JP2011231755A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the exhaust emission control device of an internal combustion engine, which suppresses the emission of nitrogen oxides.SOLUTION: The exhaust emission control device of the internal combustion engine includes: a first NOadsorption part 45 for adsorbing NOat a temperature below a first emission temperature; an NOoxidation part 46 for oxidizing nitrogen monoxide contained in the exhaust gas to nitrogen dioxide; a second adsorption part 47 for adsorbing NOat a temperature below a second emission temperature; and a NOreduction catalyst 17 arranged in the downstream of the second NOadsorption part 47. The first adsorption part 45, the second NOadsorption part 47 and the NOoxidation part 46 are arranged so that the exhaust gas flows in the NOoxidation part 46 through the first NOadsorption part 45 and the exhaust gas flowing out from the NOoxidation part 46 flows in the second NOadsorption part 47.

Description

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

Examples of exhaust gas from internal combustion engines such as diesel engines and gasoline engines include carbon monoxide (CO), unburned fuel (HC), nitrogen oxides (NO _x ), and particulate matter (PM: particulates). Contains ingredients. An exhaust gas purification device is attached to the internal combustion engine to purify these components.

As a device for removing nitrogen oxides, temporarily storing the NO _X, NO _X occluding and reducing catalyst has been known to perform the reduction at the time of releasing NO _X. The NO _X storage reduction catalyst stores NO _X when the air-fuel ratio of the exhaust gas is lean. When the stored amount of NO _X reaches an allowable amount, the stored NO _X is released by making the air-fuel ratio of the exhaust gas rich or the stoichiometric air-fuel ratio. The released NO _X is reduced to N ₂ by a reducing agent such as carbon monoxide contained in the exhaust gas. Or, as an apparatus for removing nitrogen oxides, the NO _X contained in the exhaust gas flowing out from the combustion chamber, there is known _the NO _X selective reducing catalyst for reducing selectively.

JP-A-2002-349249 discloses an exhaust gas purifying apparatus is disclosed which is equipped with _the NO _X storage reduction catalyst in the middle of an exhaust pipe through which exhaust gas flows. In this exhaust purification device, a NO ₂ generation catalyst having an enhanced function of generating NO ₂ by selectively reacting NO and oxygen in the exhaust gas is provided in the preceding stage of the NO _X storage reduction catalyst, and NO ₂ generation is performed. It is disclosed that a reducing agent can be appropriately added upstream of the catalyst.

Japanese Patent Application Laid-Open No. 2008-291672 discloses a reducing agent adsorption layer that temporarily adsorbs a reducing agent at a temperature lower than the catalyst activation temperature from the upstream side of the exhaust toward the downstream side of the catalyst carrier disposed in the exhaust passage, and the reducing agent. In this order, a plurality of selective reduction layers that purify NO _X by selective reduction reaction in response to the supply of NOx are alternately applied in this order, and the reducing agent adsorption capacity in each reducing agent adsorption layer is gradually increased from upstream to downstream. An engine exhaust gas purification apparatus designed to be weak has been disclosed.

JP 2002-349249 A JP 2008-291672 A

The NO _X storage reduction catalyst includes an absorbent having an alkali metal or the like, and NO _X is temporarily held in the form of nitrate in the absorbent and is reduced when released from the absorbent. Further, in the NO _X selective reduction catalyst, NO _X can be selectively reduced and purified by supplying a reducing agent such as ammonia. In the exhaust processing device for purifying these of the NO _X, in order to achieve the purification rate of a given of the NO _X must be equal to or greater than a predetermined temperature. In other words, the exhaust treatment device that purifies NO _X has an activation temperature that can achieve a predetermined NO _X purification rate. Below the activation temperature, NO _X cannot be sufficiently purified.

In a state where the temperature of the exhaust gas flowing into the catalyst that purifies NO _X , such as when the internal combustion engine is cold started, is low, the temperature of the catalyst is lower than the activation temperature. Catalyst lowers the purification rate of the NO _X in the operation when the low temperature, many of the NO _X there is a problem that is released.

  An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that suppresses the release of nitrogen oxides.

An exhaust purification system of an internal combustion engine of the present invention, is less than the first release temperature to adsorb NO _X, a first of the NO _X adsorbing portion that releases NO _X adsorbed to become more first release temperature, the exhaust gas and NO _X oxidation unit for oxidizing nitrogen monoxide to nitrogen dioxide contained, is less than the second release temperature to adsorb NO _X, the second of the NO _X to release the adsorbed NO _X to be a more second release temperature comprising a suction unit, the exhaust gas flowing out from the second of the NO _X adsorbing portion is disposed so as to flow, the NO _X reduction catalyst for purifying by reducing the NO _X. In the first NO _X adsorption unit, the second NO _X adsorption unit, and the NO _X oxidation unit, exhaust gas flows into the NO _X oxidation unit through the first NO _X adsorption unit, and flows out from the NO _X oxidation unit. The exhaust gas is arranged so as to flow into the second NO _X adsorption portion. Nitric oxide flowing out from the first NO _X adsorption section is oxidized in the NO _X oxidation section to change into nitrogen dioxide, and the generated nitrogen dioxide flows into the second NO _X adsorption section.

In the above invention, at least one of the first NO _X adsorbing portion and the second NO _X adsorbing portion can contain silver as a metal that adsorbs NO _X.

In the above invention, the NO _X oxidation unit is arranged downstream of the first NO _X adsorption unit in the engine exhaust passage, and the second NO _X adsorption unit is arranged downstream of the NO _X oxidation unit in the engine exhaust passage. Can be.

In the above invention, the oxidation catalyst disposed upstream of the first NO _X adsorption portion is provided, and when the temperature of the exhaust gas flowing into the oxidation catalyst is lower than a predetermined temperature, the dioxide that has flowed into the oxidation catalyst. Nitrogen changes into nitrogen monoxide by reacting with the hydrocarbons contained in the exhaust gas, and the produced nitric oxide can flow into the first NO _X adsorption section.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust gas purification apparatus of the internal combustion engine which suppresses discharge | release of nitrogen oxides can be provided.

1 is a schematic view of an internal combustion engine in an embodiment. It is a schematic cross-sectional view of the first of the NO _X holding device in the embodiment. It is an enlarged schematic sectional view of the first of the NO _X adsorbing unit in the embodiment. 6 is a time chart when NO _X purge control for releasing NO _X from the NO _X holding device is performed during normal operation of the internal combustion engine in the embodiment. It is _the amount of NO _X map per unit is discharged time from the engine body. It is a graph of _the amount of NO _X released from the NO _X adsorbing unit in the embodiment. It is a schematic diagram for explaining the function of _the NO _X holding device in the embodiment. It is a graph of the desorption amount of nitric oxide desorbed from the first NO _X adsorption part in the embodiment. It is a graph of the desorption amount of nitrogen monoxide and nitrogen dioxide desorbed from the second NO _X adsorption part in the embodiment. It is an enlarged schematic sectional view of a second of the NO _X holding device in the embodiment. It is a schematic front view of a third of the NO _X holding device in the embodiment. It is a schematic cross-sectional view of a third of the NO _X holding device in the embodiment. It is an enlarged schematic sectional view of the NO _X occluding and reducing catalyst as NO _X reduction catalyst in the embodiment. It is a schematic view of an internal combustion engine having _the NO _X selective reducing catalyst as NO _X reduction catalyst in the embodiment.

  With reference to FIGS. 1 to 14, an exhaust emission control device for an internal combustion engine in an embodiment will be described.

  FIG. 1 shows a schematic diagram of an internal combustion engine in the present embodiment. In the present embodiment, a compression ignition type diesel engine will be described as an example. The internal combustion engine in the present embodiment is arranged in an automobile among vehicles.

  The internal combustion engine includes an engine body 1. The internal combustion engine includes an exhaust purification device. The engine body 1 includes a combustion chamber 2 as each cylinder, an electronically controlled fuel injection valve 3 for injecting fuel into each combustion chamber 2, an intake manifold 4, and an exhaust manifold 5.

  The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6. An inlet of the compressor 7 a is connected to an air cleaner 9 via an intake air amount detector 8. A throttle valve 10 driven by a step motor is disposed in the intake duct 6. Further, the intake duct 6 is provided with a cooling device 11 for cooling the intake air flowing through the intake duct 6. In the embodiment shown in FIG. 1, engine cooling water is guided to the cooling device 11. The intake air is cooled by the engine cooling water.

  On the other hand, the exhaust manifold 5 is connected to the inlet of the turbine 7 b of the exhaust turbocharger 7. An outlet of the exhaust turbine 7 b of the exhaust turbocharger 7 is connected to a plurality of exhaust treatment devices for purifying exhaust gas discharged from the engine body 1.

The exhaust purification device in the present embodiment includes an oxidation catalyst 13. The oxidation catalyst 13 is connected to the outlet of the turbine 7b through the exhaust pipe 12. The exhaust purification system in the present embodiment is provided with _the NO _X holding device 15 for temporarily holding the NO _X. The NO _X holding device 15 is connected to the oxidation catalyst 13 via the exhaust pipe 12. The NO _X holding device 15 in the present embodiment is disposed in the engine exhaust passage downstream of the oxidation catalyst 13.

The exhaust purification device in the present embodiment includes a NO _X reduction catalyst 17 that purifies NO _X by reducing it. The NO _X reduction catalyst 17 is connected to the NO _X holding device 15 through the exhaust pipe 12. The NO _X reduction catalyst 17 is disposed in the engine exhaust passage downstream of the NO _X holding device 15. The exhaust treatment device included in the exhaust purification device is not limited to this form, and other exhaust treatment devices may be arranged. For example, a particulate filter that collects particulate matter may be disposed.

  An EGR passage 18 is arranged between the exhaust manifold 5 and the intake manifold 4 for exhaust gas recirculation (EGR). An electronically controlled EGR control valve 19 is disposed in the EGR passage 18. A cooling device 20 for cooling the EGR gas flowing in the EGR passage 18 is disposed in the middle of the EGR passage 18. In the embodiment shown in FIG. 1, engine cooling water is introduced into the cooling device 20. The EGR gas is cooled by the engine cooling water.

  Each fuel injection valve 3 is connected to a common rail 22 via a fuel supply pipe 21. The common rail 22 is connected to a fuel tank 24 via an electronically controlled fuel pump 23 having a variable discharge amount. The fuel stored in the fuel tank 24 is supplied into the common rail 22 by the fuel pump 23. The fuel supplied into the common rail 22 is supplied to the fuel injection valve 3 through each fuel supply pipe 21.

  The electronic control unit 30 includes a digital computer. The electronic control unit 30 in the present embodiment functions as a control device for the exhaust purification device. The electronic control unit 30 includes a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an output port 36 that are connected to each other by a bidirectional bus 31.

  The ROM 32 is a read-only storage device. The ROM 32 stores in advance information such as a map necessary for control. The CPU 34 can perform arbitrary calculations and determinations. The RAM 33 is a readable / writable storage device. The RAM 33 can store information such as an operation history and can temporarily store calculation results.

A temperature sensor 25 for detecting the temperature of the oxidation catalyst 13 is disposed downstream of the oxidation catalyst 13. Downstream of _the NO _X holding device 15, the temperature sensor 26 for detecting the temperature of the NO _X holding device 15 is disposed. Further, in the downstream of the NO _X reduction catalyst 17, a temperature sensor 27 for detecting the temperature of the NO _X reduction catalyst 17 is arranged. Output signals of these temperature sensors 25, 26, 27 are input to the input port 35 via the corresponding AD converter 37.

  The output signal of the intake air amount detector 8 is input to the input port 35 via the corresponding AD converter 37. A load sensor 41 that generates an output voltage proportional to the amount of depression of the accelerator pedal 40 is connected to the accelerator pedal 40. The output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. From the output of the crank angle sensor 42, the rotational speed of the engine body can be detected.

  On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the EGR control valve 19, and the fuel pump 23 through corresponding drive circuits 38. These devices are controlled by the electronic control unit 30.

  The oxidation catalyst 13 is a catalyst having an oxidation function. The oxidation catalyst 13 includes, for example, a base body having a passage extending in the exhaust gas flow direction inside a cylindrical case body. The substrate is formed in a honeycomb structure, for example. On the surface of the passage of the substrate, for example, a coat layer containing porous oxide powder as a support is formed, and a catalyst metal is supported on the support. As the catalyst metal, for example, a noble metal such as platinum Pt can be employed. Carbon monoxide (CO) and unburned hydrocarbon (HC) contained in the exhaust gas are oxidized by the oxidation catalyst 13 and converted into substances such as water and carbon dioxide.

The NO _X reduction catalyst 17 in the apparatus example shown in FIG. 1 has the same configuration as the three-way catalyst. The NO _X reduction catalyst 17 includes a noble metal such as platinum (Pt), palladium (Pd), and rhodium (Rh) as a catalyst metal. These noble metals are supported on a support such as aluminum oxide (Al ₂ O ₃ ). The carrier is disposed on the surface of a substrate such as honeycomb cordierite. The NO _X reduction catalyst 17 can reduce NO _X with high efficiency by making the air-fuel ratio of the inflowing exhaust gas the stoichiometric air-fuel ratio or rich.

FIG. 2 is a schematic cross-sectional view of the first NO _X holding device in the present embodiment. The first of the NO _X holding device 15 in the present embodiment, when the temperature of the exhaust gas adsorbs NO _X when cold, the temperature of the exhaust gas becomes high, the first of the NO _X to release the adsorbed NO _X The adsorption part 45 is provided. The NO _X holding device 15 includes a NO _X oxidation unit 46 for oxidizing nitrogen monoxide contained in the exhaust gas into nitrogen dioxide. Further, NO _X holding device 15, when the temperature of the exhaust gas is low adsorbs NO _X, provided the temperature of the exhaust gas becomes hot, the second of the NO _X adsorbing unit 47 to release the adsorbed NO _X. In the first NO _X adsorption unit 45, the second NO _X adsorption unit 47 and the NO _X oxidation unit 46, the exhaust gas flows into the NO _X oxidation unit 46 through the first NO _X adsorption unit 45, and NO _X The exhaust gas flowing out from the oxidation unit 46 is arranged to flow into the second NO _X adsorption unit 47.

In the first NO _X holding device 15, the first NO _X adsorption unit 45, the NO _X oxidation unit 46, and the second NO _X adsorption unit 47 are arranged in this order along the exhaust gas flow direction. Yes. The NO _X oxidation unit 46 is disposed downstream of the first NO _X adsorption unit 45, and the second NO _X adsorption unit 47 is disposed downstream of the NO _X oxidation unit 46.

FIG. 3 shows an enlarged schematic cross-sectional view of the first NO _X adsorption portion in the present embodiment. The first NO _X adsorption portion 45 in the present embodiment is formed in a honeycomb structure. In the first NO _X adsorption portion 45, a carrier 48 containing, for example, aluminum oxide is disposed on a base. The support 48 can employ any material that can support the adsorption metal 49 that adsorbs NO _X. The adsorption metal 49 is dispersed and supported on the surface of the carrier 48. The adsorption metal 49 is formed, for example, in the form of particles. The adsorbed metal 49 of the first NO _X adsorbing portion 45 in the present embodiment contains silver. As the adsorbing metal 49, any metal capable of adsorbing NO _X can be employed. For example, metals such as manganese and copper can be used. The second NO _X adsorption unit 47 in the present embodiment has a configuration similar to that of the first NO _X adsorption unit 45.

Referring to FIG. 2, in the present embodiment, first NO _X adsorption unit 45, second NO _X adsorption unit 47 and NO _X oxidation unit 46 are separated from each other, but the present invention is not limited to this configuration. The first NO _X adsorbing portion 45, the NO _X oxidizing portion 46, and the second NO _X adsorbing portion 47 are formed in this order along the flow direction of the exhaust gas on the surface of one substrate. It doesn't matter. For example, each NO _X adsorption part and NO _X oxidation part may be formed on one substrate by the zone coating method.

The oxidation unit 46 includes, for example, a substrate having a honeycomb structure having a plurality of passages, and an aluminum oxide carrier as a carrier is disposed on the surface of the base passage. The catalyst metal is supported on a support. As the catalyst metal, any metal capable of oxidizing nitric oxide to nitrogen dioxide can be employed. For example, a noble metal such as platinum Pt can be used as the catalyst metal. For example, the oxidation unit 46 may employ a configuration similar to that of the oxidation catalyst 13 disposed upstream of the NO _X holding device 15.

In the present invention, the ratio of the air and fuel (hydrocarbon) of the exhaust gas supplied to the engine intake passage, the combustion chamber, or the engine exhaust passage is referred to as the air-fuel ratio (A / F) of the exhaust gas. The first of the NO _X adsorbing unit 45, the air-fuel ratio of the exhaust gas when the lean adsorbs NO _X contained in the exhaust gas to the adsorption metal 49. NO _X contained in the exhaust gas is held by the adsorbed metal 49 in the form of silver nitrate. Alternatively, NO _X is held on the adsorbed metal 49 via oxygen. In contrast, when the air-fuel ratio of the exhaust gas is or stoichiometric air-fuel ratio when rich, NO _X held in the suction metal 49 is released.

Furthermore, the first of the NO _X adsorbing unit 45 is less than the first release temperature to adsorb NO _X, releasing NO _X adsorbed to become more first release temperature. The second of the NO _X adsorbing unit 47 is less than the second release temperature to adsorb NO _X, releasing NO _X adsorbed to become more second release temperature. In the present embodiment, since the first NO _X adsorption unit 45 and the second NO _X adsorption unit 47 have the same configuration, the first release temperature and the second release temperature are the same.

The internal combustion engine in the present embodiment performs combustion in the combustion chamber so that the air-fuel ratio of the exhaust gas flowing into the exhaust treatment device becomes lean during normal operation. The NO _X holding device 15 adsorbs NO _X contained in the exhaust gas when the temperature of the exhaust gas is lower than the first release temperature or the second release temperature.

The NO _X holding device 15 has a holdable amount that is the maximum amount that can hold NO _X. The NO _X holding device 15 cannot hold NO _X when the NO _X holding amount reaches the holdable amount. That is, NO _X contained in the exhaust gas cannot be removed. In this embodiment, during normal operation, when it reaches the retention amount judgment value amount of NO _X is predetermined held in _the NO _X holding device 15, the NO _X from _the NO _X holding device 15 performing NO _X purge control to release. As the holding amount determination value in the present embodiment, a value smaller than the NO _X holdable amount of the NO _X holding device 15 is adopted.

FIG. 4 shows a time chart of the first NO _X purge control in the present embodiment. Internal combustion engine is, until the time t ₁ continues normal operation. An exhaust purification system of an internal combustion engine in the present embodiment is provided with a detection device for detecting the amount of NO _X held in the NO _X holding device 15. The detection device in the present embodiment includes an electronic control unit 30.

Figure 5 shows a map of the NO _X amount exhausted from the engine body per unit time in the present embodiment. For example, to create a map of the emissions NOXA of the NO _X per unit time to the injection quantity TAQ of fuel injected into the combustion chamber 2 and the engine speed N to the function in advance. This map is stored in the ROM 32 of the electronic control unit 30, for example. In the present embodiment, it is equal to the amount of NO _X flowing to the NO _X amount and _the NO _X holding device 15 which is discharged from the engine body 1. With this map, it is possible to calculate the amount of NO _X that flows into the NO _X holding device 15 per unit time and is held in the NO _X holding device 15 according to the operating state. By integrating the amount of NO _X held per unit time, it can be calculated _the NO _X holding amount at an arbitrary time.

NO in the estimation of _X holding device 15 NO _X amount held in, it is also possible to subtract the amount of NO _X desorbed from the NO _X holding device. For example, to create a desorption rate of the NO _X which the temperature of the NO _X holding device to function in advance and stored in the electronic control unit 30. The temperature of the NO _X holding device 15 can be detected to estimate the NO _X desorption rate. From the releasing rate of the NO _X can be estimated desorption amount of the NO _X.

Referring to FIG. 4, the NO _X amount held in NO _X holding device 15 at time t ₁ exceeds the holding amount determination value for performing the NO _X purge control. NO _X purge control is performed from time t ₁ . In the NO _X purge control, the air-fuel ratio of the exhaust gas flowing into the NO _X holding device 15 is made the stoichiometric air-fuel ratio or rich. The exhaust purification system in the present embodiment, by performing additional auxiliary injection in the combustion chamber, and approximately stoichiometric air fuel ratio of the exhaust gas flowing into the NO _X holding device 15.

In the normal operation, fuel is injected by main injection FM at a compression top dead center TDC. In normal operation, the air-fuel ratio of the exhaust gas discharged from the engine body is lean. When the air-fuel ratio of the exhaust gas discharged from the engine body is lowered, after injection FA as auxiliary injection can be performed after main injection FM. The after injection FA is performed at a combustible time after the main injection. In the present embodiment, control is further performed to reduce the amount of intake air flowing into the combustion chamber. With reference to FIG. 1, the amount of intake air flowing into the combustion chamber 2 can be reduced by reducing the opening of the throttle valve 10. By performing this control, the air-fuel ratio of the exhaust gas flowing into the NO _X holding device 15 can be made the stoichiometric air-fuel ratio or rich. In the NO _X reduction catalyst 17 in the present embodiment, in order to improve the NO _X purification rate, the air-fuel ratio of the exhaust gas flowing into the NO _X reduction catalyst 17 may be made substantially the stoichiometric air-fuel ratio or slightly rich. preferable. By the air-fuel ratio of the exhaust gas the stoichiometric air-fuel ratio or rich, NO _X which is adsorbed in the NO _X holding device is released. _The NO _X holding amount of _the NO _X holding devices have become zero at time _{t 2.}

The configuration in which the air-fuel ratio of the exhaust gas flowing into the NO _X holding device 15 is made the stoichiometric air-fuel ratio or rich is not limited to the configuration in which after-injection is performed, and any configuration that lowers the air-fuel ratio can be adopted. For example, a fuel addition valve that supplies unburned fuel to the engine exhaust passage upstream of the NO _X holding device may be arranged. By supplying the unburned fuel from the fuel supply valve to the engine exhaust passage, it is possible to make the air-fuel ratio of the exhaust gas flowing into the NO _X holding device to the stoichiometric air-fuel ratio or rich.

The normal operation of the present invention indicates a state other than a state in which the operation state of the internal combustion engine is temporarily changed for a predetermined purpose such as warm-up operation at startup or regeneration of the particulate filter. Referring to FIG. 1, the temperature of the NO _X reduction catalyst 17 rises during normal operation of the internal combustion engine. For example, during normal operation, the NO _X reduction catalyst 17 is at or above the activation temperature.

Performed substantially the NO _X purge control to the stoichiometric air-fuel ratio of the exhaust gas flowing into the NO _X holding device, NO _X is released from _the NO _X holding device 15. The air-fuel ratio of the exhaust gas flowing out from the NO _X holding device 15 is close to the stoichiometric air-fuel ratio. For this reason, the NO _X reduction catalyst 17 can purify NO _X at a high purification rate. Thus, NO _X can be released from the NO _X holding device 15 and the NO _X reduction catalyst 17 can be brought into a state having high purification performance. The NO _X reduction catalyst 17 can effectively purify NO _X.

Meanwhile, when the exhaust gas exhausted from the engine body becomes high may NO _X held in _the NO _X holding device 15 is released. For example, when the operation is performed with a high load and a high speed, the temperature of the exhaust gas rises. In such a case, the temperature of the NO _X adsorption part of the NO _X holding device may be equal to or higher than the release temperature of each NO _X. In this case, the NO _X reduction catalyst 17 is also at a high temperature, and the NO _X reduction catalyst 17 has a higher purification performance than at a low temperature. For this, it is possible to perform the purification of the released NO _X from _the NO _X holding device 15 in the NO _X reduction catalyst 17.

Further, at the time of startup after the internal combustion engine has been stopped for a long time, the NO _X holding device 15 and the NO _X reduction catalyst 17 may be at a low temperature. For example, when a cold start is performed, the NO _X reduction catalyst 17 is below the activation temperature. When the NO _X reduction catalyst 17 is at a low temperature, NO _X is removed from the exhaust gas by adsorbing NO _X by the NO _X holding device 15.

The NO _X discharged from the engine body 1 contains nitrogen monoxide NO and nitrogen dioxide NO ₂ . Nitric oxide contained in the exhaust gas is held by the adsorbed metal 49 in the form of NO _{2 in} the adsorption section. Nitrogen dioxide is held by the adsorbing metal 49 in the form of NO _{3 in} the adsorption section. By the way, the holding power at which nitric oxide is held in the form of NO ₂ is weaker than the holding power at which nitrogen dioxide is held in the form of NO ₃ . That is, nitric oxide is more easily desorbed than nitrogen dioxide. For example, when the temperature of the NO _X adsorption unit is gradually raised, nitrogen monoxide is desorbed first, and nitrogen dioxide is desorbed thereafter. Alternatively, the removal rate when nitrogen monoxide contained in the exhaust gas is removed by adsorption is smaller than the removal rate when nitrogen dioxide is removed by adsorption.

FIG. 6 shows the amount of NO _X desorbed from the first NO _X adsorption unit when the temperature is gradually increased after the NO _X is held in the first NO _X adsorption unit in the present embodiment. A graph is shown. The horizontal axis represents the temperature of the exhaust gas flowing into the first NO _X adsorption unit. The vertical axis represents the NO _X release amount from the first of the NO _X adsorbing portion.

In the present embodiment, the temperature of each exhaust treatment device is increased by the heat of the exhaust gas. For this reason, the temperature of the exhaust gas corresponds to the temperature of each exhaust treatment device. When gradually increasing the temperature, the first peak of the NO _X emissions are expressed, second peak subsequent to the NO _X emissions are expressed. Since the holding power when nitrogen dioxide is held by adsorption is larger than the holding power when nitrogen monoxide is held by adsorption, the portion of the first peak contains a lot of nitric oxide, The portion of the second peak contains a lot of nitrogen dioxide.

By the way, in the exhaust purification device of the present embodiment, the activation temperature Tr of the NO _X reduction catalyst 17 arranged downstream of the NO _X holding device 15 is higher than the temperature Tp1 of the first peak of the NO _X release amount. Higher than the temperature Tp2 of the second peak. When the temperature of the NO _X reduction catalyst 17 becomes equal to or higher than the activation temperature Tr, even NO _X flows out from _the NO _X holding device, it is possible to effectively perform the cleaning of the NO _X in the NO _X reduction catalyst 17. The NO _X released at the second peak can be purified by the NO _X reduction catalyst 17.

FIG. 7 is a schematic diagram for explaining the function of the NO _X holding device in the present embodiment. The first NO _X adsorption unit 45, the NO _X oxidation unit 46, and the second NO _X adsorption unit 47 are arranged in this order. When the temperature of the exhaust gas is low, such as during startup, NO _X contained in the exhaust gas is retained by being adsorbed by the first NO _X adsorption unit 45 and the second NO _X adsorption unit 47. The

When comparing the nitrogen monoxide and nitrogen dioxide contained in the NO _X as described above, has the property of easily towards the nitric oxide is desorbed than nitrogen dioxide. When the temperature of the exhaust gas gradually increases, elimination of nitric oxide from the first of the NO _X adsorbing unit 45 is expressed. Referring to FIG. 6, particularly near the temperature Tp <b> 1 corresponding to the first peak, as shown by an arrow 101, nitrogen monoxide is desorbed and flows out from the first NO _X adsorption portion 45. Nitric oxide that has flowed out of the first NO _X adsorption unit 45 flows into the NO _X oxidation unit 46. In the NO _X oxidation unit 46, nitric oxide is oxidized and changed to nitrogen dioxide. Nitrogen dioxide flowing out from the NO _X oxidation unit 46 flows into the second NO _X adsorption unit 47 as indicated by an arrow 102. Nitrogen dioxide is held in the second NO _X adsorption unit 47. Nitrogen dioxide is held in the second NO _X adsorption unit 47 more reliably than nitrogen monoxide because the temperature at which the emission amount peaks when released from the NO _X adsorption unit is higher than that of nitric oxide.

The exhaust purification apparatus according to the present embodiment can change the form of nitrogen oxides from nitrogen monoxide, which is easily desorbed at low temperatures, to nitrogen dioxide in the NO _x oxidation section 46, so that the NO _x is converted into the second form. Can be held in the NO _X adsorption portion 47.

In the NO _X holding device 15 in the present embodiment, among the monoxide contained in the exhaust gas, nitrogen monoxide that has passed through the first NO _X adsorption unit 45 is also oxidized in the NO _X oxidation unit 46. nitrogen is varied, it can be held more reliably by the second of the NO _X adsorbing portion 47.

FIG. 8 shows a graph of the amount of nitric oxide flowing out from the first NO _X adsorption portion of the first NO _X holding device in the present embodiment. FIG. 9 shows a graph of the amount of NO _X flowing out from the second NO _X adsorption portion of the first NO _X holding device in the present embodiment. Graph shown in FIG. 8 and 9, it leaves enough to hold the NO _X in the first of the NO _X holding device, which is a graph of when the temperature of the exhaust gas was gradually increased.

Referring to FIG. 8, the horizontal axis indicates the temperature of the exhaust gas flowing into the first NO _X holding device, and the vertical axis indicates the amount of nitrogen monoxide released from the first NO _X adsorption portion, that is, one. It shows the amount of nitric oxide desorption. In the example shown in FIG. 8, when the temperature of the exhaust gas is approximately 100 ° C., the amount of nitrogen monoxide desorption is maximized. That is, in this temperature or higher, it can be seen that the amount of nitric oxide flowing flows out of the first adsorption unit in the NO _X oxidation unit increases. Thus, the nitric oxide flowing out from the first NO _X adsorption section is oxidized in the NO _X oxidation section and then flows into the second NO _X adsorption section.

Referring to FIG. 9, the horizontal axis indicates the temperature of the exhaust gas flowing into the first NO _X holding device, and the vertical axis indicates the NO _X amount flowing out from the second NO _X adsorption portion, that is, the first NO _X The amounts of nitric oxide and nitrogen dioxide flowing out of the _X holding device are shown. When the temperature of the exhaust gas is approximately 200 ° C., the amount of desorption of nitrogen monoxide and nitrogen dioxide is maximized. In the second NO _X adsorption unit, since a large amount of NO _X is held in the form of nitrogen dioxide, the temperature region where NO _X is released is one of the first NO _X adsorption units shown in FIG. It can be seen that the temperature is higher than the temperature region where nitrogen oxide is desorbed.

Thus, the exhaust gas purification system in the present embodiment, until the temperature of the NO _X reduction catalyst becomes equal to or higher than the activation temperature, it is possible to suppress the NO _X amount flowing out from _the NO _X holding device, of the NO _X The purification rate can be improved. In particular, an exhaust purification system in the present embodiment, may be the temperature of the exhaust gas, such as during start of the internal combustion engine is in the region lower than the normal operation, to reduce the emission of NO _X.

The NO _X oxidation unit of the exhaust purification apparatus in the present embodiment preferably has a function of oxidizing NO to NO ₂ from a low temperature state so that NO flowing out from the first adsorption unit can be sufficiently oxidized. . For example, referring to FIG. 8, the NO _X oxidation part preferably has an activation temperature of approximately 100 ° C. or more and 150 ° C. or less at which the amount of nitric oxide desorbed from the first NO _X adsorption part increases. .

Referring to FIG. 1, in the internal combustion engine in the present embodiment, an oxidation catalyst 13 is arranged upstream of NO _X holding device 15. When the temperature of the exhaust gas is low, such as when the internal combustion engine is started, the inflowing nitrogen dioxide NO ₂ reacts with unburned hydrocarbons contained in the exhaust gas and changes to nitric oxide NO in the oxidation catalyst 13. As a result, the amount of nitric oxide flowing into the NO _X holding device 15 increases. For this reason, in the internal combustion engine in which the oxidation catalyst 13 is arranged upstream of the NO _X holding device 15, the effect of the present invention becomes remarkable. By disposing the NO _X holding device in the present embodiment, the amount of NO _X discharged from the exhaust purification device can be greatly reduced.

FIG. 10 shows an enlarged schematic cross-sectional view of the second NO _X holding device in the present embodiment. The second NO _X holding device in the present embodiment is formed in a honeycomb structure having a plurality of passages. In each of the passages, a plurality of NO _X adsorption portions and NO _X oxidation portions are formed in layers, and are laminated on the surface of the base material.

In the second NO _X holding device, the second NO _X adsorption portion 54 is formed in a layered manner on the surface of the substrate 51. On the surface of the second NO _X adsorption portion 54, the NO _X oxidation portion 53 is formed in a layer shape. On the surface of the NO _X oxidation part 53, a first NO _X adsorption part 52 is formed in a layered manner. The exhaust gas proceeds in the direction indicated by the arrow 100. The exhaust gas flows in the order of the first NO _X adsorption unit 52, the NO _X oxidation unit 53, and the second NO _X adsorption unit 54 as indicated by the arrow 103.

Also in the second NO _X holding device, nitrogen monoxide flowing out from the first NO _X adsorption unit 52 is converted into nitrogen dioxide by the NO _X oxidation unit 53 and held by the second NO _X adsorption unit 54. be able to. When the exhaust gas is in a low temperature region, the amount of NO _x flowing out from the exhaust purification device can be reduced.

Next, a third NO _X holding device in the present embodiment will be described. The third NO _X holding device includes a particulate filter. A NO _X adsorption part for adsorbing NO _X and an NO _X oxidation part for oxidizing nitric oxide are formed in each passage of the particulate filter.

FIG. 11 shows a schematic front view of the third NO _X holding device in the present embodiment. FIG. 12 is a schematic cross-sectional view of the third NO _X holding device in the present embodiment. The particulate filter 16 is a filter for removing particulate matter (particulates) such as carbon particulates and ionic particulates such as sulfate contained in the exhaust gas. The particulate filter 16 in the present embodiment is formed in a cylindrical shape. FIG. 12 is a cross-sectional view along the axial direction of the cylindrical shape. The particulate filter 16 is made of a porous material such as cordierite, for example.

  The particulate filter 16 in the present embodiment has a honeycomb structure. The particulate filter 16 has a plurality of passages 60 and 61 extending along the flow direction of the exhaust gas. The downstream end of the passage 60 is closed by a plug 62. The passage 61 is closed at the upstream end by a plug 63. The passages 60 and the passages 61 are alternately arranged via thin partition walls 64. In FIG. 11, the plug 63 is hatched.

  The passage 60 through which the exhaust gas flows is surrounded by a passage 61 through which the exhaust gas flows out. The exhaust gas flowing into the passage 60 flows out to the adjacent passage 61 through the partition wall 64 as indicated by an arrow 104. Particulate matter is trapped when the exhaust gas passes through the partition wall 64. The exhaust gas flows out from the particulate filter 16 through the passage 61. In this way, the particulate matter is collected by the particulate filter.

When the amount of particulate matter deposited on the particulate filter increases, the particulate matter is combusted and regenerated by increasing the temperature of the exhaust gas flowing into the particulate filter. Referring to FIG. 12, each partition wall 64 supports a catalytic metal having an oxidation function for promoting combustion of particulate matter. For example, a noble metal catalyst metal such as platinum is supported. The partition wall 64 in which the catalytic metal is disposed functions as a NO _X oxidation unit that oxidizes nitric oxide.

In the passage 60 through which the exhaust gas flows, a first NO _X adsorption portion 52 is formed on the surface of the partition wall 64. Further, in the passage 61 through which the exhaust gas flows out, a second NO _X adsorption portion 54 is formed on the surface of the partition wall 64.

The exhaust gas flows into the particulate filter 16 as indicated by an arrow 100. The exhaust gas flows from the passage 60 toward the passage 61 as indicated by an arrow 104. At this time, the exhaust gas flows through the first NO _X adsorption unit 52, the partition wall 64 functioning as the NO _X oxidation unit, and the second NO _X adsorption unit 54 in this order.

Also in the third NO _X holding device, nitric oxide flowing out from the first NO _X adsorption unit 52 is converted into nitrogen dioxide by the NO _X oxidation unit, and is held by the second NO _X adsorption unit 54. Can do. When the exhaust gas is in a low temperature region, the amount of NO _x flowing out from the exhaust purification device can be reduced.

In the present embodiment, the description has been made by taking the first NO _X holding device to the third NO _X holding device as an example. However, the configuration of the NO _X holding device is not limited to these forms, and the exhaust gas There flows to the nO _X oxidation section through a first of the nO _X adsorbing portion, the exhaust gas flowing out from the nO _X oxide portion may be formed so as to flow into the second of the nO _X adsorbing portion.

In the NO _X holding device of the present embodiment, the NO _X adsorption unit is formed in two, but is not limited to this form, the NO _X holding device has a plurality of NO _X adsorption units, it is possible to arrange the NO _X oxide portion between the adjacent suction unit.

The NO _X holding device of the exhaust purification apparatus according to the present embodiment has the same configuration in the first NO _X adsorption unit and the second NO _X adsorption unit, but is not limited to this configuration and has a configuration different from each other. A plurality of NO _X adsorption portions may be formed.

In the present embodiment, as NO _X reduction catalyst for reducing NO _X, platinum, although a catalyst comprising catalytic metals palladium and rhodium have been described by taking as an example, but the invention is not limited to this, NO _X reduction catalyst Any catalyst capable of reducing NO _X can be employed. For example, the NO _X reduction catalyst can include a NO _X storage reduction catalyst.

FIG. 13 shows an enlarged schematic cross-sectional view of the NO _X storage reduction catalyst. In the NO _X storage reduction catalyst, a catalyst carrier 56 made of alumina, for example, is disposed on a substrate. A noble metal catalyst metal 57 is dispersed and supported on the surface of the catalyst carrier 56. A layer of NO _X absorbent 58 is formed on the surface of the catalyst carrier 56. As the catalyst metal 57, for example, platinum Pt is used. The components constituting the NO _X absorbent 58 are selected from, for example, alkali metals such as potassium K, sodium Na and cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y. At least one of these is used.

By the time the air-fuel ratio of the exhaust gas is lean (greater time than the stoichiometric air-fuel ratio), NO contained in the exhaust gas is oxidized to NO ₂ on the catalyst metal 57. NO ₂ is occluded in the NO _X absorbent 58 in the form of nitrate ions NO ₃ ⁻ . On the other hand, when the air-fuel ratio of the exhaust gas is rich (smaller than the stoichiometric air-fuel ratio) or becomes the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas decreases and the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO Go to ₂ ). _The NO _X absorbent in the 58 nitrate ions NO ₃ ^- are released from _the NO _X absorbent 58 in the form of NO _2. The released NO _X is reduced to N ₂ by unburned hydrocarbons, carbon monoxide and the like contained in the exhaust gas.

Such an NO _x storage reduction catalyst also has an activation temperature that is a temperature that achieves a predetermined purification rate. Therefore, in the case of arranging the _the NO _X storage reduction catalyst as NO _X reduction catalysts, at low temperatures of the exhaust gas region, it is possible to hold the NO _X contained in the exhaust gas at _the NO _X holding device.

Further, NO _X reduction catalyst can include _the NO _X selective reducing catalyst that selectively reduces NO _X.

Figure 14 shows a schematic diagram of an internal combustion engine _the NO _X selective reducing catalyst is arranged as a NO _X reduction catalyst. Downstream of the NO _X selective reducing catalyst 14, a temperature sensor 27 for detecting the temperature of the NO _X selective reducing catalyst 14 is arranged.

The NO _X selective reduction catalyst 14 is an exhaust treatment device that can selectively reduce NO _X by supplying a reducing agent. _The NO _X selective reducing catalyst 14 in the present embodiment, the reduction of NO _X and ammonia as a reducing agent. The NO _X selective reduction catalyst can be composed of, for example, a zeolite that adsorbs ammonia and contains a transition metal such as iron. Alternatively, it can be composed of a titania / vanadium catalyst having no ammonia adsorption function. The NO _X selective reduction catalyst 14 in the present embodiment is composed of ammonia adsorption type Fe zeolite.

The exhaust purification device includes a reducing agent supply device that supplies a reducing agent to the NO _X selective reduction catalyst 14. The reducing agent supply device includes a urea supply valve 55. The urea supply valve 55 is formed to inject urea into the engine exhaust passage. The reducing agent supply device in the present embodiment is formed so as to supply urea, but is not limited to this form, and may be formed so as to supply other reducing agents such as aqueous ammonia.

  The urea supply valve 55 is connected to the output port 36 of the electronic control unit 30 via the corresponding drive circuit 38. The urea supply valve 55 in the present embodiment is controlled by the electronic control unit 30.

When urea is supplied from the urea supply valve 55 into the exhaust gas flowing through the engine exhaust passage, the urea is hydrolyzed. Urea is hydrolyzed to produce ammonia and carbon dioxide. By supplying the produced ammonia to the NO _X selective reduction catalyst 14, the NO _X selective reduction catalyst 14 can reduce NO _X contained in the exhaust gas to nitrogen.

Such an NO _X selective reduction catalyst also has an activation temperature that exhibits a predetermined NO _X purification rate. In case of arranging the _the NO _X selective reducing catalyst as NO _X reduction catalysts, at low temperatures of the exhaust gas region, it is possible to hold the NO _X contained in the exhaust gas in _the NO _X holding device.

  The above embodiments can be combined as appropriate. In the respective drawings described above, the same or corresponding parts are denoted by the same reference numerals. In addition, said embodiment is an illustration and does not limit invention. Further, in the embodiment, changes included in the scope of claims are intended.

DESCRIPTION OF SYMBOLS 1 Engine body 2 Combustion chamber 13 Oxidation catalyst 14 NO _X selective reduction catalyst 15 NO _X holding device 16 Particulate filter 17 NO _X reduction catalyst 30 Electronic control unit 45 First NO _X adsorption part 46 NO _X oxidation part 47 Second NO _X adsorption unit 48 carrier 49 adsorbed metal 51 base material 52 first NO _X adsorption unit 53 NO _X oxidation unit 54 second NO _X adsorption unit 55 urea supply valve

Claims (4)

A first of the NO _X adsorbing portion is less than the first release temperature to adsorb NO _X, releasing NO _X adsorbed to become more first release temperature,
NO _X oxidation part that oxidizes nitrogen monoxide contained in exhaust gas to nitrogen dioxide,
A second of the NO _X adsorbing unit emitting at less than the second release temperature to adsorb NO _X, the NO _X adsorbed to become more second release temperature,
Exhaust gas flowing out from the second of the NO _X adsorbing portion is disposed so as to flow, and a NO _X reduction catalyst for purifying by reducing the NO _X,
In the first NO _X adsorption unit, the second NO _X adsorption unit, and the NO _X oxidation unit, exhaust gas flows into the NO _X oxidation unit through the first NO _X adsorption unit, and flows out from the NO _X oxidation unit. The exhaust gas is arranged so as to flow into the second NO _X adsorption portion,
Nitric oxide flowing out from the first NO _X adsorption section is oxidized in the NO _X oxidation section to change into nitrogen dioxide, and the generated nitrogen dioxide flows into the second NO _X adsorption section. An exhaust purification device for an internal combustion engine. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein at least one of the first NO _X adsorption unit and the second NO _X adsorption unit contains silver as a metal that adsorbs NO _X. The NO _X oxidation unit is disposed downstream of the first NO _X adsorption unit in the engine exhaust passage,
3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the second NO _X adsorption section is disposed downstream of the NO _X oxidation section in the engine exhaust passage. An oxidation catalyst disposed upstream of the first NO _X adsorption section;
When the temperature of the exhaust gas flowing into the oxidation catalyst is lower than a predetermined temperature, the nitrogen dioxide flowing into the oxidation catalyst reacts with the hydrocarbons contained in the exhaust gas to change into nitrogen monoxide and is generated wherein the nitric oxide is introduced into the first of the NO _X adsorbing portion, the exhaust purification system of an internal combustion engine according to any one of claims 1 to 3.

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