JP5090890B2 - Engine exhaust purification system - Google Patents

Engine exhaust purification system Download PDF

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JP5090890B2
JP5090890B2 JP2007330116A JP2007330116A JP5090890B2 JP 5090890 B2 JP5090890 B2 JP 5090890B2 JP 2007330116 A JP2007330116 A JP 2007330116A JP 2007330116 A JP2007330116 A JP 2007330116A JP 5090890 B2 JP5090890 B2 JP 5090890B2
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fin
casing
cylindrical
exhaust gas
exhaust
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JP2009150338A (en
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博昭 藤田
智 平沼
真一 斎藤
峰啓 村田
聡 山崎
康子 鈴木
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三菱ふそうトラック・バス株式会社
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Description

  The present invention relates to an exhaust purification device for an engine, and more particularly to an exhaust purification device that injects a reducing agent from an injection nozzle into exhaust gas flowing through an exhaust passage and supplies the reducing agent to a downstream aftertreatment device.
As an exhaust gas purification device that injects a reducing agent into this type of exhaust gas and supplies it to a downstream aftertreatment device, for example, there is one equipped with a selective reduction type NOx catalyst. As is well known, since the selective reduction type NOx catalyst requires ammonia (NH 3 ) to reduce NOx in the exhaust gas, urea is used as a reducing agent from the injection nozzle disposed upstream of the NOx catalyst in the exhaust passage. An aqueous solution is injected, and the urea aqueous solution is hydrolyzed by exhaust heat and water vapor in the exhaust gas to obtain NOx reduction action using ammonia.
The NOx reduction action of the NOx catalyst is strongly influenced by the supply state of the urea aqueous solution, and in order to obtain a good reduction action, the urea aqueous solution is sufficiently diffused in the exhaust gas and ammonia is evenly supplied to each part of the NOx catalyst. There is a need to. In order to achieve such a demand, various countermeasures have been proposed in which means for stirring exhaust gas is provided in the exhaust passage (see, for example, Patent Document 1).
In the technique of Patent Document 1 above, as shown in FIGS. 1 and 2, a case containing a NOx catalyst is connected to the downstream side of the exhaust pipe of the engine, a urea aqueous solution injection nozzle is provided in the exhaust pipe, and the exhaust pipe A fin device having four fins is arranged on the exhaust upstream side of the injection nozzle, and when the exhaust gas flows through the fin device, a swirling flow is generated by the action of the fins, whereby the urea aqueous solution injected by the injection nozzle It promotes diffusion into exhaust gas.
Japanese Patent No. 3892452 (FIGS. 1 and 2)
  In order to generate a strong swirling flow suitable for promoting the diffusion of the urea aqueous solution by the fin device, it is necessary to secure a certain wide fin area, and a large fin angle is set to change the flow direction of the exhaust gas at a steep angle. There is a need. However, as the fin area increases, the passage area at the position of the fin device is reduced, and as the fin angle increases, the exhaust gas flow direction is changed at a steep angle, resulting in increased pressure loss, resulting in engine exhaust. There was a problem that the pressure increased and the running performance was lowered.
Therefore, in the technique of Patent Document 1, there is a trade-off relationship between promotion of diffusion of urea aqueous solution and reduction of engine exhaust pressure, and both cannot be achieved at a high level, and there is still room for improvement.
The present invention has been made to solve such problems, and the object of the present invention is to promote both diffusion of the reducing agent and reduction of the exhaust pressure of the engine. It is another object of the present invention to provide an engine exhaust purification device that can achieve a good purification performance by supplying a reducing agent evenly and can achieve a good running performance by reducing the exhaust pressure of the engine.
In order to achieve the above object, the invention of claim 1 is characterized in that an upstream casing disposed in an exhaust passage of an engine and into which exhaust gas from the engine is introduced, and a single casing partitioned by a partition wall are upstream. A downstream casing which is formed together with the side casing and receives a reducing agent supplied therein to perform a purification action and accommodates a post-processing device; and a cylindrical shape in parallel with the upstream casing and the downstream casing It is disposed in the upstream casing in a posture in which the axes are substantially orthogonal, and one end is connected to the inclined surface of the partition wall that faces obliquely with respect to the inlet of the aftertreatment device, and through a communication hole formed in the inclined surface. The inside is communicated with the inside of the downstream casing, and the exhaust gas in the upstream casing is introduced into the inside through a large number of holes arranged on the outer peripheral surface, and fins arranged to correspond to the respective holes are used. While to rise to internally swirling flow to guide the exhaust gas flowing through the holes in a predetermined direction, and a cylindrical fin which is closed to the open end to the outside through the outer wall of the upstream casing at the other end, the upstream housing casing And an injection nozzle for injecting a reducing agent into the cylindrical fin.
  Therefore, the exhaust gas flowing in the upstream casing flows into the inside through the holes of the cylindrical fin, and at that time, the exhaust gas is guided in a predetermined direction by the fin to generate a swirling flow in the cylindrical fin. The reducing agent is injected from the injection nozzle into the exhaust gas that has caused this swirling flow, and the injected reducing agent is transferred to the downstream casing while being agitated with the exhaust gas, and the internal post-treatment device receives the supply of the reducing agent. Purifies.
With cylindrical fins, it is possible to provide fins over a wide area of the entire circumference regardless of the cross-sectional area of the passage, thereby generating a strong swirling flow against exhaust gas with a wide fin area, and reducing agent injected from the injection nozzle. Since it can diffuse well into the exhaust gas, the reducing agent can be evenly supplied to each part of the post-processing apparatus. Further, the passage area is not reduced due to the expansion of the fin area, and it is not necessary to increase the fin angle for the purpose of strengthening the swirling flow, so that the pressure loss of the exhaust gas can be suppressed.
Further, since the inside of the casing is partitioned by the partition wall and functions as the upstream and downstream casings, it can be handled as a single casing when installed on the vehicle body.
In addition, since the inclined surfaces are arranged obliquely, the communication holes have an elliptical shape, the opening area of the cylindrical fins in the downstream casing is enlarged, and the communication holes together with the inclined surfaces are the inlets of the post-processing apparatus. Therefore, the exhaust gas from inside the cylindrical fin can be smoothly guided to the aftertreatment device.
Preferably, it is desirable that the reducing agent is jetted from the jet nozzle along the axis of the cylindrical fin having a cylindrical shape. In the cylindrical fin, a swirling flow is generated in which exhaust gas is introduced from the holes on the entire circumference and the angular velocity increases toward the center. Therefore, with this configuration, the reducing agent injected along the axis has the highest angular velocity. Continue to be exposed to the water and be stirred well.
Further, as another aspect, preferably, the post-treatment device is a selective reduction type NOx catalyst, and the urea aqueous solution is injected by using the injection nozzle as a reducing agent. Therefore, in this case, since the urea aqueous solution diffuses well in the exhaust gas, ammonia produced by hydrolysis of the urea aqueous solution by the exhaust heat and water vapor in the exhaust gas is supplied evenly to each part of the NOx catalyst. The NOx purification performance can be improved.
The shape of invention of claim 2, which Oite to claim 1, each of the holes of the cylindrical fins are arrayed respectively forms a slit shape extending in the axial direction of the cylinder fins on the outer circumferential surface of the cylindrical fin, corresponding to each of the holes These fins are formed by bending the inner peripheral side or the outer peripheral side of the cylindrical fin.
Therefore, since the fin is formed simultaneously with the formation of the slit, the manufacturing process of the cylindrical fin is simplified.
  Preferably, each hole and each slit of the cylindrical fin is formed in a trapezoidal shape or a square shape.
As described above, according to the engine exhaust gas purification apparatus of the first aspect of the present invention, it is possible to achieve both the promotion of the diffusion of the reducing agent and the reduction of the exhaust pressure of the engine. The exhaust purification device can be achieved by reducing the exhaust pressure of the engine to achieve good running performance and making the upstream and downstream casings into a single casing. It can be easily installed on the vehicle body , and the exhaust gas from the inside of the cylindrical fin can be smoothly guided to the aftertreatment device to reduce the pressure loss of the exhaust gas .
According to the engine exhaust gas purification apparatus of the second aspect of the present invention, in addition to the first aspect, the fin can be formed simultaneously with the formation of the slit, thereby simplifying the manufacturing process of the cylindrical fin.
[First Embodiment]
Hereinafter, a first embodiment in which the present invention is embodied in an exhaust emission control device for a diesel engine provided with a selective reduction type NOx catalyst will be described.
FIG. 1 is an overall configuration diagram showing an engine exhaust gas purification apparatus according to this embodiment. The exhaust purification device of the present embodiment is mounted on a truck. FIG. 1 shows the engine 1 and the exhaust purification device 2 in the same arrangement as in the state of being mounted on the truck, and partially shows the underfloor of the truck. In the following description, the front-rear direction and the left-right direction are defined mainly with respect to the vehicle.
  As the body frame 3 of the truck, a so-called ladder frame in which a pair of left and right side members 3 a extending in the front-rear direction is connected to each other by a plurality of cross members 3 b (only one is shown) is adopted. A power plant such as the engine 1, a cabin, a loading platform 3 c, and the like are mounted. In FIG. 1, the vehicle body frame 3 is partially shown, and a cargo bed 3 c placed on the vehicle body frame 3 is indicated by a two-dot chain line, and the exhaust purification device 2 is installed under the floor below the cargo bed 3 c. ing.
The engine 1 is positioned between the left and right side members 3a of the body frame 3 and is configured as an in-line 6-cylinder diesel engine. Each cylinder of the engine 1 is provided with a fuel injection valve 4. Each fuel injection valve 4 is supplied with pressurized fuel from a common common rail 5, and injects fuel into the cylinder of the corresponding cylinder when the valve is opened.
An intake manifold 6 is mounted on the intake side of the engine 1, and an intake pipe 7 connected to the intake manifold 6 is provided with an air cleaner 8, a compressor 9 a of a turbocharger 9, and an intercooler 10 from the upstream side. An exhaust manifold 12 is mounted on the exhaust side of the engine 1, and a turbine 9 b of a turbocharger 9 connected coaxially with the compressor 9 a is connected to the exhaust manifold 12. An exhaust pipe 13 (exhaust passage) is connected to the turbine 9b, and the exhaust purification device 2 is provided in the exhaust pipe 13.
On the other hand, a transmission 15 is coupled to the rear portion of the engine 1, and the front end of the propeller shaft 16 is coupled to the output shaft of the transmission 15. The propeller shaft 16 extends rearward between the left and right side members 3a under the floor of the vehicle body, and its rear end is connected to left and right rear wheels via a differential gear (not shown).
The exhaust pipe 13 extends rearward between the propeller shaft 16 under the floor of the vehicle body and the right side member 3a, and a casing 22 of the exhaust purification device 2 is connected to the rear end of the exhaust pipe 13 and the exhaust pipe 13 is exhausted. A fuel injection valve 21 for forced regeneration of the DPF 28 described later is installed slightly upstream of the casing 22 of the pipe 13. The casing 22 has a cylindrical shape along the front-rear direction, and a front end of an exhaust pipe 23 (exhaust passage) is connected to the downstream end of the casing 22. The exhaust pipe 23 is curved to the right and the rear end is on the right side of the vehicle. Open. The arrangement of the exhaust purification device 2 on the vehicle body frame 3 is not limited to this. For example, the exhaust purification device 2 may be arranged on the right side of the right side member 3a.
  Although the casing 22 of the exhaust emission control device 2 is single in appearance, since the inside of the casing 22 is partitioned forward and backward by a partition wall 24, the casing 22 can be substantially regarded as a pair of front and rear casings. . Therefore, in the following description, the front space in the casing 22 partitioned by the partition wall 24 is referred to as an upstream casing 22a, and the rear space is referred to as a downstream casing 22b. The partition wall 24 has a crank shape in a plan view at a substantially central position in the front-rear direction in the casing 22, and has a central surface 24 a facing left and right, a right surface 24 b facing front and rear continuous with the front end of the central surface 24 a, and It is comprised from the left surface 24c which faced the front and back following the rear end.
A pre-stage oxidation catalyst 27 is disposed on the upstream side in the upstream casing 22a, and a wall flow type DPF (decel particulate filter) 28 for collecting PM (particulate matter) in the exhaust gas on the downstream side. Is arranged. Further, a selective reduction type NOx NOx catalyst 29 (post-treatment device) for reducing NOx in the exhaust gas by supplying ammonia (NH 3 ) is disposed on the upstream side in the downstream casing 22b, and a downstream stage is provided on the downstream side. An oxidation catalyst 30 is provided.
  FIG. 2 is a partially enlarged cross-sectional view showing a configuration around the partition wall 24 in the casing 22. A cylindrical fin 33 is disposed on the left side of the central surface 24a of the partition wall 24 in the upstream casing 22a. The cylindrical fin 33 has a cylindrical shape having the same diameter and extending in the left-right direction, and its axis L is orthogonal to the direction in which the upstream and downstream casings 22a and 22b are arranged side by side. The right end of the cylindrical fin 33 is welded to the center surface 24a, and the inside of the cylindrical fin 33 communicates with the inside of the downstream casing 22b through a communication hole 34 formed in the center surface 24a. The left end of the cylindrical fin 33 passes through the outer wall of the upstream casing 22a and opens to the outside, and the opening end is closed by a lid 35 being welded. An injection nozzle 36 is disposed in the lid 35 so as to be positioned on the axis L of the cylindrical fin 33, and a tip 36 a (shown in FIG. 3) of the injection nozzle 36 penetrates the lid 35 and enters the cylindrical fin 33. It protrudes. The injection nozzle 36 can arbitrarily inject the aqueous urea solution fed from a tank (not shown) into the cylindrical fin 33 as a reducing agent, and the injection direction of the injection nozzle 36 extends along the axis L of the cylindrical fin 33. Oriented to the center.
3 is a cross-sectional view corresponding to FIG. 2 showing the internal structure of the cylindrical fin 33, and FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. Although FIG. 4 shows a part of the outer peripheral surface of the cylindrical fin 33, the cylindrical fin 33 has the same configuration on the entire periphery.
A large number of slits 38 extending in the left-right direction are arranged in the circumferential direction on the outer peripheral surface of the cylindrical fin 33 in the upstream casing 22a, and each slit 38 has a trapezoidal shape that is long in the left-right direction. The inner peripheral side of the cylindrical fin 33 and the outer peripheral side (in the upstream casing 22a) communicate with each other. Each of the slits 38 is formed by separating a trapezoidal area from the bottom of the cylindrical fin 33 with the lower base as a base point after separating three sides other than the lower base of the trapezoid (the longer side of the two parallel sides) from the surroundings. A fin-shaped region is formed as a trapezoidal region bent at a predetermined angle α on the inner peripheral side. As a result, the fins 39 are arranged on the inner peripheral surface of the cylindrical fin 33 so as to correspond to the slits 38, and the cylindrical fin 33 is configured as a so-called circular fin. The angle α of each fin 39 is set as a suitable angle for efficiently generating a swirling flow by guiding the exhaust gas introduced into the cylindrical fin 33 through each slit 38 in a predetermined direction as will be described later. Yes.
  In the present embodiment, a straight pipe having an appropriate thickness is used as the material of the cylindrical fin 33, and each slit 38 is punched on the inner peripheral side of the cylindrical fin 33 with the lower bottom of the trapezoid as a base point. Thus, the fin 39 having a predetermined angle α is formed. According to this manufacturing procedure, since the fin 39 can be formed simultaneously with the formation of the slit 38, the manufacturing process of the cylindrical fin 33 can be simplified. However, the method of forming the slits 38 and the fins 39 is not limited to this. For example, the slits 38 and the fins 39 may be formed individually.
  On the other hand, devices such as a fuel injection valve 4 for each cylinder of the engine 1, a fuel injection valve 21 for forced regeneration, and an injection nozzle 36, and sensors (not shown) are connected to an ECU 41 (electronic control unit). Drive control is performed by the ECU 41 based on the detection information. For example, the ECU 41 operates the engine 1 by controlling the injection amount, the injection pressure, and the injection timing of the fuel injection valve 4 based on the operation state of the engine 1 such as the engine speed and load.
  Exhaust gas discharged from the operating engine 1 is introduced into the upstream casing 22a through the exhaust pipe 13, and after passing through the pre-stage oxidation catalyst 27 and the DPF 28, passes through the slits 38 of the cylindrical fins 33 located on the downstream side. Flows into the interior. In the cylindrical fin 33, urea aqueous solution is sprayed to the exhaust gas from the injection nozzle 36, and together with this urea aqueous solution, the exhaust gas is transferred rightward inside the cylindrical fin 33 and discharged into the downstream casing 22b through the communication hole 34. Thereafter, the exhaust gas passes through the NOx catalyst 29 and the post-stage oxidation catalyst 30, and is discharged to the outside from the right side of the vehicle through the exhaust pipe 23.
At this time, the DPF 28 collects PM in the exhaust gas, thereby preventing the PM from being discharged into the atmosphere. Although the amount of PM collected by the DPF 28 gradually increases with the collection of PM, the collected PM is pre-staged when the engine 1 is in a predetermined operation state (for example, an operation state where the exhaust gas temperature is relatively high). The NO 2 generated from NO in the exhaust gas by the oxidation reaction on the oxidation catalyst 27 is continuously incinerated and removed using as an oxidizing agent (continuous regeneration).
  Further, if the operation state in which the continuous regeneration action of the DPF 28 cannot be obtained is continued, the DPF 28 is clogged due to the accumulation of PM. Therefore, assuming such a situation, the ECU 41 starts from the operation state of the engine 1. Before the estimated amount of collected PM exceeds the allowable amount of the DPF 28, the PM on the DPF 28 is forcibly removed by incineration (forced regeneration). For this forced regeneration, unburned fuel injected from the fuel injection valve 21 is used, and the injected unburned fuel is supplied onto the pre-stage oxidation catalyst 27 and the downstream DPF 28 is heated by the oxidation reaction heat. PM is removed by incineration. Note that unburned fuel may be supplied onto the pre-stage oxidation catalyst 27 by post injection in the expansion stroke or exhaust stroke after the main injection.
On the other hand, the ECU 41 controls the injection amount of the urea aqueous solution from the injection nozzle 36 based on the operating state of the engine 1 and the detection value of a temperature sensor (not shown) installed in the vicinity of the injection nozzle 36. The injected urea aqueous solution is transferred together with the exhaust gas from the cylindrical fin 33 through the downstream casing 22b to the NOx catalyst 29. In this process, it is hydrolyzed by the exhaust heat and the water vapor in the exhaust gas to generate ammonia. Using the ammonia thus generated, NOx in the exhaust gas is reduced to harmless N 2 on the NOx catalyst 29. The excess ammonia generated on the CO, HC, and NOx catalyst 24 generated by PM combustion in the DPF 28 is processed by the post-stage oxidation catalyst 30.
In order to realize a good NOx reduction action on the NOx catalyst 29, it is necessary to uniformly supply ammonia to each part of the NOx catalyst 29. For this purpose, the urea aqueous solution is diffused well in the exhaust gas. Is important. As a countermeasure, in the present embodiment, the cylindrical fins 33 are provided in the casing 22, and the effects of the cylindrical fins 33 will be described in detail below.
Exhaust gas after flowing through the DPF 28 flows into the interior through the slits 38 of the cylindrical fins 33, but is guided along the inclination of the corresponding fins 39 immediately after passing through the slits 38, so that the circumferential direction of the cylindrical fins 33 The speed component is given. Therefore, as shown in FIG. 4, the exhaust gas obliquely flows in the same circumferential direction from each slit 38 of the entire circumference of the cylindrical fin 33 and turns to the center (axis L) of the cylindrical fin 33 while turning in the circumferential direction. It is gathered towards. In parallel with this, the exhaust gas is sequentially transferred to the right in the cylindrical fin 33, and as a result, the exhaust gas is transferred to the right while generating a swirling flow along the axis L of the cylindrical fin 33. When discharged from the cylindrical fin 33 into the downstream casing 22b through the communication hole 34 of the partition wall 24, the exhaust gas is not constrained by the inner peripheral surface of the cylindrical fin 33 and the turning radius is expanded, but the swirling flow is still maintained. And flows into the NOx catalyst 29 as it is.
  As described above, the urea aqueous solution is injected from the injection nozzle 36 into the exhaust gas in which the swirl flow is generated in the cylindrical fin 33, and the injected urea aqueous solution is stirred with the exhaust gas, and the cylindrical fin 33, the communication hole 34, the downstream side The NOx catalyst 29 is reached after being sequentially transferred through the casing 22b. The urea aqueous solution being transferred is diffused in the exhaust gas by the stirring action of the swirling flow, but the diffusion of the urea aqueous solution is further promoted by the following factors.
  First, in the cylindrical fin 33 of the present embodiment, a wide fin area can be set regardless of the passage area. That is, in the technique of Patent Document 1, the fin area is limited in order to secure the passage area of the exhaust pipe, but in this embodiment, the cross-sectional area of the passage in the cylindrical fin 33 (the passage area of the exhaust pipe in Patent Document 1 is It is possible to provide the fin 39 together with the slit 38 on the entire circumference of the cylindrical fin 33 regardless of the equivalent), and if necessary, the overall length of the cylindrical fin 33 can be extended or the diameter can be increased to further increase the fin area. You can also Thereby, a strong swirling flow can be generated in the exhaust gas in the cylindrical fin 33 with a wide fin area, and the urea aqueous solution injected from the injection nozzle 36 can be diffused well into the exhaust gas.
  On the other hand, the cylindrical fin 33 introduces exhaust gas from the entire circumference through the slits 38 on the outer peripheral surface to cause a swirl flow inside. This swirling flow is called a so-called free vortex in which the angular velocity increases toward the center. For example, as in the technique of Patent Document 1 in which a swirling flow is generated by a fin device provided in the exhaust pipe, the angular velocity is substantially constant and the outer circumference This is quite different from the velocity distribution where the velocity increases. Then, since the urea aqueous solution is injected from the injection nozzle 36 along the axis L that coincides with the center, the urea aqueous solution is continuously exposed to the exhaust gas having the highest angular velocity and is well stirred.
  Further, since the swirl flow flows so as to be concentrated from the outer peripheral side of the cylindrical fin 33 to the center, the aqueous solution injected from the injection nozzle 36 is always scattered around the center in the cylindrical fin 33 without scattering to the outer peripheral side. Stir with exhaust gas. The urea aqueous solution once adhered to the inner peripheral surface of the cylindrical fin 33 is difficult to diffuse into the exhaust gas. However, such a situation can be avoided and the diffusion of the urea aqueous solution can be further improved.
  Further, the exhaust gas maintains a swirling flow even after being discharged from the cylindrical fin 33 into the downstream casing 22b. However, the exhaust gas is discharged from the narrow cylindrical fin 33 into the wide downstream casing 22b, so that the exhaust gas has a turning radius. The flow situation is changed suddenly by expanding rapidly. Therefore, the exhaust gas is sufficiently agitated not only during transfer in the cylindrical fin 33 but also when discharged from the cylindrical fin 33 into the downstream casing 22b.
Due to the above factors, the urea aqueous solution is sufficiently diffused in the exhaust gas, and the ammonia generated by hydrolysis of the urea aqueous solution is evenly supplied to each part of the NOx catalyst 29. Therefore, the NOx reduction action by the NOx catalyst 29 can be maximized to effectively purify NOx contained in the exhaust gas.
On the other hand, as described above, the use of the cylindrical fins 33 expands the fin area to generate a strong swirling flow, so that the passage area is not reduced by the expansion of the fin area as in the technique of Patent Document 1, Further, there is no need to increase the fin angle for the purpose of enhancing the swirl flow. Therefore, it is possible to prevent a situation in which the pressure loss of the exhaust gas increases due to these factors, thereby reducing the exhaust pressure of the engine 1 and realizing good running performance.
In addition, since the injection nozzle 36 is provided at the left end (corresponding to the upstream side) of the cylindrical fin 33 disposed in the upstream casing 22a, the distance from the injection nozzle 36 to the NOx catalyst 29 is as shown in FIG. The diffusion time of the urea aqueous solution into the exhaust gas can be sufficiently ensured for a long time. As a result, this factor also contributes to promoting diffusion of the aqueous urea solution.
On the other hand, as apparent from FIG. 1, the inside of the casing 22 is divided into front and rear by a partition wall 24 so as to function as the upstream and downstream casings 22a and 22b. It can be handled as the casing 22. Therefore, there is also an effect that the exhaust purification device 2 can be easily installed on the vehicle body frame 3 without restricting the installation of traveling equipment such as fuel tanks and spare tires on the vehicle body frame 3.
Although description of 1st Embodiment is finished above, the structure of the exhaust gas purification apparatus 2 of this 1st Embodiment can be variously changed, and the other example is demonstrated hereafter.
5 is a cross-sectional view corresponding to FIG. 2 showing another example in which each fin 39 of the cylindrical fin 33 is bent to the outer peripheral side, and FIG. 6 is a VI-VI line of FIG. 5 showing the fin shape of the cylindrical fin 33 of another example. It is sectional drawing.
In the cylindrical fins 33 of the first embodiment, the fins 39 are bent toward the inner peripheral side, but in this alternative example, the fins 39 are bent toward the outer peripheral side. The fins 39 are arranged on the entire circumference of the cylindrical fin 33, and the slits 38 and the fins 39 have a long trapezoidal shape in the left-right direction. In such another example, the exhaust gas after flowing through the DPF 28 flows into the cylindrical fin 33 through the corresponding slit 38 immediately after being guided along the inclination of each fin 39, and the exhaust gas inflow process is the first. Although slightly different from the embodiment, the characteristic of the swirling flow generated in the cylindrical fin 33 is not different from that of the first embodiment.
FIG. 7 is a cross-sectional view corresponding to FIG. 6 showing the fin shape of another example of the cylindrical fin 33.
This another example is a combination of the fin shape of the first embodiment and the fin shape of another example shown in FIGS. 5 and 6, and the one end side of the base portion 50 left on the outer peripheral surface of the cylindrical fin 33 is the inner periphery. The fin 51a is formed by bending to the side, and the fin 51b is formed by bending the other end of the base portion 50 to the outer peripheral side. In this alternative example, the same swirling flow as in the first embodiment can be generated in the cylindrical fin 33.
FIG. 8 is a cross-sectional view corresponding to FIG. 2 showing another example in which the shape of the partition wall 24 is changed.
In this other example, the central surface 24a and the right surface 24b of the partition wall 24 of the first embodiment are changed to an inclined surface 61 arranged obliquely, and the inclined surface 61 is inclined with respect to the inlet of the NOx catalyst 29. doing. The cylindrical fin 33 opens into the downstream casing 22b with respect to the communication hole 62 formed in the inclined surface 61. However, the communication hole 62 has an elliptical shape because the inclined surface 61 is disposed obliquely. Thus, the opening area of the cylindrical fin 33 with respect to the downstream casing 22b is enlarged. Further, unlike the first embodiment in which the communication hole 34 is orthogonal to the inlet of the NOx catalyst 29, the communication hole 62 is inclined with respect to the inlet of the NOx catalyst 29 together with the inclined surface 61. Therefore, the exhaust gas from the cylindrical fin 33 can be smoothly guided to the NOx catalyst 29, and the pressure loss of the exhaust gas at this point can be reduced.
FIG. 9 is a cross-sectional view corresponding to FIG. 2 showing another example in which the cylindrical fins 33 are also provided in the downstream casing 22b.
In this alternative example, similarly to the upstream casing 22a, the same shape cylindrical fins are arranged in the downstream casing 22b (hereinafter, distinguished from the upstream cylindrical fin 71 and the downstream cylindrical fin 72). The interiors of both cylindrical fins 71 and 72 are in communication with each other. Accordingly, the exhaust gas that has caused the swirling flow in the upstream cylindrical fin 71 is transferred into the downstream cylindrical fin 72 located on the right side, and flows through the slit of the downstream cylindrical fin 72 into the downstream casing 22b. Discharged. The action of the downstream cylindrical fins 72 differs depending on the inclination direction of the fins 39. When the inclination of the fins 39 is set in the same direction as the upstream cylindrical fins 71, the downstream cylinder is not disturbed by the swirling flow. Since the slits 38 of the fins 72 are circulated, it is possible to further reduce the pressure loss of the exhaust gas at that time. Further, when the inclination of the fin 39 is set in the direction opposite to the upstream side cylindrical fin 71, the exhaust gas is guided in the direction opposite to the swirl flow when flowing through each slit 38 of the downstream side cylindrical fin 72. Therefore, the effect that the diffusion of the urea aqueous solution can be further promoted by rapidly stirring the exhaust gas at that time can be obtained.
[Second Embodiment]
Next, a second embodiment in which the present invention is embodied in an exhaust emission control device 2 for a diesel engine 1 provided with another selective reduction type NOx catalyst will be described. The exhaust purification device 2 of the present embodiment is obtained by changing the configuration of the casing 22 with respect to that of the first embodiment, and the configuration on the vehicle side other than the exhaust purification device 2 is the same as that of the first embodiment. Accordingly, the same components are assigned the same member numbers and the description thereof is omitted, and differences will be described with emphasis.
FIG. 10 is an overall configuration diagram showing the exhaust emission control device 2 for the engine 1 of the present embodiment, and FIG. 2 is a partially enlarged sectional view showing the configuration of the connection location of the upstream and downstream casings 71 and 72.
In short, in this embodiment, the upstream and downstream casings 71 and 72 are made independent of the first embodiment in which the casing 22 is integrated, and the arrangement state of the cylindrical fins 73 is changed accordingly. doing.
  Similar to the upstream casing 22a of the first embodiment, the upstream casing 71 of the present embodiment has a cylindrical shape along the front-rear direction and is installed at the same position on the vehicle body frame 3, and has an exhaust pipe 13 at its upstream end. The rear end is connected. There is no difference in that the upstream oxidation catalyst 18 and the DPF 19 are accommodated in the upstream casing 71, but in this embodiment, a space 74 is formed on the downstream side of the DPF 19, and this location is used as the downstream end of the upstream casing 71. .
  A cylindrical fin 73 is disposed in the space 74 of the upstream casing 71 so as to penetrate the upstream casing 71 in the left-right direction, and the periphery of the cylindrical fin 73 is welded to the upstream casing 71. As in the first embodiment, a lid 35 and an injection nozzle 36 are attached to the left end of the cylindrical fin 73, and slits 38 and fins 39 are arranged in the circumferential direction on the outer periphery of the cylindrical fin 73. The right end of the cylindrical fin 73 protrudes from the upstream casing 71 and extends to the right while maintaining the same diameter, and this extended portion functions as an exhaust pipe 75 (exhaust passage). The exhaust pipe 75 is curved forward and welded to the outer peripheral surface of the downstream casing 72, and the downstream casing 72 is formed in a cylindrical shape along the left-right direction and extends toward the right side. The NOx catalyst 29 and the rear-stage oxidation catalyst 30 are accommodated in the downstream casing 72, an exhaust pipe 76 (exhaust passage) is connected to the downstream end of the downstream casing 72, and the rear end of the exhaust pipe 76 opens to the right side of the vehicle. doing.
  In the exhaust emission control device 2 of the engine 1 configured as described above, the exhaust gas discharged from the engine 1 circulates through the upstream oxidation catalyst 27 and the DPF 28 in the upstream casing 71, and then the cylindrical fins 73 in the space 74. It flows into the inside through the slit 38 while being guided by the fins 39, and the urea aqueous solution is injected from the injection nozzle 36 into the exhaust gas. Further, the exhaust gas together with the urea aqueous solution is transferred to the right in the cylindrical fin 73 and introduced into the downstream casing 72 through the exhaust pipe 75, and after flowing through the NOx catalyst 29 and the post-stage oxidation catalyst 30, the exhaust gas is passed through the exhaust pipe 76. To be discharged.
  The action of the cylindrical fin 73 at this time is the same as that of the first embodiment and will not be redundantly described. However, since a wide fin area can be set regardless of the passage area, the swirl flow is strong against exhaust gas in the cylindrical fin 73. Thus, the aqueous urea solution can be diffused well in the exhaust gas, so that ammonia can be evenly supplied to each part of the NOx catalyst 29 to efficiently purify NOx. Further, the passage area is not reduced by the expansion of the fin area, and it is not necessary to increase the fin angle for the purpose of strengthening the swirling flow, so that the exhaust pressure of the engine 1 is reduced and good running performance is realized. be able to.
  In addition, in the present embodiment, since the exhaust gas is transferred from the upstream casing 71 to the downstream casing 72 via the curved exhaust pipe 75, the urea aqueous solution diffusing in the exhaust gas is passed through the curved portion. There is a tendency to be unevenly distributed on the outer peripheral side due to centrifugal force. Although this phenomenon is not preferable from the viewpoint of diffusion of the urea aqueous solution, the influence of the centrifugal force is reduced by continuously moving the exhaust gas in the exhaust pipe 75 in the circumferential direction by the swirling flow generated by the cylindrical fin 73. Thus, uneven distribution of the urea aqueous solution on the outer peripheral side can be suppressed. This also contributes to the diffusion of the urea aqueous solution, and hence the improvement of the NOx purification performance.
  On the other hand, as apparent from FIG. 10, the downstream casing 72 is positioned on the right side of the side member 3 a with respect to the upstream casing 71, so that the space required for installation of the exhaust purification device 2 as a whole is For example, it is shortened in the front-rear direction as compared with the first embodiment. Therefore, there is an effect that the vehicle body frame 3 can be mounted even on a vehicle having a short front and rear length.
  This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the exhaust purification device 2 of the diesel engine 1 including the selective reduction type NOx catalyst 29 is embodied, but the application target is not limited to this. For example, since a gasoline engine may be provided with the NOx catalyst 29 assuming a lean combustion operation, it may be applied to such a gasoline engine.
  In the above embodiment, the swirl flow by the cylindrical fins 33 and 73 is used for diffusion of the urea aqueous solution supplied to the NOx catalyst 29, but the use mode is not limited to this. For example, as is clear from the description of the DPF 28 of the above embodiment, in the forced regeneration in which the unburned fuel supplied from the fuel injection valve 21 is oxidized on the front-stage oxidation catalyst 27 to raise the temperature of the DPF 28, the front-stage oxidation catalyst 27 In order to maximize the oxidation reaction caused by the above, it is desirable to supply unburned fuel evenly to each part of the pre-stage oxidation catalyst 27. Therefore, the same cylindrical fins 33 and 73 as those in the above embodiments are provided on the upstream side of the pre-stage oxidation catalyst 27, and the fuel injection valve 21 is disposed in the cylindrical fins 33 and 73, and the swirl flow is performed in the cylindrical fins 33 and 73. The unburned fuel may be injected from the fuel injection valve 21 into the exhaust gas in which the gas is generated. In this case, the DPF 28 corresponds to the post-processing apparatus of the present invention.
  In addition, in a storage type NOx catalyst known as another NOx purification catalyst, so-called sulfur poisoning occurs in which SOx (sulfur oxide) is stored in place of NOx and the purification performance is reduced. Therefore, upstream of the NOx catalyst. It is necessary to perform a SOx purge in which a pre-oxidation catalyst is arranged and the NOx catalyst is heated by the oxidation reaction heat of unburned fuel to remove the stored SOx. Therefore, for this SOx purge, a configuration related to the cylindrical fins 33 and 73 similar to the forced regeneration of the DPF 28 may be applied. In this case, the storage-type NOx catalyst corresponds to the aftertreatment device of the present invention.
In the above embodiment, the upstream casings 22a and 71 are used for accommodating the front-stage oxidation catalyst 27 and the DPF 28. However, the use of the upstream casings 22a and 71 is not limited to this, and for example, as a casing for a silencer. Good.
Moreover, in the said embodiment, although the slit 38 which makes a trapezoid shape long in the left-right direction was formed in the cylindrical fins 33 and 73, if the exhaust gas can flow in into the cylindrical fins 33 and 73, the shape is this For example, the slits 38 may be divided in the left-right direction to form a plurality of holes.
It is a whole lineblock diagram showing the engine exhaust gas purification device of a 1st embodiment. It is a partial expanded sectional view which shows the structure of the partition periphery in a casing. It is sectional drawing corresponding to FIG. 2 which shows the internal structure of a cylindrical fin. It is the IV-IV sectional view taken on the line of FIG. 2 which shows the fin shape of a cylindrical fin. It is sectional drawing corresponding to FIG. 2 which shows another example which bent each fin of the cylindrical fin to the outer peripheral side. It is the VI-VI sectional view taken on the line of FIG. 5 which shows the fin shape of the cylindrical fin of another example. It is sectional drawing corresponding to FIG. 6 which shows the fin shape of the cylindrical fin of another example. It is sectional drawing corresponding to FIG. 2 which shows another example which changed the shape of the partition. It is sectional drawing corresponding to FIG. 2 which shows another example which arrange | positioned the cylindrical fin also to a downstream casing. It is a whole block diagram which shows the exhaust emission purification device of the engine of 2nd Embodiment. It is a partial expanded sectional view which shows the structure of the connection location of an upstream side and a downstream casing.
Explanation of symbols
1 Engine 13,23,75,76 Exhaust pipe (exhaust passage)
22a, 71 Upstream casing 22b, 72 Downstream casing 24 Partition 29 NOx catalyst (post-treatment device)
33, 73 Cylindrical fin 34, 62 Communication hole 36 Injection nozzle 61 Inclined surface L Axis

Claims (2)

  1. An upstream casing disposed in the exhaust passage of the engine and into which exhaust gas from the engine is introduced;
    A downstream casing that contains a post-processing device that forms a single casing with a partition wall and is formed together with the upstream casing, and that receives a reducing agent and performs a purification action.
    A cylindrical shape is disposed in the upstream casing in a posture in which the axis is substantially orthogonal to the direction in which the upstream casing and the downstream casing are arranged side by side, and one end is used as an inlet of the post-processing device. The interior is connected to the inside of the downstream casing through a communication hole formed in the inclined surface connected to the inclined surface of the partition wall facing obliquely, and the exhaust gas in the upstream casing is arranged on the outer peripheral surface. It is introduced therein through a number of holes that are, while to rise to internally swirling flow of the exhaust gas flowing through the respective holes by arrayed fin so as to correspond to the respective holes are guided to a predetermined direction, other A cylindrical fin whose end passes through the outer wall of the upstream casing and whose open end to the outside is closed ;
    An exhaust purification device for an engine, comprising: an injection nozzle that is disposed outside the upstream casing at a closed portion of the cylindrical fin and that injects a reducing agent into the cylindrical fin.
  2. Each hole of the cylindrical fin is formed in a slit shape extending in the axial direction of the cylindrical fin and arranged on the outer peripheral surface of the cylindrical fin, and the fin corresponding to each hole is connected to the inner peripheral side or the outer peripheral side of the cylindrical fin. exhaust purifying apparatus according to claim 1 Symbol placement engine, characterized in that it is formed by bending the side.
JP2007330116A 2007-12-21 2007-12-21 Engine exhaust purification system Expired - Fee Related JP5090890B2 (en)

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