JP2001317338A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of effectively performing the reduction of NOX and the oxidation of particulates according to an operation state and not discharging a large quantity of an untreated fuel reducing agent after the reduction of NOX is finished. SOLUTION: This exhaust emission control device is provided with a filter 22 carrying an NOX absorbent absorbing NOX or releasing the absorbed NOX and an active oxygen releasing agent accelerating the oxidation of the particulates in the exhaust gas and capable of temporarily trapping the particulates in the exhaust gas, an exhaust switching means 71 capable of switching a first flow 76 feeding the exhaust gas from one side of the filter 22 and a second flow 77 feeding the exhaust gas from the other side of the filter 22 in turn and feeding the exhaust gas to a bypass passage 73 detouring the filter 22 during the switching, a reducing agent feeding means 80 feeding the reducing agent to an exhaust passage 76 on the upstream side of the filter, and a control means guiding only part of the exhaust gas to the filter 22 and feeding the flow of the other exhaust gas to the bypass passage 73 to control the feed of the reducing agent for the reducing atmosphere when the particulate oxidizing/removing quantity of the filter 22 is estimated to be decreased.

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 an upstream side and a downstream side of a filter of a purifying device.

[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 considerably 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, if the load increases, the temperature of the exhaust gas 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 350 ゜ C to 400400C.
Even when the temperature reaches ゜ C, the fine particles may not ignite, and even if the fine particles ignite, only a part of the fine particles is burned, and a problem that a large amount of fine particles remain unburned occurs.

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 small. 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.

[0010] Once such a large amount of fine particles are deposited in a layered form, the above-described problem occurs. Therefore, 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 is increased. In consideration of the above, it is necessary to take measures to prevent a situation where a large amount of fine particles are deposited on the stack.

[0011] However, if the exhaust gas purification is performed according to the operating conditions of the internal combustion engine by merely providing the exhaust gas purification filter with a catalyst in the exhaust pipe, the above-described problem cannot be avoided.

Therefore, if the exhaust gas is alternately switched from the upstream side to the downstream side of the exhaust gas so that the particulates can be continuously burned as much as possible,
Since the fine particles are deposited on both side surfaces of the filter, the amount of the fine particles deposited per unit area can be reduced. In addition, the oxidation of the fine particles can be promoted by disturbing and flying the fine particles deposited by switching the exhaust gas flow. In this case, if the filter substrate is provided with a NOx absorbent, when there is a large amount of oxygen in the exhaust gas, the NOx in the exhaust gas is absorbed and the reducing agent is supplied to release the NOx.
It can also be purified by reduction.

As described above, in the exhaust gas purification filter in which the NOx absorbent is provided on the filter substrate to simultaneously remove the particulates and purify the NOx, there is a possibility that the oxidizing performance of the particulates in the filter may be reduced. For example, during deceleration operation of the vehicle or when the fuel injection amount is small), it is possible to employ a system in which the exhaust gas is bypassed to bypass the filter in order to prevent the deposition of fine particles exceeding the set amount on the filter. At this time, it is conceivable to install a reducing agent supply device for supplying the NOx reducing agent near the filter.

Further, if NOx reduction control is performed only during deceleration operation or when the fuel injection amount is small, when the need for NOx reduction arises during continuous high-speed running, NOx reduction is performed.
x There is a problem that reduction control cannot be performed. Therefore,
There is a need for a system that can perform NOx reduction control according to operating conditions.

Further, in the case of a device for supplying fuel (hydrocarbon HC) as a NOx reducing agent at the time of NOx reduction, a large amount of fuel is adsorbed on the filter when the reducing agent is supplied. If exhaust gas is passed through the filter immediately after the end of the release and reduction of NOx, a large amount of unoxidized HC is released to the outside, which is not preferable.

The present invention has been made in view of the above circumstances, and can reduce NOx and oxidize fine particles more effectively in accordance with the operating conditions. It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine, which can prevent the reducing agent from being released without being oxidized.

[0017]

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

That is, the invention according to the present application absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and absorbs NOx when the oxygen concentration in the inflowing exhaust gas decreases.
a NOx absorbent that releases x and an active oxygen releasing agent that promotes oxidation of fine particles in the exhaust gas, and a filter capable of temporarily capturing the fine particles in the exhaust gas; Exhaust switching means for alternately switching between a first flow to flow and a second flow to flow exhaust gas from the other side of the filter, and in the middle of the switching, exhaust gas flowing to a bypass passage bypassing the filter; It is expected that the reducing agent supply means provided between the branch point of the exhaust passage in which the flow of the exhaust gas is alternately switched by the exhaust switching means and the exhaust passage upstream of the filter, and the particulate matter oxidized removal amount of the filter will be reduced. At this time, only a part of the exhaust gas is led to the filter via an exhaust passage on the side supplying the reducing agent, and the other exhaust gas is caused to flow to the bypass passage. Control means for controlling the exhaust gas switching means and controlling the reducing agent supply means so as to supply the reducing agent so as to bring the filter into a reducing atmosphere.

The exhaust switching means may be constituted by an exhaust switching valve capable of switching the flow direction of the exhaust gas in the filter between forward and reverse directions. The reducing atmosphere of the filter is a state in which the exhaust switching valve is slightly inclined from the intermediate position so that the exhaust gas flows into the bypass passage, and the inclination of the exhaust switching valve causes a slight flow of the exhaust gas in the exhaust gas purification device. Let it. Then, the space velocity (an index indicating how many times the volume of the gas flows in the unit time, hereinafter referred to as SV) decreases, and if the reducing agent is supplied to the filter in this low SV state, a slight amount is obtained. NOx can be released with the amount of reducing agent.

As described above, since the reducing agent supply process is performed with the aim of a low SV state, the NO absorbed by the filter is effectively absorbed.
x can be released.

Further, the invention according to the present application is characterized in that, when it is expected that the removal amount of fine particles by the filter is reduced,
It may be configured such that the vehicle is decelerated or the fuel injection amount is small (including the fuel cut).

Further, the control means of the present invention according to the present invention, when the vehicle is decelerated, or when the state in which the fuel injection amount is equal to or less than the set value does not occur for a predetermined time or more, forcibly controls only a part of the exhaust gas. To the filter, controls the exhaust switching means to flow other exhaust gas to the bypass passage, and controls the reducing agent supply means to supply the reducing agent so as to bring the reducing atmosphere of the filter. May be configured.

According to this configuration, even when the flow rate of the exhaust gas does not flow through the bypass for a long time as in the case of high-speed running, the NOx releasing process can be forcibly executed. The timing for executing such NOx release processing is, for example, forcibly executed when the absorbed NOx exceeds an allowable value.

As a method of determining the NOx allowable value, for example, the amount of NOx stored in the NOx absorbent is estimated based on the operation history of the internal combustion engine (the deviation between the execution time of the lean burn operation and the stoichiometric operation time). A method of making a determination by comparing the estimated value with the maximum amount of NOx that can be stored by the NOx absorbent, or the output of the NOx sensor when the air-fuel ratio of the exhaust gas flowing into the filter is a predetermined air-fuel ratio A method of determining based on a signal value can be exemplified.

Further, the control means of the present invention according to the present invention is arranged such that only a part of the exhaust gas is guided to the filter and the other exhaust gas flows to the bypass passage for a predetermined time after the supply of the reducing agent is completed. The control is executed to maintain the exhaust gas switching means.

Since the supplied reducing agent often contains a fuel component having low reactivity, a large amount of HC remains in the filter after the supply of the reducing agent is completed. In this state, if the flow of the exhaust gas is switched by operating the exhaust switching means immediately after the end of the supply of the reducing agent, there is a risk that HC is released to the outside. Therefore, in order to suppress the release of HC, the exhaust gas switching means is maintained at the position at the time of the supply of the reducing agent for a predetermined period after the supply of the reducing agent, and the lean exhaust gas containing oxygen is taken into the filter to oxidize the HC. To promote.
However, if sudden acceleration occurs and exhaust gas containing a large amount of fine particles is generated, the holding state of the exhaust switching means is released to prevent the discharge of fine particles, and the fine particles are captured by flowing the exhaust gas into the filter. You may make it.

Further, the invention according to the present application relates to a NOx absorbent that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases. A plurality of filters that carry an active oxygen releasing agent that promotes oxidation of the fine particles in the exhaust gas, and are capable of capturing the fine particles in the exhaust gas for a period of time; and a first flow that flows the exhaust gas from one side of the filter. A second flow in which exhaust gas flows from the other side of the filter can be alternately switched, and in the middle of the switching, an exhaust switching means in which exhaust gas flows to a bypass passage bypassing the filter, and a reduction between the plurality of filters. A reducing agent supply means for supplying an agent, and the exhaust gas switching means for flowing the exhaust gas to the bypass passage when it is expected that the amount of particulates removed by the filter will be reduced. Controls the stage, characterized by comprising a control means for controlling the reducing agent supply means to supply the reducing agent so as to the filter reducing atmosphere.

When two filters, for example, are mounted in series on the exhaust gas purification device and the supply of the reducing agent is performed by a reducing agent supply device provided between the two filters, a reducing atmosphere is formed between the filters. To the filter. Therefore,
Since the filter is in a reducing atmosphere, it is not necessary to tilt the exhaust switching valve so that some exhaust gas flows into the filter, and the exhaust switching valve can be completely controlled to the neutral position, so that the exhaust switching valve can be easily controlled. Becomes

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described below with reference to FIGS. <Outline of Apparatus Configuration> FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine for a vehicle. 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, and an outlet of the exhaust turbine 21 has a casing 23 having a built-in particulate filter 22.
Is connected to an exhaust gas purification device having

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 39 for detecting the temperature of the particulate filter 22 is attached to the particulate filter 22, and the output signal of the temperature sensor 39 is a signal corresponding to A
The data is input to the input port 35 via the D converter 37. The accelerator pedal 40 has a depression amount L of the accelerator pedal 40.
Is connected, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding converter 37. Input port 3
5 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 an actuator 72 described later via a 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>
As shown in FIGS. 1, 3, and 4, an exhaust pipe 70 is connected to an outlet of the exhaust turbine 21. A first exhaust passage 76 branched from the exhaust pipe 70 and connected to one surface and the other surface of the filter 22 in the casing 23 in which the particulate filter 22 is incorporated, respectively.
Exhaust passage 77 is provided. Further, a bypass passage 73 is provided from the branch point of the first exhaust passage 76 and the second exhaust passage 77 to discharge the exhaust gas without passing through the particulate filter 22.

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. Further, a filter 2 is provided in the first exhaust passage 76.
A fuel addition nozzle 80 is provided as a reducing agent supply unit for injecting fuel into the exhaust gas flowing into the exhaust gas 2. The fuel addition nozzle 80 is connected to the CP of the electronic control unit 30.
It is controlled by control means 75 implemented on U34.

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 gas 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). Further, by controlling the negative pressure, the valve element can be maintained in an inclined state (intermediate inclined position) as shown by a two-dot chain line in FIG. 3, whereby a part of the exhaust gas is bypassed to the bypass passage 73 and , And another part can flow through the filter 22. That is, the exhaust gas switching valve 71 driven by the actuator 72 controlled by the control means 75
Is an exhaust gas switching means in the present invention.

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 77 and connects the first exhaust passage 76 to the bypass passage 73. To the exhaust pipe 70 →
Second exhaust passage 77 → filter 22 → first exhaust passage 7
6 → flows in the order of the bypass passage 73 and is released to the atmosphere.

When the valve element is at a neutral position parallel to the axis of the exhaust pipe 70 as shown by the dashed line in FIG. 3, the exhaust switching valve 71 connects the exhaust pipe 70 directly to the bypass passage 73. Therefore, the exhaust gas is supplied from the exhaust pipe 70 to the filter 2.
2 and flows into the bypass passage 73 and is released to the atmosphere.

When the valve body is at an intermediate inclined position parallel to the axis of the exhaust pipe 70, as shown by the two-dot chain line in FIG.
Therefore, a portion of the exhaust gas flows from the exhaust pipe 70 to the bypass passage 73 without passing through the filter 22 and is discharged to the atmosphere. On the other hand, due to the inclination of the valve body, another part of the exhaust gas passes through the first exhaust passage 76, passes through the filter 22 from the forward flow direction, and is introduced into the bypass passage 73.

In this state, the amount of exhaust gas flowing through the first exhaust passage 76 decreases, and the SV value decreases.
When fuel is supplied to the filter in this state, an active oxidation reaction occurs, the filter temperature rises, and the oxidation of the fine particles can be promoted.

Since 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 element, the oxidation of the fine particles is promoted, so that the fine particles can be efficiently purified. it can.

FIG. 5A is an image diagram in the case where the exhaust gas flows through the filter 22 from only one direction. The fine particles accumulate only on one surface of the filter and do not move. Not only does it hinder the purification of particulates.

FIG. 5B is an image diagram in the case where exhaust gas flows from the filter 22 from both directions. Since fine particles are disturbed on both sides of the filter in the forward flow direction and the reverse flow direction, the fine particles are disturbed on both surfaces of the filter 22 or Move around inside the substrate,
The oxidation of the fine particles can be promoted by utilizing the active points of the entire filter substrate, and the accumulation of the fine particles in the filter 22 can be further reduced. Therefore, an increase in the pressure loss of the exhaust gas can be avoided.

<Structure of Filter> FIG. 6 shows the structure of the particulate filter 22. 6A shows a front view of the particulate filter 22, and FIG. 6B shows a side sectional view of the particulate filter 22. As shown in FIGS. 6A and 6B, the particulate filter 22 has a honeycomb structure, and is a so-called wall flow type including a plurality of exhaust passages 50 and 51 extending parallel to 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. 6A, hatched portions indicate plugs 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, the exhaust gas inflow passage 50 and the exhaust gas outflow passage 51 have four exhaust gas inflow passages 50 each.
Two exhaust gas outflow passages 51 are arranged so that each exhaust gas outflow passage 51 is surrounded by four exhaust gas inflow passages 50.

The particulate filter 22 is formed 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 layer of a support is formed, and on the support, a noble metal catalyst and, when excess oxygen is present in the surroundings, takes in oxygen to retain oxygen and, when the surrounding oxygen concentration decreases, retains the retained oxygen in the form of active oxygen. An active oxygen release agent to be released and a NOx absorbent that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases are carried. ing.

Here, the air-fuel ratio of the exhaust gas flowing into the NOx absorbent refers to the ratio of air to fuel (hydrocarbon) supplied to the engine intake passage, the combustion chamber 5 and the exhaust passage upstream of the NOx absorbent. Say. When fuel (hydrocarbon) or air is not supplied into the exhaust passage upstream of the NOx absorbent, the air-fuel ratio of the inflowing exhaust gas matches the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber.

As the noble metal catalyst, platinum Pt can be used. The active oxygen releasing agent is an alkali metal such as potassium K, sodium Na, lithium Li, cesium Cs, rubidium Rb, an alkaline earth metal such as barium Ba, calcium Ca, strontium Sr,
It can be composed of at least one selected from lanthanum La, rare earths such as yttrium Y, 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 L
It is preferable to use i, cesium Cs, rubidium Rb, barium Ba, and strontium Sr.

The NOx absorbent is, for example, potassium K,
Alkaline metals such as sodium Na, lithium Li, cesium Cs, rubidium Rb, alkaline earths such as barium Ba, calcium Ca, strontium Sr;
It can be composed of at least one selected from rare earths such as lanthanum La and yttrium Y.

In this case, as the NOx absorbent, 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.

As can be seen from a comparison between the metal constituting the active oxygen releasing agent and the metal constituting the NOx absorbent, most of the metals constituting these correspond. Therefore, different metals can be used as the active oxygen releasing agent and the NOx absorbent, or the same metal can be used. When the same metal is used as the active oxygen releasing agent and the NOx absorbent, the metal simultaneously performs both the function as the active oxygen releasing agent and the function as the NOx absorbent. In this manner, what simultaneously fulfills both the function of the active oxygen releasing agent and the function of the NOx absorbent is hereinafter referred to as “active oxygen releasing / NOx absorbent”.
Called.

In this embodiment, an example will be described in which platinum Pt as a noble metal catalyst and potassium K as an active oxygen releasing / NOx absorbent are supported on a carrier such as alumina.

As described above, potassium K as an active oxygen releasing / NOx absorbent simultaneously functions as both an active oxygen releasing agent and a NOx absorbent. In this technology, the function of an active oxygen releasing agent is used to promote the oxidative removal of fine particles in exhaust gas, and the function of a NOx absorbent is used to purify NOx in exhaust gas. Hereinafter, the purifying mechanism of the exhaust gas purifying apparatus will be described focusing on the respective functions.

<Continuous oxidation treatment of fine particles by filter
Function as active oxygen release agent> First, the action of removing particulates in exhaust gas by the particulate filter 22 utilizing the function of the active oxygen release / NOx absorbent as the active oxygen release agent will be described. The function as the active oxygen releasing agent is such that the fine particles can be removed by the same mechanism even when other alkali metals, alkaline earth metals, rare earths, and transition metals are used as the active oxygen releasing agent.

A compression ignition type internal combustion engine as shown in FIG.
Combustion takes place under excess air, so the exhaust gas
Contains a large amount of excess air. That is, as shown in FIG.
In a compression ignition type internal combustion engine, the air-fuel ratio of exhaust gas is lean
It has become. Also, NO is generated in the combustion chamber 5.
The exhaust gas contains NO. Also in the fuel
Contains sulfur S, and this sulfur S is contained in the combustion chamber 5.
Reacts with oxygen in SO _Two Becomes Therefore, in the exhaust gas
SO_Two It is included. Therefore, excess oxygen, NO and S
O_Two Exhaust gas containing the particulate filter 22
Flows into the exhaust gas inflow passage 50.

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. .
In FIGS. 7A and 7B, reference numeral 60 denotes platinum Pt.
The numeral 61 indicates an active oxygen releasing / NOx absorbent 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 / NOx absorbent 61 while being oxidized on the platinum Pt, and is combined with potassium K to form nitrate ions NO ₃ as shown in FIG. ^-
, And diffuses into the active oxygen releasing / NOx absorbent 61, and a part of the nitrate ion NO ₃ ⁻ generates potassium nitrate KNO ₃ .

On the other hand, as described above, SO is contained in the exhaust gas.
₂ are also included, this SO ₂ is absorbed in the active oxygen release · NOx absorbent 61 by NO similar mechanisms. That is, as described above, oxygen O ₂ adheres to the surface of platinum Pt in the form of O ₂ ⁻ or O ²⁻ and SO 2 in the exhaust gas
₂ O ₂ on the surface of the platinum Pt ^- a or O ^2- reacts with SO _3.

Next, a part of the produced SO ₃ is made of platinum Pt.
Active oxygen release / NOx absorbent 61 while being oxidized further
Sulfate ion S is absorbed in
It diffuses into the active oxygen releasing / NOx absorbent 61 in the form of O ₄ ²⁻ to generate potassium sulfate K ₂ SO ₄ . Thus, potassium nitrate K is contained in the active oxygen release / NOx absorbent 61.
NO ₃ and potassium sulfate K ₂ SO ₄ are produced.

On the other hand, fine particles mainly composed of carbon C are generated in the combustion chamber 5, and therefore, the fine particles are contained in the exhaust gas. 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 release / NOx absorbent 61.

As described above, the fine particles 62 emit active oxygen and N
When the particles adhere to the surface of the Ox absorbent 61, the oxygen concentration decreases at the contact surface between the fine particles 62 and the active oxygen release / NOx absorbent 61. When the oxygen concentration decreases, a concentration difference occurs between the active oxygen release / NOx absorbent 61 having a high oxygen concentration and the oxygen in the active oxygen release / NOx absorbent 61 becomes fine particles 62 and the active oxygen release / NOx. Attempts to move toward the contact surface with the absorbent 61. As a result, active oxygen release / N
Potassium nitrate KNO formed in the Ox absorbent 61
₃ is decomposed into potassium K, oxygen O and NO, oxygen O is directed to the contact surface between the fine particles 62 and the active oxygen release / NOx absorbent 61, and NO is released from the active oxygen release / NOx absorbent 61 to the outside. You. NO released to the outside is oxidized on platinum Pt on the downstream side, and active oxygen release / NO is again released.
x is absorbed in the absorbent 61.

On the other hand, at this time, potassium sulfate K ₂ SO ₄ formed in the active oxygen releasing / NOx absorbent 61 is also decomposed into potassium K, oxygen O and SO _2, and the oxygen O becomes fine particles 62 and active oxygen releasing - toward the contact surface between the NOx absorbent 61, SO ₂ is released from the active oxygen release, the NOx absorbent 61 to the outside. The SO ₂ released to the outside is oxidized on platinum Pt on the downstream side, and active oxygen is released again / NOx
It is absorbed in the absorbent 61. However, potassium sulfate K ₂
Since SO ₄ is stabilized, it is difficult to release SO ₄ compared to potassium nitrate KNO ₃ .

On the other hand, the fine particles 62 and active oxygen release / NOx
Oxygen O toward the contact surface with the absorbent 61 is potassium nitrate K
It is oxygen decomposed from compounds such as NO ₃ and potassium sulfate K ₂ SO ₄ . Oxygen O decomposed from the compound has high energy and extremely high activity. Therefore, the oxygen going to the contact surface between the fine particles 62 and the active oxygen releasing / NOx absorbent 61 is active oxygen O. When the active oxygen O comes in contact with the fine particles 62, the fine particles 62 are oxidized within a short time without emitting a bright flame, and the fine particles 62 are completely eliminated. Therefore, the fine particles 62 do not accumulate on the particulate filter 22.

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. 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 particles are hardly deposited on the particulate filter 22, there is little danger that ash which is a burning residue of the particles is agglomerated, and therefore, there is little danger that the particulate filter 22 is clogged.

This 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, active oxygen release / N
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 Ox absorbent 61, active oxygen is released. SO ₃ diffused into the NOx absorbent 61 is combined with potassium K to form potassium sulfate. K ₂ SO ₄ is formed, and calcium Ca flows out of the exhaust gas outflow passage 51 through the partition wall 54 of the particulate filter 22 without binding to SO ₃ . Therefore, the pores of the particulate filter 22 are not clogged. Therefore, as described above, active oxygen release / NOx
As the absorbent 61, it is preferable to use an alkali metal or an alkaline earth metal having a higher ionization tendency than calcium Ca, that is, potassium K, lithium Li, cesium Cs, and barium Ba.

By the way, platinum Pt and active oxygen release.
Since the Ox absorbent 61 is activated as the temperature of the particulate filter 22 increases, the amount of active oxygen released by the active oxygen release / NOx absorbent 61 per unit time increases as the temperature of the particulate filter 22 increases. I do. Therefore, the amount of oxidizable and removable fine particles that can be oxidized and removed on the particulate filter 22 without emitting a luminous flame per unit time is equal to the amount of the particulate filter 2.
2 increases as the temperature increases.

The solid line in FIG. 9 shows 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 / NOx absorbent 61 as shown in FIG. Is partially oxidized, and the finely divided particles that have not been sufficiently oxidized remain on the carrier layer. Next, when the state of the insufficient amount of active oxygen continues, the fine particles that have not been oxidized remain one after another on the carrier layer, and as a result, the surface of the carrier layer remains as shown in FIG. It becomes covered with the 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. Further, the surface of the carrier layer NO by which the platinum Pt covered by the residual particulate portion 63, action of release of active oxygen by oxidizing action and the active oxygen release · NOx absorbent 61 of the SO ₂ can be 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. 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 become platinum Pt or active oxygen release / NOx absorbent 61.
Even if the fine particles are easily oxidized, the fine particles are no longer oxidized by the active oxygen O, and 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.

In practice, however, 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 operating 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 deposited fine particles, the switching valve 71 arranged in the exhaust pipe 70 is switched. When the 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 activated oxygen release and NOx absorption. The active oxygen O is released by adhering to the surface of the agent 61, 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 fine particles are removed from the particulate filter 22. Can be completely removed by oxidation.

When fine particles are deposited on the particulate filter 22, the air-fuel ratio of a part or the whole of the exhaust gas is temporarily made rich to oxidize the deposited fine particles without generating 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, the active oxygen release / NOx absorbent 61
The 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 burnt and removed at a stretch in a short time without emitting a bright flame.
The above is the mechanism for purifying fine particles utilizing the function of the active oxygen releasing / NOx absorbent as the active oxygen releasing agent.

<NO with active oxygen release / NOx absorbent>
x Purification Processing: Function as NOx Absorbing and Desorbing Agent> Next, the NOx purifying action utilizing the function of the active oxygen releasing / NOx absorbing agent as the NOx absorbent will be described. It should be noted that the function as the NOx absorbent performs the NOx purifying action by the same mechanism even when another alkali metal, alkaline earth metal or rare earth is used as the NOx absorbent.

It is considered that the NOx purifying action of the active oxygen releasing / NOx absorbent is performed by a mechanism as shown in FIG. Note that FIGS. 10A and 10B
Numeral 60 indicates platinum Pt particles, and numeral 61 indicates an active oxygen releasing / NOx absorbent containing potassium K.

First, when the air-fuel ratio of the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases,
As shown in FIG. 10A, oxygen O ₂ is replaced with O ₂ ⁻ or O ^2−.
On the surface of platinum Pt. On the other hand, NO contained in the inflowing exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of the platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ).

Next, the generated NO ₂ is absorbed in the active oxygen release / NOx absorbent 61 while being oxidized on the platinum Pt, and is combined with potassium K, and as shown in FIG. ion NO ₃ ^- in the form of active oxygen release · N
It diffuses into the Ox absorbent 61. In this way, NOx is absorbed in the active oxygen release / NOx absorbent 61.

As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of platinum Pt, and active oxygen is released.
As long as the NOx absorption capacity of the absorbent 61 is not saturated, NO ₂
There nitrate ions NO ₃ is absorbed in the active oxygen release · NOx absorbent 61 ^- is created.

On the other hand, when the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or rich, the oxygen concentration in the inflowing exhaust gas decreases, so that the amount of generated NO ₂ decreases and the reaction proceeds in the reverse direction (NO
₃ ^- → NO ₂₎ proceeds, the active oxygen release · NOx absorbent 61
The nitrate ion NO ₃ ⁻ in the inside is released from the active oxygen release / NOx absorbent 61 in the form of NO ₂ or NO. That is, when the oxygen concentration in the inflowing exhaust gas decreases, the active oxygen release / N
NOx is released from the Ox absorbent 61.

On the other hand, at this time, HC, CO
Is oxidized by reacting with oxygen O ₂ ^- or O ^2- on platinum Pt. Also, the active oxygen release / NOx released from the NOx absorbent 61 due to a decrease in the oxygen concentration in the inflow exhaust gas.
₂ or NO indicates unburned H as shown in FIG.
It reacts with C and CO to be reduced to N ₂ .

[0090] That is, HC in the inflowing exhaust gas, CO, first oxygen O ₂ on the platinum Pt ^- or O ^2- immediately be reacted with oxidized, then the platinum Pt on the oxygen O ₂ ^- or O ^2- If HC and CO still remain after consumption, this H
NOx released from active oxygen release / NOx absorbent 61 by C and CO and NOx exhausted from the internal combustion engine
Is reduced to N ₂ .

In this way, NO _{2 is} deposited on the surface of platinum Pt.
Or, when NO is no longer present, release active oxygen and NOx
NO ₂ or NO is released one after another from the absorbent 61 and further reduced to N ₂ . Therefore, NOx is released from the active oxygen release · NOx absorbent 61 in a short time when the air-fuel ratio of the exhaust gas the stoichiometric air-fuel ratio or rich, is reduced to N _2.

As described above, when the air-fuel ratio of the exhaust gas becomes lean, NOx is absorbed by the active oxygen release / NOx absorbent 61, and when the air-fuel ratio of the exhaust gas is made stoichiometric or rich, NOx is released. It is released from the absorbent 61 in a short time and is reduced to N ₂ . Therefore, emission of NOx into the atmosphere can be prevented.

By the way, as described above, in this compression ignition type internal combustion engine, normally, the stoichiometric (stoichiometric air-fuel ratio, A / F =
Since the combustion is performed in a much leaner region than in 14.6), the air-fuel ratio of the exhaust gas flowing into the filter 22 (that is, the exhaust gas flowing into the active oxygen release / NOx absorbent 61) in the normal engine operation state Is extremely lean, and NOx in the exhaust gas is absorbed by the active oxygen release / NOx absorbent 61 and N released from the active oxygen release / NOx absorbent 61
The amount of Ox is extremely small.

Therefore, in the compression ignition type internal combustion engine, the reducing agent is supplied into the exhaust gas at a predetermined timing before the NOx absorbing ability of the active oxygen releasing / NOx absorbent 61 is saturated, and the oxygen concentration in the exhaust gas is increased. And release NOx absorbed by the active oxygen release / NOx absorbent 61 to reduce N
Need to be reduced to ₂ .

Therefore, in this embodiment, the ECU 3
0 is the active oxygen release / NO from the history of the operating state of the internal combustion engine.
The amount of NOx absorbed by the x absorbent 61 is estimated, and when the estimated amount of NOx reaches a predetermined value, the air-fuel ratio of the exhaust gas is temporarily made rich to lower the oxygen concentration and simultaneously reduce The agent is supplied. Such a temporary enrichment of the air-fuel ratio of the exhaust gas is generally called a rich spike.

In this embodiment, a rich spike is realized by sub-injecting fuel into a cylinder during an expansion stroke or an exhaust stroke of the internal combustion engine. Note that rich spikes can also be realized by supplying fuel into the exhaust passage 70 upstream of the filter 22.

As described above, by executing the rich spike at a predetermined timing before the NOx absorbing ability of the active oxygen releasing / NOx absorbent 61 is saturated, NOx in the exhaust gas can be continuously purified. , NOx to the atmosphere can be prevented. The above is the NOx purification mechanism utilizing the function of the active oxygen release / NOx absorbent 61 as a NOx absorbent / release agent.

Therefore, when the active oxygen releasing / NOx absorbent 61 is used, when the air-fuel ratio of the exhaust gas flowing into the filter 22 is lean, the NO contained in the exhaust gas is reduced.
x is absorbed by the active oxygen release / NOx absorbent 61, and when the fine particles contained in the exhaust gas adhere to the active oxygen release / NOx absorbent 61, the fine particles become active oxygen released from the active oxygen release / NOx absorbent 61. Oxidized in a short time. That is, at this time, it is possible to prevent both the fine particles and the NOx in the exhaust gas from being discharged into the atmosphere.

On the other hand, when the air-fuel ratio of the exhaust gas flowing into the filter 22 becomes rich, NOx is released from the active oxygen release / NOx absorbent 61. This NOx is unburned HC,
It is reduced by CO, and thus NOx is not discharged to the atmosphere at this time. If fine particles are deposited on the filter 22 at this time, the fine particles are oxidized and removed by the active oxygen released from the active oxygen releasing / NOx absorbent 61.

Next, the switching control of the exhaust gas flow for more effectively reducing the NOx and oxidizing the fine particles according to the operating condition will be described with reference to the flowcharts of FIGS.

The flowchart shown in FIG. 11 shows an exhaust gas flow switching control routine, which is stored in advance in the ROM 32 of the ECU 30 and is executed by the CPU 34 at regular intervals. .

When the process starts, the CPU 34 determines in step 101 whether or not the vehicle is decelerating including a fuel cut. The determination as to whether or not the vehicle is in a deceleration state including a fuel cut is made by a G sensor, a sensor for detecting the amount of depression of an accelerator pedal, an engine speed sensor (crank angle sensor), a throttle opening sensor, and the like. judge.

In step 101, the CPU 34
When it is determined that the vehicle is decelerating including the fuel cut (Step 101: YES), the process proceeds to Step 102. On the other hand, when it is determined that the vehicle is not decelerating including the fuel cut (Step 101: NO), the process returns and returns to the start position. .
In the case of deceleration including a fuel cut, the temperature of the exhaust gas is low and the filter is cooled, which may reduce the ability to remove and oxidize particulates.

For this reason, the CPU 34 executes the following step 1
At 02, the exhaust switching valve 71 is slightly inclined to be in a bypass state, and a slight gas flow is created in the casing 23. Then, the state of the SV is lowered. When the reducing agent is supplied to the filter in this state, an active oxidation reaction occurs, the filter temperature rises, and the oxidation of the fine particles can be promoted. Further, since the reducing agent supply process for releasing NOx is performed aiming at the bypass time when the flow rate of exhaust gas flowing through the filter is small, NOx can be released with a small amount of reducing agent.

When the release of NOx is completed, the supply of the reducing agent is stopped. However, in step 103, after the end of the supply of the reducing agent, the CPU 34 guides only a part of the exhaust gas to the filter 22 for a predetermined period t, and causes the exhaust switching valve to flow the other exhaust gas flow rate to the bypass passage 73. 71 is maintained. Note that the predetermined time period t
Is the time required to oxidize the remaining reducing agent, and is assumed to be registered in the RAM 33 in advance. FIG. 13 shows the NOx concentration at the catalyst outlet when controlled as described above. By bypassing the exhaust gas flowing through the filter every deceleration and supplying the reducing agent at this time, the operation can be performed without exceeding the NOx allowable value.

When fuel is used as the reducing agent, since the fuel contains HC with low reactivity, a large amount of HC remains in the filter after the supply of the reducing agent. In this state, if the flow of the exhaust gas is switched by the exhaust switching valve 71 immediately after the end of the supply of the reducing agent, there is a risk that a large amount of HC is released to the outside. Therefore, in order to prevent HC release by this control, the exhaust gas switching valve 71 is maintained for a predetermined period of time t after the end of the supply of the reducing agent, and the lean exhaust gas containing oxygen is taken in to oxidize HC. Promote. In the above embodiment, the reducing agent is supplied every deceleration. However, when the estimated NOx occlusion amount is small, it is not always necessary to supply the reducing agent.

After the end of the predetermined period t, the CPU 34 sets NOx
The reduction process by release is completed (step 104), and the process returns to the start position.

In the flowchart of FIG. 11, the case where the NOx reduction control for supplying the NOx reducing agent is performed during the deceleration operation has been described. If the operation does not occur, NOx reduction control becomes impossible. Then, next, the NOx reduction control for forcibly supplying the NOx reducing agent when the deceleration state or the state where the fuel injection amount is equal to or less than the set value does not occur for a predetermined time or more will be described based on the flowchart of FIG.

The flowchart shown in FIG. 12 also shows the exhaust gas flow switching control routine.
Is stored in the ROM 32 of the CPU 3 at regular intervals.
4 is performed.

When the process starts, the CPU 34 determines the allowable NOx value in step 201. N
The method of determining the Ox allowable value is as described above.

FIG. 14 shows the output N of the NOx sensor during high-speed running.
The Ox concentration is shown over time. In this embodiment, as shown in FIG. 14, the NOx allowable value L is determined in advance and registered in the RAM 33, and the CPU 34 determines the NOx allowable value based on the NOx allowable value L.

In step 201, the CPU 34
If it is determined that the output NOx concentration is higher than the allowable value L (step 201: YES), the process proceeds to step 202,
On the other hand, when it is determined that the output NOx concentration is lower than the allowable value L (step 201: NO), the process returns.

Next, at step 202, the CPU 34 gives a slight flow to the exhaust gas switching valve 71 in a bypass state by giving a slight inclination to the exhaust gas switching valve 71, similarly to step 102. When the reducing agent is supplied to the filter in this state, an active oxidation reaction occurs, the filter temperature rises, and the oxidation of the fine particles can be promoted. Further, since the reducing agent supply process for releasing NOx is performed aiming at the bypass time when the flow rate of exhaust gas flowing through the filter is small, NOx can be released with a small amount of reducing agent.

When the release of NOx is completed, the supply of the reducing agent is stopped. However, in Step 203, the CPU 34 guides only a part of the exhaust gas to the filter 22 for a predetermined time t after the end of the supply of the reducing agent, and maintains the exhaust switching valve 71 so that another flow rate of the exhaust gas flows to the bypass passage 73. Perform control. By this control, most of the exhaust gas is bypassed for a while, so that the reducing agent adsorbed on the filter can be oxidized.

After the predetermined time t has elapsed, the CPU 34 sets NOx
The reduction process by release is completed (step 204), and the process returns to the start position.

In the invention according to the present application, the time when the particulate oxidation removal amount of the filter is expected to be small may be the time when the fuel injection amount is small in addition to the above-described deceleration.

Further, in the above-described embodiment, the case where one filter is provided in the exhaust gas purifying apparatus has been described. However, the present invention includes the case where a plurality of filters are provided in the exhaust gas purifying apparatus.

For example, as another embodiment, FIG. 15 shows a case where two filters 22a and 22b are mounted adjacent to the exhaust gas purifying apparatus, and FIG. 15 (a) is a plan view of the exhaust gas purifying apparatus. FIG. 15B is a side view of the exhaust gas purification device.

As shown in FIG. 15, the filters 22a, 22
A fuel addition nozzle 80a is provided between 2b. As described above, the fuel addition nozzle 80a is connected to the filters 22a and 22a.
When the reducing agent is supplied between the filter b
A reducing atmosphere is formed between a and 22b. Therefore, it is not necessary to incline the exhaust gas switching valve 71 to bring the filter into the reducing atmosphere as in the above-described embodiment, and it is sufficient to control the exhaust gas switching valve 71 to the intermediate position. It will be easier. Note that, in FIG. 15, components having the same reference numerals as those in FIG. 3 have the same functions, and thus description thereof will be omitted.

FIG. 16 shows a filter 2 in the exhaust gas purifying apparatus.
FIG. 16 shows a case where two 2c and 22d are mounted in series.
FIG. 16A is a plan view of the exhaust gas purification device, and FIG. 16B is a side view of the exhaust gas purification device.

In the case of this other embodiment, as shown in FIG. 16, a filter 22c is provided on the first exhaust passage side, and a filter 22d is provided on the second exhaust passage side. The fuel addition nozzle 80b is provided on the exhaust passage at an intermediate position between the filters 22c and 22d. in this way,
The fuel supply nozzle 80b may be provided between the filters 22c and 22d to supply the reducing agent.
A reducing atmosphere is formed between d. Therefore, the exhaust switching valve 7
The control of the exhaust switching valve 71 is facilitated by controlling the position of the exhaust switching valve 71 to the intermediate position. Note that, in FIG. 16, components having the same reference numerals as those in FIG. 3 have the same functions, and thus description thereof will be omitted.

The present invention also holds when a noble metal catalyst such as platinum Pt and a NOx absorbent are supported on a carrier layer formed on the filter 22. 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 as compared with the solid line shown in FIG. In this case, platinum Pt
Active oxygen is released from NO ₂ or SO ₃ held on the surface of the substrate.

As an active oxygen releasing agent, NO ₂ or SO ₃ is adsorbed and held, and these adsorbed NO ₂ or S
A catalyst that can release active oxygen from O ₃ can also be used.

According to the device of the present invention, the reducing atmosphere of the filter is formed by giving the exhaust switching valve a slight inclination from the intermediate position to create a slight flow of exhaust gas in the exhaust purification device. Since the reducing agent is supplied to the filter in the state, NOx can be released with a small amount of the reducing agent, and NOx reduction can be promoted.

Even when a deceleration state or a state in which the fuel injection amount is less than the set value does not occur for a predetermined time or more, only a part of the exhaust gas is forcibly guided to the filter to supply the reducing agent. Therefore, even when the flow rate of the exhaust gas does not flow through the bypass passage for a long time as in the case of high-speed running, the NOx releasing process can be forcibly performed.

Further, the control means maintains the exhaust switching means so as to guide only a part of the exhaust gas to the filter and flow another exhaust gas flow to the bypass passage for a predetermined period after the end of the supply of the reducing agent. Since the control is performed such that the reducing agent (HC) adsorbed on the filter can be oxidized by the lean exhaust gas containing oxygen and then released, the emission of HC can be prevented.

[0127]

As described above, according to the present invention, the reduction of NOx and the oxidation of fine particles can be more effectively performed according to the operating conditions, and the reducing agent such as fuel does not remain after the completion of NOx reduction. An exhaust gas purification device for an internal combustion engine that is not released to the outside as it is processed can be provided.

[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 gas purification device.

FIG. 5A is an image diagram showing a state in which fine particles are deposited on a filter substrate, and FIG. 5B is an image diagram showing a state in which fine particles are disturbed due to a forward flow and a backward flow of exhaust gas.

FIG. 6 is a diagram showing a particulate filter.

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

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

FIG. 9 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. 10 is a conceptual diagram showing an action of purifying NOx.

FIG. 11 is a flowchart showing an exhaust gas flow switching control in the embodiment.

FIG. 12 is a flowchart illustrating an exhaust gas flow switching control according to another embodiment.

FIG. 13 is an output NO detected by a NOx sensor during deceleration operation.
The x concentration is shown over time.

FIG. 14 is an output NO detected by a NOx sensor during high-speed running.
The x concentration is shown over time.

15 shows a case where two filters are mounted adjacent to the exhaust purification device, FIG. 15 (a) is a plan view of the exhaust purification device, and FIG. 15 (b) is a side view of the exhaust purification device. .

16 shows a case where two filters are mounted in series on the exhaust gas purification device. FIG. 16 (a) is a plan view of the exhaust gas purification device, and FIG. 16 (b) is a side view of the exhaust gas purification device.

[Explanation of symbols]

Reference Signs List 6 fuel injection valve 22 particulate filter 30 ECU 61 active oxygen release / NOx absorbent (NOx absorbent, active oxygen release agent) 70 exhaust pipe 71 exhaust switching valve (exhaust switching means) 72 actuator 73 ... bypass passage 75 ... control means 76 ... first exhaust passage 77 ... second exhaust passage 80 ... fuel addition nozzle (reducing agent supply means)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 53/86 ZAB F01N 3/08 A 53/94 B F01N 3/08 3/20 B 3/24 E 3 / 20 9/00 Z 3/24 B01D 53/36 ZAB 9/00 101B 103C 103B (72) Inventor Kazuhiro Ito 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Takamitsu Asanuma Aichi Prefecture 1 Toyota Town, Toyota City Inside Toyota Motor Co., Ltd. (72) Inventor Koichiro Nakatani 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Co., Ltd. (72) Koichi Kimura 1 Toyota Town, Toyota City, Aichi Prefecture F-term in Toyota Motor Corporation (reference) 3G090 AA03 BA01 CA00 CB00 CB24 DA13 DA18 DA20 DB07 EA05 EA06 3G091 AA02 AA10 AA11 AA18 AB06 AB13 BA13 BA14 CA12 CA13 CA15 DB10 EA00 EA01 EA07 EA15 EA22 GB01Y GB02Y GB03Y GB04Y GB05W GB06W GB17X HB03 HB05 HB06 4D048 AA06 AA13 AA14 AA18 AB01 AB02 AB07 AC02 BB02 BB14 CC25 CC26 CD05 DA01 DA02 DA05 DA08 DA10 DA20 EA

Claims (6)

[Claims] 1. A NOx absorbent that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases. An active oxygen releasing agent that promotes oxidation is supported, and a filter capable of capturing particulates in the exhaust gas for a time; a first flow of the exhaust gas flowing from one side of the filter and an exhaust gas flowing from the other side of the filter; The second flow can be alternately switched with the second flow. Exhaust switching means for flowing exhaust gas to a bypass passage bypassing the filter during the switching, and an exhaust passage in which the exhaust flow can be alternately switched by the exhaust switching means. A reducing agent supply means provided between a branch point and an exhaust passage upstream of the filter; and Only a part of the gaseous gas is guided to the filter via the exhaust passage on the side for supplying the reducing agent, and the exhaust gas switching means is controlled so that the other exhaust gas flows through the bypass passage. Control means for controlling the reducing agent supply means so as to supply the reducing agent to reduce the atmosphere. 2. The internal combustion engine according to claim 1, wherein when the particulate oxidation removal amount of the filter is expected to be small, the vehicle equipped with the internal combustion engine is decelerated or the fuel injection amount is small. Exhaust purification device. 3. When the vehicle is decelerated or when the state where the fuel injection amount is small does not occur for a predetermined time or more, only a part of the exhaust gas is forcibly guided to the filter, and the other exhaust gas is bypassed. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the exhaust gas switching device is controlled to flow through the passage, and the reducing agent supply device is controlled to supply the reducing agent to reduce the atmosphere of the filter. 4. The exhaust switching means and the reducing agent supply means are forcibly controlled on the basis of a predetermined NOx allowable value at the time of the deceleration or when the state where the fuel injection amount is small does not occur for a predetermined time or more. The exhaust gas purification device for an internal combustion engine according to claim 3. 5. A control for maintaining the exhaust switching means so that only a part of the exhaust gas is guided to the filter for a predetermined time after the supply of the reducing agent, and the other exhaust gas is caused to flow through the bypass passage. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 4. 6. A NOx absorbent that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases. A plurality of filters that carry an active oxygen releasing agent that promotes oxidation and are 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 an exhaust gas from the other side of the filter An exhaust switching unit that allows the exhaust gas to flow through a bypass passage that bypasses the filter during the switching, and a reducing agent supply that supplies a reducing agent between the plurality of filters. Means for controlling the exhaust gas switching means so as to flow the exhaust gas to the bypass passage when it is expected that the particulate matter oxidation removal amount of the filter will be small. Exhaust purifying apparatus for an internal combustion engine characterized by comprising a control means for controlling the reducing agent supply means to supply the reducing agent so as to filter the reducing atmosphere, the.