Exhaust emission control device

In an exhaust emission control device, a selective reduction catalyst 5 having a property capable of selectively reacting NOx with ammonia even in the presence of oxygen is incorporated as NOx reduction catalyst in an exhaust pipe 4 and a particulate filter 13 is arranged upstream of the catalyst. Arranged in front of the particulate filter 13 is a burner 14 for injection of fuel in moderate quantity for ignition and combustion. Interposed between the particulate filter 13 and the selective reduction catalyst 5 is an oxidation catalyst 15 which conducts oxidation treatment of unburned HC in the exhaust gas 3 and urges oxidation reaction of NO in the exhaust gas 3 into NO2.

TECHNICAL FIELD

The present invention relates to an exhaust emission control device.

BACKGROUND ART

It has been recently proposed that a particulate filter for capturing particulates in exhaust gas is incorporated in an exhaust pipe and a selective reduction catalyst capable of selectively reacting NOxwith ammonia even in the presence of oxygen is arranged downstream of the particulate filter, urea water as reducing agent being added between the selective reduction catalyst and the particulate filter, thereby attaining reduction of both the particulates and NOx.

Such addition of the urea water to the selective reduction catalyst is conducted between the particulate filter and the selective reduction catalyst. Thus, in order to ensure sufficient reaction time for pyrolysis of the urea water added to the exhaust gas into ammonia and carbon dioxide gas, it is necessary to prolong a distance between a urea water added position and the selective reduction catalyst. However, such arrangement of the particulate filter and the selective reduction catalyst substantially spaced apart from each other will extremely impair the mountability on a vehicle.

In order to overcome this, a compact exhaust emission control device as shown inFIGS. 1 and 2has been proposed by the inventor as Japanese patent application No. 2007-29923. In the exhaust emission control device of the prior application shown, incorporated in an exhaust pipe4through which exhaust gas3flows from a diesel engine1via an exhaust manifold2is a particulate filter5housed in a casing7to capture particles in the exhaust gas3; arranged downstream of and in parallel with the particulate filter5and housed in a casing8is a selective reduction catalyst6having a property capable of selectively reacting NOxwith ammonia even in the presence of oxygen. A rear end of the particulate filter5is connected to a front end of the selective reduction catalyst6through an S-shaped communication passage9such that the exhaust gas3discharged through the rear end of the particulate filter5is forwardly curved back into the front end of the adjacent selective reduction catalyst6.

As shown inFIG. 2which shows substantial parts in enlarged scale, the communication passage9is the S-shaped structure comprising a gas gathering chamber9A which encircles the rear end of the particulate filter5to gather the exhaust gas3through collision of the gas just discharged from the rear end of the particulate filter5against a wall surface and substantially perpendicular turnabout of the gas, a mixing pipe9B which extracts forward the gathered exhaust gas3from the chamber9A and which is provided with an injector10for urea water addition (urea water addition means) intermediately of the mixing pipe and a gas dispersing chamber9C which encircles the front end of the selective reduction catalyst6so as to disperse the gas3guided by the mixing pipe9B through collision of the gas against a wall surface and substantially perpendicular turnabout of the gas into the front end of the selective reduction catalyst6.

Arranged in the casing7and in front of the particulate filter5is an oxidation catalyst11for oxidization treatment of unburned fuel in the exhaust gas3, and arranged in the casing8and behind the selective reduction catalyst6is an ammonia reducing catalyst12for oxidization treatment of surplus ammonia.

With such construction being employed, particulates in the exhaust gas3are captured by the particulate filter5. The urea water is added intermediately of the mixing pipe9B and downstream of the filter into the exhaust gas3by the injector10and is pyrolyzed into ammonia and carbon dioxide gas, so that NOxin the exhaust gas3is favorably reduced and depurated by the ammonia on the selective reduction catalyst6. As a result, both the particulates and NOxin the exhaust gas3are reduced.

In this case, the exhaust gas3discharged through the rear end of the particulate filter5is forwardly curved back by the communication passage9into the front end of the adjacent selective reduction catalyst6. As a result, enough reaction time is ensured for production of ammonia from the urea water since a long distance between the urea water added position intermediately of the communication passage9and the selective reduction catalyst6is ensured and the flow of the exhaust gas3becomes turbulent due to the reversed curving to facilitate mixing of the urea water with the exhaust gas3.

Moreover, the particulate filter5and selective reduction catalyst6are arranged in parallel with each other and the communication passage9is arranged between and along the particulate filter5and selective reduction catalyst6, so that the whole structure becomes compact in size to substantially improve its mountability on a vehicle.

As a prior art literature pertinent to the invention, there exists, for example, the following Patent Literature 1.[Patent Literature 1] JP 2005-155404A

SUMMARY OF INVENTION

Technical Problems

However, the gas gathering chamber9A provides an exhaust passage in the direction different from the axis of the casing7for substantially perpendicular turnabout of the exhaust gas3, so that when a connecting flange is used for connection of the gas gathering chamber9A to the casing7, disadvantageously the flange cannot be fastened all over its peripheral direction since some portions of the flange to be fastened are obstructed by the exhaust passage. Moreover, the exhaust gas which becomes turbulent in the gas gathering chamber9A fails in favorable flow-down to the mixing pipe. Furthermore, it has been desired to enhance the rigidity of the gas gathering chamber9A and the like.

The invention was made in view of the above and has its object to provide an exhaust emission control device in which a connecting flange for connection of a gas gathering chamber is reliably fastened, the exhaust gas in the gas gathering chamber being caused to favorably flow down, the rigidity of the gas gathering chamber and the like being enhanced.

Solution to Problems

The invention is directed to an exhaust emission control device wherein an aftertreatment device for depuration of exhaust gas through passing of the gas therethrough is arranged in a casting and incorporated in an exhaust passage, said casing having an outlet connected through a connecting flange with a gas gathering chamber which in turn provides an exhaust passage in a direction different from an axis of said casing, characterized in that said gas gathering chamber is provided with a mounting portion which extends through the exhaust passage to provide a mounting opening for fastening of the connecting flange from outside, the mounting portion providing said mounting opening being provided at an outer periphery thereof with a curved surface for flow rectification of the exhaust gas.

Thus, the gas gathering chamber has the mounting opening through which the connecting flange may be fastened from outside, so that when the connecting flange is used for connection of the gas gathering chamber, portions of the connecting flange to be fastened are not obstructed by the exhaust passage, resulting in reliable fastening of the connecting flange. Moreover, the mounting portion which provides the mounting opening is provided at its outer periphery with the curved surface for flow rectification of the exhaust gas, so that upon flow-down of the exhaust gas through the exhaust passage in the gas gathering chamber, a phenomenon of fluid separation from the surrounding surface is suppressed to reduce the turbulence, resulting in favorable flow-down of the exhaust gas. Furthermore, the surfaces of the gas gathering chamber is supported by the mounting portion which provides the mounting opening so that rigidity of the gas gathering chamber and the like can be enhanced.

It is preferable in the invention that the gas gathering chamber has an outlet connected with a communication body which provides a second exhaust passage directed in a direction different from the direction of the exhaust passage, the gas gathering chamber being provided with a rectifying member which extends from the mounting portion providing the mounting opening to an inlet of the communication body. This further suppresses the phenomenon of fluid separation from the mounting portion to substantially reduce the turbulence, resulting in favorable flow-down of the exhaust gas to downstream. The surfaces of the gas gathering chamber are supported by the rectifying member, so that the rigidity of the gas gathering chamber can be enhanced. Moreover, the mounting portion is provided with the rectifying member, which can enhance the rigidity of the rectifying member.

It is also preferable in the invention that the exhaust passage is zoned by the mounting portion and the rectifying member into a passage space where the exhaust gas is rectified to flow down and a detention space where the exhaust gas lingers. With thus constructed, the passage space provides the exhaust passage of the exhaust gas and the detention space exerts heat-retention effect, so that the exhaust gas can be caused to favorably flow down to downstream.

ADVANTAGEOUS EFFECTS OF INVENTION

An exhaust emission control device according to the invention as mentioned in the above can exert various excellent effects that when the gas gathering chamber is connected through the connecting flange, the exhaust passage provides no obstruction against the portions of the connecting flange to be fastened so that the connecting flange can be reliably fastened, that the exhaust gas in the gas gathering chamber is caused to favorably flow down to downstream and that the rigidity of the gas gathering chamber and rectifying member can be enhanced.

REFERENCE SIGNS LIST

DESCRIPTION OF EMBODIMENT

An embodiment of the invention will be described in conjunction with the drawings.

FIGS. 3-5show an embodiment of the invention. In the embodiment directed to an exhaust emission control device which is substantially similar in structure to that shown inFIGS. 1 and 2mentioned in the above, a casing7with a particulate filter5(aftertreatment device) having an outlet connected with a gas gathering chamber9A which in turn provides a first exhaust passage13in a direction substantially perpendicular to (or different from) an axis of the casing7. The gas gathering chamber9A has an outlet connected with a mixing pipe9B (communication body) which in turn provides a second exhaust passage14in a direction substantially perpendicular to (or different from) the direction of flow of the exhaust passage13so that it may be substantially in parallel with the axis of the casing7.

The gas gathering chamber9A includes an entry internal space15provided at the inlet and corresponding in diameter to the casing7, an exit internal space16provided at the outlet and corresponding in diameter to the mixing pipe9B (communication body) and an intermediate internal space17for interconnection of entry and exit internal spaces5and6, these internal spaces15,16and17being defined by a flat front plate18facing to outside, a side plate19surrounding the front plate18and a flat rear plate20connected to the side plate19for formation of the intermediate internal space7.

The gas gathering chamber9A has an inlet with a connecting flange22in correspondence with a connecting flange21formed at the outlet of the casing7. The connecting flange22of the gas gathering chamber9A and the connecting flange21of the casing7are formed with holes24in a predetermined spaced-apart relationship along a peripheral edge23, the connecting flanges22and21being capable of fastened together using fastening means such as bolts and nuts (not shown) for the holes24. A spacer or plate may be interposed between the connecting flange22of the gas gathering chamber9A and the connecting flange21of the casing7. Alternatively, connection of the gas gathering chamber9A with the casing7may be provided by a connecting flange formed on one of them, the other being of any construction connectable therewith.

In the gas gathering chamber9A, with respect to one or some (one inFIGS. 3-5) of the holes24on the connecting flange22that is overlapped by the front and rear plates18and20, a mounting opening25is provided for access from outside of the chamber to the very position(s) to be fastened on the connecting flange22. The mounting opening25is provided by a cylindrical mounting portion26which extends through the first exhaust passage13and which has upper and lower ends fixed in welding to the front and rear plates18and20, respectively, so as to enhance the rigidity of the gas gathering chamber9A. The mounting portion26providing the mounting opening25is provided at its outer periphery with an arc- or wing-like curved surface26aso as to prevent fluid separation of the exhaust gas upon flow-down of the gas. There is no specific restriction with respect to a diameter of the mounting opening25, provided that fastening means (not shown) such as bolt and nut may be inserted through the opening for arrangement at the hole24of the connecting flange22; however, it is preferable that the opening is of a size which allows insertion of a socket (not shown) of an impact wrench or other tool (not shown) for fixing of the fastening means.

Arranged at an outlet of the gas gathering chamber9A is an entry cylindrical body27provided by a tip of the mixing pipe9B (communication body). The entry cylindrical body27of the mixing pipe9B (communication body) is partly cut out at its side surface to provide an inlet28leading from the gas gathering chamber9A to the mixing pipe9B (communication body).

Further, first and second rectifying members29and30are arranged in the gas gathering chamber9A, the former extending from the mounting portion26, which provides the mounting opening25, to one side edge of the inlet28of the mixing pipe9B (communication body), the latter extending from an inner surface of the side plate19, which constitutes the gas gathering chamber9A, to the other side edge of the inlet28of the mixing pipe9B (communication body). The first rectifying member29is fixed in welding to the outer periphery of the mounting portion26and fixed via a seat29ato the rear plate20of the gas gathering chamber9A and is inserted into the inlet28of the mixing pipe9B (communication body) in abutting contact with the one side edge.

The first exhaust passage13of the gas gathering chamber9A is zoned by the mounting portion26and first rectifying member29into a passage space13A where the exhaust gas is rectified to flow down and a detention space13B where the exhaust gas lingers. In the detention space13B, a partition member31is arranged to extend from the inner surface of the side plate19to the cylindrical body27for prevention of the exhaust gas from reaching backwardly of the cylindrical body27.

Next, mode of operation of the embodiment according to the invention will be described.

Attachment of the gas gathering chamber9A to the casing7is conducted such that the connecting flange22of the former and the connecting flange21of the latter are fastened together by the fastening means such as bolts and nuts using the impact wrench or other tool. In this case, where one or some of the holes24on the connecting flange22is overlapped by the arrangement of first exhaust passage13, the fastening means such as bolt and nut are fixed using the impact wrench or other tool through the mounting opening25.

The exhaust gas flows down through the gas gathering chamber9A in such a manner that the exhaust gas from the casing7is caused to flow down to the mixing pipe9B (communication body) through the entry, intermediate and exit internal spaces15,17and16. In this case, the exhaust gas is rectified in the passage space13A by the outer periphery of the mounting portion26and the first and second rectifying members29and30for prevention of turbulence due to the fluid separation of the gas, and is caused to flow down to the inlet28of the mixing pipe9B (communication body) while part of the exhaust gas lingers in the detention space13B to exert heat-retention effect.

Thus, according to the above embodiment, in the gas gathering chamber9A, the mounting opening25is provided by the mounting portion26extending through the exhaust passage13, so that connection of the gas gathering chamber9A through the connecting flange22is not obstructed by the exhaust passage13and the edge23of the connecting flange22can be reliably fastened all over its periphery at the holes24. The mounting portion26providing the mounting opening25is provided with the curved surface26afor flow rectification of the exhaust gas, so that upon flow-down of the exhaust gas in the first exhaust passage13, the phenomenon of fluid separation from the outer periphery of the mounting portion26and the like is suppressed to reduce the turbulence, resulting in favorable flow-down of the exhaust gas to downstream. Moreover, the front and rear plates18and20of the gas gathering chamber9A are supported by the mounting portion26constituting the mounting opening25, so that rigidity of the gas gathering chamber9A and first rectifying member29can be enhanced.

The outlet of the gas gathering chamber9A is connected with the mixing pipe9B (communication body) which provides the second exhaust passage14in the direction different from the flow direction of the exhaust passage13, and the first rectifying member29is arranged in the gas gathering chamber9A to extend from the mounting portion26, which provides the mounting opening25, to the inlet28of the mixing pipe9B (communication body), so that the phenomenon of fluid separation from the mounting portion26is further suppressed to substantially reduce the turbulence, resulting in favorable flow-down of the exhaust gas to downstream. Moreover, the front and rear plates18and20of the gas gathering chamber9A is supported by the first and second rectifying members29and30, so that the rigidity of the gas gathering chamber9A can be enhanced. Furthermore, the first rectifying member29is fixed to the mounting opening25or the like, so that the rigidity of first rectifying member29can be enhanced.

When the exhaust passage13is zoned by the mounting portion26and first rectifying member29into the passage space13A where the exhaust gas is rectified to flow down and the detention space13B where the exhaust gas lingers and the passage space13A provides the exhaust passage for the exhaust gas and the detention space13B provides heat-retention effect, so that the exhaust gas can be caused to favorably flow down to downstream.

It is to be understood that an exhaust emission control device according to the invention is not limited to the above-mentioned embodiment and that various changes and modifications may be made without departing from the scope of the invention. For example, in the above embodiment, the first exhaust passage is not always limited to be directed substantially perpendicular to the axis of the casing and may be directed in any direction different from the axis of the casing. The second exhaust passage is not limited to be directed substantially perpendicular to the direction of the first exhaust passage and may be directed in any direction different from the direction of the first exhaust passage. The mounting opening and/or mounting portion may be provided in plural depending upon the number of holes of the connecting flange. The gas gathering chamber has no restriction in shape provided that it can exert the effects of the invention.