JP3558055B2 - 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]
2. Description of the Related Art Conventionally, there has been known an exhaust gas purifying apparatus for an internal combustion engine in which a particulate filter for removing particulates in exhaust gas discharged from a combustion chamber is disposed in an engine exhaust passage. An example of this type of exhaust gas purifying apparatus for an internal combustion engine is disclosed in Japanese Patent Publication No. 7-106290.
[0003]
[Problems to be solved by the invention]
However, Japanese Patent Publication No. 7-106290 does not disclose that a catalyst supported on a particulate filter takes in oxygen and retains oxygen when there is excess oxygen around the catalyst. Further, Japanese Patent Publication No. 7-106290 does not disclose that the catalyst carried on the particulate filter releases the retained oxygen in the form of active oxygen when the surrounding oxygen concentration decreases. Therefore, in the catalyst of the exhaust gas purifying apparatus for an internal combustion engine described in Japanese Patent Publication No. 7-106290, oxygen is taken in when excess oxygen is present in the surroundings, and is retained when the oxygen concentration in the surroundings is reduced. Oxygen cannot be released in the form of active oxygen. Therefore, in the exhaust gas purifying apparatus for an internal combustion engine described in Japanese Patent Publication No. 7-106290, the catalyst that releases active oxygen cannot be regenerated as needed.
[0004]
Conventionally, in a diesel engine, a particulate filter is disposed in an engine exhaust passage in order to remove fine particles contained in exhaust gas, and the fine particles in the exhaust gas are once collected by the particulate filter, and the particulate filter is collected. The particulate filter is regenerated by igniting and burning the fine particles collected on the filter. However, the particulate matter collected on the particulate filter does not ignite and burn unless the temperature becomes higher than about 600 ° C., whereas the exhaust gas temperature of a diesel engine is usually much lower than 600 ° C. Therefore, it is difficult to ignite and burn the fine particles collected on the particulate filter with the exhaust gas heat.
[0005]
On the other hand, NO trapped on the particulates collected on the particulate filter₂Can be ignited and burned even at a relatively low temperature (NO₂+ C → NO + CO, NO₂+ CO → NO + CO₂, 2NO₂+ C → 2NO + CO₂). However, most of the nitrogen oxides contained in the exhaust gas are NO, and therefore NO₂NO in order to ignite and burn the fine particles by the reaction with NO₂Must be converted to In this case, if an oxidation catalyst is arranged in the engine exhaust passage upstream of the particulate filter and NO is oxidized by this oxidation catalyst, NO can be reduced to NO.₂Thus, even if the temperature is relatively low, the fine particles trapped on the particulate filter can be ignited and burned.
[0006]
On the other hand, when the exhaust gas temperature is lower than a certain temperature, for example, 350 ° C., NO in the exhaust gas is absorbed, and when the exhaust gas temperature exceeds 350 ° C., the absorbed NO is converted into NO.₂NO released in the form of_XAbsorbents are known. This NO_XThe absorbent is at least one selected from the group consisting of alkali metals such as potassium K, sodium Na and cesium Cs, alkaline earths such as barium Ba and calcium Ca, lanthanum La and rare earths such as yttrium Y, and platinum Pt. And noble metals. This NO_XWhen an absorbent is used, NO is generated when the exhaust gas temperature becomes higher than 350 ° C._XNO is released from the absorbent, and NO is oxidized by platinum Pt to form NO.₂Thus, the fine particles collected on the particulate filter are more easily ignited and burned.
[0007]
However, from NO by the oxidation catalyst to NO₂The effect of the conversion to is dependent on the exhaust gas temperature, and this conversion only takes place within a certain exhaust gas temperature range. Therefore, when the exhaust gas goes out of this exhaust gas temperature range, it is no longer changed from NO to NO.₂No conversion operation is performed, so that the particulate matter collected on the particulate filter cannot be ignited and burned. NO_XNO when using absorbent_XNO is released from the absorbent within a limited exhaust gas temperature range of 350 ° C. or more, and NO_XThere is a limit to the amount of NO released from the absorbent.
[0008]
Therefore, an oxidation catalyst is disposed in the exhaust passage upstream of the particulate filter, and NO_XAn absorbent is supported, and NO is converted from NO by the oxidation catalyst to NO.₂Load operating condition and NO_XNO is released from the absorbent and NO₂When the medium load operation state is reached, these NO₂Igniting and burning the fine particles trapped on the particulate filter by₂During a high load operation in which generation of dust is not expected, the particulate matter collected on the particulate filter is ignited and burned by raising the temperature of the exhaust gas to 600 ° C. or more.₂During low-load operation where it is not expected to generate CO2, the exhaust gas temperature is raised by an electric heater and NO₂When the exhaust gas temperature is further reduced and the load is extremely low, light oil and secondary air are supplied into the exhaust passage to ignite and burn the fine particles trapped on the particulate filter by the combustion heat of the light oil. A known diesel engine is known (see JP-A-8-338229).
[0009]
As described above, the particulate filter has conventionally been considered to trap fine particles in the exhaust gas. Therefore, conventionally, the particulate filter collected on the particulate filter, that is, the particulate filter laminated on the particulate filter is conventionally used. Every effort has been made to ignite and burn the particulates deposited in the shape. That is, once the particulates are deposited on the particulate filter in a stacked state, it becomes difficult to ignite and burn, and in this case, a high temperature of 600 ° C. or more is required to cause the deposited particulates to ignite and burn. Therefore, conventionally, one method has been to focus on how to produce a high temperature of 600 ° C. or higher.
[0010]
On the other hand, as described above, the fine particles deposited on the particulate filter₂Is reacted at a relatively low temperature, the fine particles are ignited and burned. Therefore, in this case, the fine particles deposited on the particulate filter can be ignited and burned without a high temperature of 600 ° or more. However, NO₂Since the operating region in which the gas can be generated is limited, it is not possible to ignite and burn the fine particles at a relatively low temperature in any operating region. In any case, conventionally, it is assumed that the particulate filter is for collecting fine particles, and the focus is on how to ignite and burn the fine particles deposited in a layer on the particulate filter. I was
[0011]
However, as a result of a detailed study of the behavior of the fine particles, the fine particles are not collected on the particulate filter when a certain condition is satisfied, and as soon as the fine particles adhere to the particulate filter, a certain condition is satisfied. It turned out to be oxidized in time. In other words, if the fine particles can be oxidized before they are deposited on the particulate filter in a layered manner, almost 100% of the fine particles in the exhaust gas are removed without the fine particles being trapped on the particulate filter. It turned out that we could do that.
[0012]
In addition, as a result of studying the behavior of fine particles in detail, an oxygen storage device that retains oxygen in the particulate filter when excess oxygen is present in the surroundings, and releases the retained oxygen in the form of active oxygen when the surrounding excess oxygen decreases. It has been found that when an active oxygen releasing agent is loaded, the ability to oxidize and remove particulates by the released active oxygen is significantly improved. According to further research, when this oxygen storage / active oxygen releasing agent is poisoned by specific components contained in exhaust gas, even if the surrounding excess oxygen decreases, active oxygen is hardly released. It turned out that the oxidizing ability of the particulates could not be improved so much.
[0013]
In view of the above problems, the present invention suppresses the accumulation of the particulates on the particulate filters while improving the fuel efficiency of the internal combustion engine by oxidizing the particulates with active oxygen and regenerating the particulate filters as necessary. It is an object of the present invention to provide an exhaust gas purification device for an internal combustion engine that can perform the above.
[0014]
[Means for Solving the Problems]
According to the first aspect of the present invention, in the exhaust gas purifying apparatus for an internal combustion engine, a particulate filter for removing particulates in exhaust gas discharged from a combustion chamber is arranged in an engine exhaust passage. Above, the trapped particulates are oxidized, comprising a first operation mode in which priority is given to improving fuel efficiency of the internal combustion engine, and a second operation mode in which priority is given to regeneration of the particulate filter. , Switching between the first operation mode and the second operation mode as necessaryIn the exhaust gas purifying apparatus for an internal combustion engine, when the amount of the inert gas supplied into the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and the amount of the inert gas supplied into the combustion chamber increases. When the amount is further increased, the first operating mode is selected by using an internal combustion engine in which the temperature of the fuel during combustion in the combustion chamber and the gas around it become lower than the temperature at which soot is generated and soot is hardly generated. The low-temperature combustion in which the amount of the inert gas supplied into the combustion chamber is larger than the amount of the inert gas at which the generation amount of soot becomes a peak during the low load operation of the engine and little soot is generated is executed. When the first operation mode is selected, the amount of the inert gas supplied into the combustion chamber is smaller than the amount of the inert gas at which the amount of generated soot at the time of high load operation in the engine is peaked. Normal combustion is performed When the second operation mode is selected and low engine load operation is performed, low-temperature combustion is performed, and when the second operation mode is selected and engine medium load operation is performed, auxiliary fuel injection is executed. At the same time, the main fuel injection timing is retarded, and the normal combustion is performed when the second operation mode is selected and the engine is under high load operation.An exhaust emission control device for an internal combustion engine is provided.
[0015]
In the exhaust gas purifying apparatus for an internal combustion engine according to the first aspect, a first operation mode in which priority is given to improving fuel efficiency of the internal combustion engine and a second operation mode in which priority is given to regeneration of the particulate filter. It can be switched as needed. Therefore, it is possible to suppress the accumulation of fine particles on the particulate filter while improving the fuel efficiency of the internal combustion engine. In detail, the first operation mode in which priority is given to improving the fuel efficiency of the internal combustion engine in principle is selected, and when it becomes necessary to regenerate the particulate filter, priority is given to regenerating the particulate filter. The operated second operation mode is selected. Therefore, the accumulation of fine particles on the particulate filter can be suppressed more than necessary, and the fuel consumption of the internal combustion engine can be prevented from deteriorating accordingly.Further, when the second operation mode in which the regeneration of the particulate filter is prioritized is selected and the engine is under the medium load operation, the auxiliary fuel injection is executed and the main fuel injection timing is retarded. Therefore, the temperature of the exhaust gas flowing into the particulate filter is not even during the low load operation of the engine capable of performing low-temperature combustion, and also during the middle load operation of the engine that is not the high load operation of the engine capable of discharging high-temperature exhaust gas. Can be increased, and therefore the particulate filter can be regenerated.
[0016]
According to the second aspect of the present invention, the particulate filter carries an oxygen storage / active oxygen release agent, and active oxygen released from the oxygen storage / active oxygen release agent is collected on the particulate filter. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the fine particles are oxidized.
[0017]
In the exhaust gas purifying apparatus for an internal combustion engine according to the second aspect, since the active oxygen released from the oxygen storage / active oxygen releasing agent oxidizes the trapped fine particles, the fine particles are deposited on the particulate filter as in the conventional case. Unlike the case where the fine particles emit a bright flame after being deposited in a layered form and are removed, the fine particles can be oxidized and removed without emitting a bright flame before being deposited in a layered manner on the particulate filter. it can.
[0018]
According to the third aspect of the present invention, the oxygen storage / active oxygen releasing agent takes in oxygen when there is excess oxygen in the surroundings and retains the oxygen. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the exhaust gas is discharged in the form of:
[0019]
In the exhaust gas purifying apparatus for an internal combustion engine according to the third aspect, if the surrounding oxygen concentration decreases due to the attachment of particulates or the like, the oxygen storage / active oxygen releasing agent naturally releases active oxygen to oxidize the trapped fine particles. Can be removed.
[0020]
According to the fourth aspect of the present invention, the oxygen storage / active oxygen release agent is capable of NO_XIs bound to oxygen and bound when the ambient oxygen concentration decreases._XAnd oxygen_X3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the exhaust gas is decomposed into active oxygen and released.
[0021]
In the exhaust gas purifying apparatus for an internal combustion engine according to the fourth aspect, the oxygen storage / active oxygen releasing agent contains NO in the exhaust gas._XIf the surrounding oxygen concentration decreases due to the attachment of particulates or the like, the oxygen storage / active oxygen releasing agent can naturally release active oxygen and oxidize and remove the trapped fine particles.
[0024]
Claim5According to the invention described in the above, when the second operation mode is selected and the temperature of the particulate filter is likely to rise excessively, and when low-temperature combustion is being performed, the air-fuel ratio is reduced. The main fuel injection timing is advanced when the sub fuel injection is performed and the main fuel injection timing is retarded, and the fuel injection timing is advanced when the normal combustion is performed. Claims madeAny of 1 to 4An exhaust purification device for an internal combustion engine as described above is provided.
[0025]
Claim5In the exhaust gas purifying apparatus for an internal combustion engine described in the above, even when the second operation mode in which the regeneration of the particulate filter is prioritized is selected and the low-temperature combustion is performed, the temperature of the particulate filter is reduced. When it is likely to rise excessively, the air-fuel ratio is made lean. Therefore, the temperature of the exhaust gas flowing into the particulate filter is reduced, and the temperature of the particulate filter can be prevented from excessively increasing. Further, even when the second operation mode in which the priority is given to the regeneration of the particulate filter is selected and the sub fuel injection is executed and the main fuel injection timing is retarded, the temperature of the particulate filter is reduced. Is likely to rise excessively, the main fuel injection timing is advanced. Therefore, the temperature of the exhaust gas flowing into the particulate filter is reduced, and the temperature of the particulate filter can be prevented from excessively increasing. Further, even when the second operation mode in which the regeneration of the particulate filter is prioritized is selected and normal combustion is performed, when the temperature of the particulate filter is likely to rise excessively, the fuel injection timing is increased. It is advanced. Therefore, the temperature of the exhaust gas flowing into the particulate filter is reduced, and the temperature of the particulate filter can be prevented from excessively increasing. That is, it is possible to prevent the temperature of the particulate filter from being excessively increased while the particulate filter is being regenerated, thereby preventing the particulate filter from being melted.
[0026]
Claim6According to the invention described in (1), when the main fuel injection timing is advanced when the main fuel injection timing is delayed while the sub fuel injection is executed, the sub fuel injection is stopped.5The exhaust gas purifying apparatus for an internal combustion engine according to (1) is provided.
[0027]
Claim6In the exhaust gas purifying apparatus for an internal combustion engine described in the above, when the second operation mode is selected and the temperature of the particulate filter is likely to rise excessively, the sub fuel injection is executed and the main fuel injection timing is executed. When the main fuel injection timing is advanced in the case where is retarded, the auxiliary fuel injection is stopped. For this reason, it is possible to avoid that the HC increases with the execution of the auxiliary fuel injection at such a time, and the degree of decrease in the rise of the bed temperature of the particulate filter decreases.
[0028]
Claim7According to the invention described in the above, when the second operation mode is selected and the temperature of the particulate filter is likely to excessively increase, the operation is performed when the first operation mode is selected. From claim 1, wherein the combustion is interrupted and executed.4An exhaust purification device for an internal combustion engine according to any one of the above.
[0029]
Claim7In the exhaust gas purifying apparatus for an internal combustion engine described in the above, even when the second operation mode that prioritizes the regeneration of the particulate filter is selected, when the temperature of the particulate filter is likely to rise excessively The combustion that is performed when the first operation mode in which the priority is placed on improving the fuel efficiency of the internal combustion engine is selected. Specifically, the temperature of exhaust gas flowing into the particulate filter becomes relatively low. The combustion is interrupted. For this reason, it is possible to prevent the temperature of the particulate filter from being excessively increased when the particulate filter is being regenerated, and to prevent the particulate filter from being melted.
[0030]
Claim8According to the invention described in the above, it is determined whether or not the temperature of the particulate filter is likely to rise excessively, based on an elapsed time from when the switching from the first operation mode to the second operation mode is performed. Claims to be made5 to 7An exhaust purification device for an internal combustion engine according to any one of the above.
[0031]
Claim8In the exhaust gas purifying apparatus for an internal combustion engine described in the above, it is determined whether or not the temperature of the particulate filter is likely to rise excessively based on an elapsed time from when the first operation mode is switched to the second operation mode. Is determined. Therefore, it is possible to relatively easily determine whether the temperature of the particulate filter is likely to rise excessively without actually detecting the temperature of the particulate filter.
[0032]
Claim9According to the invention described in (1), it is determined whether or not the temperature of the particulate filter is likely to rise excessively based on the exhaust gas temperature.5 to 7An exhaust purification device for an internal combustion engine according to any one of the above.
[0033]
Claim9In the exhaust gas purifying apparatus for an internal combustion engine described above, it is determined whether or not the temperature of the particulate filter is likely to rise excessively, based on the exhaust gas temperature. Therefore, it is possible to relatively accurately determine whether or not the temperature of the particulate filter is likely to rise excessively without actually detecting the temperature of the particulate filter.
[0034]
Claim10According to the invention described in (1), when it is estimated that a predetermined amount of fine particles has been deposited on the particulate filter, switching from the first operation mode to the second operation mode is performed.9An exhaust purification device for an internal combustion engine according to any one of the above.
[0035]
Claim10In the exhaust gas purifying apparatus for an internal combustion engine described in above, the particulate filter is regenerated from the first operation mode in which priority is given to improving the fuel efficiency of the internal combustion engine when it is estimated that a predetermined amount of fine particles has accumulated on the particulate filter. Switching to the second operation mode in which priority is given to this is performed. Therefore, the accumulation of fine particles on the particulate filter can be suppressed more than necessary, and the fuel consumption of the internal combustion engine can be prevented from deteriorating accordingly.
[0036]
Claim11According to the invention described in (1), a catalyst having an oxidizing function is disposed upstream of the exhaust gas flow of the particulate filter.10An exhaust purification device for an internal combustion engine according to any one of the above.
[0037]
Claim11In the exhaust gas purifying apparatus for an internal combustion engine described in (1), a catalyst having an oxidizing function is arranged on the exhaust gas flow upstream side of the particulate filter. Therefore, the exhaust gas is oxidized when passing through the catalyst, and the temperature of the exhaust gas flowing into the particulate filter can be increased by the heat of oxidation, thereby maintaining the temperature of the particulate filter at a relatively high temperature. can do. Also, the SOF acting as a binder for the fine particles is oxidized by the catalyst, and as a result, the fine particles can be hardly deposited on the particulate filter.
[0038]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0039]
FIG. 1 shows a first embodiment in which the exhaust gas purifying apparatus for an internal combustion engine of the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a spark ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake manifold 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13. A throttle valve 17 driven by a step motor 16 is arranged in the intake duct 13, and a cooling device 18 for cooling intake air flowing through the intake duct 13 is arranged around the intake duct 13. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 18, and the engine cooling water cools the intake air. In the intake duct 13, an air flow meter 44 for detecting an intake air amount, a negative pressure sensor 45 for detecting an intake pipe negative pressure, and an intake temperature sensor 46 for detecting an intake air temperature are arranged. .
[0040]
On the other hand, the exhaust port 10 is connected to an exhaust turbine 21 of an exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20, and an outlet of the exhaust turbine 21 has a particulate filter 22a and a storage-reduction NO having an oxidation function._XIt is connected to a casing 23 containing a catalyst 22b. Storage reduction type NO_XThe catalyst 22b is disposed upstream of the particulate filter 22a in the exhaust gas flow. In the modification of the present embodiment, the storage reduction type NO_XInstead of the catalyst 22b, any oxidation catalyst having an oxidation function can be provided. In the modification of the present embodiment, the particulate filter 22a and the storage reduction type NO_XInstead of arranging the catalyst 22b adjacent, for example, the storage reduction type NO_XIt is also possible to arrange the catalyst 22b apart from the particulate filter 22a. An air-fuel ratio sensor 47 is arranged in the exhaust manifold 19, and an incoming gas for detecting an incoming gas temperature which is the temperature of the exhaust gas flowing into the casing 23 is provided in the exhaust pipe 20 on the upstream side of the casing 23. A temperature sensor 39a is arranged, and an exhaust gas temperature sensor 39b for detecting an exhaust gas temperature which is the temperature of the exhaust gas flowing out of the casing 23 is arranged in the exhaust pipe 20 on the downstream side of the casing 23.
[0041]
The exhaust manifold 19 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter, referred to as EGR) passage 24, and an electrically controlled EGR control valve 25 is disposed in the EGR passage 24. Further, a cooling device 26 for cooling the EGR gas flowing in the EGR passage 24 is disposed around the EGR passage 24. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 26, and the engine cooling water cools the EGR gas. Further, a pipe catalyst 22c for purifying the EGR gas flowing into the cooling device 26 is disposed upstream of the EGR gas flow with respect to the cooling device 26. On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 27, via a fuel supply pipe 6a. Fuel is supplied into the common rail 27 from a fuel pump 28 of an electrically controlled variable discharge amount, and the fuel supplied into the common rail 27 is supplied to the fuel injection valve 6 through each fuel supply pipe 6a. A fuel pressure sensor 29 for detecting the fuel pressure in the common rail 27 is attached to the common rail 27, and the fuel pump 28 is controlled so that the fuel pressure in the common rail 27 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 29. Is controlled.
[0042]
The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31 such as a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an output port 36. Is provided. The output signal of the fuel pressure sensor 29 is input to the input port 35 via the corresponding AD converter 37. The output signals of the incoming gas temperature sensor 39a and the outgoing gas temperature sensor 39b are input to the input port 35 via the corresponding AD converters 37, respectively. The output signal of the air flow meter 44 is input to the input port 35 via the corresponding AD converter 37, and the output signal of the negative pressure sensor 45 is input to the input port 35 via the corresponding AD converter 37, and the intake air temperature sensor The output signal of 46 is input to the input port 35 via the corresponding AD converter 37. 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 the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. . The output signal of the combustion pressure sensor 43 for detecting the combustion pressure in the cylinder is input to the input port 35 via the corresponding AD converter 37. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 30 °. On the other hand, the output port 36 is connected to the fuel injection valve 6, the throttle valve driving step motor 16, the EGR control valve 25, and the fuel pump 28 via the corresponding drive circuit 38.
[0043]
FIG. 2 shows the structure of the particulate filter 22a. 2A shows a front view of the particulate filter 22a, and FIG. 2B shows a side cross-sectional view of the particulate filter 22a. As shown in FIGS. 2A and 2B, the particulate filter 22a has a honeycomb structure and includes a plurality of exhaust passages 50 and 51 extending in parallel with each other. These exhaust passages are constituted by an exhaust gas inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust gas outflow passage 51 whose upstream end is closed by a plug 53. In FIG. 2A, hatched portions indicate plugs 53. Therefore, the exhaust gas inflow passages 50 and the exhaust gas outflow passages 51 are alternately arranged with the thin partition walls 54 interposed therebetween. In other words, the exhaust gas inflow passage 50 and the exhaust gas outflow passage 51 are each surrounded by the four exhaust gas outflow passages 51, and each exhaust gas outflow passage 51 is surrounded by the four exhaust gas inflow passages 50. It is arranged so that. The particulate filter 22a is made of, for example, a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 50 is formed in the surrounding partition wall 54 as shown by an arrow in FIG. And flows out into the adjacent exhaust gas outflow passage 51.
[0044]
In the embodiment according to the present invention, the entire peripheral wall surface of each exhaust gas inflow passage 50 and each exhaust gas outflow passage 51, that is, on both side surfaces of each partition wall 54, the outer end surface of the plug 53 and the inner end surfaces of the plugs 52, 53 A layer of a support made of, for example, alumina is formed over the support, and on the support, a noble metal catalyst and, when excess oxygen is present in the surroundings, oxygen is taken in to retain oxygen, and when the oxygen concentration in the surroundings decreases, the retained oxygen is retained. An oxygen storage / active oxygen releasing agent for releasing oxygen in the form of active oxygen is supported. In this case, in the embodiment according to the present invention, platinum Pt is used as a noble metal catalyst, and an alkali metal such as potassium K, sodium Na, lithium Li, cesium Cs, rubidium Rb, or barium Ba is used as an oxygen storage / active oxygen release agent. , Calcium Ca, alkaline earth metals such as strontium Sr, lanthanum La, rare earths such as yttrium Y, and transition metals are used. In this case, as the oxygen storage / active oxygen release 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 is used. Is preferred.
[0045]
Next, the action of removing particulates in the exhaust gas by the particulate filter 22a will be described by taking as an example a case where platinum Pt and potassium K are carried on a carrier, but other noble metals, alkali metals, alkaline earth metals, rare earths, transition metals The same effect of removing fine particles can be obtained by using. In a compression ignition type internal combustion engine as shown in FIG. 1, combustion takes place under excess air, and thus the exhaust gas contains a large amount of excess air. That is, when the ratio of air and fuel supplied into the intake passage and the combustion chamber 5 is referred to as the air-fuel ratio of the exhaust gas, the air-fuel ratio of the exhaust gas is lean in a compression ignition type internal combustion engine as shown in FIG. ing. Further, since NO is generated in the combustion chamber 5, the exhaust gas contains NO. Further, the fuel contains sulfur S, which reacts with oxygen in the combustion chamber 5 to produce SO.₂It becomes. Therefore, SO in the exhaust gas₂It is included. Thus, excess oxygen, NO and SO₂Will flow into the exhaust gas inflow passage 50 of the particulate filter 22a.
[0046]
FIGS. 3A and 3B schematically show enlarged views of the surface of the carrier layer formed on the inner peripheral surface of the exhaust gas inflow passage 50. 3A and 3B, reference numeral 60 denotes platinum Pt particles, and reference numeral 61 denotes an oxygen storage / active oxygen release agent containing potassium K. As described above, since a large amount of excess oxygen is contained in the exhaust gas, when the exhaust gas flows into the exhaust gas inflow passage 50 of the particulate filter 22a, 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 oxygen storage / 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 oxygen storage / active oxygen release agent 61 in the form of potassium nitrate KNO₃Generate
[0047]
On the other hand, as described above, SO2 is contained in the exhaust gas.₂Is also included in this SO₂Is absorbed into the oxygen storage / active oxygen release agent 61 by the same mechanism as that of 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 oxygen storage / 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-Is diffused into the oxygen storage / active oxygen release agent 61 in the form of potassium sulfate K₂SO₄Generate In this manner, potassium nitrate KNO is contained in the oxygen storage / active oxygen release catalyst 61.₃And potassium sulfate K₂SO₄Is generated.
[0048]
On the other hand, in the combustion chamber 5, fine particles mainly composed of carbon C are generated, and therefore, these fine particles are contained in the exhaust gas. These fine particles contained in the exhaust gas are generated when the exhaust gas flows in the exhaust gas inflow passage 50 of the particulate filter 22a or when the exhaust gas flows from the exhaust gas inflow passage 50 to the exhaust gas outflow passage 51 in FIG. ), It contacts and adheres to the surface of the carrier layer, for example, the surface of the oxygen storage / active oxygen release agent 61 as indicated by 62.
[0049]
As described above, when the fine particles 62 adhere to the surface of the oxygen storage / active oxygen release agent 61, the oxygen concentration decreases at the contact surface between the fine particles 62 and the oxygen storage / active oxygen release agent 61. When the oxygen concentration decreases, a difference in concentration occurs between the oxygen storage / active oxygen release agent 61 having a high oxygen concentration and the oxygen in the oxygen storage / active oxygen release agent 61 is thus separated from the fine particles 62 and the oxygen storage / active oxygen release agent. Attempts to move toward the contact surface with the release agent 61. As a result, potassium nitrate KNO formed in the oxygen storage / active oxygen release agent 61₃Is decomposed into potassium K, oxygen O and NO, oxygen O is directed to the contact surface between the fine particles 62 and the oxygen storage / active oxygen release agent 61, and NO is released from the oxygen storage / 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 oxygen storage / active oxygen release agent 61.
[0050]
On the other hand, at this time, the potassium sulfate K formed in the oxygen storage / active oxygen release agent 61₂SO₄Are tightly bound, so potassium K, oxygen O and SO₂It is hard to be decomposed into. Therefore, when the ambient temperature is low, it is difficult to release active oxygen even if the oxygen concentration decreases.
[0051]
On the other hand, oxygen O heading toward the contact surface between the fine particles 62 and the oxygen storage / active oxygen releasing agent 61 is potassium nitrate KNO₃Is 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 fine particles 62 and the oxygen storage / active oxygen releasing agent 61 is active oxygen O. When the active oxygen O comes in contact with the fine particles 62, the fine particles 62 are oxidized in a short time of several minutes to several tens minutes without emitting a bright flame. The active oxygen O that oxidizes the fine particles 62 is supplied to the oxygen storage / active oxygen releasing agent 61 by NO and SO.₂It is also released when is absorbed. That is, NO_XRepresents nitrate ion NO in the oxygen storage / active oxygen release agent 61 while repeatedly bonding and separating oxygen atoms.₃ ⁻It is considered that the active oxygen diffuses in the form of, and active oxygen is generated during this time. The fine particles 62 are also oxidized by the active oxygen. Further, the fine particles 62 attached to the particulate filter 22a are oxidized by the active oxygen O, but the fine particles 62 are also oxidized by the oxygen in the exhaust gas.
[0052]
When the fine particles deposited on the particulate filter 22a in a layered manner as in the prior art are burned, the particulate filter 22a glows red and burns with a flame. Such combustion with a flame cannot be sustained unless it is at a high temperature. Therefore, in order to maintain the combustion with such a flame, the temperature of the particulate filter 22a must be maintained at a high temperature.
[0053]
On the other hand, in the present invention, the fine particles 62 are oxidized without emitting a bright flame as described above, and the surface of the particulate filter 22a does not glow at this time. In other words, in other words, in the present invention, the fine particles 62 are oxidized and removed at a considerably lower temperature than in the prior art. Therefore, the action of removing fine particles 62 that do not emit a bright flame by oxidation according to the present invention is completely different from the action of removing fine particles by conventional combustion accompanied by a flame.
[0054]
By the way, the platinum Pt and the oxygen storage / active oxygen releasing agent 61 are activated as the temperature of the particulate filter 22a increases, so that the amount of the active oxygen O released by the oxygen storage / active oxygen releasing agent 61 per unit time is limited by the particulate filter. It increases as the temperature of 22a increases. In addition, as a matter of course, the higher the temperature of the fine particles themselves, the more easily they are oxidized and removed. Accordingly, the amount of fine particles that can be removed by oxidation on the particulate filter 22a without emitting luminous flame per unit time increases as the temperature of the particulate filter 22a increases.
[0055]
The solid line in FIG. 5 indicates the amount G of the oxidizable particles that can be oxidized and removed without emitting a luminous flame per unit time, and the horizontal axis in FIG. 5 indicates the temperature TF of the particulate filter 22a. FIG. 5 shows the amount of fine particles G that can be oxidized and removed per second when the unit time is 1 second, that is, an arbitrary time such as 1 minute or 10 minutes is adopted as the unit time. be able to. For example, if 10 minutes is used as the unit time, the amount G of oxidizable and removable particles per unit time indicates the amount G of oxidizable and removable particles per 10 minutes. As shown in FIG. 5, the amount G of oxidizable particles that can be oxidized and removed without emitting a bright flame per hour increases as the temperature of the particulate filter increases.
[0056]
When the amount of fine particles discharged from the combustion chamber 5 per unit time is referred to as a discharged fine particle amount M, when the discharged fine particle amount M is smaller than the oxidizable and removable fine particles G, for example, the discharged fine particle amount M per second Is smaller than the amount G of oxidation-removable fine particles per second, or when the amount M of discharged fine particles per 10 minutes is smaller than the amount G of oxidation-removable fine particles per 10 minutes, that is, in the region I of FIG. All the particulates discharged from 5 are sequentially oxidized and removed on the particulate filter 22a within a short period of time without emitting a bright flame.
[0057]
On the other hand, when the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation, that is, in the region II of FIG. 5, the amount of active oxygen is insufficient to oxidize all the fine particles. FIGS. 4A to 4C show how the fine particles are oxidized in such a case.
[0058]
That is, when the amount of active oxygen is insufficient to oxidize all the fine particles, as shown in FIG. 4A, when the fine particles 62 adhere to the oxygen storage / active oxygen releasing agent 61, a part of the fine particles 62 Only the fine particles are oxidized, and the finely-oxidized fine particles remain on the carrier layer. Next, when the state of the shortage of the active oxygen amount continues, the fine particles which were not oxidized one after another remain on the carrier layer, and as a result, the surface of the carrier layer remains as shown in FIG. It becomes covered with the fine particle portion 63.
[0059]
Such residual fine particle portions 63 are gradually changed to carbon materials which are hardly oxidized. When the surface of the carrier layer is covered with the residual fine particle portions 63, NO, SO by platinum Pt is used.₂4 and the active oxygen releasing action of the oxygen storage / active oxygen releasing agent 61 are suppressed, so that the residual fine particle portion 63 remains as it is without being oxidized. Thus, as shown in FIG. Another fine particle 64 is deposited on the remaining fine particle portion 63 one after another. That is, the fine particles are deposited in a layered manner. When the fine particles are deposited in a layered manner as described above, the fine particles 64 are oxidized by the active oxygen O even if the fine particles are easily oxidized because they are separated from the platinum Pt and the oxygen storage / active oxygen releasing agent. Never. Therefore, further fine particles are deposited on the fine particles 64 one after another. That is, 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 fine particles accumulate on the particulate filter 22a in a layered manner. Unless the temperature of the filter 22a is increased, the deposited fine particles cannot be ignited and burned.
[0060]
As described above, in the region I of FIG. 5, the fine particles are oxidized in a short time without emitting a bright flame on the particulate filter 22a, and in the region II of FIG. 5, the fine particles are deposited on the particulate filter 22a in a stacked manner. I do. Therefore, in order to prevent the fine particles from depositing on the particulate filter 22a in a stacked state, it is necessary that the discharged fine particle amount M is always smaller than the oxidizable and removable fine particle amount G.
[0061]
As can be seen from FIG. 5, the particulate filter 22a used in the embodiment of the present invention can oxidize the fine particles even if the temperature TF of the particulate filter 22a is considerably low, and therefore the compression ignition shown in FIG. In the internal combustion engine, it is possible to maintain the amount M of discharged particulate and the temperature TF of the particulate filter 22a such that the amount M of discharged particulate is always smaller than the amount G of particulate that can be removed by oxidation. If the amount M of discharged fine particles is always smaller than the amount G of fine particles that can be removed by oxidation, no fine particles are deposited on the particulate filter 22a, and thus the back pressure does not increase at all. Therefore, the engine output does not decrease at all. On the other hand, in order to always increase the amount G of oxidizable particles that can be removed by oxidation, the amount of fuel injection is always increased to increase the temperature of the exhaust gas and the temperature TF of the particulate filter 22a to increase the amount M of the discharged particles. As a result, the fuel efficiency of the internal combustion engine decreases.
[0062]
On the other hand, as described above, once the fine particles are deposited in layers on the particulate filter 22a, it is difficult to oxidize the fine particles with the active oxygen O even if the amount M of discharged fine particles is smaller than the amount G of fine particles that can be removed by oxidation. It is. However, when the unoxidized fine particle portion is beginning to remain, that is, when the amount of exhaust fine particles M is smaller than the amount G of oxidizable and removable fine particles when the fine particles are deposited only below a certain limit, the residual fine particle portion is reduced by active oxygen O. It is oxidized and removed without producing a bright flame. Therefore, as shown in FIG. 4B, even if the discharged fine particle amount M is made smaller than the oxidatively removable fine particle amount G and the discharged fine particle amount M becomes larger than the oxidatively removable fine particle amount G as needed. In order that the surface of the carrier layer is not covered by the residual fine particle portion 63, that is, only a small amount of fine particles on the particulate filter 22a which can be oxidized and removed when the discharged fine particle amount M becomes smaller than the oxidizable and removable fine particle amount G is reduced. In general, it is also possible to maintain the amount M of discharged particulates and the temperature TF of the particulate filter 22a in order to improve the fuel efficiency of the internal combustion engine so as not to be stacked.
[0063]
Immediately after the start of the engine, the temperature TF of the particulate filter 22a is low. Therefore, at this time, the amount M of discharged fine particles is larger than the amount G of fine particles that can be removed by oxidation. Therefore, considering actual driving, it is considered that such control is more suitable for the actual situation. When the particulates are deposited on the particulate filter 22a in a layered manner, the air-fuel ratio of a part or the whole of the exhaust gas is temporarily made rich, and the exhaust gas is post-burned to raise the temperature TF of the particulate filter 22a. Thereby, the state of the particulate filter 22a is positioned in the region I of FIG. 5, whereby the fine particles deposited on the particulate filter 22a can be oxidized without emitting a bright flame. In this case, that is, when the oxygen concentration in the exhaust gas is reduced, the active oxygen O is released from the oxygen storage / active oxygen releasing agent 61 to the outside at a stretch, and the fine particles deposited by the active oxygen O released at a stretch are It is easily oxidized and easily oxidized and removed.
[0064]
On the other hand, if the air-fuel ratio of the exhaust gas is kept lean, the surface of the platinum Pt is covered with oxygen, and so-called oxygen poisoning of the platinum Pt occurs. NO when such oxygen poisoning occurs_XNO due to reduced oxidizing action on_XOf the active oxygen from the oxygen storage / 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, NO becomes NO._XNO due to enhanced oxidizing action on_XIs increased, and the amount of active oxygen released from the oxygen storage / active oxygen releasing agent 61 increases.
[0065]
Accordingly, when the air-fuel ratio is temporarily switched from lean to rich while the air-fuel ratio is maintained lean, oxygen poisoning of the platinum Pt is eliminated each time, so that active oxygen release when the air-fuel ratio is lean is released. The amount is increased, and thus the oxidizing action of the fine particles on the particulate filter 22a can be promoted.
[0066]
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.
[0067]
In making the air-fuel ratio of the exhaust gas rich, the air-fuel ratio of the exhaust gas may be made rich when it is determined that the particulates have been deposited in layers on the particulate filter 22a, or without such determination. The air-fuel ratio of the exhaust gas may be made rich periodically or irregularly. As a method of making the air-fuel ratio of the exhaust gas rich, for example, when the engine load is relatively low, the throttle valve 17 is opened so that the EGR rate (EGR gas amount / (intake air amount + EGR gas amount)) becomes 65% or more. The degree and the opening of the EGR control valve 25 are controlled, and at this time, a method of controlling the injection amount so that the average air-fuel ratio in the combustion chamber 5 becomes rich can be used. Further, in order to make the air-fuel ratio of the exhaust gas rich, in addition to the normal main fuel injection during the compression stroke, fuel may be injected into the cylinder during the exhaust stroke or the expansion stroke, or the cylinder may be injected during the intake stroke. You may inject fuel inside. These additional fuel injections may not have an interval between the main fuel injection. Further, fuel may be directly injected into the engine exhaust system.
[0068]
By the way, at the time of engine high load operation, relatively high temperature exhaust gas is supplied to the particulate filter 22a. Accordingly, the temperature TF of the particulate filter 22a is increased by the high-temperature exhaust gas, so that the fine particles deposited on the particulate filter 22a are oxidized without emitting a bright flame, while the particulates are ignited during the engine middle load operation. The temperature of the exhaust gas supplied to the particulate filter 22a is not as high as the temperature of the exhaust gas supplied to the particulate filter 22a during the high engine load operation. Therefore, during the engine middle load operation, the temperature TF of the particulate filter 22a cannot be increased so that the fine particles deposited on the particulate filter 22a by the exhaust gas are oxidized without emitting a bright flame. Therefore, in the present embodiment, in order to oxidize the fine particles deposited on the particulate filter 22a without emitting a bright flame, the auxiliary fuel injection is executed and the main fuel injection timing is retarded to remove the unburned fuel from the engine exhaust passage. The exhaust gas which is post-burned in the inside and the temperature thereof is increased accordingly is supplied to the particulate filter 22a.
[0069]
Incidentally, the fuel and the lubricating oil contain calcium Ca, and therefore, the calcium Ca is contained in the exhaust gas. This calcium Ca is SO₃In the presence of calcium sulfate CaSO₄Generate This calcium sulfate CaSO₄Is a solid and does not thermally decompose at high temperatures. Therefore, calcium sulfate CaSO₄Is produced, this calcium sulfate CaSO₄As a result, the pores of the particulate filter 22a are closed, and as a result, it becomes difficult for the exhaust gas to flow through the particulate filter 22a. In this case, when an alkali metal or an alkaline earth metal having a higher ionization tendency than calcium Ca, for example, potassium K is used as the oxygen storage / active oxygen release agent 61, SO diffuses into the oxygen storage / active oxygen release agent 61.₃Combines with potassium K to form potassium sulfate K₂SO₄And calcium Ca is SO₃The exhaust gas passes through the partition wall 54 of the particulate filter 22a without flowing into the exhaust gas outlet passage 51. Therefore, the pores of the particulate filter 22a are not clogged. Therefore, as described above, as the oxygen storage / active oxygen release agent 61, 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, strontium Sr is used. It will be preferable to use.
[0070]
FIG. 6 is a diagram showing a first operation mode in which priority is given to improving the fuel efficiency of the internal combustion engine and a second operation mode in which priority is given to regeneration of the particulate filter. In detail, FIG. 6A shows a first operation mode, and FIG. 6B shows a second operation mode. 6, the vertical axis indicates the required load L, and the horizontal axis indicates the engine speed N. In the present embodiment, usually, the first operation mode (FIG. 6 (A)) in which priority is given to improving the fuel efficiency of the internal combustion engine is selected, and the particulates deposited on the particulate filter 22a are oxidized and removed. Therefore, when the particulate filter 22a is to be regenerated, the second operation mode (FIG. 6B) in which the regeneration of the particulate filter 22a is prioritized is selected.
[0071]
In detail, as shown in FIG. 6A, the first operation mode is divided into an engine low load operation area A1 and an engine middle high load operation area A2. When the first operation mode is selected and the engine operation state is within the engine low-load operation region A1, low-temperature combustion, which will be described in detail later, that is, EGR gas in which the amount of soot generation peaks Low temperature combustion is performed in which the amount of EGR gas supplied into the combustion chamber 5 is larger than the amount and soot is hardly generated. As a result, the fuel efficiency of the internal combustion engine is improved, and the amount of soot generation and NO_XIs suppressed at the same time. On the other hand, when the first operation mode is selected and the engine operation state is in the engine middle high load operation area A2, the amount of soot generated is supplied to the combustion chamber 5 more than the peak EGR gas amount. Normal combustion in which the amount of EGR gas to be performed is small is executed. As a result, the fuel efficiency of the internal combustion engine is improved, and the amount of soot generation and NO_XIs suppressed at the same time.
[0072]
As shown in FIG. 6B, the second operation mode is divided into an engine low load operation region B1, an engine middle load operation region B2, and an engine high load operation region B3. When the second operation mode is selected and the engine operation state is within the engine low-load operation region B1, low-temperature combustion is executed as in the first operation mode. As a result, the fuel efficiency of the internal combustion engine is improved, and the amount of soot generation and NO_XIs suppressed at the same time. In addition, the air-fuel ratio of the exhaust gas becomes rich during low-temperature combustion in which the amount of EGR gas is increased, so that the unburned fuel in the exhaust gas is post-burned in the engine exhaust passage, and the temperature of the particulate filter 22a increases. The amount of active oxygen released increases, and as a result, the particulate filter 22a is regenerated. When the second operation mode is selected and the engine operation state is within the engine middle load operation region B2, the auxiliary fuel injection is executed in addition to the main fuel injection, and the main fuel injection timing is retarded. Is done. The auxiliary fuel is supplied into the engine exhaust passage without being completely burned in the combustion chamber 5, and is post-burned in the engine exhaust passage. Similarly, the main fuel whose injection timing has been retarded is also supplied to the engine exhaust passage without being completely burned in the combustion chamber 5, and is post-burned in the engine exhaust passage. As a result, the temperature of the particulate filter 22a is increased, and the particulate filter 22a is regenerated. When the second operation mode is selected and the engine operation state is within the engine high load operation region B3, the normal combustion is performed as in the first operation mode. As a result, the fuel efficiency of the internal combustion engine is improved, and the amount of soot generation and NO_XIs suppressed at the same time. In addition, since the exhaust gas temperature becomes relatively high during high engine load operation, the temperature of the particulate filter 22a is increased by the exhaust gas, and as a result, the particulate filter 22a is regenerated.
[0073]
FIG. 7 is a flowchart illustrating the operation control method according to the present embodiment. As shown in FIG. 7, when this routine is started, first, in step 100, it is determined whether or not it is time to reproduce the particulate filter 22a. Specifically, when it is estimated that a predetermined amount of fine particles have accumulated on the particulate filter 22a, it is determined that it is time to regenerate the particulate filter 22a, and the amount of fine particles accumulated on the particulate filter 22a is less than the predetermined amount. , It is determined that it is not time to reproduce the particulate filter 22a. Specifically, when a predetermined period of time determined based on the capacity of the particulate filter 22a has elapsed while combustion is being performed under the first operation mode, a predetermined amount of particulates has accumulated on the particulate filter 22a. It is estimated to be. On the other hand, it is estimated that the regeneration of the particulate filter 22a has been completed when a predetermined period determined based on the capacity of the particulate filter 22a has elapsed while combustion is being performed in the second operation mode. . In another embodiment, instead, it may be estimated that a predetermined amount of particulates has accumulated on the particulate filter 22a when the vehicle equipped with the internal combustion engine has traveled a predetermined distance. Alternatively, a back pressure sensor (not shown) is provided on the upstream side of the exhaust gas flow of the particulate filter 22a, and when the back pressure increases, it is estimated that a predetermined amount of fine particles has accumulated on the particulate filter 22a, and the back pressure decreases. At that time, it may be estimated that the regeneration of the particulate filter 22a has been completed. When the determination is NO in Step 100, the process proceeds to Step 101, and when the determination is YES in Step 100, the process proceeds to Step 102. Proceed to step 102. In step 101, the engine is operated under the first operation mode shown in FIG. On the other hand, in step 102, the operation of the engine under the second operation mode shown in FIG. 6B is performed.
[0074]
FIG. 8 is a flowchart showing a subroutine executed in step 101 of FIG. As shown in FIG. 8, when this routine is started, first, in step 200, it is determined whether or not the engine operation state is within the engine low load operation area A1 of FIG. 6A. If the determination is YES, the process proceeds to step 201, and if the determination is NO, the process proceeds to step 207. In step 201, the target opening ST of the throttle valve 17 is calculated from the map shown in FIG. 10A, and the opening of the throttle valve 17 is set to the target opening ST. Next, at step 202, the target opening SE of the EGR control valve 25 is calculated from the map shown in FIG. 10B, and the opening of the EGR control valve 25 is set as the target opening SE. Next, at step 203, the intake air amount Ga detected by the air flow meter 44 is taken in. Next, at step 204, the target air-fuel ratio A / F is calculated from the map shown in FIG. 9B. Next, at step 205, the fuel injection amount Q necessary for setting the air-fuel ratio to the target air-fuel ratio A / F is calculated based on the intake air amount Ga and the target air-fuel ratio A / F. Next, at step 206, the target fuel injection start timing θS is calculated from the map shown in FIG.
[0075]
FIG. 9A shows the target air-fuel ratio A / F in the engine low load operation region A1. In FIG. 9 (A), the curves indicated by A / F = 15.5, A / F = 16, A / F = 17, and A / F = 18 have target air-fuel ratios of 15.5, 16, and 17, respectively. , 18 and the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 9A, the air-fuel ratio is lean in the engine low-load operation region A1, and the target air-fuel ratio A / F is leaner as the required load L decreases in the engine low-load operation region A1. You. 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. 9A, as the required load L decreases, the target air-fuel ratio A / F increases. As the target air-fuel ratio A / F increases, the fuel consumption rate increases. Therefore, in order to make the air-fuel ratio as lean as possible, the embodiment according to the present invention increases the target air-fuel ratio A / F as the required load L decreases. .
[0076]
The target air-fuel ratio A / F shown in FIG. 9A 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. 9B. Also, as shown in FIG. 10A, the target opening degree ST of the throttle valve 17 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening degree SE of the EGR control valve 25 necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 9A is stored in advance in the ROM 32 in the form of a map as a function of N. As shown in FIG. 10 (B), it 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.
[0077]
On the other hand, in step 207, the target fuel injection amount Q is calculated from the map shown in FIG. 12A, and the fuel injection amount is set as the target fuel injection amount Q. Next, at step 208, the target fuel injection start timing θS is calculated from the map shown in FIG. 12B, and the fuel injection start timing is set to the target fuel injection start timing θS. Next, at step 209, the target opening ST of the throttle valve 17 is calculated from the map shown in FIG. Next, at step 210, the target opening SE of the EGR control valve 25 is calculated from the map shown in FIG. 14B, and the opening of the EGR control valve 25 is set to this target opening SE. Next, at step 211, the intake air amount Ga detected by the air flow meter 44 is taken. Next, at step 212, the actual air-fuel ratio (A / F) is calculated from the fuel injection amount Q and the intake air amount Ga._RIs calculated. Next, at step 213, the target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 214, the actual air-fuel ratio (A / F)_RIs larger than the target air-fuel ratio A / F. (A / F)_RIf> A / F, the routine proceeds to step 215, where the throttle opening correction value ΔST is decreased by a constant value α, and then the routine proceeds to step 217. (A / F)_RWhen ≤A / F, the routine proceeds to step 216, where the correction value ΔST is increased by a constant value α, and then the routine proceeds to step 217. In step 217, the final target opening ST is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 17, and the opening of the throttle valve 17 is used as the final target opening ST. That is, the actual air-fuel ratio (A / F)_RIs controlled to the target air-fuel ratio A / F.
[0078]
FIG. 13A shows the target air-fuel ratio A / F when normal combustion is performed. In FIG. 13A, curves A / F = 24, A / F = 35, A / F = 45, and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. ing. The target air-fuel ratio A / F shown in FIG. 13A 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. Further, as shown in FIG. 14A, the target opening ST of the throttle valve 17 necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening degree SE of the EGR control valve 25 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 13A is stored in advance in the ROM 32 in the form of a map as a function of N. As shown in FIG. 14 (B), a map is stored in advance in the ROM 32 as a function of the required load L and the engine speed N. Further, during normal combustion, the fuel injection amount Q is calculated based on the required load L and the engine speed N. This fuel injection amount Q 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. Similarly, during normal combustion, the fuel injection start timing θS is calculated based on the required load L and the engine speed N. The fuel injection start timing θS 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.
[0079]
Hereinafter, the above-described low-temperature combustion will be described in detail. FIG. 15 shows a change in the output torque when the air-fuel ratio A / F (horizontal axis in FIG. 15) is changed by changing the opening degree and the EGR rate of the throttle valve 17 during the low load operation of the engine, and the smoke, HC, CO, NO_X4 shows an experimental example showing a change in the emission amount of the gas. As can be seen from FIG. 15, in this experimental example, the smaller the air-fuel ratio A / F, the higher the EGR rate. When the air-fuel ratio A / F is smaller than the stoichiometric air-fuel ratio (≒ 14.6), the EGR rate is 65% or more. As shown in FIG. 15, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the amount of smoke generated increases when the EGR rate becomes close to 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.
[0080]
FIG. 16A shows a change in the combustion pressure in the combustion chamber 5 when the amount of generated smoke is the largest when the air-fuel ratio A / F is around 21, 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. 16 (A) and FIG. 16 (B), in the case of FIG. 16 (B) in which the amount of smoke generation is almost zero, FIG. 16 (A) in which the amount of smoke generation is large. It can be seen that the combustion pressure is lower than the case shown.
[0081]
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. 16B where almost no soot is generated, the combustion pressure is low, and accordingly, the combustion temperature in the combustion chamber 5 at this time is low.
[0082]
Second, when the amount of generated smoke, that is, the amount of generated soot becomes almost zero, the amount of HC and CO emissions increases as shown in FIG. This means that hydrocarbons are discharged from the combustion chamber 5 without growing to soot. That is, linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 17 are thermally decomposed when the temperature is increased in a state of lack of oxygen, soot precursors are formed, and then mainly the soot precursor is formed. A soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot production 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. 15, but HC at this time is a precursor of soot or a hydrocarbon in a state before the soot. . This HC is post-burned in the engine exhaust passage, and the exhaust gas temperature is increased.
[0083]
Summarizing these considerations based on the experimental results shown in FIGS. 15 and 16, 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 exceeded a certain temperature.
[0084]
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, the compression ratio, and the like. I can not 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. At this time NO_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.
[0085]
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 burns has an extremely large effect on suppressing the temperature of the fuel and the gas around the fuel. 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.
[0086]
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, 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 effect of the inert gas.
[0087]
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 larger the specific heat of the inert gas, the stronger the endothermic action, and therefore, the inert gas is preferably a gas having a large 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.
[0088]
FIG. 18 shows the relationship between the EGR rate and 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. 18, a curve A shows a case where the EGR gas is strongly cooled to maintain the EGR gas temperature at approximately 90 ° C., and a curve B shows a 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. As shown by the curve A in FIG. 18, when the EGR gas is cooled strongly, the amount of soot generation peaks at a point where the EGR rate is slightly lower than 50%. In this case, the EGR rate is increased to approximately 55% or more. Then, almost no soot is generated. On the other hand, as shown by the curve B in FIG. 18, 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. As shown by the curve C in FIG. 18, when the EGR gas is not forcibly cooled, the amount of soot generation reaches a peak near the EGR rate of 55%. Above a percentage, soot is hardly generated. FIG. 18 shows the amount of smoke generated when the engine load is relatively high. When the engine load decreases, the EGR rate at which the amount of soot peaks slightly decreases, and the EGR rate at which soot hardly occurs is reduced. 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.
[0089]
FIG. 19 shows a mixed gas amount of the EGR gas and the air necessary to make the temperature of the fuel and the surrounding gas during combustion lower than the temperature at which soot is generated when EGR gas is used as the inert gas; The ratio of air in the mixed gas amount and the ratio of EGR gas in the mixed gas are shown. In FIG. 19, 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 shows the required load.
[0090]
Referring to FIG. 19, 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. 19, 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. 19, 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. 15, 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.
[0091]
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. 19, 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. By the way, when the supercharging is not performed, the upper limit of the total intake gas amount X sucked into the combustion chamber 5 is Y. Therefore, in FIG.₀In the larger range, the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio unless the EGR gas ratio is reduced as the required load increases. In other words, when supercharging is not performed, the required load is L₀If the air-fuel ratio is to be maintained at the stoichiometric air-fuel ratio in a region larger than the required load, the EGR rate decreases as the required load increases.₀In the larger region, the temperature of the fuel and the surrounding gas cannot be maintained at a temperature lower than the temperature at which soot is generated.
[0092]
However, although not shown, when the EGR gas is recirculated through the EGR passage to the inlet side of the supercharger, that is, into the air suction pipe of the exhaust turbocharger, the required load becomes low.₀In the larger region, the EGR rate can be maintained at or above 55 percent, for example, 70 percent, and thus the temperature of the fuel and its surrounding gas can be maintained below the temperature at which soot is produced. That is, if the EGR gas is recirculated so that the EGR rate in the air suction pipe becomes, for example, 70%, the EGR rate of the suction gas boosted by the compressor of the exhaust turbocharger also becomes 70%, and thus the pressure is increased by the compressor. To the extent possible, the temperature of the fuel and the gas around it can be kept below the temperature at which soot is produced. Therefore, the operating range of the engine that can generate low-temperature combustion can be expanded. Request load is L₀When the EGR rate is set to 55% or more in a larger area, the EGR control valve is fully opened and the throttle valve is slightly closed.
[0093]
As described above, FIG. 19 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. NO while preventing generation of_XIs 10 p. p. m or less, and even if the air amount is larger than the air amount shown in FIG. 19, that is, even if the average value of the air-fuel ratio is 17 to 18 lean, soot generation is prevented. NO_XIs 10 p. p. m can be around or below. 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 when the combustion temperature increases, but in the present invention, the soot is suppressed to a low temperature, and soot is reduced. Not generated at all. Furthermore, NO_XOnly a very small amount is generated. In this way, when low-temperature combustion is being performed, soot is not generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean, 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.
[0094]
By the way, the fuel and the surrounding gas temperature during combustion in the combustion chamber can be suppressed below the temperature at which the growth of hydrocarbons stops halfway, only when the engine is under low load operation where the calorific value due to combustion is relatively small. Therefore, in the embodiment according to the present invention, at the time of engine low load operation, the fuel during combustion and the surrounding gas temperature are suppressed to a temperature at or below the temperature at which the growth of hydrocarbons stops halfway, so that low temperature combustion is performed. Normal combustion is performed. Here, low-temperature combustion refers to combustion in which the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of soot generation peaks, and soot is hardly generated, as is clear from the description so far. The normal combustion refers to combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot reaches a peak.
[0095]
Next, the operation control in the engine low load operation area A1 and the engine middle high load operation area A2 shown in FIG. 6A will be described with reference to FIG. FIG. 20 shows the opening of the throttle valve 17, the opening of the EGR control valve 25, 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. 20, in the engine low load operation region A1 where the required load L is low, the opening of the throttle valve 17 is gradually increased from almost fully closed to about 2/3 as the required load L increases. The degree of opening of the EGR control valve 25 is gradually increased from almost fully closed to fully open as the required load L increases. In the example shown in FIG. 20, the EGR rate in the engine low load operation region A1 is set to approximately 70%, and the air-fuel ratio is set to a slightly lean air-fuel ratio.
[0096]
In other words, in the engine low load operation region A1, the opening of the throttle valve 17 and the opening of the EGR control valve 25 are controlled so that the EGR rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. Further, in the engine low load operation region A1, 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. During idle operation, the throttle valve 17 is closed to near full closure, and at this time, the EGR control valve 25 is also closed to near full closure. When the throttle valve 17 is closed close to the fully closed state, 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, the throttle valve 17 is closed almost fully to suppress the vibration of the engine body 1.
[0097]
On the other hand, when the operation region of the engine changes from the low engine load operation region A1 to the high engine load operation region A2, the opening of the throttle valve 20 is increased stepwise from about 2/3 opening to full opening. At this time, in the example shown in FIG. 20, 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. 18) in which a large amount of smoke is generated, a large amount of smoke may be generated when the operation region of the engine changes from the low engine load operation region A1 to the high engine load operation region A2. Absent. In the engine middle high load operation region A2, normal combustion that has been performed conventionally is performed. In the engine middle high load operation region A2, the throttle valve 17 is kept fully open except for a part, and the opening of the EGR control valve 25 is gradually reduced as the required load L increases. Further, in the engine middle high load operation region A2, 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. Further, in the engine middle and high load operation region A2, the injection start timing θS is set near the compression top dead center TDC.
[0098]
FIGS. 21 and 22 are flowcharts showing a subroutine executed in step 102 of FIG. As shown in FIGS. 21 and 22, when this routine is started, first, in step 300, it is determined whether or not the engine operation state is within the engine low load operation region B1 of FIG. 6B. If the determination is YES, the process proceeds to step 201, and if the determination is NO, the process proceeds to step 301. In step 201, the target opening ST of the throttle valve 17 is calculated from the map shown in FIG. 10A in the same manner as when the first operation mode is selected (FIG. 8). The opening degree ST is set. Next, at step 202, the target opening SE of the EGR control valve 25 is calculated from the map shown in FIG. 10B in the same manner as when the first operation mode is selected (FIG. 8), and the opening of the EGR control valve 25 is calculated. Is the target opening degree SE. Next, at step 203, the intake air amount Ga detected by the air flow meter 44 is taken in the same manner as when the first operation mode was selected (FIG. 8), and then at step 204, the first operation mode was selected. Similarly to the time (FIG. 8), the target air-fuel ratio A / F is calculated from the map shown in FIG. 9B. Next, at step 205, it is necessary to set the air-fuel ratio to the target air-fuel ratio A / F based on the intake air amount Ga and the target air-fuel ratio A / F as in the case where the first operation mode is selected (FIG. 8). The fuel injection amount Q is calculated. Next, at step 206, the target fuel injection start timing θS is calculated from the map shown in FIG. 11 as in the case where the first operation mode is selected (FIG. 8).
[0099]
In step 301, it is determined whether or not the engine operation state is within the engine high load operation area B3 of FIG. 6B. If the determination is YES, the process proceeds to step 207. If the determination is NO, the process proceeds to step 302. In step 207, the target fuel injection amount Q is calculated from the map shown in FIG. 12A in the same manner as when the first operation mode is selected (FIG. 8). Is done. Next, at step 208, the target fuel injection start timing θS is calculated from the map shown in FIG. 12B in the same manner as when the first operation mode is selected (FIG. 8), and the fuel injection start timing is set to the target fuel injection timing. The start time θS is set. Next, at step 209, the target opening ST of the throttle valve 17 is calculated from the map shown in FIG. 14A in the same manner as when the first operation mode is selected (FIG. 8). Next, at step 210, the target opening SE of the EGR control valve 25 is calculated from the map shown in FIG. 14B in the same manner as when the first operation mode is selected (FIG. 8), and the opening of the EGR control valve 25 is calculated. Is the target opening degree SE. Next, at step 211, the intake air amount Ga detected by the air flow meter 44 is taken in the same manner as when the first operation mode was selected (FIG. 8). Next, at step 212, the actual air-fuel ratio (A / F) is obtained from the fuel injection amount Q and the intake air amount Ga in the same manner as when the first operation mode is selected (FIG. 8)._RIs calculated.
[0100]
Next, at step 213, the target air-fuel ratio A / F is calculated from the map shown in FIG. 13B similarly to the case where the first operation mode is selected (FIG. 8). Next, at step 214, the actual air-fuel ratio (A / F) is the same as when the first operation mode was selected (FIG. 8)._RIs larger than the target air-fuel ratio A / F. (A / F)_RIf> A / F, as in the case where the first operation mode is selected (FIG. 8), the routine proceeds to step 215, in which the throttle opening correction value ΔST is reduced by a constant value α, and then to step 217. (A / F)_RWhen ≦ A / F, the process proceeds to step 216 as in the case where the first operation mode is selected (FIG. 8), the correction value ΔST is increased by a constant value α, and then the process proceeds to step 217. In step 217, the final target opening ST is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 17 in the same manner as when the first operation mode is selected (FIG. 8). The opening 17 is the final target opening ST. That is, the actual air-fuel ratio (A / F)_RIs controlled to the target air-fuel ratio A / F.
[0101]
On the other hand, when it is determined in step 301 that the engine operation state is within the engine middle load operation area B2 in FIG. 6B, the target main fuel injection amount Q1 is determined in step 302 from the map shown in FIG. The calculated main fuel injection amount is set as the target main fuel injection amount Q1. Next, at step 303, the target main fuel injection start timing θS1 is calculated from the map shown in FIG. 23B, and the main fuel injection start timing is set to the target main fuel injection start timing θS1. In the present embodiment, the target main fuel injection start timing θS1 is delayed from the target fuel injection start timing θS in step 208 in FIG. Next, at step 304, the target auxiliary fuel injection amount Q2 is calculated from the map shown in FIG. 24A, and the auxiliary fuel injection amount is set as the target auxiliary fuel injection amount Q2. Next, at step 305, the target auxiliary fuel injection start timing θS2 is calculated from the map shown in FIG. 24 (B), and the auxiliary fuel injection start timing is set to the target auxiliary fuel injection start timing θS2. In the present embodiment, the target sub fuel injection start timing θS2 is set between the exhaust stroke and the intake stroke, and the sub fuel injection is so-called VIGOM injection. In a modification of the present embodiment, so-called pilot injection can be performed as sub-fuel injection instead of VIGOM injection. In this case, the target sub-fuel injection start timing calculated in step 303 is the target main fuel injection start timing. The compression stroke is set at the end of the compression stroke immediately before the timing θS1.
[0102]
Next, at step 306, the target opening degree ST of the throttle valve 17 is calculated from the map shown in FIG. Next, at step 307, the target opening SE of the EGR control valve 25 is calculated from the map shown in FIG. 25C, and the opening of the EGR control valve 25 is set as the target opening SE. Next, at step 308, the intake air amount Ga detected by the air flow meter 44 is taken. Next, at step 309, the actual air-fuel ratio (A / F) is calculated from the fuel injection amount Q1 and the intake air amount Ga._RIs calculated. Next, at step 310, the target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 311, the actual air-fuel ratio (A / F)_RIs larger than the target air-fuel ratio A / F. (A / F)_RIf> A / F, the routine proceeds to step 312, where the correction value ΔST of the throttle opening is decreased by a constant value α, and then the routine proceeds to step 314. (A / F)_RIf ≦ A / F, the routine proceeds to step 313, where the correction value ΔST is increased by a constant value α, and then the routine proceeds to step 314. In step 314, the final target opening ST is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 17, and the opening of the throttle valve 17 is used as the final target opening ST. That is, the actual air-fuel ratio (A / F)_RIs controlled to the target air-fuel ratio A / F.
[0103]
The target air-fuel ratio A / F when the second operation mode is selected and the engine is in the middle load operation is a function of the required load L and the engine speed N as shown in FIG. In advance in the ROM 32. Further, as shown in FIG. 25B, the target opening ST of the throttle valve 17 necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening degree SE of the EGR control valve 25 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 25A is stored in advance in the ROM 32 in the form of a map as a function of N. As shown in FIG. 25 (C), it 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. Further, when the second operation mode is selected and the engine is operating under the medium load, the main fuel injection amount Q1 is calculated based on the required load L and the engine speed N. The main fuel injection amount Q1 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. Similarly, when the second operation mode is selected and the engine is under the medium load operation, the main fuel injection start timing θS1 is calculated based on the required load L and the engine speed N. The main fuel injection start timing θS1 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. Further, when the second operation mode is selected and the engine is operating under the medium load, the auxiliary fuel injection amount Q2 is calculated based on the required load L and the engine speed N. The auxiliary fuel injection amount Q2 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. Similarly, when the second operation mode is selected and the engine is in the middle load operation, the auxiliary fuel injection start timing θS2 is calculated based on the required load L and the engine speed N. The auxiliary fuel injection start timing θS2 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.
[0104]
FIG. 26 is a flowchart showing a control method for suppressing the temperature of the particulate filter 22a from excessively increasing in the second operation mode. This routine is determined as YES in step 100 of FIG. 7, and is executed as an interrupt routine when the particulate filter 22a is being reproduced. As shown in FIG. 26, when this routine is started, first, in step 400, it is determined whether or not the temperature of the particulate filter 22a is likely to rise excessively. In the present embodiment, when YES is determined in step 100 of FIG. 7 and the elapsed time from the time when the first operation mode is switched to the second operation mode exceeds a predetermined threshold, the particulate matter It is determined that the temperature of the filter 22a is about to rise excessively. In another embodiment, instead, when the outgassing temperature from the particulate filter 22a detected by the outgassing temperature sensor 39b exceeds a predetermined threshold, the particulate filter 22a is about to rise excessively. It is also possible to make a determination. When YES is determined in Step 400, the process proceeds to Step 401, and when NO is determined, this routine is ended.
[0105]
In step 401, it is determined whether or not the engine operation state is within the engine low load operation area B1 of FIG. When the determination is YES, that is, when the engine is in the low load operation in which the second operation mode is selected and low-temperature combustion is being performed, the process proceeds to step 402, and when the determination is NO, the process proceeds to step 405. In step 402, the target air-fuel ratio A / F calculated based on the map of FIG. 9B in step 204 of FIG. 21 is made lean. As a result, the fuel that has been post-burned in the engine exhaust passage is burned in the combustion chamber 5, and an excessive increase in the exhaust gas temperature is suppressed. In step 403, it is determined whether or not the engine operation state is within the engine high load operation area B3 in FIG. When YES, that is, when the engine is in the high-load operation mode in which the second operation mode is selected and the normal combustion is being performed, the process proceeds to step 404, and when NO, that is, the second operation mode is selected. When the engine is operating at medium load and the sub fuel injection is being executed and the main fuel injection timing is retarded, the routine proceeds to step 405. In step 404, the target fuel injection start timing θS calculated based on the map in FIG. 12B in step 208 in FIG. 21 is advanced. As a result, the fuel that has been post-burned in the engine exhaust passage is burned in the combustion chamber 5, and an excessive increase in the exhaust gas temperature is suppressed. On the other hand, at step 405, the target main fuel injection start timing θS1 calculated based on the map of FIG. 23B in step 303 of FIG. 22 is advanced, and the sub fuel injection is stopped. As a result, the fuel that has been post-burned in the engine exhaust passage is burned in the combustion chamber 5, and an excessive increase in the exhaust gas temperature is suppressed.
[0106]
Preferably, the leaning of the target air-fuel ratio A / F in step 402 is gradually performed, the advance of the target fuel injection start timing θS in step 404 is gradually performed, and the target main fuel injection start timing θS1 in step 405 is performed. Is gradually advanced. Further, in another embodiment, instead of executing steps 402, 404, and 405, when it is determined in step 400 that the particulate filter 22a is about to be excessively heated, it is executed in the first operation mode. It is also possible to execute interrupted combustion. Preferably, the frequency of this interrupt execution is gradually increased.
[0107]
FIGS. 27 and 28 are diagrams showing the relationship between time and the temperature of the particulate filter 22a. More specifically, FIG. 27A shows a case where the excessive temperature rise suppression control routine for the particulate filter shown in FIG. 26 is not provided. In the case shown in FIG. 27 (A), if YES is determined in step 100 of FIG. 7 at time t1 and combustion is performed under the second operation mode, fuel is post-burned in the engine exhaust passage. The temperature of the incoming gas, which is the temperature of the exhaust gas flowing into the particulate filter 22a, and the temperature of the outgas, which is the temperature of the exhaust gas flowing out of the particulate filter 22a, rise, and the temperature of the particulate filter 22a falls within the regeneration temperature range ( T1 and T2). However, unless the particulate filter excessive temperature rise suppression control routine shown in FIG. 26 is provided, the outgassing temperature continues to rise, and the temperature of the particulate filter 22a falls within the burnout temperature region (T3 or more). I will.
[0108]
FIGS. 27 (B), 28 (A) and 28 (B) show a case where the excessive temperature rise suppression control routine for the particulate filter shown in FIG. 26 is provided. In the case shown in FIG. 27 (A), if YES is determined in step 100 of FIG. 7 at time t1 and combustion is performed under the second operation mode, fuel is post-burned in the engine exhaust passage. The incoming gas temperature and the outgoing gas temperature rise, and the temperature of the particulate filter 22a enters the regeneration temperature region (T1 to T2). Thereafter, the timing for regenerating the particulate filter 22a in step 100 of FIG. 7 at time t2 is not reached without determining that the temperature of the particulate filter 22a is about to rise excessively in step 400 of FIG. It is determined that the regeneration of the particulate filter 22a has been completed, and in step 101, the combustion under the first operation mode is performed again.
[0109]
In the case shown in FIG. 28 (A), if YES is determined in step 100 of FIG. 7 at time t1 and combustion is performed under the second operation mode, fuel is post-burned in the engine exhaust passage. The incoming gas temperature and the outgoing gas temperature rise, and the temperature of the particulate filter 22a enters the regeneration temperature region (T1 to T2). Thereafter, at time t3, it is determined in step 400 of FIG. 26 that the particulate filter 22a is about to rise excessively, and step 402, step 404, or step 405 of FIG. 26 is executed, and the temperature of the particulate filter 22a is increased. Is suppressed. Next, at time t4, NO is determined in step 400 of FIG. 26, and the combustion under the second operation mode is executed as in the period from time t1 to time t3. Next, at time t5, it is determined in step 400 of FIG. 26 that the temperature of the particulate filter 22a is about to rise excessively, and step 402, step 404, or step 405 of FIG. 26 is executed to suppress the temperature rise of the particulate filter 22a. Is done. Next, at time t6, NO is determined in step 400 of FIG. 26, and the combustion under the second operation mode is executed as in the period from time t1 to time t3. Next, at time t7, it is determined that the timing to regenerate the particulate filter 22a in step 100 of FIG. 7 is not reached, that is, it is determined that the regeneration of the particulate filter 22a has been completed. Combustion takes place.
[0110]
In the case shown in FIG. 28 (B), if YES is determined in step 100 of FIG. 7 at time t1 and combustion is performed under the second operation mode, fuel is post-burned in the engine exhaust passage. The incoming gas temperature and the outgoing gas temperature rise, and the temperature of the particulate filter 22a enters the regeneration temperature region (T1 to T2). Thereafter, at time t8, it is determined in step 400 of FIG. 26 that the temperature of the particulate filter 22a is about to rise excessively, and combustion in the first operation mode is interrupted. Next, at time t9, NO is determined in step 400 of FIG. 26, and the combustion under the second operation mode is executed as in the period from time t1 to time t8. Next, at time t10, it is determined that the timing to regenerate the particulate filter 22a in step 100 of FIG. 7 has disappeared, that is, it is determined that the regeneration of the particulate filter 22a has been completed. Combustion takes place.
[0111]
According to the present embodiment, the oxygen storage / active oxygen release agent 61 carried on the particulate filter 22a captures and holds oxygen when excess oxygen is present in the surroundings, and reduces the oxygen concentration when the surrounding oxygen concentration decreases. The retained oxygen is released in the form of active oxygen. Therefore, unlike the conventional case where the fine particles are deposited on the particulate filter and then removed by emitting a bright flame, the fine particles are deposited on the particulate filter 22a before being deposited. In addition, the fine particles can be oxidized and removed by the active oxygen released from the oxygen storage / active oxygen releasing agent 61 without emitting bright flame. Further, according to the present embodiment, the first operation mode (FIG. 6A) giving priority to improving the fuel efficiency of the internal combustion engine and the second operation mode giving priority to regeneration of the particulate filter 22a (FIG. 6B) is switched as necessary. Therefore, it is possible to suppress the accumulation of fine particles on the particulate filter while improving the fuel efficiency of the internal combustion engine. More specifically, in step 100 of FIG. 7, the first operation mode (FIG. 6A) in which priority is given to improving the fuel consumption of the internal combustion engine in principle is selected, and the particulate filter 22a is regenerated. Is selected, the second operation mode (FIG. 6B) in which the priority is given to the regeneration of the particulate filter 22a when it becomes necessary. Therefore, the accumulation of fine particles on the particulate filter 22a can be suppressed more than necessary, and the fuel consumption of the internal combustion engine can be prevented from deteriorating accordingly.
[0112]
Further, according to the present embodiment, when the second operation mode (FIG. 6B) in which priority is given to the regeneration of the particulate filter 22 a is selected, and during the engine middle load operation (FIG. In B2) of B), the sub fuel injection is executed in step 304 of FIG. 22, and the main fuel injection timing is retarded in step 303. Therefore, even when the engine is operating at low load (B1), which is capable of performing low-temperature combustion, and is not operating at high load (B3), which is capable of discharging high-temperature exhaust gas, the engine is operating under a medium load (B2). The temperature of the exhaust gas flowing into the particulate filter 22a can be increased, and therefore, the particulate filter 22a can be regenerated.
[0113]
Further, according to the present embodiment, when the second operation mode (FIG. 6B) giving priority to the regeneration of the particulate filter 22 a is selected and low-temperature combustion is being performed (FIG. 6B). 26B), when the temperature of the particulate filter 22a is likely to rise excessively, the air-fuel ratio is made lean in step 402 in FIG. Therefore, the temperature of the exhaust gas flowing into the particulate filter 22a is reduced, and the temperature of the particulate filter 22a can be prevented from excessively increasing. Further, the second operation mode (FIG. 6B) in which the priority is given to the regeneration of the particulate filter 22a is selected, the sub fuel injection is executed in step 304 of FIG. Is retarded (B2 in FIG. 6B), when the temperature of the particulate filter 22a is likely to rise excessively, the main fuel injection timing is advanced in step 405 in FIG. The auxiliary fuel injection is stopped. Therefore, the temperature of the exhaust gas flowing into the particulate filter 22a is reduced, and the temperature of the particulate filter 22a can be prevented from excessively increasing. Further, even when the second operation mode (FIG. 6B) in which the priority is given to the regeneration of the particulate filter 22a is selected and normal combustion is executed (B3 in FIG. 6B). When the temperature of the particulate filter 22a is likely to rise excessively, the fuel injection timing is advanced in step 404 in FIG. Therefore, the temperature of the exhaust gas flowing into the particulate filter 22a is reduced, and the temperature of the particulate filter 22a can be prevented from excessively increasing. That is, it is possible to prevent the temperature of the particulate filter 22a from being excessively increased during the regeneration of the particulate filter 22a, and to prevent the particulate filter 22a from being melted.
[0114]
Further, according to the above-described other embodiment, even when the second operation mode (FIG. 6B) in which the priority is given to the regeneration of the particulate filter 22a is selected, the particulate filter 22a is not used. When the first operating mode (FIG. 6 (A)) is selected when the temperature of the engine is likely to rise excessively, the first operating mode (FIG. 6 (A)) is prioritized to improve the fuel efficiency of the internal combustion engine. When the temperature of the exhaust gas flowing into the particulate filter 22a is relatively low, the combustion is interrupted. Therefore, it is possible to prevent the temperature of the particulate filter 22a from excessively rising during the regeneration of the particulate filter 22a, and to prevent the particulate filter 22a from being melted.
[0115]
Further, according to the present embodiment, whether the temperature of the particulate filter 22a is likely to rise excessively is determined in step 400 of FIG. 26 from the first operation mode (FIG. 6A) to the second operation mode (FIG. 6A). 6 (B)) is determined based on the elapsed time from when the switching to (B) was performed. Therefore, it is relatively easy to determine whether the temperature of the particulate filter 22a is likely to rise excessively without actually detecting the temperature of the particulate filter 22a.
[0116]
Further, according to the other embodiment described above, it is determined whether or not the temperature of the particulate filter 22a is likely to rise excessively, based on the exhaust gas temperature detected by the gas outlet temperature sensor 39b. Therefore, it is possible to relatively accurately determine whether or not the temperature of the particulate filter 22a is likely to rise excessively without actually detecting the temperature of the particulate filter 22a.
[0117]
Furthermore, according to the present embodiment, the storage reduction type NO having an oxidation function is provided upstream of the particulate filter 22a in the exhaust gas flow._XA catalyst 22b is provided. Therefore, the exhaust gas is oxidized when passing through the catalyst 22b, and the temperature of the exhaust gas flowing into the particulate filter 22a can be increased by the oxidizing heat, so that the temperature of the particulate filter 22a is relatively high. Temperature can be maintained. In addition, the SOF acting as a binder for the fine particles is oxidized by the catalyst 22b, and as a result, the fine particles can hardly be deposited on the particulate filter 22a.
[0118]
Further, according to the present embodiment, when it is estimated that a predetermined amount of fine particles has accumulated on the particulate filter 22a, YES is determined in step 100 of FIG. 7, and the first priority is given to improving the fuel efficiency of the internal combustion engine. Switching from the operation mode (FIG. 6 (A)) to the second operation mode (FIG. 6 (B)) giving priority to the regeneration of the particulate filter 22a is performed. Therefore, by continuing to execute step 102, it is possible to suppress the accumulation of fine particles on the particulate filter 22a more than necessary, and to prevent the fuel efficiency of the internal combustion engine from being deteriorated accordingly.
[0119]
Further, according to the present embodiment, the low-temperature combustion is executed during the low-load operation of the engine, so that the temperature of the exhaust gas flowing into the particulate filter 22a is increased as compared with the case where the normal combustion is executed during the low-load operation of the engine. be able to. Therefore, the engine operation region where the particulate filter 22a can be regenerated can be expanded as compared with the case where the low-temperature combustion is not performed. Further, according to the present embodiment, since the catalyst 22b having a relatively large capacity and having an oxidizing function is arranged on the exhaust gas flow upstream side of the particulate filter 22a, the leveled high-temperature exhaust gas is supplied to the particulate filter 22a. Therefore, it is possible to suppress the temperature of the particulate filter 22a from being excessively increased locally.
[0120]
According to the present embodiment, the length of time during which the first operation mode (FIG. 6A) is selected and the length of time during which the second operation mode (FIG. 6B) is selected are described. By appropriately setting, when the first operation mode (FIG. 6A) is selected, the temperature of the particulate filter 22a is selected when the second operation mode (FIG. 6B) is selected along with excessive accumulation of soot. Can be suppressed from excessively rising, and the temperature of the particulate filter 22a decreases as the time during which the first operation mode (FIG. 6A) is selected is too long. And suppressing the temperature of the particulate filter 22a from excessively increasing due to too long a time in which the second operation mode (FIG. 6B) is selected. Can be.
[0121]
Further, according to the present embodiment, even when the first operation mode (FIG. 6A) is selected, the low-temperature combustion is performed during the low-load engine operation, so that the temperature of the particulate filter 22a is reduced. The decrease can be suppressed. Therefore, when the operation mode is switched to the second operation mode (FIG. 6B) after the first operation mode (FIG. 6A) is selected and the low-temperature combustion is being performed, the second operation mode (FIG. 6B) is selected. The time during which FIG. 6B is selected can be shortened.
[0122]
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), NO for removal of particulates by oxidation_XIt is necessary to periodically or irregularly set the atmosphere in the vicinity of the storage reduction catalyst device to a rich air-fuel ratio. Iron or tin may be used instead of ceria.
[0123]
In the present embodiment, the particulate filter itself carries an oxygen storage / active oxygen releasing agent, and the particulates are oxidized and removed by the active oxygen released from the oxygen storage / active oxygen releasing agent. It is not intended to limit the invention. For example, active oxygen and a particulate oxidizing substance such as nitrogen dioxide that functions equivalently to 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. . Also in this case, when the temperature of the particulate filter is increased, the temperature of the particulate filter itself is increased, and the particulate filter is easily oxidized and removed.
[0124]
【The invention's effect】
According to the first aspect of the invention, it is possible to suppress the accumulation of fine particles on the particulate filter while improving the fuel efficiency of the internal combustion engine. More specifically, it is possible to suppress the accumulation of fine particles on the particulate filter more than necessary, and to prevent the fuel efficiency of the internal combustion engine from being deteriorated accordingly.In addition, the temperature of the exhaust gas flowing into the particulate filter is not even during the low load operation of the engine capable of performing low-temperature combustion and during the middle load operation of the engine that is not the high load operation of the engine capable of discharging high-temperature exhaust gas. Can be increased, and therefore the particulate filter can be regenerated.
[0125]
According to the second aspect of the present invention, unlike the conventional case, the fine particles are deposited on the particulate filter in a layered manner and then removed by emitting a bright flame. The active oxygen released by the oxygen storage / active oxygen releasing agent can oxidize and remove the fine particles without emitting a bright flame before being deposited on the laminate.
[0126]
According to the third aspect of the present invention, if the surrounding oxygen concentration is reduced due to the attachment of particulates or the like, the oxygen storage / active oxygen releasing agent naturally releases active oxygen to oxidize and remove the trapped fine particles. Can be.
[0127]
According to the fourth aspect of the present invention, the oxygen storage / active oxygen release agent contains NO in exhaust gas._XNO to occlude_XCan be reduced to the atmosphere.
[0129]
Claim5 and 6According to the invention described in (1), the temperature of the exhaust gas flowing into the particulate filter is reduced, and it is possible to avoid an excessive rise in the temperature of the particulate filter. That is, it is possible to prevent the temperature of the particulate filter from being excessively increased while the particulate filter is being regenerated, thereby preventing the particulate filter from being melted.
[0130]
Claim7According to the invention described in (1), it is possible to prevent the temperature of the particulate filter from excessively increasing during regeneration of the particulate filter, and to prevent the particulate filter from being melted.
[0131]
Claim8According to the invention described in (1), it is possible to relatively easily determine whether or not the temperature of the particulate filter is likely to rise excessively without actually detecting the temperature of the particulate filter.
[0132]
Claim9According to the invention described in (1), it is possible to relatively accurately determine whether or not the temperature of the particulate filter is likely to rise excessively without actually detecting the temperature of the particulate filter.
[0133]
Claim10According to the invention described in (1), the accumulation of fine particles on the particulate filter can be suppressed more than necessary, and the fuel consumption of the internal combustion engine can be prevented from deteriorating accordingly.
[0134]
Claim11According to the invention described in the above, the exhaust gas is oxidized when passing through the catalyst, the temperature of the exhaust gas flowing into the particulate filter can be increased by the oxidation heat, the temperature of the particulate filter is reduced It can be maintained at a relatively high temperature. Also, the SOF acting as a binder for the fine particles is oxidized by the catalyst, and as a result, the fine particles can be hardly deposited on the particulate filter.
[Brief description of the drawings]
FIG. 1 is a diagram showing a first embodiment in which an exhaust gas purification device for an internal combustion engine of the present invention is applied to a compression ignition type internal combustion engine.
FIG. 2 is a diagram showing a structure of a particulate filter 22a.
FIG. 3 is an enlarged view of a surface of a carrier layer formed on an inner peripheral surface of an exhaust gas inflow passage 50.
FIG. 4 is a view showing a state of oxidation of fine particles.
FIG. 5 is a graph showing an amount of oxidizable and removable fine particles G that can be oxidized and removed without emitting a bright flame per unit time.
FIG. 6 is a diagram illustrating a first operation mode in which priority is given to improving the fuel efficiency of the internal combustion engine and a second operation mode in which priority is given to regeneration of the particulate filter.
FIG. 7 is a flowchart illustrating an operation control method according to the first embodiment.
FIG. 8 is a flowchart showing a subroutine executed in step 101 of FIG. 7;
FIG. 9 is a diagram showing an air-fuel ratio and the like in an engine low load operation region A1.
FIG. 10 is a diagram showing a map of a target opening degree of a throttle valve and the like in an engine low load operation region A1.
FIG. 11 is a diagram showing a combustion injection start timing in an engine low load operation region A1.
FIG. 12 is a diagram showing a map of a target fuel injection amount and the like in an engine high load operation region A2.
FIG. 13 is a diagram showing an air-fuel ratio and the like in an engine middle high load operation region A2.
FIG. 14 is a diagram showing a map of a target opening degree of a throttle valve and the like in an engine middle high load operation region A2.
FIG. 15: Smoke and NO_XFIG.
FIG. 16 is a diagram showing a combustion pressure.
FIG. 17 is a diagram showing fuel molecules.
FIG. 18 is a diagram showing a relationship between a generation amount of smoke and an EGR rate.
FIG. 19 is a diagram showing a relationship between an injected fuel amount and a mixed gas amount.
FIG. 20 is a diagram showing the opening of the throttle valve 17, the opening of the EGR control valve 25, the EGR rate, the air-fuel ratio, the injection timing, and the injection amount with respect to the required load L.
FIG. 21 is a flowchart showing a subroutine executed in step 102 of FIG. 7;
FIG. 22 is a flowchart showing a subroutine executed in step 102 of FIG. 7;
FIG. 23 is a diagram showing a map of a target main fuel injection amount and the like in an engine middle load operation region B2.
FIG. 24 is a diagram showing a map of a target auxiliary fuel injection amount and the like in an engine middle load operation region B2.
FIG. 25 is a diagram showing a map of a target air-fuel ratio and the like in an engine middle load operation region B2.
FIG. 26 is a flowchart showing a control method for suppressing the temperature of the particulate filter 22a from excessively increasing in the second operation mode.
FIG. 27 is a diagram showing a relationship between time and the temperature of the particulate filter 22a.
FIG. 28 is a diagram showing a relationship between time and the temperature of the particulate filter 22a.
[Explanation of symbols]
5. Combustion chamber
6 ... Fuel injection valve
20 ... exhaust pipe
22a ... Particulate filter
25 ... EGR control valve
61 ... Oxygen storage / active oxygen release agent

Claims (11)

In an exhaust gas purifying apparatus for an internal combustion engine in which a particulate filter for removing particulates in exhaust gas discharged from a combustion chamber is disposed in an engine exhaust passage, trapped particulates are oxidized on the particulate filter, and A first operation mode in which priority is given to improving the fuel efficiency of the engine, and a second operation mode in which priority is given to regenerating the particulate filter, the first operation mode and the second operation mode In an exhaust gas purification device for an internal combustion engine, which is configured to switch between modes as needed ,
As the amount of inert gas supplied to the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas supplied to the combustion chamber further increases, When the first operation mode is selected using an internal combustion engine in which the temperature of fuel and surrounding gas during combustion in the combustion chamber is lower than the soot generation temperature and soot is hardly generated. During the low-load operation, low-temperature combustion in which the amount of inert gas supplied into the combustion chamber is larger than the amount of inert gas at which the generation amount of soot becomes a peak is performed and little soot is generated, and the first operation mode is performed. Normal combustion is performed in which the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas at which the amount of soot generated at the time of selection and during engine high load operation is peaked, and Operation mode is selected Low-temperature combustion is performed at the time of engine low-load operation, sub-fuel injection is performed at the time of engine middle-load operation when the second operation mode is selected, and the main fuel injection timing is retarded. An exhaust gas purifying apparatus for an internal combustion engine , wherein normal combustion is performed when the second operation mode is selected and the engine is under a high load operation . The particulate filter carries an oxygen storage / active oxygen release agent, and active oxygen released from the oxygen storage / active oxygen release agent oxidizes trapped fine particles on the particulate filter. 2. The exhaust gas purification device for an internal combustion engine according to claim 1. The oxygen storage / active oxygen releasing agent takes in oxygen when there is excess oxygen in the surroundings, retains oxygen, and releases the retained oxygen in the form of active oxygen when the surrounding oxygen concentration decreases. Item 3. An exhaust gas purification device for an internal combustion engine according to item 2. The oxygen storage / active oxygen releasing agent binds and retains NO _X with oxygen when excess oxygen is present in the surroundings, and converts the combined NO _X and oxygen into NO _X and active oxygen when the surrounding oxygen concentration decreases. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the exhaust gas is decomposed and released. When the second operation mode is selected and the temperature of the particulate filter is likely to rise excessively, if low-temperature combustion is being performed, the air-fuel ratio is made lean, and auxiliary fuel injection is performed. The main fuel injection timing is advanced when the main fuel injection timing is retarded, and the fuel injection timing is advanced when normal combustion is performed. An exhaust purification device for an internal combustion engine according to any one of the above. 6. The exhaust gas purification of an internal combustion engine according to claim 5, wherein the sub fuel injection is stopped when the main fuel injection timing is advanced when the sub fuel injection is executed and the main fuel injection timing is retarded. apparatus. When the second operation mode is selected and the temperature of the particulate filter is likely to rise excessively, the combustion executed when the first operation mode is selected is interrupted and executed. An exhaust purification device for an internal combustion engine according to any one of claims 1 to 4 . The method according to claim 5, wherein whether the temperature of the particulate filter is likely to rise excessively is determined based on an elapsed time from when switching from the first operation mode to the second operation mode is performed. An exhaust gas purification apparatus for an internal combustion engine according to any one of claims 7 to 13. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 5 to 7, wherein it is determined whether or not the temperature of the particulate filter is likely to rise excessively based on the exhaust gas temperature . The exhaust system according to any one of claims 1 to 9, wherein switching from the first operation mode to the second operation mode is performed when it is estimated that a predetermined amount of fine particles has accumulated on the particulate filter. Purification device. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 10, wherein a catalyst having an oxidizing function is disposed on an upstream side of an exhaust gas flow of the particulate filter .

Images