JP3525860B2 - Exhaust gas purification device for internal combustion engine - Google Patents

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 Particulates containing soot as a main component are contained in the exhaust gas of an internal combustion engine, especially a diesel engine. Since particulates are harmful substances, it has been proposed to place a filter in the engine exhaust system to collect particulates before they are released into the atmosphere. In such a filter, it is necessary to burn off the collected particulates in order to prevent an increase in exhaust resistance due to clogging.

In such filter regeneration, the particulates ignite and burn at about 600 ° C., but the exhaust gas temperature of the diesel engine is normally 6
It is considerably lower than 00 ° C, and usually means such as heating the filter itself is required. An electric heater is generally used as this heating means, but a large amount of electric power is required to heat the filter to about 600 ° C.

In Japanese Examined Patent Publication No. 7-106290, when a platinum group metal and an alkaline earth metal oxide are supported on a filter, the particulate matter on the filter is about the exhaust gas temperature at a normal time of a diesel engine. It is disclosed that it burns out continuously at 400 ° C.

[0005]

However, even if the above-mentioned filter is used, the exhaust gas temperature is always 400 ° C.
However, the diesel engine may release a large amount of particulates depending on the operating conditions, and particulates that could not be burned off may gradually accumulate on the filter at each time. is there.

When a certain amount of particulates are accumulated in this filter, the ability of burning out particulates is extremely lowered, and the filter can no longer be regenerated by itself. As described above, if the filter of this type is simply arranged in the engine exhaust system, clogging may occur relatively early.

Therefore, an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine which can prevent clogging due to trapped particulates in a particulate filter without consuming a large amount of electric power by an electric heater. Is.

[0008]

An exhaust gas purification apparatus for an internal combustion engine according to claim 1 of the present invention includes a particulate filter arranged in an engine exhaust system, and an electric heater for heating the particulate filter. And a reversing means for reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter, wherein the particulate filter has a collection wall for collecting the particulates, An active oxygen-releasing agent is carried on the wall, the collection wall has a first collection surface and a second collection surface, and the exhaust upstream side and the exhaust downstream side of the particulate filter by the reversing means. There by being reversed, the said first collecting surface of the collecting wall and said second trapping surface are used alternately to trap particulate matter, said Patikyu
The rate filter uses the active oxygen-releasing agent to remove the powder.
Oxygen can be removed depending on the temperature of the particulate filter.
It has a particle amount, and the current amount of fine particles emitted from the engine combustion chamber
When the current amount of fine particles that can be removed by oxidation will be exceeded
In addition, the electric heater is operated .

[0009]

[0010]

According to a second aspect of the present invention, there is provided an exhaust gas purification device for an internal combustion engine, which is a patty arranged in an engine exhaust system.
A particulate filter and the particulate filter
And an electric heater for heating the
To reverse the exhaust upstream side and exhaust downstream side of the filter
And a reversing means, the particulate filter
Has a collection wall for collecting particulates,
The collecting wall carries an active oxygen releasing agent, and the collecting wall
Has a first collecting surface and a second collecting surface, and
Therefore, the exhaust gas upstream side of the particulate filter and the exhaust gas
By reversing the air downstream side, the particulates
To collect the first collection surface and the first collection surface of the collection wall.
The two collection surfaces are alternately used, and the particulate filter has an amount of fine particles that can be removed by oxidation according to the temperature of the particulate filter by the active oxygen releasing agent, and the current exhaust gas state is currently required. When the amount of fine particles that can be removed by oxidation is to be reduced, the electric heater is operated.

According to a third aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the first or second aspect , wherein the exhaust gas bypasses the particulate filter. It is characterized in that the enabling bypass means is provided integrally with or separately from the reversing means, and at the time of operating the electric heater, at least a part of the exhaust gas is bypassed by the bypass means.

According to a fourth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the third aspect , wherein the bypass means adjusts the amount of exhaust gas to be bypassed. The temperature of the particulate filter heated by the electric heater is controlled.

According to a fifth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine, wherein the exhaust gas purification apparatus for an internal combustion engine according to the first or second aspect is reduced to an oxidation catalyst carried on the particulate filter. It is characterized by comprising a reducing agent supply device for supplying the agent.

According to a sixth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the fifth aspect , wherein the electric heater is operated to control the temperature of the particulate filter. The reducing agent is supplied to the oxidation catalyst by the reducing agent supply device when the temperature exceeds a preset temperature.

[0016]

1 is a schematic vertical sectional view of a four-stroke diesel engine equipped with an exhaust emission control device according to the present invention, and FIG. 2 is an enlarged vertical sectional view of a combustion chamber of the diesel engine of FIG. 3 is a bottom view of the cylinder head of the diesel engine of FIG. 1 to 3, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5a is a cavity formed on the top surface of the piston 4, and 5 is formed in the cavity 5a. A combustion chamber, 6 an electrically controlled fuel injection valve, 7 a pair of intake valves, 8 an intake port, 9 a pair of exhaust valves, and 10 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 an air cleaner 14 via an intake duct 13. A throttle valve 16 driven by an electric motor 15 is arranged in the intake duct 13. On the other hand, the exhaust port 10 is connected to the exhaust manifold 17.

As shown in FIG. 1, the exhaust manifold 17
An air-fuel ratio sensor 21 is arranged inside. The exhaust manifold 17 and the surge tank 12 are connected to each other via an EGR passage 22, and an electric control type EGR is provided in the EGR passage 22.
A control valve 23 is arranged. A cooling device 24 for cooling the EGR gas flowing in the EGR passage 22 is arranged around the EGR passage 22. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 24, 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 26, via a fuel supply pipe 25. Fuel is supplied into the common rail 26 from an electrically controlled variable fuel discharge fuel pump 27, and the fuel supplied into the common rail 26 is supplied to the fuel injection valve 6 via each fuel supply pipe 25. A fuel pressure sensor 28 for detecting the fuel pressure in the common rail 26 is attached to the common rail 26, and the fuel pump 27 so that the fuel pressure in the common rail 26 becomes a target fuel pressure based on the output signal of the fuel pressure sensor 28. Is controlled.

An electronic control unit 30 receives the output signal of the air-fuel ratio sensor 21 and the output signal of the fuel pressure sensor 28. Further, a load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, an output signal of the load sensor 41 is also input to the electronic control unit 30, and a crankshaft is further provided. For example, the output signal of the crank angle sensor 42, which generates an output pulse each time it rotates by 30 °, is also input. In this way, the electronic control unit 30 is based on various signals, the fuel injection valve 6, the electric motor 15, the EGR control valve 2
3 and the fuel pump 27 is operated.

As shown in FIGS. 2 and 3, in the embodiment according to the present invention, the fuel injection valve 6 comprises a hole nozzle having six nozzle openings, and the nozzle opening of the fuel injection valve 6 faces slightly downward with respect to the horizontal plane. Fuel F is injected at equal angular intervals. As shown in FIG. 3, two of the six fuel sprays F are scattered along the lower side surface of the valve body of each exhaust valve 9. 2 and 3 show the case where fuel injection is performed at the end of the compression stroke. At this time, the fuel spray F advances toward the inner peripheral surface of the cavity 5a and is then ignited and burned.

FIG. 4 shows a case where additional fuel is injected from the fuel injection valve 6 when the lift amount of the exhaust valve 9 is maximum during the exhaust stroke. That is, as shown in FIG. 5, the main injection Qm is performed near the compression top dead center, and then the additional fuel Qa is injected in the middle of the exhaust stroke. In this case, the fuel spray F advancing in the valve body direction of the exhaust valve 9 goes between the rear surface of the cap portion of the exhaust valve 9 and the exhaust port 10. In other words, in other words, two of the six nozzle openings of the fuel injection valve 6 discharge the fuel spray F when the additional fuel Qa is injected when the exhaust valve 9 is open. It is formed so as to face between the rear surface of the bulb portion of the valve 9 and the exhaust port 10. In the embodiment shown in FIG. 4, at this time, the fuel spray F collides with the rear surface of the bulge portion of the exhaust valve 9, and the fuel spray F that collides with the rear surface of the bulge portion of the exhaust valve 9 is reflected on the rear surface of the bulge portion of the exhaust valve 9. Then, it goes into the exhaust port 10.

Normally, the additional fuel Qa is not injected,
Only the main injection Qm is performed. FIG. 6 shows changes in the output torque when the air-fuel ratio A / F (horizontal axis in FIG. 6) is changed by changing the opening degree of the throttle valve 16 and the EGR rate during engine low load operation, and smoke, HC , C
An example of an experiment showing changes in the amounts of O and NO _x emissions is shown.
As can be seen from FIG. 6, in this experimental example, the EGR rate increases as the air-fuel ratio A / F decreases, and the theoretical air-fuel ratio (≈1
When it is 4.6) or less, the EGR rate is 65% or more.

As shown in FIG. 6, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the EGR rate becomes around 40%, and when the air-fuel ratio A / F reaches about 30, smoke is generated. The amount of generation begins to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is made smaller, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke sharply decreases this time, the EGR rate is increased to 65% or more, and the smoke becomes almost zero when the air-fuel ratio A / F is around 15.0. . That is, soot is hardly generated. At this time, the output torque of the engine slightly decreases, and N
The amount of O _x generated is considerably low. On the other hand, at this time, the amounts of HC and CO generated start to increase.

FIG. 7 (A) shows the change in combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of smoke is the largest, and FIG. 7 (B) shows the air-fuel ratio A / F. It shows a change in the combustion pressure in the combustion chamber 5 when F is around 18 and the amount of smoke generated is almost zero. As can be seen by comparing FIG. 7 (A) and FIG. 7 (B), in the case of FIG. 7 (B) where the amount of smoke generated is almost zero, the amount of smoke generated is large.
It can be seen that the combustion pressure is lower than in the case shown in (A).

From the experimental results shown in FIGS. 6 and 7, the following can be said. That is, first of all, the air-fuel ratio A / F is 1
When the amount of smoke generated is 5.0 or less and the amount of smoke is almost zero, FIG.
As shown in (3), the amount of NO _x generated is considerably reduced. N
The decrease in the amount of generated O _x means that the combustion temperature in the combustion chamber 5 is decreased, and therefore, when the soot is hardly generated, the combustion temperature in the combustion chamber 5 is decreased. I can say. The same can be said from FIG. 7. That is, the combustion pressure is low in the state shown in FIG. 7 (B) in which almost no soot is generated.
The combustion temperature inside is low.

Secondly, when the amount of smoke produced, that is, the amount of soot produced, becomes almost zero, as shown in FIG. 6, HC and CO
Emissions will increase. This means that hydrocarbons are discharged without growing to soot. That is, linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 8 are thermally decomposed to form soot precursors when the temperature is raised in a state of oxygen deficiency, and then mainly soot is formed. Soot consisting of a solid with carbon atoms gathered is produced. In this case, the actual soot formation process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. After that, it will grow to soot. Therefore, as described above, when the amount of soot generated becomes almost zero, the amounts of HC and CO emissions increase as shown in FIG. 6, but at this time, HC is a soot precursor or a hydrocarbon in the state before it. .

Summarizing these considerations based on the experimental results shown in FIGS. 6 and 7, the soot generation amount becomes almost zero when the combustion temperature in the combustion chamber 5 is low, and at this time, the soot precursor or the soot precursor The hydrocarbons in this state are discharged from the combustion chamber 5. As a result of further detailed experimental research on this, when the temperature of the fuel and the gas around it in the combustion chamber 5 is below a certain temperature, the soot growth process stops halfway, that is, the soot is generated. It was found that soot was not generated at all and soot was generated when the temperature of the fuel in the combustion chamber 5 and its surroundings fell below a certain temperature.

By the way, the temperature of the fuel and its surroundings when the hydrocarbon production process is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature depends on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. It cannot be said how many times it changes, but this certain temperature has a deep relationship with the amount of NO _x produced, and therefore this certain temperature is defined to some extent from the amount of NO _x produced. be able to. That is, as the EGR rate increases, the temperature of the fuel during combustion and the gas around it decreases, and the amount of NO _x generated decreases. At this time, soot is hardly generated when the amount of NO _x generated is about 10 p.pm or less. Therefore, the above certain temperature is NO
It is almost the same as the temperature when the amount of _x generation is around 10 p.pm or less.

Once soot is produced, this soot cannot be purified by a post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in the state before it can be easily purified by a post-treatment using a catalyst having an oxidizing function. Thus, reducing the amount of NO _x generated and discharging hydrocarbons from the combustion chamber 5 in the state of precursor of soot or in the state before it is extremely effective for purification of exhaust gas.

Now, in order to stop the growth of hydrocarbons before the soot is generated, the temperature of the fuel and the gas around it in the combustion chamber 5 during combustion is set to a temperature lower than the temperature at which the soot is generated. It needs to be suppressed. In this case, it has been found that, in order to suppress the temperature of the fuel and the gas around it, the endothermic action of the gas around the fuel when the fuel burns has an extremely large effect.

That is, if only air exists around the fuel, the evaporated fuel immediately reacts with oxygen in the air and burns. In this case, the temperature of the air separated from the fuel does not rise so much, and only the temperature around the fuel locally becomes extremely high. That is, at this time, the air separated from the fuel hardly absorbs the combustion heat of the fuel. In this case, since the combustion temperature locally becomes extremely high, the unburned hydrocarbons that have received this heat of combustion generate soot.

On the other hand, the situation is slightly different when the fuel is present in a mixed gas of a large amount of inert gas and a small amount of air.
In this case, the evaporated fuel diffuses into the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, the combustion heat is absorbed by the surrounding inert gas, so that the combustion temperature does not rise so much. That is, the combustion temperature can be kept low. That is, the presence of the inert gas plays an important role in suppressing the combustion temperature, and the combustion temperature can be suppressed low by the endothermic action of the inert gas.

In this case, in order to suppress the temperature of the fuel and the gas around it to a temperature lower than the temperature at which soot is generated, an amount of inert gas sufficient to absorb the amount of heat required to do so is required. . Therefore, if the fuel amount increases, the required amount of inert gas also increases accordingly. In this case, the larger the specific heat of the inert gas, the stronger the endothermic action. Therefore, the inert gas is preferably a gas having a large specific heat. In this respect, since CO ₂ and EGR gas have a relatively large specific heat, it can be said that it is preferable to use EGR gas as the inert gas.

FIG. 9 shows the relationship between the EGR rate and smoke when EGR gas is used as the inert gas and the cooling degree of the EGR gas is changed. That is, the curve A in FIG. 9 strongly cools the EGR gas to bring the EGR gas temperature to about 9
The curve B shows the case where the EGR gas is cooled by a small cooling device, and the curve C shows the case where the EGR gas is not forcibly cooled.

As shown by the curve A in FIG. 9, when the EGR gas is strongly cooled, the soot generation amount reaches a peak when the EGR rate is slightly lower than 50%, and in this case, the EGR rate is almost 55. Almost no soot is generated if the percentage is exceeded. On the other hand, as shown by the curve B in FIG. 9, when the EGR gas is slightly cooled, the soot generation amount reaches a peak when the EGR rate is slightly higher than 50%, and in this case, the EGR rate is approximately 65% or more. If so, soot is hardly generated.

Further, as shown by the curve C in FIG. 9, EG
When the R gas is not forcibly cooled, the EGR rate is 5
The soot generation amount peaks near 5%, and in this case, if the EGR rate is set to approximately 70% or more, soot is hardly generated. Note that FIG. 9 shows the amount of smoke generated when the engine load is relatively high. When the engine load decreases, the EGR rate at which the amount of soot generated reaches a peak slightly decreases, and soot hardly occurs. The lower limit of is also slightly lowered. Thus, the lower limit of the EGR rate at which soot is hardly generated changes depending on the cooling degree of EGR gas and the engine load.

FIG. 10 shows a mixture of EGR gas and air required to bring the temperature of the fuel and its surrounding gas at the time of combustion to a temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas. The amount of gas, the ratio of air in this mixed gas amount, and the ratio of EGR gas in this mixed gas are shown. In addition, in FIG. 10, the vertical axis represents the total intake gas amount sucked into the combustion chamber 5, and the chain line Y represents the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. ing. In addition, the horizontal axis represents the required load, and Z1 represents the low load operation region.

Referring to FIG. 10, the ratio of air, that is, the amount of air in the mixed gas, shows the amount of air required to completely burn the injected fuel. That is, in the case shown in FIG. 10, the ratio between the air amount and the injected fuel amount is the theoretical air-fuel ratio. On the other hand, in FIG. 10, the ratio of the EGR gas, that is, the amount of the EGR gas in the mixed gas makes the temperature of the fuel and its surrounding gas lower than the temperature at which soot is formed when the injected fuel is burned. Minimum required EGR
The amount of gas is shown. This EGR gas amount is approximately 55% or more in terms of EGR rate, and is 70% or more in the embodiment shown in FIG. That is, the total amount of intake gas drawn into the combustion chamber 5 is shown by the solid line X in FIG.
When the ratio of the air amount to the EGR gas amount of the total intake gas amount X is set to the ratio shown in FIG. 10, the temperature of the fuel and the gas around it becomes lower than the temperature at which soot is generated. Soot will not occur at all. Further, the NO _x generation amount at this time is around 10 p.pm or less, so that the NO _x generation amount is extremely small.

When the fuel injection amount increases, the amount of heat generated when the fuel burns increases. Therefore, in order to maintain the temperature of the fuel and the gas around it at a temperature lower than the temperature at which soot is generated, heat generated by the EGR gas is used. The amount of absorption must be increased. Therefore, as shown in FIG. 10, the EGR gas amount must be increased as the injected fuel amount is increased. That is, the EGR gas amount needs to increase as the required load increases.

On the other hand, in the load region Z2 of FIG. 10, the total intake gas amount X required to prevent the generation of soot exceeds the total intake gas amount Y that can be inhaled. Therefore, in this case, in order to supply the total intake gas amount X required to prevent the generation of soot into the combustion chamber 5, both the EGR gas and the intake air, or E
It is necessary to supercharge or pressurize the GR gas. When the EGR gas or the like is not supercharged or pressurized, the total intake gas amount X matches the total intakeable gas amount Y in the load region Z2. Therefore, in this case, in order to prevent the generation of soot, the air amount is slightly decreased to increase the EGR gas amount and the fuel is burned under the rich air-fuel ratio.

As described above, FIG. 10 shows that the fuel is stoichiometric.
Fig. 10 shows the case of combustion under
FIG. 10 shows the air flow rate in the low load operating range Z1.
Less than the amount of air
NO while preventing the generation of soot _x10p.p.m before
Can be later or less and is also shown in FIG.
In the low load area Z1
Even if it is larger than the air volume, that is, the average value of the air-fuel ratio from 17
Even if it is lean, NO while preventing the generation of soot_xFrom
The yield can be around 10p.p.m or less
It

That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excessive fuel does not grow to soot, and soot is generated. There is no. Further, at this time, a very small amount of NO _x is generated. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature becomes high, but in the present invention the combustion temperature is suppressed to a low temperature, soot Not generated at all. Furthermore, NO _x
Also produces only a very small amount.

Thus, in the engine low load operation region Z1, soot is generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean. Therefore, the amount of NO _x generated is extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time.

By the way, the temperature of the fuel and the gas around it during combustion in the combustion chamber can be suppressed below the temperature at which the growth of hydrocarbons stops halfway only when the calorific value due to combustion is relatively low and the engine load is relatively low. To be Therefore, in the embodiment according to the present invention, when the engine load is relatively low, the temperature of the fuel and the gas around it during combustion is suppressed below the temperature at which the growth of hydrocarbons stops halfway, and first combustion, that is, low temperature combustion is performed. When the engine load is relatively high, the second combustion, that is, the combustion that is more commonly performed than the conventional one is performed. It should be noted that here, the first combustion, that is, the low temperature combustion, as is clear from the above description, the amount of inert gas in the combustion chamber is larger than the worst amount of inert gas in which the amount of soot is maximized, and soot is almost generated. Second combustion, that is, combustion that is more commonly performed than before, is combustion that has less inert gas in the combustion chamber than the worst inert gas that produces maximum soot. Say

FIG. 11 shows a first operating region I in which the first combustion, that is, low temperature combustion is performed, and a second combustion region II in which the second combustion, that is, combustion by the conventional combustion method is performed. In FIG. 11, the vertical axis L indicates the accelerator pedal 40.
Represents the amount of depression, that is, the required load, and the horizontal axis N represents the engine speed. Further, in FIG. 11, X (N) indicates the first boundary between the first operating region I and the second operating region II, and Y (N) indicates the first operating region I and the second operating region II. A second boundary with region II is shown. First operating area I
Determination of the operating range from the second operating range II to the second operating range II is performed based on the first boundary X (N), and the change of the operating range from the second operating range II to the first operating range I is determined. It is performed based on the second boundary Y (N).

That is, the operating condition of the engine is the first operating region I.
If the required load L exceeds the first boundary X (N) which is a function of the engine speed N during low temperature combustion, it is determined that the operating region has moved to the second operating region II. Combustion is performed by a conventional combustion method. Next, when the required load L becomes lower than the second boundary Y (N) which is a function of the engine speed N, it is determined that the operating region has moved to the first operating region I, and low temperature combustion is performed again.

FIG. 12 shows the output of the air-fuel ratio sensor 21. As shown in FIG. 12, the output current I of the air-fuel ratio sensor 21 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 21. Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG.

FIG. 13 shows the opening of the throttle valve 16, the opening of the EGR control valve 23, the EGR rate, the air-fuel ratio, the injection timing and the injection amount with respect to the required load L. As shown in FIG. 13, in the first operating region I where the required load L is low, the opening degree of the throttle valve 16 is gradually increased from near full close to half open as the required load L increases, and the EGR
The opening degree of the control valve 23 is gradually increased from near full close to full open as the required load L increases. Also, FIG.
In the example shown in FIG. 3, the EGR rate is set to approximately 70% in the first operating region I, and the air-fuel ratio is set to a slightly lean lean air-fuel ratio.

In other words, in the first operating region I, EGR
The opening of the throttle valve 16 and the opening of the EGR control valve 23 are controlled so that the ratio becomes approximately 70% and the air-fuel ratio becomes a lean air-fuel ratio. At this time, the air-fuel ratio is controlled to the target lean air-fuel ratio by correcting the opening degree of the EGR control valve 23 based on the output signal of the air-fuel ratio sensor 21. Further, in the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS becomes late as the required load L becomes high, and the injection completion timing θE also becomes late as the injection start timing θS becomes late.

During the idling operation, the throttle valve 16 is closed close to the fully closed state, and at this time, the EGR control valve 23 is also closed close to the fully closed state. Throttle valve 1
When the valve 6 is closed to close to the fully closed state, the pressure in the combustion chamber 5 at the beginning of compression becomes low, so that the compression pressure becomes small. When the compression pressure becomes small, the compression work by the piston 4 becomes small, so that the vibration of the engine body 1 becomes small. That is, in idling operation, the throttle valve 16 is closed to close to the fully closed state in order to suppress the vibration of the engine body 1.

On the other hand, the operating region of the engine is the first operating region I
When changing from the second operating region II to the second operating region II, the opening degree of the throttle valve 16 is increased stepwise from the half open state to the full open direction. At this time, in the example shown in FIG. 13, the EGR rate is almost 70.
The air-fuel ratio is increased stepwise from a percentage to 40% or less. That is, since the EGR rate jumps over the EGR rate range (FIG. 9) in which a large amount of smoke is generated, a large amount of smoke is generated when the engine operating region changes from the first operating region I to the second operating region II. There is no.

In the second operating region II, the conventional combustion is performed. Although some soot and NO _x are generated in this combustion method, the thermal efficiency is higher than that in low temperature combustion, and therefore the engine operating range is from the first operating range I to the second operating range.
When changed to II, the injection amount is reduced stepwise as shown in FIG.

In the second operating region II, the throttle valve 16 is kept fully open except for a part, and the opening degree of the EGR control valve 23 is gradually reduced as the required load L increases. In this operating region II, the EGR rate becomes lower as the required load L becomes higher, and the air-fuel ratio becomes smaller as the required load L becomes higher. However, the air-fuel ratio is a lean air-fuel ratio even if the required load L becomes high. Further, in the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

FIG. 14 shows the air-fuel ratio A / F in the first operating region I. In FIG. 14, A / F = 15.
5, each curve shown by A / F = 16, A / F = 17, A / F = 18 has an air-fuel ratio of 15.5, 16, 17, 18 respectively.
And the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 14, the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the air-fuel ratio A / F is leaner as the required load L is lower.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, as the required load L decreases, low temperature combustion can be performed even if the EGR rate is decreased. When the EGR rate is reduced, the air-fuel ratio becomes large, so that the air-fuel ratio A / F becomes larger as the required load L becomes lower as shown in FIG. The fuel consumption rate increases as the air-fuel ratio A / F increases. Therefore, in order to make the air-fuel ratio as lean as possible, the air-fuel ratio A / F is increased as the required load L decreases in this embodiment.

It should be noted that the target opening degree ST of the throttle valve 16 required to bring the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 5 (A), it is pre-stored in the ROM 32 in the form of a map as a function of the required load L and the engine speed N, and the EGR required to make the air-fuel ratio the target air-fuel ratio shown in FIG. The target opening degree SE of the control valve 23 is shown in FIG.
As shown in (4), it is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N.

FIG. 16 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. Note that in FIG. 16, A / F = 24, A / F = 3
The curves indicated by 5, A / F = 45 and A / F = 60 respectively show the target air-fuel ratios 24, 35, 45 and 60. Throttle valve 1 required to set the air-fuel ratio to this target air-fuel ratio
The target opening degree ST of 6 is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 17 (A), and the air-fuel ratio is set to this target air-fuel ratio. Target opening degree SE of the EGR control valve 23 necessary for
Is stored in advance in the ROM 32 in the form of a map as a function of the required load L and the engine speed N, as shown in FIG. 17 (B).

As described above, in the diesel engine of this embodiment, the first combustion, that is, the low temperature combustion and the second combustion, that is, the normal combustion are performed based on the depression amount L of the accelerator pedal 40 and the engine speed N. In each combustion, the opening control of the throttle valve 16 and the EGR valve is performed in each combustion based on the depression amount L of the accelerator pedal 40 and the engine speed N according to the map shown in FIG. 15 or 17.

FIG. 18 is a plan view showing the exhaust purification system, and FIG. 19 is a side view thereof. The exhaust gas purification device includes a switching unit 71 connected to the downstream side of the exhaust manifold 17 via an exhaust pipe 18, a particulate filter 70,
A first connecting portion 72a connecting one side of the particulate filter 70 and the switching portion 71, a second connecting portion 72b connecting the other side of the particulate filter 70 and the switching portion 71, and a downstream side of the switching portion 71. Exhaust passage 73. The switching unit 71 includes a valve body 71a that allows the exhaust flow to be blocked in the switching unit 71. At one shutoff position of the valve body 71a, the upstream side in the switching unit 71 is communicated with the first connecting unit 72a and the switching unit 71 is connected.
The downstream side of the inside is communicated with the second connecting portion 72b, and the exhaust gas flows from one side of the particulate filter 70 to the other side, as indicated by an arrow in FIG.

FIG. 20 shows the other shut-off position of the valve body 71a. In this cutoff position, the switching unit 71
The upstream side of the inside is communicated with the second connection portion 72b and the downstream side of the switching portion 71 is communicated with the first connection portion 72a, and the exhaust gas is discharged from the other side of the particulate filter 70 as indicated by an arrow in FIG. Flows from one side to the other. Thus
By switching the valve body 71a, the direction of the exhaust gas flowing into the particulate filter 70 can be reversed, that is, the exhaust upstream side and the exhaust downstream side of the particulate filter 70 can be reversed.

As described above, the present exhaust gas purification apparatus can reverse the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter with a very simple structure. Also,
In the particulate filter, a large opening area is required in order to facilitate the inflow of exhaust gas. However, in the exhaust gas purification device, as shown in FIGS. It is possible to use a particulate filter having a large opening area.

Further, FIG. 21 shows an intermediate position between the two shut-off positions of the valve body 71a. At this intermediate position, the inside of the switching unit 71 is not shut off, and the exhaust gas does not pass through the particulate filter 70 having a high passage resistance, that is, as shown by the arrow in FIG. 20, the particulate filter. It bypasses 70 and flows directly to the exhaust passage 73. The opening degree of the valve body 71a can be controlled to an arbitrary position including two shutoff positions by a negative pressure actuator or a step motor.

The present exhaust gas purifying apparatus further includes an electric heater 74 arranged in the particulate filter 70, and reducing agent supply devices 75a and 75b for supplying a reducing agent such as fuel to both sides of the particulate filter 70 in a wide range. And are provided.

FIG. 22 shows the structure of the particulate filter 70. 22, (A) is a front view of the particulate filter 70, and (B) is a side sectional view. As shown in these drawings, the present particulate filter 70 has an oblong front shape and is of a wall-flow type having a honeycomb structure formed of a porous material such as cordierite, and has a large number of axis lines. It has a number of axial spaces subdivided by partitions 54 extending in the direction. In the two adjacent axial spaces, one is closed on the exhaust downstream side and the other is closed on the exhaust upstream side by the plug 53. Thus, one of the two adjoining axial spaces serves as the exhaust gas inflow passage 50 and the other serves as the outflow passage 51, and the exhaust gas flows as shown in FIG.
As shown by the arrow in (B), it always passes through the partition wall 54.
Although the particulates in the exhaust gas are very small compared with the size of the pores of the partition wall 54, they are collided and caught on the exhaust gas upstream side surface of the partition wall 54 and the pore surface in the partition wall 54. Gathered. In this way, each partition wall 54 functions as a collection wall that collects particulates. In the present particulate filter 70, in order to oxidize and remove the collected particulates, alumina or the like is used on both side surfaces of the partition wall 54 and preferably on the pore surface in the partition wall 54, which will be described below. An active oxygen releasing agent and a noble metal catalyst are supported. As described above, an electric heater is arranged in the present particulate filter 70. As shown in FIG. 19, this electric heater does not obstruct the passage of the exhaust gas through the particulate filter because it is arranged in a rectangular wave shape through the partition wall 54.

The active oxygen releasing agent is one that promotes the oxidation of particulates by releasing active oxygen, and preferably, when excess oxygen is present in the surroundings, it takes in oxygen and retains it, and When the oxygen concentration decreases, the retained oxygen is released in the form of active oxygen.

This precious metal catalyst is usually platinum Pt.
Is used, and potassium K is used as an active oxygen releasing agent.
It is selected from sodium Na, lithium Li, cesium Cs, alkali metals such as rubidium Rb, barium Ba, calcium Ca, alkaline earth metals such as strontium Sr, lanthanum La, rare earths such as yttrium Y, and transition metals. At least one is used.

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

Next, as to how the collected particulates are oxidized and removed by the particulate filter carrying the active oxygen releasing agent,
The case of platinum Pt and potassium K will be described as an example. Similar noble metals, alkali metals, alkaline earth metals, rare earths, and transition metals can be used to perform the same particulate removing action.

Diesel engines normally burn under excess air, so the exhaust gas contains a large amount of excess air. That is, when the ratio of the air supplied to the intake passage and the combustion chamber to the fuel is called the air-fuel ratio of the exhaust gas, this air-fuel ratio is lean. In the combustion chamber, N
Since O is generated, NO is contained in the exhaust gas.
Further, the fuel contains sulfur S, and this sulfur S reacts with oxygen in the combustion chamber to become SO ₂ . Therefore, the exhaust gas contains SO ₂ . Therefore excess oxygen,
The exhaust gas containing NO and SO ₂ will flow into the exhaust gas upstream side of the particulate filter 70.

23A and 23B schematically show enlarged views of the exhaust gas contact surface of the particulate filter 70. 23 (A) and (B)
In the above, 60 indicates particles of platinum Pt, and 61 indicates an active oxygen releasing agent containing potassium K.

As described above, since a large amount of excess oxygen is contained in the exhaust gas, when the exhaust gas comes into contact with the exhaust gas contact surface of the particulate filter, the oxygen O 2 as shown in FIG. ₂ attaches to the surface of platinum Pt in the form of O ₂ ⁻ or O ²⁻ . On the other hand, NO in the exhaust gas reacts with O ₂ ⁻ or O ^{2 −} on the surface of platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ). Then generated N
23. Part of O ₂ is absorbed on the active oxygen release agent 61 while being oxidized on platinum Pt, and is bonded to potassium K.
As shown in (A), nitrate ion NO ₃ ⁻ diffuses into the active oxygen release agent 61 to form potassium nitrate KNO ₃ . In this way, in this embodiment, harmful NO _x contained in the exhaust gas can be absorbed by the particulate filter 20 and the amount released into the atmosphere can be greatly reduced.

On the other hand, as described above, the exhaust gas contains SO.
₂Also included, this SO₂The same mechanism as NO
The oxygen is absorbed in the active oxygen release agent 61. That is,
As described above, oxygen O₂Is O₂ ^-Or O^2-In the form of platinum P
attached to the surface of t and SO in exhaust gas₂Is platinum P
O on the surface of t₂ ^-Or O^2-Reacts with SO₃Becomes Next
SO generated by₃Is partially oxidized on platinum Pt.
While being absorbed into the active oxygen release agent 61, potassium K
Sulfate ion SO while binding_Four ^2-Active oxygen releasing agent in the form of
61 diffuses into potassium sulfate K₂SO_FourTo generate.
In this way, potassium nitrate is contained in the active oxygen release catalyst 61.
Mu KNO₃And potassium sulfate K₂SO _FourIs generated
It

The particulates in the exhaust gas are shown in FIG.
As shown by 62 in (B), it adheres on the surface of the active oxygen release agent 61 carried by the particulate filter. At this time, the oxygen concentration decreases at the contact surface between the particulate 62 and the active oxygen release agent 61. When the oxygen concentration decreases, a difference in concentration occurs between the active oxygen release agent 61 and the active oxygen release agent 61 having a high oxygen concentration, so that the oxygen in the active oxygen release agent 61 is transferred to the contact surface between the particulate 62 and the active oxygen release agent 61. Try to move towards. As a result, potassium nitrate KNO ₃ formed in the active oxygen release agent 61 is decomposed into potassium K, oxygen O and NO, and the oxygen O moves toward the contact surface between the particulate 62 and the active oxygen release agent 61, and NO Are released from the active oxygen release agent 61 to the outside.
The NO released to the outside is oxidized on the platinum Pt on the downstream side and is again absorbed in the active oxygen release agent 61.

On the other hand, at this time, the inside of the active oxygen releasing agent 61 is formed.
Potassium sulfate K₂SO _FourAlso potassium K and acid
Element O and SO₂Is decomposed into and oxygen O is particulated
62 toward the contact surface between the active oxygen releasing agent 61 and the SO₂
Are released from the active oxygen release agent 61 to the outside. Released outside
SO issued₂Is oxidized on the platinum Pt on the downstream side.
And is absorbed again in the active oxygen release agent 61. However, sulfur
Potassium acid K₂SO_FourNitric acid because it is stabilized
Potassium KNO₃It is difficult to release active oxygen compared to.

On the other hand, oxygen O toward the contact surface between the particulate 62 and the active oxygen release agent 61 is potassium nitrate KN.
Oxygen decomposed from compounds such as O ₃ and potassium sulfate K ₂ SO ₄ . Oxygen O decomposed from the compound has high energy and has extremely high activity. Therefore, oxygen toward the contact surface between the particulate 62 and the active oxygen release agent 61 is active oxygen O. When these active oxygen O comes into contact with the particulates 62, the particulates 62 are oxidized without emitting a bright flame.

By the way, platinum Pt and active oxygen releasing agent 6
Since No. 1 is activated as the temperature of the particulate filter increases, the amount of active oxygen O released from the active oxygen release agent 61 per unit time increases as the temperature of the particulate filter increases. Therefore, the amount of oxidatively removable fine particles capable of oxidizing and removing the particulates per unit time on the particulate filter without emitting a luminous flame increases as the temperature of the particulate filter increases.

The solid line in FIG. 24 shows the amount G of oxidizable / removable fine particles that can be oxidized and removed per unit time without emitting a luminous flame. In FIG. 24, the horizontal axis represents the temperature TF of the particulate filter. The amount of particulates discharged from the combustion chamber per unit time is referred to as the amount M of discharged fine particles. When the amount M of discharged fine particles is smaller than the amount G of fine particles that can be removed by oxidation, that is, in the region I of FIG. As soon as all the particulates thus collected are collected by the particulate filter, they are oxidized and removed in the particulate filter in a short time without emitting a bright flame.

On the other hand, when the amount M of discharged particles is larger than the amount G of particles that can be removed by oxidation, that is, in the region II of FIG. 24, the amount of active oxygen is insufficient to oxidize all the particulates. FIGS. 25 (A) to 25 (C) show the state of oxidation of particulates in such a case.

That is, when the amount of active oxygen is insufficient to oxidize all the particulates, the particulate 62 is converted into the active oxygen releasing agent 61 as shown in FIG.
When it adheres to the upper part, only a part of the particulate 62 is oxidized, and the insufficiently oxidized particulate part remains on the exhaust gas upstream side surface of the particulate filter. Next, if the state in which the amount of active oxygen is insufficient continues, the particulates that have not been oxidized one after another remain on the upstream surface of the exhaust gas, and as a result, as shown in FIG. The exhaust gas upstream surface is covered by the residual particulate portion 63.

Such residual particulate portion 63
Gradually changes into carbon that is difficult to oxidize, and when the exhaust upstream surface is covered with the residual particulate portion 63, NO and SO ₂ oxidizing action of platinum Pt and active oxygen releasing action of the active oxygen releasing agent 61 occur. Suppressed. As a result, the residual particulate portion 63 can be gradually oxidized over time.
As shown in (C), the residual particulate portion 63 is
When another particulate 64 is deposited one after another on the above, that is, when the particulates are deposited in a laminated form, since these particulates are separated from platinum Pt and the active oxygen release agent, Even if particulates are easily oxidized, they are not oxidized by active oxygen. Therefore, further particulates are deposited one after another on the particulates 64. That is, if the state in which the amount M of discharged particulates is larger than the amount G of particulates that can be removed by oxidation continues, particulates will be accumulated in a layered manner on the particulate filter.

As described above, in the area I of FIG. 24, the particulates are oxidized on the particulate filter in a short time without emitting a luminous flame, and in the area II of FIG. 24, the particulates are laminated on the particulate filter. Deposits in the shape of. Therefore, if the relationship between the amount M of discharged particulates and the amount G of particles that can be removed by oxidation is set to the region I, it is possible to prevent the accumulation of particulates on the particulate filter. However, this is not always realized, and if nothing is done, particulates may be deposited on the particulate filter.

In this embodiment, the electronic control unit 3 described above is used.
The electric heater 74 and the valve body 71a are controlled by 0 according to the first flowchart shown in FIG. 26 to prevent the accumulation of a large amount of particulates on the particulate filter. This flowchart is repeated every predetermined time.
First, in step 101, the temperature TF of the particulate filter is detected. For this detection, a temperature sensor is provided in the particulate filter to directly detect. Further, the temperature of the particulate filter may be calculated based on the amount of exhaust gas flowing into the particulate filter, the temperature of the exhaust gas, and the like every predetermined time after the engine is started. Next, the load sensor 41, the crank angle sensor 42, and the like are used to grasp the current engine operating state. In the case of the diesel engine of the present embodiment, it is also known which of the two combustion methods has been adopted. By grasping this operating state, it is possible to estimate the exhaust gas amount, the exhaust gas temperature, the oxygen concentration in the exhaust gas, the discharged particulate amount, and the like.

Next, in step 103, the amount of particulates that can be oxidized and removed by the particulate filter, which is required at present, is calculated based on the oxygen concentration in the exhaust gas, the amount of particulates that are discharged, etc. The minimum temperature TFt of the filter is calculated. In step 104, the temperature change amount dTF of the particulate filter is calculated based on the current temperature TF of the particulate filter, the exhaust gas amount, the exhaust gas temperature, and the like.
Is calculated.

Next, at step 105, in the particulate filter, the temperature change amount dTF is added to the current temperature TF, and it is determined whether or not the result exceeds the minimum temperature TFt. For example, even if the current temperature TF of the particulate filter is considerably high and the exhaust gas temperature is lower than this temperature TF to lower the temperature of the particulate filter, if the judgment in step 105 is affirmed, then the problem is particularly serious. Instead, the valve body 71a is left in one of the shut-off positions and ends.

However, when the determination in step 105 is negative, the particulate matter is deposited on the particulate filter and cannot be removed by oxidation in this state. Therefore, in step 106, the electric heater 74 is used.
Is operated to raise the temperature of the particulate filter 70 to the above-mentioned minimum temperature TFt, so that the amount of particulates that can be oxidized and removed by the particulate filter 70 is increased to the present required amount.

Of course, the electric heater 74 may be operated in this way to raise the temperature of the particulate filter 70. However, in this flowchart, at this time, the valve body 71 is used.
With a set at a near the intermediate position shown in FIG. 21, at least part of the exhaust gas is bypassed without passing through the particulate filter. As a result, the heat generated by the electric heater 74 is prevented from flowing out of the particulate filter 70 together with the exhaust gas, and the electric heater 74 efficiently raises the temperature of the particulate filter 70. It is possible to reduce the power consumption for raising the temperature to the temperature TFt, and when the temperature rise of the particulate filter 70 to the minimum temperature TFt is large,
This is possible.

Of course, bypassing all the exhaust gas is most effective for reducing the power consumption of the electric heater 74 or for significantly raising the temperature of the particulate filter 70 by the electric heater 74. If particulates are included, all the particulates will be released into the atmosphere. Therefore, it is preferable to reduce the amount of bypass exhaust gas as much as possible, except when the exhaust gas does not contain any particulates as in the fuel cut when combustion is not performed. Thus, in step 107, the exhaust gas amount to be bypassed is calculated, and in step 108, the opening degree of the valve body 71a is controlled so as to realize this bypass exhaust gas amount.

By the way, the minimum temperature TFt and the temperature change amount dTF in steps 103 and 104 are when the total amount of exhaust gas flows into the particulate filter. For example, exhaust gas flowing into the particulate filter by bypass of exhaust gas is used. If the ratio is half, the amount of discharged fine particles, that is, the amount of fine particles flowing into the particulate filter is also halved, and the required minimum temperature TFt can be lowered. Further, when the exhaust gas temperature is lower than the current temperature TF of the particulate filter, the temperature change amount dTF has a negative value, but this absolute value can be reduced by bypassing the exhaust gas. When the exhaust gas does not contain particulates and the exhaust gas temperature is very low as in the fuel cut, all the exhaust gas is bypassed by using the valve body 71a as an intermediate position and the electric heater is used. It is preferable to maximize the temperature raising efficiency of the particulate filter and suppress the temperature decrease of the particulate filter due to the low temperature exhaust gas.

Further, the presently required amount of oxidatively removable fine particles calculated in step 103 is not limited to the one that can always oxidize and remove only the present amount of discharged fine particles. For example, if a fuel cut is performed during engine deceleration, etc.,
Although the amount of discharged fine particles is almost zero, the minimum temperature TFt is set to 10 by setting the amount of fine particles that can be removed by oxidation to be zero.
If the temperature is 0 ° C. or lower (see FIG. 24), when the temperature of the particulate filter actually becomes 100 ° C. or lower, the temperature of the particulate filter does not rise immediately at the time of the next engine acceleration, and almost no temperature rises. Therefore, the particulates cannot be removed by oxidation. Therefore, it is preferable that the required amount of fine particles that can be oxidized and removed is always a predetermined amount or more, that is, the minimum temperature TFt of the particulate filter does not fall below 200 ° C., for example.

Thus, in the first flow chart, when the amount of discharged particulates becomes large and exceeds the present amount of particulates that can be oxidized and removed according to the temperature of the particulate filter, and when the exhaust gas temperature becomes low and the particulates become low. When the amount of particulates that can be oxidized and removed by the particulate filter is to be reduced, the determination in step 105 is denied and the electric heater is activated to improve the amount of particulates that can be oxidized and removed by the particulate filter. Particulates do not accumulate on the curate filter. Further, by bypassing the exhaust gas when operating the electric heater, the temperature of the particulate filter can be efficiently raised. The larger the amount of bypass exhaust gas, the more efficient the temperature rise of the particulate filter. Therefore, it is possible to raise the temperature of the particulate filter to a high temperature, that is, when the electric heater is operating, the amount of bypass exhaust gas is reduced. By adjusting the temperature, the temperature of the particulate filter can be controlled to a desired temperature.

By simplifying the first flow chart, the electric heater is operated when the particulate filter falls below a set temperature (for example, 300 ° C.) to calculate the amount of fine particles that can be removed by oxidation, without calculating the amount of discharged fine particles. It may be possible to reduce the accumulation of particulates on the particulate filter by maintaining the particulate filter at a predetermined value or more. Further, for example, by grasping the engine operating state and operating the electric heater when the amount of discharged particulates exceeds the set amount to improve the amount of particulates that can be removed by oxidation, it is possible to reduce the accumulation of particulates on the particulate filter. You can

Further, in the first flow chart, after the opening degree of the valve body 71a is controlled in step 108, the valve body 71a is switched to the other shut-off position in step 109. In the wall flow type particulate filter as used in this example,
Particulate 54 is a partition wall 54 against which exhaust gas mainly collides.
Of the exhaust gas on the upstream side and the surface facing the exhaust gas flow in the pores, that is, one of the collecting surfaces of the partition wall 54 is collected by collision, and the release of the active oxygen from this one collecting surface becomes a collecting particulate. On the other hand, if it is insufficient, all of it remains without being removed by oxidation. Step 108 of the first flowchart
By the processing up to, almost no such particulates remain, but for some reason, as shown in FIG.
As shown in (A), when the particulate remains on one of the collecting surfaces of the partition wall, the switching of the valve body 71a is effective.

Because of the reverse rotation of the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter, further particulate matter does not accumulate on the particulate matter remaining on one collecting surface of the partition wall, and one particulate matter is trapped. Residual particulates are gradually oxidized and removed by the active oxygen released from the collecting surface. In addition, the particulates that remain in the pores of the partition walls, in particular, due to exhaust gas flow in the opposite direction,
As shown in FIG. 28 (B), it is easily broken and fragmented, and moves mainly in the pores to the downstream side.

As a result, many of the finely divided particulates are dispersed in the pores of the partition walls, and are directly contacted with the active oxygen releasing agent carried on the inner surfaces of the pores of the partition walls to be oxidized and removed. More opportunities. By thus supporting the active oxygen-releasing agent also in the pores of the partition wall, the residual particulates can be markedly easily oxidized and removed. Further, in addition to this oxidation removal, the other collection surface of the partition wall 54 that is upstream due to the backflow of exhaust gas, that is, the exhaust upstream surface and the inside of the pores of the partition wall 54 where the exhaust gas mainly collides at present. On the surface facing the exhaust gas flow (the relationship opposite to the one collecting surface), new particulates in the exhaust gas adhere and are oxidized and removed by the active oxygen released from the active oxygen release agent. . A part of the active oxygen released from the active oxygen release agent during the oxidative removal moves to the downstream side together with the exhaust gas, and oxidizes and removes the particulates still remaining due to the reverse flow of the exhaust gas.

That is, in the residual particulate matter on one of the collecting surfaces of the partition wall, not only the active oxygen released from this collecting surface but also the particulate matter on the other collecting surface of the partition wall due to the backflow of the exhaust gas. The remaining active oxygen used for oxidative removal comes with the exhaust gas. Thereby, the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are reversed to alternately use one of the collecting surfaces of the particulate filter partition wall and the other collecting surface for collecting the particulates. Even if a certain amount of particulates are accumulated in a layered manner on one collecting surface of the particulate filter partition wall during reverse rotation, due to the backflow of exhaust gas,
In addition to the arrival of active oxygen in the accumulated particulates, no additional particulates are accumulated, so the accumulated particulates are gradually oxidized and removed, and if there is some time before the next backflow. During this period, it can be sufficiently oxidized and removed. Of course, the valve body 71a
The switching of is not limited to after the operation of the electric heater, but may be performed regularly, irregularly, or every predetermined mileage,
It is effective for removing residual and accumulated particulates by oxidation.

In this flow chart, when the exhaust gas does not contain particulates as in the fuel cut, if the electric heater is operated and all the exhaust gases are bypassed, one of the particulate filter partition walls Even if the particulates remain on the collection surface, the particulates do not accumulate further, and the residual particulates are good due to the active oxygen released from one collection surface of the partition wall as in the case of the reverse rotation described above. Is removed by oxidation. The amount of active oxygen released from the active oxygen releasing agent is finite, and the active oxygen releasing agent must absorb the oxygen in the atmosphere as described above after releasing the active oxygen and using it for oxidizing and removing the particulates. , Cannot release active oxygen newly. In this way, when all the exhaust gas is bypassed, new oxygen is not supplied around the partition wall, and due to lack of oxygen, oxygen absorption and release by the active oxygen release agent becomes inactive, and the residual particulates are completely removed. In some cases, it cannot be removed by oxidation. Further, the particulates that are not in contact with the active oxygen-releasing agent on the partition wall are less likely to be oxidized due to lack of oxygen. Therefore, in this flowchart, when bypassing the exhaust gas,
It is not always necessary to do so, but it is preferable that at least a part of the exhaust gas passes through the particulate filter without bypassing all the exhaust gas, and oxygen is not deficient around the partition wall of the particulate filter.

FIG. 27 is a second flow chart executed in place of the first flow chart in order to prevent a large amount of particulates from accumulating on the particulate filter. This will be explained below. This flowchart is also repeated every predetermined time. First, in step 201, the temperature TF of the particulate filter is detected as in the first flowchart. Then, step 202
At this temperature TF, the first set temperature T1 (for example,
It is determined whether the temperature is 300 ° C) or higher. When this determination is affirmed, the amount of particulates that can be removed by oxidation of the particulate filter is relatively high, so it is assumed that the particulates collected by the particulate filter can be sufficiently removed by oxidation, and the valve body 71a has one side. The cutoff position remains and the process ends.

On the other hand, if the determination in step 202 is negative, the amount of particulates that can be oxidized and removed by the particulate filter is low, and in order to improve this, step 2
At 03, the electric heater 74 is activated. Next, at step 204, it is judged based on the engine operating condition or the like whether or not the current amount M of discharged particulate is equal to or less than the set amount M1. At the time of fuel cut, idling, or low temperature combustion, the exhaust gas contains almost no particulates, and this judgment is affirmed. In step 205, the valve body 71a is set to the intermediate position and all the exhaust gas is exhausted. The gas is allowed to bypass the particulate filter,
The electric heater heats up the particulate filter very efficiently. On the other hand, when the exhaust gas contains a relatively large amount of particulates, the determination in step 204 is denied, the valve body 71a is left in one of the shut-off positions, and the particulates in the exhaust gas are collected by the particulate filter. To be done.

Next, at step 207, it is judged if the temperature TF of the particulate filter is equal to or higher than the second set temperature T2. The second set temperature T2 is
For example, platinum P supported on a particulate filter
This is the activation temperature of the oxidation catalyst such as t, and when this determination is denied, the processing from step 203 is repeated. Thus, when the temperature TF of the particulate filter becomes equal to or higher than the second set temperature T2 due to the heating of the electric heater, or when it is lower than the first set temperature T1 but equal to or higher than the second set temperature T2, the determination in step 207 is affirmative. Then, in step 208, the electric heater is stopped.

Next, at step 209, the reducing agent is supplied from either side or both sides of the particulate filter 70 by the reducing agent supply device 75a or 75b when there is no exhaust gas flow in the particulate filter 70, at least. When a part of the exhaust gas flow exists, the reducing agent is supplied from the exhaust inlet side of the particulate filter 70. As a result, the reducing agent satisfactorily starts combustion by the oxidation catalyst carried by the particulate filter 70, and the particulate filter 70
Is raised above the first set temperature T1. As a result, the amount of fine particles that can be removed by oxidation is made relatively high, so that the particulates collected by the particulate filter are sufficiently oxidized and removed, and are not deposited on the particulate filter. In this flowchart, the operation of the electric heater is limited until the particulate filter reaches the second set temperature, and therefore the power consumption of the electric heater can be reduced.

Next, at step 210, since the valve body is switched to the other shut-off position, as described above, even if the particulates are deposited on one of the collecting surfaces of the particulate filter partition wall, it will be satisfactory. It can be removed by oxidation. In this flowchart, when the reducing agent is burned, if the exhaust gas contains almost no particulates, it is preferable to bypass the particulate filter to prevent heat outflow. However, if exhaust gas is not supplied to the particulate filter at all, the reducing agent may not satisfactorily burn due to lack of oxygen. In this case, the valve body 71a is slightly rotated from the intermediate position to the shutoff position side, It is sufficient that a part of the exhaust gas flows into the particulate filter.

In the present flowchart, the reducing agent supplied from the exhaust gas inlet side of the particulate filter not only heats the exhaust gas inlet portion of the particulate filter by its combustion heat, but this combustion heat is also particulated by the exhaust gas. The exhaust outlet of the filter is also heated. In this way, since the temperature of the entire particulate filter is raised, the amount of fine particles that can be oxidized and removed in the entire particulate filter is improved. Thereby, step 2
In FIG. 10, when the valve body 71a is switched to the other shut-off position, as described above, even if the particulates remain on one of the collecting surfaces of the particulate filter partition wall, this is satisfactorily oxidized and removed. The particulates started to be collected by the other collecting surface of the particulate filter partition wall can be satisfactorily oxidatively removed by the improved amount of oxidatively removable fine particles.

Reducing agent supply device 75a, 75b of this embodiment
In order to supply the reducing agent directly to the particulate filter 70, useless use of the reducing agent such as adhering to the inner walls of the connection portions 21a and 21b is prevented, and the reducing agent can be minimized to the minimum necessary. it can. Further, since the supply of the reducing agent to the particulate filter may be performed when at least a part of the exhaust gas is bypassed, the reducing agent supply device has the bypass mechanism (the switching unit 71 in the present embodiment).
(Integrated with) and the particulate filter to prevent the supplied reducing agent from bypassing the particulate filter. Further, since both are on the exhaust upstream side, the first connecting portion 72 is provided so that the reducing agent can be supplied to both sides of the particulate filter.
a and the second connecting portion 72b, a reducing agent supply device 75, respectively.
a and 75b are arranged.

However, these do not limit the present invention. For example, the supply of the reducing agent is limited only when one side of the particulate filter is at the exhaust upstream side or when all the exhaust gas is bypassed. It is also possible to omit one of the reducing agent supply devices.

Further, for example, if the reducing agent is supplied when the exhaust gas is not bypassing the particulate filter, the reducing agent may be supplied to the upstream side of the bypass mechanism by the engine fuel injection valve. The fuel may be injected in the exhaust stroke, or the low temperature combustion described above may be performed.

In the present embodiment, the electric heater 74
Two are arranged in the partition wall of the particulate filter so as to extend in the direction perpendicular to the exhaust gas flow, but of course, one may be provided, and a plurality of electric heaters parallel to the exhaust gas flow may be provided. May be arranged. Further, like the reducing agent supply device, one or two electric heaters having the same shape may be arranged adjacent to the exhaust gas inlet portion or the exhaust gas inlet portion and the gas exhaust outlet portion of the particulate filter. As described above, the number, shape, and arrangement of the electric heaters may be any as long as the particulate filters can be reliably heated without hindering the passage of exhaust gas in the particulate filters.

Further, 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 releasing agent 61 releases the active oxygen O all at once, and the active oxygen O released all at once. The accumulated particulates can be burned and removed all at once without emitting a luminous flame. Thus, when the exhaust gas upstream side and the exhaust downstream side of the particulate filter are reversed by the valve body 71a or immediately after that, the air-fuel ratio of the exhaust gas is made rich, so that the particulates on the particulate filter partition remain and accumulate. On the other collecting side, which does not
Since it is easier to release active oxygen than one of the collection surfaces,
The larger amount of active oxygen released makes it possible to more reliably oxidize and remove the residual and deposited particulates.

As a method for making the air-fuel ratio of the exhaust gas rich, for example, the above-mentioned low temperature combustion may be carried out. Of course, when switching from normal combustion to low temperature combustion, or
Prior to that, the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter may be switched. As described above, since the low temperature combustion is performed on the engine low load side, there are many occasions when the low temperature combustion is performed immediately after the fuel cut during deceleration of the engine. If the heater is operated and the valve body 71a is switched, the low temperature combustion is often carried out thereafter, and good oxidation removal of particulates is realized. It is also possible to make the air-fuel ratio of the exhaust gas rich by supplying the reducing agent with the reducing agent supply device described above.

Further, even when a large amount of particulates are deposited on one collecting surface of the particulate filter partition wall when the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are reversed, this accumulated particulate matter. Is relatively easily destroyed and subdivided by the backflow of exhaust gas, so that some of the particulates that could not be oxidized and removed in the pores of the partition wall are discharged from the particulate filter. The exhaust resistance of the particulate filter does not further increase and does not adversely affect the vehicle traveling, and new particulates can be trapped by the other trapping surface of the particulate filter partition.

When SO ₃ is present in the calcium Ca in the exhaust gas, calcium sulfate CaSO ₄ such as the above-mentioned ash is produced. This calcium sulfate C
In order to prevent the particulate filter from being clogged with aSO _4, an alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca, such as potassium K, is used as the active oxygen releasing agent 61 in the active oxygen releasing agent 61. The SO ₃ that diffuses into the potassium is combined with potassium K to form potassium sulfate K ₂ SO ₄ , and calcium Ca is converted to SO.
_It passes through the partition wall of the particulate filter without being combined with ₃ . Therefore, the particulate filter will not be clogged with ash. Thus, as described above, calcium C is used as the active oxygen release agent 61.
Alkali metal or alkaline earth metal having a higher ionization tendency than a, that is, potassium K, lithium Li, cesium C
s, rubidium Rb, barium Ba, strontium S
It will be preferred to use r.

In addition, platinum P was added to the particulate filter.
Even when only a noble metal such as t is supported, active oxygen can be released from NO ₂ or SO ₃ retained on the surface of platinum Pt. However, in this case, the solid line indicating the amount G of particles that can be removed by oxidation moves to the right side slightly as compared with the solid line shown in FIG. It is also possible to use ceria as the active oxygen releasing agent. Ceria absorbs oxygen when the oxygen concentration in the exhaust gas is high, and releases active oxygen when the oxygen concentration in the exhaust gas decreases. It is necessary to make the fuel ratio rich regularly or irregularly.

It is also possible to use a NO _x storage reduction catalyst used for purification of NO _x in the exhaust gas as the active oxygen releasing agent. In this case, the stored NO _x
In order to release SO _x and SO _x , it is necessary to at least temporarily make the air-fuel ratio of the exhaust gas rich, and it is preferable to carry out this enrichment control after the upstream side and the downstream side of the particulate filter are reversed.

In the present embodiment, the structure is simplified by integrating the reverse rotation mechanism between the exhaust gas upstream side and the exhaust downstream side of the particulate filter and the bypass mechanism of the exhaust gas particulate filter, but separately from the reverse rotation mechanism. It is also possible to provide a bypass mechanism. Further, the diesel engine of the present embodiment is assumed to be carried out by switching between low temperature combustion and normal combustion, but this does not limit the present invention, and of course, a diesel engine that carries out only normal combustion, or a patty The present invention is also applicable to a gasoline engine that discharges curates.

[0114]

As described above, according to the exhaust gas purification apparatus for an internal combustion engine of the present invention, the particulate filter disposed in the engine exhaust system, the electric heater for heating the particulate filter, and the particulate filter are provided. The exhaust gas upstream side and the exhaust downstream side are provided with a reversing means for reversing, the particulate filter has a trapping wall for trapping particulates, the trapping wall contains an active oxygen releasing agent. The trapping wall is carried and has a first trapping surface and a second trapping surface, and traps particulates by reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter by the reversing means. The first collecting surface and the second collecting surface of the collecting wall are alternately used for collecting. As a result, depending on the operating conditions, the oxidation removal by the active oxygen releasing agent may be insufficient and some particulate matter may remain on the first collecting surface of the particulate filter collecting wall. By reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter, new particulates will not be accumulated on the first collection surface of the collection wall, and will be released from the active oxygen release agent on the first collection surface. The residual particulates are gradually oxidized and removed by the active oxygen generated. At the same time, the second collection surface of the collection wall starts the collection and oxidation removal of particulates, and the remaining active oxygen used in this oxidation removal is discharged to the particulates remaining on the first collection surface together with the exhaust gas. Incoming and used to oxidize and remove residual particulates. In this way, the residual particulates can be favorably oxidized and removed by the reverse rotation of the exhaust gas upstream side and the exhaust downstream side of the particulate filter, and clogging of the particulate filter can be prevented. In addition, path
The particulate filter is activated by the active oxygen release agent.
Oxygen can be removed depending on the temperature of the particulate filter.
It has a particle amount, and the current amount of fine particles emitted from the engine combustion chamber is
When the amount of fine particles that can be removed by oxidation is exceeded,
Is the fine particles that can be removed by oxidation because the current exhaust gas state
Activate the electric heater when it is going to fall below the volume
It is supposed to do. As a result, the temperature of the particulate filter rises , the amount of fine particles that can be oxidized and removed by the active oxygen release agent increases, and it becomes difficult for particulates to remain on the collection surface, and it is possible to more reliably prevent clogging of the particulate filter. You can

[Brief description of drawings]

FIG. 1 is a schematic vertical cross-sectional view of a diesel engine including an exhaust emission control device according to the present invention.

2 is an enlarged vertical sectional view of the combustion chamber of FIG.

FIG. 3 is a bottom view of the cylinder head of FIG.

FIG. 4 is a side sectional view of a combustion chamber.

FIG. 5 is a diagram showing lift of intake and exhaust valves and fuel injection.

FIG. 6 is a diagram showing the amount of smoke and NO _x generated, and the like.

FIG. 7 is a diagram showing a combustion pressure.

FIG. 8 is a diagram showing a fuel molecule.

FIG. 9 is a diagram showing a relationship between an amount of smoke generated and an EGR rate.

FIG. 10 is a diagram showing a relationship between an injected fuel amount and a mixed gas amount.

FIG. 11 is a diagram showing a first operating region I and a second operating region II.

FIG. 12 is a diagram showing an output of an air-fuel ratio sensor.

FIG. 13 is a diagram showing the opening of a throttle valve and the like.

FIG. 14 is a diagram showing an air-fuel ratio in a first operating region I.

FIG. 15 is a diagram showing a map of a target opening degree of a throttle valve or the like.

FIG. 16 is a diagram showing an air-fuel ratio in the second combustion.

FIG. 17 is a diagram showing a target opening of a throttle valve or the like.

FIG. 18 is a plan view of the vicinity of a switching unit and a particulate filter in the engine exhaust system.

FIG. 19 is a side view of FIG.

FIG. 20 is a view showing another shut-off position of the valve body in the switching portion, which is different from FIG. 18.

FIG. 21 is a diagram showing an intermediate position of the valve element in the switching section.

FIG. 22 is a diagram showing a structure of a particulate filter.

FIG. 23 is a diagram for explaining an oxidizing action of particulates.

FIG. 24 is a diagram showing the relationship between the amount of fine particles that can be removed by oxidation and the temperature of a particulate filter.

FIG. 25 is a diagram for explaining a deposition action of particulates.

FIG. 26 is a first flowchart for preventing the accumulation of particulates on the particulate filter.

FIG. 27 is a second flowchart for preventing the accumulation of particulates on the particulate filter.

FIG. 28 is an enlarged cross-sectional view of a partition wall of the particulate filter.

[Explanation of symbols]

6 ... Fuel injection valve 16 ... Throttle valve 71 ... Switching unit 71a ... valve body 70 ... Particulate filter 74 ... Electric heater

Continuation of front page (51) Int.Cl. ⁷ identification code FI F01N 3/08 F01N 3/24 E 3/24 B01D 53/36 103C (56) Reference JP-A-7-189655 (JP, A) JP 1-182517 (JP, A) JP 7-174018 (JP, A) JP 5-214923 (JP, A) Actual development Sho 59-30507 (JP, U) (58) Fields investigated (Int .Cl. ⁷ , DB name) F01N 3/02 B01D 46/42 F01N 3/08-3/24

Claims (6)

(57) [Claims] 1. A particulate filter arranged in an engine exhaust system, an electric heater for heating the particulate filter, and a reversing means for reversing an exhaust upstream side and an exhaust downstream side of the particulate filter. The particulate filter has a trapping wall for trapping particulates, the trapping wall carries an active oxygen release agent, and the trapping wall is a first trap. Surface and a second collection surface, the exhaust upstream side and the exhaust downstream side of the particulate filter is reversed by the reversing means, to collect the particulates of the trapping wall The first collection surface and the second collection surface are used alternately, the particulate filter,
By the active oxygen releasing agent, the particulate filter
The amount of fine particles that can be oxidized and removed according to the temperature of the
The amount of fine particles emitted from the engine combustion chamber of
When the amount of fine particles exceeds
An exhaust gas purification device for an internal combustion engine, which operates an engine. 2. A particulate matter arranged in an engine exhaust system.
Heating the particulate filter and the particulate filter.
Electric heater for the above, and the particulate filter
Reversing means for reversing the exhaust upstream side and the exhaust downstream side of the
And the particulate filter is a particulate filter.
A collection wall for collecting the curate, wherein the collection wall
An active oxygen releasing agent is carried on the collecting wall, and the collecting wall is
A collecting surface and a second collecting surface;
Exhaust gas upstream side and exhaust gas downstream side of the particulate filter
Is reversed to collect particulates.
The first collection surface and the second collection surface of the collection wall for
Are used alternately, the particulate filter is
By the active oxygen releasing agent, the particulate filter
The amount of fine particles that can be oxidized and removed according to the temperature of the
The exhaust gas state of the
The electric heater is activated when it is supposed to rotate.
An exhaust emission control device for an internal combustion engine, which is characterized in that: 3. The exhaust gas is attached to the particulate filter.
The bypass means that allows the bypass
The electric heater is provided integrally with or separately from the reversing means.
When operating the exhaust gas, the bypass means
Claims characterized by bypassing at least a part
Item 3. An exhaust gas purification device for an internal combustion engine according to item 1 or 2 . 4. Bypassing by the bypass means
The electric heater by adjusting the amount of exhaust gas
Therefore, the temperature of the particulate filter to be heated
The exhaust gas purification device for an internal combustion engine according to claim 3 , wherein the exhaust gas purification device is controlled. 5. The particulate filter is supported by the particulate filter.
Reductant supply device for supplying reductant to the generated oxidation catalyst
The exhaust emission control device for an internal combustion engine according to claim 1 or 2 , further comprising: 6. The electric heater is operated to activate the putty.
When the temperature of the curate filter exceeds the set temperature
The reducing agent is supplied to the oxidation catalyst by the reducing agent supply device.
The exhaust gas purification apparatus for an internal combustion engine according to claim 5 , wherein