JP4680103B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus provided with a particulate filter that collects particulates (PM) in exhaust gas.

In general, exhaust gas from an internal combustion engine is introduced into a catalyst as a purification means, and is released into the atmosphere after purification.
Further, the catalyst is disposed in a casing, and the casing is formed in various shapes so as to effectively treat the exhaust gas with the catalyst. For example, the housing is formed in a flat shape (see Patent Document 1). In addition, a plurality of ribs are provided in the housing so as to make the flow rate distribution of the exhaust gas uniform.
JP-A-55-117018

By the way, in recent years, an exhaust emission control device in which a plurality of catalysts are housed in a box-shaped housing is known. Specifically, the interior of the housing is divided into at least two upper and lower stages, and the catalyst is arranged on each of the upper and lower stages. The box-shaped housing can be easily processed, and space saving can be achieved, so that mounting on a vehicle is improved.
However, it should be noted that when the catalyst is arranged in the vertical direction, the exhaust must be folded back. This is because there is a lot of dead volume in the passage for turning the exhaust gas, and the exhaust gas stays. And there is a problem that exhaust pressure loss and introduction of exhaust into the lower catalyst become difficult. More specifically, the pressure loss of the exhaust gas greatly affects the performance of the internal combustion engine, and when purification of PM contained in the exhaust gas is required like a diesel engine, this PM is a particulate filter ( This is because there is a concern that it accumulates on the inlet side of the DPF) and ignites at the time of forced regeneration of the DPF, both of which lead to a decrease in the reliability of the exhaust purification device.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that improves the reliability of an apparatus having a box-shaped housing.

In order to achieve the above object, an exhaust emission control device for an internal combustion engine according to claim 1 includes a box-shaped housing into which exhaust from the internal combustion engine is introduced, and a front side surface, a left side surface, and a right side surface of the housing. And an inner wall that vertically divides the interior of the housing, and an upper stage purification unit that is housed in the housing and disposed on the upper side of the inner wall, A lower-stage purification means disposed on the lower side of the inner wall, and formed in the housing, connects the upper-stage purification means and the lower-stage purification means, and directs the exhaust flow from the upper-stage purification means to the lower-stage purification means. It is characterized by comprising a path to be folded back and a flow path resistance reducing means which is formed on the inner surface of the housing and reduces the dead volume in the path to reduce the resistance to the exhaust flow.

Further, in the invention according to claim 2, the upper stage purification means has a pre-stage oxidation catalyst that oxidizes NO in the exhaust gas to generate NO ₂ and a particulate filter that captures particulates in the exhaust gas. The purifying means includes a selective reduction type NOx catalyst that purifies NOx in the exhaust gas using NH ₃ as a reducing agent, and a rear-stage oxidation catalyst that oxidizes surplus NH ₃ to generate N _2. It is characterized in that the exhaust flow from is turned back toward the NOx catalyst.

  Further, in the invention according to claim 3, the flow path resistance reducing means has a recess toward the outlet side of the filter, and the upper surface in the housing intersects the rear side surface normal to the exhaust flow direction in the filter. An upper curved surface portion that reduces the dead volume of the position, and a lower curved surface portion that forms a recess toward the inlet side of the NOx catalyst and reduces the dead volume at a position where the lower surface and the rear side surface of the housing intersect. It is characterized by.

Furthermore, in the invention according to claim 4, the upper stage purification unit has an oxidation catalyst that oxidizes NO in the exhaust to generate NO ₂ , and the lower stage purification unit captures the particulates in the exhaust. It has a particulate filter, and the passage is characterized in that the exhaust flow from the oxidation catalyst is turned back toward the filter.
In the invention according to claim 5, the flow path resistance reducing means forms a recess toward the inlet side of the filter, and the lower surface in the housing intersects the rear side surface normal to the exhaust flow direction in the filter. It includes a lower curved surface portion that reduces the dead volume of the position, and an extension portion that extends toward the filter in a manner linked to the lower curved surface portion and converges to the shape on the inlet side of the filter. .

  Therefore, according to the exhaust gas purification apparatus for an internal combustion engine of the first aspect of the present invention, in the box-shaped housing whose interior is vertically divided through the inner wall, the exhaust flow from the upper side purification means is reduced to the lower side. A passage that is folded back toward the purification means is formed, and a flow path resistance reduction means that reduces dead volume in the passage and reduces resistance to the exhaust flow is formed on the inner surface of the housing. Therefore, the accumulation of exhaust gas is avoided in the passage, and the exhaust gas from the upper stage purification unit flows smoothly and can be introduced into the lower stage purification unit. As a result, it contributes to improving the reliability of the exhaust emission control device.

According to the second aspect of the present invention, the exhaust gas from the particulate filter flows smoothly without staying at the inlet side of the selective reduction type NOx catalyst, so that the pressure loss of the exhaust gas is reduced and the internal combustion engine Improvement of fuel consumption, prevention of output reduction, etc. are achieved.
Further, according to the invention described in claim 3, the exhaust flow from the outlet side of the filter changes its direction downward along the shape of the upper curved surface portion, and then laterally along the shape of the lower curved surface portion. The direction is changed to reach the inlet side of the NOx catalyst. That is, since the location where the exhaust flow is separated in the casing is eliminated, the pressure loss of the exhaust can be more reliably reduced.

Furthermore, according to the fourth aspect of the present invention, exhaust gas from the oxidation catalyst does not stay on the inlet side of the particulate filter, so that accumulation of particulates on the inlet side is avoided. As a result, ignition of the particulates during forced regeneration can be prevented. In addition, the pressure loss of the exhaust can be reduced.
According to the fifth aspect of the present invention, the exhaust flow from the oxidation catalyst contains particulates and changes its direction in the lateral direction along the shape of the lower curved surface portion. And since the extension part connected to the lower curved surface part is formed so as to converge to the shape of the inlet side of the filter, the particulates are not accumulated in the passage, but are collected on the inlet side of the filter and collected. Introduced in. Therefore, the accumulation of particulates on the inlet side of the filter is more reliably avoided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. An exhaust gas purification apparatus for an internal combustion engine according to this embodiment is mounted on a truck 2 shown in FIG.
As shown in the figure, the truck 2 is provided with a cab 4, and a ladder-type frame 6 extends rearward under the cab 4. A diesel engine (not shown) is disposed between the cab 4 and the frame 6. The diesel engine (not shown) is disposed on the rear side of the engine, specifically on the rear surface side of the cab 4 and at an appropriate position on the right side portion of the frame 6. An exhaust purification device 8 is provided. A fuel tank 10 and a urea water tank 12 are disposed at appropriate positions on the left side of the frame 6. Then, exhaust gas from the engine is introduced into the exhaust gas purification device 8, and the introduced exhaust gas is purified and released to the outside.

  As shown in FIG. 2, the exhaust purification device 8 includes a box-shaped housing 16 formed in a substantially rectangular parallelepiped, and a pipe 14 is connected to the front side surface 17 of the housing 16. Is connected to the engine. A peripheral wall upper surface (upper surface) 18, a peripheral wall lower surface (lower surface) 19, a left side surface 20, and a right side surface 21 are disposed on each side of the front side surface 17 toward the rear of the vehicle. An opening 23 is formed at the position (FIG. 3), and this opening 23 is connected to a tail pipe (not shown). Further, an injector 38 for adding urea water (urea water) as an example of a reducing agent is disposed at an appropriate position on the peripheral wall upper surface 18. The injector 38 of this embodiment is connected to the urea water tank 12, and the urea water injection port is opened near the inside of the peripheral wall upper surface 18. Further, the peripheral wall upper surface 18, the peripheral wall lower surface 19, the left side surface 20 and the right side surface 21 are in contact with an exhaust facing surface (rear side surface) 22 at a position opposite to the front side surface 17. It is arranged to face the front side surface 17.

  As shown in FIG. 3, the housing 16 of the first embodiment is provided with an inner wall 24 that divides the interior into two upper and lower stages. The inner wall 24 includes a front side surface 17 and a left side surface. The length is fixedly supported on the right side surface 20 and the right side surface 21, but the length is not in contact with the exhaust facing surface 22. An upper stage purification unit is accommodated between the inner wall 24 and the peripheral wall upper surface 18, and a lower stage purification unit is accommodated between the inner wall 24 and the peripheral wall lower surface 19. As described above, the peripheral wall upper surface 18, the peripheral wall lower surface 19, the left side surface 20, and the right side surface 21 are arranged at positions along the exhaust flow direction in each purifying means, whereas the front side surface 17 and the exhaust facing surface 22 are It arrange | positions in the position which makes this exhaust flow direction a normal line.

Specifically, the upper stage purification means in the embodiment is a front stage oxidation catalyst 32 and a DPF (diesel particulate filter) 34, which are inserted in this order as seen in the flow direction of the exhaust gas from the engine (FIG. 3). (A)).
In pre-stage oxidation catalyst 32 and the NO in the exhaust is oxidized and generates NO _2, and supplies the DPF34 the NO ₂ as oxidizing agent. The DPF 34 is provided with a plurality of passages that connect the upstream side and the downstream side of the exhaust gas in parallel, and the upstream opening portions and the downstream opening portions of the passages are alternately closed. The DPF 34 collects particulates (PM) in the exhaust gas, and combusts the collected PM by reaction with NO ₂ supplied from the pre-stage oxidation catalyst 32.

On the other hand, the lower-stage purification means in the present embodiment is an SCR catalyst (selective reduction type NOx catalyst) 48 and a rear-stage oxidation catalyst 50, which are inserted in this order in the exhaust flow direction (FIG. 3A). .
The SCR catalyst 48 adsorbs NH ₃ added from the injector 38 and purifies NOx in the exhaust gas using the NH ₃ as a reducing agent. In the post-stage oxidation catalyst 50, when the NH ₃ becomes excessive in the SCR catalyst 48, it is oxidized to generate N ₂ , and further, in the case where CO is generated due to PM combustion in the DPF 34, this is oxidized. It is oxidized to produce the CO _2.

  Here, the outlet side of the DPF 34 and the inlet side of the SCR catalyst 48 are connected by a return passage (passage) 36. That is, in the turn-back passage 36, the exhaust flow from the DPF 34 toward the rear of the vehicle is turned back toward the front of the vehicle and directed toward the SCR catalyst 48. An upper flow separation portion (dead volume) 26 exists at the intersecting position, and a lower flow separation portion (dead volume) 28 also exists at a position where the peripheral wall lower surface 19 and the exhaust facing surface 22 intersect. In this state, vortex flows are generated in the flow separation portions 26 and 28, and the exhaust flow velocity after combustion of PM in the flow separation portions 26 and 28 becomes small and stagnates.

Therefore, in this embodiment, there is provided a flow path resistance reducing means that eliminates the plurality of flow separation portions 26 and 28 in the return passage 36 and reduces the resistance to the exhaust flow.
More specifically, as shown in FIG. 3, the flow path resistance reducing means of the present embodiment is first provided with an upper curved surface portion 40 for the flow separation portion 26. The upper curved surface portion 40 is formed of a quadrilateral cylindrical thin plate, has a recess toward the outlet side of the DPF 34, and has a center of curvature in the vicinity of the outlet side of the DPF 34. Further, the upper curved surface portion 40 is formed substantially equal to the width of the peripheral wall upper surface 18 and the exhaust facing surface 22, and is fixed to the peripheral wall upper surface 18 and the exhaust facing surface 22 by welding.

  Next, a lower curved surface portion 42 is provided for the flow separation portion 28. The lower curved surface portion 42 is also formed of a quadrangular cylindrical thin plate, has a concave portion toward the inlet side of the SCR catalyst 48, and has a center of curvature in the vicinity of the inlet side of the SCR catalyst 48. ing. The lower curved surface portion 42 is formed substantially equal to the width of the peripheral wall lower surface 19 and the exhaust facing surface 22, and is fixed to the peripheral wall lower surface 19 and the exhaust facing surface 22 by welding.

  As described above, according to the first embodiment, in the box-shaped housing 16 whose interior is vertically divided through the inner wall 24, the return passage 36 for returning the exhaust flow from the DPF 34 toward the SCR catalyst 48. An upper curved surface portion 40 and a lower curved surface portion 42 are formed on the inner surface of the casing 16 so as to eliminate the flow separation portions 26 and 28 in the folded passage 36 and reduce the resistance to the exhaust flow. Therefore, the exhaust gas is prevented from staying in the return passage 36, and the exhaust gas from the DPF 34 flows smoothly and can be introduced into the SCR catalyst 48. As a result, the pressure loss of the exhaust gas is reduced, and the fuel efficiency of the internal combustion engine is improved and the output is prevented from decreasing. This contributes to improving the reliability of the exhaust gas purification apparatus.

Moreover, since the four purification means 32, 34, 48, and 50 described above are accommodated in a box-shaped casing 16 that is vertically divided, the mounting property on the vehicle is improved, and the heat insulation in the casing 16 is maintained. The property is improved and the activity of each purification means is promoted.
Further, the exhaust flow from the outlet side of the DPF 34 changes its direction downward along the shape of the upper curved surface portion 40, and then changes its direction horizontally along the shape of the lower curved surface portion 42, so that the SCR catalyst 48. Reach the entrance side. In other words, the exhaust flow separation point is eliminated at each of the upper and lower positions in the return passage 36, so that the exhaust pressure loss can be more reliably reduced.

The present invention is not limited to the above-described first embodiment, and various modifications are possible. The exhaust purification device of the second embodiment will be described below with reference to FIG. In the description of the second embodiment, members and parts similar to those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
First, the upper stage purification means in this embodiment is the oxidation catalyst 32, and the lower stage purification means is the DPF 34, and the outlet side of the oxidation catalyst 32 and the inlet side of the DPF 34 are connected by a turn-back passage 36. That is, in the present embodiment, since the exhaust gas containing PM passes through the return passage 36, the lower flow separation portion 28 exists at a position where the peripheral wall lower surface 19 and the exhaust gas confronting surface 22 intersect. A vortex flow is generated in the flow separation unit 28, and the exhaust flow velocity in the flow separation unit 28 decreases, and PM in the exhaust gas accumulates on the flow separation unit 28.

  Therefore, in this embodiment, a flow path resistance reducing means is provided to eliminate the flow separation portion 28. Specifically, the flow path resistance reducing means is composed of a lower curved surface portion 44 and an extension portion 46, and the former lower curved surface portion 44 is formed of a truncated spherical thin plate and is an inlet of the DPF 34. A concave portion is formed toward the side, and the center of curvature is configured to exist slightly above the entrance side of the DPF 34. The lower curved surface portion 44 is fixed to the exhaust facing surface 22 by welding.

On the other hand, the latter extension portion 46 is integrally connected to the lower curved surface portion 44, extends toward the inlet side of the DPF 34, and has a shape in which the tip portion converges to the inlet side shape (for example, a circle) of the DPF 34. It is configured.
In FIG. 4, reference numeral 30 denotes a light oil addition injector 30, which injects light oil (HC) toward the exhaust during forced regeneration of the DPF 34 and raises the temperature of the DPF 34. However, the present invention is not limited to this configuration. For example, additional fuel may be injected in the expansion stroke following the post injection, that is, the main injection, and HC may be supplied into the casing 16.

  As described above, according to the second embodiment, in the box-shaped housing 16 whose interior is vertically divided through the inner wall 24, the return passage 36 for returning the exhaust flow from the oxidation catalyst 32 toward the DPF 34. A lower curved surface portion 44 and an extension portion 46 are formed on the inner surface of the housing 16 to eliminate the flow separation portion 28 in the folded passage 36 and reduce the resistance to the exhaust flow. Therefore, in the return passage 36, the exhaust from the oxidation catalyst 32 does not stay on the inlet side of the DPF 34, and accumulation of PM on the inlet side is avoided. As a result, PM is prevented from being ignited during forced regeneration, which contributes to improving the durability and reliability of the exhaust emission control device.

Further, the pressure loss of the exhaust gas can be reduced, and since these two purifying means 32 and 34 are accommodated in the casing 16 that is partitioned vertically, the mounting property to the vehicle is improved, and the casing 16 is improved. The heat retaining property is improved, and the activity of each purifying means is also promoted.
Further, the exhaust flow from the oxidation catalyst 32 changes its direction in the lateral direction along the shape of the lower curved surface portion 44. Since the extended portion 46 connected to the lower curved surface portion 44 is formed so as to converge to the shape of the inlet side of the DPF 34, PM having a large specific gravity does not accumulate on the flow separation portion 28, and the inlet side of the DPF 34 Are efficiently integrated and introduced into the DPF 34.

This is the end of the description of the embodiment of the present invention, but various modifications can be made without departing from the spirit of the present invention.
For example, in the above-described embodiment, the upper and lower two-stage casings are described. However, as long as the box-shaped casing has a folding path, the upper and lower three-stage casings may be used. Also in the second embodiment, the upper curved surface portion 40 of the first embodiment may be provided. In this case, the effect of further contributing to the reduction of the exhaust pressure loss is achieved.

Furthermore, in the above embodiment, an example in which the flow resistance reducing means separate from the housing is provided inside the housing is shown, but the dead volume in the folding path is reduced by changing the shape of the housing itself. You may let them.
By the way, in the said embodiment, although the exhaust gas purification apparatus applied to the diesel engine is demonstrated, it is not limited to the said engine, This invention is applicable to all the engines provided with DPF.

1 is a schematic view of a vehicle equipped with an exhaust gas purification apparatus for an internal combustion engine according to a first embodiment of the present invention. It is an external appearance perspective view of the exhaust gas purification apparatus of FIG. (A) is an arrow directional cross-sectional view which follows the III-III line of FIG. 2, (b) is an arrow directional cross-sectional view which follows the BB line of (a). (A) is sectional drawing of the exhaust gas purification apparatus in 2nd Example, (b) is arrow sectional drawing which follows the BB line of (a).

Explanation of symbols

8 Exhaust gas purification device 16 Housing 18 Upper surface of peripheral wall (upper surface)
19 Lower surface of peripheral wall (lower surface)
22 Exhaust opposite side (rear side)
24 inner wall 26 upper flow separation part (dead volume)
28 Lower flow separation (dead volume)
32 Pre-stage oxidation catalyst (upper side purification means)
34 DPF (upper side or lower side purification means)
36 Folding passage (passage)
40 Upper curved surface (channel resistance reduction means)
42 Lower curved surface (channel resistance reduction means)
44 Lower curved surface (channel resistance reduction means)
46 Extension (channel resistance reduction means)
48 SCR catalyst (lower purification means)
50 Second-stage oxidation catalyst (lower-stage purification means)

Claims (5)

A box-shaped housing into which exhaust from the internal combustion engine is introduced;
An inner wall that is fixedly supported on each of the front side surface, the left side surface, and the right side surface of the housing and is formed so as not to contact the exhaust-facing surface, and divides the interior of the housing vertically.
An upper stage purification unit disposed in the casing and disposed on the upper side of the inner wall; and a lower stage side purification unit disposed on the lower side of the inner wall;
A passage formed in the housing, connecting the upper-stage purification means and the lower-stage purification means, and returning an exhaust flow from the upper-stage purification means toward the lower-stage purification means;
An exhaust gas purification apparatus for an internal combustion engine, comprising: flow path resistance reduction means formed on an inner surface of the casing to reduce dead volume in the passage and thereby reduce resistance to the exhaust flow. The upper stage purification unit includes a pre-stage oxidation catalyst that oxidizes NO in the exhaust to generate NO ₂ and a particulate filter that captures particulates in the exhaust, and the lower stage purification unit reduces NH ₃ A selective reduction type NOx catalyst that purifies NOx in the exhaust gas as an agent and a post-stage oxidation catalyst that oxidizes surplus NH ₃ to generate N ₂ ;
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the passage turns an exhaust flow from the filter toward the NOx catalyst. The flow path resistance reducing means forms a recess toward the outlet side of the filter, and reduces the dead volume at the position where the upper surface in the housing and the rear side surface normal to the exhaust flow direction in the filter intersect. An upper curved surface portion that forms a recess toward the inlet side of the NOx catalyst, and a lower curved surface portion that reduces a dead volume at a position where the lower surface in the housing and the rear side surface intersect with each other. The exhaust emission control device for an internal combustion engine according to claim 2. The upper stage purification means has an oxidation catalyst that oxidizes NO in the exhaust to generate NO _2, and the lower stage purification means has a particulate filter that captures particulates in the exhaust,
2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the passage turns an exhaust flow from the oxidation catalyst toward the filter. The flow path resistance reducing means forms a recess toward the inlet side of the filter, and reduces the dead volume at the position where the lower surface in the housing intersects the rear side surface normal to the exhaust flow direction in the filter. 5. A lower curved surface portion, and an extension portion that extends toward the filter and is connected to the lower curved surface portion, and has a shape converged to the shape on the inlet side of the filter. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1.

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