JP3521878B2 - 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, simply disposing this type of filter in the engine exhaust system may cause clogging at a relatively early stage and significantly reduce the engine output.

Therefore, an object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine, which can satisfactorily oxidize and remove the particulates collected by the particulate filter and prevent clogging of the particulate filter. Is.

[0008]

An exhaust gas purification apparatus for an internal combustion engine according to claim 1 of the present invention is a particulate filter arranged in an engine exhaust system, and an exhaust gas upstream side and an exhaust gas downstream side of the particulate filter. And a reversing means for reversing, and the particulate filter is oxidized in the particulate filter,
The particulate filter has a trapping wall for trapping particulates, and the trapping wall has a first trapping surface and a second trapping surface, and the particulate filter is provided by the reversing means. The first and second collection surfaces of the collection wall are alternately used to collect particulates by reversing the exhaust upstream side and the exhaust downstream side of the The particulate filter has an oxidizing function, and the reversing means reverses the exhaust upstream side and the exhaust downstream side of the particulate filter when the temperature of the exhaust outlet of the particulate filter is higher than the temperature of the exhaust inlet. It is characterized by

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, wherein the particulate filter carries an active oxygen releasing agent. The active oxygen released from the active oxygen releasing agent oxidizes the particulates.

According to a third aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the second aspect of the present invention, 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.

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 second aspect, wherein the active oxygen release agent has excess oxygen present around it. It is characterized in that NO _x is bound to oxygen and retained, and when the ambient oxygen concentration decreases, the bound NO _x and oxygen are decomposed into NO _x and active oxygen and released.

According to a fifth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fourth aspects, wherein the reversing means is used to remove the particulate filter. Even when it is time to reverse the exhaust gas upstream side and the exhaust gas downstream side, the reverse rotation by the reversing means is postponed until the temperature of the exhaust gas outlet portion of the particulate filter becomes higher than the temperature of the exhaust gas inlet portion. .

An exhaust purification system for an internal combustion engine according to a sixth aspect of the present invention is the exhaust purification system for an internal combustion engine according to any one of the first to fourth aspects, wherein the reversing means is the particulate filter. The temperature of the exhaust outlet is higher than the temperature of the exhaust inlet, and the exhaust upstream side and the exhaust downstream side of the particulate filter are reversed during engine deceleration.

[0014]

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 in the diesel engine of FIG. Yes, FIG. 3 is a bottom view of the cylinder head in 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,
Is a combustion chamber formed in the cavity 5a, 6 is an electrically controlled fuel injection valve, 7 is a pair of intake valves, 8 is an intake port, 9
Indicates a pair of exhaust valves, and 10 indicates an exhaust port, respectively. The intake port 8 is connected to the surge tank 1 via the corresponding intake branch pipe 11.
2, the surge tank 12 is connected to the air cleaner 14 via the intake duct 13. A throttle valve 16 driven by an electric motor 15 is provided in the intake duct 13.
Are placed. 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 engine cooling water cools the EGR gas.

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 is composed of 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, of the six fuel sprays F, two fuel sprays F are scattered along the lower side surface of the valve body of each exhaust valve 9. 2 and 3 show the time when 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 toward the valve body of the exhaust valve 9 goes between the rear surface of the umbrella portion of the exhaust valve 9 and the exhaust port 10. In other words, in other words, of the six nozzle openings of the fuel injection valve 6, two nozzle openings eject the fuel spray F when the additional fuel Qa is injected while the exhaust valve 9 is open. It is formed so as to face between the rear surface of the umbrella portion of the valve 9 and the exhaust port 10. In the embodiment shown in FIG. 4, the fuel spray F collides with the rear surface of the exhaust valve 9 at this time, and the fuel spray F that collides with the rear surface of the exhaust valve 9 is reflected on the rear surface 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 , CO,
It represents the experimental examples showing the emissions changes in NO _X. Figure 6
As can be seen from this, in this experimental example, the EGR rate increases as the air-fuel ratio A / F decreases, and the theoretical air-fuel ratio (≈14.
When it is 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 smoke is generated when the air-fuel ratio A / F becomes about 30. The quantity begins to increase. Then
When the EGR rate is further increased and the air-fuel ratio A / F is reduced, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke 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 NO
The amount of _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 generated 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, the air-fuel ratio A / F is 15.
When the amount of smoke produced is less than 0 and the amount of smoke produced is almost zero, the amount of NO _x produced decreases considerably as shown in FIG. The decrease in the amount of NO _x generated 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) where soot is hardly generated, and therefore the combustion temperature in the combustion chamber 5 is low at this time.

Second, when the amount of smoke produced, that is, the amount of soot produced, becomes almost zero, the amounts of HC and CO discharged increase as shown in FIG. 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. No combustion, combustion chamber 5
It has been found that soot is produced when the temperature of the fuel inside and inside it falls 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 is closely related to the amount of NO _x produced, and therefore this certain temperature is defined to some extent from the amount of NO _x produced. can do. That is, as the EGR rate increases, the temperature of the fuel and the gas around it during combustion decreases, and the amount of NO _x generated decreases. At this time, soot is hardly generated when the amount of NO _x generated is around 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 simply be purified by post-treatment with 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. In this way, NO _X
It is extremely effective to purify the exhaust gas by reducing the amount of the exhaust gas generated and discharging hydrocarbons from the combustion chamber 5 in the state of the soot precursor or in the state before it.

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

That is, when 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 produced, 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 peaks 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, and the EGR rate at which the amount of soot generated peaks when the engine load decreases and the EGR rate at which soot hardly occurs is slightly decreased. 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 which is necessary to bring the temperature of the fuel and the gas around it to a temperature lower than the temperature at which soot is produced 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 FIG. 10, the vertical axis represents the combustion chamber 5
The total amount of intake gas sucked into the combustion chamber 5 is shown, and the chain line Y shows the total amount of intake gas that can be drawn into the combustion chamber 5 when supercharging is not performed. The horizontal axis shows the required load,
Z1 indicates a 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 proportion of EGR gas, that is, the amount of EGR gas in the mixed gas, is necessary to bring the temperature of the fuel and its surrounding gas to a temperature lower than the temperature at which soot is formed when the injected fuel is burned. The minimum EGR gas amount 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 intake gas amount sucked into the combustion chamber 5 is shown by the solid line X in FIG. 10, and the ratio of the air amount to the EGR gas amount of this total intake gas amount X is set as shown in FIG. The temperature of the fuel and the gas around it is lower than the temperature at which soot is produced,
Thus, no soot is generated. Also, NO at this time
_The amount of _X generation is around 10 p.pm or less, and therefore the amount of NO _X generation 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 intake air, or EG
It is necessary to supercharge or pressurize the R 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, in FIG. 10, 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 also 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 rises, 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 at this time lean.

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 are suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, and first combustion, that is, low temperature combustion is performed. The second combustion when the engine load is relatively high,
That is, the combustion that has been conventionally performed 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 the combustion method of. 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, referring to FIG. 13, the first operating region I and the second
The operation control in the operation area II will be schematically described.

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 about half open as the required load L increases, and the EGR control valve 23 The opening degree of is gradually increased from near full close to full open as the required load L increases. In addition, FIG.
In the example shown in (1), 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 which is slightly lean. In addition,
The air-fuel ratio at this time 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 to the fully closed state, and at this time, the EGR control valve 23 is also closed to the fully closed state. When the throttle valve 16 is closed to near full closure, the pressure in the combustion chamber 5 at the beginning of compression becomes low and 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 approximately 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. Soot and NO _X is slightly higher for although thermal efficiency as compared with low temperature combustion occurs, thus operating region of the engine is the first second from operating region I of the operation area II in the combustion process
When changed to, the injection amount is reduced stepwise as shown in FIG.

In the second operating range 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.

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), the required load L and the engine speed N
The target opening degree SE of the EGR control valve 23, which is stored in advance in the ROM 32 in the form of a map as a function of, and is required to bring the air-fuel ratio to the target air-fuel ratio shown in FIG. 14, is shown in FIG. 15 (B). As described above, 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 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. The target opening degree SE of the EGR control valve 23 required for the above 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).

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

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

FIG. 20 shows the other shut-off position of the valve body 71a. In this cutoff position, the switching unit 71
The upstream side of the inside is communicated with the second connection portion 72b and the downstream side of the switching portion 71 is communicated with the first connection portion 72a, and the exhaust gas is discharged from the other side of the particulate filter 70 as indicated by an arrow in FIG. Flows from one side to the other. Thus
By switching the valve body 71a, the direction of the exhaust gas flowing into the particulate filter 70 can be reversed, that is, the exhaust upstream side and the exhaust downstream side of the particulate filter 70 can be reversed. In FIG. 18, 43a is a first pressure sensor for detecting the exhaust pressure in the first connecting portion 72a, and 43b
Is a second pressure sensor for detecting the exhaust pressure in the second connecting portion 72b. 44a is a first temperature sensor for detecting the temperature at one end of the particulate filter 70, and 44b is a second temperature sensor for detecting the temperature at the other end of the particulate filter 70. is there.

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, as shown in FIGS. 18 and 19, it is possible to use a particulate filter having a large opening area without deteriorating the vehicle mountability.

FIG. 21 shows the structure of the particulate filter 70. Note that, in FIG. 21, (A) is a front view of the particulate filter 70, and (B) is a side sectional view. As shown in these drawings, the present particulate filter 70 has an oblong front shape and is of a wall-flow type having a honeycomb structure formed of a porous material such as cordierite, and has a large number of axis lines. It has a number of axial spaces subdivided by partitions 54 extending in the direction. In the two adjacent axial spaces, one is closed on the exhaust downstream side and the other is closed on the exhaust upstream side by the plug 53. Thus, one of the two adjoining axial spaces serves as the exhaust gas inflow passage 50 and the other serves as the outflow passage 51, and the exhaust gas flows as shown in FIG.
As shown by the arrow in (B), it always passes through the partition wall 54.
Although the particulates in the exhaust gas are very small compared to the size of the pores of the partition wall 54, they are collected by colliding with the exhaust upstream surface of the partition wall 54 and the pore surface in the partition wall 54. To be done. In this way, each partition wall 54 functions as a collection wall that collects particulates. In the present particulate filter 70, in order to oxidize and remove the collected particulates, on both side surfaces of the partition wall 54, and
Preferably, an active oxygen releasing agent and a noble metal catalyst, which will be described below, are also loaded on the surface of the pores in the partition wall 54 using alumina or the like.

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, oxygen is taken in to retain the oxygen and keep the surrounding oxygen. 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, and as an active oxygen releasing agent, potassium K, sodium Na, lithium Li, cesium Cs, alkali metals such as rubidium Rb, barium Ba, calcium Ca, strontium. 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, regarding how the collected particulates are oxidized and removed by the particulate filter carrying such an active oxygen releasing agent,
The case of platinum Pt and potassium K will be described as an example.
Similar noble metals, alkali metals, alkaline earth metals, rare earths, and transition metals can be used to perform the same particulate removing action.

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

22A and 22B schematically show enlarged views of the exhaust gas contact surface of the particulate filter 70. In FIGS. 22A and 22B, 60 indicates particles of platinum Pt, and 61 indicates an active oxygen release agent containing potassium K.

As described above, since the exhaust gas contains a large amount of excess oxygen, when the exhaust gas comes into contact with the exhaust gas contact surface of the particulate filter, 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 ). Next, a part of the NO ₂ thus generated is absorbed on the active oxygen release agent 61 while being oxidized on the platinum Pt, and is combined with the potassium K to form a nitrate ion NO ₃ ⁻ as shown in FIG. 22 (A). And diffuses into the active oxygen release agent 61 to generate potassium nitrate KNO ₃ . Thus, in this embodiment, the NO contained in the exhaust gas is
_X can be absorbed by the particulate filter 70, and the amount released into the atmosphere can be greatly reduced.

On the other hand, as described above, the exhaust gas contains SO.
_{2 is} also included, and this SO ₂ is also absorbed in the active oxygen release agent 61 by the same mechanism as NO. That is, the oxygen O ₂ as described above O ₂ ^- are attached to or O ^2- form on the surface of the platinum Pt in, SO ₂ in the exhaust gas on the surface of the platinum Pt O ₂ ^- or O ^2- and Reacts to SO ₃ . Then, a part of the generated SO ₃ is absorbed on the active oxygen releasing agent 61 while being further oxidized on the platinum Pt, and is bound to the potassium K to form the sulfate ion SO ₄ ²⁻ in the active oxygen releasing agent 61. Diffuses to produce potassium sulfate K ₂ SO ₄ . In this way, potassium nitrate KNO is stored in the active oxygen release catalyst 61.
₃ and potassium sulfate K ₂ SO ₄ are produced.

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, potassium sulfate K ₂ SO ₄ formed in the active oxygen release agent 61 is also decomposed into potassium K, oxygen O and SO _2, and oxygen O is particulate 6
SO ₂ is released from the active oxygen release agent 61 to the outside toward the contact surface between the 2 and the active oxygen release agent 61. The SO ₂ released to the outside is oxidized on the platinum Pt on the downstream side,
It is again absorbed in the active oxygen release agent 61. However, since potassium sulfate K ₂ SO ₄ is stabilized, it is more difficult to release active oxygen than potassium nitrate KNO ₃ .

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 particulate 62, the particulate 62 is oxidized in a short time of several minutes to tens of minutes without emitting a bright flame. The active oxygen O that oxidizes the particulates 62 is also released when NO and SO ₂ are absorbed by the active oxygen release agent 61. That is, NO _X
Is believed to diffuse in the form of nitrate ions NO ₃ ^{− in} the active oxygen release agent 61 while repeating the bonding and separation of oxygen atoms, and active oxygen is also generated during this period. The particulate 62 is also oxidized by this active oxygen. Further, the particulates 62 thus adhered to the particulate filter 70 are oxidized by the active oxygen O, but the particulates 62 are also oxidized by oxygen in the exhaust gas.

By the way, platinum Pt and the active oxygen release agent 61
Is activated as the temperature of the particulate filter increases, so the amount of active oxygen O released from the active oxygen release agent 61 per unit time increases as the temperature of the particulate filter increases. Also, of course,
The higher the temperature of the particulate itself, the easier it is to be oxidized and removed. Therefore, the amount of oxidatively removable fine particles capable of oxidizing and removing the particulates per unit time on the particulate filter without emitting a luminous flame increases as the temperature of the particulate filter increases.

The solid line in FIG. 23 shows the amount G of oxidatively removable fine particles that can be oxidatively removed without emitting a luminous flame per unit time, and the horizontal axis in FIG. 23 shows the temperature TF of the particulate filter. Note that FIG. 23 shows a case where the unit time is 1 second, that is, the amount G of fine particles that can be removed by oxidation per second.
Any time such as 1 minute or 10 minutes can be adopted. For example, when 10 minutes is used as the unit time, the amount G of fine particles that can be removed by oxidation per unit time represents the amount G of fine particles that can be removed by oxidation per 10 minutes, and even in this case, the unit on the particulate filter 70 is As shown in FIG. 23, the amount G of oxidatively removable fine particles that can be oxidatively removed without emitting a luminous flame per time increases as the temperature of the particulate filter 70 increases.

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, for example, per second. When the amount M of discharged fine particles is smaller than the amount G of fine particles that can be oxidized and removed per second or when the amount M of discharged fine particles per 10 minutes is smaller than the amount G of fine particles that can be oxidized and removed per 10 minutes, that is, the region of FIG. In I, all the particulates discharged from the combustion chamber are successively oxidized and removed in a short time without emitting a bright flame on the particulate filter 70.

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. 23, the amount of active oxygen is insufficient to sequentially oxidize all the particulates. FIGS. 24A to 24C 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 are not oxidized one after another remain on the exhaust gas upstream surface, 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 by the residual particulate portion 63, the platinum Pt oxidizes NO and SO ₂ and the active oxygen release agent 61 releases active oxygen. 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
Another particulate 64 is deposited on the top of the top one after another. That is, when the particulates are deposited in a laminated form, since the particulates are separated from the platinum Pt and the active oxygen releasing agent, even if they are easily oxidized, they will not be oxidized by the active oxygen. Absent. 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. 23, the particulates are oxidized on the particulate filter in a short time without emitting a luminous flame, and in the region II of FIG. 23, 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. As a result, the pressure loss of the exhaust gas flow in the particulate filter 70 does not change at all and is maintained at a substantially constant minimum pressure loss value. In this way, the reduction in engine output can be kept to a minimum. 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.
25, the switching control of the valve body 71a is performed according to the first flowchart shown in FIG. 25 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 or not it is time to switch the valve element. For example, the time when the integrated value of the traveling distance of the vehicle becomes equal to or more than the set traveling distance can be set as the valve element switching timing.

FIG. 26 is an enlarged sectional view of the partition wall 54 of the particulate filter. While the vehicle travels the set travel distance, driving in the area II of FIG. 23 may be performed, and as shown by the grid in FIG. 26 (A), the partition wall 54 on which the exhaust gas mainly collides. The exhaust gas upstream surface and the exhaust gas flow opposing surface in the pores collide and collect particulates as one collection surface and oxidize and remove by the active oxygen releasing agent, but this oxidization and removal become insufficient and Curates 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. As a result, it is preferable that the valve element switching timing is reached at least at such a particulate accumulation time point, and the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are preferably reversed. Due to this inversion, no further particulates are deposited on the particulates remaining on one of the collecting surfaces of the partition wall 54, and the residual particulates are gradually oxidized by the active oxygen released from the one collecting surface. To be removed. In addition, the particulates remaining in the pores of the partition wall are generated by the exhaust gas flow in the opposite direction.
As shown in (B), it is easily broken and subdivided, and moves to the downstream side.

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

That is, not only the active oxygen released from this collection surface but also the particulates on the other collection surface of the partition due to the backflow of exhaust gas are contained in the residual particulates on one collection surface of the partition. The remaining active oxygen used for oxidative removal comes from the exhaust gas. As a result, at the time of switching of the valve body, even if some particulates are accumulated in a layered manner on one collecting surface of the partition wall, if exhaust gas is made to flow backward, the particulates will be accumulated on the residual particulates. Also, in addition to the arrival of active oxygen, further particulates will not be deposited, so the deposited particulates will be gradually oxidized and removed, and if there is some time before the next backflow,
During this period, it can be sufficiently oxidized and removed.

The switching timing of the valve element may be set every set time instead of every predetermined traveling distance. As a matter of course, the valve body switching timing may be set irregularly instead of regularly. In any case, the valve element should be switched at least once between the engine start and the engine stop so that it is set before the residual particulates on the particulate filter are transformed into carbon that is difficult to be oxidized. Is preferred. In addition, if a large amount of particulates are oxidized and removed before they are deposited, a large amount of deposited particulates will ignite and burn at one time to generate a large amount of combustion heat, and this combustion heat will cause the particulate filter to melt. It also prevents problems such as Also,
Even if a large amount of particulates accumulates on one collecting surface of the particulate filter partition wall at the time of switching the valve body due to some factor, if the valve body is switched, the accumulated particulates will be exhaust gas in the opposite direction. Since it is relatively easily broken and fragmented by the flow, some of the fragmented particulates that could not be oxidized and removed in the pores of the partition wall are discharged from the particulate filter. Exhaust resistance will not be further increased and will not adversely affect vehicle running. Further, new collection of particulates is possible on the other collection surface of the particulate filter partition wall.

Further, the exhaust pressure P1 on one side of the particulate filter 70, that is, the exhaust pressure in the first connecting portion 72a (see FIG. 18) is measured by the first pressure sensor 43a arranged in the first connecting portion 72a. The second pressure sensor 43 arranged at the second connecting portion 72b detects the exhaust pressure P2 on the other side of the particulate filter 70, that is, the exhaust pressure in the second connecting portion 72b (see FIG. 18).
The valve body switching timing may be set when the absolute value of the differential pressure between the exhaust pressures P1 and P2 detected by b is equal to or greater than the set pressure difference. Here, the absolute value of the differential pressure is used because it is possible to grasp the increase in the differential pressure regardless of which of the first connecting portion 72a and the second connecting portion 72b is on the exhaust upstream side. At this switching timing of the valve element, since a certain amount of particulate remains in the particulate filter, it is preferable to switch the valve element 71a to reverse the exhaust upstream side and the exhaust downstream side of the particulate filter. .

As a result, the residual particulates are oxidized and removed from the particulate filter as described above. In this way, the fact that a certain amount of particulate matter remains in the particulate filter is indirectly detected using the differential pressure on both sides of the particulate filter,
It is possible to reliably prevent the further increase in the amount of particulates and the significant reduction in the engine output. Of course, in addition to this differential pressure, for example, a change in the electrical resistance value on a predetermined partition in the particulate filter is monitored, and when the electrical resistance value becomes less than or equal to a set value due to the accumulation of particulates, the particulate filter is used. It may be time to switch the valve body on the assumption that a certain amount of particulates are accumulated on the upper part, and also, in a predetermined partition wall of the particulate filter, the transmittance of light is reduced due to the accumulation of particulates, or By utilizing the fact that the reflectance decreases, it may be determined that a certain amount of particulates has accumulated on the particulate filter, and this may be used as the valve body switching timing. As described above, the valve output is switched by directly judging the remaining amount of particulates, so that it is possible to more surely prevent a large decrease in the engine output. Strictly speaking, the pressure difference between the two sides of the particulate filter also changes depending on the exhaust gas pressure discharged from the cylinder for each engine operating state. It is preferable to specify.

As described above, if the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are reversed at the time of switching the valve element, the residual and accumulated particulates can be oxidized and removed relatively favorably. In the flowchart, in order to oxidize and remove the residual and accumulated particulates even better, when it is judged in step 101 that it is time to switch the valve element, steps 102 and 10 are performed.
The process 3 is performed.

In step 102, the first temperature sensor 44
a and the temperatures of the two ends of the particulate filter 70 detected by the second temperature sensor 44b,
It is determined whether or not the current temperature To of the exhaust outlet side end is higher than the current temperature Ti of the exhaust inlet side end. When this determination is affirmative, the valve body 71a is switched in step 104. However, when the determination in step 102 is negative, in step 103, the elapsed time t after the switching timing of the valve body 71a is the set time t1.
It is determined whether or not the above. When this determination is affirmative, a large amount of particulates may accumulate on the collecting surface on the upstream side of the particulate filter partition wall at present, and the routine proceeds to step 104, where the valve body 71a is immediately switched.

On the other hand, when the determination in step 103 is negative, the process returns to step 102. Thus, the determinations in steps 102 and 103 are repeated, and when the determination in step 102 is affirmed, step 104
At, the valve body 71a is switched.

When the particulate filter has an oxidizing function by carrying an oxidation catalyst such as platinum as in the present embodiment, the particulate filter reduces the reducing substances such as HC and CO in the exhaust gas. Can be burned. The heat of combustion raises the temperature of the particulate filter to increase the amount of fine particles that can be removed by oxidation, and also raises the temperature of the particulate itself, which is advantageous for the oxidation removal of particulates.

Exhaust gas flows from the exhaust upstream surface of the particulate filter partition wall to the exhaust downstream surface through the pores of the partition wall, but on the exhaust upstream surface or the exhaust downstream surface except through the pores. Flowing along. As a result, the combustion heat at the exhaust gas inlet portion of the particulate filter (the end portion on the exhaust gas inlet side of each partition wall), together with the exhaust gas, passes through the central portion of the particulate filter (central portion of each partition wall) of the particulate filter. It moves to the exhaust outlet (the end of each partition on the exhaust outlet side) and is finally discharged from the particulate filter.

The air-fuel ratio of normal exhaust gas is lean,
Exhaust gas contains only a small amount of reducing substances, and at the exhaust gas inlet portion, a small amount of combustion heat is taken by the exhaust gas, and there is almost no rise in temperature due to combustion heat. On the other hand, in the central part, the combustion heat here is taken away by the exhaust gas, but due to heat transfer from the exhaust inlet part, the temperature rises above the exhaust inlet part, and the exhaust outlet part adds to the combustion heat here. The temperature is best raised by heat transfer from the exhaust inlet and the central part.

In this way, when a temperature difference is caused in each part of the particulate filter, a difference occurs in the degree of activation of the oxidation catalyst in each part, and the reducing substance in the exhaust gas hardly burns at the exhaust inlet part, and is mainly Combustion occurs at the exhaust outlet, and the temperature difference between each part of the particulate filter is
It becomes remarkable as shown by the dotted line in FIG.

However, even if the reducing substance is burned mainly at the exhaust outlet, this combustion heat is only discharged from the particulate filter without raising the temperature of the other parts of the particulate filter, and the particulate heat is emitted. It is not effective in improving the amount of fine particles that can be removed by oxidation of the filter.

In this flowchart, the temperature of the exhaust gas outlet is usually higher than that of the exhaust gas inlet at the time when the valve body 71a is switched, and the determination at step 102 is affirmative. The switching of 71a is performed, and as described above, the residual particulates on the trapping surface, which has been on the upstream side of the exhaust gas, are removed by oxidation, and at the same time, the new particulates on the trapping surface, which is on the upstream side of the exhaust gas, are removed. Collection is started. Further, the current exhaust gas inlet part has a relatively high temperature because it is the exhaust gas outlet part so far, and in order to burn most of the reducing substances in the exhaust gas, the combustion heat at the exhaust gas inlet part increases, Even if the exhaust gas is moved to some extent by the exhaust gas to the central portion and the exhaust outlet portion, the exhaust inlet portion can be heated relatively well.

Thus, the temperature of the exhaust gas inlet portion is kept relatively high, and for a while, most of the reducing substances in the exhaust gas can be burned at the exhaust gas inlet portion. When the reducing substance is burned mainly at the exhaust gas inlet, this combustion heat not only heats the exhaust gas inlet, but also the central portion and the exhaust gas before being discharged from the particulate filter by heat transfer by the exhaust gas. In order to raise the temperature of the outlet, the temperature distribution shown by the solid line in FIG. 29 is obtained, and the temperature of the particulate filter can be entirely raised. As a result, the reducing substance in the exhaust gas can be effectively utilized for increasing the amount of fine particles that can be removed by oxidation.

Thus, the period in which the temperature of the exhaust gas inlet is kept relatively high is not so long because the amount of the reducing substance contained in the exhaust gas in the normal lean state is small, The temperature at the exhaust inlet gradually decreases,
Finally, as described above, the temperature distribution shown by the dotted line in FIG. 29 is obtained. However, if the air-fuel ratio of the exhaust gas is rich and the exhaust gas contains a relatively large amount of reducing substances,
During that time, a relatively large amount of heat of combustion is generated at the exhaust gas inlet portion, and the temperature at the exhaust gas inlet portion can be maintained relatively high.

Thus, if the temperature of the exhaust gas inlet portion of the particulate filter is higher than that of the exhaust gas outlet portion even when the valve body 71a is switched, it is possible to immediately reverse the exhaust gas inlet portion and the exhaust gas outlet portion. It is not preferable because the reducing substance in the exhaust gas cannot be effectively used to raise the temperature of the particulate filter, and in step 103 of this flowchart, the elapsed time t after the valve body switching timing becomes the set time t1. Until then, the valve body 71a is not switched.

In this flow chart, when it becomes time to switch the valve element based on the distance traveled by the vehicle, the temperature of the exhaust inlet of the particulate filter is compared with the temperature of the exhaust outlet to actually switch the valve. Whether or not the switching of the valve body is performed arbitrarily is effective, of course, so that the temperature of the exhaust outlet of the particulate filter simply becomes higher than the temperature of the exhaust inlet. The valve element may be switched when the valve is opened.

Further, as in the second flow chart shown in FIG. 28, when the temperature To of the exhaust outlet of the particulate filter is higher than the temperature Ti of the exhaust inlet (step 2
In (01), it may be determined whether the engine is decelerating (step 202), and if the engine is decelerating, the valve element may be switched (step 203). Further, each time the temperature To of the exhaust outlet of the particulate filter becomes higher than the temperature Ti of the exhaust inlet, the valve element may be switched after the engine deceleration. The judgment during engine deceleration may be made by detecting the fuel cut signal, or by detecting the brake pedal depression signal while the vehicle is traveling, or by detecting the accelerator pedal release signal while the vehicle is traveling. May be.

In the structure of the switching portion 71 of this exhaust purification system,
During the switching of the valve body 71a, the inside of the switching portion 71 is opened, and a part of the exhaust gas directly flows into the exhaust passage 73, and thus bypasses the particulate filter. During engine deceleration, the exhaust gas contains almost no particulates because the fuel is cut or the fuel injection amount is very small. Thereby,
At this time, if the valve body is switched, even if some of the exhaust gas bypasses the particulate filter, the particulate will not be released into the atmosphere. Further, at the time of deceleration of the engine, the exhaust gas temperature becomes very low because the fuel is cut or the fuel injection amount is very small. Therefore, if the valve body is switched at this time, the particulate filter can be bypassed even with a part of the exhaust gas, and the temperature decrease of the particulate filter, that is, the reduction of the amount of fine particles that can be removed by oxidation can be suppressed. .

In the first and second flowcharts, the temperature of the exhaust gas inlet portion and the temperature of the exhaust gas outlet portion of the particulate filter are actually detected, but of course, the exhaust gas temperature which changes depending on the engine operating state. Also, the temperature of the exhaust inlet and the temperature of the exhaust outlet of the particulate filter may be estimated based on the amount of reducing substances in the exhaust gas, or only the higher temperature may be estimated. .

When the air-fuel ratio of the exhaust gas is made rich, that is, when the oxygen concentration in the exhaust gas is reduced,
The active oxygen O is released from the active oxygen release agent 61 to the outside at once. Due to the active oxygen O released all at once, the deposited particulates are easily oxidized and easily removed by oxidation.

On the other hand, when the air-fuel ratio is kept lean, the surface of platinum Pt is covered with oxygen, so-called oxygen poisoning of platinum Pt occurs. When such oxygen poisoning occurs, NO _X
Absorption efficiency of the NO _X to effect oxidation is reduced is decreased with respect to the active oxygen release amount from the active oxygen release agent 61 is lowered by thus. However the air-fuel ratio of oxygen poisoning is eliminated to when it is rich, oxygen on the platinum Pt surface is consumed, therefore NO to the air-fuel ratio becomes stronger oxidation effect on is the NO _X switched from rich to lean _X Of the active oxygen release agent 61 increases, and thus the amount of active oxygen released from the active oxygen release agent 61 increases.

Therefore, if the air-fuel ratio is occasionally switched from lean to rich while the air-fuel ratio is maintained lean, oxygen poisoning of platinum Pt is eliminated each time, so that the air-fuel ratio is lean. The amount of active oxygen released increases, and thus the oxidizing effect of the particulates on the particulate filter 70 can be promoted.

Furthermore, the elimination of this oxygen poisoning is, so to speak,
Since the reducing substance is burned, the particulate filter is heated with heat generation. As a result, the amount of fine particles that can be removed by oxidation in the particulate filter is improved, and the remaining and accumulated particulates are easily removed by oxidation. If the air-fuel ratio of the exhaust gas is made rich immediately after switching the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter by the valve body 71a, on the other collecting surface of the particulate filter partition wall where no particulate remains. Since the active oxygen is released more easily than the one collecting surface, the residual particulates on the one collecting surface can be more surely oxidized and removed by a larger amount of the released active oxygen. Of course, valve body 7
The air-fuel ratio of the exhaust gas may occasionally be made rich regardless of the switching of 1a, which makes it difficult for particulates to remain and accumulate on the particulate filter.

As a method for making the air-fuel ratio of the exhaust gas rich, for example, the above-mentioned low temperature combustion may be carried out. Of course, the time when the normal combustion is switched to the low temperature combustion may be used as the valve body switching timing. Further, in order to make the air-fuel ratio of the exhaust gas rich, the combustion air-fuel ratio may simply be made rich. In addition to the normal main fuel injection in the compression stroke, fuel may be injected (post-injection) into the cylinder in the exhaust stroke or expansion stroke by the engine fuel injection valve, or fuel may be injected into the cylinder in the intake stroke. May be jetted (rubber jet). Of course, it is not always necessary to provide an interval between the main fuel injection and the post injection or the rubber injection. It is also possible to supply fuel to the engine exhaust system.

By the way, calcium Ca in the exhaust gas produces calcium sulfate CaSO ₄ when SO ₃ is present. This calcium sulfate CaSO ₄ is difficult to be removed by oxidation and remains as ash on the particulate filter. Therefore, in order to prevent clogging of the particulate filter due to residual calcium sulfate, an alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca as the active oxygen release agent 61,
For example, it is preferable to use potassium K, so that SO ₃ that diffuses in the active oxygen release agent 61 combines with potassium K to form potassium sulfate K ₂ SO ₄ , and calcium Ca does not combine with SO _3. It passes through the partition wall of the particulate filter. Therefore, the particulate filter will not be clogged with ash.
Thus, as described above, the active oxygen releasing agent 61 is an alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca, that is, potassium K, lithium L.
It is preferable to use i, cesium Cs, rubidium Rb, barium Ba, and strontium Sr.

Further, even when a particulate filter such as platinum Pt is supported as an active oxygen releasing agent, active oxygen can be released from NO ₂ or SO ₃ retained on the surface of platinum Pt. . However, in this case, the solid line showing the amount G of fine particles that can be removed by oxidation moves to the right of the solid line shown in FIG. It is also possible to use ceria as the active oxygen releasing agent. Ceria absorbs oxygen when the oxygen concentration in the exhaust gas is high (Ce
₂ O ₃ → 2CeO ₂ ) and active oxygen is released when the oxygen concentration in the exhaust gas decreases (2CeO ₂ → Ce ₂ O ₃ ). Therefore, in order to remove particulates by oxidation, It is necessary to make the air-fuel ratio rich regularly or irregularly. Iron or tin may be used instead of ceria.

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 NO _X or SO _X , and this enrichment control is performed after reversing the upstream side and the downstream side of the particulate filter. It is preferably carried out.

In this embodiment, the particulate filter itself carries the active oxygen releasing agent, and the particulates are oxidized and removed by the active oxygen released by the active oxygen releasing agent. Is not limited. For example, active oxygen and a particulate oxide substance such as nitrogen dioxide that functions similarly to active oxygen may be released from the particulate filter or the substance carried on it, or may be allowed to flow into the particulate filter from the outside. . Even when the particulate oxidant flows in from the outside, the first collecting surface and the second collecting surface of the collecting wall are alternately used to collect the particulate matter, so that the exhaust downstream side On the other collecting surface, the new particulates will not be accumulated, and the accumulated particulates will be gradually oxidized and removed by the particulate oxidizing component flowing from the other collecting surface to form the accumulated particulates. Can be sufficiently oxidized and removed in a certain time. In the meantime, since the other collecting surface collects the particulates and oxidizes by the particulate oxidization component, the same effect as described above is obtained. Also in this case, the temperature rise of the particulate filter makes it easier to oxidize and remove by raising the temperature of the particulate itself.

The diesel engine of this embodiment switches 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.

[0112]

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 trapping wall for trapping particulates, and the trapping wall has a trapping wall for trapping the particulates. A first collection surface of the collection wall having a collection surface and a second collection surface and collecting the particulates by reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter by the reversing means. Surface and second collection surface are used alternately, the particulate filter has an oxidizing function, the reversing means, the exhaust outlet of the particulate filter When the temperature is higher than the temperature of the exhaust inlet portion, so as to reverse the exhaust upstream side of the particulate filter and the exhaust gas downstream side. As a result, depending on the operating state, the particulate filter may not sufficiently oxidize the particulates, and the particulates may remain on the one collecting surface of the particulate filter collecting wall to some extent. Due to the reversal of the exhaust gas upstream side and the exhaust downstream side of the particulate filter due to, no new particulates are deposited on this trapping surface of the trapping wall, and the residual particulates can be gradually oxidized and removed. At the same time, collection and oxidation of particulates are started by the other collection surface of the collection wall. Thus, when the first collecting surface and the second collecting surface are alternately used for collecting the particulates, each collecting surface is compared with the case where the single collecting surface is used to collect the particulates. The amount of particulates collected on the collecting surface can be reduced,
Since it is advantageous for the oxidation and removal of the particulates, the particulates do not deposit on the particulate filter, and it is possible to prevent clogging of the particulate filter. Further, the reversing means reverses the exhaust upstream side and the exhaust downstream side of the particulate filter when the temperature of the exhaust outlet of the particulate filter is higher than the temperature of the exhaust inlet. As a result, the temperature of the exhaust gas inlet portion of the particulate filter is high after the reverse rotation, and the reducing substance in the exhaust gas is burned mainly by the oxidizing function in the exhaust gas inlet portion. This combustion heat raises the temperature of the central portion of the particulate filter and the exhaust outlet portion before being discharged from the particulate filter by heat transfer due to exhaust gas,
The reducing substance in the exhaust gas can be effectively used to raise the temperature of the entire particulate filter, and the particulates can be easily oxidized and removed.

[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 a generation amount of smoke and NO _x , and the like.

FIG. 7A is a diagram showing a change in combustion pressure when the air-fuel ratio is around 21 and the amount of smoke is largest, and B is an air-fuel ratio of 1;
FIG. 8 is a diagram showing a change in combustion pressure when the amount of smoke generated is approximately zero in the vicinity of 8.

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. 15A is a diagram showing a map of a target opening of a throttle valve, and B is a diagram showing a map of a target opening of an EGR control valve.

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

FIG. 17 is a diagram showing a map of a target opening of a throttle valve, and B is a diagram showing a map of a target opening of an EGR control valve.

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. 21A is a front view showing the structure of a particulate filter, and B is a side sectional view showing the structure of the particulate filter.

FIG. 22 is a diagram for explaining the oxidizing action of particulates.

FIG. 23 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. 24 is a diagram for explaining a deposition action of particulates.

FIG. 25 is a first flowchart for preventing the accumulation of particulates on the particulate filter.

FIG. 26 is an enlarged cross-sectional view of a partition wall of the particulate filter.

FIG. 27 is a graph showing the temperature of each part of the particulate filter.

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

[Explanation of symbols]

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

Continuation of front page (51) Int.Cl. ⁷ Identification code FI F02D 41/04 380 F02D 41/04 380C 380M 41/38 41/38 B 43/00 301 43/00 301H 301T 45/00 314 45/00 314R 314Z F02M 25/07 570 F02M 25/07 570J (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/02 301 F02D 41/04 F02D 41/38 F02D 43/00 F02M 25/07

Claims (6)

(57) [Claims] 1. A particulate filter arranged in an engine exhaust system, and a reversing means for reversing an exhaust upstream side and an exhaust downstream side of the particulate filter, wherein the particulate filter collects the particulate matter. The particulates are oxidized, the particulate filter has a collection wall for collecting particulates, the collection wall has a first collection surface and a second collection surface, The first collection surface and the second collection surface of the collection wall for collecting particulates by reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter by the reversing means. Are alternately used, the particulate filter has an oxidizing function, and the reversing means is configured such that the temperature of the exhaust outlet of the particulate filter is equal to the temperature of the exhaust inlet. The exhaust gas purification device for an internal combustion engine, wherein the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter are reversed when the temperature is higher than 100 degrees. 2. The internal combustion engine according to claim 1, wherein the particulate filter carries an active oxygen releasing agent, and the active oxygen released from the active oxygen releasing agent oxidizes the particulates. Exhaust purification device. 3. 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 2. Wherein said active oxygen release agent, a NO _X and oxygen coupled with the oxygen concentration of the to and surrounding retained by bonding the excess oxygen present around the NO _X and oxygen decreases N
The exhaust emission control device for an internal combustion engine according to claim 2, characterized in that it is decomposed into _Ox and active oxygen and released. 5. The temperature of the exhaust outlet of the particulate filter becomes higher than the temperature of the exhaust inlet even when it is time to reverse the exhaust upstream side and the exhaust downstream side of the particulate filter by the reversing means. 2. The reversal by the reversing means is postponed.
5. An exhaust gas purification device for an internal combustion engine according to any one of items 1 to 4. 6. The reversing means reverses the exhaust upstream side and the exhaust downstream side of the particulate filter during engine deceleration because the temperature of the exhaust outlet of the particulate filter is higher than the temperature of the exhaust inlet. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4, characterized in that: