JP4155065B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
Conventionally, a particulate filter for collecting particulates in the inflowing exhaust gas is disposed in the exhaust passage of the internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio, and the inflowing exhaust gas NO in exhaust gas flowing in when the air-fuel ratio is lean_XNO when storing the reducing agent in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in decreases_XNO is being reduced and stored_XNO decreases in quantity_XIn order to carry the catalyst on the particulate filter and oxidize and remove the particulates collected on the particulate filter, the particulate filter is maintained while maintaining the air-fuel ratio of the exhaust gas flowing into the particulate filter lean. 2. Description of the Related Art An exhaust gas purification apparatus for an internal combustion engine that performs a particulate oxidation action that raises the temperature to a target temperature and maintains the target temperature for a target time is known (see, for example, Patent Document 1).
[0003]
NO_XNO in the catalyst_XNot only sulfur, eg SO_XIs stored in the form of sulfate, NO in the form of sulfate_XSO stored in the catalyst_XIn order to reduce the amount of NO_XMaintain the temperature of the catalyst at, for example, 550 ° C. or higher and NO_XIt is also known that it is necessary to switch the air-fuel ratio of the exhaust gas flowing into the catalyst to the stoichiometric air-fuel ratio or rich (see, for example, Patent Document 1). According to this, NO_XEven if the temperature of the catalyst is high, the air-fuel ratio of the inflowing exhaust gas is lean, or even if the air-fuel ratio of the inflowing exhaust gas is rich, NO_XIf the temperature of the catalyst is low, NO_XFrom catalyst to SO_XWill not be discharged.
[0004]
[Patent Document 1]
JP 2002-155724 A
[Patent Document 2]
JP-A-53-100314
[Patent Document 3]
JP 2000-87734 A
[0005]
[Problems to be solved by the invention]
However, according to the present inventor, NO_XNO even if the average air-fuel ratio of the exhaust gas flowing into the catalyst is kept lean_XWhen the temperature of the catalyst increases, NO_XSO in exhaust gas flowing out of catalyst_XConcentration is NO_XSO in the exhaust gas flowing into the catalyst_XIt has been confirmed that the concentration is temporarily higher than the concentration. This is NO_XNO at higher catalyst temperatures_XSO stored in the catalyst_XIs discharged and this SO_XNO without forming sulfate_XIt means that it is stored in the catalyst. Therefore, if the particulate filter oxidizes the particulate filter, NO_XSO stored from catalyst without forming sulfate_XWill be discharged.
[0006]
However, since the air-fuel ratio of the inflowing exhaust gas is lean at this time, the stored SO is not formed without sulfate.₂Is NO_XSulfate SO in the catalyst₃Oxidized to sulfate SO₃NO in the form of_XThere is a risk of being discharged from the catalyst. NO_XFrom catalyst to SO₂Even if it is discharged as it is, NO_XWhen a catalyst having oxidizing ability is disposed downstream of the catalyst, the sulfate SO is contained in the auxiliary catalyst.₃There is a risk of oxidation.
[0007]
Accordingly, an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can reduce the amount of sulfate discharged into the atmosphere.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, according to a first invention, for collecting particulates in exhaust gas flowing into an exhaust passage of an internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio. When the air-fuel ratio of the particulate filter and the inflowing exhaust gas is lean or when its temperature is low, sulfur in the inflowing exhaust gas is stored without forming sulfate, and the air-fuel ratio of the inflowing exhaust gas is In order to oxidize and remove fine particles collected on the particulate filter by arranging a sulfur storage agent that reduces the amount of sulfur stored without forming a sulfate when it becomes rich or when its temperature rises In addition, while maintaining the air-fuel ratio of the exhaust gas flowing into the particulate filter lean, the temperature of the particulate filter is raised to the target temperature and the target temperature is reached for the target time. In the exhaust gas purification apparatus for an internal combustion engine that performs the fine particle oxidation action, the air-fuel ratio of the exhaust gas flowing into the sulfur storage agent coincides with the air-fuel ratio of the exhaust gas flowing into the particulate filter. In addition, the particulate filter and the sulfur storage agent are arranged so that the temperature of the sulfur storage agent increases when the temperature of the particulate filter increases, and the temperature of the sulfur storage agent also decreases when the temperature of the particulate filter decreases. Obtain the amount of sulfur stored in the sulfur storage agent without forming a salt, and control the particulate oxidation action based on the amount of sulfur stored in the sulfur storage agent without forming the sulfate. I am doing so.
[0009]
According to a second aspect, in the first aspect, the target temperature for the fine particle oxidation action is set based on the amount of sulfur stored in the sulfur storage agent without forming the sulfate. ing.
[0010]
Further, according to a third aspect, in the second aspect, the fine particle oxidation is performed so that when the amount of sulfur stored in the sulfur storage agent without forming the sulfate is large, it is lower than when it is small. The target temperature of action is set.
[0011]
According to a fourth aspect, in the second aspect, the target time for the fine particle oxidation action is set to be longer when the target temperature for the fine particle oxidation action is low than when it is high.
[0012]
According to a fifth aspect, in the second aspect, the target temperature of the fine particle oxidation action is such that when the elapsed time from the start of the fine particle oxidation action becomes longer, the elapsed time becomes higher than when the elapsed time is short. Is set.
[0013]
According to a sixth invention, in the first invention, the sulfur flows into the sulfur storage agent during the fine particle oxidation action based on the amount of sulfur stored in the sulfur storage agent without forming the sulfate. The oxygen concentration in the exhaust gas is controlled.
[0014]
Further, according to a seventh aspect, in the sixth aspect, the oxygen concentration is lower when the amount of sulfur stored in the sulfur storage agent without forming the sulfate is larger than when it is small. Is controlling.
[0015]
According to the eighth invention, in the first invention, the amount of fine particles collected on the particulate filter is obtained, and the amount of fine particles collected on the particulate filter is determined in advance. The particulate oxidation action is performed when the first threshold value is exceeded, and the amount of sulfur stored in the sulfur storage agent without forming the sulfate is predetermined. When the amount is larger than the allowable amount, the fine particle oxidation action is prohibited regardless of the amount of fine particles collected on the particulate filter.
[0016]
According to a ninth aspect, in the eighth aspect, the second threshold amount is set such that the amount of the fine particles collected on the particulate filter is set to be larger than the first threshold amount. When exceeding, the fine particle oxidation action is performed regardless of the amount of sulfur stored in the sulfur storage agent without forming the sulfate.
[0017]
According to a tenth aspect, in the eighth aspect, sulfur does not form the sulfate when the amount of fine particles collected on the particulate filter exceeds the first threshold amount. When the amount of sulfur stored in the storage agent is larger than the allowable amount, the particulate oxidation effect is reduced after reducing the amount of sulfur stored in the sulfur storage agent without forming sulfate. Like to do.
[0018]
According to an eleventh aspect, in the first aspect, when the amount of sulfur stored in the sulfur storage agent without forming the sulfate exceeds a predetermined limit, the sulfur storage agent The amount of sulfur stored in the sulfur accumulating agent is decreased without increasing the temperature of the sulfur without forming the sulfate.
[0019]
According to a twelfth aspect of the invention, in the eleventh aspect of the invention, the particulate oxidation action is performed in order to increase the temperature of the sulfur storage agent.
[0020]
According to a thirteenth aspect of the present invention, in the first aspect, the sulfur storage agent is mixed with NO in the exhaust gas flowing in when the air-fuel ratio of the flowing exhaust gas is lean._XNO when storing the reducing agent in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in decreases_XNO is being reduced and stored_XNO decreases in quantity_XIt is formed from a catalyst.
[0021]
According to a fourteenth aspect, in the first aspect, the sulfur storage agent is supported on the particulate filter.
[0022]
In this specification, the ratio of the air supplied into the exhaust passage upstream of a certain position of the exhaust passage, the combustion chamber, and the intake passage and the reducing agent such as hydrocarbon HC and carbon monoxide CO This is called the air-fuel ratio of the exhaust gas at the position.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a case where 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.
[0024]
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 Is an exhaust valve, and 10 is an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13. A throttle valve 17 driven by a step motor 16 is disposed in the intake duct 13, and a cooling device 18 for cooling intake air flowing through the intake duct 13 is disposed around the intake duct 13. In each of the embodiments according to the present invention, the throttle opening is maintained at the maximum opening in almost all operation regions, and is made smaller than the maximum opening when the required load L becomes considerably small, and when the required load L becomes zero, a small idle opening is performed. Done.
[0025]
On the other hand, the exhaust port 10 is connected to the inlet of the exhaust turbine 21 of the exhaust turbocharger 14 via the exhaust manifold 19 and the exhaust pipe 20, and the outlet of the exhaust turbine 21 is connected to the casing 22a via the exhaust pipe 20a. A particulate filter 22b for collecting particulates in the exhaust gas is accommodated in the casing 22a, and NO is applied to the particulate filter 22b as will be described later._XA catalyst 22 is supported. The catalytic converter 22 is connected to a casing 23a via an exhaust pipe 20b, and an auxiliary catalyst 23 having oxidation ability is accommodated in the casing 23a. In this case, NO_XThe air-fuel ratio of the exhaust gas flowing into the catalyst 22 matches the air-fuel ratio of the exhaust gas flowing into the particulate filter 22b, and NO_XThe temperature of the catalyst 22 also matches the temperature of the particulate filter 22b.
[0026]
Still referring to FIG. 1, 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 provided in the EGR passage 24. Be placed. A cooling device 26 for cooling the EGR gas flowing in the EGR passage 24 is disposed around the EGR passage 24.
[0027]
On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, so-called common rail 27, through a fuel supply pipe 6a. Fuel is supplied into the common rail 27 from an electrically controlled fuel pump 28 with variable discharge amount, and the fuel supplied into the common rail 27 is supplied to the fuel injection valve 6 via 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 a fuel pump 28 is set so that the fuel pressure in the common rail 27 becomes a target fuel pressure based on an output signal of the fuel pressure sensor 29. The discharge amount is controlled.
[0028]
The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41. A ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45 and an output port 46 It comprises. The output signal of the fuel pressure sensor 29 is input to the input port 45 via the corresponding AD converter 47. The exhaust pipe 20a upstream of the particulate filter 22b includes a pressure sensor 49 for detecting the pressure in the exhaust pipe 20a, that is, the engine back pressure, and NO._XAn air-fuel ratio sensor 50 for detecting the air-fuel ratio AFPM of the exhaust gas flowing into the catalyst 22 is attached, and NO_XNO in the exhaust pipe 20b downstream of the catalyst 22_XA temperature sensor 51 for detecting the temperature of the exhaust gas flowing out from the catalyst 22 is attached. The output voltages of these sensors 48, 49 and 50 are input to the input port 45 via the corresponding AD converters 47. Here, the air-fuel ratio sensor 50 is formed of an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas. The temperature of the exhaust gas detected by the temperature sensor 51 is NO._XThe temperature of the catalyst 22 is shown.
[0029]
A load sensor 53 that generates an output voltage proportional to the amount of depression of the accelerator pedal 52 is connected to the accelerator pedal 52, and the output voltage of the load sensor 53 is input to the input port 45 via the corresponding AD converter 47. Further, a crank angle sensor 54 that generates an output pulse every time the crankshaft rotates, for example, 30 ° is connected to the input port 45. The CPU 44 calculates the engine speed N based on the output pulse from the crank angle sensor 54. On the other hand, the output port 46 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 corresponding drive circuits 48.
[0030]
NO on the partition walls of the particulate filter 22a, for example, on both side surfaces of the partition walls and the inner wall surfaces of the pores._XEach catalyst 22 is supported. This NO_XThe catalyst 22 has, for example, alumina as a carrier, and an alkali metal such as potassium K, sodium Na, lithium Li and cesium Cs, an alkaline earth such as barium Ba and calcium Ca, lanthanum La and yttrium Y on the carrier. At least one selected from rare earths and a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir are supported.
[0031]
NO_XThe catalyst is NO when the average air-fuel ratio of the exhaust gas flowing in is lean._XNO when storing the reducing agent in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in decreases_XNO is being reduced and stored_XAccumulation and reduction action to reduce the amount of.
[0032]
NO_XThe detailed mechanism of the accumulation and reduction action of the catalyst has not been fully clarified. However, the mechanism currently considered can be briefly described as follows, taking as an example the case where platinum Pt and barium Ba are supported on a carrier.
[0033]
That is, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst becomes considerably leaner than the stoichiometric air-fuel ratio, the oxygen concentration in the inflowing exhaust gas greatly increases and oxygen O₂Is O₂ ⁻Or O^2-It adheres to the surface of platinum Pt. On the other hand, NO in the inflowing exhaust gas adheres to the surface of platinum Pt and O on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with NO₂(NO + O₂→ NO₂+ O^*Where O^*Is active oxygen). Then the generated NO₂Part of the NO is being oxidized further on platinum Pt_XNitrate ion NO while being absorbed in the catalyst and combined with barium oxide BaO₃ ⁻NO in the form of_XIt diffuses into the catalyst. In this way NO_XIs NO_XStored in the catalyst.
[0034]
In contrast, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst becomes rich or stoichiometric, the oxygen concentration in the exhaust gas decreases and NO₂Production amount decreases and the reaction proceeds in the reverse direction (NO₃ ⁻→ NO + 2O^*) And thus NO_XNitrate ion NO in the catalyst₃ ⁻NO in the form of NO_XReleased from the catalyst. This released NO_XWhen the exhaust gas contains a reducing agent, that is, HC or CO, it reacts with these HC and CO to be reduced. In this way, NO on the surface of platinum Pt._XNO when no longer exists_XNO from catalyst to next_XIs released and reduced, NO_XNO stored in the catalyst_XThe amount of is gradually reduced.
[0035]
NO without forming nitrate_XStore NO_XNO without releasing_XIt is also considered possible to reduce In addition, active oxygen O^*If you pay attention to, NO_XThe catalyst is NO_XWith the accumulation and release of oxygen^*It can also be regarded as an active oxygen generating catalyst that generates
[0036]
On the other hand, the auxiliary catalyst 23 is formed of a noble metal catalyst containing noble metal such as platinum Pt without containing alkali metal, alkaline earth, and rare earth in each embodiment according to the present invention. However, the auxiliary catalyst 23 is the NO described above._XYou may form from a catalyst.
[0037]
The internal combustion engine shown in FIG. 1 continues to burn under a lean air-fuel ratio, and therefore NO._XThe air-fuel ratio of the exhaust gas flowing into the catalyst 22 is maintained lean. As a result, NO in the exhaust gas_XIs NO_XIt is stored in the catalyst 22.
[0038]
NO over time_XAccumulated NO in catalyst 22_XThe amount increases gradually. Therefore, in each embodiment according to the present invention, NO is used._XAccumulated NO in catalyst 22_XDetermine the amount, NO_XAccumulated NO in catalyst 22_XAmount is NO_XWhen the allowable amount is exceeded, NO_XNO stored in catalyst 22_XNO_XAccumulated NO in catalyst 22_XNO to reduce the amount_XThe air-fuel ratio of the exhaust gas flowing into the catalyst 22 is temporarily switched to rich.
[0039]
By the way, sulfur content is SO._XIs included in the form of NO_XNO in the catalyst 22_XNot only SO_XCan also be stored. This SO_XNO_XThe accumulation mechanism in the catalyst 22 is NO._XThis is considered to be the same as the accumulation mechanism. That is, when the case where platinum Pt and barium Ba are supported on a carrier is simply described as an example, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst 22 is lean, as described above, the oxygen O₂Is O₂ ⁻Or O^2-Attached to the surface of platinum Pt in the form of SO₂Adheres to the surface of platinum Pt and O on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with SO₃It becomes. The generated SO₃NO is being oxidized on platinum Pt_XWhile being absorbed into the catalyst 22 and combined with barium oxide BaO, sulfate ions SO₄ ⁻NO in the form of_XIt diffuses into the catalyst 22. This sulfate ion SO₄ ⁻Then barium ion Ba⁺Combined with sulfate BaSO₄Is generated.
[0040]
This sulfate BaSO₄Is difficult to decompose, NO_XEven if the air-fuel ratio of the exhaust gas flowing into the catalyst 22 is simply rich, NO_XSulfate BaSO in catalyst 22₄The amount of does not decrease. For this reason, as time passes, NO_XSulfate BaSO in catalyst 22₄The amount of NO increases, resulting in NO_XNO that the catalyst 22 can store_XThe amount of will decrease.
[0041]
However, NO_XWhile maintaining the temperature of the catalyst 22 at a required temperature, for example, 550 ° C. or higher, NO_XWhen the average air-fuel ratio of the exhaust gas flowing into the catalyst 22 is made the stoichiometric air-fuel ratio or rich, NO_XSulfate BaSO in catalyst 22₄Decomposes into SO₃NO in the form of_XReleased from the catalyst 22. This released SO₃If exhaust gas contains a reducing agent, ie, HC or CO, it reacts with HC and CO to react with SO.₂To be reduced. In this way NO_XSulfate BaSO in the catalyst 22₄SO stored in the form of_XThe amount of NO decreases gradually, at this time NO_XFrom catalyst 22 to SO_XIs SO₃It will not leak out.
[0042]
Therefore, in the first embodiment according to the present invention, NO in the form of sulfate._XSO stored in catalyst 22_XThis amount of SO_XThe amount of SO determined in advance_XWhen the allowable amount is exceeded, NO in the form of sulfate_XSO stored in catalyst 22_XTo reduce the amount of NO_XWhile maintaining the temperature of the catalyst 22 at a required temperature, for example, 550 ° C. or higher, NO_XSO that switches the average air-fuel ratio of the exhaust gas flowing into the catalyst 22 slightly slightly_XProcessing is performed.
[0043]
NO_XThere are various methods for raising the temperature of the catalyst 22, such as NO._XAn electric heater is arranged at the upstream end of the catalyst 22, and NO is generated by the electric heater._XCatalyst 22 or NO_XA method of heating the exhaust gas flowing into the catalyst 22, NO_XNO is obtained by secondarily injecting fuel into the exhaust passage upstream of the catalyst 22 and burning the fuel._XNO2 by heating the catalyst 22 or increasing the temperature of exhaust gas discharged from the internal combustion engine._XThere is a method of increasing the temperature of the catalyst 22. Here, in order to raise the temperature of the exhaust gas discharged from the internal combustion engine, for example, the injection timing of the main fuel can be retarded, or in addition to the main fuel, an additional time can be added during the expansion stroke or the exhaust stroke. Fuel can also be injected.
[0044]
On the other hand, NO_XThere are various methods for temporarily switching the air-fuel ratio of the exhaust gas flowing into the catalyst 22 to rich. For example, a method of temporarily switching the air-fuel ratio of the exhaust gas discharged from the combustion chamber 5 to rich,_XThere is a method of temporarily injecting additional fuel or reducing agent into the exhaust passage upstream of the catalyst 22. Here, in order to switch the air-fuel ratio of the exhaust gas discharged from the combustion chamber 5 to rich, for example, the air-fuel ratio of the air-fuel mixture combusted in the combustion chamber 5 can be switched to rich, or the compression top dead center In addition to the main fuel injected nearby, additional fuel can be injected during the expansion stroke or the exhaust stroke.
[0045]
In the first embodiment according to the present invention, NO_XNO in the catalyst 22_XNO_XAccumulated NO in catalyst 22_XWhen the amount is to be decreased, additional fuel Qa is injected, for example, in the exhaust stroke, as shown in FIG. In contrast, NO_XAccumulated SO in catalyst 22_XWhen the amount should be decreased, as shown in FIG. 2 (II), for example, additional fuel Qa is injected in the expansion stroke. If it does in this way, it will be in the combustion chamber 5 or NO in additional fuel Qa._XThe amount of fuel combusted in the catalyst 22 increases, so NO_XNO while maintaining the temperature of the catalyst 22 high_XIt becomes possible to make the air-fuel ratio of the exhaust gas flowing into the catalyst 22 rich. In FIG. 2, Qm indicates the main fuel that is normally injected near the compression top dead center.
[0046]
Figure 3 shows NO in the form of sulfate._XSO stored in catalyst 22_XSO to reduce the amount of_XA processing routine is shown. This routine is executed by interruption every predetermined processing cycle time. Referring to FIG. 3, first, in step 100, the total value QF of the fuel amount injected from the fuel injection valve 6 from the previous processing cycle to the current processing cycle is added to the integrated value SQF (SQF = SQF + QF). NO in the form of sulfate_XSO stored in catalyst 22_XThe amount of NO is per unit time_XSO flowing into the catalyst 22_XDepending on the integrated value of the amount of NO per unit time_XSO flowing into the catalyst 22_XThis amount depends on the amount of fuel injected from the fuel injection valve 6. Therefore, the integrated value SQF obtained by integrating the total amount QF of the fuel injected from the fuel injection valve 6 and the additional fuel within a predetermined time is NO in the form of sulfate._XSO stored in catalyst 22_XRepresents the amount of.
[0047]
In the following step 101, the integrated value SQF is calculated as the SO described above._XIt is determined whether or not it is larger than an allowable value SQFA corresponding to the allowable amount. When SQF ≦ SQFA, the processing cycle is terminated. When QS> QSA, the process proceeds to step 102._XWhile maintaining the temperature of the catalyst 22 at, for example, 550 ° C. or higher, NO_XAdditional fuel Qa is injected for a certain period of time in the expansion stroke so that the air-fuel ratio of the exhaust gas flowing into the catalyst 22 becomes slightly rich. In the subsequent step 103, the integrated value SQF is cleared.
[0048]
On the other hand, fine particles mainly composed of carbon solid contained in the exhaust gas are collected on the particulate filter 22b. As described above, the internal combustion engine shown in FIG. 1 is continuously combusted under a lean air-fuel ratio, and NO_XSince the catalyst 22 has an oxidizing ability, if the temperature of the particulate filter 22b is maintained at a temperature at which particulates can be oxidized, for example, 250 ° C. or more, the particulates are oxidized and removed on the particulate filter 22b. The
[0049]
In this case, the above-mentioned NO_XNO of catalyst 22_XAccording to the accumulation and reduction mechanism of NO_XNO in the catalyst 22_XNO is also stored when_XActive oxygen is also generated when is released. This active oxygen is oxygen O₂Therefore, the particulates deposited on the particulate filter 22b are rapidly oxidized. That is, NO on the particulate filter 22b._XWhen the catalyst 22 is supported, the particulates deposited on the particulate filter 22b are oxidized regardless of whether the air-fuel ratio of the exhaust gas flowing into the particulate filter 22b is lean or rich. In this way, the fine particles are continuously oxidized.
[0050]
However, if the temperature of the particulate filter 22b is not maintained at a temperature that can oxidize the particulates or if the amount of particulates flowing into the particulate filter 22b per unit time becomes considerably large, the particulates that accumulate on the particulate filter 22b. Gradually increases, and the pressure loss of the particulate filter 22b increases.
[0051]
Therefore, in the first embodiment according to the present invention, for example, when the amount of particulates deposited on the particulate filter 22b exceeds the allowable amount of particulates, the air-fuel ratio AFPM of the exhaust gas flowing into the particulate filter 22b is maintained lean while maintaining the particulates. Fine particle oxidation is performed such that the temperature T of the curate filter 22b is raised to the target temperature TPM and maintained at the target temperature TPM for the target time tPM. When this fine particle oxidation action is performed, the fine particles deposited on the particulate filter 22b are ignited and burned and removed.
[0052]
More specifically, in the first embodiment according to the present invention, as shown by the arrow X in FIG. 4, when the engine back pressure P detected by the pressure sensor 49 becomes higher than the first threshold value P1, It is determined that the amount of fine particles deposited on the particulate filter 22b has exceeded the allowable fine particle amount. At this time, the fine particle oxidation action is started, that is, the temperature T of the particulate filter 22b is raised. Next, when the temperature T of the particulate filter 22b reaches the target temperature TPM, the target temperature TPM is maintained, and then when the target time tPM has elapsed since the start of the particulate oxidation action, the particulate oxidation action is stopped, and therefore the particulate filter. The temperature T of 22b falls. Note that the target time tPM shown in FIG. 4 is the time during which the particulate oxidation action is performed, but also represents the time during which the temperature T of the particulate filter 22b is maintained at the target temperature TPM. Further, the target time tPM is a time necessary for making the amount of deposited fine particles on the particulate filter 22b substantially zero, for example.
[0053]
Further, in the first embodiment according to the present invention, when the particulate oxidation action is to be performed, as shown in FIG. 2 (III), for example, additional fuel Qa is injected in the expansion stroke. For this reason, the air-fuel ratio AFPM of the exhaust gas flowing into the particulate filter 22b is slightly reduced during the particulate oxidation action. In this case, when the temperature T of the particulate filter 22b is lower than the target temperature TPM, for example, the additional fuel Qa is increased, and the temperature of the exhaust gas discharged from the internal combustion engine is increased. On the other hand, when the temperature T of the particulate filter 22b is higher than the target temperature TPM, for example, the additional fuel Qa is reduced, and the temperature of the exhaust gas discharged from the internal combustion engine is lowered. In this way, the temperature T of the particulate filter 22b is maintained at the target temperature TPM.
[0054]
However, as I mentioned at the beginning, NO_XEven if the average air-fuel ratio AFPM of the exhaust gas flowing into the catalyst 22 is maintained lean, NO_XWhen the temperature of the catalyst 22 increases, NO_XSO in the exhaust gas flowing out from the catalyst 22_XConcentration is NO_XSO in the exhaust gas flowing into the catalyst 22_XIt has been confirmed that the concentration is temporarily higher than the concentration. This is NO_XWhen the temperature of the catalyst 22 increases, NO_XSO stored in catalyst 22_XIs discharged and this SO_XNO without forming sulfate_XIt means that it is stored in the catalyst 22.
[0055]
This SO_XWhat is NO_XWhether it is stored in the catalyst 22 is not necessarily clear, but is considered to be stored as follows. That is, as described above, NO_XSO in the exhaust gas flowing into the catalyst 22₂Is first stored, for example, in the form of sulfate after depositing on the platinum Pt surface. NO in the form of sulfate_XSO stored in catalyst 22_XWhen the amount of SO is small, SO deposited on the platinum Pt surface₂Form sulfates relatively easily. However, SO stored in sulfate form_XAs the amount of SO increases, the SO adhering to the platinum Pt surface₂Becomes difficult to form sulfate, SO₂It continues to adhere on the platinum Pt surface. In this way SO_XCan be stored without forming sulfate. Like this, NO_XSO stored in the form of sulfate in the catalyst 22_XIf so, SO can be stored without forming sulfate._XThere will be.
[0056]
For example, the particulate oxidation action is started and NO_XWhen the temperature of the catalyst 22 is, for example, 300 ° C. or higher, the stored SO is formed without forming a sulfate.₂Is NO_XIt is discharged from the catalyst 22. NO at this time_XSince the air-fuel ratio of the exhaust gas flowing into the catalyst 22 is maintained lean, this SO₂Is NO_XSulfate SO in the catalyst 22 or in the auxiliary catalyst 23₃There is a risk of oxidation.
[0057]
Therefore, in each example according to the present invention, NO is formed without forming a sulfate._XSO stored in catalyst 22_XThis amount of SO_XThe fine particle oxidation action is controlled on the basis of the amount of.
[0058]
NO without forming sulfate_XSO stored in catalyst 22_XIt is difficult to directly determine the amount. However, NO in the form of sulfate_XSO stored in catalyst 22_XWhen the integrated value SQF representing the amount of sulfur is small, the sulfate is easily formed as described above, and therefore the SO that can be stored without forming the sulfate._XWhen the integrated value SQF becomes large and the accumulated value SQF becomes large, it is difficult to form sulfates, so SO that can be stored without forming sulfates._XThe amount of
[0059]
Then, the integrated value SQF is NO in the form of sulfate._XSO stored in catalyst 22_XNot only represents the amount of NO, but also NO without forming sulfate_XSO stored in catalyst 22_XIt means that the amount of. NO in the form of sulfate_XSO stored in catalyst 22_XAmount of NO_XSO flowing into the catalyst 22_XConsidering that it is required based on the amount of NO, NO without forming sulfate_XSO stored in catalyst 22_XNo amount of NO_XSO flowing into the catalyst 22_XIt will be determined based on the amount of.
[0060]
In the first embodiment according to the present invention, NO is formed without forming sulfate._XSO stored in catalyst 22_XRepresents the amount of SO_XThe count value QS is set as the integrated value SQF. On top of that, this SO_XWhen the count value QS is larger than the allowable value QSA, the particulate oxidation action is prohibited.
[0061]
That is, when the engine back pressure P becomes higher than the first threshold value P1 as shown by the arrow X in FIG._XWhen the count value QS is larger than the allowable value QSA, the particulate oxidation action is not performed, that is, the particulate oxidation action is prohibited. SO_XThe count value QS is large, so NO without forming sulfate_XSO stored in catalyst 22_XThis is because if a fine particle oxidation action is performed when the amount of selenium is large, a high concentration of sulfate may be discharged into the atmosphere.
[0062]
NO without forming sulfate_XSO stored in catalyst 22_XIs NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst 22 becomes rich, NO_XEven if the temperature of the catalyst 22 is relatively low, the SO₂NO in the form of_XIt is discharged from the catalyst 22. NO_XWhen the air-fuel ratio AFPM of the exhaust gas flowing into the catalyst 22 is rich, the air-fuel ratio of the exhaust gas flowing into the auxiliary catalyst 23 is also rich, and therefore NO._XSO discharged from the catalyst 22₂Is sulphate SO even in the auxiliary catalyst 23.₃Not oxidized until.
[0063]
Therefore, when QS> QSA, as shown in FIG. 5, NO is formed without forming sulfate._XSO stored in catalyst 22_XIn order to reduce the amount of NO, for example to almost zero, NO_XA rich process for temporarily changing the air-fuel ratio AFPM of the exhaust gas flowing into the catalyst 22 to rich is performed.
[0064]
In this case, NO_XThe air-fuel ratio AFPM of the exhaust gas flowing into the catalyst 22 is held at the target rich air-fuel ratio AFNS for the target time tNS. These target rich air-fuel ratio AFNS and target time tNS can be made constant. However, NO without forming sulfate_XSO stored in catalyst 22_XWhen the amount of NO is large, NO is not formed without the formation of sulfate compared to when it is small._XSO stored in catalyst 22_XThe amount of reducing agent required to reduce the amount of is increased. Therefore, the target rich air-fuel ratio AFNS and the target time tNS are set to SO._XIt can also be set according to the count value QS. That is, as shown in FIG._XThe target rich air-fuel ratio AFNS can be set so as to be smaller when the count value QS is large than when it is small, or as shown in FIG._XThe target time tNS can be set to be longer when the count value QS is large than when it is small. When the rich process is to be performed, for example, as shown in FIG. 2I, additional fuel Qa is injected in the exhaust stroke.
[0065]
In rich processing, NO_XThe temperature of the catalyst 22 is set to the SO described above._XIt is not necessary to exceed the temperature required for processing. Therefore, in the rich processing of the first embodiment according to the present invention, NO is used._XNO while keeping the temperature of the catalyst 22 from exceeding the required temperature_XThe air-fuel ratio AFPM of the exhaust gas flowing into the catalyst 22 is temporarily switched to rich.
[0066]
Next, when the rich process is completed, as shown in FIG._XThe count value QS is cleared, and then the particulate oxidation action is started. At this time, NO without forming sulfate_XSO stored in catalyst 22_XThe amount of sulfite is almost zero, so even if the fine particle oxidation action is performed, sulfate SO₃There is no fear of being discharged.
[0067]
Even when the engine back pressure P becomes higher than the first threshold value P1, the SO_XIf the count value QS is larger than the allowable value QSA, the particulate oxidation action is prohibited. However, when the engine back pressure P is higher than the second threshold P2, which is higher than the first threshold P1, the SO_XRegardless of the count value QS, fine particle oxidation is performed. If the rich processing is performed by prohibiting the particulate oxidation action when the amount of the deposited particulate on the particulate filter 22b is large, the amount of the deposited particulate may be considerably increased when the rich processing is completed. When the particulate oxidation action is performed in this state, the deposited particulates on the particulate filter 22b are oxidized at the same time, and as a result, the temperature T of the particulate filter 22b is rapidly increased locally and the particulate filter 22b may be melted. is there. Therefore, when the engine back pressure P is higher than the second threshold value P2, and therefore the amount of deposited particulates on the particulate filter 22b is considerably large, the particulate oxidation action is not prohibited, and the deposited particulates are immediately oxidized and removed. Yes.
[0068]
However, at this time SO_XIn some cases, the count value QS is large. Therefore, if fine particle oxidation is performed in this state, a high concentration of sulfate SO is obtained.₃As described above, there is a risk that the gas will be discharged. Therefore, in the first embodiment according to the present invention, the control parameter of the particulate oxidation action is set to SO._XIt is set based on the count value QS.
[0069]
That is, in the first embodiment according to the present invention, as shown in FIG._XWhen the count value QS is large, the target temperature TPM is set lower than when the count value QS is small. NO without forming sulfate_XSO stored in catalyst 22_XNO per unit time_XThe amount discharged from the catalyst 22 is NO._XIt increases as the temperature T of the catalyst 22 increases. So, SO_XThe count value QS is large, so NO without forming sulfate_XSO stored in catalyst 22_XNO when there is a lot of_XThe temperature T of the catalyst 22 is prevented from becoming high.
[0070]
When the target temperature TPM is low, the oxidation rate of the deposited fine particles on the particulate filter 22b is low, that is, it takes a long time to oxidize almost all the deposited fine particles on the particulate filter 22b. Therefore, in the first embodiment according to the present invention, the target time tPM is made longer when the target temperature TPM is low than when it is high.
[0071]
That is, SO_XWhen the count value QS is small, the target temperature TPM is raised and the target time tPM is shortened as shown in FIG. In contrast, SO_XWhen the count value QS is large, the target temperature TPM is lowered as shown in FIG. 8B, and the target time tPM is lengthened. In this way, a high concentration of sulfate SO in the atmosphere.₃The particulate matter deposited on the particulate filter 22b can be surely oxidized and removed while preventing the discharge of water.
[0072]
Here, as shown in FIG. 7, the target temperature TPM is set between a lower limit value TL, eg, 300 ° C., and an upper limit value UL, eg, 650 ° C. This is because when the temperature T of the particulate filter 22b is lower than the lower limit value TL, the oxidation of the fine particles is not promoted, and when the temperature T is higher than the upper limit value UL, the particulate filter 22b may be melted.
[0073]
Further, when the engine back pressure P becomes higher than the first threshold value P1, the SO_XEven when the count value QS is smaller than the allowable value QSA, the SO_XThe target temperature TPM and the target time tPM are set based on the count value QS, and the particulate oxidation action is performed according to the target temperature TPM and the target time tPM.
[0074]
FIG. 9 shows an exhaust purification control routine of the first embodiment according to the present invention. This routine is executed by interruption every predetermined processing cycle time.
[0075]
Referring to FIG. 9, first, at step 110, the integrated value SQF obtained at step 100 of FIG._XThe count value is QS. In the following step 111, it is determined whether or not the engine back pressure P is higher than the first threshold value P1. When P ≦ P1, the processing cycle is terminated. When P> P1, the routine proceeds to step 112, where SO_XIt is determined whether or not the count value QS is larger than the allowable value QSA. When QS ≦ QSA, the routine proceeds to step 113 where the particulate oxidation action routine is executed. This fine particle oxidation action routine is shown in FIG.
[0076]
On the other hand, when QS> QSA, the routine proceeds to step 114 where it is judged if the engine back pressure P is higher than the second threshold value P2. When P> P2, the routine proceeds to step 113 where a particulate oxidation action routine is executed. When P ≦ P2, the routine proceeds to step 115 where the rich processing routine is executed. This rich processing routine is shown in FIG. Next, the routine proceeds to step 113, where the particulate oxidation action routine is executed.
[0077]
Referring to FIG. 10 showing the particulate oxidation action routine, first, at step 120, the target temperature TPM is calculated from the map of FIG. 7, and at step 121, the target time tPM is calculated from the map of FIG. Additional fuel Qa is injected during the stroke. In the following step 123, it is determined whether or not the target time tPM has elapsed since the particulate oxidation action was started. When the target time tPM has not elapsed, the process returns to step 122, and when the target time tPM has elapsed, the processing cycle is terminated.
[0078]
Referring to FIG. 11 showing the rich processing routine, first, at step 130, the target rich air-fuel ratio AFNS is calculated from the map of FIG. 6A, and at step 131, the target time tNS is calculated from the map of FIG. 6B. In the subsequent step 132, additional fuel Qa is injected into the exhaust stroke. In the following step 133, it is determined whether or not the target time tNS has elapsed since the rich process was started. When the target time tNS has not elapsed, the routine returns to step 132, and when the target time tNS has elapsed, the routine proceeds to step 134 where SO_XThe count value QS is cleared.
[0079]
Next, a second embodiment according to the present invention will be described.
[0080]
Aside from when the above-described rich treatment is performed immediately before, as the elapsed time from the start of the particulate oxidation action becomes longer, NO is not formed without forming a sulfate._XSO stored in catalyst 22_XThe amount of is gradually reduced. Thus, NO without forming sulfate_XSO stored in catalyst 22_XWhen the amount of the particulate matter decreases, even if the temperature T of the particulate filter 22b increases, the high concentration sulfate SO₃Is not discharged.
[0081]
Therefore, in the second embodiment according to the present invention, the target temperature TPM of the fine particle oxidation action is set so that the longer the elapsed time after the fine particle oxidation action is started, the higher the elapsed time is. That is, in the example shown in FIG. 12, every time the particulate oxidation action is performed for the time dt, the target temperature TPM is increased stepwise from the initial value TPMi by dT. This initial value TPMi can be obtained from, for example, the map of FIG. When the target temperature TPM is raised to the upper limit temperature TMAX, the target temperature TPM is held at the upper limit temperature TMAX.
[0082]
FIG. 13 shows the fine particle oxidation routine of the second embodiment according to the present invention. This particulate oxidation action routine is executed in step 113 of FIG.
[0083]
Referring to FIG. 13, first, at step 140, TPM is calculated from the map of FIG. 7, and this TPM is set as the initial value TPMi of the target temperature. In the subsequent step 141, the target time tPM is calculated from the map of FIG. 7, and in the subsequent step 142, for example, additional fuel Qa is injected during the expansion stroke. In the next step 143, it is determined whether or not the target time tPM has elapsed since the particulate oxidation action was started. When the target time tPM has not elapsed, the routine proceeds to step 144, where the target temperature TPM is updated according to the map of FIG. 12, for example, and then the routine returns to step 142. Next, when the target time tPM has elapsed, the processing cycle is terminated.
[0084]
Since the other configuration and operation of the exhaust gas purification apparatus are the same as those of the first embodiment described above, description thereof is omitted.
[0085]
Next, a third embodiment according to the present invention will be described.
[0086]
NO_XSO discharged from the catalyst 22_XSulfate SO₃As mentioned above, NO is discharged in the form of NO._XSO in the catalyst 22₂Sulfate SO₃This is thought to be due to oxidation. Then, even if fine particle oxidation is performed, sulfate SO₃If you can suppress the oxidation to NO_XSulfate SO discharged from the catalyst 22₃The amount of can be suppressed. On the other hand, sulfate SO₃NO is easily oxidized to NO_XThis depends on the oxygen concentration in the exhaust gas flowing into the catalyst 22.
[0087]
Therefore, in the third embodiment according to the present invention, NO is formed without forming sulfate._XSO stored in catalyst 22_XNO during the fine particle oxidation so that it is lower than when it is small when the amount is large_XThe oxygen concentration in the exhaust gas flowing into the catalyst 22 is controlled. Specifically, SO_XWhen the count value QS is large, the target lean air-fuel ratio AFL is set so as to be smaller than when the count value QS is small._XThe air-fuel ratio AFPM of the exhaust gas flowing into the catalyst 22 is controlled so as to coincide with the target lean air-fuel ratio AFL. In this case, when the air-fuel ratio AFPM of the inflowing exhaust gas is leaner than the target lean air-fuel ratio AFL, for example, the additional fuel Qa is increased, and when the air-fuel ratio AFPM of the inflowing exhaust gas is richer than the target lean air-fuel ratio AFL, for example The fuel Qa is reduced.
[0088]
As a result, sulfate SO₃The particulates deposited on the particulate filter 22b can be surely oxidized and removed while suppressing the generation of. In the third embodiment according to the present invention, the target temperature TPM and the target time tPM of the particulate oxidation action are set to constant values.
[0089]
FIG. 15 shows a fine particle oxidation routine according to the third embodiment of the present invention. This particulate oxidation action routine is executed in step 113 of FIG.
[0090]
Referring to FIG. 15, first, at step 150, the target lean air-fuel ratio AFPM is calculated from the map of FIG. 14, and at subsequent step 151, for example, additional fuel Qa is injected during the expansion stroke. In the subsequent step 152, it is determined whether or not the target time tPM has elapsed since the particulate oxidation action was started. When the target time tPM has not elapsed, the process returns to step 151, and when the target time tPM has elapsed, the processing cycle ends.
[0091]
In the third embodiment according to the present invention, as in the embodiment described with reference to FIGS. 12 and 13, the target lean air-fuel ratio AFL is increased as the elapsed time of the particulate oxidation action becomes longer. Also good.
[0092]
Since the other configuration and operation of the exhaust gas purification apparatus are the same as those of the first embodiment described above, description thereof is omitted.
[0093]
Next, a fourth embodiment according to the present invention will be described.
[0094]
First, the SO in FIG._XThe SO of the fourth embodiment according to the present invention with reference to the processing routine_XProcessing will be described. This routine is executed by interruption every predetermined processing cycle time.
[0095]
Referring to FIG. 16, first, in step 160, the total value QF of the fuel amount injected from the fuel injection valve 6 from the previous processing cycle to the current processing cycle is added to the integrated value SQF (SQF = SQF + QF). This integrated value SQF is NO in the form of sulfate._XSO stored in catalyst 22_XRepresents the amount. In the following step 161, the integrated value SQF is SO._XIt is determined whether or not it is larger than an allowable value SQFA corresponding to the allowable amount. When SQF ≦ SQFA, the processing cycle is terminated. When QS> QSA, the routine proceeds to step 162, where it is determined whether or not the required load L is higher than a set load X (N) determined as a function of the engine speed N. Determined. When L ≦ X (N), the processing cycle is terminated. On the other hand, when L> X (N), the routine proceeds to step 163, where NO_XWhile maintaining the temperature of the catalyst 22 at, for example, 550 ° C. or higher, NO_XAdditional fuel Qa is injected for a certain period of time in the expansion stroke so that the air-fuel ratio of the exhaust gas flowing into the catalyst 22 becomes slightly rich. In the following step 164, the integrated value SQF is cleared.
[0096]
That is, as shown in FIG. 17, since the combustion temperature is low during low load operation where the required load L is lower than the set load X (N), NO_XIn order to maintain the temperature of the catalyst 22 at, for example, 550 ° C. or higher, a large amount of additional fuel Qa is required. On the other hand, since the combustion temperature is high during a high load operation in which the required load L is higher than the set load X (N), a large amount of additional fuel Qa is not required.
[0097]
Therefore, in the fourth embodiment according to the present invention, when SQF> SQFA, when L ≦ X (N), SO_XNo processing is performed, and SQF> SQFA, and if L> X (N), SO_XProcessing is performed. In this way, NO_XNO in the form of sulfate from the catalyst 22_XSO stored in catalyst 22_XThe amount of fuel required to reduce the amount of fuel can be reduced.
[0098]
Such SO_XOnce treated, NO in the form of sulfate_XSO stored in catalyst 22_XAs well as the amount of NO without forming sulfate_XSO stored in catalyst 22_XThe amount of_XSince the air-fuel ratio of the exhaust gas flowing into the catalyst 22 is rich, the sulfate SO₃Is not generated.
[0099]
In the fourth embodiment according to the present invention, the particulate oxidation action is performed when the engine back pressure P exceeds the threshold value PA. However, this threshold PA is equal to the previous SO._XIt is set according to the elapsed time tSR after the processing is performed, and in the example shown in FIG. 18, it is set to be smaller when the elapsed time tSR is longer than when it is shorter.
[0100]
More specifically, as shown in FIGS. 19A and 19B, when the engine back pressure P exceeds a threshold value PA, a particulate oxidation action is performed as indicated by an arrow Z. Here, when the elapsed time tSR is short and therefore the threshold value PA is large, as shown in FIG. 19A, the time from the previous fine particle oxidation action to the next fine particle oxidation action is performed. The interval INT becomes longer, and the frequency of performing the fine particle oxidation action becomes lower. On the other hand, when the elapsed time tSR is long and the threshold value PA is small, as shown in FIG. 19B, the time interval INT is shortened, and the execution frequency of the particulate oxidation action is increased.
[0101]
As mentioned above, NO without forming sulfate_XSO stored in catalyst 22_XIf the fine particle oxidation action is performed when the amount of sulfite is large, a high concentration of sulfate SO₃May be released into the atmosphere. However, conversely, NO without forming sulfate_XSO stored in catalyst 22_XIf the fine particle oxidation action is performed while the amount of sulfite is small, a high concentration of sulfate SO₃Will not be discharged. This is the basic concept of the fourth embodiment according to the present invention.
[0102]
SO_XUnless treated, NO in the form of sulfate_XSO stored in catalyst 22_XThe amount of NO does not decrease, so as the elapsed time tSR increases, NO in the sulfate form_XSO stored in catalyst 22_XThe amount of increases gradually. Thus, the elapsed time tSR is NO in the form of sulfate._XSO stored in catalyst 22_XRepresents the amount.
[0103]
On the other hand, as described above, NO in the form of sulfate._XSO stored in catalyst 22_XWhen there is a large amount of SO, compared to when it is small, SO_XNO without forming sulfate_XEasily stored in the catalyst 22, so NO without forming sulfate_XSO stored in catalyst 22_XIt is believed that the amount of increases rapidly.
[0104]
Therefore, NO without forming sulfate_XSO stored in catalyst 22_XIn order to perform fine particle oxidation while the amount of NO is small, NO in the form of sulfate_XSO stored in catalyst 22_XIt is necessary to shorten the time interval INT of the fine particle oxidation action when the amount of is large is smaller than when it is small.
[0105]
Therefore, in the fourth embodiment according to the present invention, the threshold value PA is made smaller when the elapsed time tSR is longer than when it is shorter.
[0106]
As described above with reference to FIG. 16, in the fourth embodiment according to the present invention, NO in the form of sulfate._XSO stored in catalyst 22_XAmount of SO_XEven if the allowable amount is exceeded, as long as the engine low load operation with L ≦ X (N) is performed, SO_XProcessing is not performed. Therefore, NO in the form of sulfate_XSO stored in catalyst 22_XThe amount of NO may be significantly increased, and at this time NO without forming sulfate._XSO stored in catalyst 22_XThe amount of can be quite large.
[0107]
Even in such a case, in the fourth embodiment according to the present invention, since the frequency of the fine particle oxidation action is increased, NO is formed without forming sulfate._XSO stored in catalyst 22_XIs prevented from increasing, and therefore high concentrations of sulfate SO₃Is prevented from being discharged.
[0108]
Sulfate SO discharged into the atmosphere when fine particle oxidation is performed₃The amount of NO is NO without the formation of sulfate at the start of particulate oxidation._XSO stored in catalyst 22_XThis SO is determined according to the amount of_XIs determined in accordance with the threshold value PA. In the fourth embodiment according to the present invention, the sulfate SO discharged into the atmosphere when the particulate oxidation action is performed.₃The threshold value PA is set in advance so that the amount is maintained below the allowable limit.
[0109]
By the way, NO is formed without forming sulfate at the time when the particulate oxidation action is started in this way._XSO stored in catalyst 22_XFocusing on the amount of NO, in the fourth embodiment according to the present invention, NO is formed without forming sulfate._XSO stored in catalyst 22_XIt can also be seen that the particulate oxidation action is performed when the amount exceeds a certain fixed amount. In this case, a certain amount is the sulfate SO described above.₃This is equivalent to the allowable limit for and is hereinafter referred to as a limit amount.
[0110]
NO without forming sulfate_XSO stored in catalyst 22_XWhen the amount of SO exceeds this limit_XThe rich process described with reference to the process and FIGS. 5 and 6 may be performed. However, considering the fuel consumption rate and engine back pressure, the particulate oxidation action is preferable.
[0111]
Therefore, generally speaking in the fourth embodiment according to the present invention, NO is formed without forming a sulfate._XSO stored in catalyst 22_XWhen the amount exceeds the predetermined limit, NO_XNO without increasing the temperature of the catalyst 22 to form sulfate_XSO stored in catalyst 22_XIt means that the amount of is reduced.
[0112]
FIG. 20 shows an exhaust purification control routine of the fourth embodiment according to the present invention. This routine is executed by interruption every predetermined processing cycle time.
[0113]
Referring to FIG. 20, first, in step 170, the previous SO._XAn elapsed time tSR after the processing is performed is calculated. In the subsequent step 171, the threshold value PA is calculated from the map of FIG. In the following step 172, it is determined whether or not the engine back pressure P is higher than a threshold value PA. When P ≦ PA, the processing cycle is terminated, and when P> PA, the routine proceeds to step 173, where, for example, a particulate oxidation action routine shown in FIG. 10 is executed.
[0114]
Since the other configuration and operation of the exhaust gas purification apparatus are the same as those of the first embodiment described above, description thereof is omitted.
[0115]
In each of the embodiments according to the present invention described so far, NO_XThe catalyst 22 is supported on the particulate filter 22b. However, NO_XThe catalyst 22 may be formed separately from the particulate filter 22b and disposed in the exhaust passage downstream of the particulate filter 22b. Further, as in each of the embodiments according to the present invention described above, by controlling the air-fuel ratio and temperature of the exhaust gas discharged from the internal combustion engine, NO._XIf the air-fuel ratio and temperature of the exhaust gas flowing into the catalyst 22 or the particulate filter 22b are controlled, NO_XThe catalyst 22 may be disposed in the exhaust passage upstream of the particulate filter 22b.
[0116]
【The invention's effect】
The amount of sulfate discharged into the atmosphere can be reduced.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
FIG. 2 is a diagram for explaining an additional fuel.
FIG. 3 SO_XIt is a flowchart which shows a process routine.
FIG. 4 is a view for explaining a fine particle oxidizing action.
FIG. 5 is a diagram for explaining a first embodiment according to the present invention;
FIG. 6 is a diagram showing a target rich air-fuel ratio AFNS and a target time tNS.
FIG. 7 is a diagram showing a target temperature TPM and a target time tPM.
FIG. 8 is a diagram for explaining a difference in temperature change.
FIG. 9 is a flowchart for executing an exhaust purification control routine.
FIG. 10 is a flowchart for executing a fine particle oxidation routine.
FIG. 11 is a flowchart for executing a rich processing routine;
FIG. 12 is a diagram showing a change in a target temperature TPM.
FIG. 13 is a flowchart for executing a particulate oxidation action routine according to a second embodiment of the present invention.
FIG. 14 is a diagram showing a target lean air-fuel ratio AFL.
FIG. 15 is a flowchart for executing a fine particle oxidation action routine according to a third embodiment of the present invention;
FIG. 16 shows SO of the fourth embodiment according to the present invention._XIt is a flowchart for performing a processing routine.
FIG. 17 is a diagram showing a set load X (N).
FIG. 18 is a diagram showing a threshold value PA.
FIG. 19 is a diagram for explaining a time interval INT.
FIG. 20 is a flowchart for executing an exhaust purification control routine of a fourth embodiment according to the present invention.
[Explanation of symbols]
1 ... Engine body
20a, 20b ... exhaust pipe
22 ... NO_Xcatalyst
22a ... Particulate filter

Claims (14)

In the exhaust passage of the internal combustion engine where the combustion is continuously performed under the lean air-fuel ratio, the particulate filter for collecting particulates in the inflowing exhaust gas, and the air-fuel ratio of the inflowing exhaust gas is lean When or when the temperature is low, sulfur in the inflowing exhaust gas is stored without forming sulfate, and when the air-fuel ratio of the inflowing exhaust gas becomes rich or the temperature becomes high, sulfate is formed. In order to oxidize and remove fine particles collected on the particulate filter, an air-fuel ratio of the exhaust gas flowing into the particulate filter is set. An internal combustion engine that performs particulate oxidation that raises the temperature of the particulate filter to a target temperature and maintains the target temperature for a target time while maintaining a lean state. When the temperature of the particulate filter rises so that the air-fuel ratio of the exhaust gas flowing into the sulfur storage agent coincides with the air-fuel ratio of the exhaust gas flowing into the particulate filter, the sulfur storage agent The particulate filter and the sulfur storage agent are arranged so that the temperature of the particulate filter rises and the temperature of the sulfur storage agent decreases when the temperature of the particulate filter decreases, and it is stored in the sulfur storage agent without forming sulfate. An exhaust emission control device for an internal combustion engine, wherein the amount of sulfur being obtained is determined, and the particulate oxidation action is controlled based on the amount of sulfur stored in the sulfur storage agent without forming the sulfate. The exhaust emission control device for an internal combustion engine according to claim 1, wherein a target temperature of the particulate oxidation action is set based on the amount of sulfur stored in the sulfur storage agent without forming the sulfate. 3. The internal combustion engine according to claim 2, wherein the target temperature of the fine particle oxidation action is set so as to be lower when the amount of sulfur stored in the sulfur storage agent without forming the sulfate is larger than when it is small. Exhaust purification equipment. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the target time for the fine particle oxidation action is set to be longer when the target temperature for the fine particle oxidation action is low than when it is high. The exhaust emission control device for an internal combustion engine according to claim 2, wherein the target temperature of the fine particle oxidation action is set so that the elapsed time from the start of the fine particle oxidation action becomes longer than that when the elapsed time is short. . The oxygen concentration in the exhaust gas flowing into the sulfur storage agent during the particulate oxidation action is controlled based on the amount of sulfur stored in the sulfur storage agent without forming the sulfate. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1. The exhaust emission control device for an internal combustion engine according to claim 6, wherein the oxygen concentration is controlled to be lower when the amount of sulfur stored in the sulfur accumulating agent without forming the sulfate is large than when it is small. . When the amount of fine particles collected on the particulate filter is determined and the amount of fine particles collected on the particulate filter exceeds a predetermined first threshold amount, the fine particle oxidation is performed. When the amount of sulfur stored in the sulfur storage agent without forming the sulfate is larger than a predetermined allowable amount, it is collected on the particulate filter. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the particulate oxidation action is prohibited regardless of the amount of particulates that are applied. When the amount of fine particles collected on the particulate filter exceeds a second threshold amount set larger than the first threshold amount, the sulfur storage agent is formed without forming the sulfate. The exhaust emission control device for an internal combustion engine according to claim 8, wherein the particulate oxidation action is performed regardless of the amount of sulfur stored in the interior. When the amount of the fine particles collected on the particulate filter exceeds the first threshold amount, the amount of sulfur stored in the sulfur storage agent without forming the sulfate is the allowable amount. 9. The exhaust gas purification of an internal combustion engine according to claim 8, wherein the particulate oxidation action is performed after the amount of sulfur stored in the sulfur storage agent is reduced without forming a sulfate salt when the amount is greater than apparatus. When the amount of sulfur stored in the sulfur storage agent without forming the sulfate exceeds a predetermined limit, the temperature of the sulfur storage agent is increased to form sulfur without forming the sulfate. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the amount of sulfur stored in the storage agent is reduced. The exhaust emission control device for an internal combustion engine according to claim 11, wherein the particulate oxidation action is performed in order to raise the temperature of the sulfur storage agent. The sulfur storage agent, the air-fuel ratio of the inflowing exhaust gas is stored in the NO _X in the exhaust gas flowing at the time of the lean air-fuel ratio of the inflowing exhaust gas includes the reducing agent in the exhaust gas when the reduced in which the accumulated amount of which NO _X that stored by reducing NO _X and has an exhaust purification system of an internal combustion engine according to claim 1 formed from NO _X catalyst decreases. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the sulfur storage agent is carried on the particulate filter.

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