DE102016210541A1 - Exhaust after-treatment device with NOx storage and SCR - Google Patents

Abstract

The invention relates to an exhaust aftertreatment device (1) with an elongated housing (2), which in turn in a first end portion (2a), a first gas treatment section (2b) with a NOx storage catalyst (3), a connecting portion (2c), a second gas treatment section (2d) having a second gas treatment device (4, 5) and a second end section (2e) is divided, wherein the treated exhaust gas in the region of the connecting portion (2c) in the exhaust gas aftertreatment device (1), wherein the connecting portion (2c ) allows the incoming exhaust gas to flow through the NOx storage catalyst (3) toward the first end portion (2a), to be deflected 180 ° there, and then to flow in the opposite direction through the NOx storage catalyst (3) into the connecting portion (2c ) and from there through second gas treatment device (4, 5) flows. According to the invention, the second gas treatment device (4, 5) includes an SCR exhaust aftertreatment device (4), and the connection section (2c) includes a switchable exhaust gas diverter (9, 10) selectively connecting the exhaust gas entering the exhaust aftertreatment device (1) into the NOx Storage Catalyst (3) or bypassing the NOx storage catalyst (3) in the second gas treatment device (4, 5) can flow.

Description

The invention relates to an exhaust gas aftertreatment device having the features of the preamble of claim 1.

Such an exhaust gas aftertreatment device is made DE 20 2015 106 054 U1 known as a motor vehicle exhaust aftertreatment device with a catalyst and a particulate filter, which are housed one behind the other in an elongate housing, which in turn into a first end portion, a catalyst portion in which the catalyst is located, a connecting portion, a particulate filter Portion, in which the particulate filter is located, and a second end portion, in which a gas outlet opening of the exhaust gas aftertreatment device is located, is divided. The catalyst has a central tubular part and a shell-shaped part surrounding it, each extending in the longitudinal direction of the exhaust gas aftertreatment device and communicating with each other in the first end section. In addition, the exhaust gas aftertreatment device has a gas inlet opening arranged in the region of the connection section, which is in flow connection with the upstream end of the central tubular part of the catalyst facing away from the first end section. Thus, the exhaust gas to be treated enters the exhaust gas aftertreatment device in the region of the connection section, then flows through the catalyst in the direction of the first end section, ie, in a direction away from the particle filter is deflected by 180 ° at the first end section, then flows through the catalyst second time in the direction of the particle filter and then this towards the second end portion. By the U-shaped deflection of the exhaust gases in the catalyst and the close coupling of catalyst and particulate filter in a common housing, among other things, the existing space in the engine compartment space can be better utilized. The catalyst may also be a NOx storage catalyst, and in the region of the connection portion, an injector for injecting a chemical for selective catalytic reduction (SCR) may be arranged.

Internal combustion engines often generate significant amounts of nitrogen oxides (NOx, ie NO and NO ₂ ) during operation. Especially in diesel and petrol engines used in motor vehicles, the amounts of nitrogen oxide in the exhaust gas are generally above the permissible limits, so that an exhaust aftertreatment to reduce the NOx emissions is necessary. In many engines, the reduction of nitrogen oxides by the non-oxidized constituents contained in the exhaust gas, namely by carbon monoxide (CO) and unburned hydrocarbons (HC), using a three-way catalyst. However, this process is not available in particular in the case of diesel and Otto lean-burn engines, since the reduction of NOx is not or hardly occurs due to the high proportion of oxygen in the exhaust gas. In the case of lean-burn engines, therefore, a lean NOx trap (LNT) is often used, which absorbs and stores the nitrogen oxides contained in the exhaust gas of the internal combustion engine. For this purpose, the nitrogen oxides are oxidized in the lean, ie oxygen-rich exhaust gas under the action of a noble metal catalyst and absorbed in a NOx storage material and thus removed from the exhaust gas stream. If the nitrogen oxide uptake capacity is exhausted, as monitored by a NOx sensor, a purge or purge cycle is performed by momentarily adjusting a rich, reducing exhaust gas mixture. When purging the cached nitrogen oxides are released back into the exhaust stream and reduced by the present in the rich atmosphere carbon monoxide and incompletely burned hydrocarbons to nitrogen.

A disadvantage of NOx storage catalysts is the limited temperature window that can be achieved in achieving adequate NOx conversion efficiency. Above a maximum LNT operating temperature, the NOx conversion efficiency becomes inefficient, or the catalyst even undergoes unintentional aging and deterioration of the catalyst properties.

For nitrogen oxide reduction at higher exhaust gas temperatures than the maximum LNT operating temperature are suitable SCR exhaust aftertreatment, d. H. with Selective Catalytic Reaction (SCR). SCR exhaust aftertreatment devices are z. B. SCR catalysts and SCR-coated diesel particulate filter, called SDPF.

For selective catalytic reduction, ammonia (NH ₃ ) is admixed to the exhaust gas, in the case of motor vehicle internal combustion engines in the form of an aqueous urea solution called AdBlue. The urea dosing must correspond to the current nitrogen oxide emission of the internal combustion engine and therefore depends on the current operating conditions of the engine. If the dosage is too low, too little nitrogen oxide is reduced to comply with the pollutant limits. If the dosage is too high, excess ammonia enters the exhaust gas, which is called NH ₃ slip. This must be prevented because ammonia is harmful to health, even in very small concentrations leads to an odor nuisance and may affect downstream exhaust aftertreatment devices.

Exhaust aftertreatment devices are also known which have both a NOx Storage catalyst as well as an SCR exhaust aftertreatment device included, for. B. from the DE 10 2010 010 039 B4 in which several individual gas treatment devices are connected in series. When the NOx trap catalyst is no longer efficient enough at high exhaust temperatures, excess NOx is converted to the SCR exhaust aftertreatment device by urea injection.

The invention is based on the object to provide an exhaust aftertreatment device, which allows a simple and compact design under virtually all operating conditions, a good NOx conversion efficiency.

This object is achieved by an exhaust gas aftertreatment device having the features of claim 1.

Advantageous developments of the invention are specified in the dependent claims.

According to the invention, the second gas treatment device includes an SCR exhaust aftertreatment device, and the connection section includes a switchable Abgasumlenkeinrichtung that selectively flow the incoming exhaust gas into the NOx storage catalytic converter or bypassing the NOx storage catalyst in the second gas treatment device.

In a preferred embodiment, the NOx storage catalyst has a central tubular part and a shell-shaped part surrounding it, each extending in the longitudinal direction of the exhaust gas after-treatment device and in fluid communication with each other in the first end section, and the exhaust gas after-treatment device has one located in the region of the connection section Gas inlet opening, which is depending on the switching state of Abgasumlenkeinrichtung either with the remote from the first end portion end of the jacket-shaped part of the NOx storage catalyst or with the second gas treatment device in flow communication. In this embodiment, the flow through the NOx storage catalyst is the other way round as that in the generic DE 20 2015 106 054 U1 is described.

In a preferred embodiment, the Abgasumlenkeinrichtung has a arranged in the gas inlet opening of the exhaust aftertreatment device and movable between two positions bypass flap and disposed in the connecting portion baffle which can flow in a first position of the bypass valve entering the connecting portion exhaust gas into the NOx storage catalyst and in a second position of the bypass valve allows the incoming exhaust gas to flow into the second gas treatment device. In this case, in the first position of the bypass flap, the exhaust deflection device can connect an exhaust gas inlet pipe of the exhaust gas aftertreatment device to the jacket-shaped part of the NOx storage catalytic converter, which can contain a NOx storage material. Preferably, the envelope-shaped part contains all the storage material of the NOx storage catalyst, but part of it may also be located in the central tubular part.

In a preferred embodiment, the housing and the gas treatment devices are cylindrical, wherein the baffle has approximately the shape of a conical surface portion or the axially lower half of a torus.

An injector for injecting a chemical for selective catalytic reduction in the SCR exhaust aftertreatment device is preferably arranged in the region of the connection section.

The second gas treatment device can consist of either a passive or active SCR catalyst and a diesel particulate filter or an SCR-coated diesel particulate filter (SDPF).

The exhaust aftertreatment device according to the invention is particularly suitable for more or less vertical arrangement in a motor vehicle with internal combustion engine such that the first gas treatment section substantially above and the second gas treatment section substantially below an exhaust gas outlet opening of the internal combustion engine, which may also be a turbocharger outlet, arranged in the engine compartment is, wherein the connecting portion is arranged approximately at the height of the exhaust gas outlet opening in the engine compartment.

In this way, the space above the exhaust gas outlet for the catalyst can be used, and below extends only the SCR catalyst and the diesel particulate filter or a SDPF, so that even below the exhaust gas outlet space is gained.

The U-shaped deflection of the exhaust gases in the catalyst and the close coupling of the different gas treatment sections in a common housing also have the advantage that the individual gas treatment sections heat up faster and more vigorously during operation, which makes the light-off conditions of the exhaust aftertreatment device easier even with the lower exhaust gas temperatures aimed for today can be met.

The following is a description of embodiments with reference to the drawings. Show:

1 a schematic longitudinal sectional view through a compact exhaust aftertreatment device with NOx storage catalyst and SCR in a first switching state; and

2 a schematic longitudinal sectional view through the exhaust aftertreatment device of 1 in a second switching state.

As in 1 and 2 shown contains an exhaust aftertreatment device 1 an elongated cylindrical housing 2 , in turn, in a first end section 2a , an LNT section 2 B , a connecting section 2c , an SCR / particulate filter section 2d and a second end portion 2e is divided.

A hollow cylindrical NOx storage catalytic converter 3 is in the LNT section 2 B of the housing 2 housed, and an SCR catalyst 4 and a diesel particulate filter 5 (or a corresponding pooled gas treatment facility such as an SCR Coated Diesel Particulate Filter, called SDPF) are in the SCR / Particulate Filter section 2d of the housing 2 accommodated. The NOx storage catalyst 3 , the SCR catalyst 4 and the diesel particulate filter 5 are each (hollow) cylindrical substrates which are coated with suitable catalytically or filtering acting materials.

The connecting section 2c connects the LNT section 2 B such with the SCR / particulate filter section 2d in that exhaust gas, which is the NOx storage catalyst 3 has passed through the SCR catalyst 4 and then the diesel particulate filter 5 flows through. After the exhaust the diesel particulate filter 5 has passed through, it emerges from a gas outlet pipe 6 at the second end portion 2e the exhaust aftertreatment device 1 from and is deflected to a muffler, not shown, and / or the like.

The NOx storage catalyst 3 contains a central tubular part 3a and a jacket-shaped part radially surrounding it 3b each extending in the longitudinal direction of the exhaust gas aftertreatment device and within the first end portion 2a in fluid communication with each other.

The jacket-shaped part 3b of the NOx storage catalyst 3 contains its NOx storage material. Possibly also located in the central tubular part 3a a NOx storage material.

The exhaust aftertreatment device 1 also contains a gas inlet pipe 7 at a gas inlet 8th in the connecting section 2a empties. In the area of the gas inlet opening 8th is a movable bypass flap 9 arranged, and in the connecting section 2a is a baffle 10 arranged. The baffle 10 forms one within the connection section 2a lying rigid partition between the shell-shaped part 3b of the NOx storage catalyst 3 and its central part 3c ,

Except for the area where it is with the bypass door 9 connected, the baffle can 10 have approximately the shape of a conical surface portion or the axially lower half of a torus, with its top a streamlined annular channel between the gas inlet opening 8th and the lower end of the jacket-shaped part 3b of the NOx storage catalyst 3 form and also with its bottom a streamlined transition between the central part 3c of the NOx storage catalyst 3 and the SCR catalyst 4 train.

In a first, in 1 shown position of the bypass flap 9 steer the bypass flap 9 and the baffle 10 the exhaust gas from the gas inlet opening 8th in the coat-shaped part 3b of the NOx storage catalyst 3 , In the first end section 2a the exhaust gas is deflected by 180 ° and then flows through the central part 3a of the NOx storage catalyst 3 , the room in the connecting section 2a below the bypass flap 9 and the baffle 10 and then the SCR catalyst 4 and the diesel particulate filter 5 ,

In a second, in 2 shown position of the bypass flap 9 steer the bypass flap 9 and the baffle 10 the exhaust gas from the gas inlet opening 8th at the NOx storage catalyst 3 passing directly into the SCR catalyst 4 and the diesel particulate filter 5 ,

An injector 11 for injecting a chemical for selective catalytic reduction extends through a wall of the housing 2 into the space below the bypass flap 9 and the baffle 10 in the connecting section 2a to which in the SCR catalyst 4 flowing exhaust gas z. B. to mix a urea solution.

The compact exhaust aftertreatment device 1 can be operated in two operating modes.

Under conditions in which the exhaust gas temperatures for NOx storage in the NOx storage catalytic converter 3 are favorable, there is the bypass flap 9 in the in 1 shown, upwardly directed position, so that the incoming exhaust the jacket-shaped part 3b of the NOx storage catalyst 3 towards the first end section 2a flows through, is deflected there by 180 ° and then in the opposite direction through the central part 3a of the NOx storage catalyst 3 , then with continuous expansion of the flow cross-section through the space below the bypass flap 9 and the baffle 10 in the connecting section 2a and then through the SCR catalyst 4 and the diesel particulate filter 5 in the second end section 2e flows as in 1 displayed with flow arrows. In this mode, the injector remains 11 inactive.

Under conditions in which the exhaust gas temperatures for NOx storage in the NOx storage catalytic converter 3 are unfavorable because it has a poor NOx conversion efficiency and / or age, the bypass damper is located 9 in the in 2 shown, downwardly steering position, so that the NOx storage catalyst 3 It is not flowed through by exhaust gas, but the incoming exhaust gas via the connecting portion 2a where he has the injector 11 Urea solution admixed by the SCR catalyst 4 and the diesel particulate filter 5 flows as in 2 displayed with flow arrows.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 202015106054 U1 [0002, 0012]
• DE 102010010039 B4 [0007]

Claims (9)

Exhaust aftertreatment device ( 1 ) containing several gas treatment devices ( 3 . 4 . 5 ), which in succession in an elongated housing ( 2 ), which are arranged in sequence in a first end section ( 2a ), a first gas treatment section ( 2 B ), in which a first gas treatment device in the form of a NOx storage catalyst ( 3 ), a connecting section ( 2c ), a second gas treatment section ( 2d ), in which a second gas treatment device ( 4 . 5 ), and a second end portion ( 2e ), wherein the exhaust gas to be treated in the region of the connecting portion ( 2c ) into the exhaust aftertreatment device ( 1 ), wherein the connecting section ( 2c ) it allows the incoming exhaust gas the NOx storage catalyst ( 3 ) towards the first end portion ( 2a ) flows through, is deflected there by 180 ° and then in the opposite direction through the NOx storage catalyst ( 3 ) in the connecting section ( 2c ) and from there by second gas treatment device ( 4 . 5 ) towards the second end portion ( 2e ), characterized in that the second gas treatment device ( 4 . 5 ) an SCR exhaust aftertreatment device ( 4 ) and that the connecting section ( 2c ) a switchable Abgasumlenkeinrichtung ( 9 . 10 ) that contains the exhaust gas aftertreatment device ( 1 ) entering exhaust gas optionally in the NOx storage catalyst ( 3 ) or bypassing the NOx storage catalyst ( 3 ) into the second gas treatment device ( 4 . 5 ). Exhaust aftertreatment device ( 1 ) according to claim 1, characterized in that the NOx storage catalyst ( 3 ) a central tubular part ( 3a ) and a surrounding jacket-shaped part ( 3b ), each in the longitudinal direction of the exhaust aftertreatment device ( 1 ) and in the first end section ( 2a ) are in fluid communication with each other, and that the exhaust aftertreatment device ( 1 ) one in the region of the connection section ( 2c ) arranged gas inlet opening ( 8th ), which depending on the switching state of the Abgasumlenkeinrichtung ( 9 . 10 ) either with that of the first end portion ( 2a ) facing away from the envelope-shaped part ( 3b ) of the NOx storage catalyst ( 3 ) or with the second gas treatment device ( 4 . 5 ) is in flow communication. Exhaust aftertreatment device ( 1 ) According to claim 1 or 2, characterized in that the Abgasumlenkeinrichtung ( 1 ) one in or the gas inlet opening ( 8th ) of the exhaust aftertreatment device ( 1 ) and movable between two positions bypass flap ( 9 ) as well as one in the connecting section ( 2c ) arranged deflecting plate ( 10 ), which in a first position of the bypass flap ( 9 ) that in the connecting section ( 2c ) entering exhaust gas into the NOx storage catalyst ( 3 ) flows and in a second position of the bypass flap in the connecting section ( 2c ) entering the second gas treatment device ( 4 . 5 ). Exhaust aftertreatment device ( 1 ) according to claim 2 and claim 3, characterized in that the Abgasumlenkeinrichtung ( 9 . 10 ) in the first position of the bypass flap ( 9 ) an exhaust gas inlet pipe ( 7 ) of the exhaust aftertreatment device with the jacket-shaped part ( 3b ) of the NOx storage catalyst ( 3 ) connects. Exhaust aftertreatment device ( 1 ) according to claim 4, characterized in that the jacket-shaped part ( 3b ) of the NOx storage catalyst ( 3 ) contains a NOx storage material. Exhaust aftertreatment device ( 1 ) according to one of claims 3 to 5, characterized in that the housing ( 2 ) and the two gas treatment devices are cylindrical, wherein the baffle ( 10 ) has approximately the shape of a conical surface portion or the axially lower half of a torus. Exhaust aftertreatment device ( 1 ) according to one of the preceding claims, characterized in that an injector ( 11 ) for injecting a chemical for selective catalytic reduction in the region of the connecting portion ( 2c ) is arranged. Exhaust aftertreatment device ( 1 ) according to one of the preceding claims, characterized in that the second gas treatment device ( 4 . 5 ) either from an SCR catalyst ( 4 ) and a diesel particulate filter ( 5 ) or an SCR-coated diesel particulate filter. Exhaust aftertreatment device ( 1 ) according to one of the preceding claims, characterized in that the exhaust aftertreatment device ( 1 ) is arranged in a motor vehicle with an internal combustion engine, wherein the first gas treatment section ( 2 B ) substantially above and the second gas treatment section ( 2d ) is arranged substantially below an exhaust gas outlet opening of the internal combustion engine in the engine compartment and wherein the connecting portion ( 2c ) is arranged approximately at the height of the exhaust gas outlet opening in the engine compartment.

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