JP3525854B2 - 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 arrange a filter for trapping particulates in the engine exhaust system before release to 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.

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 this filter is used, the exhaust gas temperature is not always about 400 ° C, and a large amount of particulates from the diesel engine may be generated depending on the operating condition. May be released, and particulates that could not be burned off at each time may gradually build up on the filter.

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 purifying apparatus for an internal combustion engine, which can surely oxidize and remove the particulates trapped by the reverse flow of exhaust gas and prevent the particulate filter from being clogged. Is.

[0008]

According to a first aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine, a particulate filter disposed in an engine exhaust system, and an exhaust gas upstream side and an exhaust gas downstream side of the particulate filter. And a reducing agent supply means for supplying a reducing agent from the upstream side of the reversing means to the particulate filter, and the particulate filter collects the particulates. A trapping wall for carrying an oxidation catalyst and an active oxygen releasing agent, the trapping wall having a first trapping surface and a second trapping surface, and By means of reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter by means, the first collection surface and the second collection surface of the collection wall for collecting particulates, Each other is used, the reducing agent supply means
At least by the reversing means.
Exhaust upstream side and exhaust downstream side of the air filter are reversed
The reducing agent is supplied before and after time .

According to a second aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the first aspect of the present invention, wherein the active oxygen release agent has excess oxygen present in the surroundings. It is characterized in that it takes in oxygen, retains oxygen, and releases the retained oxygen in the form of active oxygen when the surrounding oxygen concentration decreases.

[0010]

According to a third aspect of the present invention, there is provided the exhaust gas purification apparatus for an internal combustion engine according to the first or second aspect , wherein the reversing means includes a valve body. By switching the valve body from the first position to the second position, the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are reversed, and the valve body is switched from the first position to the second position. , At least part of the exhaust gas bypasses the particulate filter, and when the valve body is located between the first position and the second position, the reducing agent is supplied by the reducing agent supply means. The feature is that the supply of the agent is stopped.

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 first or second aspect , wherein the exhaust gas purification apparatus for an internal combustion engine is always downstream of the particulate filter in an engine exhaust system. An exhaust throttle valve is provided at a position where the temperature of the particulate filter is lower than a set temperature, and the exhaust throttle valve suppresses passage of exhaust gas to make the temperature of the particulate filter equal to or higher than the set temperature. After that, the reducing agent is supplied by the reducing agent supply means.

An exhaust purification system for an internal combustion engine according to a fifth aspect of the present invention is the exhaust purification system for an internal combustion engine according to the first or second aspect , wherein the reversing means includes a valve body, and By switching the valve body from the first position to the second position, the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are reversed, and the valve body is switched from the first position to the second position. At least a part of the exhaust gas bypasses the particulate filter, and the reducing agent supply means supplies the reducing agent to the engine exhaust system at a low pressure, and the reducing agent of the engine exhaust system. An exhaust throttle valve is provided on the downstream side of the supply position of the reducing agent by the supply means, and the passage of exhaust gas is suppressed by the exhaust throttle valve when the engine is decelerated, and Wherein wherein reversing the exhaust upstream side of the particulate filter and an exhaust downstream side I.

According to a sixth aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine, wherein a particulate filter arranged in an engine exhaust system and an exhaust upstream side and an exhaust downstream side of the particulate filter are reversed. And a reversing unit for reversing the particulate filter, the particulate filter having a trapping wall for trapping particulates, the trapping wall carrying an oxidation catalyst and an active oxygen releasing agent, The collecting wall has a first collecting surface and a second collecting surface, and the exhaust upstream side and the exhaust downstream side of the particulate filter are reversed by the reversing means to collect the particulates. The first collecting surface and the second collecting surface of the collecting wall are alternately used, and both side portions of the particulate filter have a higher acid than the central portion of the particulate filter. Characterized in that it has the ability.

According to a seventh aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the sixth aspect , wherein the active oxygen release agent has excess oxygen in the surroundings. It is characterized in that it takes in oxygen, retains oxygen, and releases the retained oxygen in the form of active oxygen when the surrounding oxygen concentration decreases.

[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 19 connected to a downstream side of the exhaust manifold 17 via an exhaust pipe 18, a particulate filter 20,
A first connecting portion 21a connecting one side of the particulate filter 20 and the switching portion 19, a second connecting portion 21b connecting the other side of the particulate filter 20 and the switching portion 19, and a downstream side of the switching portion 19. And an exhaust passage 22 of. The switching unit 19 includes a valve body 19a that allows the exhaust flow to be blocked in the switching unit 19. The valve body 19a is driven by a negative pressure actuator, a step motor, or the like. At one shut-off position of the valve body 19a, the upstream side in the switching unit 19 is communicated with the first connecting unit 21a, and the downstream side in the switching unit 19 is the second connecting unit 21b.
And the exhaust gas, as shown by the arrow in FIG.
The particulate filter 20 flows from one side to the other side.

FIG. 20 shows the other shut-off position of the valve body 19a. At this cutoff position, the switching unit 19
The upstream side of the inside is communicated with the second connection portion 21b and the downstream side of the switching portion 19 is communicated with the first connection portion 21a, and the exhaust gas is discharged from the other side of the particulate filter 20 as indicated by an arrow in FIG. Flows from one side to the other. Thus
By switching the valve body 19a, the direction of the exhaust gas flowing into the particulate filter 20 can be reversed, that is, the exhaust upstream side and the exhaust downstream side of the particulate filter 20 can be reversed.

As described above, the present exhaust gas purification apparatus makes it possible to 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 to facilitate the inflow of exhaust gas,
In this exhaust emission control device, a particulate filter having a large opening area can be used without deteriorating the vehicle mountability.

On the other hand, in the present exhaust gas purifying apparatus, in order to reverse the exhaust upstream side and the exhaust downstream side of the particulate filter, the valve body 19a is rotated from one shut-off position to the other shut-off position. As shown in FIG. 21, the exhaust gas is released into the atmosphere without passing through the particulate filter. Further, this exhaust gas purification device is shown in FIGS.
As shown in FIG. 9, the exhaust pipe 18 located upstream of the switching unit 19 is provided with a reducing agent supply device 23 for supplying a reducing agent such as fuel to the particulate filter 20. Further, regardless of the reverse rotation of the exhaust gas upstream side and the exhaust downstream side of the particulate filter 20 by the valve body 19a, the exhaust gas whose opening can be controlled by a step motor or the like is always located at the downstream side of the particulate filter 20. A throttle valve 24 is arranged.

FIG. 22 shows the structure of the particulate filter 20. Note that, in FIG. 22, (A) is a front view of the particulate filter 20, and (B) is a side sectional view. As shown in these figures, the present particulate filter 20 has an oblong front shape and is of a wall-flow type having a honeycomb structure formed of a porous material such as cordierite. 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 20, 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 also on the pore surface in the partition wall 54, which will be described below. The active oxygen releasing agent and the precious metal catalyst are supported.

The active oxygen releasing agent is one which 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.

As the noble metal catalyst, platinum Pt is usually used. As the active oxygen releasing agent, potassium K, sodium Na, lithium Li, cesium Cs, alkali metals such as rubidium Rb, barium Ba, calcium Ca, strontium are used. An alkaline earth metal such as Sr,
At least one selected from lanthanum La, rare earths such as yttrium Y, and transition metals 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, how the collected particulates are oxidized and removed by the particulate filter carrying such an active oxygen releasing agent will be described.
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,
Exhaust gas containing NO and SO ₂ flows into the exhaust gas upstream side of the particulate filter 20.

23A and 23B schematically show enlarged views of the exhaust gas contact surface of the particulate filter 20. 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, SO is contained in the exhaust gas.
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 1 is activated as the temperature of the catalytic converter becomes higher, the amount of active oxygen O released from the active oxygen release agent 61 per unit time increases as the temperature of the catalytic converter becomes higher. Therefore, the amount of oxidatively removable fine particles capable of oxidizing and removing the particulates per unit time on the catalytic converter 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 oxidatively removable fine particles which can be oxidatively removed without emitting a luminous flame per unit time. 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 fine particles is larger than the amount G of fine 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 region I of FIG. 24, the particulates are oxidized on the particulate filter in a short time without emitting a luminous flame, and in the region II of FIG. 24, the particulates are stacked 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.
26, the supply control of the reducing agent supply device 23 and the switching control of the valve body 19a are performed according to the first flowchart shown in FIG. The amount of fine particles is increased to prevent the accumulation of particulates on the particulate filter. This flowchart is repeated every predetermined time. First, in step 101, it is determined whether the integrated time t is equal to or longer than the set time ts. This integrated time t is the integrated time after switching the valve body 19a. When the determination in step 101 is negative, the integration time t is integrated in step 106 and the process ends, but when the determination is affirmative, the process proceeds to step 102. In step 102, the supply of the reducing agent is started by the reducing agent supply device 23. Then, in step 102,
The valve body 19a is switched. That is, the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are reversed. Next, in step 104, the supply of the reducing agent is stopped, the integrated time t is reset to 0 in step 105, and the integrated time t is newly added in step 106, and the process ends.

The particulate filter 20 of this embodiment.
As described above, the oxidation catalyst such as platinum Pt is supported, but since the exhaust gas of the diesel engine does not usually contain a reducing agent such as HC and CO, the particulates are not included. The temperature of the filter is not raised by the heat of combustion of the reducing agent. Thereby, the temperature of the particulate filter mainly depends only on the exhaust gas temperature. Thus, the exhaust gas inlet portion (exhaust inlet side end portion of each partition wall) of the particulate filter is maintained at the exhaust gas temperature, and in particular, the exhaust gas outlet portion (exhaust outlet side end portion of each partition wall) is heated by the exhaust gas. Due to the outflow, the temperature is considerably lower than the exhaust gas inlet.

Even if the reducing agent is supplied by the reducing agent supply device after the valve element 19a is switched to reverse the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter, the present exhaust gas inlet portion is kept at a low temperature in this way. If so, the reducing agent cannot be satisfactorily combusted by the oxidation catalyst at the exhaust gas inlet, and the temperature of the particulate filter cannot be raised as a whole. However, in the first flowchart, the valve element is switched at every set time ts, and the reducing agent is supplied by the reducing agent supply device before switching the valve element, so the particulate filter maintained at the exhaust gas temperature. In the exhaust gas inlet portion of, the reducing agent burns relatively well by the oxidation catalyst to generate a relatively large amount of heat of combustion. As a result, the exhaust gas inlet portion of the particulate filter rises in temperature, and a relatively large amount of combustion heat arrives at the exhaust gas outlet portion in excess of the heat outflow, and the temperature rises significantly above the exhaust gas inlet portion.

Next, since the exhaust gas upstream side and the exhaust gas downstream side are reversed by the valve body, the reducing agent supplied by the time the supply of the reducing agent is stopped is heated to the present exhaust gas inlet. Good combustion is performed in the section, and a larger amount of combustion heat is generated to further raise the temperature of the exhaust gas inlet portion and significantly raise the temperature of the exhaust gas outlet portion. In this way, it is possible to effectively raise the temperature of the entire particulate filter by using a relatively small amount of reducing agent, and to significantly improve the amount of fine particles that can be removed by oxidation. Even if the operation in II is frequently performed and a certain amount of particulates remains and accumulates on the particulate filter, the particulates can be excellently oxidized and removed. Also,
Before switching the valve element, the oxidation catalyst in the exhaust gas inlet portion of the particulate filter has a soluble organic component (S
Often poisoned by OF) and deteriorated in function, as described above, after the exhaust upstream side and the exhaust downstream side are reversed, this oxidation catalyst, which is located at the exhaust outlet part, has a large temperature rise. Therefore, SOF poisoning can be recovered well.

FIG. 27 is an enlarged sectional view of the partition wall 54 of the particulate filter. During the set time ts, the operation in the area II in FIG. 24 may be performed, and the operation in FIG.
As shown by the lattice in (A), the exhaust gas upstream collision surface with which the exhaust gas mainly collides and the exhaust gas flow opposing surface in the pores collide and collect particulates as one collection surface, Although it is oxidized and removed by the active oxygen releasing agent, this oxidation and removal may be insufficient and particulates may remain. At this point, the exhaust resistance of the particulate filter is not so bad as to adversely affect the running of the vehicle, but if particulates are further accumulated, a problem such as a significant decrease in engine output occurs. At this point, if the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are reversed, further particulate matter will not be accumulated on the particulate matter remaining on one collecting surface of the partition wall 54, and one of the particulate matter will not be accumulated. The residual particulates are gradually oxidized and removed by the active oxygen released from the collecting surface. Further, in particular, the particulates remaining in the pores of the partition wall are easily broken and fragmented by the exhaust gas flow in the opposite direction, and are moved to the downstream side, as shown in FIG.

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 that are still deposited by the backflow of the exhaust gas.

That is, not only the active oxygen released from this collecting surface but also the particulates on the other collecting surface of the partition due to the backflow of the exhaust gas are contained in the residual particulates on one collecting surface of the dividing wall. The remaining active oxygen used for oxidative removal comes with the exhaust gas. As a result, at the time of switching the valve element, even if some particulates are accumulated in a layered manner on one collecting surface of the partition wall,
If the exhaust gas is made to flow backward, in addition to the active oxygen reaching the particulates deposited on the residual particulates, further particulates will not be deposited, so the deposited particulates will be gradually oxidized and removed. ,
If there is a certain amount of time before the next backflow, it can be sufficiently oxidized and removed during this period. In this way, the deposited particulates can be oxidized and removed only by the backflow of the exhaust gas, but if the amount of particulates that can be removed by oxidation is increased by raising the temperature of the particulate filter, the residual and deposited particulates can be reliably and compared. It is possible to oxidize and remove in a relatively short time.

In the first flow chart, since the switching of the valve element is performed at every set time ts, even if the operation in the region II of FIG. 24 is frequently performed during this time, the valve element is switched at the switching point. A large amount of particulates will not be deposited on the particulate filter, and the particulates deposited on the particulate filter will not be left for a long period of time to be transformed into carbon that is difficult to be oxidized. In this way, as described above, the residual and accumulated particulates can be reliably removed by oxidation, and a large amount of the accumulated particulates burn at once, which generates a large amount of heat of combustion and melts the particulate filter. The problem of does not occur.
Of course, the switching timing of the valve body is not limited to each set time, and may be set for each set travel distance. Further, a large amount of particulates may not be deposited and the deposited particulates may be transformed into carbonaceous matter. It may be an arbitrary time such as not. Further, the diesel engine of this embodiment switches between the first combustion and the second combustion, and as described above, the first combustion has a relatively large amount of HC and CO in the exhaust gas, that is, reduction. Contains agents. Accordingly, the first combustion may be used as the reducing agent supply means without switching the reducing agent supply device to the engine exhaust system, and the valve element may be switched during the execution of the first combustion.

If the exhaust gas contains a reducing agent and is burned by the oxidation catalyst, the oxygen concentration in the exhaust gas will decrease. As a result, active oxygen O is released from the active oxygen release agent 61 to the outside at once, and the particulates accumulated by the released active oxygen O at once can be easily burned and removed at once without emitting a bright flame. After the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are reversed by the valve body 19a, the other collecting surface of the particulate filter partition wall in which the particulates do not remain is compared with the one collecting surface. Therefore, since the active oxygen is easily released, the combustion of the reducing agent after the reversal releases a large amount of the active oxygen, and the residual particulates can be more reliably oxidized and removed.

In this way, in addition to reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter, supplying the reducing agent before and after this reversal is very effective in removing residual and accumulated particulates by oxidation. Is effective for. However, as described above, in the structure of the switching unit 19 of the present embodiment, a part of the exhaust gas bypasses the particulate filter 20 while the valve body 19a is being switched from one blocking position to the other blocking position. Will end up. As a result, at this time, if the reducing agent is supplied, the reducing agent will be released into the atmosphere. Therefore, during switching, it is preferable to interrupt the supply of the reducing agent by the reducing agent supply device 23 when the valve element 19a is located between the one blocking position and the other blocking position.

If the exhaust gas contains particulates during the switching of the valve element, the particulates will be released into the atmosphere. FIG. 28 shows
It is a second flowchart for preventing this and oxidizing and removing the deposited particulates. This flowchart is
In addition to controlling the reducing agent supply device and the valve element, it also controls the exhaust throttle valve, which is repeated every predetermined time. First, at step 201, it is judged if the temperature T of the particulate filter is equal to or higher than the set temperature Ts. When this determination is denied, such as when the engine is started, the amount of fine particles that can be oxidized and removed in the active oxygen release agent is low, and the temperature of the particulate filter must be raised immediately. Thereby, the process proceeds to step 202, and the supply of the reducing agent is started. However, at this set temperature Ts, the oxidation catalyst is not sufficiently activated and the reducing agent cannot be combusted sufficiently. Therefore, in step 203, the exhaust throttle valve 24 is decreased in opening degree from full opening,
The heat of the exhaust gas effectively acts on the particulate filter, and at least the exhaust gas inlet portion of the particulate filter is heated to the activation temperature of the oxidation catalyst.

Here, in order to reduce the cost of the reducing agent supply device 23 for supplying the reducing agent to the engine exhaust system,
It is preferred that the reducing agent be injected at low pressure.
Further, the control unit including a valve body for starting and stopping the supply of the reducing agent requires high heat resistance in order to be installed in the vicinity of the engine exhaust system. It is preferably installed separately from the engine exhaust system. Thus, the control unit and the reducing agent supply position of the engine exhaust system are connected by the supply pipe made of stainless steel or the like. In such a configuration, the relatively long supply pipe has a large volume, and the reducing agent injected at a low pressure through this large volume automatically increases when the exhaust gas pressure at the reducing agent supply position of the engine exhaust system increases. Supply will be stopped. As a result, even if the supply of the reducing agent is started by controlling the reducing agent supply device, if the exhaust gas pressure at the reducing agent supply position of the engine exhaust system increases due to the reduction of the opening of the exhaust throttle valve, the reducing agent is actually reduced. Therefore, the reducing agent is not supplied to the particulate filter while the exhaust gas inlet portion of the particulate filter is heated to the activation temperature of the oxidation catalyst.

Next, at step 204, when the exhaust throttle valve is fully opened, the exhaust gas pressure at the reducing agent supply position of the engine exhaust system decreases, and the reducing agent is actually supplied to the engine exhaust system. The reducing agent is supplied to the exhaust gas inlet portion of the particulate filter whose temperature has been raised to the activation temperature of the oxidation catalyst, and the particulate filter is further heated by the combustion heat of the reducing agent, so that the amount of fine particles that can be removed by oxidation can be increased. . The temperature sensor arranged in the particulate filter may be used for the determination in step 201, but the temperature of the particulate filter may be estimated from the current engine operating state, and the particulate sensor may be used when the engine is started. Assuming that the temperature of the filter is equal to or lower than the set temperature, step 202 to step 20 are performed each time the engine is started.
You may make it implement the process of 5. In addition, the reducing agent supply device does not have such a configuration, but supplies the reducing agent by exhaust stroke fuel injection using the engine fuel injection valve, or supplies the reducing agent to the engine exhaust system at high pressure. As described above, if it is possible to supply the reducing agent to the particulate filter as intended, the reducing agent may be supplied after the opening degree of the exhaust throttle valve is increased in step 204.

On the other hand, when the determination in step 201 is affirmative, it is determined in step 206 whether or not the engine is decelerating. If this judgment is denied, the process ends, but if affirmed, step 20
Proceeding to 7, the supply of reducing agent is started. Next, at step 208, the opening of the exhaust throttle valve 24 is decreased from full opening. At this time, the reducing agent is actually supplied to the particulate filter by slowing down the opening degree reduction rate or by performing the process of step 208 with a predetermined time provided after the process of step 207. As a result, in the particulate filter, as described in the first flowchart, the exhaust inlet portion is heated by the combustion of the reducing agent at the exhaust inlet portion, and the exhaust outlet portion is heated more than the exhaust inlet portion. After that, as the opening degree of the exhaust throttle valve 24 decreases, the exhaust gas pressure at the reducing agent supply position in the engine exhaust system increases, and the reducing agent supply is actually stopped.

Next, at step 209, the valve body is switched, that is, the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are reversed. At this time, since the engine is being decelerated, the fuel is cut or the fuel injection amount is small, so that the exhaust gas contains almost no particulates. Moreover, since the supply of the reducing agent is stopped, the reducing agent is not contained in the exhaust gas. Therefore, even if the exhaust gas bypasses the particulate filter during the switching of the valve body, the particulate and the reducing agent are not released into the atmosphere.
Further, the reduction of the opening degree of the exhaust throttle valve during deceleration of the engine can increase the vehicle braking force by the engine braking action.

Next, at step 210, the opening degree of the exhaust throttle valve is fully opened, the exhaust gas pressure at the reducing agent supply position in the engine exhaust system is lowered, and the reducing agent supply is restarted. Then, at step 211. The supply of reducing agent is stopped. As a result, the reducing agent is supplied to the current exhaust gas inlet portion of the particulate filter, which has been set to a high temperature, and in order to satisfactorily combust this reducing agent, the exhaust gas inlet portion is further heated by a large amount of combustion heat. At the same time, the temperature of the exhaust outlet is raised significantly. In this way, it is possible to effectively raise the temperature of the entire particulate filter by using a relatively small amount of reducing agent, and to significantly improve the amount of fine particles that can be removed by oxidation.

Thus, in this flowchart, the valve element is switched with the supply of the reducing agent each time the engine is decelerated. The judgment at the time of deceleration of the engine may be made by detecting the depression of the brake pedal or the release of the accelerator pedal. In this way, it is not considered that the engine deceleration is not performed for a long period of time, and while the valve body is switched, even if the operation in the region II in FIG. 24 is frequently performed, a large amount of particulates is generated. It is not deposited on the filter, and the deposited particulates on the particulate filter are not left to stand for a long period of time to be transformed into carbon. As a result, the residual and deposited particulates can be reliably oxidized and removed as described above, and a large amount of the deposited particulates burn at one time, which generates a large amount of combustion heat and melts the particulate filter. There is no such problem. The position of the exhaust throttle valve is preferably always at the exhaust downstream side of the particulate filter in order to raise the temperature of the particulate filter by the exhaust gas. If it is used only for stopping the supply, the downstream side of the reducing agent supply position may be the upstream side of the particulate filter.

In the first and second flow charts, the reducing agent is supplied mainly before and after the switching of the valve body. Of course, at least the temperature of the inlet of the particulate filter is at the activation temperature of the oxidation catalyst. If it is above, you may make it always supply a reducing agent. As a result, the temperature of the particulate filter is always sufficiently raised and the amount of fine particles that can be removed by oxidation is always maintained at a high level, so that it is possible to almost prevent the particulates from accumulating on the particulate filter. However, when the temperature of the particulate filter becomes equal to or higher than a predetermined temperature, when fuel is used as the reducing agent,
Since the sulfur content in the fuel causes sulfate to be generated in the oxidation catalyst, it is preferable to stop supplying the fuel as the reducing agent when the temperature reaches or exceeds the predetermined temperature.

FIG. 29 is a view showing a particulate filter having a structure different from that described above. This particulate filter carries an oxidation catalyst and an active oxygen releasing agent in the central portion 20a 'and both end portions 20b. 'And 20c'
In the case of (1), a large amount of the oxidation catalyst is supported so that it has a higher oxidation ability than the central portion. As a result, if the reducing agent is supplied to the particulate filter before and after the switching of the valve body as in the first flowchart and the second flowchart, even if the reducing agent is in a very small amount, it will flow into the particulate filter. Shortly after
The one end portion 20b 'or 20c' which is the exhaust gas inlet portion of the particulate filter having a high oxidation ability is surely combusted, and the heat of combustion further raises the other end portion which is the exhaust gas outlet portion of the particulate filter. Further, by switching the valve element, a reducing agent is supplied to the other end, and even if the reducing agent is in a very small amount, the reducing agent is surely burned at the other end having a high oxidizing ability at high temperature. This combustion heat further raises the temperature of the other end and raises the temperature of the one end of the particulate filter, which serves as the exhaust gas outlet, above the other end. Thus
Compared with the particulate filter shown in FIG. 18, it is possible to reliably raise the temperature of the entire particulate filter with a smaller amount of reducing agent.

Even if the reducing agent is not particularly supplied, the exhaust gas inlet portion of the particulate filter has a high oxidizing ability at all times.
Reducing components such as C and CO can be reliably burned, and it is possible to raise the temperature of the entire particulate filter relatively well simply by switching the valve element.

When the temperature of the entire particulate filter is raised in this way, the amount of fine particles that can be oxidized and removed in the central portion 20a is increased, and the particulates that remain and accumulate on the particulate filter can be satisfactorily oxidized and removed. Of course, both ends of the particulate filter can carry not only an oxidation catalyst, but also an active oxygen releasing agent, so that the particulates remaining and accumulated on both ends of the particulate filter can be effectively oxidized and removed by the active oxygen. can do.

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 catalytic converter without being combined with ₃ . Therefore, the particulate filter will not be clogged with ash. Thus, as described above, as the active oxygen releasing agent 61, an 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, or strontium Sr is used. Will be preferred.

Further, even if only a noble metal such as platinum Pt is supported on the particulate filter as an active oxygen releasing agent, NO ₂ or SO ₃ retained on the surface of platinum Pt is retained.
Can release active oxygen. 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 concentration of oxygen in the exhaust gas is high, and releases active oxygen when the concentration of oxygen in the exhaust gas decreases, so for the purpose of oxidizing and removing particulates,
It is necessary to make the air-fuel ratio of exhaust gas rich at regular or irregular intervals.

It is also possible to use, as the active oxygen releasing agent, a NO _x storage reduction catalyst used for purifying NO _x in the exhaust gas. In this case, it is necessary to at least temporarily make the air-fuel ratio of the exhaust gas rich in order to release the stored NO _x and SO _x, and to supply the reducing agent in the first flowchart and the second flowchart,
It can also be used as this enrichment control.

The diesel engine of this embodiment is designed to switch between low-temperature combustion and normal combustion, but this does not limit the present invention. Of course, a diesel engine that only performs normal combustion, or The present invention can be applied to a gasoline engine that discharges particulates.

[0106]

As described above, according to the exhaust gas purifying apparatus for an internal combustion engine of the present invention, the particulate filter disposed in the engine exhaust system and the exhaust upstream side and the exhaust downstream side of the particulate filter are reversed. And a reducing agent supply means for supplying a reducing agent from the upstream side of the reversing means to the particulate filter, and the particulate filter has a collection wall for collecting the particulates. The trapping wall carries an oxidation catalyst and an active oxygen releasing agent, and the trapping wall has a first trapping surface and a second trapping surface, and the reversing means exhausts the particulate filter upstream side and exhausts the particulate filter. By reversing the downstream side, the first collecting surface and the second collecting surface of the collecting wall are alternately used to collect the particulates. 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. Oxidized removal is gradually started by the activated oxygen. 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. Arrives and oxidizes and removes 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. Moreover, the reverse
Exhaust gas upstream side of particulate filter
And before and after the time that the downstream side of exhaust gas is reversed, the reducing agent from the upstream side of the reversing means into the particulate filter by the reducing agent supply means Ru is supplied. As a result, the oxidation catalyst carried on the particulate filter burns the reducing agent, and the heat of combustion raises the temperature of the particulate filter to improve the amount of oxidatively removable fine particles, and the burning of the reducing agent causes the particulate matter in the exhaust gas to be exhausted. The oxygen concentration decreases, which also improves the amount of fine particles that can be removed by oxidation. In this way, the amount of fine particles that can be oxidized and removed by the particulate filter is greatly improved by supplying the reducing agent, and the particulates that remain and accumulate on the particulate filter can be more reliably oxidized and removed in a relatively short time.

Further, according to another exhaust gas purification apparatus for an internal combustion engine of the present invention, a particulate filter arranged in the engine exhaust system and an exhaust upstream side and an exhaust downstream side of the particulate filter are reversed. The particulate filter has a trapping wall for trapping particulates, and the trapping wall carries an oxidation catalyst and an active oxygen releasing agent, and the trapping wall is The trapping filter has a collecting surface and a second collecting surface, and the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are reversed by the reversing means, so that the first part of the collecting wall for collecting the particulates. The collecting surface and the second collecting surface are alternately used, and both side portions of the particulate filter have a higher oxidizing ability than the central portion of the particulate filter. As a result, similarly to the above, the residual particulates can be satisfactorily 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. Further, since the oxidizing ability on both sides of the particulate filter is enhanced, even if the exhaust gas contains only a small amount of reducing substance, this reducing substance is satisfactorily combusted, and the particulate heat is generated by this combustion heat. The temperature of the filter can be raised to increase the amount of fine particles that can be oxidized and removed, and the particulates that remain and accumulate on the particulate filter can be oxidized and removed more reliably and in a relatively short time.

[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 an enlarged cross-sectional view of a partition wall of the particulate filter.

FIG. 28 is a second flowchart for preventing the accumulation of particulates on the particulate filter.

FIG. 29 is a plan view of a part of the engine exhaust system showing another structure of the particulate filter.

[Explanation of symbols]

6 ... Fuel injection valve 16 ... Throttle valve 19 ... Switching unit 19a ... Valve 20 ... Particulate filter

Continuation of front page (51) Int.Cl. ⁷ Identification code FI B01D 46/42 B01D 46/42 B 53/94 53/36 103C (56) Reference JP-A-6-159037 (JP, A) JP-A 5-98939 (JP, A) Actual development Sho 59-30507 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/02 F01N 3/08 B01D 46/42 B01D 53 / 94

Claims (7)

(57) [Claims] 1. A particulate filter arranged in an engine exhaust system, a reversing means for reversing the exhaust upstream side and the exhaust downstream side of the particulate filter, and the particulate filter from the upstream side of the reversing means. Reducing agent supply means for supplying a reducing agent to the particulate filter, the particulate filter has a trapping wall for trapping particulates, and the trapping wall has an oxidation catalyst and active oxygen release. An agent is carried, 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 are reversed by the reversing means. , The first collection surface and the second collection surface of the collection wall are alternately used to collect particulates, and the reducing agent supply means is at least the above-mentioned.
Exhaust of the particulate filter by reversing means
Before and after the upstream side and exhaust downstream side are reversed.
An exhaust emission control device for an internal combustion engine, characterized in that it supplies a reducing agent . 2. The active oxygen releasing agent takes in oxygen to retain oxygen when excess oxygen exists in the surroundings, and releases the retained oxygen in the form of active oxygen when the ambient oxygen concentration decreases. The exhaust emission control device for an internal combustion engine according to claim 1. 3. The reversing means includes a valve body,
By switching the body from the first position to the second position,
Exhaust gas upstream side and exhaust gas downstream side of the particulate filter
And the valve body is rotated from the first position to the second position.
At least one exhaust gas
Part bypasses the particulate filter
And the valve body has the first position and the second position.
When it is located between the
2. The supply of the reducing agent is stopped.
2. An exhaust gas purification device for an internal combustion engine according to item 2. 4. The particulates in the engine exhaust system are always said.
An exhaust throttle valve is installed on the downstream side of the rate filter.
The temperature of the particulate filter is set to the set temperature.
When the temperature is lower than the
The temperature of the particulate filter by suppressing the excess.
The temperature is set to be equal to or higher than the preset temperature, and then the reducing agent supply means is used.
The reducing agent is supplied by
Item 3. An exhaust gas purification device for an internal combustion engine according to item 1 or 2 . 5. The reversing means comprises a valve body, and the valve
By switching the body from the first position to the second position,
Exhaust gas upstream side and exhaust gas downstream side of the particulate filter
And the valve body is rotated from the first position to the second position.
At least one exhaust gas
Part bypasses the particulate filter
The reducing agent supply means is designed to
The reducing agent is supplied by pressure, and the above-mentioned return of the engine exhaust system is performed.
Downstream of the reducing agent supply position by the original material supply means
Is equipped with an exhaust throttle valve, which is used when the engine is decelerated.
The exhaust valve suppresses the passage of exhaust gas and the valve
Exhaust upstream side of the particulate filter by the body
And the downstream side of the exhaust gas is reversed.
Is an exhaust emission control device for an internal combustion engine according to 2 . 6. A particulate matter arranged in an engine exhaust system.
Filter and the exhaust of the particulate filter
And a reversing means for reversing the flow side and the exhaust downstream side.
The particulate filter is a particulate filter.
Has a collection wall for collecting the
A catalyst and an active oxygen releasing agent are supported, and the collection wall is a first
It has a collecting surface and a second collecting surface, and the reversing means is used to
The exhaust upstream side and exhaust downstream side of the ticulate filter are
By being reversed, it collects particulates.
The first collection surface and the second collection surface of the collection wall
Used alternately, both sides of the particulate filter
Compared to the central part of the particulate filter
And an exhaust purification device for an internal combustion engine, which has a high oxidation ability . 7. The active oxygen-releasing agent is an excessive oxygen
In the presence of oxygen uptake and retains oxygen and the surrounding acid
When the elemental concentration decreases, the retained oxygen is released in the form of active oxygen
The exhaust gas purification device for an internal combustion engine according to claim 6 , wherein: