JP3607987B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
Particulates mainly composed of soot are contained in the exhaust gas of internal combustion engines, particularly diesel engines. Since particulates are harmful substances, it has been proposed to arrange a filter for collecting particulates in the engine exhaust system before release into the atmosphere. Such a filter is required to burn off the collected particulates in order to prevent an increase in exhaust resistance due to clogging.
[0003]
In such filter regeneration, ignition and combustion occur when the particulates reach approximately 600 ° C., but the exhaust gas temperature of the diesel engine is considerably lower than 600 ° C. at normal times, and usually means such as heating the filter itself. is required.
[0004]
In Japanese Patent Publication No. 7-106290, if a platinum group metal and an alkaline earth metal oxide are supported on a filter, the particulates on the filter are about 400 ° C., which is the exhaust gas temperature of a diesel engine at normal times. It is disclosed that it burns continuously.
[0005]
Even if the particulate filter can burn out the particulates in the exhaust gas before it is released into the atmosphere, the particulate filter will prevent the engine exhaust itself from becoming a large exhaust resistance. It has a larger cross-sectional area than the passage cross-sectional area of the system, and in practice it is not easy to arrange in the engine exhaust system.
[0006]
In order to facilitate the arrangement of the particulate filter in the engine exhaust system, Japanese Utility Model Laid-Open No. 1-149915 proposes to arrange the particulate filter in a muffler having a relatively large cross-sectional area in the engine exhaust system. Has been.
[0007]
[Problems to be solved by the invention]
Thus, the problem of vehicle mountability is solved by arranging the particulate filter in the muffler. By the way, the exhaust gas passing through the muffler in which the particulate filter is disposed may contain harmful substances other than the particulates, and a catalyst device for purifying these harmful substances is required. If such a catalyst device is arranged on the downstream side of the muffler, it is difficult to raise the temperature by the exhaust gas because it is far from the engine body, so the catalyst is not activated in the catalyst device, and harmful substances that pass through the muffler are It is released into the atmosphere without being purified well.
[0008]
Therefore, the object of the present invention is to oxidize the particulates collected by disposing the particulate filter in the muffler on the particulate filter, and prevent harmful substances other than particulates from being released into the atmosphere through the muffler. It is an object of the present invention to provide an exhaust emission control device for an internal combustion engine.
[0009]
[Means for Solving the Problems]
An exhaust emission control device for an internal combustion engine according to claim 1 of the present invention includes a muffler located in an engine exhaust system, and the particulates in the exhaust gas collected and collected in the muffler. A particulate filter that oxidizes the curate; and a catalyst device that is disposed in the muffler and is located downstream of the particulate filter.In the exhaust gas purification apparatus for an internal combustion engine, the inside of the muffler is partitioned into at least a first chamber and a second chamber, and the particulate filter is disposed in the first chamber located upstream from the second chamber, The catalyst device is disposed in the second chamber, and includes a reversing means for reversing the exhaust upstream side and the exhaust downstream side of the particulate filter in the first chamber, and the particulate filter captures the particulates. A collecting wall for collecting, the collecting wall having a first collecting surface and a second collecting surface, and the exhaust filter downstream side and the exhaust upstream side of the particulate filter by the reverse means. The first collecting surface and the second collecting surface of the collecting wall are alternately used to collect the particulates by being reversed.
[0011]
And claims according to the invention2An exhaust emission control device for an internal combustion engine according to claim 1,1In the exhaust gas purification apparatus for an internal combustion engine according to the item 1, an active oxygen release agent is supported on the particulate filter, and the active oxygen released from the active oxygen release agent oxidizes the particulate.
[0012]
And claims according to the invention3An exhaust emission control device for an internal combustion engine according to claim 1,2In the exhaust gas purification apparatus for an internal combustion engine according to claim 1, the active oxygen release agent takes in oxygen when excess oxygen is present in the surrounding area and retains oxygen, and when the surrounding oxygen concentration decreases, the retained oxygen is converted into the form of active oxygen. It is characterized by being discharged with
[0013]
And claims according to the invention4An internal combustion engine exhaust gas purification apparatus according to claim 13The exhaust gas purification apparatus for an internal combustion engine according to any one of the above, wherein the catalyst device carries an oxidation catalyst.
[0014]
And claims according to the invention5An internal combustion engine exhaust gas purification apparatus according to claim 13The exhaust gas purification apparatus for an internal combustion engine according to any one of the above, wherein the catalyst device is NO_XIt is characterized by carrying a catalyst.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic longitudinal sectional view of a four-stroke diesel engine equipped with an exhaust emission control device 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. It is a bottom view of the cylinder head in the diesel engine of. Referring to FIGS. 1 to 3, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5a is a cavity formed on the top surface of the piston 4, and 5 is formed in the cavity 5a. The 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 disposed in the intake duct 13. On the other hand, the exhaust port 10 is connected to the exhaust manifold 17.
[0016]
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 EGR gas is cooled by the engine cooling water.
[0017]
On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, so-called common rail 26, via a fuel supply pipe 25. Fuel is supplied into the common rail 26 from an electrically controlled fuel pump 27 with variable discharge amount, 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, and a fuel pump 27 is set so that the fuel pressure in the common rail 26 becomes a target fuel pressure based on an output signal of the fuel pressure sensor 28. The discharge amount is controlled.
[0018]
An electronic control unit 30 receives an output signal from the air-fuel ratio sensor 21 and an output signal from 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, and an output signal of the load sensor 41 is also input to the electronic control unit 30. For example, an output signal of a crank angle sensor 42 that generates an output pulse every 30 ° rotation 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.
[0019]
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 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 are scattered along the lower 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 combusted.
[0020]
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 traveling in the direction of the valve body of the exhaust valve 9 is directed between the rear surface of the umbrella portion of the exhaust valve 9 and the exhaust port 10. That is, in other words, of the six nozzle ports of the fuel injection valve 6, two of the nozzle ports discharge the fuel spray F when 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 back of the umbrella part of the exhaust valve 9 at this time, and the fuel spray F that collides with the back of the umbrella part of the exhaust valve 9 is reflected on the back of the umbrella part of the exhaust valve 9. To the exhaust port 10.
[0021]
Normally, no additional fuel Qa is injected, and only main injection Qm is performed. FIG. 6 shows the change in output torque when the air-fuel ratio A / F (horizontal axis in FIG. 6) is changed by changing the opening degree and EGR rate of the throttle valve 16 during engine low load operation, and smoke, HC , CO, NO_xThe experiment example which shows the change of the discharge amount of is shown. As can be seen from FIG. 6, in this experimental example, the EGR rate increases as the air-fuel ratio A / F decreases, and the EGR rate is 65% or more when the air-fuel ratio is less than the theoretical air-fuel ratio (≈14.6).
[0022]
As shown in FIG. 6, when the air-fuel ratio A / F is decreased by increasing the EGR rate, the EGR rate becomes around 40% and the amount of smoke generated increases when 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 decreased, the amount of smoke generated increases rapidly and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke suddenly decreases, the EGR rate is increased to 65% or more, and when the air-fuel ratio A / F is near 15.0, the smoke becomes almost zero. . That is, almost no wrinkles occur. At this time, the output torque of the engine slightly decreases, and NO_xThe amount of generation is considerably low. On the other hand, the generation amount of HC and CO starts increasing at this time.
[0023]
FIG. 7A shows a change in combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is near 21 and the amount of smoke generated is the largest, and FIG. 7B shows that the air-fuel ratio A / F is 18. A change in the combustion pressure in the combustion chamber 5 when the amount of smoke generated in the vicinity is almost zero is shown. As can be seen by comparing FIG. 7A and FIG. 7B, the case of FIG. 7B where the amount of smoke generated is almost zero is shown in FIG. 7A where the amount of smoke generated is large. It can be seen that the combustion pressure is lower than the case.
[0024]
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 smoke generated is almost zero, as shown in FIG._xThe amount of generated is significantly reduced. NO_xThe reduction in the amount of generation means that the combustion temperature in the combustion chamber 5 has decreased, and therefore it can be said that the combustion temperature in the combustion chamber 5 is low when soot is hardly 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 therefore the combustion temperature in the combustion chamber 5 is low at this time.
[0025]
Secondly, when the amount of smoke generated, that is, the amount of soot is substantially zero, the HC and CO emissions increase as shown in FIG. This means that the hydrocarbons are discharged without growing to the soot. That is, linear hydrocarbons and aromatic hydrocarbons as shown in FIG. 8 contained in the fuel are thermally decomposed to form soot precursors when the temperature is raised in an oxygen-deficient state. A soot made of a solid in which carbon atoms are assembled is produced. In this case, the actual soot formation process is complicated, and it is not clear what form the soot precursor will take, but in any case the hydrocarbons shown in FIG. After that, it will grow up to heels. Therefore, as described above, when the generation amount of soot becomes almost zero, the emission amount of HC and CO increases as shown in FIG. 6. At this time, HC is a precursor of soot or a hydrocarbon in the previous state. .
[0026]
Summarizing these considerations based on the experimental results shown in FIGS. 6 and 7, the amount of soot generated becomes almost zero when the combustion temperature in the combustion chamber 5 is low, and at this time, the soot precursor or the previous state Hydrocarbons are discharged from the combustion chamber 5. As a result of repeated experimental research on this in detail, when the temperature of the fuel in the combustion chamber 5 and the gas surrounding it is below a certain temperature, the soot growth process stops midway, that is, soot It was found that soot was not generated at all, and soot was generated when the temperature of the fuel in the combustion chamber 5 and the surrounding temperature became below a certain temperature.
[0027]
By the way, when the hydrocarbon generation process stops in the state of soot precursor, the temperature of the fuel and its surroundings, that is, the above-mentioned certain temperature changes depending on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. I can't say how many times, but this certain temperature is NO_xTherefore, this certain temperature is NO._xIt can be defined to some extent from the generation amount of. That is, as the EGR rate increases, the temperature of the fuel during combustion and the surrounding gas decreases, and NO_xThe amount of generation decreases. At this time NO_xOf 10 p. p. When it becomes around m or less, wrinkles hardly occur. Therefore, the above mentioned temperature is NO_xOf 10 p. p. It almost corresponds to the temperature when it is around m or below.
[0028]
Once soot is produced, it cannot simply be purified by post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in the previous state can be easily purified by post-treatment using a catalyst having an oxidation function. Like this, NO_xIt is extremely effective for purifying exhaust gas to reduce the generation amount of hydrocarbons and to discharge hydrocarbons from the combustion chamber 5 in the state of soot precursor or in front thereof.
[0029]
Now, in order to stop the growth of hydrocarbons in a state before soot is generated, it is necessary to suppress the temperature of the fuel and the surrounding gas in the combustion chamber 5 to a temperature lower than the temperature at which soot is generated. There is. In this case, in order to suppress the temperature of the fuel and the gas around it, it has been found that the endothermic effect of the gas around the fuel when the fuel burns has a very large influence.
[0030]
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 away from the fuel does not increase so much, and only the temperature around the fuel becomes extremely high locally. That is, at this time, the air away from the fuel hardly performs the endothermic action of the combustion heat of the fuel. In this case, since the combustion temperature becomes extremely high locally, the unburned hydrocarbons that have received this heat of combustion produce soot.
[0031]
On the other hand, the situation is slightly different when 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 around and reacts with oxygen mixed in the inert gas and burns. In this case, since the combustion heat is absorbed by the surrounding inert gas, 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 kept low by the endothermic action of the inert gas.
[0032]
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 soot is generated, an amount of inert gas that can absorb a sufficient amount of heat is required. Therefore, if the amount of fuel increases, the amount of inert gas required increases accordingly. In this case, the greater 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. This point, CO₂Since EGR gas has a relatively large specific heat, it can be said that it is preferable to use EGR gas as an inert gas.
[0033]
FIG. 9 shows the relationship between the EGR rate and smoke when EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 9, curve A shows the case where the EGR gas is strongly cooled and the EGR gas temperature is maintained at about 90 ° C., and 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.
[0034]
As shown by curve A in FIG. 9, when the EGR gas is cooled strongly, soot generation peaks when the EGR rate is slightly lower than 50%. In this case, the EGR rate is increased to about 55% or more. If you do, almost no wrinkles will occur. On the other hand, as shown by the curve B in FIG. 9, when the EGR gas is slightly cooled, the amount of soot generated peaks when the EGR rate is slightly higher than 50%. In this case, the EGR rate is almost 65% or more. If this is done, almost no wrinkles will occur.
[0035]
Further, as shown by the curve C in FIG. 9, when the EGR gas is not forcibly cooled, the amount of soot generated reaches a peak when the EGR rate is around 55%. In this case, the EGR rate is approximately 70%. If the percentage is exceeded, almost no wrinkles occur. FIG. 9 shows the amount of smoke generated when the engine load is relatively high. When the engine load is reduced, the EGR rate at which the amount of soot reaches a peak slightly decreases, and the EGR rate at which soot hardly occurs. The lower limit is also slightly reduced. Thus, the lower limit of the EGR rate at which soot hardly occurs varies depending on the degree of cooling of the EGR gas and the engine load.
[0036]
FIG. 10 shows the amount of mixed gas of EGR gas and air necessary for making the temperature of the fuel and the surrounding gas lower than the temperature at which soot is generated when EGR gas is used as the inert gas. And the ratio of the air in this gas mixture amount, and the ratio of the EGR gas in this gas mixture are shown. In FIG. 10, the vertical axis indicates the total intake gas amount sucked into the combustion chamber 5, and the chain line Y indicates the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis indicates the required load, and Z1 indicates the low load operation region.
[0037]
Referring to FIG. 10, the ratio 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 air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 10, the ratio of EGR gas, that is, the amount of EGR gas in the mixed gas is used to make the temperature of the fuel and its 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 EGR rate, and is 70% or more in the embodiment shown in FIG. That is, if the total intake gas amount sucked into the combustion chamber 5 is a solid line X in FIG. 10, the ratio of the air amount and the EGR gas amount in the total intake gas amount X is a ratio as shown in FIG. The temperature of the fuel and the surrounding gas is lower than the temperature at which soot is produced, and so no soot is produced. Also, NO at this time_xThe amount generated is 10 p. p. around m or less, so NO_xThe amount of generated is extremely small.
[0038]
If 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 amount of EGR gas must be increased as the amount of injected fuel increases. That is, the amount of EGR gas needs to increase as the required load increases.
[0039]
On the other hand, in the load region Z2 of FIG. 10, the total intake gas amount X necessary for preventing the generation of soot exceeds the total intake gas amount Y that can be sucked. Therefore, in this case, in order to supply the total intake gas amount X necessary for preventing the generation of soot into the combustion chamber 5, it is necessary to supercharge or pressurize both the EGR gas and the intake air, or the EGR gas. When EGR gas or the like is not supercharged or pressurized, the total intake gas amount X coincides with 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 decreased to increase the amount of EGR gas, and the fuel is burned under a rich air-fuel ratio.
[0040]
As described above, FIG. 10 shows the case where the fuel is burned under the stoichiometric air-fuel ratio, but 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 rich, NO is generated while preventing the generation of soot._xOf 10 p. p. m or less, and even in the low load region Z1 shown in FIG. 10, even if the air amount is larger than the air amount shown in FIG. NO while preventing the occurrence of soot even if lean_xOf 10 p. p. It can be around m or less.
[0041]
That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but the combustion temperature is suppressed to a low temperature, so that the excess fuel does not grow to soot, and so no soot is generated. At this time, NO_xHowever, only 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 is high, but in the present invention the soot is suppressed to a low temperature, so Not generated at all. In addition, NO_xHowever, only a very small amount is generated.
[0042]
As described above, in the engine low load operation region Z1, 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, no soot is generated._xThe amount of generated is extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time.
[0043]
By the way, the temperature of the fuel during combustion in the combustion chamber and the surrounding gas can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops midway only when the heat generated by 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 temperature of the fuel during combustion and the surrounding gas temperature are suppressed to a temperature below the temperature at which hydrocarbon growth stops halfway, so that the first combustion, that is, low temperature combustion is performed. When the engine load is relatively high, the second combustion, that is, the combustion normally performed conventionally is performed. Here, the first combustion, that is, low temperature combustion, as is clear from the above description, the amount of inert gas in the combustion chamber is larger than the worst inert gas amount at which the amount of soot generation is maximum, and soot is almost generated. The second combustion, that is, the combustion that is normally performed in the past, is combustion in which the amount of inert gas in the combustion chamber is smaller than the worst inert gas amount that generates the largest amount of soot. Say.
[0044]
FIG. 11 shows a first operation 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 amount of depression 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 the 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. A second boundary with region II is shown. The change determination of the operation region from the first operation region I to the second operation region II is performed 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 change determination of the operation region is performed based on the second boundary Y (N).
[0045]
That is, when the engine operating state is in the first operating region I and low-temperature combustion is being performed, if the required load L exceeds the first boundary X (N) that is a function of the engine speed N, the operating region is It is determined that the operation has shifted to the second operation region II, and combustion by the conventional combustion method is performed. Next, when the required load L becomes lower than the second boundary Y (N) that is a function of the engine speed N, it is determined that the operating region has shifted to the first operating region I, and low temperature combustion is performed again.
[0046]
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, operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG.
[0047]
FIG. 13 shows the opening degree of the throttle valve 16, the opening degree 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 operation region I where the required load L is low, the opening degree of the throttle valve 16 is gradually increased from nearly fully closed to about half-open as the required load L increases, and the EGR control valve 23 As the required load L increases, the degree of opening is gradually increased from near full close to full open. Further, in the example shown in FIG. 13, in the first operating region I, the EGR rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.
[0048]
In other words, in the first operating region I, the EGR rate is approximately 70%, and the opening degree of the throttle valve 16 and the opening degree of the EGR control valve 23 are controlled so that 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 degree 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 also delayed as the injection start timing θS is delayed.
[0049]
During the idling operation, the throttle valve 16 is closed to near full close. At this time, the EGR control valve 23 is also closed to close to full close. When the throttle valve 16 is closed to close to the fully closed state, the pressure in the combustion chamber 5 at the start of compression becomes low, so the compression pressure becomes small. When the compression pressure is reduced, the compression work by the piston 4 is reduced, so that the vibration of the engine body 1 is reduced. That is, during idling operation, the throttle valve 16 is closed to close to the fully closed state in order to suppress vibration of the engine body 1.
[0050]
On the other hand, when the engine operating region changes from the first operating region I to the second operating region II, the opening of the throttle valve 16 is increased stepwise from the half-open state to the fully-open direction. At this time, in the example shown in FIG. 13, the EGR rate is decreased in a stepped manner from approximately 70% to 40% or less, and the air-fuel ratio is increased in a stepped manner. That is, since the EGR rate exceeds the EGR rate range (FIG. 9) that generates a large amount of smoke, 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.
[0051]
Conventional combustion is performed in the second operation region II. In this combustion method, soot and NO_XHowever, when the engine operating region is changed from the first operating region I to the second operating region II, the injection amount is reduced stepwise as shown in FIG. To be harassed.
[0052]
In the second operation region II, the throttle valve 16 is held in a fully open state except for a part thereof, and the opening degree of the EGR control valve 23 is gradually reduced as the required load L increases. In this operation 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 made 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.
[0053]
FIG. 14 shows the air-fuel ratio A / F in the first operating region I. In FIG. 14, the curves indicated by A / F = 15.5, A / F = 16, A / F = 17, and A / F = 18 have 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 operation region I, and in the first operation region I, the air-fuel ratio A / F is leaner as the required load L becomes lower.
[0054]
That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, low temperature combustion can be performed even if the EGR rate is reduced as the required load L is reduced. When the EGR rate is lowered, the air-fuel ratio increases, so as shown in FIG. 14, the air-fuel ratio A / F increases as the required load L decreases. As the air-fuel ratio A / F increases, the fuel consumption rate improves. Therefore, in order to make the air-fuel ratio as lean as possible, in this embodiment, the air-fuel ratio A / F increases as the required load L decreases.
[0055]
Note that the target opening ST of the throttle valve 16 required to set the air-fuel ratio to the target air-fuel ratio shown in FIG. 14 is a function of the required load L and the engine speed N as shown in FIG. The target opening degree 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 the ROM 32 in advance as shown in FIG. And is stored in advance in the ROM 32 in the form of a map as a function of the engine speed N.
[0056]
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, the curves indicated by A / F = 24, A / F = 35, A / F = 45, and A / F = 60 indicate the target air-fuel ratios 24, 35, 45, and 60, respectively. The target opening ST of the throttle valve 16 necessary for setting the air-fuel ratio to the target air-fuel ratio is previously stored 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. The target opening degree SE of the EGR control valve 23 necessary for setting the air-fuel ratio to the target air-fuel ratio is stored 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 advance in the form of a map.
[0057]
Thus, in the diesel engine of the present embodiment, the first combustion, that is, low-temperature combustion, and the second combustion, that is, normal combustion are switched based on the depression amount L of the accelerator pedal 40 and the engine speed N. In each combustion, based on the depression amount L of the accelerator pedal 40 and the engine speed N, the opening control of the throttle valve 16 and the EGR valve is performed by the map shown in FIG.
[0058]
FIG. 18 is a plan sectional view showing the exhaust emission control device. The exhaust purification device is configured in the muffler 100. The muffler 100 is located, for example, in the most downstream part of the engine exhaust system. The muffler 100 is partitioned into a first chamber 101, a second chamber 102, and a third chamber 103 that are adjacent to each other in the longitudinal direction. In the first chamber 101 located on the most upstream side, the particulate filter 70 is disposed on both sides of the first filter 101 leaving a space. A switching unit 71 that connects the muffler 100 to the engine exhaust system is provided outside the muffler 100. The switching unit 71 is a switching valve capable of blocking the upstream opening 71b used for connection with the engine exhaust system, the downstream opening 71c facing the upstream opening 71b, and the upstream opening 71b and the downstream opening 71c. 71a.
[0059]
The switching portion 71 is further provided with a first opening 71d communicating with the upstream opening 71b and a second opening 71e communicating with the downstream opening 71c at one blocking position of the valve body 71a shown in FIG. Yes. The first opening 71 d is communicated with one space in the first chamber 101 in the muffler 100 by the first connecting pipe 72. The second opening 71 e of the switching unit 71 is communicated with the other space in the first chamber 101 in the muffler 100 by the second connection pipe 73. Further, the downstream opening 71 c of the switching unit 71 is communicated with the second chamber 102 in the muffler 100 by the third connection pipe 74.
[0060]
In the muffler 10, the first chamber 101 is adjacent to the third chamber 103, and the third chamber 103 is adjacent to the second chamber 102. In the second chamber 102, the catalyst device 75 is arranged with spaces on both sides thereof. The third connecting pipe 74 passes through one space of the first chamber 101, the other space, the particulate filter 70, the third chamber 103, the other space of the second chamber 102, and the catalyst device 75. The second chamber 102 is open to one space.
[0061]
At one blocking position of the valve body 71a, as shown by an arrow in FIG. 18, the exhaust gas flows into the switching portion 71 from the upstream opening 71b and then passes through the first connection pipe 72 from the first opening 71d. 100 flows into one space in the first chamber 101, and passes through the particulate filter 70 from the one space to the other space in the first chamber 101. Thereafter, the second chamber 71 reaches the second opening 71e of the switching unit 71 through the second connection pipe 73 from the other space of the first chamber 101, passes through the downstream opening 71c of the switching unit 71, and passes through the third connection pipe 74. It flows into one space in the second chamber 102 of the muffler 100. Thereafter, the second chamber 102 passes through the catalyst device 75 from one space to the other space, and the third chamber 104 is connected to the third chamber 103 through the third series pipe 104 that communicates the other space of the second chamber 102 with the third chamber 103. It flows into the chamber 103 and passes through the second chamber 102 and is discharged from the third chamber 103 into the atmosphere via the second communication pipe 105 that communicates the third chamber 103 and the outside of the muffler 100.
[0062]
Thus, in the muffler 10, the first chamber 101 is the most upstream side, the second chamber 102 is the next upstream side, not the third chamber 103 adjacent to the first chamber 101, and the third chamber 103 is the most downstream side. It has become. The substantial volume of the second chamber 102, that is, the volume excluding the volume excluded by the third connection pipe 74, the second communication pipe 105, and the support itself of the catalyst device 75 (excluding the space in the support). Is smaller compared to the same substantial volume of the first chamber 101 and the third chamber 103, so that the exhaust gas contracts as it flows from the first chamber 101 into the second chamber 102. The sound pressure is lowered by expanding when the second chamber 102 flows into the third chamber 103.
[0063]
The valve body 71a is rotated by a negative pressure actuator, a step motor, or the like, and can be set not only to the one blocking position shown in FIG. 18 but also to the other blocking position shown in FIG. In this other blocking position, the exhaust gas flows into the switching portion 71 from the upstream opening 71b and then flows through the second opening 71e through the second connecting pipe 73 as shown by the arrow in FIG. It flows into the other space in one chamber 101 and passes through the particulate filter 70 from the other space toward one space in the first chamber 101. Thereafter, the first chamber 101 reaches the first opening 71 d of the switching unit 71 via the first connection pipe 72 from one space, passes through the downstream opening 71 c of the switching unit 71, and flows into the third connection pipe 74. Thereafter, like the one blocking position, the second chamber 102 passes through the catalytic device 75 and flows into the third chamber 103, where it is released into the atmosphere.
[0064]
Thus, in the present exhaust purification apparatus, since the switching filter 71 and the particulate filter 70 are arranged in the partitioned first chamber 101 in the muffler 100, the valve element 71a is moved from one of the shut-off positions to the other. By switching, it becomes possible to easily reverse the exhaust upstream side and the exhaust downstream side of the particulate filter 70 disposed in the first chamber 101. At any shut-off position, the exhaust gas flows from the first chamber 101 into the third chamber 103 via the second chamber 102 in the muffler 100, so that the sound pressure can be reduced well.
[0065]
Further, when the valve body 71a is switched from one of the two shut-off positions to the other, the valve body 71a is in the intermediate position as shown in FIG. 20, and the exhaust gas is the first of the muffler 100 as shown by the arrows in FIG. It will flow into the second chamber 102 without passing through the chamber 101, that is, without passing through the particulate filter 70.
[0066]
In the particulate filter, a large opening area is required for facilitating the inflow of exhaust gas. However, in the present exhaust purification apparatus, the particulate filter is placed in a muffler that has an inherently large cross-sectional area in the engine exhaust system. By disposing, the vehicle can be easily mounted.
[0067]
FIG. 21 shows the structure of the particulate filter 70. 21A is a front view of the particulate filter 70, and FIG. 21B is a side sectional view (a side sectional view at a position different from the penetration position of the third connecting pipe 74). As shown in these drawings, the particulate filter 70 has an oblong front shape in which the lateral width shown in FIG. 18 is larger than the height, and is made of a porous material such as cordierite, for example. The wall flow type has a honeycomb structure and has a large number of axial spaces subdivided by a large number of partition walls 54 extending in the axial direction. In the two adjacent axial spaces, one is closed on the exhaust downstream side by the plug 53 and the other is closed on the exhaust upstream side. 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. Particulates in the exhaust gas are very small compared to the size of the pores of the partition wall 54, but collide with the exhaust upstream surface of the partition wall 54 and the surface of the pores in the partition wall 54 and are collected. 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 collected particulates, alumina or the like is used on both side surfaces of the partition wall 54, and preferably on the pore surface in the partition wall 54, as described below. An active oxygen release agent and a noble metal catalyst are supported.
[0068]
The active oxygen release agent is an agent that promotes oxidation of particulates by releasing active oxygen. Preferably, oxygen is taken in and retained when excess oxygen is present in the surroundings, and the oxygen concentration in the surroundings is increased. When lowered, the retained oxygen is released in the form of active oxygen.
[0069]
As the noble metal catalyst, platinum Pt is usually used, and as the active oxygen release agent, alkali metals such as potassium K, sodium Na, lithium Li, cesium Cs, and rubidium Rb, barium Ba, calcium Ca, and strontium Sr are used. At least one selected from alkaline earth metals, lanthanum La, rare earths such as yttrium Y, and transition metals is used.
[0070]
In this case, as the active oxygen release 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, and strontium Sr are used. preferable.
[0071]
Next, how the collected particulates are oxidized and removed by such a particulate filter carrying an active oxygen release agent will be described by taking platinum Pt and potassium K as an example. The same particulate removal action can be performed using other noble metals, alkali metals, alkaline earth metals, rare earths, and transition metals.
[0072]
In a diesel engine, combustion is usually performed under excess air, and therefore 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 called 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. The fuel also contains sulfur S, which reacts with oxygen in the combustion chamber to react with SO.₂It becomes. Therefore, in the exhaust gas, SO₂It is included. Therefore excess oxygen, NO and SO₂The exhaust gas containing the gas flows into the exhaust upstream side of the particulate filter 70.
[0073]
22A and 22B schematically show an enlarged view of the exhaust gas contact surface in the particulate filter 70. FIG. In FIGS. 22A and 22B, reference numeral 60 denotes platinum Pt particles, and reference numeral 61 denotes an active oxygen release agent containing potassium K.
[0074]
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-It adheres to the surface of platinum Pt. On the other hand, NO in the exhaust gas is O on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂). Then the generated NO₂Part of the oxygen is absorbed on the active oxygen release agent 61 while being oxidized on platinum Pt, and is combined with potassium K, as shown in FIG.₃ ⁻Diffused into the active oxygen release agent 61 in the form of potassium nitrate KNO₃Is generated. Thus, in this embodiment, NO contained in the exhaust gas._xCan be absorbed by the particulate filter 70, and the amount released into the atmosphere can be greatly reduced.
[0075]
On the other hand, as described above, the exhaust gas contains SO.₂Is also included, this SO₂Is absorbed into the active oxygen release agent 61 by the same mechanism as NO. That is, as described above, oxygen O₂Is O₂ ⁻Or O^2-Is attached to the surface of platinum Pt in the form of SO₂Is O on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with SO₃It becomes. The generated SO₃Is partly oxidized on platinum Pt while being absorbed in the active oxygen release agent 61 and combined with potassium K, sulfate ions SO.₄ ^2-Diffused into the active oxygen release agent 61 in the form of potassium sulfate K₂SO₄Is generated. In this way, potassium nitrate KNO is contained in the active oxygen release catalyst 61.₃And potassium sulfate K₂SO₄Is generated.
[0076]
Particulates in the exhaust gas adhere to the surface of the active oxygen release agent 61 carried on the particulate filter, as indicated by 62 in FIG. At this time, the oxygen concentration at the contact surface between the particulate 62 and the active oxygen release agent 61 decreases. When the oxygen concentration is lowered, a difference in concentration occurs between the active oxygen release agent 61 having a high oxygen concentration, and therefore oxygen in the active oxygen release agent 61 is brought into contact with the particulate 62 and the active oxygen release agent 61. Try to move towards. As a result, potassium nitrate KNO formed in the active oxygen release agent 61₃Is decomposed into potassium K, oxygen O, and NO, oxygen O goes to the contact surface between the particulate 62 and the active oxygen release agent 61, and NO is 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.
[0077]
On the other hand, potassium sulfate K formed in the active oxygen release agent 61 at this time₂SO₄Also potassium K, oxygen O and SO₂The oxygen O is directed to the contact surface between the particulate 62 and the active oxygen release agent 61, and SO₂Is released from the active oxygen release agent 61 to the outside. SO released to the outside₂Is oxidized on the platinum Pt on the downstream side and is absorbed again into the active oxygen release agent 61. However, potassium sulfate K₂SO₄Is stabilized, potassium nitrate KNO₃It is difficult to release active oxygen compared to.
[0078]
On the other hand, the oxygen O toward the contact surface between the particulate 62 and the active oxygen release agent 61 is potassium nitrate KNO.₃And potassium sulfate K₂SO₄It is oxygen decomposed from a compound such as Oxygen O decomposed from the compound has high energy and has extremely high activity. Therefore, the oxygen directed 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 several tens of minutes without emitting a luminous flame. Further, the active oxygen O that oxidizes the particulate 62 is transferred to the active oxygen release agent 61 by NO and SO.₂Is also released when is absorbed. That is, NO_XNitrate ions NO in the active oxygen release agent 61 while repeatedly binding and separating oxygen atoms₃ ⁻The active oxygen is generated during this period. The particulate 62 is also oxidized by this active oxygen. Further, the particulates 62 adhering to the particulate filter 70 in this manner are oxidized by the active oxygen O, but these particulates 62 are also oxidized by oxygen in the exhaust gas.
[0079]
By the way, since platinum Pt and the active oxygen release agent 61 are activated as the temperature of the particulate filter increases, the amount of active oxygen O released from the active oxygen release agent 61 per unit time increases as the temperature of the particulate filter increases. To do. As a matter of course, the higher the temperature of the particulate itself, the easier it is to be removed by oxidation. Therefore, the amount of fine particles that can be removed by oxidation without emitting a luminous flame per unit time on the particulate filter increases as the temperature of the particulate filter increases.
[0080]
The solid line in FIG. 23 indicates the amount G of fine particles that can be removed by oxidation without emitting a bright flame per unit time. In FIG. 23, the horizontal axis indicates the temperature TF of the particulate filter. FIG. 23 shows the amount G of fine particles that can be oxidized and removed per second when the unit time is 1 second. As this unit time, an arbitrary time such as 1 minute or 10 minutes is adopted. be able to. For example, when 10 minutes is used as the unit time, the oxidizable and removable fine particle amount G per unit time represents the oxidizable and removable fine particle amount G per 10 minutes. Even in this case, the unit on the particulate filter 70 As shown in FIG. 23, the amount G of fine particles that can be removed by oxidation without emitting a bright flame per hour increases as the temperature of the particulate filter 70 increases.
[0081]
Now, when the amount of particulate discharged from the combustion chamber per unit time is referred to as discharged particulate amount M, when this discharged particulate amount M is smaller than the oxidizable and removable particulate amount G, for example, the amount of particulate discharged per second. When M is less than the amount G of fine particles that can be removed by oxidation per second, or when the amount M of fine particles discharged per 10 minutes is smaller than the amount of fine particles G that can be removed by oxidation every 10 minutes, that is, in region I in FIG. All the particulates discharged from the chamber are sequentially oxidized and removed within the short time without emitting a bright flame on the particulate filter 70. In contrast, when the amount M of discharged particulate is larger than the amount G of particulate 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 particulate oxidation in such a case.
[0082]
That is, when the amount of active oxygen is insufficient to oxidize all the particulates, if the particulates 62 adhere on the active oxygen release agent 61 as shown in FIG. Particulates that are only oxidized and not fully oxidized remain on the exhaust upstream side of the particulate filter. Next, when the state where the amount of active oxygen is deficient continues, the particulate portion that has not been oxidized from one to the next remains on the exhaust upstream surface. As a result, as shown in FIG. The exhaust upstream surface is covered with the residual particulate portion 63.
[0083]
Such residual particulate portion 63 gradually changes to a carbonaceous material that is difficult to oxidize, and when the exhaust upstream surface is covered with the residual particulate portion 63, NO and SO by platinum Pt.₂The active oxygen release action by the active oxygen release agent 61 is suppressed. Accordingly, the residual particulate portion 63 can be gradually oxidized over time, but another particulate 64 is placed on the residual particulate portion 63 from the next to the next as shown in FIG. And deposit. That is, when the particulates are deposited in a laminated form, these particulates are separated from platinum Pt and the active oxygen release agent, so that even if the particulates are easily oxidized, they are oxidized by active oxygen. Absent. Therefore, further particulates are deposited on the particulate 64 one after another. In other words, 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 accumulate on the particulate filter in a stacked manner.
[0084]
In this way, in the region I in FIG. 23, the particulates are oxidized on the particulate filter in a short time without emitting a bright flame, and in the region II in FIG. 23, the particulates are deposited on the particulate filter in a stacked manner. To do. Therefore, if the relationship between the discharged fine particle amount M and the oxidizable and removable fine particle amount G is in the region I, the accumulation of particulates on the particulate filter can be prevented. 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. Thus, a reduction in engine output can be kept to a minimum. However, this is not always realized, and if nothing is done, particulates may accumulate on the particulate filter.
[0085]
In the present embodiment, the valve body 71a of the switching unit 71 is rotated from the current shut-off position to the other shut-off position for each set time or set travel distance so that the exhaust upstream side and the exhaust downstream side of the particulate filter 70 are reversed. It is supposed to let you.
[0086]
FIG. 25 is an enlarged cross-sectional view of the partition wall 54 of the particulate filter. As described above, the exhaust upstream surface of the partition wall 54 where the exhaust gas mainly collides and the exhaust gas flow facing surface in the pores collide and collect the particulates as one of the collection surfaces, and the active oxygen release agent Although the collected particulates are oxidized and removed by the released active oxygen, the operation in the region II in FIG. 23 may be performed while traveling for the set time or the set travel distance, and FIG. As indicated by the lattice, particulate removal may remain due to insufficient oxidation removal. The exhaust resistance of the particulate filter accompanying such accumulation of particulates does not adversely affect the running of the vehicle, but if particulates accumulate further, problems such as a significant decrease in engine output occur. However, if the exhaust upstream side and the exhaust downstream side of the particulate filter are reversed at this point, no further particulates accumulate on the particulate remaining on one of the collecting surfaces of the partition wall 54. Residual particulates are gradually oxidized and removed by the active oxygen released from one of the collecting surfaces. Further, the particulates remaining in the pores of the partition walls are easily broken down and subdivided as shown in FIG. 25B by the exhaust gas flow in the reverse direction, and move downstream.
[0087]
As a result, many of the finely divided particulates are dispersed in the pores of the partition walls, i.e., the particulates flow and directly with the active oxygen release agent supported on the pore inner surfaces of the partition walls. There are many opportunities for contact and oxidation removal. In this way, by supporting the active oxygen release agent in the pores of the partition walls, the residual particulates can be remarkably easily removed by oxidation. Further, in addition to this oxidation removal, the other collection 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 mainly collides and the inside of the pores On the exhaust gas flow facing surface (which is on the side 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 oxidation removal moves to the downstream side together with the exhaust gas, and the remaining particulates are oxidized and removed by the backflow of the exhaust gas.
[0088]
That is, the residual particulates on one collecting surface in the partition wall are not only for the active oxygen released from this collecting surface, but also for the oxidation removal of the 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. As a result, even if particulates are accumulated to some extent on one collecting surface of the partition wall at the time of switching of the valve body, if the exhaust gas flows backward, the particulates accumulated on the residual particulates In addition to the arrival of active oxygen, no further particulates are deposited, so the deposited particulates are gradually oxidized and removed. Oxidation removal is possible.
[0089]
Thus, by reversing the exhaust upstream side and the exhaust downstream side of the particulate filter, the first collection surface and the second collection surface of the particulate filter collection wall are used alternately, and a single collection is always performed. Compared to collecting particulates on the collecting surface, the amount of particulates collected on each collecting surface can be reduced, which is advantageous for removing particulates by oxidation, and depositing the particulates on the particulate filter. Can be difficult. When a relatively large amount of particulates accumulates on the particulate filter, when the temperature of the deposited particulates is raised to about 600 ° C. due to some factor, the deposited particulates burn at a time to generate a large amount of combustion heat. Since the particulate filter may melt, it is important to make it difficult to deposit the particulate on the particulate filter as in this embodiment.
[0090]
The switching of the valve body may be performed irregularly even if it is not performed periodically, such as every set time or set travel distance. Further, the valve body may be switched every time the engine is decelerated. For the determination at the time of engine deceleration, it is possible to detect an operation that the driver intends to decelerate the vehicle, for example, release of an accelerator pedal, depression of a brake pedal, fuel cut, or the like.
[0091]
Further, the valve body may be switched when the amount of particulate accumulation on the particulate filter reaches a set amount. For the estimation of the particulate deposition amount, for example, the differential pressure between the upstream side and the downstream side of the particulate filter 70 that increases with the increase in the particulate deposition amount can be used. The electrical resistance value on the predetermined partition wall of the particulate filter that decreases with an increase in the amount of deposited particulate may be used, and light transmission on the predetermined partition wall of the particulate filter that decreases with an increase in the amount of particulate deposition. Rate or reflectance may be used. Further, based on the graph of FIG. 23, when the amount M of discharged particulate estimated from the current engine operating state exceeds the amount G of particulate that can be removed by oxidation considering the temperature of the particulate filter estimated from the current engine operating state. The difference (M−G) may be integrated as the particulate deposition amount.
[0092]
Further, when the air-fuel ratio of the exhaust gas is made rich, that is, when the oxygen concentration in the exhaust gas is lowered, the active oxygen O is released from the active oxygen release agent 61 to the outside at once. With the active oxygen O released at once, the deposited particulates are easily oxidized and easily removed by oxidation. On the other hand, when 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. When such oxygen poisoning occurs, NO_XNO is reduced due to reduced oxidation_XAs a result, the active oxygen release amount from the active oxygen release agent 61 is reduced. However, when the air-fuel ratio is made rich, oxygen on the platinum Pt surface is consumed, so that oxygen poisoning is eliminated. Therefore, when the air-fuel ratio is switched again from rich to lean, NO._XNO to increase the oxidation effect on_XAs a result, the active oxygen release amount from the active oxygen release agent 61 increases. Accordingly, when the air-fuel ratio is maintained lean, the oxygen poisoning of platinum Pt is eliminated every time the air-fuel ratio is temporarily switched from lean to rich, so that active oxygen release when the air-fuel ratio is lean is performed. The amount increases, and thus the oxidation action of the particulates on the particulate filter 70 can be promoted. Furthermore, the elimination of oxygen poisoning is, so to speak, the combustion of the reducing substance, so that the temperature of the particulate filter is raised 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 residual and deposited particulates can be easily removed by oxidation. If the air-fuel ratio of the exhaust gas is made rich immediately after switching between the exhaust upstream side and the exhaust downstream side of the particulate filter by the valve body 71a, the other collection surface in the particulate filter partition wall where no particulates remain is obtained. Since the active oxygen is easily released as compared with the one collecting surface, the remaining particulates on the one collecting surface can be more reliably oxidized and removed by the active oxygen released in a larger amount. Of course, the air-fuel ratio of the exhaust gas may be occasionally enriched regardless of the switching of the valve body 71a, so that it is difficult for the particulates to remain and accumulate on the particulate filter.
[0093]
As a method for enriching the air-fuel ratio of the exhaust gas, for example, the low-temperature combustion described above may be performed. Alternatively, the combustion air-fuel ratio may be simply made rich. In addition to normal main fuel injection in the compression stroke, fuel may be injected into the cylinder (post-injection) in the exhaust stroke or expansion stroke by the engine fuel injection valve, or fuel in the cylinder in the intake stroke. May be jetted (bi-rubber jet). Of course, it is not always necessary to provide an interval between the post injection or the big rubber injection and the main fuel injection. It is also possible to supply fuel to the engine exhaust system.
[0094]
By the way, in the particulate filter of the present embodiment, as described above, NO in the exhaust gas._XAs described above, the structure of the particulate filter is a wall flow type in which the exhaust gas passes through the pores of the collection wall, and the exhaust gas generally flows along the partition wall supporting the catalyst. In order to allow the same amount of exhaust gas to pass through in comparison with a typical catalyst device, the size between the collection walls must be larger than the size between the partition walls. Thereby, the opportunity for the exhaust gas to come into contact with the active oxygen release agent supported on the surface of the collection wall in the particulate filter is less than the chance to come into contact with the catalyst in the monolith type catalyst device. Further, when the exhaust gas passes through the pores of the collection wall, it comes into contact with the active oxygen release agent carried in the pores, but mainly the active gas carried on the surface of the collection wall. Contact with oxygen release agent only. However, the catalyst support area on the surface of the collection wall is not so large due to the large number of pores. Thus, NO_XEven if an active oxygen release agent that absorbs oxygen is supported on the particulate filter, NO in the exhaust gas_XCan not be sufficiently purified.
[0095]
In this embodiment, the position always on the downstream side of the particulate filter irrespective of the reverse of the exhaust upstream side and the downstream exhaust side of the particulate filter disposed in the first chamber 101 of the muffler 100, that is, the muffler 100. The catalyst device 75 is disposed in the second chamber 102. Since the catalyst device 75 is disposed in the muffler 100 together with the particulate filter 70, the particulate filter is formed by oxidizing and removing particulates by active oxygen in the particulate filter 70 and burning a reducing substance in the noble metal catalyst. When the temperature is raised, the entire muffler 100 is heated. Thereby, as compared with the case where the catalyst device is disposed on the downstream side of the muffler, the chance that the present catalyst device 75 is maintained at a high temperature by receiving heat from the muffler 100 increases. Thus, there are many opportunities for the catalyst supported on the catalyst device 75 to be activated.
[0096]
As a result, the catalyst device 75 can be made to use the above-mentioned noble metal catalyst and a substance that can be used as an active oxygen release agent as NO._XNO supported in the particulate filter by being supported as an occlusion reduction catalyst_XCan be absorbed satisfactorily and the amount released into the atmosphere can be sufficiently reduced. Of course, the NO carried on the catalyst device 73_XThe catalyst is NO_XWithout being limited to the occlusion reduction catalyst, for example, NO_XOther types of NO, such as selective reduction catalysts_XIt is good also as a catalyst which purifies.
[0097]
Further, as described above, when rich exhaust gas containing a reducing substance flows into the particulate filter, or when exhaust gas containing a relatively large amount of HC and CO flows into the particulate filter by performing low temperature combustion. In addition, all of the reducing material is oxidized by the noble metal catalyst of the particulate filter or released from the active oxygen release agent._XIt is not necessarily used to reduce the amount of the substance, and it is necessary to purify the reducing substance that passes through the particulate filter. NO in catalyst device 75_XIf the storage reduction catalyst is supported, the precious metal catalyst and released NO_XHowever, if the catalyst device 75 supports at least an oxidation catalyst such as a noble metal catalyst, the reduction material passing through the particulate filter can be purified. Is possible.
[0098]
As described above, when switching the valve body 71a, the valve body 71a is in the intermediate position as shown in FIG. 20, and the exhaust gas bypasses the particulate filter. Even at this time, since the exhaust gas passes through the catalyst device 75, harmful substances in the exhaust gas can be purified well by the catalyst device 75. However, since the particulates in the exhaust gas cannot be purified by the catalyst device 75, the switching of the valve body 71a is preferably performed at the time of engine deceleration where the particulates are not included in the exhaust gas due to fuel cut. .
[0099]
In addition, when the fuel is cut, the exhaust gas temperature is low and the temperature of the particulate filter may be lowered. Therefore, in order to keep the particulate filter's oxidizable and removable fine particle amount high, the valve element 71a should be actively used during engine deceleration. Therefore, it is preferable that the exhaust gas bypasses the particulate filter as an intermediate position.
[0100]
FIG. 26 is a cross-sectional plan view showing a modification of the above-described exhaust purification device. In the exhaust purification apparatus and the exhaust purification apparatus described above, the same elements are denoted by the same reference numerals. The difference between the two exhaust purification devices will be described below. In this exhaust purification apparatus, the second connection pipe 73 ′ that connects the other space in the first chamber 101 of the muffler 100 and the second opening 71 e of the switching unit 71 is connected to the one space in the first chamber 101 and the particulate filter. 70. As a result, the second connecting pipe does not protrude to the side of the muffler 100, and the muffler mounting capability of the muffler as the exhaust purification device can be improved.
[0101]
In the above-described exhaust purification device, the particulate filter 70 and the catalyst device 75 are arranged in the expansion type muffler. However, this does not limit the present invention, and if a particulate filter is arranged on the upstream side and a catalyst device is arranged on the downstream side in other systems, for example, an interference type, resonance type, or sound absorption type muffler, It is possible to increase the temperature of the catalyst device satisfactorily and increase the chance that the catalyst is activated, and it is possible to satisfactorily reduce harmful substances released through the muffler into the atmosphere.
[0102]
By arranging the particulate filter 70 in one compartment (first chamber) of the muffler, as described above, the exhaust upstream side and the exhaust downstream side of the particulate filter are reversed by the combination with the switching unit 71. Of course, when this reverse rotation mechanism is not provided, it is not necessary to arrange the particulate filter and the catalyst device in separate compartments, and it is also possible to arrange them adjacent to each other in the same compartment. . In this case, the inside of the muffler need not be partitioned into a plurality of compartments.
[0103]
By the way, calcium Ca in the exhaust gas is SO.₃In the presence of calcium sulfate CaSO₄Is generated. This calcium sulfate CaSO₄Is hardly removed by oxidation and remains as ash on the particulate filter. Therefore, in order to prevent the particulate filter from being clogged due to residual calcium sulfate, it is preferable to use an alkali metal or alkaline earth metal, such as potassium K, which has a higher ionization tendency than calcium Ca as the active oxygen release agent 61. , Thereby diffusing into the active oxygen release agent 61₃Binds potassium K and potassium sulfate K₂SO₄Calcium Ca is SO₃It passes through the partition wall of the particulate filter without being combined with. Therefore, the particulate filter is not clogged by ash. Thus, as described above, as the active oxygen release 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, strontium Sr is used. Is preferred.
[0104]
Further, even when a particulate filter is loaded with only a noble metal such as platinum Pt as an active oxygen release agent, NO retained on the surface of platinum Pt.₂Or SO₃Active oxygen can be released from However, in this case, the solid line indicating the amount G of fine particles that can be removed by oxidation moves slightly to the right as compared with the solid line shown in FIG. It is also possible to use ceria as the active oxygen release agent. Ceria absorbs oxygen when the oxygen concentration in the exhaust gas is high (Ce₂O₃→ 2CeO₂), Active oxygen is released when the oxygen concentration in the exhaust gas decreases (2CeO)₂→ Ce₂O₃Therefore, it is necessary to enrich the air-fuel ratio in the exhaust gas regularly or irregularly in order to oxidize and remove particulates. Instead of ceria, iron or tin may be used.
[0105]
Moreover, NO in exhaust gas as an active oxygen release agent_xNO used for purification_xIt is also possible to use an occlusion reduction catalyst. In this case, NO_xOr SO_xIn order to release the exhaust gas, it is necessary to at least temporarily enrich the air-fuel ratio of the exhaust gas.
[0106]
In this embodiment, the particulate filter itself carries the active oxygen release agent, and the particulates are oxidized and removed by the active oxygen released by the active oxygen release agent. However, this limits the present invention. It is not a thing. For example, the active oxygen and the particulate oxidation component such as nitrogen dioxide that functions in the same manner as the active oxygen may be released from the particulate filter or a substance carried on the particulate filter or may flow into the particulate filter from the outside. . Even when particulate oxidation components flow from the outside, it is possible to prevent the accumulation of particulates by alternately using the first and second collection surfaces of the collection wall to collect the particulates. It is effective for. That is, no particulates are newly deposited on one of the collection surfaces on the exhaust downstream side, and this accumulated particulate is gradually removed by oxidation by the particulate oxidizing component flowing from the other collection surface. Thus, the deposited particulate can be sufficiently oxidized and removed in a certain time. In the meantime, the other collecting surface is oxidized by the particulate oxidation component together with the collection of the particulates, and thus the same effect as described above is brought about.
[0107]
The diesel engine of the present embodiment is switched between low-temperature combustion and normal combustion, but this does not limit the present invention. Of course, a diesel engine that performs only normal combustion or a particulate is used. The present invention is also applicable to a gasoline engine that discharges.
[0108]
【The invention's effect】
As described above, according to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the muffler located in the engine exhaust system and the particulates in the exhaust gas that are disposed in the muffler are collected, and the collected particulates are There are provided a particulate filter to be oxidized, and a catalyst device which is disposed in the muffler and is located on the downstream side of the particulate filter. As a result, the particulate filter that requires a relatively large cross-sectional area is disposed in a muffler having a relatively large cross-sectional area in the engine exhaust system, so that there is no problem of vehicle mountability. In addition, a catalyst device is arranged in the muffler on the downstream side of the particulate filter, and in this catalyst device, there are many opportunities for activation of the catalyst supported by heat received from the muffler maintained at a relatively high temperature. Before harmful substances other than particulates are discharged from the muffler in which the particulate filter is disposed, the harmful substances can be well purified and released into the atmosphere.
[0109]
Also, MaThe inside of the hula is divided into at least a first chamber and a second chamber, a particulate filter is disposed in the first chamber located upstream from the second chamber, a catalyst device is disposed in the second chamber, A reversing means for reversing the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter in the chamber, the particulate filter has a collecting wall for collecting the particulates, the collecting wall being the first A collecting surface and a second collecting surface, and the reversing means reverses the exhaust gas downstream side and the exhaust gas upstream side of the particulate filter so as to collect the particulates so as to collect the particulates. The collecting surface and the second collecting surface are used alternately.To becomeThus, it is possible to make it difficult for the particulates to be deposited on the particulate filter. That is, depending on the operating state, particulate oxidation may be insufficient, and some particulates may remain on the first collection surface of the particulate filter collection wall. By reversing the exhaust upstream side and the exhaust downstream side, new particulates are not deposited on the first collection surface of the collection wall, and the accumulated particulates can be gradually oxidized and removed. At the same time, particulate collection and oxidation are started by the second collection surface of the collection wall. In this way, when the first collection surface and the second collection surface are alternately used for collecting particulates, each collection is always compared to the case where the particulates are collected by a single collection surface. It is possible to reduce the amount of particulates collected on the collecting surface, which is advantageous for removing the particulates by oxidation.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view of a diesel engine equipped with an exhaust emission control device according to the present invention.
FIG. 2 is an enlarged longitudinal 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 intake / exhaust valve lift and fuel injection.
FIG. 6 Smoke and NO_xIt is a figure which shows the generation amount of etc.
FIG. 7 is a diagram showing combustion pressure.
FIG. 8 is a diagram showing fuel molecules.
FIG. 9 is a diagram showing the relationship between the amount of smoke generated and the EGR rate.
FIG. 10 is a diagram showing the relationship between the amount of injected fuel and the amount of mixed gas.
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.
14 is a diagram showing an air-fuel ratio in a first operating region I. FIG.
FIG. 15 is a view showing a map of a target opening degree of a throttle valve or the like.
FIG. 16 is a diagram showing an air-fuel ratio in the second combustion.
FIG. 17 is a diagram showing a target opening degree of a throttle valve or the like.
FIG. 18 is a cross-sectional plan view showing the exhaust emission control device.
FIG. 19 is a plan view of the exhaust gas purification apparatus showing a valve body blocking position different from FIG. 18;
FIG. 20 is a plan view of the exhaust purification device showing an intermediate position of the valve body.
FIG. 21 is a diagram illustrating a structure of a particulate filter.
FIG. 22 is a diagram for explaining the oxidizing action of particulates.
FIG. 23 is a graph showing the relationship between the amount of fine particles that can be removed by oxidation and the temperature of the particulate filter.
FIG. 24 is a diagram for explaining the particulate deposition action.
FIG. 25 is an enlarged cross-sectional view of a partition wall of a particulate filter.
26 is a cross-sectional plan view showing a modification of the exhaust emission control device of FIG.
[Explanation of symbols]
6 ... Fuel injection valve
16 ... Throttle valve
70 ... Particulate filter
71 ... switching part
71a ... Valve
75 ... Catalyst device
100 ... Muffler

Claims (5)

A muffler located in the engine exhaust system, a particulate filter disposed in the muffler for collecting particulates in the exhaust gas, and oxidizing the collected particulates, and disposed in the muffler An exhaust gas purification apparatus for an internal combustion engine comprising a catalyst device located downstream of the particulate filter , wherein the muffler is partitioned into at least a first chamber and a second chamber, and upstream of the second chamber The particulate filter is disposed in the first chamber located in the first chamber, the catalyst device is disposed in the second chamber, and the exhaust upstream side and the exhaust downstream side of the particulate filter in the first chamber are reversed. The particulate filter has a collecting wall for collecting particulates, and the collecting wall is a first wall. A collecting surface and a second collecting surface, and the reversing means reverses the exhaust downstream side and the exhaust upstream side of the particulate filter so as to collect the particulates to collect the particulates. An exhaust purification device for an internal combustion engine, wherein the first collection surface and the second collection surface are used alternately . The exhaust purification device for an internal combustion engine according to claim 1 , wherein an active oxygen release agent is supported on the particulate filter, and active oxygen released from the active oxygen release agent oxidizes the particulate . 3. The active oxygen release agent according to claim 2, wherein oxygen is taken in and retained when excess oxygen is present in the surrounding area, and released in the form of active oxygen when the surrounding oxygen concentration is lowered. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 3, wherein the catalyst device carries an oxidation catalyst . The catalytic converter exhaust gas control apparatus according to any one of claims 1 to 3, characterized in that carrying the NO _X catalyst.

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