JP2010031718A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device inhibiting accumulation of solids formed from urea water and securing satisfactory exhaust emission control efficiency. <P>SOLUTION: Communication between an upstream side casing 30 and a downstream side casing 34 is provided by a communication path 32 including a first and a second bending part 32a, 32b, and an ammonia selective reduction NOx catalyst 40 selectively reducing NOx in exhaust gas is held in the downstream side casing 34 as reducing agent. Urea water is injected from an urea water injector 44 to exhaust gas flowing in the communication path 32 from the upstream side casing 30. Heat insulating material 56 inhibiting heat radiation from an inside of the communication path 32 to an outside is provided at a zone covering at least part of zone of an inside wall surface of the communication path 32 where the exhaust gas flowing in the first bending part 32a collides with the first bending part 32a. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device provided with urea water supply means for supplying urea water into exhaust gas in order to supply ammonia to a selective ammonia selective reduction catalyst using ammonia as a reducing agent.

Exhaust gas discharged from an engine such as a diesel engine contains particulates, NOx (nitrogen oxides), and the like, which are air pollutants.
Therefore, with regard to particulates, a technology has been conventionally known in which a particulate filter is provided in the exhaust passage of the engine, and the particulates contained in the exhaust are collected by the particulate filter so that the particulates are not released into the atmosphere. ing.

  For NOx, an ammonia selective reduction type NOx catalyst is disposed in the exhaust passage of the engine, and ammonia is supplied to the ammonia selective reduction type NOx catalyst as a reducing agent so that NOx is selectively reduced to purify the exhaust gas. An exhaust emission control device is known. In the ammonia selective reduction type NOx catalyst used here, urea water is supplied into the exhaust on the upstream side, and ammonia generated by hydrolysis of the urea water by the heat of the exhaust is supplied. Then, the NOx reduction between the supplied ammonia and NOx in the exhaust gas is promoted by the ammonia selective reduction type NOx catalyst, whereby NOx is reduced and the exhaust gas is purified.

  As described above, in order to make the exhaust purification device perform a desired exhaust purification function, it is common to employ a plurality of exhaust purification means, and the casing for housing the exhaust purification means employs the exhaust purification means. Depending on the situation, it may be divided into multiple parts. For example, as described above, in order to efficiently collect particulates and reduce NOx, a combination of a particulate filter and an ammonia selective reduction type NOx catalyst is used as an exhaust purification device. Has been proposed by.

The exhaust emission control device of Patent Document 1 includes an upstream casing and a downstream casing that is disposed on the downstream side of the upstream casing and communicates with the upstream casing through a communication path. A upstream oxidation catalyst is accommodated in the upstream casing, and a particulate filter is accommodated downstream of the upstream oxidation catalyst. The pre-oxidation catalyst is used to oxidize NO (nitrogen monoxide) in the exhaust gas to generate NO ₂ (nitrogen dioxide), and to perform continuous regeneration of the particulate filter with this NO ₂ .

On the other hand, an ammonia selective reduction type NOx catalyst is accommodated in the downstream casing, and a downstream oxidation catalyst for detoxifying the ammonia flowing out from the ammonia selective reduction type NOx catalyst downstream of the ammonia selective reduction type NOx catalyst Is housed.
The communication passage that connects the upstream casing and the downstream casing is provided with a urea water injector that injects and supplies urea water into the exhaust gas in the communication passage. The urea water injected from the urea water injector is hydrolyzed by the heat of the exhaust to become ammonia, and is supplied as a reducing agent to the ammonia selective reduction type NOx catalyst.

In this way, when the casing is divided into two parts to accommodate a plurality of exhaust gas purification means, a communication path for communicating both the casings is provided. For example, in the case of an exhaust emission control device used for an engine mounted on a vehicle, the upstream casing and the downstream casing are not necessarily arranged linearly for the convenience of the layout of the on-vehicle equipment. The passage may be provided with a bent portion corresponding to the arrangement of both casings.
JP 2007-162487 A

  However, in the exhaust gas purification apparatus in which such a communication path having a bent portion is used, when urea water is supplied into the exhaust gas flowing in the communication path, the urea water atomized in the exhaust gas communicates in the bent portion. It becomes easy to collide with the inner wall surface of the passage. The temperature of the inner wall surface of the communication path is lower than the temperature of the exhaust gas flowing inside because the outer wall portion of the communication path is in contact with the outside air. For this reason, when urea water atomized in the exhaust gas collides with the inner wall surface of the communication path, it is liquefied on the wall surface, and solid matter such as solid urea is generated by evaporation of water, and is deposited on the inner wall surface of the communication path. There is a problem of end up. If such solid matter accumulates in the communication passage, the flow resistance of the exhaust gas in the communication passage increases and the engine operating efficiency decreases, and the amount of ammonia supplied to the ammonia selective reduction type NOx catalyst is insufficient. Thus, there arises a problem that the exhaust gas purification efficiency by the ammonia selective reduction type NOx catalyst is lowered.

  In order to avoid such a problem, the lower limit value of the exhaust temperature permitting the supply of urea water is increased, and the urea water is supplied only at a relatively high exhaust temperature, thereby atomizing the inner wall surface of the communication passage. It is necessary to make it difficult to liquefy even when the urea water collides, and to make the deposited solid matter gasify again and easily disappear. However, if the lower limit value of the exhaust temperature that permits the supply of urea water is increased in this way, the operating range of the engine that can supply urea water is narrowed, so that sufficient ammonia is supplied to the ammonia selective reduction type NOx catalyst. There is a problem that the exhaust gas purification efficiency of the ammonia selective reduction type NOx catalyst is lowered.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an exhaust purification device capable of suppressing solid accumulation generated from urea water and ensuring good exhaust purification efficiency. It is to provide.

  In order to achieve the above object, an exhaust emission control device according to the present invention includes a first casing that is disposed in an exhaust passage of an engine and contains exhaust purification means for purifying the exhaust of the engine, and a downstream side of the first casing. The second casing interposed in the exhaust passage, and the first casing and the second casing are communicated with each other with a bent portion, and the exhaust discharged from the first casing is guided to the second casing. A communication passage, an ammonia selective reduction type NOx catalyst housed in the second casing and selectively reducing NOx in the exhaust gas using ammonia as a reducing agent, and the first casing to the second casing via the communication passage. Urea water supply means for supplying urea water into the flowing exhaust gas, and a heat dissipation suppressing member provided at the bent portion for suppressing heat dissipation from the inside of the communication path to the outside Characterized in that it comprises (Claim 1).

  According to the exhaust emission control device configured as described above, the exhaust gas that has passed through the first casing flows into the second casing through the communication path. At this time, the urea water supply means supplies urea water into the exhaust gas flowing from the first casing to the second casing through the communication path. The urea water supplied into the exhaust gas is hydrolyzed by the heat of the exhaust gas, and ammonia is generated. The ammonia thus generated flows into the ammonia selective reduction type NOx catalyst in the downstream casing. In the ammonia selective reduction type NOx catalyst, the NOx in the exhaust gas is selectively reduced using ammonia in the exhaust gas as a reducing agent. Is purified.

  A part of the exhaust gas containing the urea water atomized by being supplied from the urea water supply means changes the flow direction while colliding with the inner wall surface of the communication path together with the urea water when passing through the bent portion, and downstream of the bent portion. It flows toward the side. Since the bending portion is provided with a heat dissipation suppressing member that suppresses heat dissipation from the inside of the communication passage to the outside, the temperature of the inner wall surface of the communication passage in the bending portion does not decrease from the temperature of the exhaust flowing inside. It is suppressed. Therefore, even when urea water contained in the exhaust collides with the inner wall surface of the communication path when the exhaust gas passes through the bent portion, generation of solid substances such as solid urea on the inner wall surface of the communication path is suppressed. The

In the exhaust emission control device, the communication path includes an inner pipe through which the engine exhaust flows and an outer pipe provided outside the inner pipe with a space between the inner pipe and the inner pipe. You may make it have the double pipe structure which becomes. In this case, the heat dissipation suppressing member may be a heat insulating material interposed between the inner tube and the outer tube at the bent portion (claim 2).
When the exhaust emission control device is configured in this way, the communication passage has a double pipe structure, so heat dissipation from the inside of the communication passage to the outside is suppressed, and a decrease in the inner wall surface temperature of the inner pipe is suppressed. In addition, the heat radiation from the inside of the communication path to the outside is suppressed by the heat insulating material interposed between the inner pipe and the outer pipe at the bent portion. Therefore, the decrease in the inner wall surface temperature of the inner tube is more effectively suppressed at the bent portion, and solid urea on the inner wall surface of the inner tube can be prevented even if urea water contained in the exhaust collides with the inner wall surface of the inner tube. The production of solids such as is further suppressed.

Specifically, in the exhaust purification apparatus, the heat insulating material is an inner wall surface of the inner tube in which exhaust gas flowing into the bent portion collides at the bent portion in a space between the inner tube and the outer tube. It may be interposed in a region covering at least a part of the region (Claim 3).
When the exhaust gas purification apparatus is configured in this way, the inner wall surface temperature of the inner pipe in the region where the heat insulating material is interposed between the inner pipe and the outer pipe is determined by the double pipe structure of the communication path and the heat insulating material. It is suppressed well by the dressing. Here, the region in which such a heat insulating material is interposed is a region that covers at least a part of the region of the inner wall surface of the inner tube where the exhaust gas flowing into the bent portion collides with the bent portion, and thus is included in the exhaust gas. Even if the urea aqueous solution collides with the inner wall surface of the inner tube, in this region, it is possible to reliably suppress the generation of solid substances such as solid urea on the inner wall surface of the inner tube.

More specifically, in the exhaust gas purification apparatus, the heat insulating material is disposed in a region outside the bending direction of the bending portion in the space between the inner tube and the outer tube in the bending portion. It may be interposed (Claim 4).
Most of the exhaust gas flowing into the bent portion and the urea water contained in the exhaust gas collide with a region of the inner wall surface of the inner tube that is outside the bent direction of the bent portion. Therefore, by interposing a heat insulating material in the region between the inner tube and the outer tube in the bent portion that is on the outer side with respect to the direction in which the bent portion bends, a solid on the inner wall surface of the inner tube is formed. Generation of solid substances such as urea can be effectively suppressed.

Alternatively, the heat dissipation suppressing member may be a cover member provided outside the communication path so as to cover the communication path in the bent portion.
By covering the communication path with the cover member at the bent portion, heat dissipation from the inside of the communication path to the outside is suppressed, and a decrease in the inner wall surface temperature of the communication path is suppressed. Therefore, even if the urea water contained in the exhaust collides with the inner wall surface of the communication path, the generation of solid substances such as solid urea on the inner wall surface of the communication path is suppressed.

Specifically, in the exhaust emission control device, the cover member is provided with a space between the communication passage, and heat insulation is provided in the space between the cover member and the communication passage in the bent portion. A material may be interposed (Claim 6).
When the exhaust emission control device is configured in this manner, the cover member is provided at the bent portion, so that heat radiation from the inside of the communication path to the outside is suppressed, and a decrease in the inner wall surface temperature of the communication path is suppressed. In addition, heat radiation from the inside of the communication path to the outside is suppressed by the heat insulating material interposed between the cover member and the communication path. Therefore, in the bent portion, a decrease in temperature on the inner wall surface of the communication path is more effectively suppressed, and even if urea water contained in the exhaust collides with the inner wall surface of the communication path, solid urea on the inner wall surface of the communication path The production of solids such as is further suppressed.

More specifically, in the exhaust gas purification apparatus, the heat insulating material is an inner side of the communication path where exhaust gas flowing into the bent portion collides at the bent portion in a space between the cover member and the communication path. You may interpose in the area | region which covers at least one part of the area | region of a wall surface (Claim 7).
When the exhaust emission control device is configured in this way, the inner wall surface temperature of the communication path in the region where the heat insulating material is interposed between the cover member and the communication path is satisfactorily suppressed by the cover member and the heat insulating material. Here, the region in which such a heat insulating material is interposed is a region that covers at least a part of the region of the inner wall surface of the communication path where the exhaust gas flowing into the bent portion collides with the bent portion, and thus is included in the exhaust gas. Even if the urea aqueous solution collides with the inner wall surface of the communication path, in this region, generation of solid substances such as solid urea on the inner wall surface of the communication path can be reliably suppressed.

More specifically, in the exhaust purification apparatus, the heat insulating material is disposed in a region outside the bending direction of the space between the cover member and the communication path in the bending portion. It may be interposed (claim 8).
Most of the exhaust gas that has flowed into the bent portion and the urea water contained in the exhaust gas collide with the inner wall surface of the communication path in the region that is outside the bent direction of the bent portion. Therefore, by interposing a heat insulating material in a region outside the bending direction of the space between the cover member and the communication path in the bent portion, a solid on the inner wall surface of the communication path is formed. Generation of solid substances such as urea can be effectively suppressed.

Further, in the exhaust purification apparatus, when the communication path has a plurality of bent portions, the collision plate may be provided at a bent portion on the most upstream side among the bent portions of the communication path. .
When the heat radiation suppressing member is not provided in the bent portion, as described above, the urea water atomized in the exhaust collides with the inner wall surface of the communication path in the bent portion, and becomes a solid material by depriving heat. For this reason, solids are likely to be generated particularly in the first collision portion. Therefore, when the communication passage has a plurality of bent portions, by providing a heat radiation suppressing member at the most upstream bent portion, the solid matter from urea water accompanying the collision with the communication passage of urea water contained in the exhaust gas Generation and deposition are well suppressed.

  The first casing has a cylindrical shape, the second casing has a cylindrical shape, and is disposed laterally with respect to the central axis of the first casing. One end of the communication passage is at the first casing. The other end may be connected to the side wall of the second casing, and the urea water supply means injects urea water into the communication path connected to the first casing. You may do it.

  In the case of the exhaust gas purification apparatus configured as described above, the communication path whose one end is connected to the side wall of the first casing is arranged laterally with respect to the central axis of the first casing by being bent by the bent portion. The other end is connected to the side wall of the second casing.

  According to the exhaust emission control device of the present invention, the temperature of the inner wall surface of the communication path in the bent portion is the exhaust gas flowing in the bent portion by providing the heat dissipation suppressing member in the bent portion for suppressing heat dissipation from the inside of the communication passage to the outside. The decrease from the temperature is suppressed. For this reason, when the exhaust gas passes through the bent portion, even if urea water contained in the exhaust collides with the inner wall surface of the communication path, the generation and deposition of solid substances such as solid urea on the inner wall surface of the communication path Can be suppressed.

  Therefore, it is not necessary to increase the lower limit of the exhaust temperature that permits the supply of urea water to prevent the solid matter produced from urea water from accumulating, and without reducing the operating range of the engine that can supply urea water. I'm sorry. In addition, it is possible to prevent an insufficient supply amount of ammonia to the ammonia selective reduction type NOx catalyst accompanying the production of solids such as urea from urea water. As a result, it is possible to secure the ammonia supply amount required for the ammonia selective reduction type NOx catalyst, and it is possible to maintain the exhaust purification efficiency of the ammonia selective reduction type NOx catalyst favorably.

  Further, as in the exhaust purification device of claim 2, when the communication path has a double pipe structure and a heat insulating material is interposed between the inner pipe and the outer pipe at the bent portion, the double pipe structure is used. By suppressing the heat radiation from the inside of the communication path to the outside, a decrease in the temperature of the inner wall surface of the inner pipe is suppressed, and the heat release from the inside of the communication path is suppressed by the heat insulating material. Therefore, the decrease in the inner wall surface temperature of the inner tube is more effectively suppressed at the bent portion, and solid urea on the inner wall surface of the inner tube can be prevented even if urea water contained in the exhaust collides with the inner wall surface of the inner tube. The production of solid matter such as can be more favorably suppressed.

Further, as in the exhaust emission control device according to claim 3, when the heat insulating material is interposed in a region covering at least part of the region of the inner wall surface of the inner pipe where the exhaust gas flowing into the bent portion collides with the bent portion, the heat insulating material In the region where the is interposed, the production of solid substances such as solid urea on the inner wall surface of the inner tube can be reliably suppressed.
Further, as in the exhaust emission control device according to claim 4, when a heat insulating material is interposed in a region outside the bending direction of the space between the inner tube and the outer tube in the bent portion. In addition, the temperature drop of the inner wall surface of the inner pipe in the region where the exhaust gas and the urea water in the exhaust gas easily collide is well suppressed, and the generation of solid substances such as solid urea on the inner wall surface of the inner pipe is effectively suppressed. be able to.

  Further, as in the exhaust emission control device according to claim 5, when the communication path is covered with the cover member at the bent portion, heat radiation from the inside of the communication path to the outside is suppressed by the cover member, and the inner wall surface of the communication path A decrease in temperature is suppressed. For this reason, even when the urea water contained in the exhaust collides with the inner wall surface of the communication path when the exhaust gas passes through the bent portion, the generation of solid substances such as solid urea on the inner wall surface of the communication path is improved. Can be suppressed.

  Further, when the heat insulating material is interposed between the cover member and the communication path as in the exhaust gas purification apparatus of the sixth aspect, the heat dissipation from the inside to the outside of the communication path by the cover member is suppressed, so that the communication path In addition to suppressing a decrease in the inner wall surface temperature, heat radiation from the inside of the communication path to the outside is suppressed by a heat insulating material interposed between the cover member and the communication path. Therefore, in the bent portion, a decrease in temperature on the inner wall surface of the communication path is more effectively suppressed, and even if urea water contained in the exhaust collides with the inner wall surface of the communication path, solid urea on the inner wall surface of the communication path The production of solids such as can be suppressed even better.

Further, as in the exhaust emission control device according to claim 7, when the heat insulating material is interposed in a region covering at least a part of the region of the inner wall surface of the communication passage where the exhaust gas flowing into the bent portion collides with the bent portion, Even if the urea water contained collides with the inner wall surface of the communication path, in this region, the production of solid substances such as solid urea on the inner wall surface of the communication path can be reliably suppressed.
Further, as in the exhaust emission control device according to claim 8, when a heat insulating material is interposed in a region outside the bending direction of the bending portion in the space between the cover member and the communication path in the bending portion. In addition, the temperature drop of the inner wall surface of the communication path in the exhaust gas and the area where urea water in the exhaust gas easily collides is well suppressed, and the generation of solid substances such as solid urea on the inner wall surface of the communication path is effectively suppressed. be able to.

In addition, when the communication passage has a plurality of bent portions as in the exhaust emission control device of claim 9, heat radiation is suppressed at the most upstream bent portion where solid matter is easily generated from urea water atomized in the exhaust gas. Since the member is provided, it is possible to satisfactorily suppress the generation and accumulation of solid matter from the urea water accompanying the collision with the inner wall surface of the urea water communication path included in the exhaust gas.
According to the exhaust emission control device of the tenth aspect, the second casing is disposed laterally with respect to the central axis of the first casing, one end of the communication passage is connected to the side wall of the first casing, and the other end Is connected to the side wall of the second casing, the communication path has a bent portion having a relatively high degree of bending. The greater the degree of bending, the greater the possibility of generation of solid matter due to the collision of urea water with the inner wall surface of the communication path. Therefore, the present invention is particularly effective for an exhaust purification device having such a communication path. is there.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram of a four-cylinder diesel engine (hereinafter referred to as an engine) to which an exhaust emission control device according to a first embodiment of the present invention is applied. First, the first embodiment will be described with reference to FIG. The configuration of the exhaust emission control device will be described.
The engine 1 is mounted on a vehicle (not shown) as a power source for driving the vehicle. The engine 1 includes a high-pressure accumulator chamber (hereinafter referred to as a common rail) 2 common to each cylinder. In the engine 1, high-pressure fuel supplied from a fuel injection pump (not shown) and stored in the common rail 2 is supplied to a fuel injection valve 4 provided in each cylinder, and fuel is supplied from each fuel injection valve 4 into each cylinder. Is injected.

  The intake passage 6 is equipped with a turbocharger 8. The intake air drawn from an air cleaner (not shown) flows into the compressor 8a of the turbocharger 8 from the intake passage 6, and the intake air supercharged by the compressor 8a is intercooler. 10 and the intake control valve 12 are introduced into the intake manifold 14. An intake air amount sensor 16 for detecting an intake air flow rate to the engine 1 is provided upstream of the compressor 8a in the intake passage 6.

On the other hand, an exhaust port (not shown) through which exhaust is discharged from each cylinder of the engine 1 is connected to an exhaust pipe 20 via an exhaust manifold 18. An EGR passage 24 that communicates the exhaust manifold 18 and the intake manifold 14 via the EGR valve 22 is provided between the exhaust manifold 18 and the intake manifold 14.
The exhaust pipe 20 is connected to the exhaust aftertreatment device 28 via the turbine 8 b of the turbocharger 8 and the exhaust throttle valve 26. The rotating shaft of the turbine 8b is mechanically connected to the rotating shaft of the compressor 8a, and the turbine 8b receives the exhaust flowing in the exhaust pipe 20 and drives the compressor 8a.

  The exhaust after-treatment device 28 includes a cylindrical upstream casing (first casing) 30 and a downstream casing (second casing) 34 that is communicated with the downstream side of the upstream casing 30 through a communication passage 32 to form a cylinder. It consists of. A pre-stage oxidation catalyst 36 is accommodated in the upstream casing 30, and a particulate filter (hereinafter referred to as a filter) 38 is accommodated on the downstream side of the pre-stage oxidation catalyst 36. These pre-stage oxidation catalyst 36 and filter 38 correspond to the exhaust purification means of the present invention.

  The filter 38 is provided for collecting particulates in the exhaust gas and purifying the exhaust gas of the engine 1. The filter 38 is made of a honeycomb-type ceramic body, and a large number of passages communicating with the upstream side and the downstream side are arranged side by side, and the upstream side opening and the downstream side opening of the passage are alternately closed. Particulates in the exhaust are collected as the exhaust flows inside.

Since the pre-stage oxidation catalyst 36 oxidizes NO (nitrogen monoxide) in the exhaust gas to generate NO ₂ (nitrogen dioxide), the pre-stage oxidation catalyst 36 and the filter 38 are arranged in this manner, so that the filter 38 captures them. The collected particulates react with NO ₂ supplied from the pre-stage oxidation catalyst 36 to be oxidized, whereby the filter 38 is continuously regenerated.

On the other hand, in the downstream casing 34, an ammonia selective reduction type NOx catalyst (hereinafter referred to as an SCR catalyst) 40 that purifies exhaust by selectively reducing NOx (nitrogen oxide) in exhaust using ammonia in exhaust as a reducing agent. And a downstream oxidation catalyst 42 for removing ammonia flowing out from the SCR catalyst 40 from the exhaust gas. The post-stage oxidation catalyst 42 also has a function of oxidizing CO (carbon monoxide) generated when particulates are incinerated by forced regeneration of the filter 38 and discharging it into the atmosphere as CO ₂ (carbon dioxide). Yes.

  A urea water injector (urea water supply means) 44 is provided on the downstream side of the filter 38 of the upstream casing 30 to inject and supply urea water into the exhaust gas flowing out from the filter 38 and flowing into the communication passage 32. The urea water is supplied to the urea water injector 44 from a urea water tank (not shown). Further, an exhaust gas temperature sensor 46 that detects the temperature of the exhaust gas that flows out of the filter 38 and flows into the communication passage 32 is provided in the vicinity of the urea water injector 44.

  As shown in FIG. 1, the urea water injector 44 and the exhaust temperature sensor 46 are attached to a step portion formed in a direction approaching the central axis from the peripheral surface of the cylindrical upstream casing 30. By mounting the urea water injector 44 and the exhaust temperature sensor 46 at such a position, the exhaust temperature detection point of the exhaust temperature sensor 46 is brought closer to the central portion of the exhaust gas flowing out from the filter 38 to improve the detection accuracy of the exhaust temperature. In addition, the urea water injected from the urea water injector 44 is diffused as evenly as possible into the exhaust gas flowing out from the filter 38.

The urea water injected from the urea water injector 44 is atomized in the exhaust gas, hydrolyzed by the heat of the exhaust gas, converted into ammonia, and supplied to the SCR catalyst 40. The SCR catalyst 40 reduces NOx to harmless N ₂ by promoting a denitration reaction between the supplied ammonia and NOx in the exhaust. At this time, if ammonia flows out of the SCR catalyst 40 without reacting with NOx, the ammonia is removed from the exhaust gas by the post-stage oxidation catalyst 42.

The exhaust aftertreatment device 28 shown in FIG. 1 corresponds to the arrangement of the upstream casing 30 and the downstream casing 34 when viewed from above, and the downstream casing 34 is conveniently mounted on the vehicle. Is arranged laterally with respect to the central axis of the upstream casing 30 having a cylindrical shape.
The upstream end of the communication path 32 is connected to the side wall of the upstream casing 30 via an outflow portion 30 a provided on the side wall of the upstream casing 30 at a position downstream of the filter 38. On the other hand, the downstream end of the communication path 32 is connected to the side wall of the downstream casing 34 via an inflow portion 34 a provided on the side wall of the downstream casing 34 at a position upstream of the SCR catalyst 40. . And in order to enable such a connection, the communicating part 32 has two bent parts, a first bent part 32a and a second bent part 32b downstream of the first bent part 32a.

  On the side wall of the downstream casing 34 at a position downstream of the rear-stage oxidation catalyst 42, an outflow portion 34b extending in the opposite direction in plan view to the extending direction of the inflow portion 34a is provided, A tail pipe 48 for releasing the exhaust gas that has passed through the downstream casing 34 into the atmosphere is connected to the side wall of the downstream casing 34 via the outflow portion 34b. Therefore, the exhaust pipe 20 and the tail pipe 48 correspond to the exhaust passage in the present invention.

  The urea water injector 44 is mounted at a position facing the outflow portion 30 a of the upstream casing 30, and the urea water injection direction is directed to the communication path 32 as indicated by a one-dot chain line in FIG. 1. Since the outer wall surface of the communication path 32 is exposed to the outside air, the inner wall surface of the communication path 32 is at a temperature lower than the temperature of the exhaust flowing inside, and the urea water atomized in the exhaust is When it collides with the inner wall surface of the communication path 32, urea water may be liquefied again due to a decrease in temperature and may adhere to the inner wall surface of the communication path 32. From the urea water adhering to the inner wall surface, the water of the urea water evaporates due to the heat of the exhaust, so that solids such as urea (hereinafter collectively referred to as urea) are deposited and deposited on the inner wall surface of the communication path 32. To do.

  Therefore, in the present embodiment, the exhaust gas that flows out from the filter 38 and then flows into the communication path 32 and flows toward the downstream casing 34, as described above, from the urea water injector 44 toward the communication path 32. By injecting the urea water, it is possible to prevent the injected urea water from colliding with the inner wall surface of the communication path 32 as much as possible, and to suppress the deposition of urea solid matter on the inner wall surface of the communication path 32. Yes.

  The engine 1 supplies fuel supply control for supplying an amount of fuel required for operation of the engine 1 from the fuel injection valve 4 to each cylinder, and an amount of urea water required for the SCR catalyst 40 is urea water. An ECU 50 is provided that performs overall control for maintaining good operating performance and exhaust purification performance of the engine 1, such as urea water supply control for supplying from the injector 44. In order to perform these controls, on the input side of the ECU 50, in addition to the intake air amount sensor 16 and the exhaust gas temperature sensor 46, a rotational speed sensor 52 that detects the rotational speed of the engine 1, and the depression amount of an accelerator pedal (not shown) Various sensors such as an accelerator opening sensor 54 are detected. On the other hand, various devices such as the fuel injection valve 4, the intake control valve 12, the EGR valve 22, the exhaust throttle valve 26, and the urea water injector 44 are connected to the output side of the ECU 50 as the above-described various control targets.

  Since the urea water supply control performed by the ECU 50 is already widely known, a detailed description thereof is omitted here, but the ECU 50 supplies urea water into the exhaust based on the detection value of the exhaust temperature sensor 46. When it is determined that the exhaust temperature can be supplied without hindrance, the required amount of urea water is supplied to the SCR catalyst 40 based on the NOx emission amount from the engine 1 obtained from the detection values of various sensors. The urea water injector 44 is controlled.

  In order to prevent the urea water supplied from the urea water injector 44 from colliding with the inner wall surface of the communication path 32, the urea water is injected into the communication path 32 as described above. The first bent portion 32a and the second bent portion 32b have two bent portions, and when the exhaust gas passes through the communication path 32, the urea water atomized in the exhaust gas is the first and second bent portions. There is a possibility of colliding with the inner wall surfaces of 32a and 32b. When such a collision occurs, the urea water atomized in the exhaust gas is liquefied on the inner wall surface of the colliding communication passage 32, and as described above, urea solid matter is deposited and deposited on the inner wall surface. It will be. In particular, since the first bent portion 32a is located on the most upstream side among the plurality of bent portions of the communication passage 32, most of the urea water contained in the exhaust gas is first inside the communication passage 32 in the first bent portion 32a. There is a possibility of colliding with the wall. Accordingly, the first bent portion 32 a can be a portion where urea is easily deposited in the communication path 32.

  If the precipitation and deposition of urea solids in the communication path 32 continues, the exhaust flow resistance in the communication path 32 increases, the exhaust pressure of the engine 1 increases, and the operating efficiency of the engine 1 decreases. There is a possibility that the amount of ammonia supplied to the SCR catalyst 40 is reduced from the required amount, and the selective reduction of NOx by the SCR catalyst 40 is not sufficiently performed. Therefore, in the present embodiment, among the two bent portions of the first bent portion 32a and the second bent portion 32b, the first bent portion 32a in which urea solids are most likely to precipitate as described above, The structure for suppressing the heat radiation from the outside to the outside and suppressing the temperature drop of the inner wall surface of the communication passage 32 is provided.

Hereinafter, such a configuration provided in the communication path 32 will be described in detail with reference to FIGS. 2 and 3. 2 is a schematic cross-sectional view showing the first bent portion 32a of the communication passage 32 and its peripheral portion, and FIG. 3 is a schematic cross-sectional view taken along line III-III in FIG.
The communication path 32 is configured by a double pipe including an inner pipe 32c through which exhaust gas flows and an outer pipe 32d provided outside the inner pipe 32c and having an outer wall surface touching the outside air. An air layer is formed between the inner tube 32c and the outer tube 32d, and the heat of the exhaust gas flowing in the inner tube 32c is difficult to escape into the outside air.

  Of the space between the inner tube 32c and the outer tube 32d in the first bent portion 32a, most of the region of the inner wall surface of the inner tube 32c where the exhaust gas flowing into the first bent portion 32a collides with the first bent portion 32a. As shown in FIG. 2 and FIG. 3, a heat insulating material (heat radiation suppressing member) 56 is interposed in the region that covers. The heat insulating material 56 is made of, for example, glass wool or rock wool having heat resistance. In the portion where the heat insulating material 56 is provided, in addition to the double tube structure composed of the inner tube 32c and the outer tube 32d, such a heat insulating material 56 is provided, so that the portion without the heat insulating material 56 is provided. Thus, the heat radiation from the inside of the communication path 32 to the outside is further suppressed, and the temperature drop of the inner wall surface of the inner pipe 32c is favorably suppressed.

  Most of the exhaust gas that flows into the first bent portion 32a in the direction of the arrow A in FIG. 2 and collides with the inner wall surface of the inner pipe 32c in the first bent portion 32a is the progress of the exhaust gas. It collides with the inner wall surface of the inner tube 32c positioned in the direction, that is, the inner wall surface of the inner tube 32c that is on the outer side with respect to the direction in which the first bent portion 32a bends. Therefore, as shown in FIG. 2, the heat insulating material 56 covers most of the region of the inner pipe 32 c located in the traveling direction of the exhaust gas flowing into the first bent portion 32 a with the overall flow direction as the direction of the arrow A. In this way, the first bent portion 32a is interposed between the inner tube 32c and the outer tube 32d.

3 is a cross-sectional view taken along the line III-III in FIG. 2, and the upper side is the outer side with respect to the bending direction on the paper surface of FIG. The upper part of the circumference of the inner tube 32c is provided so as to cover the portion above the central axis of the inner tube 32c.
By providing the heat insulating material 56 in such a region, most of the region of the inner wall surface of the inner tube 32c where the exhaust gas flowing into the first bent portion 32a collides with the first bent portion 32a, that is, the urea water in the exhaust gas is discharged. The region of the inner wall surface of the inner tube 32c that is likely to collide is covered with the heat insulating material 56 interposed between the inner tube 32c and the outer tube 32d, and the temperature drop is reliably suppressed.

Thereby, even if urea water contained in the exhaust flows into the first bent portion 32a together with the exhaust and collides with the inner wall surface of the inner pipe 32c in the first bent portion 32a, urea or the like from the urea water in the exhaust Precipitation and deposition of solid matter can be suppressed satisfactorily and reliably.
Therefore, in the urea water supply control from the urea water injector 44 performed by the ECU 50, the lower limit of the exhaust temperature that permits the supply of urea water for the purpose of preventing accumulation of solid matter generated from the urea water in the first bent portion 32a. It is not necessary to increase the value, and the operating range of the engine 1 that enables the supply of urea water can be expanded as compared with the conventional urea water supply control. In addition, it is possible to prevent an insufficient supply amount of ammonia to the SCR catalyst 40 due to the generation of solids such as urea from urea water. As a result, it is possible to appropriately secure the ammonia supply amount necessary for the SCR catalyst 40, and to maintain the exhaust purification efficiency of the SCR catalyst 40 favorably.

  Furthermore, in the first embodiment, as described above, the heat insulating material 56 is provided only in the region where the collision between the urea water in the exhaust and the inner wall surface of the inner pipe 32c is likely to occur in the first bent portion 32a. Precipitation and deposition of solid substances such as urea from urea water in the exhaust gas can be effectively suppressed while suppressing the amount of heat insulating material 56 used. Therefore, the material cost of the exhaust purification device can be kept low.

  Note that the region where the heat insulating material 56 is provided is not limited to the above-described region, and a solid state precipitation from urea water in the first bent portion 32a, a temperature distribution on the inner wall surface of the inner tube 32c, and the like are previously tested. The heat insulating material 56 may be provided in a region where the possibility of precipitation of solid matter from urea water due to a decrease in the inner wall surface temperature of the inner tube 32c is considered in the first bent portion 32a. . However, when the heat insulating material 56 is provided in the region adopted in the first embodiment, the heat insulating material 56 is provided in the region where the collision between the urea water and the inner wall surface of the inner pipe 32c is likely to occur as described above. Since it did in this way, the effect that precipitation and deposition of solid substances, such as urea, can be suppressed favorably and reliably can be acquired notably. In addition, although the material cost of the exhaust purification device increases, the heat insulating material 56 may be provided on the entire circumference in the circumferential direction of the first bent portion 32a.

  Next, an exhaust emission control device according to a second embodiment of the present invention will be described in detail. The engine system to which the exhaust emission control device according to the second embodiment is applied is configured as shown in FIG. 1 as in the first embodiment described above. The exhaust gas purification apparatus according to the second embodiment is different from the first embodiment described above in the configuration of the first bent portion 32a of the communication path 32. In the following, the same members as those in the first embodiment will not be described in detail by using the same reference numerals as the corresponding members in the first embodiment, and detailed descriptions will be given focusing on the portions that are different from the first embodiment. .

FIG. 4 is a schematic configuration diagram showing the first bent portion 32a of the communication passage 32 and its peripheral portion in the exhaust gas purification apparatus according to the second embodiment. 5 is a schematic sectional view taken along the line VV in FIG. 4, and FIG. 6 is a schematic sectional view taken along the line VI-VI in FIG.
The communication path 32 has a double pipe structure including an inner pipe 32c and an outer pipe 32d, as in the first embodiment. As shown in FIGS. 4 to 6, the first bent portion 32 a of the communication path 32 is provided with a cover member (heat radiation suppressing member) 156 so as to cover the entire circumference in the circumferential direction of the first bent portion 32 a. Yes. The cover member 156 is formed using, for example, an aluminum material or a steel plate plated with aluminum.

  The cover member 156 is divided into two along the central axis, and each includes a cover main body 156a and a flange portion 156b joined when the two cover main bodies 156a are combined with each other to form the cover member 156. The flange portions 156b joined when the cover member 156 is formed are fixed to each other via bolts 156c and nuts 156d. Further, the two cover main bodies 156a have a space between the outer pipe 32d and the outer pipe 32d by screwing a screw 156e to the bracket 158 welded to the outer wall surface of the outer pipe 32d of the communication path 32. It is fixed to 32d.

  Thus, by providing the cover member 156 so as to cover the first bent portion 32a of the communication path 32, the portion where the cover member 156 is provided has a double tube structure of the inner tube 32c and the outer tube 32d. In addition to the suppression of heat radiation from the inside of the communication path 32 to the outside, the cover member 156 suppresses the heat radiation from the inside of the communication path 32 to the outside, and the temperature decrease of the inner wall surface of the inner pipe 32c is favorably suppressed.

  The region of the inner wall surface of the inner pipe 32c where the exhaust gas flowing into the first bent portion 32a collides at the first bent portion 32a with the overall flow direction as indicated by the arrow A in FIG. 6 is the cover member 156 as described above. Even if urea water contained in the exhaust flows into the first bent portion 32a together with the exhaust and collides with the inner wall surface of the inner pipe 32c in the first bent portion 32a, the cover member as described above is covered. By suppressing the temperature decrease by 156, precipitation and deposition of solid substances such as urea from urea water in the exhaust can be satisfactorily suppressed.

Therefore, in the urea water supply control from the urea water injector 44 performed by the ECU 50, the lower limit of the exhaust temperature that permits the supply of urea water for the purpose of preventing accumulation of solid matter generated from the urea water in the first bent portion 32a. It is not necessary to increase the value, and the operating range of the engine 1 that enables the supply of urea water can be expanded as compared with the conventional urea water supply control. In addition, it is possible to prevent an insufficient supply amount of ammonia to the SCR catalyst 40 due to the generation of solids such as urea from urea water. As a result, it is possible to appropriately secure the ammonia supply amount necessary for the SCR catalyst 40, and to maintain the exhaust purification efficiency of the SCR catalyst 40 favorably.
In the present embodiment, the entire first bent portion 32a is covered with the cover member 156 in the axial direction of the communication passage 32. However, only a part of the first bent portion 32a is covered with the cover member 156. May be. In this case, the state of precipitation of the solid matter from the urea water in the first bent portion 32a and the temperature distribution on the inner wall surface of the inner pipe 32c are grasped in advance by experiments or the like, and the portion where the solid matter is most likely to precipitate is centered. Further, it is effective to cover a part of the first bent portion 32a with the cover member 156.

  In the present embodiment, a space is provided between the cover main body 156a of the cover member 156 and the outer tube 32d of the communication path 32, and the cover member 156 is provided in the first bent portion 32a. You may make it interpose a heat insulating material in a part of formed space. Therefore, hereinafter, an exhaust emission control device having such a heat insulating material between the cover main body 156a and the outer pipe 32d of the communication passage 32 will be described with reference to FIGS. 7 and 8 as a modification of the present embodiment.

  In addition, the engine system to which this exhaust purification device is applied is also configured as shown in FIG. 1 as in the first embodiment described above, and the exhaust purification device of this modification is provided with a heat insulating material, The configuration is the same as in the second embodiment described above. Hereinafter, the same members as those in the first and second embodiments are denoted by the same reference numerals as the corresponding members in the first and second embodiments, and detailed description thereof is omitted, which is different from the first and second embodiments. Detailed explanation will be given focusing on the part.

FIG. 7 is a schematic cross-sectional view showing the first bent portion 32a of the communication passage 32 and its peripheral portion in the exhaust purification apparatus of the present modification, similarly to FIG. 6, and FIG. 8 is a VIII-VIII line in FIG. It is a schematic sectional drawing in alignment with.
As described above, the present modification is different from the second embodiment only in that the heat insulating material 256 is provided. In other words, in the present modification, in the space between the outer tube 32d and the cover member 156 in the first bent portion 32a, the exhaust gas flowing into the first bent portion 32a collides with the inner tube 32c that collides with the first bent portion 32a. As shown in FIGS. 7 and 8, a heat insulating material (heat dissipation suppressing member) 256 is interposed in a region that covers most of the wall surface region. The heat insulating material 256 is made of glass wool or rock wool having heat resistance, for example. In the portion where the heat insulating material 256 is provided, the heat insulating material 256 is provided by providing such a heat insulating material 256 in addition to the double tube structure including the inner tube 32c and the outer tube 32d and the cover member 156. Heat radiation from the inside of the communication passage 32 to the outside is further suppressed as compared with the portion where the inner tube 32c is not formed, and the temperature drop of the inner wall surface of the inner tube 32c is further suppressed.

  Most of the exhaust gas that flows into the first bent portion 32a in the direction of the arrow A in FIG. 7 and collides with the inner wall surface of the inner pipe 32c in the first bent portion 32a is the progress of the exhaust gas. It collides with the inner wall surface of the inner tube 32c positioned in the direction, that is, the inner wall surface of the inner tube 32c that is on the outer side with respect to the direction in which the first bent portion 32a bends. Therefore, as shown in FIG. 7, the heat insulating material 256 covers most of the region of the inner pipe 32 c located in the traveling direction of the exhaust gas flowing into the first bent portion 32 a with the overall flow direction as the direction of the arrow A. As described above, the first bent portion 32a is interposed between the outer tube 32d and the cover member 156.

8 is a cross-sectional view taken along line VIII-VIII in FIG. 7, and the upper side is the outer side with respect to the bending direction on the paper surface of FIG. 8, but the heat insulating material 256 is a cross section shown in FIG. In FIG. 3, the upper portion of the inner tube 32c is provided so as to cover the portion above the central axis of the inner tube 32c, that is, the upper half of the circumference of the inner tube 32c.
By providing the heat insulating material 256 in such a region, most of the region of the inner wall surface of the inner tube 32c where the exhaust gas flowing into the first bent portion 32a collides with the first bent portion 32a, that is, urea water in the exhaust gas is discharged. The region of the inner wall surface of the inner tube 32c that is likely to collide is covered with the heat insulating material 256 interposed between the cover member 156 and the outer tube 32d, and the temperature drop is reliably suppressed.

Thereby, even if urea water contained in the exhaust flows into the first bent portion 32a together with the exhaust and collides with the inner wall surface of the inner pipe 32c in the first bent portion 32a, urea or the like from the urea water in the exhaust Solid matter precipitation and deposition can be suppressed even better and reliably.
Therefore, in the urea water supply control from the urea water injector 44 performed by the ECU 50, the lower limit of the exhaust temperature that permits the supply of urea water for the purpose of preventing accumulation of solid matter generated from the urea water in the first bent portion 32a. It is not necessary to increase the value, and the operating range of the engine 1 that enables the supply of urea water can be expanded as compared with the conventional urea water supply control. In addition, it is possible to prevent an insufficient supply amount of ammonia to the SCR catalyst 40 due to the generation of solids such as urea from urea water. As a result, it is possible to appropriately secure the ammonia supply amount necessary for the SCR catalyst 40, and to maintain the exhaust purification efficiency of the SCR catalyst 40 favorably.

  Furthermore, in this modification, the heat insulating material 256 is provided only in the region where the collision between the exhaust gas in the first bent portion 32a and the urea water in the exhaust gas and the inner wall surface of the inner pipe 32c is likely to occur. While suppressing the amount of material 256 used, precipitation and deposition of solid substances such as urea from urea water in the exhaust gas can be effectively suppressed. Therefore, the material cost of the exhaust purification device can be kept low.

  Note that the region where the heat insulating material 256 is provided is not limited to the above-described region, and the solid state precipitation from the urea water in the first bent portion 32a, the temperature distribution of the inner wall surface of the inner tube 32c, and the like are previously tested. The heat insulating material 256 may be provided in a region where the possibility of solid matter precipitation from the urea water is high in the first bent portion 32a. However, when the heat insulating material 256 is provided in the region employed in the above modification, it is possible to obtain a remarkable effect that the precipitation and deposition of solid substances such as urea can be suppressed well and reliably. Further, although the material cost of the exhaust purification device increases, the heat insulating material 256 may be provided on the entire circumference of the first bent portion 32a.

  Although the description of the exhaust emission control device according to the embodiment of the present invention has been completed above, the present invention is not limited to the first embodiment, the second embodiment, or the modifications thereof, and various modifications can be made. For example, in each embodiment and modification, the communication path 32 has a double pipe structure, but a communication path having a single pipe structure may be adopted. In this case, although the effect of suppressing the temperature drop by the double tube structure cannot be obtained, the effect by the heat insulating material and the cover member can be obtained similarly.

  Moreover, in each embodiment and modification, the heat insulating material and cover member corresponded to the heat-radiation suppression member of this invention only in the 1st bending part 32a of the most upstream among the 1st bending parts 32a and the 2nd bending parts 32b. However, a similar heat dissipation suppressing member may be provided in the second bent portion 32b. In this case, the second bent portion 32b may be the same type as the heat dissipation suppressing member provided in the first bent portion 32a, or each of the first bent portion 32a and the second bent portion 32b may be implemented. You may make it select and employ | adopt the heat dissipation suppression member of a different type from the heat dissipation suppression member used by the form and the modification, respectively. Furthermore, the present invention can be similarly applied to the case where a communication passage having three or more bent portions is used. In this case as well, it is effective to provide the heat dissipation suppressing member only at the most upstream bent portion, but the heat dissipation suppressing member may be provided at a predetermined number of bent portions or all the bent portions from the upstream side. Good.

  Moreover, in 2nd Embodiment, although the cover member 156 spaced apart from the communicating path 32 in the 1st bending part 32a was used as a heat dissipation suppression member of this invention, a cover member is attached so that it may closely_contact | adhere to the outer wall surface of the communicating path 32. You may make it provide. In this case, it is more effective to form the cover member with a heat insulating material made of glass wool or rock wool having heat resistance, for example. Furthermore, in the second embodiment, the cover member 156 has a two-part structure. However, when the cover member is formed of a heat insulating material, for example, a belt-shaped heat insulating material may be wound around the outer wall surface of the communication path 32.

Moreover, the division method of the cover member 156 in the second embodiment is an example, and the number of divisions and the form of division can be variously changed as necessary. Further, the division of the cover member 156 is not essential, and the cover member may be attached to the communication path without being divided.
In the above-described embodiment, the present invention is applied to the exhaust aftertreatment device 28 in which the downstream casing 34 is disposed laterally with respect to the central axis of the upstream casing 30. It is not limited. For example, even in an exhaust aftertreatment device in which a downstream casing is disposed in the direction of the central axis of the upstream casing and both casings communicate with each other through a communication path having a bent portion, The effect of can be obtained.

  Furthermore, in the above embodiment, the upstream oxidation catalyst 36 and the filter 38 are accommodated in the upstream casing 30, and the SCR catalyst 40 and the downstream oxidation catalyst 42 are accommodated in the downstream casing 34. The exhaust purification member housed in the casing is not limited to this. The SCR catalyst is housed in the downstream casing, and the downstream casing is connected to the upstream casing through a communication passage having a bent portion. The same effect can be obtained if the exhaust aftertreatment device is configured to supply urea water into the exhaust gas flowing toward the front.

  In the above embodiment, the engine 1 is a four-cylinder diesel engine. However, the number of cylinders and the type of the engine 1 are not limited thereto, and urea water is supplied and NOx in the exhaust gas is exhausted by the SCR catalyst. Similarly, the present invention can be applied to any engine in which selective reduction is performed.

1 is an overall configuration diagram of an engine system to which an exhaust emission control device according to an embodiment of the present invention is applied. It is a schematic sectional drawing which shows the principal part of a communicating path in the exhaust gas purification apparatus which concerns on 1st Embodiment of this invention. It is a schematic sectional drawing which follows the III-III line | wire in FIG. It is a schematic block diagram which shows the principal part of a communicating path in the exhaust gas purification apparatus which concerns on 2nd Embodiment of this invention. It is a schematic sectional drawing which follows the VV line in FIG. It is a schematic sectional drawing which follows the VI-VI line in FIG. It is a schematic sectional drawing which shows the modification of 2nd Embodiment similarly to FIG. It is a schematic sectional drawing which follows the VIII-VIII line in FIG.

Explanation of symbols

1 Engine 20 Exhaust pipe (exhaust passage)
30 Upper casing (first casing)
32 communication path 32a first bent portion 32b second bent portion 34 downstream casing (second casing)
36 Pre-oxidation catalyst (exhaust gas purification means)
38 Particulate filter (exhaust gas purification means)
40 SCR catalyst (ammonia selective reduction type NOx catalyst)
44 Urea water injector (urea water supply means)
48 Tail pipe (exhaust passage)
56,256 Heat insulation material (heat dissipation suppression member)
156 Cover member (heat dissipation suppression member)

Claims (10)

A first casing that is disposed in an exhaust passage of the engine and contains exhaust purification means for purifying the exhaust of the engine;
A second casing interposed in the exhaust passage downstream of the first casing;
A communication path that communicates the first casing and the second casing with a bent portion, and guides the exhaust discharged from the first casing to the second casing;
An ammonia selective reduction type NOx catalyst housed in the second casing and selectively reducing NOx in the exhaust gas using ammonia as a reducing agent;
Urea water supply means for supplying urea water into the exhaust gas flowing from the first casing to the second casing via the communication path;
An exhaust purification device, comprising: a heat dissipation suppressing member provided at the bent portion and suppressing heat dissipation from the inside of the communication path to the outside. The communication path has a double-pipe structure including an inner pipe through which the engine exhaust flows and an outer pipe provided outside the inner pipe with a space between the inner pipe and the inner pipe. And
2. The exhaust emission control device according to claim 1, wherein the heat radiation suppressing member is a heat insulating material interposed between the inner tube and the outer tube at the bent portion.   In the space between the inner tube and the outer tube, the heat insulating material covers at least a part of the region of the inner wall surface of the inner tube where the exhaust gas flowing into the bent portion collides with the bent portion. The exhaust emission control device according to claim 2, wherein the exhaust purification device is interposed.   The heat insulating material is interposed in a region outside the bending direction of the bending portion in a space between the inner tube and the outer tube in the bending portion. Item 6. The exhaust emission control device according to Item 3.   2. The exhaust emission control device according to claim 1, wherein the heat dissipation suppressing member is a cover member provided outside the communication path so as to cover the communication path at the bent portion. The cover member is provided with a space between the communication path,
The exhaust emission control device according to claim 5, wherein a heat insulating material is interposed in a space between the cover member and the communication path in the bent portion.   In the space between the cover member and the communication path, the heat insulating material covers an area that covers at least a part of an area of the inner wall surface of the communication path where the exhaust gas that has flowed into the bent section collides with the bending section. The exhaust emission control device according to claim 6, wherein the exhaust purification device is interposed.   The heat insulating material is interposed in a region outside the bending direction of the bending portion in a space between the cover member and the communication path in the bending portion. Item 8. The exhaust emission control device according to Item 7. The communication path has a plurality of bent portions,
2. The exhaust emission control device according to claim 1, wherein the heat dissipation suppressing member is provided at a most upstream bent portion of the bent portions of the communication path. The first casing has a cylindrical shape,
The second casing has a cylindrical shape and is disposed laterally with respect to the central axis of the first casing,
The communication path has one end connected to the side wall of the first casing and the other end connected to the side wall of the second casing.
The exhaust purification device according to claim 1, wherein the urea water supply means injects urea water into the communication path connected to the first casing.

Images