phantom line in FIG. 5 to the position indicated by the solid line to switch the flow of the exhaust gas 7 to the flow toward the bypass passage 19. In FIG. 5, reference numeral 26a denotes a stainless steel knit spring seal for gas sealing mounted on the outer periphery of the butterfly valve 26.

  Here, the tilting shaft 27 of the butterfly valve 26 penetrates both sides of the housing 25 through a gas seal mechanism (not shown) so as to be rotatable, and is pivotally supported by a bearing member 28 outside the housing 25. The bearing member 28 is integrally formed of cast parts as shown in FIGS.

  That is, in the example shown here, the inlet flange 29 of the housing 25 of the flow path switching means 20 is integrally formed, and the butterfly valve is provided on both sides of the gas inlet 30 opened to the inlet flange 29. A pair of bearing arms 31 are provided so as to support the 26 tilting shafts 27, and the left and right end portions of the tilting shaft 27 protruding from the housing 25 are pivotally supported by the bearing arms 31. The gas inlet 30 is fitted with an inlet pipe portion 32 of a housing 25 and fixed by welding or the like.

  Further, the outer peripheral portion of the housing 25 is encapsulated by glass wool 33 which is a heat insulating material, and the glass wool 33 is covered and held by a cover 34 mounted on the outside thereof.

  Further, the opening / closing operation of the flow path switching means 20 as described above is performed by rotating the tilting shaft 27 via a lever mechanism (not shown) by the actuator 35 provided in the housing 25, and the actuator 35 is driven. The control signal 20a of the control device 21 responsible for forced regeneration of the particulate filter 11 is controlled. When the forced regeneration of the particulate filter 11 is executed by the control device 21, the exhaust gas 7 The flow is switched to the bypass channel 19 side.

  The control device 21 includes a detection signal 22a from an accelerator sensor 22 (load sensor) that detects the accelerator opening as a load of the diesel engine 1, and a detection from a rotation sensor 23 that detects the rotational speed of the diesel engine 1. A signal 23a is input, and a control signal 24a for instructing the fuel injection timing and the injection amount is output to the fuel injection device 24 for injecting fuel into each cylinder of the diesel engine 1. It has become.

  Here, the fuel injection device 24 is composed of a plurality of injectors (not shown) provided for each cylinder, and the solenoid valves of these injectors are appropriately controlled to open by the control signal 24a to inject fuel. Although the timing and the injection amount are appropriately controlled, the control signal 24a for performing the fuel injection control in the normal mode is determined based on the detection signals 22a and 23a from the accelerator sensor 22 and the rotation sensor 23 described above. On the other hand, when forced regeneration of the particulate filter 11 is performed, the mode is switched from the normal mode to the forced regeneration mode, and following the main injection of fuel performed near the compression top dead center (crank angle 0 °). As a result, post-injection is performed at a non-ignition timing that is later than the compression top dead center (start timing is in the range of crank angle 90 ° to 120 °). So that the control signal 24a is determined.

  That is, when post injection is performed at the non-ignition timing later than the compression top dead center following the main injection, unburned fuel (mainly hydrocarbons) is added to the exhaust gas 7 by the post injection. Thus, hydrocarbons (HC gas) generated by the unburned fuel are discharged from the diesel engine 1 together with the exhaust gas 7.

  Note that the switching from the normal mode to the forced regeneration mode in the control device 21 described above estimates the accumulation amount in the particulate filter 11 based on the operating state of the diesel engine 1, and the estimated accumulation amount is a predetermined upper limit value. It is sufficient to switch the mode when the value exceeds.

  For example, while estimating the amount of particulate generation based on the operating state of the diesel engine 1, it is determined whether or not the processing amount of the particulate is in a regeneration region that exceeds the collected amount for the current operating state, A function of excluding the particulate generation amount while the operating state is determined to be in the regeneration region and integrating only the particulate generation amount in the non-regeneration region to obtain the accumulation amount in the particulate filter 11. It is only necessary that the control device 21 has all of them so that the control device 21 can estimate the amount of accumulated particulates.

  Thus, in the exhaust emission control device configured as described above, when it becomes necessary to perform forced regeneration of the particulate filter 11, the control device 21 switches from the normal mode to the forced regeneration mode, and the control device 21 In response to the control signal 24a, the fuel injection device 24 performs fuel addition by post injection, while the actuator 35 that receives the control signal 20a from the control device 21 rotates the tilt shaft 27 via a lever mechanism (not shown). The butterfly valve 26 tilts from the position indicated by the phantom line in FIG. 5 to the position indicated by the solid line to switch the flow of the exhaust gas 7 to the flow toward the bypass flow path 19. Since the adsorbing catalyst 17 is bypassed and guided directly to the oxidation catalyst 16, hydrocarbons generated from the added fuel are led to the oxidation catalyst 16 without delay. It is possible to immediately generate heat of reaction.

  In addition, the NOx adsorption catalyst 17 becomes a heat accumulator, which makes it difficult for the temperature of the exhaust gas 7 to rise, or the NOx adsorption catalyst 17 generates a large amount of light hydrocarbons at the discharge temperature, thereby oxidizing the latter stage. The possibility of causing a rapid temperature increase of the catalyst 16 is avoided in advance.

  Further, since the tilting shaft 27 of the butterfly valve 26 in the flow path switching means 20 is pivotally supported by a bearing member 28 of a cast part, this type of cast part does not include internal distortion, so that the heat deformation of the bearing member 28 is performed. (Casting parts are simply formed by cooling and hardening the melt in the mold and contain almost no internal distortion like rolled parts and forged parts. There is no fear of thermal deformation even if heated below), and the possibility that the butterfly valve 26 may malfunction due to the tilting shaft 27 of the butterfly valve 26 being displaced from the center position should be eliminated.

Further, since the remaining portion of the flow path switching means 20 excluding the cast parts of the bearing member 28 is divided and formed by thin sheet metal parts having a small heat mass, the heat mass as a whole of the flow path switching means 20 can be kept small. Therefore, the temperature of the exhaust gas 7 during the forced regeneration of the particulate filter 11 can be easily increased.

Therefore, according to the above embodiment, when the particulate filter 11 is forcibly regenerated by the addition of fuel, even if the NOx adsorption catalyst 17 is provided upstream of the particulate filter 11, the exhaust gas is discharged by the flow path switching means 20. 7 is switched to the bypass flow path 19 to bypass the NOx adsorption catalyst 17, hydrocarbons generated from the added fuel can be led to the oxidation catalyst 16 without delay, and reaction heat can be immediately generated. If the adsorption catalyst 17 becomes a heat storage body, it becomes difficult for the temperature of the exhaust gas 7 to rise, or if the NOx adsorption catalyst 17 generates a large amount of light hydrocarbons at the release temperature, The possibility of causing a rapid temperature rise can be avoided in advance, and furthermore, by integrally forming the bearing member 28 with cast parts, While the malfunction of the butterfly valve 26 due to thermal deformation is prevented, the remaining part of the flow path switching means 20 excluding the cast parts of the bearing member 28 is divided into thin sheet metal parts so that the entire flow path switching means 20 is configured. Therefore, the forced regeneration of the particulate filter 11 can be performed satisfactorily without hindrance.

  In addition, particularly in the case of this embodiment, the outer peripheral portion of the housing 25 of the flow path switching means 20 is encapsulated by the glass wool 33, so that the heat retaining property of the flow path switching means 20 is increased and the flow path switching means 20 is improved. The heat loss due to the heat radiation of the exhaust gas 7 passing to the outside air can be reduced, so that the temperature of the exhaust gas 7 during the forced regeneration of the particulate filter 11 can be further increased.

  Further, in the present embodiment, the inlet flange 29 of the housing 25 of the flow path switching means 20 is also integrally formed with the cast part that forms the bearing member 28, so that the bearing member 28 is connected to the flow path switching means 20. Assembling can be performed at the same time as the assembling of the inlet flange 29, and the work of assembling the flow path switching means 20 can be saved.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment. In the previous embodiment, the oxidation catalyst is configured separately from the particulate filter. Employs a plug-type particulate filter in which the plug that seals the inlet side of each flow path is placed at a position where the required length enters the flow path from the inlet side end face. It is also possible to support the oxidation catalyst raw material in the range from the position where the plug body is disposed to the entry side end surface and to form the oxidation catalyst integrally with the front part of the particulate filter itself. Shows a case where fuel is added to exhaust gas by adding post-injection at the timing of non-ignition following fuel main injection as fuel addition means for adding fuel to exhaust gas. The exhaust pipe It is also possible to equip the flow side with a separate injector and directly inject fuel into the exhaust pipe. Insulation materials other than glass wool may be used, and the scope of the present invention is not deviated. Of course, various changes can be made.

It is the schematic which shows an example of the form which implements this invention. It is sectional drawing which shows typically the structure of the particulate filter of FIG. FIG. 2 is a perspective view showing the details of the oxidation catalyst of FIG. FIG. 2 is a perspective view showing the details of the NOx adsorption catalyst of FIG. It is sectional drawing which shows the detail of the flow-path switching means of FIG. It is sectional drawing which shows the detail of the bearing member of FIG. It is an arrow directional view of the VII-VII direction of FIG. It is an arrow directional view of the VIII-VIII direction of FIG.

Explanation of symbols

7 Exhaust gas 9 Exhaust pipe 11 Particulate filter 16 Oxidation catalyst 17 NOx adsorption catalyst 19 Bypass flow path 20 Flow path switching means 21 Control device 24 Fuel injection device (fuel addition means)
25 Housing 26 Butterfly valve 27 Tilt shaft 28 Bearing member 29 Inlet flange 33 Glass wool (heat insulating material)

Claims (3)

A particulate filter provided in the middle of the exhaust pipe with an oxidation catalyst attached to the inlet side, and provided at the front stage of the particulate filter to simultaneously adsorb NOx and hydrocarbons in the exhaust gas at low exhaust temperature conditions, and and a the adsorbed NOx adsorption catalyst to NO ₂ in NOx is reacted with nitrous oxide hydrocarbons the oxidation product of the hydrocarbon reduces and purifies the exhaust gas by the fuel addition means at the upstream side of the NOx adsorption catalyst An exhaust gas purification apparatus for forcibly regenerating the particulate filter by burning the collected particulates by reaction heat when hydrocarbons generated from the added fuel undergo an oxidation reaction with an oxidation catalyst. Bypass flow path that directs exhaust gas to the oxidation catalyst by bypassing the NOx adsorption catalyst and flow path switching that switches the exhaust gas flow to the bypass flow path during forced regeneration The flow path switching means is configured to switch the flow path using a butterfly valve, and a bearing member that pivotally supports both ends of the tilting shaft of the butterfly valve is integrally formed of a cast part, and An exhaust emission control device characterized in that the remaining part of the flow path switching means excluding cast parts of the bearing member is divided and configured with thin sheet metal parts.   2. The exhaust emission control device according to claim 1, wherein an inlet flange of a housing of the flow path switching means is also integrally formed with a cast part constituting the bearing member.   The exhaust emission control device according to claim 1 or 2, wherein an outer peripheral portion of the housing of the flow path switching means is encapsulated by a heat insulating material.

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