JP2013122177A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve deterioration in fuel consumption for NOreduction, in an exhaust emission control device for an internal combustion engine with a NOreduction catalyst device carrying a base metal catalyst and having low NOreduction performance.SOLUTION: A NOreduction catalyst device 40 carrying a base metal catalyst is disposed at a third exhaust passage 30 positioned at a downstream side of a confluence part 100 between a first exhaust passage 10 of a first cylinder group and a second exhaust passage 20 of a second cylinder group. A NOstorage device 50 is disposed at the second exhaust passage. A communication passage 60 communicating the second exhaust passage at a downstream side of the NOstorage device with the third exhaust passage at a downstream side of the NOstorage device is provided. When a combustion air-fuel ratio of the first cylinder group is made rich and when a combustion air-fuel ratio of the second cylinder group is made lean, exhaust gas flowing out from the NOstorage device passes through the communication passage. When the combustion air-fuel ratio of the second cylinder group is made rich, the exhaust gas flowing out from the NOstorage device passes through the NOreduction catalyst device.

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

HC in exhaust gas, CO, and to purify NO _X, it is known to place a three-way catalytic converter in the engine exhaust system. However, a noble metal catalyst such as platinum generally used in a three-way catalyst device is expensive, and it has been proposed to use a base metal catalyst instead of the noble metal catalyst (see Patent Document 1).

However, this way the three-way catalytic converter, or use a base metal catalyst instead of the noble metal catalyst, or, when a portion of a noble metal catalyst or replace the base metal catalyst, reduction performance of the NO _X is reduced as NO _X reducing catalyst device for the, the combustion air-fuel ratio in the slightly richer than the stoichiometric air-fuel ratio, it is considered possible to facilitate the reduction of NO _X by increasing the concentration of the reducing substance such as HC and CO in the exhaust gas.

JP2011-125862A

As described above, in the exhaust purification system for an internal combustion engine having a reducing capability is low NO _X reduction catalyst device of the NO _X carries a base metal catalyst, the combustion air-fuel ratio to satisfactorily reduce NO _X than the stoichiometric air-fuel ratio If it is made rich, fuel consumption will be greatly degraded.

Accordingly, the present invention purposes, in the exhaust purification system for an internal combustion engine having a reducing capability is low NO _X reduction catalyst device of the NO _X carries a base metal catalyst, the fuel consumption for the reduction of the NO _X in the exhaust gas It is to improve the deterioration.

An exhaust emission control device for an internal combustion engine according to claim 1 of the present invention is an exhaust purification device for a multi-cylinder internal combustion engine having at least a first cylinder group consisting of one cylinder and a second cylinder group consisting of other cylinders. Te, NO _X reduction catalyst device arranged for carrying a base metal catalyst in the third exhaust passage located downstream from the merging portion of the second exhaust gas passage of the second cylinder group to the first exhaust passage of the first cylinder group is the the second exhaust gas passage occludes NO _X in the exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, NO _X air-fuel ratio of the exhaust gas which is occluded becomes richer than the stoichiometric air-fuel ratio _the NO _X storage device is arranged to release the communication passage for communicating the downstream side of the NO _X reduction catalyst device at the downstream side of the third exhaust passage of the _the NO _X storage device of the second exhaust passage is provided , The combustion air-fuel ratio of the first cylinder group And richer than Ronsora ratio, exhaust gas flowing out of the _the NO _X storage device when the leaner than the combustion air-fuel ratio the stoichiometric air-fuel ratio of the second cylinder group is made to pass through the communication passage, said second cylinder When the combustion air-fuel ratio of the group is made richer than the stoichiometric air-fuel ratio, the exhaust gas flowing out from the NO _x storage device is made to pass through the NO _x reduction catalyst device.

An exhaust purification system of an internal combustion engine according to claim 2 of the present invention, in the exhaust purification system of an internal combustion engine according to claim 1, when _the NO _X storage amount of the _the NO _X storage device is set amount, the second The combustion air-fuel ratio of the cylinder group is switched from lean to rich than the stoichiometric air-fuel ratio.

  An internal combustion engine exhaust gas purification apparatus according to a third aspect of the present invention is the internal combustion engine exhaust gas purification apparatus according to the first or second aspect, wherein the third exhaust path is located downstream of the connection position of the communication path. The oxidation catalyst device is arranged.

  According to a fourth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the third aspect, wherein the oxidation catalyst device has an ammonia storage function.

According to the exhaust gas purification apparatus for an internal combustion engine according to claim 1 of the present invention, an exhaust gas purification apparatus for a multi-cylinder internal combustion engine having at least a first cylinder group consisting of one cylinder and a second cylinder group consisting of other cylinders. An NO _x reduction catalyst device carrying a base metal catalyst is disposed in a third exhaust passage located downstream from the junction of the first exhaust passage of the first cylinder group and the second exhaust passage of the second cylinder group. is, the second exhaust gas passage occludes NO _X in the exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, the NO _X air-fuel ratio occluding becomes richer than the stoichiometric air-fuel ratio of the exhaust gas A NO _x storage device for discharging is disposed, and a communication passage is provided for communicating the downstream side of the NO _x storage device in the second exhaust passage and the downstream side of the NO _x reduction catalyst device in the third exhaust passage, and the first cylinder group Make the combustion air-fuel ratio of the engine richer than the theoretical air-fuel ratio, Exhaust gas flowing out from _the NO _X storage device when the combustion air-fuel ratio of the second cylinder bank to leaner than the stoichiometric air-fuel ratio is adapted to pass through the communication passage. Thereby, the exhaust gas of the rich first cylinder group than the stoichiometric air-fuel ratio passes through the first exhaust passage flows into the NO _X reduction catalyst device of the third exhaust passage, the reducing performance of the NO _X carries a base metal catalyst Even with a low NO _x reduction catalyst device, NO _x in the exhaust gas can be reduced and purified well by using HC and CO in the exhaust gas.

On the other hand, NO _X in the exhaust gas of lean second cylinder group than the stoichiometric air-fuel ratio, for reduction performance of the NO _X can not be satisfactorily cleaned in the low NO _X reduction catalyst device disposed in the second exhaust passage Is stored in the NO _X storage device. In this way, atmospheric release of NO _x discharged from each cylinder of the internal combustion engine can be sufficiently suppressed, and NO _x can be reduced as compared with the case where the combustion air-fuel ratio of all cylinders is made richer than the stoichiometric air-fuel ratio. The deterioration of fuel consumption can be improved.

Further, when the rich than the stoichiometric air-fuel ratio of the combustion air-fuel ratio of the second cylinder group, in order _the NO _X storage device that releases NO _X occluding the exhaust gas flowing out from _the NO _X storage devices NO _X reduction catalyst device is adapted to pass through, NO _X released from _the NO _X storage device with NO _X discharged from the first cylinder group, rich exhaust gas the stoichiometric air-fuel ratio from the first cylinder group and the second cylinder group use HC and CO contained in the can reduced performance of the NO _X is also well purified in low NO _X reduction catalyst device.

According to the exhaust purification device for an internal combustion engine according to claim 2 of the present invention, in the exhaust purification device for the internal combustion engine according to claim 1, when the NO _x storage amount of the NO _x storage device becomes a set amount, The combustion air-fuel ratio of the second cylinder group is switched from lean to rich than the stoichiometric air-fuel ratio. As a result, even if the NO _X storage amount of the NO _X storage device is saturated, the combustion air-fuel ratio of the second cylinder group is prevented from continuing to be leaner than the stoichiometric air-fuel ratio.

According to the exhaust purification device for an internal combustion engine according to claim 3 of the present invention, in the exhaust purification device for the internal combustion engine according to claim 1 or 2, the downstream side of the connection position of the communication passage in the third exhaust passage. Is provided with an oxidation catalyst device. Thereby, when the combustion air-fuel ratio of the second cylinder group is leaner than the stoichiometric air-fuel ratio, a part of the HC and CO contained in the exhaust gas of the first cylinder group richer than the stoichiometric air-fuel ratio is NO _X. Even if it flows out from the reduction catalyst device, the oxidation catalyst device can be satisfactorily oxidized and purified using oxygen contained in the exhaust gas of the second cylinder group that is leaner than the stoichiometric air-fuel ratio.

According to the exhaust gas purification apparatus for an internal combustion engine according to claim 4 of the present invention, in the exhaust gas purification apparatus for the internal combustion engine according to claim 3, the oxidation catalyst device has an ammonia storage function. Thereby, even if NO _{x in} the exhaust gas of the first cylinder group richer than the stoichiometric air-fuel ratio is reduced in the NO _x reduction catalyst device and ammonia is generated, it can be occluded by the ammonia occlusion function of the oxidation catalyst device. . The ammonia occluded in the oxidation catalyst device thus becomes the set amount of the NO _x occlusion amount of the NO _x occlusion device, so that the combustion air-fuel ratio of the second cylinder group becomes richer than the stoichiometric air fuel ratio, and the NO _x occlusion device removes the NO _x when but released, even if outflow without some of the NO _X is purified in NO _X reduction catalyst device, in the oxidation catalyst device can be satisfactorily reduced and purified by ammonia being occluded.

1 is a schematic view showing an exhaust gas purification apparatus for an internal combustion engine according to the present invention. It is a flowchart which shows control of the exhaust gas purification apparatus of FIG.

  FIG. 1 is a schematic view showing an exhaust gas purification apparatus for an internal combustion engine according to the present invention. The internal combustion engine is, for example, an in-cylinder injection spark ignition four-cylinder internal combustion engine. The # 1 cylinder is a first cylinder group consisting of at least one cylinder, and the # 2 cylinder, # 3 cylinder and # 4 cylinder are a second cylinder group consisting of other cylinders. Of course, the total number of cylinders, the number of cylinders constituting the first cylinder group, and the number of cylinders constituting the second cylinder group are examples, and any of them can be set arbitrarily.

10 is a first exhaust passage of the first cylinder group, and 20 is a second exhaust passage of the second cylinder group. A NO _x reduction catalyst device 40 is disposed in the third exhaust passage 30 located downstream of the joining portion 100 between the first exhaust passage 10 and the second exhaust passage 20. The NO _x reduction catalyst device 40 is not an expensive noble metal catalyst such as platinum Pt such as a general three-way catalyst device, but a copper Cu, iron Fe, silver Ag, gold Au or the like on a substrate having a honeycomb structure. The base metal catalyst is supported on alumina or ceria as a carrier. Further, the NO _x reduction catalyst device 40 may be one in which the amount of expensive noble metal catalyst used is reduced by replacing a part of the noble metal catalyst of a general three-way catalyst device with a base metal catalyst.

Further, a NO _x storage device 50 is disposed on the downstream side of the exhaust manifold 21 in the second exhaust passage 20. The NO _x storage device 50 is, for example, a device in which palladium Pd or the like is supported on a honeycomb structure substrate using zirconia ZrO ₂ or the like as a carrier, and in the exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. of occluding NO _X, those air-fuel ratio of the exhaust gas to release the NO _X occluding becomes richer than the stoichiometric air-fuel ratio. _The NO _X storage device 50 is, for example, alkali metal (K, Na) and alumina or the like as a carrier or alkaline earth metal (Ba, Sr) and precious metals (Pt, Pd, Rh) and general _the NO _X storage bearing the A reduction catalyst device may be used.

A communication passage 60 that communicates the downstream side of the NO _x storage device 50 in the second exhaust passage 20 and the downstream side of the NO _x reduction catalyst device 40 in the third exhaust passage 30 is a NO _x storage device 50 in the second exhaust passage 20. Are connected via a switching valve 70 arranged on the downstream side. By setting the switching valve 70 to the first position, the exhaust gas of the second cylinder group passes through the communication passage 60 and reaches the downstream side of the NO _x reduction catalyst device 40 in the third exhaust passage 30 as indicated by the solid line arrow. Merge into the three exhaust passages 30. On the other hand, by setting the switching valve 70 to the second position, the exhaust gas of the second cylinder group passes through the second exhaust passage 20 as it is and does not pass through the communication passage 60 as shown by the dotted arrows. In the part 100, the exhaust gas flows into the third exhaust passage 30 together with the exhaust gas of the first cylinder group.

Above of the NO _X reduction catalyst device 40, compared to the typical three-way catalytic converter which carries a noble metal catalyst, for reduction performance decreases, sufficiently reduces and purifies NO _X in the exhaust gas of the stoichiometric air-fuel ratio Therefore, the combustion air-fuel ratio must be slightly richer than the stoichiometric air-fuel ratio (for example, air-fuel ratio 14) to increase the concentration of reducing substances in the exhaust gas so that NO _x can be sufficiently reduced. However, if the combustion air-fuel ratio is made richer than the stoichiometric air-fuel ratio in all the cylinders, fuel consumption will deteriorate.

  In order to improve this problem, the exhaust emission control device is controlled by an electronic control device (not shown) according to the flowchart shown in FIG. First, in step 101, the combustion air-fuel ratio of the first cylinder group (# 1 cylinder) is made slightly richer (for example, air-fuel ratio 14) than the stoichiometric air-fuel ratio. In order to enable such control of the combustion air-fuel ratio of the first cylinder group, the first air-fuel ratio of the exhaust gas of the first cylinder group is detected upstream of the merging portion 100 of the first exhaust passage 10. An air-fuel ratio sensor 11 is arranged.

Next, at step 102, it is determined whether or not the NO _X storage amount A of the NO _X storage device 50 has reached the set amount A ′. For example, 22 is the NO _X concentration sensor disposed downstream of _the NO _X storage device 50 can detect the NO _X concentration flowing out from _the NO _X storage device 50. Thereby, when the NO _X concentration detected by the NO _X concentration sensor 22 has become higher than the set concentration, _the NO _X storage amount A of _the NO _X storage device 50 reaches the set amount A ', _the NO _X storage device 50 It can be determined that the amount of NO _x flowing out from the fuel has increased.

If the determination in step 102 is negative, in step 103, the combustion air-fuel ratio of the second cylinder group (# 2, # 3, and # 4) is made leaner than the stoichiometric air-fuel ratio (for example, air-fuel ratio 15). . In order to enable such control of the combustion air-fuel ratio of the second cylinder group, the exhaust gas empty of the second cylinder group is interposed between the exhaust manifold 21 of the second exhaust passage 10 and the NO _x storage device 50. A second air-fuel ratio sensor 23 for detecting the fuel ratio is arranged. Next, at step 104, the switching valve 70 is set to the first position, and the exhaust gas of the second cylinder group passes through the communication passage 60 and downstream of the NO _x reduction catalyst device 40 in the third exhaust passage 30 as shown by the solid line. It is made to merge with the 3rd exhaust passage 30 in the side.

For example, without placing the NO _X concentration sensor 22, NO since _the NO _X storage amount A of _X storage device 50 is 0, _the NO _X storage device in the lean air-fuel ratio operation of the second cylinder bank each time 50 _{If the} amount of NO _X newly stored (which can be mapped for each engine operating state) is integrated, the current NO _X storage amount A can be estimated.

Exhaust gas rich first cylinder group than the stoichiometric air-fuel ratio passes through the first exhaust passage 10 flows into the third exhaust passage 30 of the NO _X reduction catalyst device 40, NO _X reduction catalyst device 40 is supported base metal catalyst However, NO _x in the exhaust gas can be reduced and purified well by using HC and CO in the exhaust gas.

On the other hand, NO _{x in} the exhaust gas of the second cylinder group that is leaner than the stoichiometric air-fuel ratio cannot be purified well by the NO _x reduction catalyst device 40 carrying the base metal catalyst, and is therefore disposed in the second exhaust passage 20. The NO _x storage device 50 is stored. Thus, it is possible to sufficiently suppress the air release of the NO _X discharged from each cylinder of the internal combustion engine, improve the deterioration of fuel consumption as compared with the case where a richer than the stoichiometric air-fuel ratio combustion air-fuel ratio of all cylinders can do.

When such a flow is repeated, the NO _x storage amount A of the NO _x storage device 50 becomes the set amount A ′, the determination of step 102 is affirmed, and in step 105, the combustion air-fuel ratio of the second cylinder group is increased. The air / fuel ratio is made slightly richer (for example, air / fuel ratio 14) than the stoichiometric air / fuel ratio. Next, at step 106, the switching valve 70 is set to the second position, and the exhaust gas of the second cylinder group does not pass through the communication passage 60 but passes through the second exhaust passage 20 as it is, as indicated by a dotted arrow. The merging portion 100 flows into the third exhaust passage 30 together with the exhaust gas of the first cylinder group.

Thereby, the exhaust gas of a rich air-fuel ratio flows into _the NO _X storage device 50 is NO _X is released from _the NO _X storage device, thus released NO _X flows into the NO _X reduction catalyst device 40, the first cylinder NO _x reduction catalyst device carrying base metal catalyst by using HC and CO contained in exhaust gas richer than stoichiometric air-fuel ratio from first cylinder group and second cylinder group together with NO _x discharged from the group 40 can be purified well.

Next, at step 107, it is determined whether or not the elapsed time t since the rich air-fuel ratio of the second cylinder group has reached the set time t ′, and when this determination is negative, the storage NO _X Is insufficient, and the NO _X storage amount A of the NO _X storage device 50 has not decreased to 0, the processing of steps 105 and 106 is continued. On the other hand, when the elapsed time t has reached the set time t 'is, NO as _the NO _X storage amount A of _X storage device 50 is decreased to 0, the process proceeds to step 103, the stoichiometric air-fuel ratio of the combustion air-fuel ratio of the second cylinder group In step 104, the switching valve 70 is set to the first position.

By the way, in the present exhaust purification apparatus, an oxidation catalyst device 80 carrying a base metal catalyst (or a noble metal catalyst) is disposed downstream of the connection position of the communication passage 60 in the third exhaust passage 30. Thereby, when the combustion air-fuel ratio of the second cylinder group is leaner than the stoichiometric air-fuel ratio, a part of the HC and CO contained in the exhaust gas of the first cylinder group richer than the stoichiometric air-fuel ratio is NO _X. Even if it flows out from the reduction catalyst device 40, the oxidation catalyst device 80 can be favorably oxidized and purified using oxygen contained in the exhaust gas of the second cylinder group that is leaner than the stoichiometric air-fuel ratio.

The oxidation catalyst device 80 has an ammonia occlusion function by, for example, carrying a super strong acid-treated zirconia ZrO ₂ , copper Cu or iron Fe as a support of zeolite ZSM5 or SAPO on a honeycomb structure substrate. It is preferable to make it. As a result, even if NO _{x in} the exhaust gas of the first cylinder group richer than the stoichiometric air-fuel ratio is reduced in the NO _x reduction catalyst device and ammonia is generated (CO + H ₂ O → H ₂ + CO ₂ , 2NO + 2CO + 3H ₂ → 2NH ₃ + 2CO ₂ ), and can be stored by the ammonia storage function of the oxidation catalyst device 80. Ammonia thus occluded in the oxidation catalyst device 80, the combustion air-fuel ratio of the second cylinder bank _the NO _X storage amount A of _the NO _X storage device 50 becomes a set amount A 'is richer than the stoichiometric air-fuel ratio, NO _X Even when a part of the NO _x flows out without being purified in the NO _x reduction catalyst device 40 when NO _x is released from the occlusion device 50, the oxidation catalyst device 80 satisfactorily reduces with the stored ammonia. It can be purified (6NO + 4NH ₃ → 5N ₂ + 6H ₂ O). Further, when the combustion air-fuel ratio of the second cylinder group is leaner than the stoichiometric air-fuel ratio, even if a slight amount of NO _x leaks from the NO _x storage device 50, the oxidation catalyst device 80 performs reduction purification with the stored ammonia. can do.

10 First exhaust passage 20 second exhaust gas passage 30 third exhaust passage 40 NO _X reduction catalyst device 50 NO _X occluding device 60 communication path 70 switch valve 80 oxidation catalyst device

Claims (4)

An exhaust purification device for a multi-cylinder internal combustion engine having a first cylinder group consisting of at least one cylinder and a second cylinder group consisting of other cylinders, wherein the first exhaust passage and the second cylinder of the first cylinder group NO _X reduction catalyst device carrying a base metal catalyst in the third exhaust passage is arranged to be positioned on the downstream side of the merging portion of the second exhaust gas passage of the group, said the second exhaust gas passage air-fuel ratio is the stoichiometric air-exhaust gas when more fuel ratio is lean to occlude NO _X in the exhaust gas, the air-fuel ratio of the exhaust gas is arranged _the NO _X storage device that releases NO _X occluding becomes richer than the stoichiometric air-fuel ratio, the second exhaust passage A communication passage is provided that communicates the downstream side of the NO _X storage device and the downstream side of the NO _X reduction catalyst device of the third exhaust passage, and the combustion air-fuel ratio of the first cylinder group is made richer than the stoichiometric air-fuel ratio. , The combustion air-fuel ratio of the second cylinder group When to leaner than Ronsora ratio exhaust gas flowing out of the _the NO _X storage device is adapted to pass through the communication passage, the NO _X when the rich than the stoichiometric air-fuel ratio of the combustion air-fuel ratio of the second cylinder group An exhaust gas purification apparatus for an internal combustion engine, characterized in that exhaust gas flowing out from the storage device passes through the NO _x reduction catalyst device. 2. The exhaust of the internal combustion engine according to claim 1, wherein when the NO _X storage amount of the NO _X storage device reaches a set amount, the combustion air-fuel ratio of the second cylinder group is switched from lean to rich than the stoichiometric air-fuel ratio. Purification equipment.   3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein an oxidation catalyst device is disposed downstream of the connection position of the communication passage in the third exhaust passage.   The exhaust purification device for an internal combustion engine according to claim 3, wherein the oxidation catalyst device has an ammonia storage function.

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