JP3552674B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine.
[0002]
[Prior art]
The exhaust gas of an internal combustion engine, particularly a diesel engine, contains particulates mainly composed of soot. Since particulates are harmful substances, it has been proposed to arrange a filter in the engine exhaust system for trapping the particulates before releasing them to the atmosphere. In such a filter, it is necessary to burn out the collected particulates in order to prevent an increase in exhaust resistance due to clogging.
[0003]
In such filter regeneration, the particulates are ignited and burned at about 600 ° C., but the exhaust gas temperature of the diesel engine is much lower than 600 ° C. in the normal state, and the filter itself is usually heated. is necessary.
[0004]
Japanese Patent Publication No. 7-106290 discloses that if a platinum group metal and an alkaline earth metal oxide are supported on a filter, particulates on the filter can be reduced to about 400 ° C., which is the normal exhaust gas temperature of a diesel engine. It is disclosed that it is continuously burned off.
[0005]
[Problems to be solved by the invention]
However, even if this filter is used, the exhaust gas temperature is not always about 400 ° C., and a large amount of particulates may be discharged from the diesel engine depending on the operating condition. Particulates that could not be burned off over time can gradually build up on the filter.
[0006]
In this filter, if a certain amount of particulates accumulates, the ability to burn out the particulates is extremely reduced, so that the filter can no longer be regenerated by itself. Thus, simply arranging this type of filter in the engine exhaust system may cause clogging relatively early, resulting in a significant decrease in engine output.
[0007]
Accordingly, an object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine that can oxidize and remove particulates collected by a particulate filter in a favorable manner and prevent the particulate filter from being clogged.
[0008]
[Means for Solving the Problems]
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1 according to the present invention is disposed in an engine exhaust system.Wall-flow type honeycomb structureA particulate filter, and reversing means for reversing the exhaust upstream side and the exhaust downstream side of the particulate filter.And beforeThe particulate filter has a collecting wall for collecting particulates,An active oxygen releasing agent is supported on the collection wall,The collecting wall has a first collecting surface and a second collecting surface,When particulates remain on the current exhaust upstream collection surface of the first collection surface and the second collection surfaceThe first and second trapping surfaces of the trapping wall for trapping particulates are obtained by reversing the exhaust upstream side and the exhaust downstream side of the particulate filter by the reversing means. And are alternately used.
[0010]
Claims according to the present invention2The exhaust gas purifying apparatus for an internal combustion engine described in claim1In the exhaust gas purifying apparatus for an internal combustion engine described in the above, the active oxygen releasing agent takes in oxygen to retain oxygen when there is excess oxygen in the surroundings, and converts the retained oxygen into active oxygen when the surrounding oxygen concentration decreases. It is characterized by being released.
[0011]
Claims according to the present invention3The exhaust gas purifying apparatus for an internal combustion engine described in claim1 or 2In the exhaust gas purifying apparatus for an internal combustion engine described in the above, the reversing means reverses the exhaust gas upstream side and the exhaust downstream side of the particulate filter every predetermined time or every predetermined traveling distance.
[0012]
Claims according to the present invention4The exhaust gas purifying apparatus for an internal combustion engine described in claim1 or 2In the exhaust gas purifying apparatus for an internal combustion engine described in the above, when the differential pressure between the exhaust upstream side and the exhaust downstream side of the particulate filter becomes equal to or higher than a set differential pressure, the reversing means is provided on the exhaust upstream side of the particulate filter. And the exhaust downstream side is reversed.
[0013]
Claims according to the present invention5The exhaust gas purifying apparatus for an internal combustion engine described in claim1 or 2In the exhaust gas purifying apparatus for an internal combustion engine described in the above, the reversing means reverses the exhaust upstream side and the exhaust downstream side of the particulate filter when the particulate accumulation amount of the particulate filter becomes equal to or greater than a set accumulation amount. It is characterized by doing.
[0014]
Claims according to the present invention6The exhaust gas purifying apparatus for an internal combustion engine described in claim1 or 2In the exhaust gas purifying apparatus for an internal combustion engine described in (1), the oxygen concentration in the exhaust gas is occasionally reduced.
[0015]
Claims according to the present invention7The exhaust gas purifying apparatus for an internal combustion engine according to the above is disposed in the engine exhaust system.Wall-flow type honeycomb structureA particulate filter, and reversing means for reversing an exhaust upstream side and an exhaust downstream side of the particulate filter, wherein the particulate filter carries an active oxygen releasing agent and releases the active oxygen releasing agent. The active oxygen thus collected oxidizes the trapped particulates of the particulate filter, and the active oxygen releasing agent becomes NO when excess oxygen exists in the surroundings._XIs bound to oxygen and bound when the ambient oxygen concentration decreases._XAnd oxygen_XAnd the active oxygen are decomposed and released.The particulate filter has a collecting wall for collecting the particulates, and the collecting wall has a first collecting surface and a second collecting surface. Having a collecting surface,When particulates remain on the current exhaust upstream collection surface of the first collection surface and the second collection surfaceThe first and second trapping surfaces of the trapping wall for trapping particulates are obtained by reversing the exhaust upstream side and the exhaust downstream side of the particulate filter by the reversing means. Are alternately used to occasionally reduce the concentration of oxygen in the surroundings.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic longitudinal sectional view of a four-stroke diesel engine provided with an exhaust gas purifying apparatus according to the present invention, FIG. 2 is an enlarged longitudinal sectional view of a combustion chamber in the diesel engine of FIG. 1, and FIG. FIG. 4 is a bottom view of a cylinder head in the diesel engine of FIG. 1 to 3, reference numeral 1 denotes an engine body, 2 denotes a cylinder block, 3 denotes a cylinder head, 4 denotes a piston, 5a denotes a cavity formed on the top surface of the piston 4, and 5 denotes a cavity formed in the cavity 5a. A combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is a pair of intake valves, 8 is an intake port, 9 is a pair of exhaust valves, and 10 is 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.
[0017]
As shown in FIG. 1, an air-fuel ratio sensor 21 is disposed in the exhaust manifold 17. The exhaust manifold 17 and the surge tank 12 are connected to each other via an EGR passage 22, and an electrically controlled EGR control valve 23 is disposed in the EGR passage 22. A cooling device 24 for cooling the EGR gas flowing in the EGR passage 22 is disposed 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.
[0018]
On the other hand, each fuel injection valve 6 is connected via a fuel supply pipe 25 to a fuel reservoir, a so-called common rail 26. Fuel is supplied into the common rail 26 from an electric control type variable discharge fuel pump 27, and the fuel supplied into the common rail 26 is supplied to the fuel injection valve 6 through 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. The fuel pump 27 is controlled so that the fuel pressure in the common rail 26 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 28. Is controlled.
[0019]
An electronic control unit 30 receives an output signal of the air-fuel ratio sensor 21 and an output signal of the fuel pressure sensor 28. A load sensor 41 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 40 is connected to the accelerator pedal 40, and an output signal of the load sensor 41 is also input to the electronic control unit 30. For example, an output signal of the crank angle sensor 42 that generates an output pulse every time the motor rotates by 30 ° is also input. Thus, the electronic control unit 30 operates the fuel injection valve 6, the electric motor 15, the EGR control valve 23, and the fuel pump 27 based on various signals.
[0020]
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 ports, and the nozzle port of the fuel injection valve 6 is equiangularly slightly downward with respect to the horizontal plane. Fuel F is injected at intervals. As shown in FIG. 3, two of the six fuel sprays F scatter along the lower surface of the valve body of each exhaust valve 9. FIGS. 2 and 3 show a 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.
[0021]
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, a case is shown in which 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 traveling in the valve body direction of the exhaust valve 9 is directed between the back of the head of the exhaust valve 9 and the exhaust port 10. That is, in other words, two of the six nozzle ports of the fuel injection valve 6 emit fuel spray F when additional fuel Qa is injected while the exhaust valve 9 is open. It is formed so as to be directed between the back surface of the head of the valve 9 and the exhaust port 10. In this case, in the embodiment shown in FIG. 4, at this time, the fuel spray F collides with the back of the exhaust valve 9, and the fuel spray F colliding with the back of the exhaust valve 9 reflects on the back of the exhaust valve 9. Then, it goes into the exhaust port 10.
[0022]
Normally, no additional fuel Qa is injected, and only the main injection Qm is performed. FIG. 6 shows a change in the output torque when the air-fuel ratio A / F (horizontal axis in FIG. 6) is changed by changing the opening degree and the EGR rate of the throttle valve 16 during the engine low load operation, and the smoke, HC, and the like. , CO, NO_X4 shows an experimental example showing a change in the emission amount of the gas. 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 EGR rate is 65% or higher when the air-fuel ratio is equal to or less than the stoichiometric air-fuel ratio (比 14.6).
[0023]
As shown in FIG. 6, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the amount of smoke increases when the EGR rate becomes about 40% and the air-fuel ratio A / F becomes about 30. To start. Next, 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 is sharply reduced. When the EGR rate is increased to 65% or more, and the air-fuel ratio A / F becomes about 15.0, the smoke becomes almost zero. . That is, almost no soot is generated. At this time, the output torque of the engine slightly decreases, and NO_XThe amount of generation is considerably low. On the other hand, at this time, the generation amounts of HC and CO begin to increase.
[0024]
FIG. 7A shows a change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of generated smoke is the largest, and FIG. The graph shows a change in the combustion pressure in the combustion chamber 5 when the amount of generated smoke is almost zero in the vicinity. As can be seen by comparing FIG. 7 (A) and FIG. 7 (B), FIG. 7 (B) in which the amount of smoke generation is almost zero is shown in FIG. 7 (A) where the amount of smoke generation is large. It can be seen that the combustion pressure is lower than in the case.
[0025]
The following can be said from the experimental results shown in FIGS. That is, first, when the air-fuel ratio A / F is 15.0 or less and the amount of generated smoke is almost zero, as shown in FIG._XThe amount of generation of methane is considerably reduced. NO_XThe decrease in the amount of generation means that the combustion temperature in the combustion chamber 5 has decreased. Therefore, it can be said that the combustion temperature in the combustion chamber 5 is low when little soot is generated. The same can be said from FIG. That is, in the state shown in FIG. 7B where almost no soot is generated, the combustion pressure is low, and thus the combustion temperature in the combustion chamber 5 is low at this time.
[0026]
Second, when the amount of generated smoke, that is, the amount of generated soot becomes substantially zero, the amount of HC and CO emissions increases as shown in FIG. This means that hydrocarbons are emitted without growing to soot. That is, the linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 8 are thermally decomposed when the temperature is increased in a state of lack of oxygen, soot precursors are formed, and then mainly, A soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot generation process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. It will grow to soot. Therefore, as described above, when the amount of soot generation becomes almost zero, the emission amounts of HC and CO increase as shown in FIG. 6, but HC at this time is a precursor of soot or a hydrocarbon in a state before the soot. .
[0027]
Summarizing these considerations based on the experimental results shown in FIGS. 6 and 7, when the combustion temperature in the combustion chamber 5 is low, the amount of generated soot becomes almost zero. The hydrocarbon will be discharged from the combustion chamber 5. As a result of further detailed experimental research on this, when the temperature of the fuel and the surrounding gas in the combustion chamber 5 is lower than a certain temperature, the growth process of the soot is stopped halfway, that is, the soot is It was found that no soot was generated, and soot was generated when the temperature of the fuel and its surroundings in the combustion chamber 5 became lower than a certain temperature.
[0028]
By the way, the temperature of the fuel and its surrounding when the process of producing hydrocarbons is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature varies depending on various factors such as the type of fuel, the air-fuel ratio and the compression ratio, It is not possible to say how many times, but this certain temperature is NO_XIs closely related to the amount of NOx generated, so that this certain temperature is NO_XCan be defined to some extent from the amount of occurrence of. That is, as the EGR rate increases, the fuel temperature during combustion and the gas temperature around the fuel decrease, and the NO_XGeneration amount decreases. NO at this time_XIs 10 p. p. When the value is about m or less, soot is hardly generated. Therefore, the above certain temperature is NO_XIs 10 p. p. m The temperature substantially coincides with the temperature when the temperature becomes lower or higher or lower.
[0029]
Once soot has been produced, it cannot be purified by post-treatment simply using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in the state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Thus, NO_XIt is extremely effective in purifying exhaust gas to reduce the generation amount of methane and to discharge hydrocarbons from the combustion chamber 5 in the state of a precursor of soot or before the soot.
[0030]
Now, in order to stop the growth of hydrocarbons before the soot is generated, it is necessary to suppress the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 to a temperature lower than the temperature at which the soot is generated. There is. In this case, it has been found that the endothermic effect of the gas around the fuel when the fuel is burned has an extremely large effect in suppressing the temperature of the fuel and the gas around the fuel.
[0031]
That is, if there is only air 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 becomes extremely high locally. That is, at this time, the air separated from the fuel hardly absorbs the heat of combustion heat of the fuel. In this case, since the combustion temperature becomes extremely high locally, the unburned hydrocarbons that have received the heat of combustion will generate soot.
[0032]
On the other hand, when fuel is present in a mixed gas of a large amount of inert gas and a small amount of air, the situation is slightly different. In this case, the evaporated fuel diffuses to the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, the combustion temperature does not rise so much because the combustion heat is absorbed by the surrounding inert gas. 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 kept low by the endothermic effect of the inert gas.
[0033]
In this case, in order to suppress the temperature of the fuel and the surrounding gas to a temperature lower than the temperature at which the soot is formed, an amount of the inert gas is required to be able to absorb enough heat to do so. Therefore, if the amount of fuel increases, the required amount of inert gas increases accordingly. In this case, the endothermic effect becomes stronger as the specific heat of the inert gas increases, so that the inert gas preferably has a higher specific heat. In this regard, CO₂Since EGR gas has a relatively large specific heat, it can be said that it is preferable to use EGR gas as the inert gas.
[0034]
FIG. 9 shows the relationship between the EGR rate and the smoke when the EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 9, the curve A shows the case where the EGR gas is cooled strongly and the EGR gas temperature is maintained at approximately 90 ° C., and the curve B shows the case where the EGR gas is cooled by a small cooling device. Curve C shows the case where the EGR gas is not forcibly cooled.
[0035]
As shown by the curve A in FIG. 9, when the EGR gas is strongly cooled, the soot generation amount peaks at a point where the EGR rate is slightly lower than 50%. In this case, the EGR rate is increased to about 55% or more. Then, almost no soot is generated. On the other hand, as shown by the curve B in FIG. 9, when the EGR gas is slightly cooled, the amount of soot generation peaks at a point where the EGR rate is slightly higher than 50%, and in this case, the EGR rate is increased to about 65% or more. So that almost no soot is generated.
[0036]
When the EGR gas is not forcibly cooled as shown by the curve C in FIG. 9, the amount of soot generation reaches a peak near the EGR rate of 55%. Above a percentage, soot is hardly generated. FIG. 9 shows the amount of smoke generated when the engine load is relatively high. When the engine load is small, the EGR rate at which the amount of soot peaks slightly decreases, and the EGR rate at which soot is hardly generated is shown. Also lowers slightly. As described above, the lower limit of the EGR rate at which almost no soot is generated varies depending on the degree of cooling of the EGR gas and the engine load.
[0037]
FIG. 10 shows a mixed gas amount of the EGR gas and the air necessary to make the temperature of the fuel during combustion and the surrounding gas temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas; And the ratio of air in the mixed gas amount and the ratio of EGR gas in the mixed gas. In FIG. 10, the vertical axis indicates the total intake gas amount sucked into the combustion chamber 5, and the dashed line Y indicates the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. I have. The horizontal axis indicates the required load, and Z1 indicates the low load operation region.
[0038]
Referring to FIG. 10, the proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air necessary to completely burn the injected fuel. That is, in the case shown in FIG. 10, the ratio between the amount of air and the amount of injected fuel is the stoichiometric 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 is necessary to make the temperature of the fuel and the surrounding gas 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 the 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 represented by a solid line X in FIG. 10, and the ratio between the air amount and the EGR gas amount in the total intake gas amount X is as shown in FIG. The temperature of the fuel and the gas around it will be lower than the temperature at which soot is produced, so that no soot is generated. Also, NO_XThe amount generated is 10 p. p. m around or below and therefore NO_XIs extremely small.
[0039]
As the amount of fuel injection increases, the amount of heat generated when the fuel burns increases. Therefore, in order to maintain the temperature of the fuel and the surrounding gas at a temperature lower than the temperature at which soot is generated, the amount of heat absorbed by the EGR gas Must be increased. Therefore, as shown in FIG. 10, the EGR gas amount must be increased as the injected fuel amount increases. That is, the EGR gas amount needs to increase as the required load increases.
[0040]
On the other hand, in the load region Z2 in FIG. 10, the total intake gas amount X necessary to prevent the generation of soot exceeds the total intake gas amount Y that can be sucked. Therefore, in this case, it is necessary to supercharge or pressurize both the EGR gas and the intake air or the EGR gas in order to supply the total intake gas amount X necessary for preventing the generation of soot into the combustion chamber 5. When the EGR gas or the like is not supercharged or pressurized, the total intake gas amount X matches the total intake gas amount Y that can be sucked in the load region Z2. Therefore, in this case, in order to prevent the generation of soot, the amount of air is slightly reduced to increase the amount of EGR gas, and the fuel is burned under a rich air-fuel ratio.
[0041]
As described above, FIG. 10 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, even if the air amount is smaller than the air amount shown in FIG. 10 in the low load operation region Z1 shown in FIG. That is, even if the air-fuel ratio is made rich, NO_XIs 10 p. p. m or less, and even if the air amount is larger than the air amount shown in FIG. 10 in the low load region Z1 shown in FIG. 10, that is, the average value of the air-fuel ratio is 17 to 18. NO while preventing soot generation even when lean_XIs 10 p. p. m can be around or below.
[0042]
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 excess fuel does not grow to soot, and thus no soot is generated. At this time, NO_XOnly a very small amount 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 increases, but in the present invention, the soot is suppressed to a low temperature, so the soot is reduced. Not generated at all. Furthermore, NO_XOnly a very small amount is generated.
[0043]
As described above, in the engine low load operation region Z1, no soot is generated regardless of the air-fuel ratio, that is, regardless of whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean, and NO_XIs 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.
[0044]
By the way, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber can be suppressed to a temperature at or below the temperature at which the growth of hydrocarbons stops halfway, only when the heat generation amount due to combustion is small and the engine load is relatively low. Therefore, in the embodiment according to the present invention, when the engine load is relatively low, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas temperature around the combustion to a temperature at which the growth of hydrocarbons stops halfway. Then, when the engine load is relatively high, the second combustion, that is, the combustion that is usually performed conventionally, is performed. Here, the first combustion, that is, low-temperature combustion, as is clear from the description so far, the amount of inert gas in the combustion chamber is larger than the worst inert gas amount at which the generation amount of soot is maximum, and soot is almost generated. The second combustion, that is, the combustion that is usually performed in the past, is the combustion in which the amount of inert gas in the combustion chamber is smaller than the worst inert gas amount that produces the largest amount of soot. Say
[0045]
FIG. 11 shows a first operation region I in which first combustion, that is, low-temperature combustion is performed, and a second combustion region II in which second combustion, that is, combustion by a conventional combustion method, is performed. In FIG. 11, the vertical axis L indicates the depression amount of the accelerator pedal 40, that is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 11, X (N) indicates a first boundary between the first operation region I and the second operation region II, and Y (N) indicates the first operation region I and the second operation region. The second boundary with the area II is shown. The determination of the change of the operation region from the first operation region I to the second operation region II is made based on the first boundary X (N), and the change from the second operation region II to the first operation region I is performed. The determination of the change of the operating region is performed based on the second boundary Y (N).
[0046]
That is, if the required load L exceeds a first boundary X (N), which is a function of the engine speed N, when the operating state of the engine is in the first operating region I and low-temperature combustion is being performed, the operating region is changed. It is determined that the operation has shifted to the second operation region II, and combustion is performed by the conventional combustion method. Next, when the required load L becomes lower than a second boundary Y (N) which is a function of the engine speed N, it is determined that the operation region has shifted to the first operation region I, and low-temperature combustion is performed again.
[0047]
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.
[0048]
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 of the throttle valve 16 is gradually increased from almost fully closed to about half-open as the required load L increases, and the EGR control valve 23 Is gradually increased from near fully closed to fully open as the required load L increases. In the example shown in FIG. 13, in the first operation region I, the EGR rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.
[0049]
In other words, in the first operating region I, the opening of the throttle valve 16 and the opening of the EGR control valve 23 are controlled such that the EGR rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. The air-fuel ratio at this time is controlled to the target lean air-fuel ratio by correcting the opening of the EGR control valve 23 based on the output signal of the air-fuel ratio sensor 21. 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 is delayed as the required load L is increased, and the injection completion timing θE is delayed as the injection start timing θS is delayed.
[0050]
At the time of idling operation, the throttle valve 16 is closed to almost fully closed, and at this time, the EGR control valve 23 is also closed to almost fully closed. When the throttle valve 16 is closed close to the fully closed position, the pressure in the combustion chamber 5 at the start of compression decreases, so that the compression pressure decreases. When the compression pressure decreases, the compression work by the piston 4 decreases, so that the vibration of the engine body 1 decreases. That is, at the time of idling operation, the throttle valve 16 is closed to almost fully closed in order to suppress the vibration of the engine body 1.
[0051]
On the other hand, when the operating region of the engine changes from the first operating region I to the second operating region II, the opening degree of the throttle valve 16 is increased stepwise from the half-open state to the fully open state. At this time, in the example shown in FIG. 13, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. 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 operation region of the engine changes from the first operation region I to the second operation region II. There is no.
[0052]
In the second operation region II, the conventional combustion is performed. In this combustion method, soot and NO_XIs generated, but the thermal efficiency is higher than that of low-temperature combustion. Therefore, when the operating region of the engine changes from the first operating region I to the second operating region II, the injection amount decreases stepwise as shown in FIG. I'm sullen.
[0053]
In the second operating region II, the throttle valve 16 is held in a fully open state except for a part, and the opening of the EGR control valve 23 is gradually reduced as the required load L increases. In this operating region II, the EGR rate decreases as the required load L increases, and the air-fuel ratio decreases as the required load L increases. However, the air-fuel ratio is a lean air-fuel ratio even when the required load L increases. In the second operation region II, the injection start timing θS is set near the compression top dead center TDC.
[0054]
FIG. 14 shows the air-fuel ratio A / F in the first operation region I. In FIG. 14, each curve indicated by A / F = 15.5, A / F = 16, A / F = 17, and A / F = 18 has air-fuel ratios of 15.5, 16, 17, and 18, respectively. Time is shown, 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 becomes leaner as the required load L decreases.
[0055]
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 reduced. When the EGR rate is reduced, the air-fuel ratio increases. Therefore, as shown in FIG. 14, as the required load L decreases, the air-fuel ratio A / F increases. As the air-fuel ratio A / F increases, the fuel consumption rate increases. Therefore, in order to make the air-fuel ratio as lean as possible, in this embodiment, the air-fuel ratio A / F is increased as the required load L decreases.
[0056]
It should be noted that the target opening ST of the throttle valve 16 required for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. 14 is represented as a function of the required load L and the engine speed N as shown in FIG. The target opening SE of the EGR control valve 23 necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. 14 is stored in advance in the ROM 32 as shown in FIG. And in the form of a map as a function of the engine speed N in the ROM 32 in advance.
[0057]
FIG. 16 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 16, curves indicated by A / F = 24, A / F = 35, A / F = 45, and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. The target opening degree ST of the throttle valve 16 necessary for setting the air-fuel ratio to the target air-fuel ratio is stored in the ROM 32 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG. The target opening SE of the EGR control valve 23 required to set the air-fuel ratio to the target air-fuel ratio is calculated as a function of the required load L and the engine speed N as shown in FIG. It is stored in the ROM 32 in the form of a map in advance.
[0058]
Thus, in the diesel engine of the present embodiment, the first combustion, that is, the low temperature combustion, and the second combustion, that is, the normal combustion are switched based on the depression amount L of the accelerator pedal 40 and the engine speed N, In each combustion, the opening degree control of the throttle valve 16 and the EGR valve is performed based on the depression amount L of the accelerator pedal 40 and the engine speed N by using a map shown in FIG. 15 or FIG.
[0059]
FIG. 18 is a plan view showing the exhaust gas purification device, and FIG. 19 is a side view thereof. The present exhaust gas purification apparatus includes a switching section 71 connected to the downstream side of the exhaust manifold 17 via an exhaust pipe 18, a particulate filter 70, and a first section connecting one side of the particulate filter 70 and the switching section 71. The switching unit 71 includes a connecting portion 72a, a second connecting portion 72b that connects the other side of the particulate filter 70 and the switching portion 71, and an exhaust passage 73 downstream of the switching portion 71. The switching unit 71 includes a valve body 71a that can shut off the exhaust gas flow in the switching unit 71. The valve body 71a is driven by a negative pressure actuator, a step motor, or the like. At one of the shutoff positions of the valve body 71a, the upstream side in the switching section 71 is communicated with the first connection section 72a, and the downstream side in the switching section 71 is communicated with the second connection section 72b. As shown by the arrows, the particulate filter 70 flows from one side to the other side.
[0060]
FIG. 20 shows the other blocking position of the valve body 71a. In this shutoff position, the upstream side in the switching section 71 is communicated with the second connection section 72b, and the downstream side in the switching section 71 is communicated with the first connection section 72a, and the exhaust gas is discharged as shown by an arrow in FIG. , Flows from the other side of the particulate filter 70 to one side. Thus, by switching the valve body 71a, the direction of the exhaust gas flowing into the particulate filter 70 can be reversed, that is, it is possible to reverse the exhaust upstream side and the exhaust downstream side of the particulate filter 70. Become.
[0061]
As described above, the present exhaust gas purification apparatus can reverse the exhaust gas upstream side and the exhaust downstream side of the particulate filter with a very simple configuration. Further, the particulate filter requires a large opening area in order to facilitate the flow of exhaust gas. However, in the present exhaust gas purifying apparatus, as shown in FIGS. Instead, a particulate filter having a large opening area can be used.
[0062]
On the other hand, in order to reverse the exhaust upstream side and the exhaust downstream side of the particulate filter, the present exhaust gas purification apparatus is configured as shown in FIG. 21 while rotating the valve body 71a from one of the two shut-off positions to the other. As shown, the exhaust gas is released into the atmosphere without passing through the particulate filter.
[0063]
FIG. 22 shows the structure of the particulate filter 70. 22A is a front view of the particulate filter 70, and FIG. 22B is a side sectional view. As shown in these figures, the particulate filter 70 has an elliptical front shape, and is, for example, 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 directional partitions 54. In the two adjacent axial spaces, one is closed downstream of the exhaust and the other is closed upstream of the exhaust by a plug 53. Thus, one of the two adjacent axial spaces becomes the exhaust gas inflow passage 50 and the other becomes the outflow passage 51, and the exhaust gas always passes through the partition wall 54 as shown by the arrow in FIG. Although the particulates in the exhaust gas are very small compared to the size of the pores of the partition wall 54, they collide with and collect on the upstream surface of the partition wall 54 and the surface of the pores in the partition wall 54. Is done. Thus, each partition wall 54 functions as a collecting wall for collecting particulates. In the present particulate filter 70, in order to oxidize and remove the trapped particulates, the following description will be given using alumina or the like on both surfaces of the partition walls 54, and preferably also on the surface of the pores in the partition walls 54. An active oxygen releasing agent and a noble metal catalyst are supported.
[0064]
The active oxygen releasing agent promotes the oxidation of particulates by releasing active oxygen.Preferably, when there is excess oxygen in the surroundings, it takes in oxygen to retain oxygen and reduce the surrounding oxygen concentration. When lowered, the retained oxygen is released in the form of active oxygen.
[0065]
As a noble metal catalyst, platinum Pt is usually used, and as an active oxygen releasing agent, an alkali metal such as potassium K, sodium Na, lithium Li, cesium Cs, or rubidium Rb, barium Ba, calcium Ca, or strontium Sr is used. At least one selected from alkaline earth metals, rare earths such as lanthanum La, yttrium Y, and transition metals is used.
[0066]
In this case, as the active oxygen releasing agent, an alkali metal or an alkaline earth metal having a higher ionization tendency than calcium Ca, that is, potassium K, lithium Li, cesium Cs, rubidium Rb, barium Ba, and strontium Sr may be used. preferable.
[0067]
Next, how the collected particulates are oxidized and removed by the particulate filter supporting such an active oxygen releasing agent will be described with reference to platinum Pt and potassium K as an example. The same particulate removal effect can be obtained by using other noble metals, alkali metals, alkaline earth metals, rare earths, and transition metals.
[0068]
Diesel engines usually burn under excess air, so the exhaust gas contains a large amount of excess air. That is, when the ratio of air and fuel supplied to the intake passage and the combustion chamber is referred to as the air-fuel ratio of the exhaust gas, the air-fuel ratio is lean. Further, since NO is generated in the combustion chamber, the exhaust gas contains NO. Further, the fuel contains sulfur S, which reacts with oxygen in the combustion chamber to produce SO.₂It becomes. Therefore, SO in the exhaust gas₂It is included. Thus, excess oxygen, NO and SO₂Will flow into the exhaust gas upstream of the particulate filter 70.
[0069]
FIGS. 23A and 23B schematically show enlarged views of the exhaust gas contact surface of the particulate filter 70. FIG. In FIGS. 23A and 23B, reference numeral 60 denotes platinum Pt particles, and reference numeral 61 denotes an active oxygen releasing agent containing potassium K.
[0070]
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, as shown in FIG.₂Is O₂ ⁻Or O^2-On the surface of platinum Pt. On the other hand, NO in the exhaust gas becomes O 2 on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂). NO generated next₂Is absorbed in the active oxygen releasing agent 61 while being oxidized on the platinum Pt, and combined with potassium K to form nitrate ions NO as shown in FIG.₃ ⁻Is diffused into the active oxygen releasing agent 61 in the form of potassium nitrate KNO₃Generate Thus, in this embodiment, the NO contained in the exhaust gas_XIs absorbed by the particulate filter 70, and the amount of emission into the atmosphere can be greatly reduced.
[0071]
On the other hand, as described above, SO2 is contained in the exhaust gas.₂Is also included in this SO₂Is also absorbed into the active oxygen releasing agent 61 by the same mechanism as NO. That is, as described above, the oxygen O₂Is O₂ ⁻Or O^2-Is attached to the surface of platinum Pt in the form of₂Is O on the surface of platinum Pt₂ ⁻Or O^2-Reacts with SO₃It becomes. Then the generated SO₃Is absorbed in the active oxygen releasing agent 61 while being further oxidized on the platinum Pt, and combined with potassium K to form sulfate ions SO.₄ ^2-In the active oxygen releasing agent 61 in the form of potassium sulfate K₂SO₄Generate Thus, potassium nitrate KNO is contained in the active oxygen release catalyst 61.₃And potassium sulfate K₂SO₄Is generated.
[0072]
The particulates in the exhaust gas adhere to the surface of the active oxygen releasing agent 61 carried on the particulate filter, as indicated by 62 in FIG. At this time, the oxygen concentration decreases at the contact surface between the particulate 62 and the active oxygen releasing agent 61. When the oxygen concentration decreases, a concentration difference occurs between the active oxygen releasing agent 61 having a high oxygen concentration and the oxygen in the active oxygen releasing agent 61. Try to move towards. As a result, potassium nitrate KNO formed in the active oxygen releasing agent 61₃Is decomposed into potassium K, oxygen O and NO, oxygen O is directed to the contact surface between the particulate 62 and the active oxygen releasing agent 61, and NO is released from the active oxygen releasing agent 61 to the outside. The NO released to the outside is oxidized on platinum Pt on the downstream side, and is again absorbed in the active oxygen releasing agent 61.
[0073]
On the other hand, at this time, potassium sulfate K formed in the active oxygen releasing agent 61₂SO₄Also potassium K, oxygen O and SO₂Oxygen O is directed to the contact surface between the particulate 62 and the active oxygen releasing agent 61,₂Is released from the active oxygen releasing agent 61 to the outside. SO released outside₂Is oxidized on platinum Pt on the downstream side, and is again absorbed in the active oxygen releasing agent 61. However, potassium sulfate K₂SO₄Is stable because potassium nitrate KNO₃It is difficult to release active oxygen as compared with.
[0074]
On the other hand, oxygen O toward the contact surface between the particulate 62 and the active oxygen releasing agent 61 is potassium nitrate KNO₃And potassium sulfate K₂SO₄Is oxygen decomposed from such a compound. Oxygen O decomposed from the compound has high energy and extremely high activity. Therefore, the oxygen going to the contact surface between the particulate 62 and the active oxygen releasing agent 61 is active oxygen O. When the active oxygen O comes in contact with the particulate 62, the particulate 62 is oxidized in a short time of several minutes to several tens minutes without emitting a bright flame. The active oxygen O that oxidizes the particulate 62 is supplied to the active oxygen releasing agent 61 by NO and SO.₂Is also released when is absorbed. That is, NO_XRepresents nitrate ion NO in the active oxygen releasing agent 61 while repeatedly bonding and separating oxygen atoms.₃ ⁻It is thought that it diffuses in the form of, and active oxygen is also generated during this time. The particulate 62 is also oxidized by the active oxygen. Further, the particulates 62 thus adhered on the particulate filter 70 are oxidized by the active oxygen O, but these particulates 62 are also oxidized by the oxygen in the exhaust gas.
[0075]
By the way, the platinum Pt and the active oxygen releasing agent 61 are activated as the temperature of the particulate filter increases, so that the amount of active oxygen O released from the active oxygen releasing agent 61 per unit time increases as the temperature of the particulate filter increases. I do. Naturally, the higher the temperature of the particulates themselves, the more easily they are oxidized and removed. Therefore, the amount of oxidizable particles that can oxidize and remove particulates per unit time on the particulate filter without emitting luminous flame per unit time increases as the temperature of the particulate filter increases.
[0076]
The solid line in FIG. 24 indicates the amount G of the oxidizable particles that can be oxidized and removed without emitting a bright flame per unit time, and in FIG. 24, the horizontal axis indicates the temperature TF of the particulate filter. FIG. 24 shows the case where the unit time is 1 second, that is, the amount G of the oxidizable / removable fine particles per second. However, an arbitrary time such as 1 minute or 10 minutes is adopted as the unit time. be able to. For example, when 10 minutes is used as the unit time, the amount G of oxidizable and removable particles per unit time represents the amount G of oxidizable and removable particles per 10 minutes. As shown in FIG. 24, the amount G of oxidizable particles that can be oxidized and removed without emitting bright flame per hour increases as the temperature of the particulate filter 70 increases.
[0077]
When the amount of particulates discharged from the combustion chamber per unit time is referred to as an 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, the amount of discharged fine particles per second When M is smaller than the amount G of oxidizable and removable particles per second, or when the amount M of discharged particles per 10 minutes is smaller than the amount G of oxidizable and removable particles per 10 minutes, that is, in the region I in FIG. All the particulates discharged from the chamber are sequentially oxidized and removed in a short time on the particulate filter 70 without emitting a bright flame.
[0078]
On the other hand, when the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation, that is, in the region II in FIG. 24, the amount of active oxygen is insufficient to sequentially oxidize all the particulates. FIGS. 25A to 25C show how particulates are oxidized in such a case.
[0079]
That is, when the amount of active oxygen is insufficient to oxidize all the particulates, when the particulates 62 adhere to the active oxygen releasing agent 61 as shown in FIG. Only the particulates are oxidized, and the particulates that have not been sufficiently oxidized remain on the exhaust upstream side of the particulate filter. Next, when the state of the shortage of the active oxygen amount continues, the particulate portion which has not been oxidized from one to the next remains on the exhaust upstream surface, and as a result, as shown in FIG. The exhaust upstream surface is covered with the residual particulate portion 63.
[0080]
Such a residual particulate portion 63 is gradually transformed into a carbon material which is hardly oxidized, and when the exhaust upstream surface is covered with the residual particulate portion 63, NO, SO by platinum Pt is formed.₂And the active oxygen releasing action of the active oxygen releasing agent 61 is suppressed. As a result, the residual particulate portion 63 can be gradually oxidized with time, but another particulate 64 is successively formed on the residual particulate portion 63 as shown in FIG. And accumulate. That is, when the particulates are deposited in a layered manner, these particulates are separated from the platinum Pt and the active oxygen releasing agent, so that even if the particulates are easily oxidized, they cannot be oxidized by the active oxygen. Absent. Therefore, further particulates accumulate on this particulate 64 one after another. In other words, if the state in which the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation continues, the particulates will be deposited in layers on the particulate filter.
[0081]
As described above, in the region I of FIG. 24, the particulates are oxidized in a short time without emitting a bright flame on the particulate filter, and in the region II of FIG. 24, the particulates are deposited on the particulate filter in a layered manner. I do. Therefore, if the relationship between the discharged fine particle amount M and the oxidizable and removable fine particle amount G 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 is maintained at a substantially constant minimum pressure loss value without changing at all. In this way, a reduction in engine power can be kept to a minimum. However, this is not always achieved, and if nothing is done, particulates may accumulate on the particulate filter.
[0082]
In this embodiment, the electronic control unit 30 controls the switching of the valve body 71a in accordance with the first flowchart shown in FIG. 26 to prevent the accumulation of particulates on the particulate filter. This flowchart is repeated every predetermined time. First, in step 101, a running distance integrated value A of the vehicle is calculated. Next, at step 102, it is determined whether or not the running distance integrated value A has become equal to or greater than the set running distance As. When this determination is denied, the process ends as it is, but when affirmed, the process proceeds to step 103. In step 103, the running distance integrated value A is reset to 0, and in step 104, the valve body 71a is switched from one shut-off position to the other shut-off position. That is, the exhaust gas upstream and the exhaust downstream of the particulate filter are reversed.
[0083]
FIG. 27 is an enlarged sectional view of the partition wall 54 of the particulate filter. While the vehicle travels the set traveling distance As, the driving in the region II of FIG. 24 may be performed, and as shown by the grid in FIG. The surface on the exhaust upstream side and the surface facing the exhaust gas flow in the pores collide and collect the particulates as one collecting surface, and are oxidized and removed by the active oxygen releasing agent. Particulates may remain. At this time, the exhaust resistance of the particulate filter does not adversely affect the running of the vehicle, but if the particulates accumulate further, a problem such as a drastic decrease in engine output occurs. In the first flowchart, at this point, the exhaust gas upstream and the exhaust downstream of the particulate filter are reversed. As a result, no more particulates accumulate on the particulates remaining on one of the trapping surfaces of the partition wall 54, and the residual particulates are gradually oxidized and removed by the active oxygen released from the one collecting surface. Is done. Further, the particulates remaining in the pores of the partition walls are easily broken and fragmented by the exhaust gas flow in the opposite direction, as shown in FIG. 27B, and move downstream.
[0084]
As a result, many of the finely divided particulates are dispersed in the pores of the partition walls, that is, the particulates flow directly to the active oxygen releasing agent supported on the inner surfaces of the pores of the partition walls. The chance of being oxidized and removed by contact increases. By carrying the active oxygen releasing agent also in the pores of the partition walls, residual particulates can be remarkably easily oxidized and removed. Furthermore, in addition to this oxidation removal, the other trapping surface of the partition wall 54 that has become upstream due to the backflow of the exhaust gas, that is, the exhaust upstream surface of the partition wall 54 where the exhaust gas currently mainly collides and the inside of the pores On the exhaust gas flow-facing surface (which is on the opposite side 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 releasing agent. . A part of the active oxygen released from the active oxygen releasing agent at the time of these oxidative removal moves to the downstream side together with the exhaust gas, and oxidizes and removes the particulates still remaining due to the backflow of the exhaust gas.
[0085]
That is, the residual particulates on one collecting surface of the partition wall include not only the active oxygen released from this collecting surface but also the oxidative removal of particulates on the other collecting surface of the partition wall by the backflow of exhaust gas. The remaining active oxygen used comes from the exhaust gas. Thereby, even when the particulates are deposited to some extent on one of the collecting surfaces of the partition wall at the time of switching the valve body, if the exhaust gas is made to flow backward, the particulates are deposited on the residual particulates. In addition to the arrival of active oxygen, there is no further accumulation of particulates, so the accumulated particulates are gradually oxidized and removed, and if there is some time before the next backflow, sufficient It can be removed by oxidation.
[0086]
In the first flowchart, the switching of the valve body is performed every predetermined traveling distance, but may be performed every set time. Of course, the valve body may be switched irregularly, not regularly. In any case, switching of the valve element is preferably performed at least once between engine start and engine stop so as to be performed before residual particulates on the particulate filter are changed into carbon material which is hardly oxidized. . Also, oxidizing and removing particulates before a large amount of particulates are deposited means that a large amount of the deposited particulates ignite and burn at a time to generate a large amount of combustion heat, and the combustion heat damages the particulate filter. And other problems can be prevented. Further, even if a large amount of particulates accumulates on one collecting surface of the particulate filter partition wall at the time of switching of the valve element for some reason, if the valve element is switched, the accumulated particulates will be in the opposite direction. Some of the finely divided particulates that could not be oxidized and removed in the pores of the partition walls are discharged from the particulate filter because they are relatively easily broken and fragmented by the exhaust gas flow. The exhaust resistance of the filter is not further increased and does not adversely affect the running of the vehicle. Further, on the other collecting surface of the particulate filter partition wall, a new particulate can be collected.
[0087]
FIG. 28 shows a second flowchart for the switching control of the valve body 71a. This flowchart is also repeated every predetermined time. First, in step 201, the exhaust pressure P1 on one side of the particulate filter 70, that is, the exhaust pressure in the first connection portion 72a (see FIG. 18) is detected by a pressure sensor arranged in the first connection portion 72a. . Next, in step 202, the exhaust pressure P2 on the other side of the particulate filter 70, that is, the exhaust pressure in the second connection portion 72b (see FIG. 18) is detected by a pressure sensor arranged in the second connection portion 72b. .
[0088]
In step 203, it is determined whether or not the absolute value of the differential pressure of the exhaust pressure detected in steps 201 and 202 is equal to or greater than the set pressure difference Ps. Here, the reason why the absolute value of the differential pressure is used is that the rise in the differential pressure can be grasped regardless of which of the first connection portion 72a and the second connection portion 72b is on the exhaust upstream side. When the determination in step 203 is denied, the process ends as it is. When this determination is affirmed, the valve element 71a is switched in step 204 because a certain amount of particulate remains in the particulate filter. The exhaust upstream side and the exhaust downstream side of the particulate filter are reversed.
[0089]
Thereby, as described above, the residual particulates are oxidized and removed from the particulate filter. In this way, it is indirectly detected that a certain amount of particulates remains in the particulate filter by using the differential pressure on both sides of the particulate filter. Can be reliably prevented. Of course, in addition to the differential pressure, for example, a change in the electric resistance value on a predetermined partition wall of the particulate filter is monitored. It may be determined that a certain amount of particulates is deposited on the upper part.In addition, at a predetermined partition wall of the particulate filter, the light transmittance is reduced due to the deposition of the particulates, or the light reflectance is reduced. By utilizing the decrease, it is also possible to determine that a certain amount of particulates has accumulated on the particulate filter. As described above, by directly determining the residual of the particulates and switching the valve body, it is possible to more reliably prevent a large decrease in the engine output. Strictly speaking, the differential pressure on both sides of the particulate filter also changes depending on the exhaust gas pressure discharged from the cylinder in each engine operating state. Therefore, in determining the accumulation of particulates, the engine operating state is specified. Is preferred.
[0090]
Reversing the exhaust upstream and downstream of the particulate filter in this way is very effective to enable the oxidization and removal of the residual and deposited particulates, and occasionally without judging the timing. Even if the valve body is switched, a large decrease in engine output due to a large amount of particulate accumulation can be sufficiently prevented.
[0091]
By the way, in the structure of the switching unit 71 of the present embodiment, as described above, a part of the exhaust gas bypasses the particulate filter 70 while the valve body 71a is switched from one of the two shut-off positions to the other. . Accordingly, if the exhaust gas contains particulates at this time, the particulates are released to the atmosphere. In order to prevent this, as shown in a third flowchart shown in FIG. 29, the valve element 71a may be switched when the fuel cut is being performed. At the time of fuel cut, no exhaust gas contains particulates because combustion is not performed in the cylinder. The fuel cut may be determined by using a fuel cut signal given to the fuel injection valve.The depression of the brake pedal may be detected while the vehicle is running, or the accelerator pedal may be pressed while the vehicle is running. Release may be detected.
[0092]
At the time of fuel cut, the temperature of the exhaust gas is extremely low, so bypassing the particulate filter even with some exhaust gas at this time suppresses the temperature decrease of the particulate filter, that is, the decrease in the amount of fine particles that can be removed by oxidation It is also effective to do.
[0093]
When the air-fuel ratio of the exhaust gas is made rich, that is, when the oxygen concentration in the exhaust gas is reduced, the active oxygen releasing agent 61 releases the active oxygen O to the outside at a stretch. Due to the active oxygen O released at once, the deposited particulates are easily oxidized and easily oxidized and removed.
[0094]
On the other hand, if the air-fuel ratio is maintained lean, the surface of platinum Pt is covered with oxygen, and so-called oxygen poisoning of platinum Pt occurs. NO when such oxygen poisoning occurs_XNO due to reduced oxidizing action on_XOf the active oxygen from the active oxygen releasing agent 61 is reduced. However, when the air-fuel ratio is made rich, oxygen on the surface of platinum Pt is consumed, so that oxygen poisoning is eliminated. Therefore, when the air-fuel ratio is switched from rich to lean again, NO_XNO due to enhanced oxidizing action on_XOf the active oxygen releasing agent 61 increases, thereby increasing the amount of active oxygen released from the active oxygen releasing agent 61.
[0095]
Therefore, when the air-fuel ratio is temporarily switched from lean to rich while the air-fuel ratio is maintained lean, oxygen poisoning of platinum Pt is eliminated each time, and active oxygen release when the air-fuel ratio is lean is eliminated. The amount is increased, and thus the oxidizing action of the particulate on the particulate filter 70 can be promoted.
[0096]
Further, since the elimination of the oxygen poisoning is, so to speak, combustion of a reducing substance, the temperature of the particulate filter is increased with heat generation. As a result, the amount of fine particles that can be oxidized and removed in the particulate filter is improved, and the oxidization and removal of residual and deposited particulates is facilitated. If the air-fuel ratio of the exhaust gas is made rich immediately after switching between the exhaust gas upstream side and the exhaust downstream side of the particulate filter by the valve body 71a, the other collecting surface in the particulate filter partition wall in which no particulate remains remains. Since the active oxygen is more easily released than the one collecting surface, the residual particulates on the one collecting surface can be more reliably oxidized and removed by a larger amount of the released active oxygen. Of course, the air-fuel ratio of the exhaust gas may be occasionally made rich irrespective of the switching of the valve body 71a, so that the particulates hardly remain and accumulate on the particulate filter.
[0097]
As a method of making the air-fuel ratio of the exhaust gas rich, for example, the above-described low-temperature combustion may be performed. Of course, it is also possible to switch between the exhaust upstream side and the exhaust downstream side of the particulate filter at the time of switching from the normal combustion to the low-temperature combustion or prior to that. Further, in order to make the air-fuel ratio of the exhaust gas rich, the combustion air-fuel ratio may simply be made rich. Further, 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 the expansion stroke by the engine fuel injection valve, or the fuel may be injected into the cylinder in the intake stroke. May be jetted (bi rubber jet). Of course, the post injection or the rubber injection does not necessarily require an interval between the post injection and the rubber injection. It is also possible to supply fuel to the engine exhaust system. Further, as described above, since the low-temperature combustion is performed on the low engine load side, the low-temperature combustion is performed immediately after the fuel cut at the time of engine deceleration. Thus, in the control according to the third flowchart, the low-temperature combustion is performed immediately after the switching of the valve body 71a, and the air-fuel ratio of the exhaust gas is often made rich.
[0098]
By the way, calcium Ca in the exhaust gas is SO₃Is present, calcium sulfate CaSO₄Generate This calcium sulfate CaSO₄Is difficult to be oxidized and removed, and remains on the particulate filter as ash. Therefore, in order to prevent clogging of the particulate filter due to residual calcium sulfate, it is preferable to use an alkali metal or alkaline earth metal having a higher ionization tendency than calcium Ca, for example, potassium K, as the active oxygen releasing agent 61. , Whereby SO diffuses into the active oxygen releasing agent 61.₃Combines with potassium K to form potassium sulfate K₂SO₄And calcium Ca is SO₃Pass through the partition of the particulate filter without being combined with Therefore, the particulate filter is not clogged by the 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, and strontium Sr is used. Is preferred.
[0099]
Further, even if only a noble metal such as platinum Pt is supported on a particulate filter as an active oxygen releasing agent, NO retained on the surface of platinum Pt₂Or SO₃Can release active oxygen. However, in this case, the solid line indicating the amount of fine particles G that can be removed by oxidation moves slightly to the right as compared with the solid line shown in FIG. Ceria can also be used as an active oxygen releasing agent. Ceria absorbs oxygen when the oxygen concentration in the exhaust gas is high (Ce₂O₃→ 2 CeO₂), Release active oxygen when the oxygen concentration in the exhaust gas decreases (2CeO)₂→ Ce₂O₃), It is necessary to make the air-fuel ratio in the exhaust gas rich periodically or irregularly in order to remove particulates by oxidation. Iron or tin may be used instead of ceria.
[0100]
Also, NO in the exhaust gas is used as an active oxygen releasing agent._XNO used for purification_XIt is also possible to use a storage reduction catalyst. In this case, NO_XOr SO_XIt is necessary to at least temporarily make the air-fuel ratio of the exhaust gas rich in order to discharge the exhaust gas, and it is preferable to perform this enrichment control after the reversal of the upstream and downstream sides of the particulate filter.
[0102]
Although the diesel engine of the present embodiment is configured to switch between low-temperature combustion and normal combustion, the present invention is not limited to the present invention. Needless to say, a diesel engine or a particulate that performs only normal combustion is used. The present invention is applicable to an exhaust gasoline engine.
[0103]
【The invention's effect】
Thus, according to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the exhaust gas purifying apparatus is disposed in the engine exhaust system.Wall-flow type honeycomb structureA particulate filter, and reversing means for reversing the exhaust upstream side and the exhaust downstream side of the particulate filter., PaThe particulate filter has a collecting wall for collecting particulates,An active oxygen releasing agent is supported on the collecting wall,The collecting wall has a first collecting surface and a second collecting surface,When particulates remain on the current exhaust upstream collection surface of the first collection surface and the second collection surfaceThe first and second collection surfaces of the collection wall are used alternately to collect particulates by reversing the exhaust upstream side and the exhaust downstream side of the particulate filter by the reversing means. It is supposed to be. As a result, depending on the operation state, the particulate filter may not be sufficiently oxidized by the particulate filter, and some of the particulate may remain on one collecting surface of the particulate filter collecting wall. Due to the reversal of the particulate filter on the exhaust upstream side and the exhaust downstream side, no new particulates accumulate on this collecting surface of the collecting wall, and the residual particulates can be gradually removed by oxidation. At the same time, the collection and oxidation of the particulates are started by the other collection surface of the collection wall. Thus, when the first and second collecting surfaces are used alternately for collecting particulates, each collecting surface is compared to a case where a single collecting surface is used to collect particulates. Since the amount of trapped particulates on the collecting surface can be reduced, which is advantageous for removing particulates by oxidation, there is no accumulation of particulates in the particulate filter, preventing clogging of the particulate filter. can do.
[0104]
According to another exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the exhaust gas purifying apparatus is disposed in the engine exhaust system.Wall-flow type honeycomb structureA particulate filter, and a reversing means for reversing an exhaust upstream side and an exhaust downstream side of the particulate filter, wherein the particulate filter carries an active oxygen releasing agent, and the active filter released from the active oxygen releasing agent. Oxygen oxidizes the trapped particulates, and the active oxygen releasing agent turns NO when there is excess oxygen around it._XIs bound to oxygen and bound when the ambient oxygen concentration decreases._XAnd oxygen_XThe particulate filter has a collecting wall for collecting particulates, and the collecting wall has a first collecting surface and a second collecting surface. And havingWhen particulates remain on the current exhaust upstream collection surface of the first collection surface and the second collection surfaceThe first and second collection surfaces of the collection wall are used alternately to collect particulates by reversing the exhaust upstream side and the exhaust downstream side of the particulate filter by the reversing means. Occasionally, the ambient oxygen concentration is reduced. Depending on the operating condition, the particulate filter may not be sufficiently oxidized by the particulate filter, and some particulate may remain on one of the collecting surfaces of the particulate filter collecting wall. By alternately using the first collecting surface and the second collecting surface for collecting the curated material, clogging of the particulate filter can be prevented. For the oxidative removal of the particulates, active oxygen released from an active oxygen releasing agent carried on the particulate filter is used. This active oxygen releasing agent, together with oxygen, contains NO in exhaust gas._XAnd the NO held together with active oxygen by lowering the oxygen concentration_XIt emits. Occasionally, when the oxygen concentration is reduced, the residual particulates on the particulate filter can be better oxidized and removed by the active oxygen thus forcibly released. In addition, the released NO_XCan be reduced and purified by a reducing substance contained in the exhaust gas. As a result, particulates and NO in the exhaust gas_XCan be purified at the same time.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view of a diesel engine provided with an exhaust gas purification device according to the present invention.
FIG. 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. 1;
FIG. 4 is a side sectional view of a combustion chamber.
FIG. 5 is a diagram showing lift and fuel injection of intake and exhaust valves.
FIG. 6: smoke and NO_XFIG.
7A is a diagram showing a change in combustion pressure when the amount of generated smoke is the largest when the air-fuel ratio is around 21, and FIG. 7B is a diagram showing a combustion pressure when the amount of generated smoke is almost zero when the air-fuel ratio is around 18; FIG. It is a figure showing a change.
FIG. 8 is a diagram showing fuel molecules.
FIG. 9 is a diagram showing a relationship between a generation amount of smoke 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 operation region I and a second operation region II.
FIG. 12 is a diagram showing an output of an air-fuel ratio sensor.
FIG. 13 is a diagram showing an opening degree of a throttle valve and the like.
FIG. 14 is a diagram showing an air-fuel ratio in a first operation region I.
15A is a diagram showing a map of a target opening of a throttle valve, and FIG. 15B 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 the second combustion.
17A is a diagram showing a map of a target opening of a throttle valve, and FIG. 17B is a diagram showing a map of a target opening of an EGR control valve.
FIG. 18 is a plan view showing the vicinity of a switching unit and a particulate filter in an engine exhaust system.
FIG. 19 is a side view of FIG. 18;
FIG. 20 is a view showing another blocking position of the valve body in the switching unit different from that in FIG. 18;
FIG. 21 is a view showing an intermediate position of a valve body in a switching unit.
FIG. 22A is a front view showing the structure of a particulate filter, and FIG. 22B is a side sectional view showing the structure of the particulate filter.
FIG. 23 is a diagram for explaining the 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 view for explaining the accumulation action of particulates.
FIG. 26 is a first flowchart for preventing accumulation of particulates on a particulate filter.
FIG. 27 is an enlarged sectional view of a partition wall of the particulate filter.
FIG. 28 is a second flowchart for preventing accumulation of particulates on the particulate filter.
FIG. 29 is a third flowchart for preventing 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

Claims (7)

Comprising a wall flow type particulate filter forming a honeycomb structure disposed in the engine exhaust system, and a reversing means for reversing the exhaust upstream side of the particulate filter and the exhaust gas downstream side, before Symbol particulate filter Has a collecting wall for collecting particulates, the collecting wall carries an active oxygen releasing agent, and the collecting wall has a first collecting surface and a second collecting surface. When the particulates remain on the current exhaust upstream collection surface of the first collection surface and the second collection surface, the exhaust gas is exhausted to the exhaust upstream side of the particulate filter by the reverse rotation means. An internal combustion engine, wherein the first collection surface and the second collection surface of the collection wall are used alternately to collect particulates by reversing the downstream side. Exhaust purification equipment . 2. The active oxygen releasing agent according to claim 1, wherein when excess oxygen is present in the surroundings, the active oxygen releasing agent takes in oxygen to retain the oxygen, and releases the retained oxygen in the form of active oxygen when the surrounding oxygen concentration decreases. An exhaust purification device for an internal combustion engine according to claim 1. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the reversing means reverses the upstream side and the downstream side of the exhaust of the particulate filter every predetermined time or every predetermined traveling distance . The reversing means reverses the exhaust upstream side and the exhaust downstream side of the particulate filter when a differential pressure between an exhaust upstream side and an exhaust downstream side of the particulate filter becomes equal to or higher than a set differential pressure. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 2 , wherein: 3. The method according to claim 1, wherein the reversing means reverses the exhaust upstream side and the exhaust downstream side of the particulate filter when the particulate accumulation amount of the particulate filter becomes equal to or greater than a set accumulation amount. An exhaust purification device for an internal combustion engine according to claim 1. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 2 , wherein the oxygen concentration in the exhaust gas is occasionally reduced . A wall-flow-type particulate filter having a honeycomb structure disposed in an engine exhaust system, and reversing means for reversing an exhaust upstream side and an exhaust downstream side of the particulate filter, the particulate filter comprising: carrying the active oxygen release agent, the oxidizing the trapped particulate active oxygen release active oxygen released from the dosage is the particulate filter, the active oxygen release agent, the NO _X when the excess oxygen present in the ambient oxygen is bound and held and the NO _X and oxygen coupled with the oxygen concentration of the ambient drops is intended to release decomposed into NO _X and active oxygen, the particulate filter, collecting particulates A collecting wall, the collecting wall having a first collecting surface and a second collecting surface, and the first collecting surface and the second collecting surface. When the particulates remain on the current exhaust upstream collecting surface of the filter, the exhaust upstream and downstream of the particulate filter are reversed by the reversing means, so that the particulates are trapped. The exhaust gas purifying apparatus for an internal combustion engine, wherein the first collecting surface and the second collecting surface of the collecting wall are alternately used for collecting, and occasionally lowers the oxygen concentration in the surroundings. .

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