JP2001280117A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) Abstract: By switching an exhaust switching valve, exhaust gas flows from one side and the other side of a filter, soot (particulate matter) in the exhaust gas deposited on a filter carrying an oxidation catalyst. In the exhaust gas purifying apparatus which is capable of continuously burning by disturbing the exhaust gas control method, it is possible to prevent HC and SOF from adhering to the exhaust gas switching valve and to prevent the exhaust gas switching valve from sticking. SOLUTION: By switching an exhaust switching valve 71, exhaust gas flows from one side and the other side of the filter, so that soot (particulate matter) in the exhaust gas deposited on the filter carrying the oxidation catalyst is disturbed. So that the combustion can be continuously performed, and an oxidation catalyst 80 is provided upstream of the exhaust gas switching valve to remove HC and SOF attached to the exhaust gas switching valve before reaching the exhaust gas switching valve. This prevents the exhaust switching valve from sticking.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an exhaust gas purifying apparatus capable of alternately switching exhaust gas from upstream and downstream of a filter of a purifier.

[0002]

2. Description of the Related Art Conventionally, in a diesel engine, a particulate filter is disposed in an engine exhaust passage to remove fine particles such as soot contained in exhaust gas, and the fine particles in the exhaust gas are removed by the particulate filter. The particulate filter is collected once, and the particulate filter collected on the particulate filter is ignited and burned to regenerate 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 the 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 exhaust gas heat,
In order to ignite the fine particles collected on the particulate filter by the heat of the exhaust gas, the fine particles must be ignited at a low temperature.

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 particulates supporting a catalyst have been conventionally used in order to lower the ignition temperature of fine particles. Filters are known.

For example, Japanese Patent Publication No. 7-106290 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. In this particulate filter, the fine particles are ignited at a relatively low temperature of approximately 350 ° C. to 400 ° C., and then continuously burned.

[0005]

In a diesel engine, when the load increases, the exhaust gas temperature reaches from 350 ° C. to 400 ° C. Therefore, the above particulate filter apparently reduces the exhaust gas when the engine load increases. It seems that the gas heat can ignite and burn the fine particles. However, in practice, the exhaust gas temperature is increased from 350 ° C to 400 ° C.
Even if the temperature reaches ° C, the fine particles may not ignite, and even if the fine particles are ignited, only a part of the fine particles will burn and a large amount of fine particles will remain unburned.

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. At this time, when the temperature of the exhaust gas changes from 350 ° C. to 400 ° C., the fine particles on the particulate filter become It is ignited and then burned continuously.

However, when the amount of fine particles contained in the exhaust gas increases, other fine particles deposited on the particulate filter accumulate on the particulate filter before the fine particles are completely burned, and as a result, the fine particles are deposited on the particulate filter. Fine particles are deposited in a layered manner. When the particulates are deposited on the particulate filter in this manner, some of the particulates that are likely to come into contact with oxygen are burned, but the remaining particulates that are hard to contact with oxygen do not burn, and thus a large amount of particulates Will remain unburned. Therefore, when the amount of fine particles contained in the exhaust gas increases, a large amount of fine particles continue to be deposited on the particulate filter.

On the other hand, when a large amount of fine particles accumulate on the particulate filter, the accumulated fine particles gradually become difficult to ignite and burn. It is considered that the reason why it becomes difficult to burn is that carbon in the fine particles changes to graphite or the like which is difficult to burn during deposition. In fact, if a large amount of fine particles continue to accumulate on the particulate filter, the deposited fine particles will 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. Becomes 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 continue to deposit on the particulate filter, it is difficult to ignite the fine particles deposited by the exhaust gas heat. Become.

Further, when the deposited fine particles are burned, the ash, ie, ash, which is a burning residue, is condensed into large lumps, and the ash clumps cause pores of the particulate filter to be clogged. The number of clogged pores gradually increases over time, and thus the pressure loss of the exhaust gas flow in the particulate filter increases. If the pressure loss of the exhaust gas flow is increased, the output of the engine is reduced, and this also poses the problem that the particulate filter must be replaced with a new one early.

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 on the stack.

[0011] If a conventional exhaust purification filter with a catalyst is provided in the exhaust pipe, and the exhaust purification is performed according to the operating condition of the internal combustion engine, the continuous combustion process is performed as follows.
The above problems cannot be avoided.

Therefore, by allowing the exhaust gas to be alternately switched from the upstream side and the downstream side of the exhaust gas through the filter of the purification device so that the particulates can be continuously burned as much as possible, the particulate matter is deposited on both side surfaces of the filter. Since the particles are deposited, the amount of the particles deposited per unit area can be reduced.
Fine particles deposited by the backflow can be disturbed and blown off, and if an oxygen releasing agent is provided inside the filter substrate, the amount of fine particles that can move around the inside and burn can be increased.

In order to obtain the above-mentioned effects by switching the exhaust gas flow in this way, it is necessary to provide a switching valve in the exhaust pipe. (Solvent organic component) and the like may adhere to the seating surface of the exhaust pipe. This phenomenon is likely to occur especially when stopping for a long time.

The present invention has been made in view of the above points, and the present invention relates to an exhaust gas purification apparatus in which exhaust gas can be alternately switched from an upstream side to an exhaust side by a switching valve through a filter provided with a catalyst. It is an object to prevent the switching valve from sticking.

[0015]

Means for Solving the Problems To achieve the above object, an exhaust gas temperature raising apparatus for an internal combustion engine according to the present invention employs the following means.

That is, according to the present invention, there is provided a filter which carries an active oxygen releasing agent and is capable of trapping particulates such as soot in an exhaust gas (also referred to as particulate matter) for a period of time; An exhaust switching valve that alternately switches between a first flow to flow and a second flow to flow exhaust gas from the other side of the filter, and a temperature raising unit that raises the temperature of the filter to improve the oxidation rate of the fine particles, An oxidation catalyst provided on the exhaust upstream side of the exhaust switching valve;
It is characterized by having.

The switching control of the exhaust switching valve is usually performed at every deceleration,
It is performed every predetermined time, every predetermined traveling distance, etc., and is not particularly limited. Further, the present invention, an active oxygen releasing agent is supported,
A filter capable of capturing particulates in the exhaust gas for a period of time, a first flow in which the exhaust gas flows from one side of the filter and a second flow in which the exhaust gas flows from the other side of the filter are alternately driven by driving the valve element. An exhaust switching valve for switching, and control means for stopping the valve body at a position where the contact area between the valve body and the inner wall surface of the exhaust passage becomes as small as possible when the vehicle is stopped is provided.

Here, in addition to a first exhaust passage through which exhaust gas flows from one side of the filter and a second exhaust passage through which exhaust gas flows from the other side of the filter, a first exhaust passage and a second exhaust passage are provided. Without passing through any of the passages, having a bypass passage bypassing the filter, further comprising abnormality detection means for detecting abnormal clogging of the filter, wherein when the abnormality detecting means detects abnormal clogging of the filter, It is preferable to discharge the exhaust gas from the bypass passage.

The first exhaust passage, the second exhaust passage, and the bypass passage may be switched by the exhaust switching valve. The above configurations can be combined with each other as much as possible.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings. <Outline of Apparatus Configuration> 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 electric control type fuel injection valve, 7 is an intake valve,
Reference numeral 8 denotes an intake port, 9 denotes an exhaust valve, and 10 denotes 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 through the intake duct 13 is arranged around the intake duct 13. In the embodiment shown in FIG.
8 and 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, an outlet of the exhaust turbine 21 is connected to an oxidation catalyst 80, and an outlet of the oxidation catalyst 80 is particulate. It is connected to an exhaust purification device having a casing 23 with a built-in filter 22.

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. Also, the EGR passage 24
A cooling device 26 for cooling the EGR gas flowing in the EGR passage 24 is disposed around the cooling device 26. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 26, and the EGR gas is cooled by the engine cooling water. 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. 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. Also,
A temperature sensor 81 for detecting a catalyst temperature is attached to the oxidation catalyst 80, and a temperature sensor 39 for detecting the temperature of the particulate filter 22 is attached to the particulate filter 22.
The output signal of 39 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 L of the access pedal 40 is connected to the access pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding 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 EGR control valve 25, the fuel pump 28, and the actuator 72 via the corresponding drive circuit 38.

FIG. 2A shows the relationship between the required torque TQ, the depression amount L of the accelerator pedal 40, and the engine speed N. In FIG. 2A, each curve represents an equal torque curve, a curve indicated by TQ = 0 indicates that the torque is zero, and the remaining curves have TQ = a,
The required torque gradually increases in the order of TQ = b, TQ = c, and TQ = d. As shown in FIG. 2B, the required torque TQ shown in FIG. 2A is determined in advance in the form of a RO as a function of the depression amount L of the accelerator pedal 40 and the engine speed N.
It is stored in M32. In the embodiment according to the present invention, the required torque TQ corresponding to the depression amount L of the accelerator pedal 40 and the engine speed N is first calculated from the map shown in FIG. 2B, and the fuel injection amount is calculated based on the required torque TQ. Are calculated. <Structure of Exhaust Purification Device> The exhaust purification device is shown in FIGS.
As shown in FIG. 4, an oxidation catalyst 80 is connected to an outlet of the exhaust turbine 21, and an exhaust pipe 70 is connected to an outlet of the oxidation catalyst 80. A first exhaust passage 76 and a second exhaust passage 77 are provided, which branch off from the exhaust pipe 70 and are connected to one surface and the other surface of the filter 22 in the casing 23 in which the particulate filter 22 is built. Have been. Further, the first exhaust passage 7
6 and a bypass passage 73 for discharging the exhaust gas without passing through the particulate filter 22 from the branch point of the second exhaust passage 77.

An exhaust switching valve 71 is provided at a branch point between the first exhaust passage 76 and the second exhaust passage 77. The exhaust switching valve 71 is driven by an actuator 72 to select a first exhaust passage 76 to flow exhaust gas from one side of the filter 22 (a forward flow) and a second flow (a forward flow).
And the second flow (backflow) in which the exhaust gas flows from the other side of the filter 22 by selecting the exhaust passage 77 of the filter 22.

Here, the casing 23 for accommodating the filter 22 is disposed immediately above the exhaust pipe 70 forming the bypass passage 73, and the first exhaust pipe branched from the exhaust pipe 70 is provided on both sides of the casing 23. The passage 76 and the second exhaust passage 77 are connected. The filter 22 in the casing 23 has a length in the width direction orthogonal to the length direction longer than the length in the length direction when the passage direction of the exhaust gas is the length direction. With such a configuration, the space for mounting the exhaust gas purification device including the casing 23 containing the filter 22 in the vehicle can be reduced.

The actuator 72 is driven and controlled by control means 75 implemented on the CPU 34 of the electronic control unit 30, and is driven by a control signal from the output port 36. Further, the actuator 72 is driven by a negative pressure formed as the internal combustion engine is driven. When the negative pressure is not applied, the actuator 72 is moved to a position (forward flow position) for selecting the first exhaust passage 76. To control the valve body to the neutral position when the first negative pressure is applied, and to select the second exhaust passage 77 when the second negative pressure stronger than the first negative pressure is applied. The valve body is controlled to the position (backflow position).

When the valve body is in the forward flow position shown by the broken line in FIG. 3, the exhaust switching valve 71 connects the exhaust pipe 70 to the first exhaust passage 76 and connects the second exhaust passage 77 to the bypass passage 73. To the exhaust pipe 70
The first exhaust passage 76, the filter 22, the second exhaust passage 77, and the bypass passage 73 flow in this order, and are discharged to the atmosphere.

When the valve body is at the reverse flow position shown by the solid line in FIG. 3, the exhaust switching valve 71 connects the exhaust pipe 70 to the second exhaust passage pipe 51 and connects the first exhaust passage 76 to the bypass passage. 73, the exhaust gas passes through the exhaust pipe 70.
The gas flows through the second exhaust passage 77, the filter 22, the first exhaust passage 76, and the bypass passage 73 in this order, and is discharged to the atmosphere.

When the valve body is at a neutral position parallel to the axis of the exhaust pipe 70, the exhaust gas is discharged from the exhaust pipe 70 because the exhaust switching valve 71 connects the exhaust pipe 70 directly to the bypass passage 73. The gas flows into the bypass passage 73 without passing through the filter 22 and is released to the atmosphere.

The fine particles such as soot move around in the base material of the filter 22 by repeating the forward flow and the reverse flow by switching the valve body, so that the oxidation of the fine particles such as soot is promoted.
It is possible to efficiently purify fine particles such as soot.

FIG. 5A is an image diagram when exhaust gas flows through the filter 22 from one direction only. Fine particles such as soot accumulate only on one surface of the filter and do not move, and the pressure loss of the exhaust gas increases. In addition to preventing the purification of fine particles such as soot.

FIG. 5B is an image diagram in the case where exhaust gas is caused to flow through the filter 22 from both directions. Since fine particles such as soot are disturbed in both the forward flow direction and the reverse flow direction on both surfaces of the filter 22, both surfaces of the filter 22 are disturbed. In addition, or around the inside of the base material, the active points of the entire filter base material can be used to promote oxidation of fine particles such as soot, and the accumulation of particulate matter in the filter 22 can be reduced. it can. Therefore, an increase in the pressure loss of the exhaust gas can be avoided. <Structure of Filter and Continuous Oxidation of Fine Particle> FIG. 6 shows the structure of the particulate filter 22. 6A is a front view of the particulate filter 22, and FIG. 6B is a front view of the particulate filter 22.
FIG. As shown in FIGS. 6A and 6B, the particulate filter 22 has a honeycomb structure and includes a plurality of exhaust gas inflow passages 50 and an exhaust gas outflow passage 51 extending in parallel with each other. This is a so-called wall flow type. 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. 3A, a hatched portion indicates a plug 53.
Therefore, the exhaust gas inflow passages 50 and the exhaust gas outflow passages 51 are alternately arranged with the thin partition walls 54 interposed therebetween. In other words, each of the exhaust gas inflow passages 50 and the exhaust gas outflow passage 51 is surrounded by four exhaust gas outflow passages 51, and each of the exhaust gas outflow passages 51 has four exhaust gas outflow passages 51.
It is arranged so as to be surrounded by the two exhaust gas inflow passages 50.

The particulate filter 22 is made of a porous material such as cordierite, so that the exhaust gas flowing into the exhaust gas inflow passage 50 is
As shown by an arrow in (B), it flows out into the adjacent exhaust gas outflow passage 51 through the inside of the surrounding partition wall 54.

In the embodiment according to the present invention, for example, alumina is formed on the peripheral wall surface of each exhaust gas inflow passage 50 and each exhaust gas outflow passage 51, that is, on both side surfaces of each partition wall 54 and on the inner wall surface of the pores inside the partition wall 54. A noble metal catalyst is formed on the carrier.If there is excess oxygen around the carrier, oxygen is taken in to retain oxygen, and when the surrounding oxygen concentration decreases, the retained oxygen is converted into active oxygen. , An active oxygen releasing agent to be released at the time.

In this case, in the embodiment according to the present invention, platinum Pt is used as the noble metal catalyst, and potassium K, sodium Na, lithium Li,
Cesium Cs, alkali metals such as rubidium Rb, barium Ba, calcium Ca, alkaline earth metals such as strontium Sr, lanthanum La, yttrium Y
And at least one selected from rare earths and transition metals.

In this case, as the active oxygen releasing agent, an alkali metal or an alkaline earth metal having a higher ionization tendency than calcium Ca, ie, potassium K, lithium Li,
It is preferable to use cesium Cs, rubidium Rb, barium Ba, and strontium Sr.

Next, the action of the particulate filter 22 for removing fine particles from the exhaust gas will be described.
The case where potassium and potassium K are carried will be described as an example, but the same fine particle removing action can be performed by using other noble metals, alkali metals, alkaline earth metals, rare earths, and transition metals.

In a compression ignition type internal combustion engine as shown in FIG. 1, combustion takes place under excess air, and therefore the exhaust gas contains a large amount of excess air. That is, if the ratio between air and fuel supplied into the intake passage, the combustion chamber 5 and the exhaust passage 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. It is lean. Further, since NO is generated in the combustion chamber 5, NO is contained in the exhaust gas. The fuel contains sulfur S
This sulfur S reacts with oxygen in the combustion chamber 5 to become SO 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. 7A and 7B schematically show enlarged views of the inner peripheral surface of the exhaust gas inflow passage 50 and the surface of the carrier layer formed on the inner wall surface of the pores in the partition wall 54. FIG. .
In FIGS. 7A and 7B, reference numeral 60 denotes platinum Pt.
And 61 denotes an active oxygen releasing agent containing potassium K.

As described above, since a large amount of excess oxygen is contained in the exhaust gas, when the exhaust gas flows into the exhaust gas inflow passage 50 of the particulate filter 22, FIG.
As shown in (A), these oxygens O ₂ are converted to O ₂ ⁻ or O ^2−.
On the surface of platinum Pt. On the other hand, NO in the exhaust gas on the surface of the platinum Pt O ₂ ^- reacting or O ^2- as, NO
₂ (2NO + O ₂ → 2NO ₂ ). Next, a part of the generated NO ₂ is absorbed in the active oxygen releasing agent 61 while being oxidized on the platinum Pt, and is combined with potassium K in FIG.
As shown in (A), the nitric acid ions are diffused into the active oxygen releasing agent 61 in the form of NO ₃ ⁻ , and some nitrate ions NO ₃ ⁻ generate potassium nitrate KNO ₃ .

On the other hand, as described above, SO is contained in the exhaust gas.
₂ is also included, this SO ₂ is absorbed in the active oxygen release agent 61 by a NO similar mechanisms. That is,
Oxygen O ₂ as described above O ₂ ^- or platinum O ^2- in the form Pt
Are attached on the surface, SO ₂ in the exhaust gas is platinum Pt
Or O ^2- reacts with the SO ₃ ^- O ₂ at the surface of the.

Next, the produced SO_ThreePart of is platinum Pt
Absorbed in the active oxygen releasing agent 61 while being oxidized further
And sulfate ion SO while binding with potassium K_Four ^2-Form of
And diffused into the active oxygen releasing agent 61, and potassium sulfate K_TwoS
O_FourGenerate Thus, the active oxygen releasing catalyst 61
Inside is potassium nitrate KNO_ThreeAnd potassium sulfate K_TwoS
O_Four Is generated.

On the other hand, fine particles mainly composed of carbon C are generated in the combustion chamber 5, so that the exhaust gas contains these fine particles. These fine particles contained in the exhaust gas are exhausted from the particulate filter 2.
2B, when flowing in the exhaust gas inflow passage 50 or when going from the exhaust gas inflow passage 50 to the exhaust gas outflow passage 51, as shown by 62 in FIG. It contacts and adheres to the surface of the oxygen releasing agent 61.

As described above, the fine particles 62 are
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
Is decomposed into NO and the oxygen O is directed to the contact surface between the fine particles 62 and the active oxygen releasing agent 61, and NO is
1 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.

On the other hand, 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 the oxygen O becomes fine particles 62 and the active oxygen releasing agent 61 towards the contact surface, SO ₂ is released from the active oxygen release agent 61 to the outside. SO released to the outside
₂ is oxidized on platinum Pt on the downstream side, and is again absorbed in the active oxygen releasing agent 61.

However, since potassium sulfate K ₂ SO ₄ is stabilized, active oxygen is hardly released as compared with potassium nitrate KNO ₃ . On the other hand, the fine particles 62 and the active oxygen releasing agent 6
Oxygen O toward the contact surface with 1 is oxygen decomposed from a compound such as potassium nitrate KNO ₃ or 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. These active oxygen O are fine particles 62
The fine particles 62 are oxidized within a short period of time without emitting a bright flame, and the fine particles 62 disappear completely. Therefore, the fine particles 62 are dispersed in the particulate filter 22.
Does not accumulate on top.

The particulate filter 2 as in the prior art
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. The combustion with such a flame cannot be sustained unless it is at a high temperature. Therefore, in order to maintain the combustion with such a flame, the temperature of the particulate filter 22 must be maintained at a high temperature.

On the other hand, in the present invention, the fine particles 62 are oxidized without emitting a bright flame as described above, and the surface of the particulate filter 22 does not glow at this time. 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, fine particles 6 which do not emit a bright flame according to the present invention 6
The action of removing fine particles by oxidation of 2 is completely different from the action of removing fine particles by conventional combustion accompanied by a flame.

The action of removing fine particles by oxidation of the fine particles is performed at a considerably low temperature. Therefore, the temperature of the particulate filter 22 does not rise so much, and there is almost no risk of the particulate filter 22 being deteriorated. Further, since no fine particles are deposited on the particulate filter 22, there is little danger that the ash, which is a burning residue of the fine particles, is agglomerated, and therefore, there is less danger that the particulate filter 22 is clogged.

The clogging is mainly caused by calcium sulfate CaSO ₄ . That is, the fuel and the lubricating oil contain calcium Ca, and therefore the exhaust gas contains calcium Ca. This calcium Ca is SO ₃
Produces calcium sulfate CaSO ₄ when present. This calcium sulfate CaSO ₄ is solid and does not thermally decompose even at high temperatures. Therefore, calcium sulfate CaSO ₄ is generated, and if the pores of the particulate filter 22 are closed by the calcium sulfate CaSO ₄ , clogging occurs.

However, in this case, the active oxygen releasing agent 6
When an alkali metal or an alkaline earth metal having a higher ionization tendency than calcium Ca, such as potassium K, is used, SO ₃ diffused into the active oxygen releasing agent 61 combines with potassium K to form potassium sulfate K ₂ SO ₄ . Calcium Ca passes through the partition wall 54 of the particulate filter 22 without binding to SO _3, and
Outflow into 1. Therefore, the particulate filter 22
No pores are 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 Cs, rubidium Rb, barium Ba, and strontium Sr is used. It will be preferable.

Incidentally, 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 and removable fine particles that can be oxidized and removed without emitting a bright flame per unit time on the particulate filter 22 is:
The temperature increases as the temperature of the particulate filter 22 increases.

The solid line in FIG. 9 indicates the amount G of the oxidizable and removable fine particles that can be oxidized and removed without emitting a bright flame per unit time. In FIG. 9, the horizontal axis represents 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, in the region I of FIG. As soon as all the fine particles come into contact with the particulate filter 22, they are oxidized and removed on the particulate filter 22 within a short period of 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. 9, the amount of active oxygen is insufficient to oxidize all the fine particles.
FIGS. 8A to 8C show how the fine particles are oxidized in such a case.

That is, when the amount of active oxygen is insufficient to oxidize all the fine particles, the fine particles 62 adhere to the active oxygen releasing agent 61 as shown in FIG.
Only part of 2 is oxidized, and the finely oxidized fine particles remain on the carrier layer. Next, when the state where the amount of active oxygen is insufficient continues, the fine particles which have not been oxidized one after another remain on the carrier layer, and as a result, FIG. 8 (B)
As shown in (2), the surface of the carrier layer is covered with the residual fine particle portion 63.

The residual fine particle portion 6 covering the surface of the carrier layer
3 gradually changes to a carbon material that is hardly oxidized, and thus 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, the oxidizing action of NO and SO ₂ by platinum Pt and the releasing action of active oxygen by the active oxygen releasing agent 61 are suppressed. As a result, as shown in FIG. 8C, another fine particle 64 is deposited on the remaining fine particle portion 63 one after another.

When the fine particles are deposited in a layered manner in this way, even if the fine particles are easily oxidized because they are separated from the platinum Pt and the active oxygen releasing agent 61, they are already oxidized by the active oxygen O. Without
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.

As described above, in the region I of FIG. 9, the fine particles are oxidized within a short time without emitting a bright flame on the particulate filter 22, and in the region II of FIG. 9, the fine particles are laminated on the particulate filter 22. Deposit in a shape. Therefore, the fine particles are
It is desirable that the relationship between the amount M of discharged fine particles and the amount G of fine particles that can be oxidized and removed at all times is in the range of the region I so as not to be deposited in a stacked manner on the upper surface.

However, in practice, it is almost impossible to make the amount M of discharged fine particles smaller than the amount G of fine particles that can be removed by oxidation in all operating states. For example, when the engine is started, the temperature of the particulate filter 22 is usually low,
Therefore, at this time, the amount M of discharged fine particles is usually larger than the amount G of fine particles that can be removed by oxidation. When the amount M of discharged fine particles becomes larger than the amount G of fine particles that can be removed by oxidation as immediately after the start of the engine, the non-oxidized fine particles begin to remain on the particulate filter 22.

As described above, depending on the operation conditions, the amount M of the discharged fine particles may be larger than the amount G of the fine particles that can be removed by oxidation, and the fine particles may be deposited on the particulate filter 22 in a layered manner.

In order to oxidize and remove the accumulated fine particles, the exhaust gas switching valve 71 disposed in the exhaust pipe 70 is switched. When the exhaust switching valve 71 is switched, the exhaust upstream side and the exhaust downstream side of the particulate filter 22 are reversed, and in the portion that was on the exhaust downstream side of the particulate filter 22 before the switching, the fine particles were reduced to the active oxygen releasing agent 61. The active oxygen O is released by adhering to the surface of the substrate, and the fine particles are oxidized and removed. Part of the released active oxygen O moves to the exhaust gas downstream of the particulate filter 22 together with the exhaust gas, and oxidizes and removes the fine particles deposited there. Here, as described above, the fine particles are disturbed in the forward flow direction and the reverse flow direction on both surfaces of the particulate filter 22, move around on both surfaces of the particulate filter 22, or inside the base material, and meet the active points of the entire filter base material and oxidize. Is done.

When the fine particles which have not been oxidized in this way are starting to accumulate on the particulate filter 22, the upstream and downstream sides of the exhaust of the particulate filter 22 are reversed, so that the particulate filter 22 Can be completely removed by oxidation.

When particulates accumulate on the particulate filter 22, the air-fuel ratio of a part or the whole of the exhaust gas is temporarily made rich, so that the accumulated particulates are oxidized without emitting a bright flame. . When the air-fuel ratio of the exhaust gas is made rich, that is, when the oxygen concentration in the exhaust gas is reduced, active oxygen O is released from the active oxygen releasing agent 61 to the outside at a stretch, and the active oxygen O released at a stretch accumulates. The burned fine particles can be burnt and removed at once in a short time without emitting a bright flame. <Purification by Oxidation Catalyst Upstream of Exhaust Switching Valve> An oxidation catalyst 80 is provided upstream of the exhaust switching valve. By providing this oxidation catalyst, HC components and SOF are removed, so that HC components and SOF flowing to the exhaust downstream side are reduced, and sticking to the valve seat of the exhaust switching valve is correspondingly prevented.

Further, heat is generated when the reducing agent is oxidized by the oxidation catalyst 80, so that the temperature of the exhaust gas passing through the exhaust gas switching valve 71 is warmed, and SOF and HC are less likely to adhere. A device in which the oxidation catalyst 80 is provided upstream of the exhaust gas switching valve 71 is useful when performing a temperature rise control in a system that performs a low-temperature combustion control. During low-temperature combustion, soot is not easily generated, but SOF is easily discharged.

If the SOF discharged during low-temperature combustion and the fine particles discharged during normal combustion are alternately supplied to the valve, the valve may stick and become inoperable. In addition, since the valve element tends to stick at low temperatures, the possibility of sticking of the valve element increases when returning from the normal operation to the low-temperature combustion state.

Therefore, by arranging the oxidation catalyst 80 upstream of the exhaust gas switching valve 71, the oxidation catalyst 80 can be used even during low-temperature combustion.
The SOF and HC are oxidized at this time, so that the SOF and HC adhering to the exhaust switching valve 71 are reduced, and the risk of sticking is reduced.

Here, the low-temperature combustion control will be described for reference. As the amount of inert gas in the combustion chamber 5 of the internal combustion engine increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas in the combustion chamber further increases, the combustion in the combustion chamber decreases. The temperature of the fuel and its surrounding gas is lower than the soot generation temperature, and soot is hardly generated. This state is referred to as a low-temperature combustion state. To achieve this, a recirculation device that recirculates exhaust gas discharged from the combustion chamber 5 of the internal combustion engine into the engine intake passage may be provided. In this case, the inert gas comprises recirculated exhaust gas.

As shown in FIG. 10, when the air-fuel ratio A / F is decreased by increasing the EGR rate, the smoke is reduced when the EGR rate becomes close to 40% and the air-fuel ratio A / F becomes about 30. The generation starts to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke is sharply reduced. When the EGR rate is increased to 65% or more and the air-fuel ratio A / F is around 15.0, the smoke becomes almost zero. . That is, almost no soot is generated. At this time, the output torque of the engine slightly decreases, and N
The generation amount of Ox is considerably reduced. On the other hand, at this time, HC,
The amount of generated CO starts to increase.

FIG. 11A shows the change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 18 and the amount of smoke generated is the largest. FIG. 11B shows the air-fuel ratio A / F. F is 13
The graph shows changes in the combustion pressure in the combustion chamber 5 when the amount of generated smoke is almost zero in the vicinity. FIG. 11 (A) and FIG.
As can be seen from comparison with FIG. 11B, the combustion pressure is lower in the case of FIG. 11B where the amount of smoke generation is almost zero than in the case of FIG. 11A where the amount of smoke generation is large. You can see that.

The following can be said from the experimental results shown in FIG. 10 and FIG. That is, first, when the air-fuel ratio A / F is 15.0 or less and the amount of generated smoke is almost zero, the amount of generated NOx is considerably reduced as shown in FIG. The decrease in the amount of generated NOx means that the combustion temperature in the combustion chamber 5 has decreased. Therefore, it can be said that the combustion temperature in the combustion chamber 5 is low when little soot is generated. . The same can be said from FIG. That is, FIG. 11B in which almost no soot is generated.
In the state shown in (1), the combustion pressure is low, so that the combustion temperature in the combustion chamber 5 is low at this time.

Second, when the amount of generated smoke, that is, the amount of generated soot becomes almost zero, as shown in FIG.
O emission increases. This means that hydrocarbons are emitted without growing to soot. That is, linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 12 are thermally decomposed when the temperature is increased in a state of lack of oxygen, soot precursors are formed, and then mainly, Soot consisting of a solid aggregate of carbon atoms is produced. in this case,
The actual process of producing soot is complicated, and it is not clear what form the soot precursor takes, but in any case, FIG.
Hydrocarbons such as those shown in Figure 2 will grow to soot via soot precursors. Therefore, when the amount of generated soot becomes almost zero as described above, HC and C are reduced as shown in FIG.
At this time, HC is a soot precursor or a hydrocarbon in a state before the O. FIG. 10 and FIG.
Summarizing these considerations based on the experimental results shown in FIG. 1, when the combustion temperature in the combustion chamber 5 is low, the amount of soot generation becomes almost zero, and at this time, the precursor of soot or the hydrocarbon in the state before it is burned. It will be discharged from the chamber 5. As a result of further detailed experimental research on this, if the temperature of the fuel and the surrounding gas in the combustion chamber 5 is lower than a certain temperature, the growth process of soot is stopped halfway,
That is, no soot is generated, and soot is generated when the temperature of the fuel and its surroundings in the combustion chamber 5 exceeds a certain temperature.

FIG. 13 shows the relationship between the EGR rate and smoke when the EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 13, a curve A shows a case where the EGR gas is strongly cooled to maintain the EGR gas temperature at approximately 90 ° C., and a curve B shows a case where the EGR gas is cooled by a small cooling device. Curve C shows the case where the EGR gas is not forcibly cooled.

As shown by the curve A in FIG. 13, when the EGR gas is intensely cooled, the amount of soot generation peaks at a point where the EGR rate is slightly lower than 50%. Above a percentage, little soot is generated. On the other hand, when the EGR gas is slightly cooled as shown by the curve B in FIG.
When the R rate is slightly higher than 50%, the amount of soot generation reaches a peak. In this case, if the EGR rate is set to approximately 65% or more, soot is hardly generated.

As shown by the curve C in FIG.
When the GR gas is not forcibly cooled, the generation amount of soot becomes a peak near the EGR rate of 55%, and in this case, if the EGR rate is set to about 70% or more, almost no soot is generated. FIG. 13 shows the amount of smoke generated when the engine load is relatively high, and EGR at which the amount of soot reaches a peak when the engine load becomes small.
The rate slightly decreases, and the lower limit of the EGR rate at which almost no soot is generated also slightly decreases. As described above, the lower limit of the EGR rate at which almost no soot is generated varies depending on the degree of cooling of the EGR gas and the engine load. <Control of Exhaust Switching Valve> As described above, by providing the oxidation catalyst 80 upstream of the filter, the exhaust switching valve 7 is controlled.
However, even if the oxidation catalyst 80 is not provided, the control means 75 can also prevent the exhaust switching valve 71 from sticking to the valve seat by performing the control described below. You.

That is, as shown in FIG. 14, it is determined whether or not the engine has stopped (step 101). When the engine has stopped, the degree of the negative pressure for driving the actuator is controlled by the control means 75 to the first level. As the negative pressure, the valve body is set to the neutral position (step 102).

The neutral position is a position where the contact area between the valve body and the inner wall surface (valve seat) of the exhaust passage is as small as possible. When the engine does not stop, the exhaust switching valve 71 is switched by the normal control.

A program for this control is stored in the ROM, and is repeatedly executed at predetermined time intervals. If this control and the provision of an oxidation catalyst upstream of the filter are used in combination, the prevention of sticking of the exhaust switching valve 71 to the valve seat becomes more effective. <Control at the Time of Abnormality> Here, as shown in FIG. 15, a back pressure sensor 90 for detecting the back pressure of the filter 22 is provided on the exhaust downstream side of the filter 22. Back pressure sensor 9
The output signal of 0 is output to the ECU via the corresponding AD converter 37.
30 is input to an input port 35. Abnormality detecting means 91 is realized on the CPU. When the back pressure of the filter 22 detected by the back pressure sensor 90 becomes lower than a predetermined value, the abnormality detecting means 91 is clogged. Is determined. In addition, whether it is abnormal or not
Instead of the detection of the back pressure, when the engine speed becomes equal to or less than the predetermined value due to the effect of clogging of the filter 22, the detection of the engine speed may be determined to be abnormal.

This abnormality detecting means 91 is a program
The information is stored in the OM and is repeatedly executed at predetermined time intervals to be realized on the CPU. Then, as shown in FIG. 16, when the abnormality detecting means 91 detects abnormal clogging of the filter 22 from the detected value of the back pressure or the detected value of the engine speed (step 201), the control means 75 sets the exhaust switching valve to neutral. Drive to the position (step 202). Then, the exhaust gas flows through the first side where the exhaust gas flows from one side of the filter 22.
Flows without passing through any of the exhaust passage 76 and the second exhaust passage 77 for flowing exhaust gas from the other side of the filter,
It is discharged from the bypass passage 73 bypassing the filter 22.

When the abnormality is detected once and the control to the neutral position is performed, the valve body is held at the neutral position unless the control is released by a predetermined procedure.

[0081]

The exhaust gas can be alternately flown from both sides of the filter by providing an exhaust switching valve. Therefore, when the exhaust gas is flown into the filter from only one direction, the oxidation reaction can be used only on one of the partition surfaces and the inside of the partition. However, the amount of soot that accumulates in the unit area increases, and the oxidation performance decreases.On the other hand, in the present invention, the exhaust gas flows from both sides of the filter by using the forward flow and the reverse flow alternately. The soot is agitated and moves around the partition wall surface and the inside of the partition wall, and the catalytically active sites on the entire partition wall surface and the inside of the partition wall can be effectively used. Therefore, the oxidation of soot can be promoted, the purification can be performed more continuously, and the exhaust gas purification performance can be enhanced.

Further, according to the present invention, since the sticking of the exhaust gas switching valve can be prevented, the above effects can be obtained more reliably.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing a required torque of an engine.

FIG. 3 is a top view showing the exhaust gas purification device.

FIG. 4 is a front view showing an exhaust purification device.

FIG. 5A is an image diagram showing a state in which particulate matter is deposited on a filter substrate, and FIG. 5B is an image diagram showing a state in which the particulate matter is disturbed by forward and backward flows of exhaust gas.

FIG. 6 is a diagram showing a particulate filter;

FIG. 7 is a conceptual diagram showing the oxidizing action of fine particles.

FIG. 8 is a conceptual diagram showing a deposition action of fine particles.

FIG. 9 is a diagram showing the relationship between the amount of fine particles that can be removed by oxidation and the temperature of a particulate filter

FIG. 10 is a diagram showing amounts of smoke and NOx generated, etc.

FIG. 11 is a diagram showing a combustion pressure.

FIG. 12 is a view showing fuel molecules.

FIG. 13 is a diagram showing the relationship between the amount of smoke generated and the EGR rate;

FIG. 14 is a flowchart illustrating an example of control of an exhaust switching valve.

FIG. 15 is a diagram illustrating an example of a case where abnormality detection is performed;

FIG. 16 is a flowchart illustrating an example of controlling an exhaust switching valve when an abnormality is detected.

[Explanation of symbols]

 22: particulate filter 71: exhaust gas switching valve 75: control means 80: oxidation catalyst

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 53/94 F01N 3/20 P F01N 3/08 3/24 E 3/20 B01J 20/04 B 3 / 24 B01D 53/36 ZAB // B01J 20/04 103C (72) Inventor Toshiaki Tanaka 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F term (reference) 3G090 AA03 BA01 CA01 CB24 EA02 EA06 3G091 AA02 AA11 AA18 AB02 AB13 BA07 BA25 BA38 CA13 CA26 GA06 GA16 GA24 GB10Z HA15 HA19 HB05 4D048 AA14 AB01 BA03X BA14X BA15Y BA18Y BA30X BA41X BB02 BB14 CC25 CC26 CC38 CC46 CD05 DA01 DA02 DA05 DA20 EA04 4D058 JA32 A02A02 A02 A02 A02 GA01 GA06

Claims (3)

[Claims] 1. A filter carrying an active oxygen releasing agent and capable of capturing particulates in exhaust gas for a time, a first flow of exhaust gas flowing from one side of the filter and a filter flowing exhaust gas from the other side of the filter. 2. An exhaust gas purification apparatus for an internal combustion engine, comprising: an exhaust switching valve that alternately switches between the two flows; and an oxidation catalyst provided on the exhaust upstream side of the exhaust switching valve. 2. A filter carrying an active oxygen releasing agent and capable of temporarily capturing fine particles in exhaust gas, a first flow of exhaust gas flowing from one side of the filter and a filter flowing exhaust gas from the other side of the filter. An exhaust switching valve for alternately switching between the two flows by driving the valve body, and a control means for stopping the valve body at a position where the contact area between the valve body and the inner wall surface of the exhaust passage becomes as small as possible when the vehicle stops. An exhaust gas purification device for an internal combustion engine, comprising: 3. A first exhaust passage through which exhaust gas flows from one side of the filter, a second exhaust passage through which exhaust gas flows from the other side of the filter, and a first exhaust passage and a second exhaust passage. A bypass passage which bypasses the filter without passing through any of the passages, further comprising abnormality detection means for detecting abnormal clogging of the filter, wherein the abnormality detection means detects abnormal clogging of the filter; 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein exhaust gas is discharged from the exhaust gas.