JP2003227332A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for enabling a predetermined control of temperature rise without misfire under low temperature and light load conditions even in the case of a low compression ratio engine. <P>SOLUTION: This device comprises an NOx occlusion agent 20 that occludes NOx in exhaust gas when an air-fuel ratio of flowing exhaust gas is lean, and releases the occluded NOx when the air-fuel ratio of the flowing exhaust gas becomes a theoretical air-fuel ratio or rich; a temperature rising means for controlling the temperature rise of the NOx occlusion agent 20; an operating condition detecting means for detecting an operating condition of an internal combustion engine; and a combustion type heater 60 for supplying evaporated fuel to a suction system. When the temperature rising means rises the temperature of the NOx occlusion agent 20 to a predetermined temperature based on the operating condition of the internal combustion engine detected by the operating condition detecting means, the fuel heated and evaporated by the combustion type heater 60 is supplied to the suction system (a suction pipe 9). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, internal combustion engines mounted in automobiles,
In particular, diesel engines and lean burn engines that can burn an air-fuel mixture that is in an oxygen excess state (so-called lean air-fuel mixture)
In a gasoline engine, a technique of disposing an NOx storage agent in the exhaust system of this internal combustion engine has been proposed. As one of the NOx storage agents, it stores nitrogen oxides (NOx) in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and it stores it when the oxygen concentration of the inflowing exhaust gas is low and a reducing agent is present. An occlusion reduction type NOx catalyst is known that reduces nitrogen oxide (NOx) to nitrogen (N ₂ ) while releasing it.

When the NOx storage reduction catalyst is arranged in the exhaust system of an internal combustion engine, nitrogen oxides (NOx) in the exhaust gas are generated when the internal combustion engine is operated in lean combustion and the air-fuel ratio of the exhaust gas becomes high.
Is stored in the NOx storage reduction catalyst, and when the air-fuel ratio of the exhaust flowing into the NOx storage reduction catalyst becomes low, the nitrogen oxides (NOx) stored in the NOx storage reduction catalyst are released and nitrogen ( N ₂ ).

By the way, the NOx storage reduction catalyst contains sulfur oxides (S) produced by combustion of sulfur contained in fuel.
Ox) is also stored by the same mechanism as NOx. SOx stored in this way is less likely to be released than NOx,
x Accumulates in the catalyst. This is called sulfur poisoning (SOx poisoning), and the NOx purification rate decreases, so SOx is added at an appropriate time.
It is necessary to perform poisoning recovery processing to recover from poisoning. This poisoning recovery process is performed by passing exhaust gas, which has a reduced oxygen concentration while the NOx catalyst has a high temperature (for example, about 600 to 650 ° C.), to the NOx catalyst.

However, since the temperature of the exhaust gas during the lean burn operation is low, it is difficult to raise the temperature of the catalyst to the temperature required to recover SOx poisoning. In such a case, by supplying the fuel into the exhaust gas, it is possible to raise the temperature of the catalyst and reduce the oxygen concentration of the exhaust gas.

For example, in the exhaust gas purification apparatus for an internal combustion engine described in Japanese Patent Laid-Open No. 11-343836, when it is necessary to recover the poisoning of the NOx storage reduction catalyst, the NOx storage reduction catalyst flows into the NOx storage reduction catalyst. While maintaining the air-fuel ratio of the exhaust gas near the stoichiometric air-fuel ratio, the air-fuel ratio is intermittently made smaller than the stoichiometric air-fuel ratio. As a result, most of the time during the recovery of poisoning is maintained at the air-fuel ratio near the stoichiometric air-fuel ratio, so it is possible to suppress the generation of hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas. Become.

Further, by intermittently making the air-fuel ratio smaller than the theoretical air-fuel ratio, the average air-fuel ratio during the poisoning recovery becomes leaner than the theoretical air-fuel ratio, but the sulfur poisoning of the NOx catalyst is recovered. Is possible.

[0008]

In the exhaust gas purification apparatus described in the above publication, when the temperature of the NOx storage reduction catalyst and the amount of stored sulfur oxides satisfy the conditions for starting the poisoning recovery control, the storage reduction type The temperature rise control of the NOx catalyst is performed.

However, the so-called low compression ratio engine (ε <
In 16.5), since the compression end temperature becomes low, if an attempt is made to raise the exhaust gas temperature flowing into the NOx catalyst by a normal method under conditions of low temperature and light load, misfire may occur.

That is, the exhaust gas recirculated by an exhaust gas recirculation device (hereinafter referred to as an EGR device) that reduces intake air to raise the exhaust gas temperature and recirculates a part of the exhaust gas of the exhaust system to the intake system. The amount is increased to suppress a decrease in intake air temperature and exhaust gas temperature, and the unburned fuel component in the exhaust gas is increased by retarding the fuel injection timing. When the NOx storage agent is subjected to oxidation reaction to raise the temperature of the NOx storage agent (hereinafter referred to as temperature raising control),
Combustion of the internal combustion engine becomes extremely unstable, which may cause misfire.

In other words, in the case of a low compression ratio engine, there is a region where the above-mentioned temperature raising control for the NOx catalyst cannot be executed due to misfire.

The present invention has been made to solve the above problems, and even a low compression ratio engine can perform a predetermined temperature rise control under a low temperature and a light load condition without causing misfire. The technical challenge is to provide the technology.

[0013]

In order to achieve the above object, the exhaust gas purifying apparatus for an internal combustion engine of the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine of the present invention stores the NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean and releases the stored NOx when the air-fuel ratio of the inflowing exhaust becomes the stoichiometric air-fuel ratio or rich. And a temperature raising means for controlling temperature rise of the NOx storage agent,
An operating state detecting means for detecting an operating state of the internal combustion engine, a combustion type heater for supplying vaporized fuel to the intake system,
The temperature raising means, when raising the temperature of the NOx storage agent to a predetermined temperature based on the operating state of the internal combustion engine detected by the operating state detecting means, the fuel heated and vaporized by the combustion heater Is supplied to the intake system.

The greatest feature of the present invention is that, in the exhaust gas purification apparatus for an internal combustion engine having a low compression ratio, when it is necessary to raise the temperature of the NOx storage agent under a condition where a misfire is likely to occur, a combustion type heater is used for the intake system. By supplying the vaporized fuel, it is possible to raise the temperature of the NOx storage agent to a required temperature without misfire under any low temperature and light load condition.

In the exhaust gas purifying apparatus for an internal combustion engine thus configured, the vaporized fuel is supplied to the intake system when the temperature raising control is executed. Thus, as a means for raising the temperature of the NOx storage agent, even if control is performed such that the fuel injection is retarded and the amount of fuel that reaches the NOx storage agent unburned is increased,
The occurrence of misfire is effectively suppressed.

The combustion heater is equipped with electronic ignition means,
It is desirable that the electric energy supplied to the electronic ignition means is suppressed and the fuel is heated to a temperature at which it is only vaporized without being ignited. The use of the combustion heater here does not supply the electric energy supplied to the glow, which is an igniter, to the extent to which the fuel burns, but to a certain temperature only when the fuel vaporizes, preferably to about 600 ° C. Only heat it.

Thus, the supplied fuel is vaporized and decomposed and reformed into components on the low boiling point side and supplied to the combustion chamber, so that the main combustion is stabilized and the misfire injection timing retard amount increases. . Therefore, the exhaust temperature can be raised to a higher temperature.

The NOx occluding agent may be carried on a particulate filter for temporarily trapping fine particles in exhaust gas.

Further, when excess oxygen exists in the surroundings, the oxygen is occluded and retained, and when the surrounding oxygen concentration is reduced, the retained oxygen is released as active oxygen. It may be carried on top of which the particulates deposited on the filter are oxidized by the released active oxygen.

The active oxygen releasing agent may be selected from alkali metals, alkaline earth metals, rare earths and transition metals.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, for example, when it is necessary to recover poisoning of the NOx storage agent (catalyst poisoning by hydrocarbons and sulfur oxides), main combustion is performed. While maintaining a stable state, the NOx storage agent is heated to the temperature required for poisoning recovery by the heat of oxidation reaction of the fuel supplied into the exhaust gas. After that, when the operating state of the internal combustion engine shifts to the light load region, the poisoning is recovered.

When the NOx storage agent is carried on a particulate filter (hereinafter referred to as a filter) for temporarily trapping particulates in the exhaust gas, the filter temperature is set to oxidize and remove the particulates trapped by the filter. The temperature raising control for raising the temperature is executed.

As described above, according to the present invention, NO is used for various purposes.
x When it is necessary to raise the temperature of the occlusion agent, the temperature rise control can be executed without stabilizing the main combustion and causing misfire.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings. Here, the case where the exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.

FIG. 1 is a diagram showing a schematic structure of an internal combustion engine and an intake / exhaust system thereof to which the exhaust gas purification apparatus according to this embodiment is applied, and FIG. 2 is a diagram showing details of a combustion heater.

The internal combustion engine 1 shown in FIG. 1 is a 4-cylinder water-cooled 4-cycle diesel engine. An intake branch pipe (not shown) is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe communicates with a combustion chamber of each cylinder via an intake port. The intake branch pipe is connected to the intake pipe 9, and the intake pipe 9 is connected to the air cleaner box 10. In the intake pipe 9 downstream of the air cleaner box 10,
An air flow meter 11 that outputs an electric signal corresponding to the mass of intake air flowing through the intake pipe 9 is attached.

The internal combustion engine 1 is provided with a combustion type multi-purpose heater (hereinafter referred to as a combustion type heater) 60, which will be described.

As shown in FIG. 2, the combustion type heater 60 has an outer cylinder 140, an intermediate cylinder 141 installed in the outer cylinder 140, and an intermediate cylinder 141, and is independent of the internal combustion engine 1. The combustion cylinder 142 for burning the fuel for the internal combustion engine 1 is provided.

The combustion cylinder 142 includes a vaporization glow plug (not shown) for vaporizing the fuel, and an ignition glow plug (not shown) for igniting the fuel vaporized by the vaporization glow plug. is doing. A single glow plug may be used as both the vaporization glow plug and the ignition glow plug.

A combustion gas passage 201 for flowing the combustion gas generated in the combustion cylinder 142 is formed between the intermediate cylinder 141 and the combustion cylinder 142. The intermediate cylinder 14
1, a combustion gas discharge port 145 that connects the combustion gas passage 201 to the outside of the outer cylinder 140.
Are formed.

Next, in the combustion cylinder 142, the fuel introduction pipe 27
Are connected. The fuel introducing pipe 27 is connected to the fuel pump 26 as shown in FIG.
The fuel discharged from No. 6 is supplied to the combustion cylinder 142 via the fuel introduction pipe 27.

On the other hand, the outer cylinder 140 has the combustion cylinder 1
Blower fan 149 for sending combustion air to 42
And a motor 150 that rotationally drives the blower fan 149.
A housing 148 in which is installed is attached.

The housing 148 has an intake port 1 for taking in combustion air into the housing 148.
51 is formed. As shown in FIG. 2, an intake introduction passage 18 is connected to the intake port 151, and the intake introduction passage 18 is connected to an intake pipe 9 downstream of the air cleaner 10.

An on-off valve 29 for opening and closing the flow of intake air in the intake air introduction passage 18 is provided in the middle of the intake air introduction passage 18. An actuator (not shown) configured by a step motor or the like to open and close the on-off valve 29 is attached to the on-off valve 29. By opening and closing the opening / closing valve 29, intake air is sent to the combustion heater 60 when necessary, and the vaporized fuel is mixed with the intake air. Further, the on-off valve 29 is closed during normal operation, and the intake air reaches the internal combustion engine 1 without passing through the combustion heater 60.

On the other hand, an exhaust port 145 is provided at one end of the combustion gas passage 201, and one end of the heater exhaust passage 31 is connected to this exhaust port 145. On the other hand, the other end of the heater exhaust passage 31 is connected to the intake pipe 9 downstream of the intake introduction passage 18.

Further, the outer cylinder 140 and the intermediate cylinder 141
An in-heater cooling water passage 200 for flowing the cooling water of the internal combustion engine 1 is formed between and. The outer cylinder 140 has a cooling water introduction port 143 for taking cooling water into the heater cooling water passage 200 and a cooling water discharge port 144 for discharging cooling water in the heater cooling water passage 200. Has been formed.

As shown in FIG. 2, the cooling water introduction port 143 communicates with a water jacket (not shown) of the internal combustion engine 1 through a cooling water introduction pipe 22, and the cooling water discharge port 144 has the water jacket. And a cooling water discharge pipe 23.

An electric water pump 24 is provided in the middle of the cooling water introducing pipe 22 so that the cooling water flowing in the water jacket of the internal combustion engine 1 is forcibly sent to the cooling water introducing port 143. Has become.

The heater core 30 of the indoor heating device is arranged in the middle of the cooling water discharge pipe 23, and the heat of the cooling water flowing through the cooling water discharge pipe 23 is transferred to the heating air.

Further, the cooling water flowing through the in-heater cooling water passage 200 cools the exhaust gas mixed with the vaporized fuel discharged from the combustion type heater 60, and it can be adjusted so as to reach a predetermined temperature. .

The combustion type heater 60 constructed in this way
Supplies vaporized fuel to the combustion chamber of the internal combustion engine 1,
The internal combustion engine 1 is activated when it is necessary to preheat the main body of the internal combustion engine 1, promote warm-up, improve the performance of the indoor heating device, or the like.

Specifically, in the combustion heater 60, the motor 150 operates the blower fan 149 to supply a part of the intake air flowing in the intake pipe 3 to the combustion cylinder 142 of the combustion heater 60, and the fuel pump 26. However, the fuel in a fuel tank (not shown) is sucked up and supplied to the combustion cylinder 142 of the combustion heater 60. Then, the glow plug of the combustion cylinder 142 is energized, and the mixer of the intake air sent by the blower fan 149 and the fuel supplied by the fuel pump 26 is heated by the glow plug and vaporized.

Here, when vaporized fuel is supplied to the internal combustion engine 1, that is, the particulate filter 2 described later.
When the temperature increase control of 0 is performed, the electric energy supplied to the glow plug is suppressed and the fuel is heated to a temperature of about 600 ° C. such that the fuel is vaporized without being ignited. When the vaporization glow plug and the ignition glow plug are separately provided, the fuel is vaporized and not ignited by energizing only the vaporization glow plug. As a result, the supplied fuel, light oil, is vaporized and decomposed and reformed into components on the low boiling point side and supplied to the combustion chamber, so that main combustion is stabilized.

The fuel vaporized in the combustion cylinder 145 is pushed out of the combustion cylinder 145 into the combustion gas passage 201 by the pressure of the intake air sent out by the blower fan 149, and then discharged from the combustion gas passage 201 into the combustion gas discharge port 145. To be done. The combustion gas discharged to the discharge port 145 is sent to the combustion chamber of the internal combustion engine 1 via the heater exhaust passage 31 and the intake pipe 9.

When the vaporized fuel is not supplied, that is, when warming up at the time of starting the internal combustion engine 1 or circulating cooling water to the heater core 30 is required, the temperature of the glow plug is set to 1,00.
It is heated to near 0 ° C. to vaporize and ignite the fuel and supply air to continuously burn it. In this case, the supplied fuel completely burns, and most of the combustion energy of the fuel is used to raise the temperature of the supplied air.
Therefore, the water pump 24 operates and the internal combustion engine 1
The cooling water in the water jacket is heated by being pumped to the cooling water introduction port 143 of the combustion heater 60.

The cooling water pumped to the cooling water introduction port 143 of the combustion type heater 60 by the water pump 24 is
From the cooling water introduction port 143 to the heater cooling water passage 20
It is guided to 0, passes through the in-heater cooling water passage 200, and is then discharged to the cooling water discharge port 144.

At this time, the heat of the combustion gas flowing in the combustion gas passage 201 is transferred to the cooling water flowing in the heater cooling water passage 200 via the wall surface of the intermediate cylinder 144, and the temperature of the cooling water rises. In this way, the in-heater cooling water passage 200 and the combustion gas passage 201 realize a heat exchange section.

The cooling water thus heated is discharged from the cooling water discharge port 144 to the cooling water discharge pipe 23,
It is returned to the inside of the water jacket of the internal combustion engine 1 via the heater core 30 and circulates in the water jacket. In the heater core 30, a part of the heat of the cooling water is transferred to the heating air to raise the temperature of the heating air.

Further, in FIG. 1, a compressor housing 15a of a centrifugal supercharger (turbocharger) 15 which operates by using heat energy of exhaust gas as a drive source is provided in the intake pipe 9 downstream of the combustion heater 60. The intake pipe 9 downstream of 15a is provided with an intercooler 16 for cooling the intake air that has become hot due to being compressed in the compressor housing 15a.

In the intake system thus constructed, the intake air that has flowed into the air cleaner box 10 is cleaned by the air filter (not shown) in the air cleaner box 10 to remove dust and the like from the intake air and then the intake pipe. 9 through the combustion type heater 60 or not, and flows into the compressor housing 15a.

The intake air flowing into the compressor housing 15a is compressed by the rotation of the compressor wheel installed in the compressor housing 15a. The intake air that has been compressed in the compressor housing 15a and has a high temperature is cooled by the intercooler 16,
If necessary, the flow rate is adjusted by the intake throttle valve 13 to flow into the intake branch pipe. As described above, the intake throttle valve 13 that adjusts the flow rate of the intake air flowing through the intake pipe 9 is provided at the portion located downstream of the compressor housing 15a. The intake throttle valve 13 is provided with an intake throttle actuator 14 configured by a step motor or the like to open and close the intake throttle valve 13.

The intake air that has flowed into the intake branch pipe is distributed to the combustion chamber of each cylinder 2. Then, the fuel injected from the fuel injection valve of each cylinder 2 is used as an ignition source for combustion. When the mixture of vaporized fuel and intake air supplied in the combustion heater 60 is supplied to the combustion chamber, the total of the vaporized fuel and the fuel injected in the combustion chamber should be supplied in the fuel chamber. It is the total amount of fuel.

On the other hand, an exhaust branch pipe is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe communicates with a combustion chamber of each cylinder via an exhaust port (not shown).

The exhaust branch pipe is connected to the turbine housing 15b of the centrifugal supercharger 15. The turbine housing 15b is connected to an exhaust pipe 19, and the exhaust pipe 19 is connected downstream to a muffler (not shown).

In the middle of the exhaust pipe 19, a storage reduction type N
A particulate filter carrying an Ox catalyst (hereinafter,
Simply called a filter. ) 20 are provided. An exhaust temperature sensor 24 that outputs an electric signal corresponding to the temperature of the exhaust gas flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 upstream of the filter 20.

In the exhaust system thus constructed, the air-fuel mixture (burnt gas) burned in each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust branch pipe through the exhaust port, and then the exhaust branch pipe is centrifuged. It flows into the turbine housing 15b of the supercharger 15. The exhaust gas that has flowed into the turbine housing 15b utilizes the thermal energy of this exhaust gas to produce the turbine housing 1
A turbine wheel rotatably supported in 5b is rotated. At that time, the rotational torque of the turbine wheel is transmitted to the compressor wheel of the compressor housing 15a described above.

The exhaust gas discharged from the turbine housing 15b flows into the filter 20 through the exhaust pipe 19 to collect particulates (PM) in the exhaust gas and remove or purify harmful gas components. The exhaust gas from which PM is collected by the filter 20 and the harmful gas components are removed or purified is released into the atmosphere via the muffler.

The exhaust branch pipe and the intake branch pipe communicate with each other through an exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 25 for recirculating a part of exhaust gas flowing in the exhaust branch pipe to the intake branch pipe. Has been done. A solenoid valve or the like is provided in the middle of the EGR passage 25, and the EGR passage is formed in accordance with the magnitude of the applied power.
A flow rate adjusting valve (hereinafter, referred to as an EGR valve) 26 that changes a flow rate of exhaust gas (hereinafter, referred to as an EGR gas) flowing in the passage 25 is provided.

In the exhaust gas recirculation mechanism having such a structure, when the EGR valve 26 is opened, the EGR passage 25 becomes conductive, and a part of the exhaust gas flowing through the exhaust branch pipe flows into the EGR passage 25. Then, it is led to the intake branch pipe.

The EGR gas recirculated from the exhaust branch pipe to the intake branch pipe through the EGR passage 25 is introduced into the combustion chamber of each cylinder while being mixed with the fresh air flowing from the upstream side of the intake branch pipe.

Here, the EGR gas contains an inert gas component such as water (H ₂ O) and carbon dioxide (CO ₂ ) which does not burn by itself and has a high heat capacity. Therefore, when EGR gas is contained in the air-fuel mixture, the combustion temperature of the air-fuel mixture is lowered, and thus nitrogen oxide (NOx)
Is suppressed.

Next, the filter 20 according to this embodiment will be described.

FIG. 3 is a sectional view of the filter 20. FIG. 3A is a diagram showing a lateral cross section of the filter 20. FIG. 3B is a diagram showing a vertical cross section of the filter 20.

As shown in FIGS. 3A and 3B, the filter 20 is of a so-called wall flow type having a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. These exhaust flow passages are composed of an exhaust inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust outflow passage 51 whose upstream end is closed by a plug 53. The hatched portion in FIG. 3A indicates the plug 53. Therefore, the exhaust inflow passages 50 and the exhaust outflow passages 51 are alternately arranged via the thin partition walls 54. In other words, in the exhaust inflow passage 50 and the exhaust outflow passage 51, each exhaust inflow passage 50 is surrounded by four exhaust outflow passages 51, and each exhaust outflow passage 51 includes four exhaust inflow passages 50.
It is arranged to be surrounded by.

The filter 20 is made of a porous material such as cordierite, so that the exhaust gas flowing into the exhaust gas inflow passage 50 flows in the surrounding partition wall 54 as shown by the arrow in FIG. 3 (B). It flows out into the adjacent exhaust outflow passage 51.

In the present invention, a carrier layer made of alumina, for example, is formed on the peripheral wall surfaces of each exhaust inflow passage 50 and each exhaust outflow passage 51, that is, on both side surfaces of each partition wall 54 and on the inner wall surfaces of the pores in each partition wall 54. It is formed, and the NOx storage reduction catalyst is carried on this carrier.

Next, the function of the NOx storage reduction catalyst carried by the filter 20 according to the present embodiment will be described.

The filter 20 uses, for example, alumina as a carrier, and potassium (K) and sodium (N) are deposited on the carrier.
a), an alkali metal such as lithium (Li) or cesium (Cs), an alkaline earth such as barium (Ba) or calcium (Ca), and a rare earth such as lanthanum (La) or yttrium (Y). And at least one of them is carried and a noble metal such as platinum (Pt). In the present embodiment, barium (Ba) and platinum (Pt) are supported on a carrier made of alumina, and ceria (Ce ₂ O ₃ ) having an O ₂ storage capacity is further supported.
An NOx storage reduction catalyst was added.

The NOx catalyst thus constructed stores the nitrogen oxides (NOx) in the exhaust gas when the oxygen concentration of the exhaust gas flowing into the NOx catalyst is high.

On the other hand, the NOx catalyst releases the stored nitrogen oxides (NOx) when the oxygen concentration of the exhaust gas flowing into the NOx catalyst decreases. At that time, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) exists in the exhaust gas, the NOx catalyst converts the nitrogen oxide (NOx) released from the NOx catalyst into nitrogen (N). It can be reduced to ₂ ).

By the way, when the internal combustion engine 1 is in the lean burn operation, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine 1 becomes a lean atmosphere and the oxygen concentration of the exhaust gas becomes high.
Nitrogen oxides (NOx) contained in the exhaust gas will be stored in the NOx catalyst, but if the lean burn operation of the internal combustion engine 1 is continued for a long period of time, the NOx storage capacity of the NOx catalyst will be saturated and Nitrogen oxides (NOx) are not removed by the NOx catalyst and are released into the atmosphere.

In particular, in a diesel engine such as the internal combustion engine 1, a lean air-fuel ratio air-fuel mixture is burned in most operating regions, and the exhaust air-fuel ratio becomes lean air-fuel ratio in most operating regions accordingly. Therefore, N of NOx catalyst
Ox storage capacity is easily saturated.

Therefore, when the internal combustion engine 1 is in the lean burn operation, the oxygen concentration in the exhaust gas flowing into the NOx catalyst is lowered and the concentration of the reducing agent is increased before the NOx storage capacity of the NOx catalyst is saturated, It is necessary to release and reduce nitrogen oxides (NOx) stored in the NOx catalyst.

As a method for reducing the oxygen concentration in this way, fuel addition in the exhaust gas, low temperature combustion as described above, and the cylinder 2
Methods such as fuel injection during the inward expansion stroke are conceivable.

In the present embodiment, the unburned fuel can be supplied into the exhaust gas by performing the sub-injection with a timing delayed from the main injection, separately from the main injection of the fuel in the cylinder 2. As a result, fuel (light oil) as a reducing agent is added to the exhaust gas flowing through the exhaust pipe 19 upstream of the filter 20 to reduce the oxygen concentration of the exhaust gas flowing into the filter 20 and increase the concentration of the reducing agent.

The exhaust gas having a low oxygen concentration formed as described above flows into the filter 20, and the nitrogen oxide (NOx) stored in the filter 20 is released and reduced to nitrogen (N ₂ ). Become.

The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 35 for controlling the internal combustion engine 1. The ECU 35 is a unit that controls the operating state of the internal combustion engine 1 in accordance with the operating conditions of the internal combustion engine 1 and the driver's request.

The ECU 35 has an air flow meter 11,
Various sensors such as the exhaust temperature sensor 24 are connected via electric wiring, and the output signals of the various sensors described above are transmitted to the ECU 35.
It is designed to be input to.

On the other hand, a fuel injection valve, an intake throttle actuator 14, an EGR valve 26, etc. are connected to the ECU 35 via electrical wiring, and the ECU 35 can control the above-mentioned respective parts.

Here, the ECU 35, as shown in FIG. 4, is connected to each other by a bidirectional bus 350, C,
The input port 356 includes a PU 351, a ROM 352, a RAM 353, a backup RAM 354, an input port 356, and an output port 357.
And an A / D converter (A / D) 355 connected to.

The input port 356 inputs the output signals of a sensor that outputs a digital signal format signal such as the crank position sensor 33, and outputs those output signals to C
It is transmitted to the PU 351 and the RAM 353.

Further, the input port 356 is inputted through an A / D 355 which is a sensor that outputs a signal in an analog signal format, such as the air flow meter 11, the exhaust temperature sensor 24, the accelerator opening sensor 36, etc. Those output signals are transmitted to the CPU 351 and the RAM 353.

The output port 357 is connected to the fuel injection valve, the intake throttle actuator 14, the EGR valve 26, the water-cooled exhaust cooler 28, the on-off valve 29, etc. via electrical wiring, and outputs a control signal output from the CPU 351. , To the fuel injection valve, the intake throttle actuator 14, the EGR valve 26, etc. described above.

The ROM 352 is a fuel injection control routine for controlling the fuel injection valve, an intake throttle control routine for controlling the intake throttle valve 13, an EGR control routine for controlling the EGR valve 26, a reducing agent in the filter 20. NOx purification control routine for adding NO to release stored NOx, poisoning recovery control routine for recovering SOx poisoning of the filter 20, particulate combustion control routine for burning and removing particulates collected by the filter 20, etc. It stores the application program of.

The ROM 352 stores various control maps in addition to the above application programs. The control map is, for example, a fuel injection amount control map showing the relationship between the operating state of the internal combustion engine 1 and the basic fuel injection amount (basic fuel injection time), and the relationship between the operating state of the internal combustion engine 1 and the basic fuel injection timing. Fuel injection timing control map shown,
An intake throttle valve opening control map showing the relationship between the operating state of the internal combustion engine 1 and the target opening degree of the intake throttle valve 13, and an EGR showing the relationship between the operating state of the internal combustion engine 1 and the target opening degree of the EGR valve 26.
A valve opening control map, a reducing agent addition control map showing a relationship between an operating state of the internal combustion engine 1 and a reducing agent target addition amount (or a target exhaust air-fuel ratio), and the like.

The RAM 353 stores the output signal from each sensor, the calculation result of the CPU 351 and the like. The calculation result is, for example, an engine speed calculated based on a time interval at which a crank position sensor (not shown) outputs a pulse signal. These data are rewritten to the latest data each time the crank position sensor outputs a pulse signal.

The backup RAM 354 is a non-volatile memory capable of storing data even after the internal combustion engine 1 is stopped.

The CPU 351 operates in accordance with the application program stored in the ROM 352 to perform fuel-injection valve control, intake throttle control, EGR control, N
Ox purification control, poisoning recovery control, particulate combustion control, etc. are executed.

In the poisoning recovery control, the CPU 351
A poisoning recovery process is performed to recover the poisoning of the filter 20 due to the oxide.

Here, sulfur (S) is used as the fuel for the internal combustion engine 1.
When such fuel is burned in the internal combustion engine 1, sulfur oxides (SOx) such as sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) are generated.

Sulfur oxide (SOx) flows into the filter 20 together with exhaust gas and is stored in the filter 20 by the same mechanism as nitrogen oxide (NOx).

Specifically, when the oxygen concentration of the exhaust gas flowing into the filter 20 is high, sulfur oxides (S ₂ ) such as sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) in the inflowing exhaust gas are included.
Ox) is oxidized on the surface of platinum (Pt) and stored in the filter 20 in the form of sulfate ions (SO ₄ ²⁻ ). Furthermore,
The sulfate ions (SO ₄ ²⁻ ) stored in the filter 20 are
Sulfate (BaS) combined with barium oxide (BaO)
O ₄ ) is formed.

By the way, sulfate (BaSO ₄ ) is more stable and less likely to decompose than barium nitrate (Ba (NO ₃ ) ₂ ), and is decomposed even when the oxygen concentration of the exhaust gas flowing into the filter 20 becomes low. Instead, they remain in the filter 20.

Sulfate in the filter 20 (BaS
As the amount of O ₄ ) increases, the nitrogen oxides (N
Barium oxide (B) that can participate in the storage of Ox)
Since the amount of aO) decreases, so-called SOx poisoning occurs in which the NOx storage capacity of the filter 20 decreases.

As a method for recovering SOx poisoning of the filter 20, the ambient temperature of the filter 20 is raised to a high temperature range of about 600 to 650 ° C. and the oxygen concentration of the exhaust gas flowing into the filter 20 is lowered. ,
Barium sulfate (BaSO) stored in the filter 20
₄₎ the SO ₃ ^- and SO ₄ ^- and pyrolyzed, followed by SO ₃ ^- and SO ₄
^- it can be exemplified a method of reducing the ^- is reacted with a hydrocarbon in the exhaust gas (HC) and carbon monoxide (CO) gaseous SO ₂ and.

Therefore, in the poisoning recovery process according to the present embodiment, the CPU 351 first executes the catalyst temperature raising control for raising the bed temperature of the filter 20, and then lowers the oxygen concentration of the exhaust gas flowing into the filter 20. .

In the catalyst temperature raising control, the CPU 351 first determines if the sulfur poisoning recovery should be performed, that is,
This control is started when a flag indicating that these controls should be executed is set.

In the case of sulfur poisoning regeneration, the condition for starting is determined by the fuel consumption integrated amount, the output signal from the NOx sensor (not shown), the traveling distance of the vehicle, and the like.
Here, since the NOx storage reduction catalyst carried on the filter 20 is poisoned by the sulfur component in the fuel, the integrated consumption amount of fuel is stored in the RAM 353, and when the addition amount of this fuel reaches a predetermined amount, It may be used as a start condition for the sulfur poisoning recovery control. Further, as sulfur poisoning progresses, NO
The amount of NOx absorbed by the x catalyst decreases, and the amount of NOx flowing downstream of the filter 20 increases. Therefore, a NOx sensor (not shown) may be provided downstream of the filter 20, the output signal thereof may be monitored, and the condition for starting the sulfur poisoning recovery control may be set when the NOx flow amount exceeds a predetermined amount. Further, when the vehicle travel distance becomes equal to or greater than the predetermined value, it is determined that the sulfur poisoning needs to be recovered, and at this time, the sulfur poisoning recovery control flag is set.

When this flag is set, the CPU 3
First, 51 identifies the operating state of the internal combustion engine 1 based on the information from the accelerator opening sensor 36 and the crank position sensor 33. When the operating state of the internal combustion engine 1 is a light load, the combustion heater 60 is operated to open the on-off valve 29 to send vaporized fuel (light oil) to the intake pipe 9 and supply it to the combustion chamber. At the same time, the timing of fuel injection in each cylinder is retarded. By delaying the fuel injection timing in this way, it is possible to increase the amount of fuel supplied into the exhaust gas as an unburned component without burning in the cylinder.

FIG. 5 is a diagram showing a comparison between the case where vaporized fuel (combustible gas) is supplied to the combustion chamber by the combustion heater 60 and the case where this is not supplied. Here, when the vaporized fuel is not supplied, the exhaust temperature is 400 ° C or lower, but by supplying this, the exhaust temperature is about 600 ° C.
You can see that it can be raised to.

When the temperature of the mixture of vaporized fuel and intake air that has passed through the combustion heater 60 is equal to or higher than a predetermined temperature, it is controlled and cooled by adjusting the amount of cooling water flowing through the in-heater cooling water passage 200.

The reason why the exhaust temperature rises as described above is as follows.
This is because the misfire limit when the fuel injection timing is retarded is expanded to the side away from the top dead center, and a large amount of high temperature unburned fuel components will be present in the exhaust gas. The unburned fuel components are oxidized in the filter 20, and the heat generated during the oxidation raises the bed temperature of the filter 20.

Further, in addition to the above method, the CPU 351 is provided with a reducing agent injection valve (not shown) in the exhaust passage 19 and injects fuel from the reducing agent injection valve in the filter 20 in the catalyst temperature raising control. The fuel may be oxidized and the heat generated at that time may increase the temperature rise of the filter 20. At this time, the injection amount of the fuel injected from the reducing agent injection valve is set so that the injection interval is shorter than the fuel injection performed at the time of NOx release / reduction and the air-fuel ratio at that time is higher.

However, if the temperature of the filter 20 rises excessively,
Since the heat deterioration of the filter 20 may be induced, it is preferable that the secondary injection fuel amount and the additional fuel amount be feedback-controlled based on the output signal value of the exhaust temperature sensor 24.

When the bed temperature of the filter 20 rises to a high temperature range of, for example, 630 ° C. by the catalyst temperature increasing method as described above, the CPU 351 causes the fuel in the exhaust gas to decrease the oxygen concentration of the exhaust gas flowing into the filter 20. Supply.

If excessive fuel is supplied, the fuel may rapidly burn in the filter 20 to overheat the filter 20, or the excessive fuel may unnecessarily cool the filter 20. It is preferable that the CPU 351 feedback-control the fuel supply amount based on the output signal of the air-fuel ratio sensor (not shown).

When the poisoning recovery process is executed in this way,
When the bed temperature of the filter 20 is high, the oxygen concentration of the exhaust gas flowing into the filter 20 becomes low, so that barium sulfate (BaSO ₄ ) stored in the filter 20 is thermally decomposed into SO ₃ ⁻ and SO ₄ ^−. , SO ₃ ⁻ and SO ₄ ⁻ react with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas and are reduced, so that SOx poisoning of the filter 20 is restored.

Next, the CPU 351 controls the exhaust temperature sensor 2
The output signal of No. 4 is read and the temperature of the filter 20 is estimated. The temperature of the filter 20 is estimated from the intake air amount (output signal of the air flow meter 11), the rotation speed, the load, the fuel injection amount, and the like. Further, the temperature of the filter 20 may be obtained by mapping a value obtained by an experiment in advance. Further, a temperature sensor may be provided in the filter 20 to directly measure the temperature of the filter 20.

In this way, the calculated actual temperature is compared with the target temperature of the filter 20 (for SOx poisoning recovery, for example, 630 ° C.). Then, when the actual filter 20 temperature is higher than the target temperature, the fuel addition amount is reduced, while when the actual filter 20 temperature is lower than the target temperature, the fuel addition amount is increased. .

In the low load region, the temperature of the filter 20 is maintained at 630 ° C., which is required for SOx poisoning recovery, so that the SOx poisoning recovery can be started immediately.

When the temperature of the filter 20 is raised to the predetermined temperature in this way, the oxygen concentration is reduced as described above to recover the SOx poisoning. <Other Embodiments> In the above-described embodiment, as an example of the temperature raising control, the case of SOx poisoning recovery of the NOx storage agent carried on the filter 20 has been described, but the temperature raising control raises the temperature of the filter 20. It is not limited to this, and the particles in the exhaust gas captured by the filter 20 may be removed from the filter 20 in some cases.

The filter 20 has a catalyst supported on the surface in contact with the exhaust gas, and can lower the ignition temperature of the fine particles by the catalytic action and burn and remove the fine particles at a relatively low temperature. As such a filter, for example, a filter carrying a mixture of a white metal metal and an alkaline earth metal oxide is known. With this filter, almost 350
The fine particles can be ignited at a relatively low temperature of about 400 ° C. to 400 ° C., and can be continuously burned.

However, if particles are deposited on the filter 20 one after another, the filter may be clogged. In this case, it is necessary to burn and remove the particulates at an appropriate time when the particulate deposition amount is relatively small so that the filter is not damaged by the temperature rise due to the rapid combustion of the particulates. In that case, filter 2
0 is raised to about 600 ° C. to perform filter regeneration control for burning and removing fine particles.

In this filter regeneration control, the CPU 351
However, it is determined whether or not the particulates need to be oxidized and removed (hereinafter referred to as filter regeneration). In this case, for example, the exhaust pipe 1 before and after the filter 20 detected by a differential pressure sensor (not shown)
When the differential pressure in 9 becomes a predetermined value or more, the filter 20
It can be presumed that a certain amount or more of fine particles were deposited on the surface. In this way, if a certain amount of fine particles or more are deposited, the filter regeneration control flag is set.

If this flag is set, the CPU
351 executes temperature raising control to raise the filter bed temperature to a temperature range in which fine particles can burn. This specific method is the same as the method described in the previous embodiment. In this way, the bed temperature of the filter 20 is raised to the predetermined temperature.

When such filter regeneration control is executed, the particulates accumulated on the filter 20 are burned and removed from the filter 20 to regenerate the particulate collecting ability of the filter 20.

As described above, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, when the temperature raising control for the filter 20 is executed, the fuel vaporized by the combustion heater 60 is placed in the combustion chamber of the internal combustion engine 1. Since it can be sent, even if the intake is throttled during the temperature rise control and the fuel injection in the combustion chamber is retarded, it is possible to prevent the combustion from becoming unstable and to prevent misfire.

[0118]

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, misfire is suppressed even when the intake throttle and the fuel injection are retarded in a low compression ratio engine at a low temperature and a light load. Predetermined temperature rise control for the exhaust gas purification device is possible.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an internal combustion engine and an intake / exhaust system thereof to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied.

FIG. 2 is a schematic configuration diagram of a combustion heater.

FIG. 3A is a view showing a lateral cross section of the particulate filter. (B) is a figure which shows the longitudinal cross section of a particulate filter.

FIG. 4 is a block diagram showing an internal configuration of an ECU.

FIG. 5 is a diagram showing a relationship between an exhaust temperature and a misfire limit.

[Explanation of symbols]

1 ... Internal combustion engine 9 ... Intake pipe 18 ... Exhaust gas introduction passage 19 ... Exhaust pipe 20 ... Particulate filter 24 ... Exhaust gas temperature sensor 25 ... EGR passage 26 ... EGR valve 30: Heater core 31 ... Heater exhaust passage 35 ... ECU 60 ... Combustion heater

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01J 20/34 F01N 3/02 321A F01N 3/02 321 321B 321G 3/08 A 3/08 3/10 A 3/10 3/28 301C 3/28 301 B01D 46/42 B F02M 31/06 F02M 31/06 A // B01D 46/42 B01D 53/36 101B 103B 103C (72) Inventor Shinobu Ishiyama Toyota City, Aichi Prefecture Toyota Town No. 1 Toyota Motor Co., Ltd. (72) Inventor Naofumi Kumata No. 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Masaaki Kobayashi No. 1 Toyota Town, Aichi Prefecture Toyota Motor Corporation Stock In-company (72) Inventor Daisuke Shibata 1 Toyota-cho, Toyota-shi, Aichi Toyota Automobile Co., Ltd. (72) Inventor Takahiro Oha Toyota Town, Toyota City, Chichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Akihiko Negami 1 Toyota Town, Toyota City, Aichi Toyota Motor Co., Ltd. F Term (reference) 3G090 AA03 BA01 DA04 DA09 DA10 DA12 DA13 DA18 DA20 EA04 EA05 EA06 EA07 3G091 AA02 AA10 AA11 AA18 AA28 AB06 AB13 BA00 BA11 BA14 BA32 BA33 CA13 CB07 CB08 DA01 DA02 DB10 EA01 EA05 EA07 EA15 EA17 EA32 EA34 FA02 FA04 FA12 FA13 FB02 FB10 FB11 FB12 FC02 FC07 GA06 GA16 GA20 GA23 GB01W GB02W GB03W GB04W GB05W GB06W GB10W GB16X GB17X HA14 HA36 HA39 HA42 HB03 HB05 HB06 4D048 AA06 AA14 AB01 AB02 BA10X BA14X BA15X BA18X BA19X BA30X BA41X BB02 BB14 CC52 CD05 DA01 DA02 DA03 DA06 DA13 DA20 EA04 4D058 JA32 JB03 JB06 MA44 SA08 4G066 AA13A AA13B AA16A AA16B AA20C AA37A AA37B BA07 BA22 CA23 CA28 CA37 DA02 GA01 GA06

Claims (5)

[Claims] 1. A NOx storage agent that stores NOx in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and releases and reduces the stored NOx when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich; The temperature raising means includes a temperature raising means for controlling the temperature rise of the storage agent, an operating state detecting means for detecting an operating state of the internal combustion engine, and a combustion heater for supplying vaporized fuel to the intake system. However, when the NOx storage agent is heated to a predetermined temperature based on the operating state of the internal combustion engine detected by the operating state detection means, the fuel heated by the combustion heater and vaporized is supplied to the intake system. An exhaust emission control device for an internal combustion engine, characterized by: 2. The combustion heater comprises an electronic ignition means,
The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the electric energy supplied to the electronic ignition means is suppressed and the fuel is heated to a temperature at which it is vaporized without ignition. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the NOx storage agent is carried by a particulate filter for temporarily trapping particulates in the exhaust gas. 4. A filter for an active oxygen-releasing agent which occludes oxygen and retains oxygen when excess oxygen is present in the surroundings, and releases the retained oxygen as active oxygen when the ambient oxygen concentration decreases. The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 3, wherein the exhaust gas is carried on the surface of the filter, and the fine particles deposited on the filter are oxidized by the released active oxygen. 5. The exhaust gas purification device for an internal combustion engine according to claim 4, wherein the active oxygen releasing agent is selected from an alkali metal, an alkaline earth metal, a rare earth or a transition metal.