JP2007239752A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

The present invention provides a technology capable of removing NOx and particulate matter while reducing the number of filters or catalysts in an exhaust gas purification apparatus for an internal combustion engine.
A particulate filter provided in an exhaust passage of an internal combustion engine, capable of temporarily collecting particulate matter in the exhaust, and carrying a urea hydrolysis catalyst, an ammonia selective reduction catalyst, and an ammonia oxidation catalyst; Urea supply means for supplying urea from upstream of the particulate filter 5, a large amount of ammonia selective reduction catalyst is supported in the central portion B of the particulate filter, and the ammonia oxidation catalyst is downstream of the upstream side of the particulate filter. A large amount is carried by B.
[Selection] Figure 4

Description

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

Diesel engines are excellent in economic efficiency, but removal of particulate matter (Particulate Matter: hereinafter referred to as “PM”) represented by soot, which is a suspended particulate matter contained in exhaust gas, is an important issue. It has become. For this reason, a technique is known in which a particulate filter (hereinafter simply referred to as “filter”) for collecting PM is provided in the exhaust system of a diesel engine so that PM is not released into the atmosphere.

  This filter can prevent PM in the exhaust gas from being collected once and released into the atmosphere. However, when PM collected by the filter accumulates on the filter, the filter may be clogged. If this clogging occurs, the pressure of the exhaust gas upstream of the filter may increase, leading to a decrease in the output of the internal combustion engine and damage to the filter. In such a case, the PM deposited on the filter can be removed by igniting and burning. The removal of PM deposited on the filter in this way is called filter regeneration.

On the other hand, as one means for reducing nitrogen oxide (NOx) contained in the exhaust gas of an internal combustion engine capable of lean combustion, a lean NOx catalyst such as a selective reduction type NOx catalyst or an occlusion reduction type NOx catalyst is known.

The selective reduction type NOx catalyst has a nitrogen oxide (N
A catalyst for reducing Ox).

  To purify nitrogen oxides (NOx) using this selective reduction type NOx catalyst, an appropriate amount of reducing agent is required. Techniques using hydrocarbons (HC), ammonia-derived compounds, and the like as the reducing agent have been developed.

For example, in the technique described in Patent Document 1, a filter capable of collecting particulate matter and supporting an oxidation catalyst is provided in the exhaust passage, and urea is further added to the filter. Urea is hydrolyzed to produce ammonia, which is oxidized to NO ₂ by the oxidation catalyst. The NO ₂ particulate matter collected by the filter is removed by this NO ₂ . Further, NOx flowing out from the filter is removed by a NOx catalyst provided downstream of the filter.
JP 2000-8833 A

However, since it is necessary to provide a filter and a NOx catalyst, it is difficult to secure a mounting space in the vehicle and the cost is increased.

The present invention has been made in view of the above-described problems, and provides a technique capable of removing NOx and particulate matter while reducing the number of filters or catalysts in an exhaust purification device of an internal combustion engine. The purpose is to do.

In order to achieve the above object, the exhaust gas purification apparatus for an internal combustion engine of the present invention employs the following means. That is,
A particulate filter provided in an exhaust passage of the internal combustion engine, capable of temporarily collecting particulate matter in the exhaust, and carrying an ammonia selective reduction catalyst;
Urea supply means for supplying urea from upstream of the particulate filter;
It is provided with.

  The most important feature of the present invention is that, in an exhaust gas purification apparatus for an internal combustion engine, NOx reducing ability is added to the particulate filter, and particulate matter in the exhaust gas is collected and NOx is purified by a single filter. .

In the exhaust gas purification apparatus for an internal combustion engine configured as described above, particulate matter contained in the exhaust gas is collected by the particulate filter when the exhaust gas passes through the particulate filter. Further, NOx in the exhaust is reduced by an ammonia selective reduction catalyst. Here, by supporting the ammonia selective reduction catalyst on the particulate filter, the contact area between the ammonia selective reduction catalyst and the exhaust is widened, so the chance that NOx in the exhaust contacts the ammonia reduction catalyst increases. Therefore, the NOx reduction rate by the ammonia reduction catalyst can be improved. In this way, it is possible to remove particulate matter in the exhaust gas and purify NOx with a single filter.

  In the present invention, a urea hydrolysis catalyst may be further provided.

  With the urea hydrolysis catalyst, urea can be easily converted into ammonia, and with the ammonia selective reduction catalyst, ammonia can be reduced as NOx using ammonia as a reducing agent.

  In the present invention, the urea hydrolysis catalyst may be at least one of alumina, titania, silica, zirconia, and zeolite.

  By using such a material, urea can be efficiently hydrolyzed.

  In the present invention, the ammonia selective reduction catalyst may be at least one of titania-vanadium, zeolite, chromium, manganese, molybdenum, and tungsten.

  By using such a material, it is possible to efficiently reduce NOx.

  In the present invention, more ammonia selective reduction catalyst may be supported in the partition wall than the wall surface of the partition wall of the particulate filter.

Innumerable pores serving as exhaust passages exist in the wall surface of the particulate filter. As the exhaust gas passes through the pores, particulate matter contained in the exhaust gas is collected. Here, by supporting the ammonia selective reduction catalyst in the partition wall, the surface of the ammonia selective reduction catalyst in contact with the exhaust can be widened, and the reduction of NOx is facilitated. In addition, other types of catalysts can be supported on the wall surfaces of the partition walls.

  In the present invention, a large amount of the ammonia selective reduction catalyst may be supported at the center of the particulate filter.

  By carrying a large amount of the ammonia selective reduction catalyst in the center of the particulate filter, it is possible to carry other types of catalysts on the upstream side and downstream side of the particulate filter.

  In the present invention, an ammonia oxidation catalyst may be supported on the particulate filter.

  By supporting the ammonia oxidation catalyst in this manner, even if urea is excessively supplied to the ammonia selective reduction catalyst, urea can be oxidized by the ammonia oxidation catalyst, so that release of urea into the atmosphere is prevented. It becomes possible to suppress.

  In the present invention, an ammonia oxidation catalyst may be provided downstream of the particulate filter.

  By doing so, it is possible to oxidize urea flowing out from the particulate filter with the downstream ammonia oxidation catalyst and suppress the release of urea into the atmosphere.

  In the present invention, the urea hydrolysis catalyst may be supported more on the upstream side than on the downstream side of the particulate filter.

  Since the exhaust gas passing through the filter first passes through the upstream side of the filter, if urea is hydrolyzed at this location, ammonia can be supplied to the downstream ammonia selective reduction catalyst.

  In the present invention, the urea hydrolysis catalyst may be supported more on the wall surface of the partition wall of the particulate filter facing the upstream side than the wall surface of the partition wall of the particulate filter facing the downstream side.

  Since the exhaust gas flowing into the partition wall of the particulate filter first passes through the wall facing the upstream side, if urea is hydrolyzed at this location, the ammonia generated when it passes through the ammonia selective reduction catalyst It becomes possible to supply to.

  In the present invention, the ammonia oxidation catalyst may be supported more on the downstream side than on the upstream side of the particulate filter.

  Since the exhaust gas reaches the ammonia oxidation catalyst after passing through the ammonia selective reduction catalyst, the ammonia flowing out from the ammonia selective reduction catalyst can be oxidized and removed by the ammonia oxidation catalyst.

  In the present invention, the ammonia oxidation catalyst may be supported more on the wall surface of the partition wall of the particulate filter facing downstream than the wall surface of the partition wall of the particulate filter facing upstream.

  The exhaust gas flowing out from the partition wall of the particulate filter must pass through the wall facing the downstream side. By supporting the ammonia oxidation catalyst on this wall, the ammonia flowing out from the ammonia selective reduction catalyst is oxidized and removed. It becomes possible to do.

  In the present invention, particulate matter collection amount estimation means for estimating the amount of particulate matter collected by the particulate filter, and the amount of particulate matter estimated by the particulate matter collection amount estimation means And a temperature raising means for raising the temperature of the particulate filter when the amount exceeds a predetermined amount.

When the amount of the particulate matter collected by the filter increases, there is a risk of causing a decrease in engine output or damage to the filter. When the collection amount of the particulate matter estimated by the particulate matter collection amount estimation means becomes a predetermined amount or more, the temperature of the particulate filter is raised by the temperature raising means. Thereby, the oxidation of the particulate matter can be promoted and removed.

In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, particulate particulate collection and NOx purification are combined into one filter by supporting an ammonia selective reduction catalyst, urea hydrolysis catalyst and ammonia oxidation catalyst on a particulate filter. Can be easily mounted on the vehicle.

<First Embodiment>
Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings. Here, the case where the exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.

  FIG. 1 is a diagram showing a schematic configuration of an engine and its intake / exhaust system according to the present embodiment.

  An engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.

  An exhaust branch pipe 3 is connected to the engine 1, and each branch pipe of the exhaust branch pipe 3 communicates with the combustion chamber of each cylinder 2 via an exhaust port (not shown). An exhaust pipe 4 is connected to the exhaust branch pipe 3.

  A particulate filter (hereinafter simply referred to as a filter) 5 is provided in the middle of the exhaust pipe 4. An exhaust gas temperature sensor 6 that outputs an electrical signal corresponding to the temperature of the exhaust gas that circulates is attached upstream of the filter 5.

  In the exhaust system configured as described above, the air-fuel mixture (burned gas) combusted in each cylinder 2 of the engine 1 is discharged to the exhaust branch pipe 3 through the exhaust port, and then from the exhaust branch pipe 3 to the filter 5. Inflow. The filter 5 collects PM in the exhaust gas and reduces NOx.

  Next, the filter 5 according to the present embodiment will be described.

FIG. 2 is a cross-sectional view of the filter 5. FIG. 2A is a diagram showing a cross section in the horizontal direction of the filter 5. FIG. 2B is a view showing a longitudinal section of the filter 5.

  As shown in FIGS. 2A and 2B, the filter 5 is a so-called wall flow type having a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. These exhaust flow passages include an exhaust inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust outflow passage 51 whose upstream end is closed by a plug 53. In FIG. 2A, hatched portions indicate plugs 53. Therefore, the exhaust inflow passages 50 and the exhaust outflow passages 51 are alternately arranged via the thin partition walls 54. In other words, the exhaust inflow passage 50 and the exhaust outflow passage 51 are arranged such that each exhaust inflow passage 50 is surrounded by four exhaust outflow passages 51 and each exhaust outflow passage 51 is surrounded by four exhaust inflow passages 50.

  The filter 5 is made of a porous material such as cordierite, for example, and has numerous pores. Accordingly, the exhaust gas flowing into the exhaust inflow passage 50 flows out into the adjacent exhaust outflow passage 51 through the surrounding partition wall 54 as indicated by an arrow in FIG.

  Here, in the conventional exhaust gas purification apparatus for an internal combustion engine, an ammonia oxidation catalyst is separately provided downstream of the ammonia selective reduction catalyst. When a urea hydrolysis catalyst is provided, a urea hydrolysis catalyst is separately provided upstream of the ammonia selective reduction catalyst. In addition, a filter may be provided to collect PM in the exhaust. As described above, when a plurality of catalysts and filters are separately provided, a space for attaching the respective catalysts and filters is required, and there is a possibility that some restrictions may be imposed when mounted on a vehicle. In addition, the installation of a plurality of catalysts and filters increases the cost. The higher the purification rate, the more the catalyst capacity increases, and the mountability deteriorates and the cost increases. Further, when the catalyst capacity increases, the heat capacity of the catalyst also increases. Therefore, when it is necessary to raise the temperature of the catalyst and the filter during PM regeneration, for example, if the temperature of the filter is raised by supplying fuel, the consumption of fuel As the amount increases, the fuel consumption is reduced.

  Therefore, in the present embodiment, an ammonia selective reduction catalyst is supported in the partition wall 54 of the filter 5, and further, a urea hydrolysis catalyst is supported on the surface of the partition wall 54 on the exhaust inflow passage 50 side, and the partition wall on the exhaust outflow passage 51 side. An ammonia oxidation catalyst was supported on the surface of 54 to reduce the number of catalysts and filters. Thus, the decrease in exhaust temperature can be suppressed by reducing the number of catalysts and filters.

  FIG. 3 is an enlarged view of a partition wall cross section (X portion in FIG. 2B) of the filter.

  Exhaust gas flows in the direction of the arrow. The urea hydrolysis catalyst 501 is carried on the wall surface of each exhaust inflow passage 50 on the exhaust inflow side, and the ammonia selective reduction catalyst 502 is carried on the pore surface inside the filter partition wall 54. An ammonia oxidation catalyst 503 is supported on the wall surface of the exhaust outlet passage 51. Therefore, the exhaust gas passing through the partition wall 54 passes through the urea hydrolysis catalyst 501, the ammonia selective reduction catalyst 502, and the ammonia oxidation catalyst 503 in this order.

  The filter 5 according to the present embodiment can be manufactured as follows, for example. First, the entire filter 5 is immersed in a tank filled with an ammonia selective reduction catalyst, and the ammonia selective reduction catalyst is supported in the pores. Next, the pores of the filter 5 are filled with a filler so that gas and liquid cannot pass through the partition wall 54. The filler used at this time has a property of sublimating at a high temperature. Thereafter, only the wall surface of each exhaust inflow passage 50 on the side into which exhaust flows is immersed in the urea hydrolysis catalyst, and then only the wall surface of each exhaust outflow passage 51 on the side from which exhaust flows out is immersed in the ammonia oxidation catalyst. Finally, the temperature of the filter 5 is raised to sublimate the filler in the pores.

  In this way, the urea hydrolysis catalyst 501 is carried on the wall surfaces of the exhaust inflow passages 50 on the exhaust inflow side, and the ammonia selective reduction catalyst 502 is carried on the inner wall surfaces of the pores inside the filter partition wall 54. The ammonia oxidation catalyst 503 can be carried on the wall surface of each exhaust outflow passage 51 on the side from which gas flows out.

  Here, the urea hydrolysis catalyst 501 is at least one of alumina, titania, silica, zirconia, and zeolite.

  The ammonia selective reduction catalyst 502 is at least one of titania-vanadium, zeolite, chromium, manganese, molybdenum, and tungsten.

In the filter 5 configured in this way, the urea aqueous solution that has reached the urea hydrolysis catalyst 501 is hydrolyzed to generate ammonia. This ammonia flows into the partition wall 54 together with the exhaust gas, and the ammonia selective reduction catalyst 502 reduces NO and NO ₂ in the exhaust gas. The ammonia that has not reacted with the ammonia selective reduction catalyst 502 is oxidized by the ammonia oxidation catalyst 503 when flowing out of the partition wall 54.

Such a reaction suppresses the release of ammonia into the atmosphere while purifying NOx in the exhaust gas.

  In the present embodiment, a urea addition mechanism for adding a urea aqueous solution to the filter 5 is provided. The urea addition mechanism includes a tank 7 for storing an aqueous urea solution, a supply pipe 8 that is a flow path for the urea aqueous solution, a pump 9 that is interposed in the flow path, and an injection nozzle 10 that injects the urea aqueous solution into the exhaust pipe 4. Configured.

  In the urea addition mechanism configured as described above, a urea aqueous solution adjusted in advance to a predetermined concentration is stored in the tank 7, and when the pump 9 is operated, the urea aqueous solution is pumped out of the tank 7. Then, the urea aqueous solution reaches the injection nozzle 10 through the supply pipe 8. The urea aqueous solution that has reached the injection nozzle 10 is injected into the exhaust pipe 4 when the injection nozzle 10 is opened, and flows downstream along with the exhaust flowing from the upstream of the exhaust pipe 4. The amount of the urea aqueous solution injected at this time is adjusted by the valve opening time of the injection nozzle 10.

The urea aqueous solution that has reached the urea hydrolysis catalyst 501 is hydrolyzed as shown by the following formula to generate ammonia.
(NH ₂ ) ₂ CO + H ₂ O → CO ₂ + 2NH ₃

When this ammonia reaches the ammonia selective reduction catalyst 502, NO and NO ₂ in the exhaust are reduced as shown in the following equation.
6NO + 4NH ₃ → 5N ₂ + 6H ₂ O
6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O

By the way, even if the injection amount of the urea aqueous solution is controlled so that the equivalent ratio of the NOx amount flowing into the ammonia selective reduction catalyst 502 and urea in the urea aqueous solution becomes 1, not all NOx can be reduced. Here, the NOx reduction rate can be improved by supplying an excessive amount of the urea aqueous solution. However, when an aqueous urea solution is supplied excessively, excess ammonia is adsorbed on the ammonia selective reduction catalyst 502. The ammonia adsorbed in this way flows out from the ammonia selective reduction catalyst 502 when the flow rate of the exhaust gas increases at a high load or the like, so that it is necessary to treat this ammonia.

In this embodiment, ammonia is oxidized and removed by the ammonia oxidation catalyst 503. That is, in an oxygen-excess atmosphere, NO is generated from a part of ammonia by the following formula.
4NH ₃ + 5O ₂ → 4NO + 6H ₂ O

The NO produced in this way reacts with the remaining ammonia as shown in the following formula.
4NH ₃ + 4NO + 5O ₂ → 4N ₂ + 6H ₂ O

  By such a reaction, ammonia is removed and release into the atmosphere is suppressed.

The engine 1 configured as described above is provided with an electronic control unit (ECU) 11 for controlling the engine 1. This ECU 11
Is a unit that controls the operating state of the engine 1 in accordance with the operating conditions of the engine 1 and the driver's request.

Various sensors are connected to the ECU 11 through electric wiring, and output signals of the various sensors are E.
Input to the CU11. On the other hand, the ECU 11 is connected to a pump 9, an injection nozzle 10 and the like via electric wiring so that these can be controlled. The ECU 11 can store various application programs and various control maps and control the urea addition mechanism described above.

  By the way, when PM collected by the filter 5 accumulates on the filter 5, the filter 5 may be clogged. If this clogging occurs, the pressure of the exhaust gas upstream of the filter 5 may increase, leading to a decrease in the output of the engine 1 and damage to the filter 5. In such a case, it is necessary to regenerate the filter 5 to remove PM accumulated on the filter 5. In order to regenerate such a filter, it is necessary to raise the temperature of the filter 5.

  The regeneration of the filter 5 is performed when the amount of PM collected by the filter 5 exceeds a predetermined allowable amount. The allowable value is a value that can avoid a decrease in the output of the engine 1 and damage to the filter 5 and is obtained by experiments or the like. Further, the amount of PM collected by the filter 5 is, for example, a differential pressure sensor (not shown) that detects the differential pressure before and after the filter 5 is attached, and the amount of PM according to the detected value of the differential pressure sensor is previously tested. It is possible to obtain it by obtaining the above. Further, a PM generation amount map corresponding to the operating state can be obtained in advance by experiments or the like, and the PM generation amount obtained from this map can be integrated to obtain the collected amount of PM. Furthermore, the PM accumulation amount may be estimated according to the vehicle travel distance or travel time.

  As a method of regenerating such a filter 5, after adding fuel to the exhaust gas or increasing the amount of recirculated EGR gas to increase the amount of soot generated to a maximum, further increase the amount of EGR gas. Possible methods include low temperature combustion (Japanese Patent No. 3116876) to be increased, sub-injection in which fuel is injected again during the expansion stroke after the main injection for injecting fuel for engine output or during the exhaust stroke.

  For example, the fuel injected by the sub-injection burns in the cylinder 2 to raise the gas temperature in the cylinder 2 and lower the oxygen concentration in the cylinder 2. Gas that has combusted in the cylinder 2 and has risen in temperature becomes exhaust gas, reaches the filter through the exhaust pipe 4, and increases the temperature of the filter. Thereby, PM is burned and removed. The temperature of the filter 5 is estimated based on the output signal of the exhaust temperature sensor 6, and is raised to a predetermined temperature while preventing the filter 5 from overheating.

  Here, the relationship between the accelerator opening, the engine speed, and the sub-injection amount or sub-injection timing is obtained in advance through experiments or the like and mapped and stored in the ECU 11. The amount of sub-injection and the injection timing can be calculated from the map, the accelerator opening, and the engine speed.

  Further, when urea is added to the filter 5 by the urea addition mechanism, heat is generated by a chemical reaction. Therefore, if PM is regenerated at this time, the temperature of the filter can be easily increased.

As described above, according to the present embodiment, the ammonia selective reduction catalyst 502 is supported in the partition wall 54 of the filter 5, and the urea hydrolysis catalyst 501 is supported on the surface of the partition wall 54 on the exhaust flow side. Further, the ammonia oxidation catalyst 503 is supported on the surface of the partition wall 54 on the exhaust gas outlet side, so that the number of catalysts and filters can be reduced. Then, PM in the exhaust can be collected by the filter 5, and NOx can be purified by the ammonia selective reduction catalyst 502.

<Second Embodiment>
This embodiment is different from the first embodiment in the following points. That is, in this embodiment, urea is added to the peripheral wall surfaces of the exhaust inflow passages 50 and the exhaust outflow passages 51 on the upstream side of the filter, that is, on both side surfaces of the upstream partition walls 54 and on the pore inner wall surfaces in the partition walls 54. The cracking catalyst is supported, and ammonia is selected on the peripheral wall surfaces of each exhaust inflow passage 50 and each exhaust outflow passage 51 in the center of the filter, that is, on both side surfaces of each partition wall 54 and on the pore inner wall surface in the partition wall The reduction catalyst is supported, and ammonia oxidation is performed on the peripheral wall surfaces of the exhaust inflow passages 50 and the exhaust outflow passages 51 on the downstream side of the filter, that is, on both side surfaces of the partition walls 54 on the downstream side and on the inner wall surfaces of the pores in the partition walls 54. The catalyst is supported. In this embodiment, although the positional relationship of the catalyst supported on the filter 5 is different from that in the first embodiment, the basic configuration of the engine 1 and other hardware to be applied is as follows. Since it is common with the first embodiment, the description is omitted.

  FIG. 4 is a diagram showing the arrangement relationship of the catalyst supported on the filter according to the present embodiment. In the figure, a range A is a urea hydrolysis catalyst, a range B is an ammonia selective reduction catalyst, and a range C is an ammonia oxidation catalyst.

  The filter according to the present embodiment can be manufactured as follows, for example. First, after filling the pores in the range of A with the filler, the range of A and B is immersed in a tank filled with the ammonia selective reduction catalyst. This filler has the property of sublimating with increasing temperature. Thereby, the ammonia selective reduction catalyst is supported in the range of B. Next, the temperature of the filter is raised and the filler in the pores in the range of A is sublimated. After this, only the range of A is immersed in the urea hydrolysis catalyst, and then only the range of C is immersed in the ammonia oxidation catalyst. In this manner, the urea hydrolysis catalyst can be supported in the range A, the ammonia selective reduction catalyst can be supported in the range B, and the ammonia oxidation catalyst can be supported in the range C.

In the filter configured as described above, the urea aqueous solution ejected from the ejection nozzle first passes through the range A. Here, the urea aqueous solution is hydrolyzed to generate ammonia. The generated ammonia flows downstream along with the exhaust gas and passes through the range B. At that time, NO and NO ₂ in the exhaust are reduced.

  When the flow rate of the exhaust gas increases at a high load or the like, the ammonia flowing out from the ammonia selective reduction catalyst is oxidized when passing through the C range. Thereby, ammonia is removed and release into the atmosphere is suppressed.

  The method for removing the PM collected by the filter is the same as that in the first embodiment, and the description thereof is omitted.

  As described above, according to the present embodiment, the urea hydrolysis catalyst, the ammonia selective reduction catalyst, and the ammonia oxidation catalyst are supported in this order from the upstream side of the filter 5 to reduce the number of catalysts and filters. it can. The PM in the exhaust gas can be collected by the filter 5, and NOx can be purified by the ammonia selective reduction catalyst.

<Third Embodiment>
FIG. 5 is a diagram showing the positional relationship between the catalyst and the filter according to the present embodiment.

  This embodiment is different from the first embodiment in the following points. That is, in the present embodiment, a urea hydrolysis catalyst 12, a particulate filter 5 carrying an ammonia selective reduction catalyst, and an ammonia oxidation catalyst 13 are provided in this order from the upstream side in the exhaust pipe. Note that the present embodiment differs from the first embodiment in that the urea hydrolysis catalyst 12 and the ammonia oxidation catalyst 13 are separated, but the engine 1 and other hardware to be applied are different. Since the basic configuration is the same as that of the first embodiment, the description thereof is omitted.

  In the exhaust gas purification apparatus for an internal combustion engine configured as described above, the urea aqueous solution injected from the injection nozzle 10 first passes through the urea hydrolysis catalyst 12. Here, the urea aqueous solution is hydrolyzed to generate ammonia.

This ammonia flows out from the urea hydrolysis catalyst 12 together with the exhaust gas. The ammonia flowing downstream reduces NO and NO ₂ in the exhaust when passing through the particulate filter 5 carrying the ammonia selective reduction catalyst. Further, PM in the exhaust gas is collected from the filter 5.

  Then, when the flow rate of the exhaust gas increases at the time of high load or the like, the ammonia flowing out from the ammonia selective reduction catalyst is oxidized when passing through the most downstream ammonia oxidation catalyst 13. Thereby, ammonia is removed and release into the atmosphere is suppressed.

  Note that the method for removing the PM collected by the filter 5 is the same as that in the first embodiment, and the description thereof will be omitted.

As described above, according to the present embodiment, the urea hydrolysis catalyst 12, the filter 5 carrying the ammonia selective reduction catalyst, and the ammonia oxidation catalyst 13 are provided in the middle of the exhaust pipe 4 in order from the upstream side. The number of filters can be reduced. The PM in the exhaust gas can be collected by the filter 5, and NOx can be purified by the ammonia selective reduction catalyst.

<Fourth embodiment>
FIG. 6 is a diagram showing the positional relationship between the catalyst and the filter according to the present embodiment.

  This embodiment is different from the first embodiment in the following points. That is, in this embodiment, the oxidation catalyst 14 is provided in the exhaust pipe upstream of the filter. Although the present embodiment differs from the first embodiment in that an oxidation catalyst is provided upstream of the filter, the basic configuration of the engine 1 and other hardware to be applied is as follows. Since it is common with the first embodiment, the description is omitted.

In the exhaust gas purification apparatus for an internal combustion engine thus configured, NO in the exhaust gas is oxidized by the oxidation catalyst 14 to become NO ₂ . This NO ₂ is easier to react with the ammonia selective reduction catalyst than NO. Therefore, the reduction rate of NOx can be improved and the amount of NOx released into the atmosphere can be reduced.

Further, the oxidation catalyst 14 can suppress the hydrocarbon (HC) and carbon monoxide (CO) in the exhaust from being oxidized and released into the atmosphere, and further the hydrocarbon (HC) and monoxide. Since heat is generated when carbon (CO) is oxidized, the downstream filter 5 can be heated. Here, the ammonia selective reduction catalyst cannot sufficiently reduce NOx unless the temperature is, for example, 350 ° C. or higher. However, since the temperature of the filter 5 can be raised by the heat generated in the oxidation catalyst 14 even when the engine is started, NOx can be reduced.

  The oxidation catalyst 14 shown in the present embodiment can be provided upstream of the filter 5 shown in the second and third embodiments, and the same effect can be obtained.

It is a figure which shows schematic structure of the engine by the 1st form, and its intake / exhaust system. (A) is a figure which shows the horizontal cross section of a particulate filter. (B) is a figure which shows the longitudinal direction cross section of a particulate filter. It is an enlarged view of the partition surface (X part in FIG. 2 (B)) of the filter. It is the figure which showed the arrangement | positioning relationship of the catalyst carry | supported by the filter by 2nd Embodiment. It is the figure which showed the arrangement | positioning relationship of the catalyst and filter by 3rd Embodiment. It is the figure which showed the arrangement | positioning relationship of the catalyst and filter by 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Cylinder 3 ... Exhaust branch pipe 4 ... Exhaust pipe 5 ... Particulate filter 6 ... Exhaust temperature sensor 7 ... Tank 8 .... Supply pipe 9 ... Pump 10 ... Injection nozzle 11 ... ECU
12 ... urea hydrolysis catalyst 13 ... ammonia oxidation catalyst 14 ... oxidation catalyst 50 ... exhaust inflow passage 51 ... exhaust outflow passage 52 ... plug 53 ... plug 54 ... partition 501 ·· Urea hydrolysis catalyst 502 ·· Ammonia selective reduction catalyst 503 ·· Ammonia oxidation catalyst

Claims (3)

A particulate filter provided in an exhaust passage of the internal combustion engine, capable of temporarily collecting particulate matter in the exhaust gas, and supporting a urea hydrolysis catalyst, an ammonia selective reduction catalyst, and an ammonia oxidation catalyst;
Urea supply means for supplying urea from upstream of the particulate filter;
With
A large amount of the ammonia selective reduction catalyst is supported at the center of the particulate filter,
An exhaust gas purification apparatus for an internal combustion engine, wherein the ammonia oxidation catalyst is supported more on the downstream side than on the upstream side of the particulate filter.   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising an ammonia oxidation catalyst downstream of the particulate filter.   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein more urea hydrolysis catalyst is supported on the upstream side than the downstream side of the particulate filter.

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