CN100410503C - Exhaust purification device for internal combustion engines - Google Patents

Abstract

The three-way catalyst (30) is composed of a small-pore catalyst element (30a) having an average opening size smaller than the molecular size of HC on the coating and a small-pore catalyst element (30a) having an average opening size larger than the molecular size of the HC on the coating. The composition of the macropore catalyst element (30b) of the macropore group.

Description

Exhaust purification device for internal combustion engines

technical field

The invention relates to an exhaust purification device of an internal combustion engine, in particular to a technology for improving the purification efficiency of a three-way catalyst.

Background technique

Generally, three-way catalysts are widely used as exhaust purification catalysts for internal combustion engines for vehicles. The three-way catalyst tries to optimize the oxidation of HC (hydrocarbon), CO (carbon monoxide) and the reduction of NO _X by controlling the exhaust air-fuel ratio near the theoretical air-fuel ratio (stoichiometric ratio), which can promote exhaust gas purify.

Also, recently, there has been developed an exhaust purification device in which the catalyst, for example, is made into a porous structure, _NOx , oxygen (O ₂ ), HC, and CO are trapped in the pores, and HC and CO are trapped in the pores in a reducing atmosphere. Trapped in pores, and oxidized with captured _NOx and _O2 , on the other hand, _NOx and _O2 are trapped in pores in an oxidizing atmosphere, and _NOx is reduced with captured HC and CO.

Even also develop such a kind of technology, in the porous structure, make the pores smaller to hinder the reductant HC from getting close to the oxidation catalyst, so that only the reaction that is useful for the purification of _NOx can be promoted (for example: refer to the Japan National Special Publication No. 2001-525241).

However, in general three-way catalysts, the redox reaction between CO and _NOx is faster than the redox reaction between HC and _NOx , and if HC and CO can be separated, the oxidation of CO and _NOx is given priority The reduction reaction can improve the purification performance of _NOx .

However, because HC and CO in the exhaust gas are mixed in a reducing atmosphere, the technology disclosed in the previous porous structure including the publication cannot capture HC and CO separately, so the presence of macromolecular HC hinders the presence of small molecule CO There is a problem that the oxidation-reduction reaction with _NOx cannot promote the oxidation-reduction reaction of CO and _NOx which has a high reaction rate. There is also a problem that if the oxidation-reduction reaction of CO and NO _x cannot be promoted in this way, a part of CO will react with O ₂ , resulting in insufficient O ₂ for oxidizing HC.

Contents of the invention

The present invention is made to solve the above-mentioned problems, and the purpose is to provide an exhaust purification device for an internal combustion engine, which actively separates HC and CO, and preferentially occurs the oxidation-reduction reaction of CO and _NOx on the catalyst, thereby improving exhaust purification. performance.

In order to achieve the above object, the exhaust purification device of the internal combustion engine of the present invention is characterized in that a three-way catalyst is provided on the exhaust passage of the internal combustion engine, and the three-way catalyst is composed of one or more catalyst elements, and the coating There are two or more groups of pores with different average opening sizes.

According to this, multiple components (such as oxidizing agent and reducing agent) in the exhaust gas can be screened and captured in each catalyst element according to the size of the molecule, and the oxidation reaction and the reduction reaction can be carried out well without the hindrance of other components, and the purification of exhaust gas can be improved. performance.

Ideally, the three-way catalyst is composed of a small pore catalyst element with a small pore group with an average opening size smaller than the specified size on the coating, and a large pore group with an average opening size larger than the specified size on the coating. The composition of large and fine pore catalyst elements is appropriate.

According to this, among a plurality of components (such as oxidizing agent and reducing agent) in the exhaust gas, the components with small molecules can be trapped in the catalyst elements with small pores, and the components with large molecules can be captured in the catalyst elements with large pores. That is, it can separate and capture components with small molecules and components with large molecules, and can carry out oxidation reaction and reduction reaction well without the hindrance of other components, thereby improving exhaust gas purification performance.

In this case, it is desirable that the three-way catalyst is composed of a small-pore catalyst element with an average opening size smaller than the molecular size of the HC on the coating, and a small-pore catalyst element having an average opening size smaller than the molecular size of the HC on the coating. Composition of macroporous catalyst elements with macroporous groups of large molecular size.

According to this, among the various components in the exhaust gas (such as O ₂ , NO _X , HC, CO, H ₂ ), especially CO, O ₂ , NO _X , and H ₂ with small molecules can be separated and captured into fine particles. Among the porous catalyst elements, the HC with large molecular weight is separated and captured into the large-pore catalyst elements, and the oxidation-reduction reaction of CO and NO _X is given priority over the oxidation-reduction reaction of HC and NO _X mainly in an oxidizing atmosphere, without the hindrance of HC , can promote the reaction well, and can improve the purification performance of NO _x . Furthermore, since the oxidation-reduction reaction of CO and _NOx is promoted, _O2 can be fully used for the oxidation reaction with HC, and the purification performance of HC can also be improved. Therefore, the exhaust purification performance can be comprehensively improved.

Also, preferably, the small-pore catalyst element and the large-pore catalyst element are arranged in series when viewed in the exhaust gas flow direction.

According to this, small-molecule CO and macromolecule HC can be reliably separated and captured sequentially into the small-pore catalyst element and the large-pore catalyst element.

In this case, it is preferable that the small-pore catalyst element is arranged on the exhaust gas upstream side, and the large-pore catalyst element is arranged on the exhaust gas downstream side.

Accordingly, the small molecule CO can be separated and captured into the small-pore catalyst element on the upstream side of the exhaust gas, and the macromolecule HC can be separated and captured into the large-pore catalyst element on the exhaust gas downstream side. Therefore, the oxidation-reduction reaction of CO and _NOx , which has a faster reaction rate, is performed preferentially over the oxidation-reduction reaction of HC and _NOx , so that the purification performance of _NOx can be improved. Furthermore, since the oxidation-reduction reaction of CO and _NOx is performed preferentially, _O2 can be fully used for the oxidation reaction with HC on the exhaust gas downstream side, and the purification performance of HC can also be improved. Therefore, the exhaust purification performance can be comprehensively improved.

Furthermore, preferably, the small-pore catalyst elements and the large-pore catalyst elements are preferably arranged in layers.

Accordingly, the small molecule CO and the large molecule HC can be separated and captured into the small pore catalyst element and the large pore catalyst element, and the temperature of the small pore catalyst element and the large pore catalyst element can be raised approximately simultaneously at the time of cold start, etc. , to make it active.

In this case, it is preferable that the small-pore catalyst element is arranged on the surface layer side, and the large-pore catalyst element is arranged on the inner layer side.

Accordingly, the small molecule CO can be separated and captured into the small-pore catalyst element on the surface side, and the macromolecule HC can be separated and captured into the large-pore catalyst element on the inner side, and the reaction can be reliably performed on the surface side. The oxidation-reduction reaction of CO and _NOx is prioritized over the oxidation-reduction reaction of HC and _NOx , which can improve the purification performance of _NOx . Furthermore, since the oxidation-reduction reaction of CO and _NOx is performed preferentially, _O2 can be fully used for the oxidation reaction with HC on the inner layer side, and the purification performance of HC can also be improved. Thereby, exhaust gas purification performance can be improved overall.

Furthermore, it is desirable to have air-fuel ratio adjustment means for periodically switching the air-fuel ratio of the exhaust gas flowing into the three-way catalyst between a lean air-fuel ratio and a rich air-fuel ratio.

Accordingly, an oxidizing atmosphere and a reducing atmosphere can be generated periodically, for example, the small molecules CO and macromolecules HC captured in the reducing atmosphere are used in the redox reaction in the oxidizing atmosphere, and these small molecules are repeatedly treated in the reducing atmosphere. Continuous capture of CO and macromolecular HC can efficiently maintain good exhaust purification performance.

In this case, it is better to switch to the oxidizing atmosphere before the capture amount of the small molecule CO in the reducing atmosphere reaches the excess amount, and to switch to the reducing atmosphere before the capture amount of the macromolecule _NO in the oxidizing atmosphere reaches the excess amount. Maintain good exhaust purification performance.

Description of drawings

The features of this invention, including other objects and advantages, will be explained in the following description of the drawings. In the drawings, the same reference characters designate the same or like parts throughout the drawings, wherein:

Fig. 1 is a schematic structural view of an internal combustion engine exhaust purification device of the first embodiment of the present invention mounted on a vehicle;

Fig. 2 is a quarter part (a) showing the unit grid of the small-pore catalyst element, an enlarged view (b) of the catalyst coated on the quarter part, and one particle on the washcoat (w/c) Expanded view of (c);

Fig. 3 is a quarter part (a) showing the unit grid of the large-pore catalyst element, an enlarged view (b) of the catalyst coated on the quarter part, and one particle on the washcoat (w/c) Expanded view of (c);

Fig. 4 shows the frequency distribution of the pore opening size (solid line) on the small pore catalyst element and the pore opening size (dotted line) on the large pore catalyst element, and each average opening size X and average opening size Y;

Fig. 5 is a flow chart showing a control program of _O2F /B control in the first embodiment;

Fig. 6 is the figure that represents the three-way catalyst of other embodiment of the 1st embodiment;

Fig. 7 is the figure that represents the 2nd embodiment three-way catalyst;

Fig. 8 is the figure that represents the three-way catalyst of other embodiment of the 2nd embodiment;

Fig. 9 is a diagram representing a quarter of the unit lattice of the three-way catalyst in the third embodiment;

Fig. 10 is a diagram showing a quarter of the unit lattice of the three-way catalyst in the fourth embodiment;

Fig. 11 is a flowchart of a control program of A/F conversion control in the fifth embodiment.

Detailed ways

Next, embodiments of the present invention will be described with reference to the drawings.

First, the first embodiment will be described.

Referring to FIG. 1 , it is a schematic structural view of an exhaust gas purification device of an internal combustion engine of the present invention mounted on a vehicle. Next, the structure of the exhaust gas purification device will be described.

As shown in this figure, on the cylinder head 2 of the internal combustion engine body (such as a gasoline engine, hereinafter referred to as the engine) 1, a spark plug 4 is installed on each cylinder, and the spark plug 4 is connected with an ignition coil 8 that outputs a high voltage. .

In the cylinder head 2, intake ports are formed for each cylinder, and one end of an intake manifold 10 is connected to each intake port in order to communicate with each intake port. An electromagnetic fuel injection valve 6 is installed on the intake manifold 10 , and the fuel injection valve 6 is connected with a fuel supply device (not shown) having a fuel tank through a fuel pipe 7 .

On the upstream side of the fuel injection valve 6 on the intake manifold 10, an electromagnetic throttle valve 14 that adjusts the amount of intake air is provided, and a throttle opening sensor (TPS) that detects the valve opening of the throttle valve 14 is provided at the same time. )16. Furthermore, an air flow sensor 18 for measuring the amount of lean air is interposed upstream of the throttle valve 14 .

Also, exhaust ports are formed for each cylinder on the cylinder head 2, and one end of an exhaust manifold 12 is connected to each exhaust port so as to communicate with each exhaust port.

The other end of the exhaust manifold 12 is connected to an exhaust pipe (exhaust channel) 20, which is sandwiched with a triple-effect catalyst device as an exhaust purification catalyst device, which is made into a single type and has a lattice-shaped carrier cross section. Catalyst 30.

The coating on the carrier surface of the three-way catalyst 30 has any one of copper (Cu), cobalt (Co), silver (Ag), platinum (Pt), rhodium (Rh), and palladium (Pd) as the active metal.

In addition, the three-way catalyst 30 has a large number of fine pores formed on the coating in addition to the active metal. Specifically, the three-way catalyst 30 is composed of a small-pore catalyst element 30a having a group of small pores whose average opening size is smaller than the molecular size (predetermined size) of HC and having an average opening size larger than the molecular size of HC. The large-pore catalyst element 30b of the large-pore group is composed. The small pore catalyst element 30a is arranged on the exhaust gas upstream side, and the large pore catalyst element 30b is arranged in series with the small pore catalyst element 30a on the exhaust gas downstream side.

That is, with reference to Fig. 2, represent the quarter part (a) of the unit lattice of small pores catalyst element 30a, and represent the enlarged view (b) and coating (w/ As shown in the enlarged view (c) of one particle in c), a large number of small pores S having an opening size smaller than the molecular size of HC are formed on the coating layer of the small-pore catalyst element 30a.

Also, with reference to Fig. 3, it shows a quarter part (a) of the large pores catalyst element 30b unit lattice, and represents an enlarged view (b) and coating (w/ As shown in the enlarged view (c) of one particle in c), a large number of large pores L having an opening size larger than the molecular size of HC are formed on the coating layer of the large-pore catalyst element 30b.

That is, with reference to Fig. 4, the frequency distribution of the pore opening size (solid line) on the small pore catalyst element 30a and the pore opening size (dotted line) on the large pore catalyst element 30b is shown, respectively representing the average opening size x As for the average opening size Y, a difference is provided between the average opening size of pores in the small pore catalyst element 30a and the large pore catalyst element 30b. Therefore, the three-way catalyst 30 can capture CO, O ₂ , NO _x , and H ₂ , which are smaller in molecular size than HC, in the small pores S on the small pore catalyst element 30a on the upstream side of the exhaust gas, and can capture HC having a large molecular size is trapped in the large pores L on the large pore catalyst element 30b on the exhaust gas downstream side.

For example, the opening size of the pores is controlled by a soaking method or a CVD (Chemical Vapor Deposition: Chemical Vapor Deposition) method.

左右。又，大细孔催化剂要素30b例如是沸石5A、ZSM-5、β等，其直径是5～

左右。另外，大细孔催化剂要素30b也可以是此外的一般的催化剂(例如，以Al₂O₃等为主成分的催化剂)。The small-pore catalyst element 30a is, for example, zeolite 3A, Ca-morilite, etc., and its diameter is 3-3.

about. Again, the macroporous catalyst element 30b is, for example, zeolite 5A, ZSM-5, β, etc., and its diameter is 5-5

about. In addition, the large-pore catalyst element 30b may be another general catalyst (for example, a catalyst mainly composed of Al ₂ O ₃ or the like).

As substances that have been effectively controlled in pore size, there are zeolite, SAPO (silicoaluminophosphate), and ALPO (aluminum phosphate), but not limited thereto. If there is a substance with a different pore size, any substance other than the above may be used. Substances for screening HC, CO, NO _x , H ₂ , etc. can also be used for substances of any size and shape other than those mentioned above.

On the upstream side of the three-way catalyst 30 in the exhaust pipe 20, an air-fuel ratio sensor 22 for detecting an exhaust air-fuel ratio (exhaust gas A/F) based on the oxygen concentration in the exhaust gas is disposed. An O ₂ sensor is used as the air-fuel ratio sensor 22 , and a linear A/F sensor (LAFS) or the like may be used.

ECU (Electronic Control Unit) 40 has: input and output devices, storage devices (ROM, RAM, non-volatile RAM, etc.), central processing unit (CPU), timing timer, etc. Comprehensive control of the gas purification device.

The input side of the ECU 40 is connected to various sensors such as the crank angle sensor 42 for detecting the crank angle of the engine 1 in addition to the TPS 16 , the air flow sensor 18 , and the air-fuel ratio sensor 22 , and inputs detection information from these sensors. In addition, the engine rotational speed Ne is detected based on crank angle information from the crank angle sensor 42 .

On the other hand, the output side of the ECU is connected to various output devices such as the fuel injection valve 6, the ignition coil 8, and the throttle valve 14, and the fuel injection amount and fuel injection time calculated based on the detection information from various sensors , ignition time, etc. are output to these output devices respectively.

Specifically, the air-fuel ratio is set to an appropriate target air-fuel ratio (target A/F) based on the detection information from various sensors, and the fuel that meets the target A/F amount is injected from the fuel injection valve 6 in due time, and then the The throttle valve 14 is adjusted to an appropriate opening, and the spark plug 4 is used to implement spark ignition in good time.

In more detail, based on the information from the air-fuel ratio sensor 22, the exhaust gas A/F performs O ₂ feedback (O ₂ F/B) control in order to achieve the target A/F (eg, stoichiometric ratio), and the fuel injection amount accordingly In fact, the exhaust A/F changes periodically around the target A/F between the rich air-fuel ratio (rich A/F) side and the lean air-fuel ratio (lean A/F) side (air-fuel ratio adjustment means).

Next, the operation of the exhaust purification device of the present invention having the above-mentioned configuration will be described.

Referring to Fig. 5, the control program of the O ₂ F/B control is represented by a flow chart, and the following description will be made along this flow chart.

First, in step S10, it is judged whether the exhaust A/F is currently lean A/F or rich A/F based on the information from the air-fuel ratio sensor 22, that is, the O ₂ sensor. If it is determined that the A/F is lean, rich operation is performed in step S12. Specifically, the fuel injection amount is corrected incrementally.

When the rich operation is performed in this way, the exhaust gas A/F becomes rich A/F, the exhaust gas contains a large amount of HC and CO, and the three-way catalyst 30 becomes a reducing atmosphere.

As will be described later, before the three-way catalyst 30 becomes a reducing atmosphere, the small pores S of the small-pore catalyst element 30a trap _NOx and _O2 having a molecular size smaller than HC, so once the three-way catalyst 30 becomes a reducing atmosphere, , then these NO _X and O ₂ are released and undergo redox reactions with CO and HC in the exhaust gas. At this time, because the redox reaction between CO and _NOx is faster than the redox reaction between HC and _NOx , the released _NOx reacts preferentially with CO, and the released _O2 reacts well with HC. reaction.

And, if NO _x and O ₂ are released sufficiently, the small pores S of the small pore catalyst element 30a on the exhaust gas upstream side capture well CO and H ₂ whose molecular size is smaller than that of HC, and on the other hand, the exhaust gas downstream side The large pores L of the large pore catalyst element 30b capture HC having a large molecular size well. That is, in the three-way catalyst 30, CO and HC are actively separated and captured in the small-pore catalyst element 30a and the large-pore catalyst element 30b, respectively.

Thereafter, if it is judged to be rich A/F based on the judgment in step S10, lean operation is performed in step S14 this time. Specifically, the fuel injection amount is corrected by decreasing the amount.

When the lean operation is performed in this way, the exhaust gas A/F becomes lean A/F, the exhaust gas contains a large amount of O ₂ and NO _x , and the three-way catalyst 30 becomes an oxidizing atmosphere.

As mentioned above, the captured CO, H ₂ , and HC are released and undergo redox reactions with O ₂ and NO _X in the exhaust gas. At this time, since CO and HC are separated and captured in the small pore catalyst element 30a and the large pore catalyst element 30b as described above, CO and _H2 are released in the small pore catalyst element 30a on the upstream side of the exhaust gas, At the same time, the reaction rate of the oxidation-reduction reaction of CO and _NOx is faster than the redox reaction of HC and _NOx , so the CO released in the small-pore catalyst element 30a on the upstream side of the exhaust gas and the _NOx in the exhaust gas have priority and Respond reliably. And, by using CO for the reaction with _NOx in this way, the HC released from the large-pore catalyst element 30b on the exhaust gas downstream side fully reacts with _O2 in the exhaust gas.

That is, the exhaust gas purifying device of the first embodiment switches the exhaust A/F between lean A/F and rich A/F by O ₂ F/B control to generate an oxidizing atmosphere and a reducing atmosphere favorably, In a reducing atmosphere, CO and HC are repeatedly and continuously captured on the three-way catalyst 30 in the state of separation of CO and HC. In an oxidizing atmosphere, the released CO and _H are not hindered by the released HC and are combined with the _NOx in the exhaust gas. Responds preferentially and reliably to improve the purification performance of NO _X. Also, since CO and H ₂ are used in the reaction with NO _x in this way, the released HC reacts sufficiently with O ₂ in the exhaust gas to improve the purification performance of HC. As a result, the exhaust purification performance of the three-way catalyst 30 is comprehensively improved and maintained at a high level.

In addition, here, as shown in FIG. 1, the three-way catalyst 30 in which the small-pore catalyst element 30a and the large-pore catalyst element 30b are completely connected in the direction of the exhaust flow has been described as an example. The catalyst element 30a and the large-pore catalyst element 30b are not necessarily connected. As another example, as shown in FIG.

Next, a second embodiment will be described.

The second embodiment differs from the first embodiment only in that the three-way catalyst 30 is replaced with a three-way catalyst 301 .

As shown in FIG. 7, the three-way catalyst 301 is composed of a large pore catalyst element 301a having an average pore opening size larger than the molecular size of HC and a small pore catalyst element 301b having an average pore size smaller than the molecular size of HC. The fine-pore catalyst element 301a is arranged on the exhaust gas upstream side, and the small-pore catalyst element 301b is arranged on the exhaust gas downstream side. That is, in the three-way catalyst 301 , the arrangement of the small-pore catalyst elements and the large-pore catalyst elements is reversed from that of the above-mentioned three-way catalyst 30 .

Next, the operation of the case where the large-pore catalyst element 301a is arranged on the exhaust gas upstream side and the small-pore catalyst element 301b is arranged on the exhaust gas downstream side will be described.

In rich operation under O ₂ F/B control, the three-way catalyst 301 is in a reducing atmosphere. As above, captured _NOx and O ₂ are released to undergo oxidation-reduction reactions with CO and HC in the exhaust gas. At this time, because the reaction rate of the oxidation-reduction reaction of CO and _NOx is faster than that of HC and _NOx , the released _NOx reacts preferentially with CO, and on the other hand, the released _O2 reacts well with HC .

In this way, after the _NOx and _O2 are fully released, the large pores L of the large-pore catalyst element 301a on the upstream side of the exhaust gas can capture HC with a large molecular size well, and on the other hand, the small pores L on the downstream side of the exhaust gas The small pores S of the pore catalyst element 301b capture well CO and H ₂ whose molecular size is smaller than that of HC, and in the three-way catalyst 301, HC and CO are actively separated and captured in the large pore catalyst element 301a similarly to the above. And in the small pore catalyst element 301b.

On the other hand, during lean operation, the three-way catalyst 301 is in an oxidizing atmosphere, and the captured HC, CO, and H ₂ are released to undergo oxidation-reduction reactions with O ₂ and NO _x in the exhaust gas. At this time, HC and CO are separated and captured in the large-pore catalyst element 301a and the small-pore catalyst element 301b as described above, so the released HC and the exhaust gas are mixed in the large-pore catalyst element 301a on the upstream side of the exhaust The _O2 in the gas reacts well, and in the small-pore catalyst element 301b on the downstream side of the exhaust gas, released CO and _H2 react well with _NOx in the exhaust gas without being hindered by the released HC.

Thereby, the purification performance of _NOx and the purification performance of HC are improved at the same time, and the exhaust purification performance of the three-way catalyst 301 is comprehensively improved.

In addition, in this case, the large-pore catalyst element 301a and the small-pore catalyst element 301b do not necessarily have to be integrated. As another example, as shown in FIG. 8, the large-pore catalyst element 301a and the small-pore catalyst element 301b Can be spaced in the direction of exhaust flow.

Next, a third embodiment will be described.

In the third embodiment, the only point that the three-way catalyst 30 is replaced with the three-way catalyst 302 is different from the above-mentioned first embodiment.

Referring to Fig. 9, it shows a quarter of a unit grid of a three-way catalyst 302, the three-way catalyst 302 is composed of a small pore catalyst element 302a with a pore average opening size smaller than the molecular size of HC and a pore average opening size The large-pore catalyst elements 302b having a molecular size larger than that of HC are arranged in layers, the small-pore catalyst elements 302a are arranged on the surface layer side, and the large-pore catalyst elements 302b are arranged on the inner layer side.

Next, the operation of the case where the small-pore catalyst element 302a is arranged on the surface layer side and the large-pore catalyst element 302b is arranged on the inner layer side will be described.

In rich operation under O ₂ F/B control, the three-way catalyst 302 is in a reducing atmosphere. As above, captured NO _x and O ₂ are released to undergo oxidation-reduction reactions with CO and HC in the exhaust gas. At this time, because the reaction rate of the oxidation-reduction reaction of CO and _NOx is faster than that of HC and _NOx , the released _NOx reacts preferentially with CO, and on the other hand, the released _O2 reacts well with HC .

In this way, after the _NOx and _O2 are sufficiently released, the small pores S of the small-pore catalyst element 302a on the surface layer side can capture CO and _H2 having a molecular size smaller than that of HC, while the small pores S on the inner layer side The large pores L of the large pore catalyst element 302b capture HC with a large molecular size well through the gaps in the small pore catalyst element 302a, and in the same way as above, in the three-way catalyst 302, HC and CO are actively separated and captured respectively. In the small pore catalyst element 302a and the large pore catalyst element 302b.

On the other hand, during lean operation, the three-way catalyst 302 is in an oxidizing atmosphere, and the captured HC, CO, and H ₂ are released to undergo oxidation-reduction reactions with O ₂ and NO _x in the exhaust gas. At this time, as described above, HC and CO are separated and captured in the small-pore catalyst element 302a and the large-pore catalyst element 302b, respectively, and CO and _H2 are released in the small-pore catalyst element 302a on the surface layer side. The reaction rate of the oxidation-reduction reaction of _NOx is faster than the redox reaction of HC and _NOx , so CO and _H2 released in the small-pore catalyst element 302a on the surface side react preferentially and reliably with _NOx in the exhaust gas . And, by using CO for the reaction with _NOx in this way, HC released from the large-pore catalyst element 302b on the inner layer side fully reacts with _O2 in the exhaust gas.

Thereby, the purification performance of _NOx and the purification performance of HC are improved at the same time, and the exhaust purification performance of the three-way catalyst 302 is comprehensively improved.

Also, if the small pore catalyst element 302a and the large pore catalyst element 302b are to be formed into layers like this, the small pore catalyst element 302a and the large pore catalyst element 302b are substantially simultaneously activated when the engine 1 is started in a cold state. Warm up for good activity.

Next, a fourth embodiment will be described.

The fourth embodiment differs from the third embodiment only in that the three-way catalyst 302 is replaced with the three-way catalyst 303 .

Referring to Fig. 10, it shows a quarter part of the three-way catalyst 303 unit lattice, and this three-way catalyst 303 is made of, the large pore catalyst element 303a with the average opening size of the pores larger than the molecular size of HC and the average opening size ratio of HC The small-pore catalyst elements 303b having small molecular sizes are arranged in layers, the large-pore catalyst elements 303a are arranged on the surface layer side, and the small-pore catalyst elements 303b are arranged on the inner layer side. That is, in the three-way catalyst 303 , the arrangement of the small-pore catalyst elements and the large-pore catalyst elements is opposite to that of the three-way catalyst 302 .

Next, the operation of the case where the large-pore catalyst element 303a is arranged on the surface layer side and the small-pore catalyst element 303b is arranged on the inner layer side will be described.

In rich operation under O ₂ F/B control, the three-way catalyst 303 is in a reducing atmosphere. As above, captured NO _x and O ₂ are released to undergo oxidation-reduction reactions with CO and HC in the exhaust gas. At this time, because the reaction rate of the oxidation-reduction reaction of CO and _NOx is faster than that of HC and _NOx , the released _NOx reacts preferentially with CO, and on the other hand, the released _O2 reacts well with HC .

Like this, NO _X and _O After being fully released, the large pores L of the large-pore catalyst element 303a on the surface layer side trap HC with a large molecular size well, and on the other hand, the small-pore catalyst elements on the inner layer side The small pores S of 303b capture well CO having a molecular size smaller than HC, and in the same way as above, in the three-way catalyst 303, HC and CO are actively separated and captured in the large pore catalyst element 303a and the small pore catalyst element, respectively. 303b.

On the other hand, when lean operation is performed, the three-way catalyst 303 is in an oxidizing atmosphere, and the captured HC and CO are released to undergo oxidation-reduction reactions with O ₂ and NO _x in the exhaust gas. At this time, since HC and CO are separated and captured in the large-pore catalyst element 303a and the small-pore catalyst element 303b as described above, the HC released in the large-pore catalyst element 303a on the surface layer side is mixed with the exhaust gas. _O2 reacts well. The CO released in the small-pore catalyst element 303b on the inner layer side reacts relatively favorably with NO _x in the exhaust gas without much hindrance from the released HC.

Thereby, the purification performance of _NOx and the purification performance of HC are improved at the same time, and the exhaust purification performance of the three-way catalyst 303 is improved overall.

Also, in this case, if the large-pore catalyst element 303a and the small-pore catalyst element 303b are to be formed into layers, the large-pore catalyst element 303a and the small-pore catalyst element will be separated when the engine 1 is started in a cold state. 303b heats up roughly at the same time for good activity.

Next, a fifth embodiment will be described.

The fifth embodiment differs from the first embodiment only in that A/F switching (air-fuel ratio adjustment means) is forcibly performed instead of the O ₂ F/B control.

Referring to Fig. 11, the control program of the A/F conversion control is shown by a flowchart, and the following description will be made along this flowchart.

First, in step 20, it is judged whether or not the timer has counted the predetermined time t1. The predetermined time t1 is set at a time when the amount of CO captured by the small-pore catalyst 30 a of the three-way catalyst 30 is expected to reach a saturated state, that is, to be excessive , for example, through previous experiments. That is, in step S20, it is judged whether or not the capture amount of CO is about to reach an excess amount.

If the result of the judgment in step S20 is negative (No), if it is judged that the predetermined time t1 has not elapsed, it can be judged that CO can be captured sufficiently, and the process proceeds to step S22 to perform or continue the rich operation. On the other hand, if the judgment result is affirmative (Yes) and it is judged that the predetermined time t1 has elapsed, the process proceeds to step S24.

In step S24, it is judged whether the timing timer has timed the prescribed time t2, and the prescribed time t2-t1 is set at, for example, when the amount of NO _x captured by the small-pore catalyst 30a of the three-way catalyst 30 is predicted to be saturated through previous experiments, i.e. broken over an excessive amount of time. That is, in step S24, it is judged whether or not the _NOx trapping amount is about to reach the excess amount.

If the result of the judgment in step S24 is negative (No), if it is judged that the predetermined time t2 has not passed, it can be judged that the _NOx can be captured sufficiently, and the process proceeds to step S26 to perform or continue lean operation. On the other hand, if the judgment result is affirmative (Yes) and it is judged that the predetermined time t2 has elapsed, the process proceeds to step S28 and the timer is reset to 0. In this way, thereafter, the rich operation and the lean operation are repeated.

That is, in the fifth embodiment, the exhaust gas A/F is efficiently shifted between the rich A/F and the lean A/F within the range in which the CO and NOx capture amounts of the three-way catalyst 30 do not reach the excessive amount. switch between.

Therefore, in the exhaust purification system of the fifth embodiment, the exhaust A/F is efficiently switched between the lean A/F and the rich A/F by the A/F switching control to generate an oxidizing atmosphere and Reducing atmosphere, in the reducing atmosphere, CO and HC are repeatedly and continuously captured in the three-way catalyst 30 in the state of separation of CO and HC, and in the oxidizing atmosphere, the released CO is not hindered by the released HC and _NOx in the exhaust gas Responds preferentially and reliably to improve the purification performance of NO _X. Also, since CO is used for the reaction with NO _x in this way, the released HC reacts sufficiently with O ₂ in the exhaust gas to improve the purification performance of HC. As a result, the exhaust gas purification performance of the three-way catalyst 30 is finally comprehensively improved and always well maintained.

In addition, here, the three-way catalyst 30 of the first embodiment has been described, but it is not limited thereto, and the three-way catalysts 301, 302, and 303 of the second to fourth embodiments can also be applied to the first embodiment. 5 examples.

In addition, in the above-described embodiment, the three-way catalyst is provided with a small-pore catalyst element and a large-pore catalyst element having different average opening sizes of pores to separate CO and HC, two components in the exhaust gas. However, it is also possible to arrange three or more catalyst elements (pore groups) according to the average opening size of finer pores according to the captured components, and to separate three or more components in the exhaust gas. Also, the components in the separated exhaust gas are not limited to CO and HC, and the separated components can be appropriately selected as necessary.

In addition, in the above-mentioned embodiment, a gasoline engine is used as the engine 1, but the engine 1 may be a diesel engine.

Having thus described the invention, it will be obvious that the invention may be varied in various ways. Such changes are not to be regarded as departing from the spirit and scope of the present invention, and all such modifications obvious to those skilled in the art are intended to be included within the scope of the following claims.

Claims (2)

1. An exhaust purification device of an internal combustion engine, characterized in that, having a three-way catalyst (30, 301, 302, 303) on the exhaust passage of the internal combustion engine, The three-way catalyst is composed of one or more catalyst elements, and the coating has more than two pore groups with different average opening sizes, The three-way catalyst is composed of a small-pore catalyst element with a group of small pores with a small average opening size that can separate CO, _O2 , _NOx , and _H2 whose molecular size is smaller than that of hydrocarbons. (30a, 301b, 302a, 303b), the coating has a large-pore catalyst element (30b, 301a, 302b, 303a) composed of large-pore groups with a large average opening size capable of capturing said hydrocarbons, The small-pore catalyst element (30a) is arranged on the exhaust gas upstream side, and the large-pore catalyst element (30b) is arranged on the exhaust gas downstream side. 2. the exhaust purification device of internal combustion engine as claimed in claim 1, is characterized in that, Furthermore, there is an air-fuel ratio adjustment means for periodically switching the air-fuel ratio of the exhaust gas flowing into the three-way catalyst between a lean air-fuel ratio and a rich air-fuel ratio.

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