JP2001317333A - Exhaust emission control method and exhaust emission control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an output torque fluctuation when controlling the temperature of a particulate filter by employing a new method. SOLUTION: The quantity of the fuel fed to a combustion chamber is controlled according to a required load. The exhaust gas discharged from the combustion chamber is again circulated to the combustion chamber. The particulate filter 22 is arranged in an engine exhaust passage. The particulate quantity discharged from the combustion chamber 5 per unit time is made smaller than an oxidizable/removable particulate quantity capable of being oxidized and removed without generating a luminous flame per unit time on the particulate filter 22, thereby the particulates in the exhaust gas are oxidized and removed without generating the luminous flame when flowing into the particulate filter 22. When it is judged that the temperature of the particulate filter should be raised, the quantity of the exhaust circulated to the combustion chamber is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying method and an exhaust gas purifying apparatus.

[0002]

2. Description of the Related Art Conventionally, in a diesel engine, a particulate filter is disposed in an engine exhaust passage in order to remove fine particles contained in exhaust gas, and the fine particles in the exhaust gas are once collected by the particulate filter. In addition, the particulate filter is regenerated by igniting and burning the fine particles collected on the particulate filter. However, the fine particles trapped on the particulate filter do not ignite unless the temperature becomes higher than about 600 ° C., whereas the exhaust gas temperature of a diesel engine is usually much lower than 600 ° C. Therefore, it is difficult to ignite the fine particles collected on the particulate filter with the heat of the exhaust gas, and the ignition temperature of the fine particles is required to ignite the fine particles collected on the particulate filter with the heat of the exhaust gas. Must be lowered.

By the way, it has been known that if a catalyst is supported on a particulate filter, the ignition temperature of fine particles can be reduced. Therefore, various types of particulate filters supporting a catalyst have conventionally been used in order to lower the ignition temperature of fine particles. Is known. For example, Tokuho 7-10
Japanese Patent No. 6290 discloses a particulate filter in which a mixture of a platinum group metal and an alkaline earth metal oxide is supported on the particulate filter. With this particulate filter, it is almost 350 ° C to 400 ° C.
The particles are ignited at a relatively low temperature of ° C. and then burned continuously.

[0004] In a diesel engine, when the load increases, the exhaust gas temperature reaches from 350 ° C to 400 ° C. Therefore, at first glance, the particulate filter described above causes the exhaust gas heat to ignite and burn fine particles when the engine load increases. Looks like it can. However, actually, even when the temperature of the exhaust gas reaches 350 ° C. to 400 ° C., the fine particles may not ignite, and even if the fine particles ignite, only a part of the fine particles burn, and a large amount of the fine particles remains unburned. Is generated.

That is, when the amount of fine particles contained in the exhaust gas is small, the amount of fine particles adhering to the particulate filter is small.
When the temperature rises to 400 ° C., the fine particles on the particulate filter are ignited and then continuously burned. However, when the amount of fine particles contained in the exhaust gas increases, the fine particles adhered on the particulate filter accumulate on the fine particles before the fine particles completely burn, and as a result, the fine particles accumulate on the particulate filter. Deposit in a shape. When the fine particles are deposited on the particulate filter in this manner, some of the fine particles that easily come into contact with oxygen are burned, but the remaining fine particles that are hard to contact with oxygen do not burn, and thus a large amount of fine particles burn. Will remain. Therefore, when the amount of fine particles contained in the exhaust gas increases, a large amount of fine particles will continue to be deposited on the particulate filter.

On the other hand, when a large amount of fine particles are deposited on the particulate filter, the deposited fine particles gradually become difficult to ignite and burn. It is considered that the reason why it becomes difficult to burn in this way is probably that carbon in the fine particles changes to graphite or the like which is difficult to burn during the deposition. In fact, if a large amount of fine particles continue to deposit on the particulate filter, the deposited fine particles do not ignite at a low temperature of 350 ° C. to 400 ° C., and a high temperature of 600 ° C. or more is required to ignite the deposited fine particles. However, in a diesel engine, the exhaust gas temperature does not usually reach a high temperature of 600 ° C. or more. Therefore, if a large amount of fine particles are continuously deposited on the particulate filter, it becomes difficult to ignite the fine particles deposited by the exhaust gas heat. .

On the other hand, if the exhaust gas temperature can be raised to a high temperature of 600 ° C. or more at this time, the deposited fine particles ignite, but in this case, another problem occurs. That is, in this case, when the deposited fine particles are ignited, they emit a bright flame and burn, and at this time, the temperature of the particulate filter is kept at 8 for a long time until the combustion of the deposited fine particles is completed.
Maintained above 00 ° C. However, when the particulate filter is exposed to a high temperature of 800 ° C. or more for a long time as described above, the particulate filter deteriorates early, and therefore, there is a problem that the particulate filter must be replaced with a new one early. Occurs.

When the accumulated fine particles are burned, the ash condenses into large lumps, and the lumps of ash cause clogging of the pores of the particulate filter. The number of clogged pores gradually increases over time, and thus the pressure loss of the exhaust gas flow in the particulate filter increases. When the pressure loss of the exhaust gas flow is increased, the output of the engine is reduced, and this also causes a problem that the particulate filter must be replaced with a new one at an early stage.

Once such a large amount of fine particles are deposited in a layered manner, various problems as described above occur. Therefore, the amount of fine particles contained in the exhaust gas and the amount of fine particles that can be burned on the particulate filter are reduced. In consideration of the balance, it is necessary to prevent a large amount of fine particles from depositing in a layered manner. However, in the particulate filter described in the above-mentioned publication, no consideration is given to the balance between the amount of fine particles contained in the exhaust gas and the amount of fine particles that can be burned on the particulate filter, and as described above, Various problems will arise.

In the particulate filter described in the above-mentioned publication, when the exhaust gas temperature becomes lower than 350 ° C., the fine particles are not ignited, and thus the fine particles accumulate on the particulate filter. In this case, if the amount of deposition is small, the deposited fine particles are burned when the exhaust gas temperature changes from 350 ° C. to 400 ° C., but if a large amount of fine particles are deposited in a stack, the exhaust gas temperature changes from 350 ° C. to 400 ° C. When the particles accumulate, they do not ignite, and even if they are ignited, some of the particles do not burn, resulting in unburned residues.

In this case, if the temperature of the exhaust gas is increased before a large amount of fine particles are deposited in a stack, the deposited fine particles can be burned without remaining unburned. However, in the particulate filter described in the above-mentioned publication, Such a thing is not considered at all, and when a large amount of fine particles are deposited in a stacked manner, all the deposited fine particles cannot be burned unless the exhaust gas temperature is raised to 600 ° C. or more.

In order to solve such a problem, the amount of fine particles contained in the exhaust gas and the amount of fine particles that can be burned on the particulate filter are controlled so as not to deposit a large amount of fine particles in a stacked manner. An exhaust gas purification method and an exhaust gas purification device have already been filed by the present applicant (Japanese Patent Application No. 2000-43571).

[0013]

In the above publication, the exhaust gas discharged from the combustion chamber for a certain purpose is circulated again into the combustion chamber. Here, in the above publication, various methods can be considered as a method of controlling the temperature of the particulate filter. However, when the temperature of the particulate filter is controlled using these methods, the exhaust gas that is recirculated into the combustion chamber in accordance with the method is controlled. Unless the amount of gas is changed, the output torque may fluctuate greatly.

Accordingly, an object of the present invention is to provide an internal combustion engine in which exhaust gas discharged from a combustion chamber is circulated again into the combustion chamber by employing a novel method and controlling the output torque when the temperature of the particulate filter is controlled. The purpose is to reduce the fluctuation.

[0015]

According to a first aspect of the present invention, in order to achieve the above object, the amount of fuel supplied to a combustion chamber is controlled in accordance with a required load, and the exhaust gas discharged from the combustion chamber is combusted again. In an internal combustion engine that circulates through the chamber,
As a particulate filter for removing particulates in the exhaust gas discharged from the combustion chamber, the amount of particulates discharged from the combustion chamber per unit time can be reduced on the particulate filter without emitting a bright flame per unit time. When the amount of particulates that can be removed by oxidation is smaller than the amount of particulates that can be removed by oxidation, the particulates in the exhaust gas are oxidized and removed without emitting a bright flame when they flow into the particulate filter, and the amount of particulates discharged is temporarily smaller than the amount of particulates that can be removed by oxidation. Even if the amount increases, the fine particles on the particulate filter are deposited only below a certain limit.When the amount of discharged fine particles is smaller than the amount of fine particles that can be oxidized and removed, the fine particles on the particulate filter are oxidized and removed without producing a bright flame. Oxidation using a particulate filter Even though the amount of particulates that can be removed depends on the temperature of the particulate filter, the amount of particulates discharged is usually smaller than the amount of particulates that can be oxidized and removed, and the amount of particulates discharged temporarily becomes larger than the amount of particulates that can be removed by oxidation. Thereafter, the amount of discharged particulates and the temperature of the particulate filter are maintained so that when the amount of discharged particulates becomes smaller than the amount of particulates that can be removed by oxidation, only particulates of a certain amount or less that can be removed by oxidation are deposited on the particulate filter. Thereby, the particulates in the exhaust gas are oxidized and removed on the particulate filter without emitting a bright flame, and when it is determined that the temperature of the particulate filter should be increased, the exhaust gas flow is throttled, thereby Raise the temperature of the particulate filter, and When focused exhaust gas flow in order to increase the degree to reduce the amount of exhaust gas to be circulated to the combustion chamber.

In the second invention, in the first invention,
By restricting the exhaust gas flow, the flow velocity of the exhaust gas passing through the particulate filter can be reduced. In a third aspect based on the first aspect, the exhaust gas flow is reduced by a time determined based on the amount of fine particles deposited on the particulate filter.

In a fourth aspect, in the first aspect,
A noble metal catalyst is supported on the particulate filter. According to a fifth aspect of the present invention, in the fourth aspect, there is provided an active oxygen releasing agent which takes in oxygen to retain oxygen when there is excess oxygen in the surroundings and releases the retained oxygen in the form of active oxygen when the surrounding oxygen concentration decreases. Carry on the particulate filter, release active oxygen from the active oxygen release agent when the fine particles adhere to the particulate filter, and oxidize the fine particles attached to the particulate filter by the released active oxygen. I have.

In the sixth invention, in the fifth invention,
The active oxygen releasing agent comprises an alkali metal or an alkaline earth metal or a rare earth or transition metal. According to a seventh aspect, in the sixth aspect, the alkali metal and the alkaline earth metal are made of a metal having a higher ionization tendency than calcium. In an eighth aspect based on the fifth aspect, the air-fuel ratio of a part or the whole of the exhaust gas is temporarily made rich to oxidize the fine particles adhering to the particulate filter.

According to a ninth aspect of the present invention, in order to achieve the above object, the amount of fuel supplied to the combustion chamber is controlled in accordance with a required load, and the exhaust gas discharged from the combustion chamber is circulated again to the combustion chamber. In the internal combustion engine, a particulate filter for removing particulates in the exhaust gas discharged from the combustion chamber is disposed in the engine exhaust passage, and the particulate filter is used as the particulate filter. If the amount of fine particles is smaller than the amount of oxidizable particles that can be oxidized and removed without emitting a bright flame per unit time on the particulate filter, the fine particles in the exhaust gas oxidize without emitting a bright flame when they flow into the particulate filter. Even if the amount of removed particulates is temporarily greater than the amount of particulates that can be removed by oxidation, When particulates are deposited only below a certain limit on the rate filter, a particulate filter that allows the particulates on the particulate filter to be oxidized and removed without producing a bright flame when the amount of discharged particulates becomes smaller than the amount of particulates that can be removed by oxidation. Use
Assuming that the amount of fine particles that can be removed by oxidation depends on the temperature of the particulate filter, the amount of discharged fine particles is usually smaller than the amount of fine particles that can be removed by oxidation, and the amount of discharged fine particles temporarily exceeds the amount of fine particles that can be removed by oxidation. Also then
In order to maintain the amount of discharged particulates and the temperature of the particulate filter so that only particulates of a certain amount or less that can be oxidized and removed are deposited on the particulate filter when the amount of discharged particulates becomes smaller than the amount of particulates that can be removed by oxidation. Control means, whereby the particulates in the exhaust gas are oxidized and removed on the particulate filter without emitting a bright flame, and when it is determined that the temperature of the particulate filter should be raised, the control means Means for reducing the exhaust gas flow, thereby increasing the temperature of the particulate filter, and reducing the amount of exhaust gas circulated to the combustion chamber when the exhaust gas flow is reduced to increase the temperature of the particulate filter. .

In a tenth aspect based on the ninth aspect, the flow rate of the exhaust gas passing through the particulate filter is reduced by restricting the exhaust gas flow. In an eleventh aspect based on the tenth aspect, an exhaust throttle valve is disposed downstream of the particulate filter, and the exhaust gas flow is throttled by the exhaust throttle valve.

In a twelfth aspect based on the ninth aspect, in the ninth aspect, the particulate filter includes a plurality of exhaust passages extending in parallel with each other, and one of the adjacent exhaust passages is closed at an upstream end by a plug. The downstream end of the adjacent exhaust passage is closed by a stopper, and the catalyst is carried on the wall surface of the exhaust passage and the wall surface of the stopper.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below 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 is also applicable 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 Are exhaust valves, 10
Indicates exhaust ports, respectively. 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 mass flowmeter 13a for detecting the mass flow rate of the air to be taken in is attached to the intake pipe 13b on the upstream side of the compressor 15. 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 through the intake duct 13 is arranged around the intake duct 13. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 18,
The intake air is cooled by the engine cooling water. On the other hand, the exhaust port 10 is connected to an exhaust turbine 21 of the exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20, and an outlet of the exhaust turbine 21 is connected to a casing 23 having a built-in particulate filter 22.

The exhaust manifold 19 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter, EGR) passage 24, and an electrically controlled EGR passage is provided in the EGR passage 24.
A control valve 25 is arranged. 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 engine cooling water cools the EGR gas. On the other hand, each fuel injection valve 6
Is connected to a fuel reservoir, a so-called common rail 27, via a fuel supply pipe 6a. Fuel is supplied into the common rail 27 from a fuel pump 28 of an electrically controlled variable discharge amount, and the fuel supplied into the common rail 27 is supplied to the fuel injection valve 6 through 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 the fuel pump 28 is controlled 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. Is controlled.

The electronic control unit 30 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35, An output port 36 is provided. The output signal of the fuel pressure sensor 29 is input to the input port 35 via the corresponding AD converter 37. 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 set to a corresponding AD signal.
The signal is input to the input port 35 via the converter 37. The output signal of the mass flow meter 13a is output to the corresponding AD converter 37.
Through the input port 35. 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, by 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 EG via a corresponding drive circuit 38.
It is connected to the R control valve 25 and the fuel pump 28.

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 FIGS. 2A and 2B, the particulate filter 22 has a honeycomb structure and includes a plurality of exhaust passages 50 and 51 extending in parallel with each other. These exhaust passages are constituted by 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.

In FIG. 2A, hatched portions indicate plugs 53. Therefore, the exhaust gas inflow passage 50 and the exhaust gas outflow passage 51 are formed of thin partition walls 54.
Are alternately arranged via 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. Are arranged as follows.

The particulate filter 22 is formed of a porous material such as cordierite, for example, so that the exhaust gas flowing into the exhaust gas inflow passage 50 is surrounded by the surroundings as shown by arrows in FIG. Partition wall 54
It flows out into the adjacent exhaust gas outflow passage 51 through the inside. In the embodiment of the present invention, the peripheral wall surface of each exhaust gas inflow passage 50 and each exhaust gas outflow passage 51, that is, each partition 54
A layer of a carrier made of, for example, alumina is formed over the entire surface on both side surfaces of the plug, the outer end face of the plug 53 and the inner end faces of the plugs 52 and 53, and a noble metal catalyst and excess oxygen And an active oxygen releasing agent that takes in oxygen to retain oxygen when it is present and releases the retained oxygen in the form of active oxygen when the surrounding oxygen concentration decreases.

In the embodiment of the present invention, platinum Pt is used as a noble metal catalyst, and alkali metal such as potassium K, sodium Na, lithium Li, cesium Cs, rubidium Rb, barium Ba, calcium Ca as an active oxygen releasing agent. And at least one selected from alkaline earth metals such as strontium Sr, lanthanum La, rare earths such as yttrium Y, and transition metals.

As an active oxygen releasing agent, calcium C
It is preferable to use an alkali metal or alkaline earth metal having a higher ionization tendency than a, that is, potassium K, lithium Li, cesium Cs, rubidium Rb, barium Ba, and strontium Sr. Next, the action of removing particulates in the exhaust gas by the particulate filter 22 will be described by taking as an example a case where platinum Pt and potassium K are carried on a carrier, but other noble metals, alkali metals,
A similar effect of removing fine particles can be obtained by using an alkaline earth metal, a rare earth, or a transition metal.

In a compression ignition type internal combustion engine as shown in FIG. 1, combustion takes place under excess air, so that the exhaust gas contains a large amount of excess air. That is, if the ratio of air and fuel supplied to the intake passage and the combustion chamber 5 is referred to as the air-fuel ratio of the exhaust gas, the air-fuel ratio of the exhaust gas in the compression ignition type internal combustion engine as shown in FIG. I have. Since NO is generated in the combustion chamber 5, NO is contained in the exhaust gas.
It is included. The fuel contains a sulfur component S. The sulfur component S reacts with oxygen in the combustion chamber 5 to form a sulfur component S.
It becomes O ₂ . Therefore, SO ₂ is contained in the exhaust gas. Therefore, exhaust gas containing excess oxygen, NO and SO ₂ flows into the exhaust gas inflow passage 50 of the particulate filter 22.

FIGS. 3A and 3B schematically show enlarged views of the surface of the carrier layer formed on the inner peripheral surface of the exhaust gas inflow passage 50. FIG. 3A and 3B, reference numeral 60 denotes platinum Pt particles, and reference numeral 61 denotes an active oxygen releasing agent containing potassium K. When the exhaust gas because the exhaust gas as described above contains a large amount of excess oxygen flows into the exhaust gas inflow passages 50 of the particulate filter 22 3 These oxygen O ₂ as shown in (A) platinum Pt in or O ^2- in the form ^- but O ₂
Adheres to the surface of On the other hand, NO in the exhaust gas is platinum Pt.
Reacts with O ₂ ⁻ or O ²⁻ on the surface of NO to form NO ₂ (2NO + O ₂ → 2NO ₂ ). NO ₂ generated
Is partially oxidized on platinum Pt while active oxygen releasing agent 61
As shown in FIG. 3 (A), it is absorbed into the active oxygen releasing agent 61 and diffuses into the active oxygen releasing agent 61 in the form of nitrate ion NO ₃ ⁻ to form potassium nitrate KNO ₃ .

On the other hand, as described above, SO is contained in the exhaust gas.
_TwoIs also included in this SO_TwoIs the same mechanism as NO
The active oxygen is released into the active oxygen releasing agent 61 by the system. Ie
As described above, oxygen O_TwoIs O_Two ^-Or O^2-Platinum in the form of
SO on the surface of Pt and in the exhaust gas_TwoIs platinum
O on the surface of Pt_Two ^-Or O^2-Reacts with SO_ThreeTona
You. Then the generated SO_ThreePart of the surface is further platinum on Pt
While being oxidized into the active oxygen releasing agent 61,
Sulfate SO while binding to_Four ^2-Active acid in the form of
Potassium sulfate K_TwoSO_FourRaw
To achieve. In this way, the active oxygen releasing catalyst 61 contains nitric acid.
Potassium KNO_ThreeAnd potassium sulfate K _TwoSO_FourIs raw
Is done.

On the other hand, fine particles mainly composed of carbon C are generated in the combustion chamber 5, and therefore these fine particles are contained in the exhaust gas. These fine particles contained in the exhaust gas are generated when the exhaust gas flows in the exhaust gas inflow passage 50 of the particulate filter 22.
Alternatively, the exhaust gas outflow passage 51
3B, it comes into contact with and adheres to the surface of the carrier layer, for example, the surface of the active oxygen releasing agent 61 as indicated by 62 in FIG.

As described above, the fine particles 62 serve as the active oxygen releasing agent 6
1 and the fine particles 62 and the active oxygen releasing agent 6
At the contact surface with No. 1, the oxygen concentration decreases. When the oxygen concentration decreases, a difference in concentration occurs between the active oxygen releasing agent 61 having a high oxygen concentration and the oxygen in the active oxygen releasing agent 61 is directed toward the contact surface between the fine particles 62 and the active oxygen releasing agent 61. Try to move. As a result, potassium nitrate KNO ₃ formed in the active oxygen releasing agent 61 becomes potassium K and oxygen O
And NO are decomposed, and oxygen O is directed to the contact surface between the fine particles 62 and the active oxygen releasing agent 61, while NO is released from the active oxygen releasing agent 61 to the outside. The NO released to the outside is oxidized on platinum Pt on the downstream side, and is absorbed again in the active oxygen releasing agent 61.

At this time, potassium sulfate K ₂ SO ₄ formed in the active oxygen releasing agent 61 is also decomposed into potassium K, oxygen O and SO _2, and oxygen O is formed between the fine particles 62 and the active oxygen releasing agent 61. Towards the contact surface, while SO ₂ is released from the active oxygen releasing agent 61 to the outside. The SO ₂ released to the outside is oxidized on platinum Pt on the downstream side,
It is again absorbed in the active oxygen releasing agent 61. However, since potassium sulfate K ₂ SO ₄ is stabilized, potassium nitrate K
It is harder to release active oxygen than NO ₃ .

The fine particles 62 and the active oxygen releasing agent 61
The oxygen O heading toward the contact surface is oxygen decomposed from compounds such as potassium nitrate KNO ₃ and potassium sulfate K ₂ SO ₄ . Oxygen O decomposed from the compound has high energy and extremely high activity. Therefore, the oxygen that goes to the contact surface between the fine particles 62 and the active oxygen releasing agent 61 is active oxygen O. When the active oxygen O comes into contact with the fine particles 62, the fine particles 62 are immediately oxidized without emitting a bright flame, and the fine particles 62 are completely eliminated.
Therefore, the fine particles 62 are
Does not accumulate on top.

The conventional particulate filter 2
When the fine particles deposited in a stack on the combustor 2 are burned, the particulate filter 22 glows red and burns with a flame. Such combustion with a flame cannot be sustained unless it is at a high temperature, so that the temperature of the particulate filter 22 must be maintained at a high temperature in order to maintain the combustion with such a flame.

On the other hand, in the present invention, the fine particles 62 are oxidized without emitting a bright flame as described above, and at this time, the surface of the particulate filter 22 does not glow. In other words, in other words, in the present invention, the fine particles 62 are oxidized and removed at a considerably lower temperature than in the prior art. Therefore, the action of removing fine particles 62 that do not emit bright flame by oxidation according to the present invention is completely different from the action of removing fine particles by conventional combustion involving a flame.

By the way, platinum Pt and active oxygen releasing agent 6
1 is activated as the temperature of the particulate filter 22 increases, so that the amount of active oxygen O that the active oxygen releasing agent 61 can release per unit time increases as the temperature of the particulate filter 22 increases. Therefore, the amount of oxidizable particles that can be oxidized and removed on the particulate filter 22 without emitting luminous flame per unit time increases as the temperature of the particulate filter 22 increases.

The solid line in FIG. 5 indicates the amount of fine particles G that can be oxidized and removed without emitting a bright flame per unit time. In FIG. 5, the horizontal axis indicates the temperature TF of the particulate filter 22. When the amount of fine particles discharged from the combustion chamber 5 per unit time is referred to as a discharged fine particle amount M, when the discharged fine particle amount M is smaller than the oxidizable and removable fine particles G, that is, when the discharged fine particle amount M is in the region I in FIG. As soon as all the fine particles discharged from the filter contact the particulate filter 22, they are oxidized and removed on the particulate filter 22 in a short time without emitting a bright flame.

On the other hand, when the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation, that is, in the region II in FIG. 5, the amount of active oxygen is insufficient to oxidize all the fine particles. FIGS. 4A to 4C show how the fine particles are oxidized in such a case. In other words, when the amount of active oxygen is insufficient to oxidize all the fine particles, the fine particles 62 are used as the active oxygen releasing agent 6 as shown in FIG.
When the fine particles 62 adhere to the surface of the carrier 1, only a part of the fine particles 62 is oxidized, and the finely oxidized fine particles remain on the carrier layer. Next, when the state of the shortage of the active oxygen amount continues, the fine particles which were not oxidized one after another remain on the carrier layer, and as a result, as shown in FIG. It becomes covered with the residual fine particle portion 63.
The residual fine particle portion 63 covering the surface of the carrier layer is gradually transformed into a carbon material which is hardly oxidized, and therefore, the residual fine particle portion 63 tends to remain as it is. When the surface of the carrier layer is covered with the residual fine particle portion 63, platinum P
The oxidation of NO and SO ₂ by t and the release of active oxygen by the active oxygen release agent 61 are suppressed. As a result, as shown in FIG. 4C, another fine particle 64 is deposited on the remaining fine particle portion 63 one after another. That is, the fine particles are deposited in a layered manner. When the fine particles are deposited in a layered manner in this manner, these fine particles are separated from the platinum Pt and the active oxygen releasing agent 61, so that even if the fine particles are easily oxidized, they are no longer oxidized by the active oxygen O. Therefore, further fine particles are deposited on the fine particles 64 one after another. That is, when the state in which the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation continues, the fine particles are deposited on the particulate filter 22 in a layered manner. Unless the temperature of 22 is raised, the deposited fine particles cannot be ignited and burned.

As described above, in the region I of FIG. 5, the fine particles are oxidized in a short time without emitting a bright flame on the particulate filter 22, and in the region II of FIG. Deposit in a shape. Therefore, in order to prevent the fine particles from depositing on the particulate filter 22 in a layered manner, the amount M of discharged fine particles must always be smaller than the amount G of fine particles that can be removed by oxidation.

As can be seen from FIG. 5, the particulate filter 22 used in the embodiment of the present invention can oxidize the fine particles even if the temperature TF of the particulate filter 22 is considerably low. In the illustrated compression ignition type internal combustion engine, it is possible to maintain the amount M of discharged particulate and the temperature TF of the particulate filter 22 so that the amount M of discharged particulate is always smaller than the amount G of particulate that can be removed by oxidation.

Therefore, in the first embodiment of the present invention, the amount M of discharged fine particles and the temperature TF of the particulate filter 22 are maintained such that the amount M of discharged fine particles is always smaller than the amount G of fine particles that can be removed by oxidation. As described above, if the amount M of discharged fine particles is always smaller than the amount G of fine particles removable by oxidation, the fine particles hardly accumulate on the particulate filter 22, and the back pressure hardly increases. Therefore, the engine output does not decrease.

However, as described above, once the fine particles are deposited in layers on the particulate filter 22, even if the discharged fine particle amount M becomes smaller than the oxidizable and removable fine particle amount G, the fine particles are oxidized by the active oxygen O. It is difficult. However, when the non-oxidized fine particle portion is beginning to remain, that is, when the fine particles are deposited only below a certain limit, if the exhaust fine particle amount M becomes smaller than the oxidizable and removable fine particle amount G, the residual fine particle portion becomes active oxygen. O is oxidized and removed without emitting a bright flame.

Therefore, in the second embodiment of the present invention, the amount M of discharged fine particles is usually smaller than the amount G of fine particles removable by oxidation, and the amount M of discharged fine particles is temporarily larger than the amount G of fine particles removable by oxidation. 4B, the carrier layer can be oxidized and removed so that the surface of the carrier layer is not covered with the residual fine particle portion 63, that is, when the amount M of discharged fine particles becomes smaller than the amount G of fine particles that can be removed by oxidation. The amount M of discharged particulates and the temperature TF of the particulate filter 22 are maintained so that only a small amount of particulates below a certain limit is deposited on the particulate filter 22.

In particular, immediately after the start of the engine, the temperature TF of the particulate filter 22 is low. Therefore, at this time, the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation. Therefore, it is considered that the second embodiment is more suitable for actual driving. Next, control of the amount M of discharged particulate and the temperature TF of the particulate filter 22 in the above embodiment will be described. The amount M of discharged fine particles is determined by the amount of air sucked into the combustion chamber 5 (hereinafter, referred to as the amount M).
(Intake amount) and the EGR gas amount. Therefore, in the above embodiment, the opening degree of the throttle valve 17 and the opening degree of the EGR control valve 25 are controlled such that the amount M of the discharged fine particles becomes smaller than the amount G of the fine particles removable by oxidation.

The internal combustion engine in the above embodiment is controlled so that the amount of fuel injected from the fuel injection valve (hereinafter, the injected fuel amount) increases as the required load increases. In other words, if the required load is positively increased, the amount of injected fuel increases, so that the combustion temperature in the combustion chamber increases and the temperature of the exhaust gas also increases. Therefore, the temperature of the particulate filter 22 also increases. Therefore, in the present embodiment, as shown in FIG. 1, an exhaust throttle valve 39a is disposed downstream of the particulate filter 22, and when it is determined that the temperature of the particulate filter 22 should be increased, the exhaust throttle valve 39a The exhaust gas flow is reduced by reducing the opening of the filter, thereby increasing the temperature of the particulate filter 22. That is, if the opening degree of the exhaust throttle valve 39a is reduced, the required load increases, and accordingly, the amount of injected fuel also increases, and thus the temperature of the exhaust gas is increased. Therefore, the exhaust throttle valve 3
If the opening of 9a is reduced, the particulate filter 2
2 can be raised.

There is another advantage in reducing the opening of the exhaust throttle valve 39a when the temperature of the particulate filter 22 is to be raised. That is, the fact that the temperature of the particulate filter 22 should be raised means that the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation. Here, if the opening degree of the exhaust throttle valve 39a is reduced, the flow velocity of the exhaust gas passing through the particulate filter 22 is reduced. According to this, since the exhaust gas passes through the particulate filter 22 relatively slowly, sufficient time for oxidizing the fine particles can be secured. Further, since the amount of the fine particles flowing into the particulate filter 22 is also reduced, the discharged fine particle amount M is smaller than the oxidizable and removable fine particle amount G.
For these reasons, when the temperature of the particulate filter 22 should be increased, that is, when the amount M of discharged particulates is greater than the amount G of particulates that can be removed by oxidation, the exhaust throttle valve 39a
Reducing the degree of opening has the advantage that particulates can be reliably oxidized and removed in the particulate filter 22 also for the reasons described above.

This is particularly advantageous for an internal combustion engine of the type in which the amount of injected fuel is reduced to zero when the engine is decelerated. That is, in such an internal combustion engine, when the injection fuel amount is set to zero at the time of engine deceleration, the injection fuel amount is increased even if the opening degree of the exhaust throttle valve 39a is reduced to increase the temperature of the particulate filter 22. Although not possible, as described above, the particulate filter 2
Since the flow velocity of the exhaust gas passing through 2 is reduced, the amount M of the discharged fine particles becomes smaller than the amount G of the fine particles that can be oxidized and removed, so that the fine particles can be reliably oxidized and removed in the particulate filter 22.

In the above embodiment, the exhaust throttle valve 39 is used.
Although a is arranged downstream of the particulate filter 22, it may be arranged upstream of the particulate filter 22 as long as the flow of exhaust gas discharged from the combustion chamber 5 can be reduced. By the way, as described above, when the temperature of the particulate filter 22 is to be raised and the opening degree of the exhaust throttle valve 39a is reduced, the flow rate of the exhaust gas passing through the exhaust turbine 21 decreases. For this reason, the supercharging pressure decreases. Here, if the control is performed as in the above embodiment, the opening of the throttle valve 17 and the opening of the EGR control valve 25 are controlled so that the amount M of discharged particulates becomes smaller than the amount G of particulates that can be removed by oxidation. That is, the throttle valve 17 and the EGR control valve 25 are controlled based on the amount M of discharged particulates, not the amount of intake air. For this reason, the intake air amount decreases as the supercharging pressure decreases, and as a result, the EGR gas amount increases relatively to the intake air amount. For this reason, the combustion of the fuel in the combustion chamber 5 deteriorates, and the engine output torque sharply decreases.

Therefore, in the present invention, the exhaust throttle valve 39a is used to increase the temperature of the particulate filter 22.
When the opening degree of the EGR control valve 25 is reduced, the opening degree of the EGR control valve 25 is reduced so that a sufficient amount of air for burning the fuel injected into the combustion chamber 5 flows into the combustion chamber 5. In other words, in the present invention, when the opening degree of the exhaust throttle valve 39a is reduced to increase the temperature of the particulate filter 22, the opening of the EGR control valve 25 is controlled so that the fluctuation of the engine output torque falls within an allowable range. Decrease the degree. The opening of the throttle valve 17 may be increased at the same time as the opening of the EGR control valve 25 is decreased. Thus, according to the present invention, the engine output torque is prevented from greatly fluctuating when the temperature of the particulate filter is raised. The exhaust throttle valve 39a is a step motor 39b.
Driven. The step motor 39b is connected to the output port 36 via the corresponding drive circuit 38.

By the way, even if the amount M of discharged particulates and the temperature TF of the particulate filter 22 are controlled so that the first embodiment or the second embodiment can be executed, the particulates are stacked on the particulate filter 22. In some cases. In such a case, the particulates deposited on the particulate filter 22 can be oxidized without emitting a bright flame by temporarily making the air-fuel ratio of a part or the whole of the exhaust gas rich.

That is, when the air-fuel ratio of the exhaust gas is made rich to lower the oxygen concentration in the exhaust gas, the active oxygen releasing agent 6
Active oxygen O is released to the outside at a stretch, and the fine particles deposited by the active oxygen O released at a stretch are oxidized and removed without emitting a bright flame. Further, the poisoning of the metal surface is recovered by the enrichment, so that the subsequent oxidation activity is improved, and the oxidation of the fine particles is promoted. In this case, the air-fuel ratio of the exhaust gas may be made rich when the particulates are deposited on the particulate filter 22 in a stacked manner, or the exhaust gas may be periodically exhausted regardless of whether the particulates are deposited in a stacked manner. May be rich.

As a method of making the air-fuel ratio of the exhaust gas rich, for example, when the engine load is relatively low, the EGR rate (EG
The opening degree of the throttle valve 17 and the opening degree of the EGR control valve 25 are controlled so that the R gas amount / (intake air amount + EGR gas amount) becomes 65% or more. At this time, the average air-fuel ratio in the combustion chamber 5 is reduced. A method of controlling the injection amount so as to be rich can be used.

FIG. 6 shows an example of the operation control routine of the internal combustion engine described above. Referring to FIG. 6, first, in step 100, it is determined whether or not to execute the temperature raising process. When it is necessary to perform the temperature raising process, the exhaust throttle valve is closed in step 101, and step 10
In step 2, the opening of the EGR control valve 25 is controlled, and in step 103, the fuel injection amount is controlled. On the other hand, when it is determined in step 100 that it is not necessary to perform the temperature raising process, it is determined in step 104 whether the average air-fuel ratio in the combustion chamber 5 should be made rich.

When it is not necessary to make the average air-fuel ratio in the combustion chamber 5 rich, the opening degree of the throttle valve 17 is controlled in step 105 so that the amount M of discharged particulates becomes smaller than the amount G of particulates that can be removed by oxidation. At 106, the opening degree of the EGR control valve 25 is controlled.
At 7, the fuel injection amount is controlled. Step 1
When it is determined in 04 that the average air-fuel ratio in the combustion chamber 5 should be made rich, the opening of the throttle valve 17 is controlled in step 108 so that the EGR rate becomes 65% or more.
The opening of the control valve 25 is controlled, and the fuel injection amount is controlled in step 110 so that the average air-fuel ratio in the combustion chamber 5 becomes rich.

Incidentally, the fuel and the lubricating oil contain calcium Ca, and therefore, the calcium Ca is contained in the exhaust gas. This calcium Ca produces calcium sulfate CaSO ₄ when SO ₃ is present. This calcium sulfate CaSO ₄ is solid and does not thermally decompose even at high temperatures. Therefore, when the calcium sulfate CaSO ₄ is generated, the pores of the particulate filter 22 are blocked by the calcium sulfate CaSO ₄ , and as a result, it becomes difficult for the exhaust gas to flow through the particulate filter 22.

In this case, when an alkali metal or an alkaline earth metal having a higher ionization tendency than calcium Ca, such as potassium K, is used as the active oxygen releasing agent 61, SO ₃ diffused into the active oxygen releasing agent 61 binds to potassium K. To form potassium sulfate K ₂ SO ₄ and calcium Ca
Pass through the partition wall 54 of the particulate filter 22 without being combined with SO ₃ and flow out into the exhaust gas outflow passage 51. Therefore, the pores of the particulate filter 22 are not clogged. Therefore, as described above, as the active oxygen releasing agent 61, an alkali metal or an alkaline earth metal having a higher ionization tendency than calcium Ca, that is, potassium K, lithium Li, cesium C
s, rubidium Rb, barium Ba, strontium S
It will be preferable to use r.

The present invention also relates to a particulate filter 2
The present invention can also be applied to a case where only a noble metal such as platinum Pt is supported on a carrier layer formed on both side surfaces of the substrate 2. However, in this case, the solid line indicating the amount of fine particles G that can be removed by oxidation moves slightly to the right side as compared with the solid line shown in FIG.
In this case, active oxygen is released from NO ₂ or SO ₃ held on the surface of platinum Pt.

Further, according to the present invention, an oxidation catalyst is disposed in the exhaust passage upstream of the particulate filter 22, and the NO in the exhaust gas is converted into NO ₂ by the oxidation catalyst.
_{The present} invention is also applicable to an exhaust gas purifying apparatus in which the particles ₂ are reacted with fine particles deposited on the particulate filter 22 to oxidize the fine particles with the NO ₂ .

[0062]

According to the present invention, in the internal combustion engine in which the exhaust gas discharged from the combustion chamber is circulated again into the combustion chamber, a new method is adopted and even when the temperature of the particulate filter is controlled. Output torque fluctuation is kept small.

[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.

FIG. 3 is a view for explaining an oxidizing action of fine particles.

FIG. 4 is a diagram for explaining a deposition action of fine particles.

FIG. 5 is a graph showing the relationship between the amount of fine particles that can be removed by oxidation and the temperature of a particulate filter.

FIG. 6 is a flowchart for controlling the operation of the internal combustion engine.

[Explanation of symbols]

 5: Combustion chamber 6: Fuel injection valve 22: Particulate filter 25: EGR control valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 25/07 570 F02M 25/07 570J (72) Inventor Shinya Hirota 1st Toyota Town, Toyota City, Aichi Prefecture Toyota Auto Inside Car Co., Ltd. (72) Inventor Kazuhiro Ito 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Co., Ltd. (72) Inventor Koichiro Nakaya 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Koichi Kimura 1 Toyota Town, Toyota City, Aichi Prefecture F-term in Toyota Motor Corporation (reference) 3G062 AA01 EA10 EB04 ED08 FA12 GA22 3G065 AA01 AA04 AA09 CA12 DA04 GA08 3G090 AA03 BA01 CB25 DA01 DA09 DA13 DA18 DA20 EA05 EA06 3G301 HA02 HA06 HA13 JA21 LB11 MA01 MA11 ND03 NE01 PD11Z

Claims (12)

[Claims] 1. An internal combustion engine in which an amount of fuel supplied to a combustion chamber is controlled according to a required load, and exhaust gas discharged from the combustion chamber is circulated again to the combustion chamber. As a particulate filter for removing fine particles in exhaust gas, the amount of fine particles discharged from the combustion chamber per unit time can be oxidized and removed on the particulate filter without emitting luminous flame per unit time. When the amount of the fine particles in the exhaust gas is smaller than the possible amount of fine particles, the fine particles in the exhaust gas are oxidized and removed without emitting a bright flame when flowing into the particulate filter. When the amount of particulates deposited on the particulate filter is less than a certain limit, the A particulate filter is used in which the particulates on the particulate filter are oxidized and removed without emitting a bright flame when the amount of the particulates becomes smaller than the amount of the particulates that can be removed by oxidation. The amount of the discharged fine particles is usually smaller than the amount of the oxidizable and removable fine particles, and even if the amount of the discharged fine particles temporarily exceeds the amount of the oxidizable and removable fine particles, the amount of the discharged fine particles is The amount of discharged particulates and the temperature of the particulate filter are maintained so that only particles of a certain amount or less that can be oxidized and removed when the amount becomes smaller than the amount of particles that can be removed by oxidation are deposited on the particulate filter. Particles in the filter emit a bright flame on the particulate filter When it is determined that the temperature of the particulate filter should be increased, the exhaust gas flow is throttled, thereby increasing the temperature of the particulate filter and thereby increasing the temperature of the particulate filter. An exhaust gas purification method that reduces the amount of exhaust gas circulated to the combustion chamber when the flow is restricted. 2. The exhaust gas purifying method according to claim 1, wherein the flow rate of the exhaust gas passing through the particulate filter is reduced by restricting the exhaust gas flow. 3. The exhaust gas purifying method according to claim 1, wherein the exhaust gas flow is throttled for a time determined based on the amount of fine particles deposited on the particulate filter. 4. The exhaust gas purifying method according to claim 1, wherein a noble metal catalyst is supported on the particulate filter. 5. An active oxygen releasing agent that takes in oxygen and retains oxygen when there is excess oxygen in the surroundings, and releases the retained oxygen in the form of active oxygen when the surrounding oxygen concentration decreases, is supported on the particulate filter. The method according to claim 4, wherein when the fine particles adhere to the particulate filter, active oxygen is released from the active oxygen releasing agent, and the released fine particles oxidize the fine particles adhered to the particulate filter. Exhaust gas purification method. 6. The exhaust gas purifying method according to claim 5, wherein the active oxygen releasing agent comprises an alkali metal, an alkaline earth metal, a rare earth, or a transition metal. 7. The exhaust gas purification method according to claim 6, wherein the alkali metal and the alkaline earth metal are made of a metal having a higher ionization tendency than calcium. 8. The method according to claim 5, wherein the air-fuel ratio of a part or the whole of the exhaust gas is temporarily made rich to oxidize the fine particles adhering to the particulate filter.
The exhaust gas purification method according to any one of the above. 9. An internal combustion engine in which the amount of fuel supplied to a combustion chamber is controlled according to a required load, and exhaust gas discharged from the combustion chamber is circulated again to the combustion chamber. A particulate filter for removing particulates in the exhaust gas discharged from the chamber is arranged, and as the particulate filter, the amount of particulates discharged from the combustion chamber per unit time is reduced per unit time on the particulate filter. When the amount of fine particles in the exhaust gas that can be oxidized and removed without emitting a bright flame is smaller than the amount of fine particles in the exhaust gas, the fine particles in the exhaust gas are oxidized and removed without emitting a bright flame and the amount of the discharged fine particles is temporarily reduced. Even if the amount of fine particles that can be removed by oxidation is larger than When the amount of accumulated particulates is less than the predetermined limit, the particulates on the particulate filter can be oxidized and removed without emitting a bright flame when the amount of the discharged particulates is smaller than the amount of particulates that can be removed by oxidation. The amount of the removable fine particles depends on the temperature of the particulate filter, the amount of the discharged fine particles is usually smaller than the amount of the fine particles that can be removed by oxidation, and the amount of the discharged fine particles is temporarily larger than the amount of the fine particles that can be removed by oxidation. Even if the amount of discharged particulates becomes smaller than the amount of particulates that can be removed by oxidation, the amount of particulates discharged and the amount of particulates are reduced so that only particulates of a certain amount or less that can be oxidized and removed are deposited on the particulate filter. A control means for maintaining the temperature of the curable filter; Therefore, the particulates in the exhaust gas are oxidized and removed on the particulate filter without emitting a bright flame, and when it is determined that the temperature of the particulate filter should be increased, the control means reduces the exhaust gas flow, and The amount of exhaust gas that is circulated to the combustion chamber when the flow rate of the exhaust gas passing through the particulate filter is reduced, thereby increasing the temperature of the particulate filter, and the exhaust gas flow is reduced to increase the temperature of the particulate filter. An exhaust gas purifying device comprising a means for reducing exhaust gas. 10. The exhaust gas purifying apparatus according to claim 9, wherein the flow rate of the exhaust gas passing through the particulate filter is reduced by restricting the exhaust gas flow. 11. The exhaust gas purifying apparatus according to claim 10, wherein an exhaust throttle valve is arranged downstream of the particulate filter, and the exhaust gas flow is throttled by the exhaust throttle valve. 12. The particulate filter includes a plurality of exhaust passages extending in parallel with each other, and one of the adjacent exhaust passages has an upstream end closed by a plug and the other of the adjacent exhaust passages. The exhaust gas purifying apparatus according to claim 9, wherein the downstream end is closed by a plug, and a catalyst is supported on a wall surface of the exhaust passage and a wall surface of the plug.