JP3642017B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
Particularly in a compression ignition type internal combustion engine, it is required to purify particulates and nitrogen oxides (NO _x ) in exhaust gas discharged from the engine combustion chamber. Filter for trapping particulate in order to purify process these particulates and NO _X (particulate filter) in the exhaust purification apparatus JP 9-159037 which was supported _the NO _X absorbent for purifying NO _X It is disclosed in the publication.
[0003]
[Problems to be solved by the invention]
If the fine particles and NO _X was to purification treatment by the exhaust gas purifying device was supported _the NO _X absorbent in the particulate filter as disclosed in the above publication, for example, by fine particles trapped by the particulate filter In some cases, the NO _X absorbent is covered, and NO _X cannot be purified.
[0004]
It is an object of the present invention is to purify process the fine particles and NO _X in the exhaust gas together with a high purification rate.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, in the first invention, a particulate filter for collecting particulates in the exhaust gas is disposed in the engine exhaust passage, and a NOx purification catalyst is provided in the engine exhaust passage upstream of the particulate filter. In the exhaust gas purification apparatus for an internal combustion engine, the NOx purification catalyst absorbs NOx in the exhaust gas and flows into the NOx purification catalyst when the air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst is lean. When the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or rich, a NOx purification catalyst that releases absorbed NOx is employed, and when the air-fuel ratio of the exhaust gas flowing into the particulate filter is lean The air-fuel ratio of the exhaust gas that absorbs oxygen in the exhaust gas and flows into the particulate filter is the stoichiometric air-fuel ratio or the The oxygen absorbent which acts as an oxidation catalyst while releasing oxygen that absorbed the blood was carried on the particulate filter by the air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst the stoichiometric air-fuel ratio or rich NOx is released from the NOx purification catalyst, and the released NOx is reduced and purified.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to the illustrated embodiments. FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a spark ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Is an exhaust valve, and 10 is an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13. A throttle valve 17 driven by a step motor 16 is arranged in the intake duct 13, and a cooling device 18 for cooling intake air flowing in the intake duct 13 is arranged around the intake duct 13. In the embodiment shown in FIG. 1, engine cooling water is guided into the cooling device 18, and the intake air is cooled by this engine cooling water. On the other hand, the exhaust port 10 is connected to an exhaust turbine 21 of an exhaust turbocharger 14 through an exhaust manifold 19 and an exhaust pipe 20, the casing 44 an outlet of the exhaust turbine 21 with a built-in _the NO _X absorbent 43 via an exhaust pipe 20a The casing 44 is connected to a casing 23 containing the particulate filter 22.
[0008]
The exhaust manifold 19 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 24, and an electrically controlled EGR control valve 25 is disposed in the EGR passage 24. A cooling device 26 for cooling the EGR gas flowing in the EGR passage 24 is disposed around the EGR passage 24. In the embodiment shown in FIG. 1, engine cooling water is guided into the cooling device 26, and the EGR gas is cooled by this engine cooling water. On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, so-called common rail 27, through a fuel supply pipe 6a. Fuel is supplied into the common rail 27 from an electrically controlled fuel pump 28 with variable discharge amount, and the fuel supplied into the common rail 27 is supplied to the fuel injection valve 6 via each fuel supply pipe 6a. A fuel pressure sensor 29 for detecting the fuel pressure in the common rail 27 is attached to the common rail 27, and a fuel pump 28 is configured so that the fuel pressure in the common rail 27 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 29. The discharge amount is controlled.
[0009]
The electronic control unit 30 comprises a digital computer, and is connected to each other by a bidirectional bus 31. 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. It comprises. The output signal of the fuel pressure sensor 29 is input to the input port 35 via the corresponding AD converter 37. Further, a temperature sensor 39 for detecting the temperature of the particulate filter 22 is attached to the particulate filter 22, and an output signal of the temperature sensor 39 is input to the input port 35 via the corresponding AD converter 37. The output signal of the mass flow meter 13a 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 depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and 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, 30 °. On the other hand, the output port 36 is connected to the fuel injection valve 6, the throttle valve driving step motor 16, the EGR control valve 25, and the fuel pump 28 via corresponding drive circuits 38.
[0010]
FIG. 2 shows the structure of the particulate filter 22. 2A is a front view of the particulate filter 22, and FIG. 2B is a side sectional view of the particulate filter 22. As shown in FIG. As shown in FIGS. 2A and 2B, the particulate filter 22 has a honeycomb structure and includes a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. These exhaust flow passages include an exhaust gas inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust gas outflow passage 51 whose upstream end is closed by a plug 53.
[0011]
In FIG. 2A, the hatched portion shows a plug 53. Therefore, the exhaust gas inflow passage 50 and the exhaust gas outflow passage 51 are alternately arranged via the thin partition walls 54. In other words, the exhaust gas inflow passage 50 and the exhaust gas outflow passage 51 are each surrounded by the four exhaust gas outflow passages 51, and each exhaust gas outflow passage 51 is surrounded by the four exhaust gas inflow passages 50. Arranged so that.
[0012]
The particulate filter 22 is made of, for example, a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 50 is contained in the surrounding partition wall 54 as indicated by an arrow in FIG. Through the exhaust gas outflow passage 51 adjacent thereto.
In addition, the particulate filter 22 of this embodiment carries an oxygen absorbent such as cerium Ce. The oxygen absorbent absorbs oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas flowing into the particulate filter 22 is lean, and the air-fuel ratio of the exhaust gas flowing into the particulate filter 22 becomes the stoichiometric air-fuel ratio or rich. Then, the absorbed oxygen is released.
[0013]
On the other hand, the NO _x absorbent 43 carries a noble metal such as platinum Pt. _The NO _X absorbent 43 absorbs NO _X in the exhaust gas when the air-fuel ratio of the exhaust gas flowing therein is lean, the air-fuel ratio is stoichiometric or rich exhaust gas flowing into the NO _X absorbent 43 Then, the absorbed NO _x is released.
In this specification, the air-fuel ratio of the exhaust gas means the fuel introduced into the combustion chamber 5 (in the system in which fuel is injected into the engine exhaust passage on the upstream side of the NO _x absorbent 43, the fuel is injected by the system. In a system in which air is injected into the engine exhaust passage on the upstream side of the NO _x absorbent 43 in the amount of air introduced into the combustion chamber 5 with respect to the amount of fuel Means the ratio of the amount of
[0014]
Next, the exhaust purification process in the present embodiment will be described. The internal combustion engine of this embodiment is operated in a state where the air-fuel ratio is lean in most engine operation regions. Therefore, the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 43 and the particulate filter 22 is also lean. For this reason, when the internal combustion engine is operated with its air-fuel ratio lean, NO _x in the exhaust gas is absorbed by the NO _x absorbent 43 and particulates in the exhaust gas are collected by the particulate filter 22. The oxygen in the exhaust gas is absorbed by the oxygen absorbent carried on the particulate filter 22.
[0015]
By the way, there is a limit to the amount of NO _x that can be absorbed by the NO _x absorbent 43. Thus the amount of the NO _X that is absorbed in the NO _X absorbent 43 (NO _X absorption) must the NO _X that is absorbed reduced and purified before exceeding the limit value. Otherwise NO _X in the exhaust gas flows out into _the NO _X absorbent 43 downstream without being absorbed in the NO _X absorbent 43. Therefore, in this embodiment, the air-fuel ratio in the combustion chamber 5 is made rich before the NO _x absorption amount exceeds the limit value, or fuel is injected from the fuel injection valve 6 during the second half of the engine expansion stroke or the engine exhaust stroke. air-fuel ratio is flowing rich exhaust gas to _the NO _X absorbent 43, thereby to release the NO _X from _the NO _X absorbent 43, reduced and purified by these released NO _X hydrocarbons in the exhaust gas (HC) To do.
[0016]
On the other hand, the amount of fine particles that can be collected by the particulate filter 22 is also limited. However, the collected fine particles are combusted when the temperature in the particulate filter 22 exceeds a certain temperature, and are purified by this. Therefore, as long as the temperature in the particulate filter 22 is maintained at a temperature equal to or higher than the ignition temperature of the particulates, the amount of particulates collected in the particulate filter 22 does not reach the limit value, but is actually collected. In this embodiment, the amount of collected fine particles is increased by increasing the temperature of the exhaust gas before or when the amount of collected fine particles reaches its limit value. Force burning.
[0017]
Thus, according to the present embodiment, NO _x and fine particles in the exhaust gas can be purified at a high purification rate.
Now, as in this embodiment, the exhaust purification apparatus configured by disposing the NO _X absorbent 43 as the NO _X purification catalyst in the engine exhaust passage on the upstream side of the particulate filter 22 has the following advantages.
[0018]
Exhaust purifying apparatus of the present embodiment possesses more of the NO _X absorbent as compared with the case of carrying _the NO _X absorbent in the particulate filter 22 because it has a separate _the NO _X absorbent and the particulate filter 22 be able to. For this reason, the NO _x purification rate in the exhaust purification system of this embodiment is high. This is the first advantage.
The receiving _the NO _X absorbent combustion heat of the particulate in the particulate filter 22 in the exhaust purification apparatus by supporting _the NO _X absorbent in the particulate filter 22 is directly, although _the NO _X absorbent is thermally deteriorated, the present embodiment In the exhaust purification apparatus of the example, the NO _x absorbent 43 is disposed upstream of the particulate filter 22, so that the NO _x absorbent 43 does not receive the heat of combustion of the fine particles, and therefore the NO _x absorbent 43 is thermally deteriorated. There is nothing. This is the second advantage.
[0019]
In particular, when the air-fuel ratio of the exhaust gas becomes rich, unburned HC and soluble organic substances are contained in the exhaust gas, and when these flow into the particulate filter 22, they act as a binder that links the particulates. Therefore, there is a high possibility that the fine particles are clogged in the pores of the particulate filter 22. Particulates upstream of the pore clogging of the particulate filter 22 because these unburnt HC and combustible organic substances are oxidized and removed by _the NO _X absorbent 43 of the filter 22 in the exhaust purification system of the present embodiment to which Is very unlikely. This is the third advantage.
[0020]
Further, in the case of an exhaust gas purification device in which exhaust gas flows directly into the particulate filter 22 without passing through the NO _x absorbent 43, variations occur in the temperature distribution of the wall surface of the particulate filter 22 on the exhaust gas inflow side. . This is due to the variation in the temperature distribution in the exhaust gas. However, according to the exhaust gas purification apparatus of the present embodiment, the exhaust gas passes through the NO _x absorbent 43, so that the temperature distribution in the exhaust gas becomes uniform. Therefore, the wall surface of the particulate filter 22 on the side where the exhaust gas flows in is uniformed. The temperature distribution is uniform. Accordingly, a considerably low temperature region is not formed on the wall surface of the particulate filter 22, and therefore, particulates are burned on the entire wall surface, thus preventing the particulates from clogging the pores of the particulate filter 22. . This is the fourth advantage.
[0021]
The flows out from _the NO _X absorbent 43 without being consumed by the HC component _the NO _X absorbent 43 in the exhaust gas when the rich air-fuel ratio of the exhaust gas to release NO _X from _the NO _X absorbent 43 May flow into the particulate filter 22. At this time, as described above, the HC component binds the fine particles, and clogs the pores of the particulate filter 22. However, in this embodiment, an oxygen absorbent is supported on the particulate filter 22, and this oxygen absorbent has a function of releasing oxygen when the surrounding atmosphere becomes rich. Therefore, the HC component flowing into the particulate filter 22 absorbs this oxygen. Oxidized and removed by oxygen released from the agent. Therefore, clogging of the particulate filter 22 is prevented. This is the fifth advantage. As can be seen from this, the oxidation absorbent acts as an oxidation catalyst.
[0022]
Further, if the exhaust gas contains a sulfur component, the sulfur component adheres to the oxygen absorbent carried on the particulate filter 22 and its oxygen absorption capacity is reduced. However, in the exhaust purification apparatus of the present invention, the NO _x absorbent 43 is disposed upstream of the particulate filter 22, and the sulfur component in the exhaust gas is processed by the NO _x absorbent 43, so that the oxygen in the particulate filter 22 The absorbent is not deteriorated by the sulfur component. This is the sixth advantage.
[0023]
Note the air-fuel ratio of the exhaust gas flowing into the place of _the NO _X absorbent as NO _X purification catalyst may be employed a catalyst capable of purifying the NO _X even lean.
[0024]
【The invention's effect】
According to the present invention disposed NO _X purification catalyst upstream of the particulate filter, purify NO _X in NO _X purification catalyst, NO _X purification because so trapping particulate in the particulate filter The fine particles do not cover the catalyst metal of the catalyst. Therefore, NO _x and fine particles can be purified at a high purification rate.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
FIG. 2 is a diagram showing a particulate filter.
[Explanation of symbols]
1 ... engine body 5 ... combustion chamber 22 ... particulate filter 43 ... NO _X absorbent

Claims (1)

In the exhaust gas purification apparatus for an internal combustion engine, a particulate filter for collecting particulates in the exhaust gas is disposed in the engine exhaust passage, and a NOx purification catalyst is disposed in the engine exhaust passage upstream of the particulate filter. As the purification catalyst, when the air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst is lean, the NOx in the exhaust gas is absorbed and the air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst becomes the stoichiometric air-fuel ratio or rich. In this case, a NOx purification catalyst that releases the absorbed NOx is employed, and further, when the air-fuel ratio of the exhaust gas flowing into the particulate filter is lean, the oxygen in the exhaust gas is absorbed and the particulate filter When the air-fuel ratio of the exhaust gas flowing into the engine becomes the stoichiometric air-fuel ratio or rich, the absorbed oxygen is released The oxygen absorbing agent which acts as an oxidation catalyst carried on the particulate filter, NOx is released from the NOx purifying catalyst by the stoichiometric air-fuel ratio or rich air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst, release An exhaust purification device for an internal combustion engine that reduces and purifies the NOx that has been discharged.

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