WO2011157323A1

WO2011157323A1 - Exhaust gas purifying catalytic apparatus and exhaust emission control apparatus

Info

Publication number: WO2011157323A1
Application number: PCT/EP2011/002270
Authority: WO
Inventors: Hiroaki Fujita
Original assignee: Daimler Ag
Priority date: 2010-06-14
Filing date: 2011-05-06
Publication date: 2011-12-22
Also published as: JP2012002082A

Abstract

To provide an exhaust gas purifying catalytic apparatus and an exhaust emission control apparatus, which can prevent pressure loss and reduction in exhaust temperature without bringing about weight increase and cost increase. An exhaust gas purifying catalytic apparatus has a cylindrical casing (21), at least two selective reduction type catalysts (22) disposed in series in a direction of an axis of the cylindrical casing (21), a first space (26) provided between the two selective reduction type catalysts (22) in the cylindrical casing (21), second spaces (27) provided at respective ones of both ends in the cylindrical casing (21 ), an exhaust gas inlet (24) provided in one of the first space (26) and the second space (27), and an exhaust gas outlet (25) provided in the other one of the first space (26) and the second space (27).

Description

Daimler AG

Exhaust Gas Purifying Catalytic Apparatus and Exhaust Emission Control Apparatus

The present invention relates to an exhaust purification catalytic apparatus, and in particular to an exhaust purification catalytic apparatus that removes NOx (nitrogen oxide) in exhaust, and an exhaust emission control apparatus in which the exhaust purification catalytic apparatus is installed.

As an exhaust emission control apparatus for purifying exhaust by reducing NOx which is one of contaminants included in exhaust from an internal combustion engine (hereafter referred to as the engine), there has been used an exhaust emission control apparatus that reduces NOx in exhaust by supplying ammonia as a reducing agent to an SCR catalyst.

In this exhaust emission control apparatus using the SCR catalyst, by supplying urea water into exhaust upstream of the SCR catalyst, ammonia produced by decomposition of the urea water through exhaust heat is supplied to the SCR catalyst. The SCR catalyst is formed of a catalytic metal supported on a carrier having a honeycomb structure in which a plurality of minute holes parallel in the axial direction are in communication with each other. Ammonia supplied to the SCR catalyst is absorbed once onto the SCR catalyst, and denization of the ammonia and NOx in exhaust is promoted by the SCR catalyst, so that the NOx is reduced.

Incidentally, in view of manufacturability, SCR catalysts are standardized, and in the case of the standardized SCR catalysts, the amount of NOx reduced by one SCR catalyst is limited to some extent. For this reason, in the case of a large displacement engine of a large truck or the like (generally, a diesel engine), a plurality of SCR catalysts are installed so as to secure catalytic capacity. In this case, as shown in FIG. 13, there is a catalytic apparatus in which a plurality of (two in FIG. 13) SCR catalysts 62 are disposed in series in one casing 61 (see FIG. 2 of Patent Literature 1 ). To tolerate dimensional errors of outer peripheries of the SCR catalysts 62 with respect to an inner periphery of the casing 61 , the outer peripheries of the SCR catalysts 62 are surrounded by mat materials 69. Also, there is a catalytic apparatus in which a plurality of (two in FIG. 14) SCR catalysts 72 are disposed in respective casings 71 , the plurality of casings 71 are disposed in parallel, upstream ends of exhaust inlets 74a are gathered together and connected to an inlet pipe 74, downstream ends of exhaust outlets 75a of the casings 71 are gathered together and connected to an outlet pipe 75 (see FIG. 3 of Patent Literature 1 ). In the general catalytic apparatuses as shown in FIGS. 13 and 14, standardized products can be used as not only SCR catalysts but also casings (those having cylindrical shapes of standardized dimensions).

Moreover, as a catalytic apparatus with a parallel arrangement, there is one in which a plurality of (two in FIG. 15(a))) SCR catalysts 82 are disposed in respective casings 81 , the plurality of casings 81 are disposed in parallel in a tightly-sealed case 86, two rectangular partition plates 87 having round holes 88 as shown in FIG. 15(b) partition the interiors of the casings 81 into upstream portions and downstream portions. In this case, specially-shaped casings are used.

Japanese Unexamined Patent Publication (Kohyo) No. H10-511038

However, when the plurality of SCR catalysts 62 are disposed in series as shown in FIG. 13 (serial flow path system), there is the problem that pressure loss increases with increase in the number of SCR catalysts as compared to a case where a single SCR catalyst is used. On the other hand, when the plurality of SCR catalysts 72 are disposed in parallel as shown in FIG. 14 (parallel flow path system), there is the advantage that pressure loss decreases with increase in the number of SCR catalysts as compared to a case where a single SCR catalyst is used, but the problem that the size and weight of the apparatus increase, resulting in cost increase because the plurality of SCR catalysts 72 are disposed in the respective casings 71 newly arises.

Also, when the plurality of SCR catalysts 82 are disposed in parallel in the case 86 as shown in FIG. 15, the size and weight of the apparatus increase, resulting in cost increase due to the need to provide the partition plates 87. Additionally, standardized products cannot be used as the casings, resulting in a further increase in cost.

Moreover, to reduce NOx using SCR catalysts, exhausted temperature must be maintained high, but the parallel flow path system as shown in FIG. 14 has the problem that the surface area of the entire apparatus increases because the plurality of SCR catalysts 72 are disposed in the respective casings 71 , and therefore, heat insulation properties decrease as compared to the serial flow path system as shown in FIG. 13.

Additionally, in the case of the parallel flow path system as shown in FIG. 14, the number of end plates 71a of the casings 71 to which the pipes 74a into which exhaust flows are connected increases with increase in the number of SCR catalysts 72. For this reason, the parallel flow path system as shown in FIG. 14 has the problem that even when exhaust at high temperature flows into the casings 71 , the temperature of the exhaust decreases before the exhaust flows into the catalysts because there are a large number of end plates 71a being in contact with outside air, and thus heat dissipation is further promoted.

Regarding ease of mounting in, for example, placing an exhaust emission control apparatus under a vehicle floor, flexibility in arrangement and ease of mounting are required to be enhanced.

The present invention has been developed in view of the above described problems, and it is an object of the present invention to provide an exhaust purification catalytic

apparatus and an exhaust emission control apparatus that can reduce pressure loss and decrease in exhaust temperature.

To solve the above described problems, the exhaust purification catalytic apparatus according to the present invention is comprised of a cylindrical casing, at least two selective reduction type catalysts disposed in series along an axis of the cylindrical casing, a first space provided between the two selective reduction type catalysts in the cylindrical casing, second spaces provided at respective ones of both ends of the cylindrical casing, an exhaust inlet provided in one of the first space and the second space, and exhaust outlets provided in the other one of the first space and the second spaces.

In other words, the exhaust purification catalytic apparatus according to the present invention is comprised of the exhaust inlet provided in the first space, and the exhaust outlets provided in the respective second spaces, or is comprised of the exhaust outlet provided in the first space, and the exhaust inlets provided in the respective second spaces.

It is preferred that the exhaust purification catalytic apparatus according to the present invention is further comprised of a pipe gathering portion that gathers the exhaust inlets or the exhaust outlets provided in the second spaces.

In other words, it is preferred that in the case where the exhaust inlets are provided in the second spaces, the pipe gathering portion is constructed such that exhaust branches from an upstream side to a downstream side, and in the case where the exhaust outlets are provided in the second spaces, the pipe gathering portion is constructed such that exhaust gathers from an upstream side to a downstream side.

Also, it is preferred that the exhaust purification catalytic apparatus according to the present invention is plane-symmetrical about the first space.

Also, the exhaust purification catalytic apparatus according to the present invention is comprised of a primary catalytic device disposed such that exhaust flows in a vehicle width direction, an exhaust purification catalytic apparatus described above as a secondary catalytic device disposed downstream of the primary catalytic device such that exhaust flows in a vehicle width direction, and a communication path that communicates an exit portion of the primary catalytic device and an entrance portion of the secondary catalytic device with each other, wherein the secondary catalytic device is disposed in the rear of a rear end of the primary catalytic device or in front of a front end of the primary catalytic device relative to the vehicle width direction.

It is preferred that the communication path is comprised of a first portion that extends from the exit portion of the primary catalytic device in the vehicle width direction on the secondary catalytic device side, a second portion that extends in a direction opposite to the first portion and in the vehicle width direction toward the entrance portion of the secondary catalytic device, and a third portion that is smoothly curved and connects the first portion and the second portion together. Further, it is preferred that the third portion is curved three-dimensionally along an outer periphery of the cylindrical casing.

According to the exhaust purification catalytic apparatus of the present invention, because the parallel flow path system can be realized by providing the exhaust inlets or the exhaust outlets in the respective second spaces although at least two selective reduction type catalysts are disposed in series one cylindrical casing, pressure loss can be reduced as compared to a single selective reduction type catalyst as well as the serial flow path system.

Moreover, because a plurality of selective reduction type catalysts are disposed in series one cylindrical casing although the parallel flow path system is adopted, the surface area of the casing being in contact with outside air can be small, and heat dissipation can be reduced. Further, in the case where the exhaust inlet is provided in the first space provided between the selective reduction type catalysts, there are no end plates of the casing being in contact with outside air unlike the general parallel flow path system, and hence exhaust at high temperature can be caused to flow into the selective reduction type catalysts without decreasing the temperature of the exhaust, and heat dissipation can be further reduced.

Moreover, in the case where the exhaust inlet is provided in the first space provided between the selective reduction type catalysts, the directions of exhaust flow in the exhaust inlet and the selective reduction type catalysts intersect with each other (for example, 90 degrees different), and hence an eddying flow is produced in an arena between the exhaust inlet and each selective reduction type catalyst, and diffusion of urea water as a reducing agent supplied upstream of the selective reduction type catalysts is promoted, so that the urea water can be more uniformly supplied to the selective reduction type catalysts.

Further, because the selective reduction type catalysts are disposed in one cylindrical casing, the entire apparatus can be made compact, and weight and cost thereof can be reduced.

For the reasons stated above, improvement of engine performance, weight reduction, price reduction, and increase in the rate of purification of NOx in exhaust can be realized at the same time in a balanced manner.

Moreover, in the case where there is the pipe gathering portion that gathers the exhaust inlets provided in the respective second spaces, exhaust flowing into the selective reduction type catalysts from the exhaust inlets is substantially equally divided, and accordingly, the flow rate of the exhaust decreases to substantially half. For this reason, the time that elapses before urea water as a reducing agent supplied upstream of the selective reduction type catalysts flows into the selective reduction type catalysts can be increased, and formation of ammonia due to hydrolysis of the urea water and diffusion of the ammonia into the exhaust can be satisfactory.

On the other hand, in the case where there is the pipe gathering portion that gathers the exhaust outlets provided in the respective second spaces, purified exhaust can be emitted from one outlet, and hence exhaust at high temperature can be guided to such a place as not cause heat damage to peripheral components and emitted.

Moreover, in the case where the exhaust purification catalytic apparatus is plane- symmetrical about the first space, exhaust flowing into the selective reduction type catalysts can be substantially equally divided, and hence the purification rate of NOx in exhaust can be further increased. Further, the arrangement of the exhaust purification catalytic apparatus can be simplified, and cost can be reduced.

According to the exhaust emission control apparatus of the present invention, flexibility in mounting the primary catalytic device in the vehicle width direction can be increased, and ease of mounting the primary catalytic device can be enhanced without increasing the entire length of the exhaust emission control apparatus comprised of the primary catalytic device and the secondary catalytic device. Also, flexibility in mounting the secondary catalytic device in the vehicle width direction can be increased, and ease of mounting the secondary catalytic device can be enhanced.

Moreover, in the case where the communication path is comprised of the first portion that extends from the exit portion of the primary catalytic device in the vehicle width direction on the secondary catalytic device side, the second portion that extends in a direction opposite to the first portion and in the vehicle width direction toward the entrance portion of the secondary catalytic device, and the third portion that is smoothly curved and connects the first portion and the second portion together, a sufficient length of the communication path can be secured, and mixing of the urea can be promoted, so that the reducing agent can be uniformly supplied to the selective reduction type catalysts.

Further, in the case where the third portion is curved three-dimensionally along the outer periphery of the cylindrical casing, the communication path can be formed along an outer shape of the casing, and hence a sufficient length of the communication path can be secured while making the entire exhaust emission control apparatus more compact.

FIG. 1 is an axial cross-sectional view schematically showing a principle of an exhaust purification catalytic apparatus according to a first embodiment of the present invention.

FIG. 2 is a perspective view schematically showing the principle of the exhaust purification catalytic apparatus according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an overall arrangement of an exhaust emission control apparatus according to the first embodiment of the present invention.

FIG. 4 is a diagram showing an overall arrangement of an exhaust emission control apparatus according to a second embodiment of the present invention.

FIG. 5 is a perspective view schematically showing a first variation of a communication path in the exhaust emission control apparatuses according to the first and second embodiments of the present invention.

FIG. 6 is a cross-sectional view schematically showing a second variation of the communication path in the exhaust emission control apparatuses according to the first and second embodiments of the present invention.

FIG. 7 is a perspective view schematically showing a third variation of the communication path in the exhaust emission control apparatuses according to the first and second embodiments of the present invention.

FIG. 8 is a cross-sectional view schematically showing a principle of an exhaust purification catalytic apparatus according to a third embodiment of the present invention. FIG. 9 is a cross-sectional view schematically showing a principle of an exhaust purification catalytic apparatus according to a fourth embodiment of the present invention. FIG. 10 is a cross-sectional view schematically showing a principle of an exhaust purification catalytic apparatus according to a fifth embodiment of the present invention. FIG. 11 is a cross-sectional view schematically showing a principle of an exhaust purification catalytic apparatus according to a sixth embodiment of the present invention. FIG. 12 is a schematic diagram showing of an exhaust emission control apparatus according to a seventh embodiment of the present invention.

FIG. 13 is a schematic cross-sectional view useful in explaining conventional problems in a case where a plurality of SCR catalysts are disposed in series in one casing.

FIG. 14 is a schematic cross-sectional view useful in explaining conventional problems in a case where a plurality of SCR catalysts are accommodated in respective casings and disposed in parallel.

FIGS. 15(a) and 15(b) are views useful in explaining conventional problems in a case where a plurality of SCR catalysts are accommodated in respective casings and further disposed in parallel in a case, in which FIG. 15(a) is a schematic cross-sectional view, and FIG. 15(b) is a schematic diagram showing a partition plate that holds the casings.

The present invention will now be described in detail with reference to the drawings showing preferred embodiments thereof.

A description will now be given of an exhaust purification catalytic apparatus and an exhaust emission control apparatus according to a first embodiment of the present invention with reference to FIGS. 1 to 3.

FIG. 3 is a diagram showing an overall arrangement of the exhaust emission control apparatus according to the present embodiment. The exhaust emission control apparatus according to the present embodiment is mounted on a truck. FIG. 3 shows a layout of an internal combustion engine 1 and the exhaust emission control apparatus 2 mounted on the truck, and underfloor essential portions of the truck are indicated by a two-dot chain line. It should be noted that in the following description, a longitudinal direction and a width direction are defined based on a vehicle.

As a chassis construction of the truck, a ladder frame is adopted. The ladder frame 30 is constructed such that a pair of right and left side rails 30a extended in a longitudinal direction of a vehicle body are connected to each other by a plurality of cross members 30b (only one is shown), a power plant such as the internal combustion engine 1 , a cabin of the vehicle body, a truck bed 30c, and so on are mounted on the ladder frame 30. In FIG. 3, a part of the pair of right and left side rails 30a of the ladder frame 30 and a part of the truck bed 30c mounted on the ladder frame 30 are indicated by the two-dot chain line, and the exhaust emission control apparatus 2 is mounted under a floor of the truck bed 30c.

The internal combustion engine 1 is located between the right and left side rails 30a of the ladder frame 30 and constructed as an in-line-six engine here. Cylinders of the internal combustion engine 1 are equipped with respective fuel injection valves 31. Each fuel injection valve 31 is supplied with pressurized fuel from a common rail 32, and injects fuel into the corresponding cylinder with valve opening.

An intake manifold 33 is mounted on an intake side of the internal combustion engine 1 , and in an intake path 34 connected to the intake manifold 33, an air cleaner 35, a compressor 36a of a turbocharger 36, and an intercooler 37 are provided in this order from an upstream side. An exhaust manifold 38 is mounted on an exhaust side of the internal combustion engine 1 , and a turbine 36b of the turbocharger 36 coaxially connected to the compressor 36a is connected to the exhaust manifold 38. An exhaust path 39 is connected to the turbine 36b, and the exhaust emission control apparatus 2 is provided in the exhaust path 39.

On the other hand, a transmission 40 is joined to a rear portion of the internal combustion engine 1 , and a front end of a propeller shaft 41 is connected to an output shaft of the transmission 40. The propeller shaft 41 is extended rearward under a floor of the vehicle body and between the right and left side rails 30a, and has a rear end thereof connected to right and left rear wheels via a differential gear, not shown.

The exhaust path 39 is extended rearward under the right side rail 30a. In typical trucks, the exhaust path 39 is extended to a rear part of the vehicle body, and constituent members of the exhaust emission control apparatus 2 are disposed in series in the exhaust path 39. However, in the truck according to the present embodiment, an underfloor space in the longitudinal direction is limited due to the length of the truck bed, and hence the exhaust path 39 is turned around rightward to emit exhaust sideways. Due to the turned-around exhaust path 39, the layout of the exhaust emission control apparatus 2 mounted in the exhaust path 39 is L-shaped in plan view. A detailed description thereof will be given below.

In a midstream portion of the exhaust path 39, a primary catalytic device 10 that is disposed such as to direct the flow of exhaust in the longitudinal direction of the vehicle (the direction of the length of the vehicle) and has a cylindrical casing 11 in the

longitudinal direction is connected directly below the right side rail 30a. A front oxidation catalyst 12 is disposed on an upstream side inside the casing 11 , and a particulate filter (diesel particulate filter, hereafter referred to as the DPF) 13 for collecting particulate mater (hereafter referred to as the PM) such as soot included in exhaust is disposed on a downstream side inside the casing 11 , and further, a space called a mixing chamber 14 is formed downstream of the DPF 13.

A communication pipe (communication path) 19 is disposed in the mixing chamber 14 of the casing 11 such as to pass through the casing 11 in the width direction. The

communication pipe 19, which is the most common cylindrical pipe, constitutes a part of the exhaust path 39, and has an inner diameter thereof set to be substantially equal to that of the communication pipe 19. In the exhaust emission control apparatus 2 according to the present embodiment, an upstream end 10a of the communication pipe 19 is disposed such as pass through the casing 11. Holes, not shown, which communicate the inside and outside of the communication pipe 19 penetrate a part of the communication pipe 19 which is exposed (inserted) into the mixing chamber 14, and the interior of the mixing chamber 14 and the interior of the communication pipe 19 communicate with each other via these holes. It should be noted that the way in which the mixing chamber 14 and the communication pipe 19 are communicated with each other is not limited to this, and the communication pipe 19 may be supported in a cantilever form on an outlet side and have an opening end on the injection nozzle 15 side to communicate with the mixing chamber 14.

An injection nozzle 15, which is fixed to the upstream end 9a of the communication pipe 19, is configured to be capable of arbitrarily injecting urea water pressure-fed from a tank, not shown, as a reducing agent into the communication pipe 19. Devices such as the fuel injection valves 31 of the internal combustion engine and the injection nozzle 15, and sensors, not shown, are connected to an ECU (electronic control unit) 42, and the devices such as the fuel injection valves 31 and the injection nozzle 15 are drive by the ECU 42 based on detection information from the sensors.

Exhaust having passed through the interior of the primary catalytic device 10 flows out into the communication pipe 19 via outlets such as the holes. A downstream end 19b of the communication pipe 19 is welded to an outer peripheral surface of a cylindrical casing 21 of an exhaust purification catalytic apparatus 20 as a second catalytic unit, described later, and communicates an exit portion of the primary catalytic device 10 and an exhaust inlet 24, which is an entrance portion of the exhaust purification catalytic apparatus 20, with each other.

The exhaust purification catalytic apparatus 20 as the secondary catalytic device has an L-shaped layout in which it is disposed outside the right side rail 30a and in the rear of a rear end 10a of the primary catalytic device 10 with respect to the direction of the vehicle length so that that exhaust can flow in the direction of the vehicle width. The exhaust purification catalytic apparatus 20 is constructed such that a selective reduction type catalysts (SCR catalysts) 22 that purify exhaust by reducing NOx included in exhaust through supply of ammonia, and rear oxidization catalysts 23 that remove surplus ammonia are provided inside the cylindrical casing 21 along the width of the vehicle.

Further, the exhaust purification catalytic apparatus 20 is provided with an outlet pipe 28b, which is a part of the exhaust path 39, and the outlet pipe 28b is curved rightward and opened laterally in the vehicle body.

It should be noted that the outlet pipe 28b constitutes a part of the exhaust path 39.

In the exhaust emission control apparatus 2 according to the present embodiment, because the exhaust purification catalytic apparatus 20 is disposed rearward of the rear end 10a of the primary catalytic device 10 with respect to the direction of the vehicle length, and hence as compared to a case where the primary catalytic device 10 and the exhaust purification catalytic apparatus 20 are disposed in series, the flexibility in mounting the primary catalytic device 10 in the direction of the vehicle width can be increased, and the primary catalytic device 10 can be mounted with ease. Further, flexibility in disposing the exhaust purification catalytic apparatus 20, which is long in the axial direction, in the direction of the vehicle length can be ensured.

Referring now to FIGS. 1 and 2, a description will be given of a principle of the exhaust purification catalytic apparatus 20 according to the present embodiment. FIG. 1 is an axial cross-sectional view schematically showing the principle of the exhaust purification catalytic apparatus 20 according to the present embodiment, and FIG. 2 is a perspective view thereof.

Referring to FIGS. 1 and 2, the exhaust purification catalytic apparatus 20 The exhaust purification catalytic apparatus 20 is constructed such that two selective reduction type catalysts (SCR catalysts) 22 that purify exhaust by reducing NOx included in exhaust through supply of ammonia, and two rear oxidization catalysts 23 that remove surplus ammonia are provided inside the cylindrical casing 21. These SCR catalysts 22 and rear oxidization catalysts 23 are disposed in series in the along an axis of the cylindrical casing 21. It should be noted that the number of SCR catalysts 22 is not limited to the above, but two or more SCR catalysts 22 may be disposed in the cylindrical casing 21. Also, the locations of the rear oxidization catalysts 23 are not limited to the above, but they may be provided as separate units downstream of the exhaust purification catalytic apparatus 20.

The two SCR catalysts 22 are spaced apart from each other, and the exhaust inlet 24 is provided in a space (first space) 26 between the SCR catalysts 22. The two SCR catalysts 22 are disposed such as to face each other across the exhaust inlet 24, and the rear oxidization catalysts 23 are disposed downstream of the respective SCR catalysts 22. The rear oxidization catalysts 23 are arranged such that their downstream sides are spaced apart from end faces of the cylindrical casing 21 , and a space (second space) 27 is provided at each of both ends of the cylindrical casing 21. In the second spaces 27, exhaust outlets 25 are formed in outer peripheral surfaces of the cylindrical casing 21. Moreover, to tolerate dimensional errors of outer peripheries of the SCR catalysts 22 and the rear oxidization catalysts 23 relative to the cylindrical casing 21 , the outer peripheries of the SCR catalysts 22 and the rear oxidization catalysts 23 (these outer peripheries are also cylindrical) are surrounded by mat materials 29.

A pipe gathering portion 28, which is comprised of a joint pipe 28a and an outlet pipe 28b and is for gathering exhaust, is connected to the two exhaust outlets 25 provided in the outer peripheral surfaces of the cylindrical casing 21. The joint pipe 28a is comprised of first portions 281 communicating with the second spaces 27 via the exhaust outlets 25, and a second portion 282 connecting the first portions 281 at both ends together, and the outlet pipe 28b is communicated with an intermediate portion of the second portion 282 of the joint pipe 28a. It should be noted that in FIGS. 1 to 3 and FIGS. 4 to 11 referred to later, corners of the joint pipe 28a are bent at right angles, but actually, they are formed in a curved pattern with a predetermined radius R. With the above described embodiment, purified exhaust can be emitted from one outlet, and hence the exhaust at temperature can be guided to a place that does not cause heat damage to peripheral parts and emitted. It should be noted that the exhaust purification catalytic apparatus 20 according to the present embodiment is plane-symmetrical about the first space 26. Namely, the exhaust purification catalytic apparatus 20 according to the present embodiment is plane-symmetrical about a plane that is perpendicular to the axial direction of the cylindrical first space 26 in the central portion of the first space 26.

Because the exhaust emission control apparatus 2 and the exhaust purification catalytic apparatus 20 according to the present embodiment is arranged as described above, exhaust is purified in a manner described hereafter.

When the internal combustion engine 1 is operating, exhaust emitted from the internal combustion engine 1 is introduced into the primary catalytic device 10 via an upstream area of the exhaust path 39 to passes through the front oxidation catalyst 12 and the DPF 13, and then transferred into the mixing chamber 14 and introduced into the

communication pipe 19 via the holes of the communication pipe 19. Then, the exhaust flows in the communication pipe 19, is introduced into the exhaust purification catalytic apparatus 20 as the secondary catalytic device to pass through the SCR catalysts 22 and the rear oxidization catalysts 23, and then emitted into the atmosphere from the exhaust outlets 25 and the exhaust pipe 28b. On this occasion, the DPF 13 collects PM in the exhaust, and the SCR catalysts 22 reduces NOx in the exhaust. This prevents emission of harmful components into the atmosphere.

In further detail, after the DPF 13 collects the PM in the exhaust, the injection nozzle 15 provided at the upstream end of the communication pipe 19 injects urea water into the exhaust. The injected exhaust is hydrolyzed by exhaust heat to produce ammonia while mixing with the exhaust in the communication pipe 19, and is supplied from the exhaust inlet 24 to the SCR catalysts 22 in the exhaust purification catalytic apparatus 20.

On this occasion, because the directions in which the exhaust flows in the exhaust inlet 24 and the SCR catalysts 22 intersect with each other, and particularly because in the present embodiment, the directions of the exhaust flow significantly change by 90 degrees when going from the exhaust inlet 24 toward the SCR catalysts 22, the exhaust flowing from the exhaust inlet 24 produces an eddying flow in the first space 26. As a result, diffusion of the urea is promoted, and hence the urea is more uniformly supplied to the SCR catalysts 22. Moreover, because the exhaust inlet 24 is provided in the first space 26, there are no end plates of the cylindrical casing 21 which contact outside air, the exhaust at high temperature can be caused to flow into the SCR catalysts 22 without bringing about a decrease in the temperature of the exhaust.

The exhaust flowing into the cylindrical casing 21 changes its flowing direction and substantially equally flows into the two SCR catalysts 22. Specifically, because the parallel flow path system is adopted although the SCR catalysts 22 are disposed in series in the cylindrical casing 21 , pressure loss can be reduced as compared to a single SCR catalyst 22 as well as the serial flow path system. Ammonia supplied to the SCR catalysts 22 is absorbed onto the SCR catalysts 22 once, a denitration reaction between the ammonia and NOx in the exhaust is promoted by the SCR catalysts 22 to thus reduce the NOx, and surplus ammonia is removed by the rear oxidization catalysts 23 to pass through the joint pipe 28a via the exhaust outlets 25 and emitted from the outlet pipe 28b.

FIGS. 5 to 7 show variations of the communication pipe 19 in the exhaust emission control apparatus 2 according to the present embodiment. The communication pipe 19 is required to a certain length so as to satisfactorily diffuse the urea water supplied from the injection nozzle 15, but because in the exhaust purification catalytic apparatus 20 according to the present embodiment, the exhaust inlet 24 is provided in the first space 26 of the cylindrical casing 21 , there is only a short distance from an exit portion of the primary catalytic device 10 to the exhaust purification catalytic apparatus 20, and hence the communication pipe 19 is short. The variations described hereafter solve this problem.

FIG. 5 is a perspective view schematically showing a first variation of the communication pipe 19in the exhaust emission control apparatus 2 according to the present embodiment. The communication pipe 19 shown in FIG. 5 has a first straight portion (first portion) 19a that linearly extends in the direction of the vehicle width on the exhaust purification catalytic apparatus 20 side from the exit portion of the primary catalytic device 10, not shown, and a curved portion 19d that is curved along an outer periphery of the cylindrical casing 21 and toward the exhaust inlet 24 of the exhaust purification catalytic apparatus 20. Because the outer periphery of the cylindrical casing 21 is a curved surface, the exhaust inlet 24 can be provided in any directions of 360 degrees, and hence the curved portion 19a of the communication pipe 19 can be adjusted according to the position of the exhaust inlet 24.

FIG. 6 is a cross-sectional view schematically showing a second variation of the communication pipe 19in the exhaust emission control apparatus 2 according to the present embodiment. The communication pipe 19 shown in FIG. 6 has a first straight portion (first portion) 19a that linearly extends in the direction of the vehicle width on the exhaust purification catalytic apparatus 20 side from the exit portion of the primary catalytic device 10, a second straight portion (second portion) 19b that linearly extends in a direction opposite to the first straight portion 19a and in the direction of the vehicle width toward the exhaust inlet 24 of the exhaust purification catalytic apparatus 20, and a third straight portion 19c that is smoothly curved and connects the first straight portion 19a and the second straight portion 19b to each other, and thus the communication pipe 19 is J- shaped as viewed laterally. It should be noted that in the present variation, because the communication pipe 19 is curved on the same plane, the exhaust inlet 24 is formed on the same plane as the exit portion of the primary catalytic device 10, and hence the communication pipe 19 can be adjusted by changing the lengths of the first straight portion 9a and the second straight portion 19b and the interval between them.

FIG. 7 is a perspective view schematically showing a second variation of the

communication pipe 19in the exhaust emission control apparatus 2 according to the present embodiment. The communication pipe 19 shown in FIG. 7 has a first straight portion (first portion) 19a that linearly extends in the direction of the vehicle width on the exhaust purification catalytic apparatus 20 side from the exit portion of the primary catalytic device 10, not shown, a second straight portion (second portion) 19b that linearly extends in a direction opposite to the first straight portion 19a and in the direction of the vehicle width toward the exhaust inlet 24 of the exhaust purification catalytic apparatus 20, and a third portion 19c that is smoothly curved and connects the first straight portion 19a and the second straight portion 19b to each other.

In the present variation, the communication pipe 19 is curved three-dimensionally along an outer periphery surface of the cylindrical casing 21. Also, because the outer periphery of the cylindrical casing 21 is a curved surface, the exhaust inlet 24 can be provided in any directions of 360 degrees, and hence the third portion 19c of the communication pipe 19 can be adjusted according to the position of the exhaust inlet 24. Further, as compared to the second variation, because the communication pipe 19 is curved along the outer periphery surface of the cylindrical casing 21 , the communication pipe 19 can be made compact.

Next, a description will now be given of an exhaust emission control apparatus 2 according to a second embodiment of the present invention with reference to FIG. 4. It should be noted that the components and others same as those of the first embodiment are designated by the same reference symbols, description of which, therefore, is omitted. Referring to FIG. 4, the exhaust emission control apparatus 2 according to the present embodiment is arranged in the same way as the one according to the first embodiment except for portions related to its layout. Thus, the primary catalytic device 10 and the exhaust purification catalytic apparatus 20 according to the first embodiment can be applied to the exhaust emission control apparatus 2 according to the present embodiment, and the first to third variations (FIGS. 5 to 7) of the communication pipe 19 according to the first embodiment can also be applied to the exhaust emission control apparatus 2 according to the present embodiment.

In the present embodiment, the exhaust purification catalytic apparatus 20 is disposed on a side of the primary catalytic device 10 relative to the direction of the vehicle length such that exhaust flows in the direction of the vehicle width, and thus they are disposed in a T- shaped layout. The primary catalytic device 10 is disposed under the side rail 30a such that a right generating line of the casing 11 overlaps a right end of the side rail 30a.

Because the exhaust emission control apparatus 2 according to the present embodiment is arranged as described above, the same effects regarding the exhaust purification catalytic apparatus 20 obtained in the first present embodiment can be obtained, and additionally, the entire length of the exhaust emission control apparatus 2 in the direction of the vehicle length can be further reduced. However, the exhaust emission control apparatus 2 according to the present embodiment has a lower degree of flexibility in installing the primary catalytic device 10 in the vehicle width direction.

Next, a description will now be given of an exhaust purification catalytic apparatus according to a third embodiment of the present invention with reference to FIG. 8. It should be noted that the components and others same as those of the first embodiment are designated by the same reference symbols, description of which, therefore, is omitted. Referring to FIG. 8, the exhaust purification catalytic apparatus 20 according to the present embodiment is arranged in the same way as the exhaust purification catalytic apparatus 20 according to the first embodiment except for portions related to the exhaust outlets 25 and the pipe gathering portion 28.

The exhaust outlets 25 of the exhaust purification catalytic apparatus 20 according to the present embodiment are provided in respective ones of both end faces 21 a of the cylindrical casing 21 , and the pipe gathering portion 28 comprised of the joint pipe 28a and the outlet pipe 28b is connected to the exhaust outlets 25. The joint pipe 28a communicates with both of the second spaces 27 via the exhaust outlets 25 provided in end faces 21 a of the cylindrical casing 21 , and is comprised of the first portion 281 , which is comprised of a portion extending along an axis of the cylindrical casing 21 and a portion extending along the diameter of the cylindrical casing 21 , and a second portion 282 connecting the first portions 281 at both ends together. The outlet pipe 28b is

communicated with an intermediate portion of the second portion 282 of the joint pipe 28a.

Because the exhaust purification catalytic apparatus 20 according to the present embodiment is arranged as described above, the same effects regarding the exhaust purification catalytic apparatus 20 obtained in the first present embodiment can be obtained, and additionally, because the exhaust outlets 25 are provided along the axis of the cylindrical casing 21 as is the case with the SCR catalysts 22 and the rear oxidization catalysts 23, exhaust having passed through the rear oxidization catalysts 23 can be smoothly emitted. Moreover, because purified exhaust can be emitted from one outlet, exhaust at high temperature can be guided to such a place as not cause heat damage to peripheral components and emitted.

It should be noted that the exhaust purification catalytic apparatus 20 according to the present embodiment can be applied to the exhaust emission control apparatuses 2 according to the first and second embodiments. In this case, because the exhaust purification catalytic apparatus 20 according to the present embodiment is longer in the vehicle width direction than the exhaust purification catalytic apparatuses 20 according to the first and second embodiments, it must be disposed in the vehicle with consideration to this point.

Next, a description will now be given of an exhaust emission control apparatus according to a fourth embodiment of the present invention with reference to FIG. 9. It should be noted that the components and others same as those of the first embodiment are designated by the same reference symbols, description of which, therefore, is omitted.

Referring to FIG. 9, the exhaust purification catalytic apparatus 20 according to the present embodiment is arranged in the same way as the exhaust purification catalytic apparatus 20 according to the first embodiment except for portions related to the exhaust outlets 25 and the pipe gathering portion 28.

The exhaust outlets 25 of the exhaust purification catalytic apparatus 20 according to the present embodiment are provided in respective ones of both end faces 21a of the cylindrical casing 21 as is the case with the exhaust purification catalytic apparatus 20 according to the third embodiment, but there is not provided the pipe gathering portion 28 that gathers exhaust in one place. Only the outlet pipes 28 communicating with the second spaces 27 are connected to the exhaust outlets 25, and purified exhaust is emitted from each of the two outlets.

Because the exhaust purification catalytic apparatus 20 according to the present embodiment is arranged as described above, the same effects regarding the exhaust purification catalytic apparatus 20 obtained in the first present embodiment can be obtained, and additionally, because the exhaust outlets 25 are provided along the axis of the cylindrical casing 21 as is the case with the SCR catalysts 22 and the rear oxidization catalysts 23, exhaust having passed through the rear oxidization catalysts 23 can be smoothly emitted. Moreover, because the flow rate of exhaust at exhaust outlet ends decreases to half, pressure loss can be further reduced.

Moreover, the exhaust outlets 25 may be provided on the outer periphery of the cylindrical casing 21 as is the case with the exhaust purification catalytic apparatus 20 according to the first embodiment.

Next, a description will now be given of an exhaust emission control apparatus according to a fifth embodiment of the present invention with reference to FIG. 10. It should be noted that the components and others same as those of the first to fourth embodiments are designated by the same reference symbols, description of which, therefore, is omitted.

Referring to FIG. 10, in the exhaust purification catalytic apparatus 20 according to the present embodiment, the exhaust inlets 24 are provided in the second spaces 27 provided at respective both ends of the cylindrical casing 21 , and the exhaust outlet 25 is provided in the first space 26. Further, a branch pipe 48a that communicates with the communication pipe 19 in the middle portion thereof is connected to upstream sides of the exhaust inlets 24, and communicates with both of the second spaces 27 via the exhaust inlets 24. A pipe gathering portion 48 of the exhaust purification catalytic apparatus 20 according to the present embodiment is comprised of the communication pipe 19 and the branch pipe 48a.

The branch pipe 48a is comprised of first portions 481 that communicate with both of the second spaces 27 via the exhaust inlets 24 provided in the outer periphery of the cylindrical casing 21 , and a second portion 482 that connects the first portions 481 at both ends to each other, and the communication pipe 19 is communicated with a middle portion of the second portion 482. On the other hand, the outlet pipe 28b is connected to the exhaust outlet 25 provided in the first space 26, and purified exhaust is emitted from the outlet pipe 28b.

In the exhaust purification catalytic apparatus 20 according to the present embodiment as well, the SCR catalysts 22 and the rear oxidization catalysts 23 are disposed in series along the axis of the cylindrical casing 21 , but because exhaust flows in a direction opposite to those in the first to fourth embodiments. Accordingly, the SCR catalysts 22 are disposed at both ends of the cylindrical casing 21 , and the rear oxidization catalysts 23 are disposed in a central part of the cylindrical casing 21. It should be noted that the exhaust purification catalytic apparatus 20 according to the present embodiment is arranged in the same way as the exhaust purification catalytic apparatus 20 according to the first embodiment except for the above portions.

Because the exhaust purification catalytic apparatus 20 according to the present embodiment is arranged as described above, exhaust flowing through the interior of the communication pipe flows into the branch pipe 48a of the pipe gathering portion 48, and thus the exhaust is substantially equally divided, and accordingly, the flow rate of the exhaust decreases to substantially half. For this reason, the time that elapses before urea water supplied upstream of the exhaust purification catalytic apparatus 20 flows into the SCR catalysts 22 can be increased, and formation of the ammonia due to hydrolysis of the urea water and diffusion of the ammonia into the exhaust can be satisfactory.

The exhaust flowing into the branch pipe 48a is introduced into the second spaces 27 via the exhaust inlets 24 provided at both ends of the cylindrical casing 21. The exhaust then passes through the SCR catalysts 22 and the rear oxidization catalysts 23, then flows through the exhaust outlets 25 to be emitted into the atmosphere from the outlet pipe 28b. Because the exhaust caused to flow into the cylindrical casing 21 by the branch pipe 48a is substantially equally divided to flow into the two SCR catalysts 22, the parallel flow path system can be realized although the SCR catalysts 22 are disposed in series in the cylindrical casing 21. Thus, pressure loss can be reduced as compared to a single SCR catalyst 22 as well as the serial flow path system.

It should be noted that the exhaust purification catalytic apparatus 20 according to the present embodiment can be applied to the exhaust emission control apparatuses 2 according to the first and second embodiments. In this case, in the exhaust purification catalytic apparatus 20 according to the present embodiment, both ends of the branch pipe 48a and the cylindrical casing 21 must be heat-insulated using a heat insulator or the like.

Next, a description will now be given of an exhaust emission control apparatus according to a sixth embodiment of the present invention with reference to FIG. 11. It should be noted that the components and others same as those of the first to fifth embodiments are designated by the same reference symbols, description of which, therefore, is omitted.

Referring to FIG. 11 , the exhaust purification catalytic apparatus 20 according to the present embodiment is arranged in the same way as the exhaust purification catalytic apparatus 20 according to the fifth embodiment except for portions related to the exhaust inlets 25 and the branch pipe 48a.

The exhaust inlets 24 of the exhaust purification catalytic apparatus 20 according to the present embodiment are provided in respective ones of both end faces 21a of the cylindrical casing 21 , and the branch pipe 48a is connected to the exhaust inlets 24. The branch pipe 48a communicates with both of the second spaces 27 via the exhaust inlets 24 provided in the end faces 21a of the cylindrical casing 21 , and is comprised of first portions 481 comprised of a portion extending along the axis of the cylindrical casing 21 and a portion extending from the portion along the diameter of the cylindrical casing 21 , and a second portion 482 that connects the first portions 481 at both ends together. The communication pipe 19 is communicated with a middle portion of the second portion 482 of the branch pipe 48a.

Because the exhaust purification catalytic apparatus 20 according to the present embodiment is arranged as described above, the effects regarding the exhaust purification catalytic apparatus 20 obtained in the fifth embodiment can be obtained, and additionally, because the exhaust outlet 25 is provided along the axis of the cylindrical casing 21 as is the case with the SCR catalysts 22 and the rear oxidization catalysts 23, exhaust having passed through the rear oxidization catalysts 23 can be smoothly emitted. Moreover, because purified exhaust can be emitted from one outlet, exhaust at high temperature can be guided to such a place as not cause heat damage to peripheral components and emitted.

It should be noted that the exhaust purification catalytic apparatus 20 according to the present embodiment can be applied to the exhaust emission control apparatuses 2 according to the first and second embodiments. In this case, as is the case with the exhaust purification catalytic apparatus 20 according to the fifth embodiment, both ends of the branch pipe 48a and the cylindrical casing 21 must be heat-insulated using a heat insulator or the like. Moreover, because the exhaust purification catalytic apparatus 20 according to the present embodiment is longer in the vehicle width direction than the exhaust purification catalytic apparatuses 20 according to the first and second

embodiments, it must be disposed in the vehicle with consideration to this point.

Next, a description will now be given of an exhaust emission control apparatus according to a seventh embodiment of the present invention with reference to FIG. 12. It should be noted that the components and others same as those of the first and second

embodiments are designated by the same reference symbols, description of which, therefore, is omitted.

FIG. 12 is a schematic diagram showing of the exhaust emission control apparatus according to the present embodiment. Referring to FIG. 12, the exhaust purification catalytic apparatus 20 according to the present embodiment is arranged in the same way as the exhaust purification catalytic apparatus 20 according to the first embodiment except for its layout. Thus, the primary catalytic device 10 and the exhaust purification catalytic apparatus 20 according to the first embodiment can be applied to the exhaust emission control apparatuses 2 according to the present embodiment. Further, the first to third variations (FIGS. 5 to 7) of the communication pipe 19 according to the first embodiment can also be applied to the exhaust emission control apparatuses 2 according to the present embodiment. Moreover, the exhaust purification catalytic apparatuses 20 according to the third to sixth embodiments can also be applied to the exhaust emission control apparatuses 2 according to the present embodiment.

In the present embodiment, it is assumed that the exhaust emission control apparatuses 2 is mounted on a tractor which is short in the vehicle length direction, and the primary catalytic device 10 and the exhaust purification catalytic apparatus 20 are disposed under the respective right and left side frames 30d such that exhaust flows in the vehicle width direction. In the figure, thick arrows indicate flows of exhaust. Exhaust emitted from the internal combustion engine 1 is introduced into the primary catalytic device 10 via an exhaust path (not shown), passes through the interior of the primary catalytic device 10, flows through a communication pipe (not shown) to be introduced into the exhaust purification catalytic apparatus 20. The exhaust then passes through SCR catalysts (not shown) and rear oxidization catalysts (not shown), and is then emitted into the

atmosphere via an outlet pipe (not shown).

Because the exhaust emission control apparatus 2 according to the present embodiment is arranged as described above, the effects regarding the exhaust purification catalytic apparatus 20 obtained in the first present embodiment can be obtained, and additionally, because the entire length of the exhaust emission control apparatus 2 can be further reduced, and hence the exhaust emission control apparatus 2 according to the present embodiment is effective in a case where a sufficient space cannot be secured in the vehicle length direction.

While the present invention has been described with reference to an exemplary embodiment, it is to be understood that the invention is not limited to the disclosed exemplary embodiment, but various changes may be made without departing from the spirit of the invention.

Although in the above described first embodiment, the exhaust purification catalytic apparatus is located rearward of a rear end of the primary catalytic device relative to the vehicle length direction, the exhaust purification catalytic apparatus is located frontward of a front end of the primary catalytic device. Also, although the exhaust purification catalytic apparatuses according to the above described embodiments are plane-symmetrical about the first space, the present invention is not limited to this. Moreover, although inner diameters of flow paths and outer diameters of catalysts are usually cylindrical, other tube shapes may be used. Daimler AG

Reference Signs List

1 Internal combustion engine

2 Exhaust emission control apparatus

10 Primary catalytic device

19 Communication pipe (communication path)

20 Exhaust purification catalytic apparatus (secondary catalytic device)

21 Cylindrical casing

22 SCR catalyst (selective reduction type catalyst)

24 Exhaust inlet

25 Exhaust outlet

26 First space

27 Second space

28, 48 Pipe gathering portion

Claims

Daimler AG CLAIMS

1. An exhaust gas purifying catalytic apparatus, comprising:

a cylindrical casing;

at least two selective reduction type catalysts disposed in series in a direction of an axis of said cylindrical casing;

a first space provided between said two selective reduction type catalysts in said cylindrical casing;

second spaces provided at respective ones of both ends in said cylindrical casing; an exhaust gas inlet provided in one of said first space and said second space; and

an exhaust gas outlet provided in the other one of said first space and said second space.

2. An exhaust purification catalytic apparatus according to claim 1 , further

comprising a pipe gathering portion that gathers said exhaust inlets or said exhaust outlets provided in said second spaces.

3. An exhaust purification catalytic apparatus according to claim 1 or 2, which is

plane-symmetrical about said first space.

4. An exhaust emission control apparatus comprising:

a primary catalytic device disposed such that exhaust flows in a vehicle width direction;

an exhaust purification catalytic apparatus according to any of claims 1 to 3 as a secondary catalytic device disposed downstream of said primary catalytic device such that exhaust flows in a vehicle width direction; and

a communication path that communicates an exit portion of said primary catalytic device and an entrance portion of said secondary catalytic device with each other, wherein said secondary catalytic device is disposed in rear of a rear end of said primary catalytic device or in front of a front end of said primary catalytic device relative to the vehicle width direction.

5. An exhaust emission control apparatus according to claim 4, wherein said

communication path comprises:

a first portion that extends from the exit portion of said primary catalytic device in the vehicle width direction on the secondary catalytic device side;

a second portion that extends in a direction opposite to said first portion and in the vehicle width direction toward the entrance portion of said secondary catalytic device; and

a third portion that is smoothly curved and connects said first portion and said second portion together.

6. An exhaust emission control apparatus according to claim 5, wherein said third portion is curved three-dimensionally along an outer periphery of said cylindrical casing.