JP2004076682A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To supply secondary air to an exhaust emission control device with a simple structure. <P>SOLUTION: An NO<SB>x</SB>catalyst 22 is arranged in the exhaust passage of an internal combustion engine where the air-fuel ratio of air-fuel mixture to be burnt in a combustion engine is kept lean, and an auxiliary catalyst 23 having oxidizing ability is arranged in the exhaust passage on the downstream side of the NO<SB>x</SB>catalyst 22. An intake duct 13 between the compressor 15 of an exhaust air turbo charger and a cooling device 18 for cooling the air discharged from a compressor 15 is connected to an exhaust pipe 20b between the NO<SB>x</SB>catalyst 22 and the auxiliary catalyst 23 through a secondary air passage 31, and a secondary air control valve 33 is arranged in the secondary air passage 31. In order to reduce the accumulated SO<SB>x</SB>quantity in the NO<SB>x</SB>catalyst 22 when stopping the fuel supply in an engine decelerating operation, the secondary air control valve 33 is opened while temporarily holding the average air-fuel ratio of the exhaust gas carried into the NO<SB>x</SB>catalyst 22 in a rich state to supply the air discharged from the compressor 15 to the auxiliary catalyst 23 through the secondary air passage 31. <P>COPYRIGHT: (C)2004,JPO

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]
Conventionally, NO in the exhaust gas flowing when the air-fuel ratio of the exhaust gas flowing into the exhaust passage of the internal combustion engine in which the air-fuel ratio of the air-fuel mixture burned in the combustion chamber is lean is kept lean._XNO when the reducing agent is contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas decreases_XNO stored and reduced_XNO decreases the amount of_XPlace catalyst and NO_XTo reduce the amount of sulfur stored in the catalyst, NO_X2. Description of the Related Art There is known an exhaust gas purifying apparatus for an internal combustion engine which temporarily keeps an air-fuel ratio of exhaust gas flowing into a catalyst rich.
[0003]
In this case, NO_XIn order to reliably and quickly reduce the amount of sulfur stored in the catalyst, NO_XIt is preferable to increase the richness of the air-fuel ratio of the exhaust gas flowing into the catalyst. However, if the rich degree is increased, NO_XExcess HC and CO will be supplied to the catalyst, so that NO_XA large amount of HC and CO is emitted from the catalyst and may be emitted into the atmosphere. When the rich degree is increased, NO_XHydrogen sulfide H discharged from the catalyst₂The amount of S may increase.
[0004]
So, NO_XAn auxiliary catalyst having oxidizing ability is arranged in an exhaust passage downstream of the catalyst, and NO_XIn order to reduce the amount of sulfur stored in the catalyst, NO_XWhile temporarily keeping the air-fuel ratio of the exhaust gas flowing into the catalyst rich, the NO_X2. Description of the Related Art An exhaust gas purifying apparatus for an internal combustion engine in which secondary air is supplied into an exhaust passage between a catalyst and an auxiliary catalyst is known (see JP-A-2000-110552). In this way, a large amount of HC, CO, H₂S is oxidized, and therefore HC, CO, H discharged to the atmosphere₂The amount of S can be reduced.
[0005]
[Problems to be solved by the invention]
However, in the above-mentioned exhaust gas purification apparatus, secondary air is supplied using an air pump, that is, an air pump must be newly provided. Therefore, there is a problem that not only the configuration of the exhaust gas purification device becomes complicated but also the cost increases.
[0006]
Accordingly, an object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can supply secondary air with a simple configuration.
[0007]
[Means for Solving the Problems]
According to a first aspect of the present invention, an air-fuel ratio of an air-fuel mixture burned in a combustion chamber is maintained in a lean air-fuel ratio in an exhaust passage of an internal combustion engine. NO in exhaust gas that sometimes flows in_XNO when the reducing agent is contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas decreases_XNO stored and reduced_XNO decreases the amount of_XA catalyst is arranged and the NO_XIn an exhaust gas purification device for an internal combustion engine in which an auxiliary catalyst having oxidizing ability is arranged in an exhaust passage downstream of a catalyst, a compressor of a supercharger is arranged in an intake passage._XA secondary air passage is provided for communicating the exhaust passage between the catalyst and the auxiliary catalyst with each other, and a secondary air control valve is arranged in the secondary air passage._XWhile temporarily keeping the air-fuel ratio of the exhaust gas flowing into the catalyst rich, the secondary air control valve is opened to reduce the air discharged from the compressor to NO._XThe air is supplied through a secondary air passage into an exhaust passage between the catalyst and the auxiliary catalyst.
[0008]
According to a second aspect of the present invention, in the first aspect, a cooling device for cooling air discharged from the compressor is disposed in the intake passage downstream of the compressor, and a cooling device for cooling the secondary air passage. The end opens into the intake passage between the compressor and the cooling device.
[0009]
According to a third aspect of the present invention, an air-fuel ratio of an air-fuel mixture burned in a combustion chamber is maintained in a lean air-fuel ratio in an exhaust passage of an internal combustion engine. NO in exhaust gas that sometimes flows in_XNO when the reducing agent is contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas decreases_XNO stored and reduced_XNO decreases the amount of_XA catalyst is arranged and the NO_XIn an exhaust gas purifying apparatus for an internal combustion engine in which an auxiliary catalyst having oxidizing ability is disposed in an exhaust passage downstream of a catalyst, an intake passage upstream of a throttle valve,_XA secondary air passage is provided for communicating the exhaust passage between the catalyst and the auxiliary catalyst with each other, and a secondary air control valve is disposed in the secondary air passage. The flow rate of the exhaust gas flowing through the exhaust passage is predetermined. NO is less than the maximum allowable_XWhile the air-fuel ratio of the exhaust gas flowing into the catalyst is temporarily kept rich, the throttle valve is temporarily opened and closed while the secondary air control valve is opened, and the intake pulsation flows into the intake passage upstream of the throttle valve. , The air in the intake passage upstream of the throttle valve is reduced to NO._XThe air is supplied through a secondary air passage into an exhaust passage between the catalyst and the auxiliary catalyst.
[0010]
According to a fourth aspect, in the third aspect, a cooling device for cooling air discharged from the compressor is disposed in an intake passage between the compressor and the throttle valve, and the secondary air The inflow end of the passage opens into the intake passage between the cooling device and the throttle valve.
[0011]
According to a fifth aspect of the present invention, an air-fuel ratio of an air-fuel mixture burned in a combustion chamber is maintained in a lean air-fuel ratio in an exhaust passage of an internal combustion engine. NO in exhaust gas that sometimes flows in_XNO when the reducing agent is contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas decreases_XNO stored and reduced_XNO decreases the amount of_XA catalyst is arranged and the NO_XIn an exhaust gas purifying apparatus for an internal combustion engine in which an auxiliary catalyst having an oxidizing ability is disposed in an exhaust passage downstream of a catalyst, an air tank for storing pressurized air is provided, and the air tank is connected to a NO._XConnected to the exhaust passage between the catalyst and the auxiliary catalyst, NO_XWhile temporarily keeping the air-fuel ratio of the exhaust gas flowing into the catalyst rich, the secondary air control valve is opened and the pressurized air in the air tank is reduced to NO._XThe gas is supplied into the exhaust passage between the catalyst and the auxiliary catalyst.
[0012]
According to a sixth aspect of the present invention, in the fifth aspect, a negative pressure pump for forming a negative pressure in the negative pressure tank is provided. The discharged air is stored in the air tank.
[0013]
Further, according to the seventh invention, in the first, third, or fifth invention, NO_XTo reduce the amount of sulfur stored in the catalyst, NO_XThe air-fuel ratio of the exhaust gas flowing into the catalyst is temporarily kept rich.
[0014]
According to the eighth invention, in the first, third or fifth invention, the secondary air is supplied such that the air-fuel ratio of the exhaust gas flowing into the auxiliary catalyst becomes lean.
[0015]
BEST MODE FOR CARRYING OUT 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.
[0016]
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 branch pipe 11, and the surge tank 12 is connected to an outlet of 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 in the intake duct 13 upstream of the throttle valve 17. Is done. In the embodiment according to the present invention, the throttle opening DT is maintained at the maximum opening DTm in almost all the operation ranges. When the required load L becomes considerably small, the throttle opening DT is made smaller than the maximum opening DTm, and when the required load L becomes zero, the throttle opening DT becomes small. The idle opening degree DTi is set.
[0017]
On the other hand, the exhaust port 10 is connected to an inlet of an exhaust turbine 21 of the exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20, and an outlet of the exhaust turbine 21 is connected to a casing 22a via an exhaust pipe 20a. A particulate filter 22b for collecting fine particles in the exhaust gas is accommodated in the casing 22a, and a NO._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 oxidizing ability is accommodated in the casing 23a.
[0018]
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. Further, a cooling device 26 for cooling the EGR gas flowing in the EGR passage 24 is disposed around the EGR passage 24.
[0019]
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.
[0020]
Furthermore, NO_XA secondary air supply nozzle 30 for supplying secondary air into the exhaust pipe 20b is mounted in the exhaust pipe 20b between the catalyst 22 and the auxiliary catalyst 23. The secondary air supply nozzle 30 is connected to the intake duct 13 between the compressor 15 and the cooling device 18 of the exhaust turbocharger 14 via the secondary air passage 31. In the secondary air passage 31, a check valve 32 that can only flow from the intake duct 13 to the exhaust pipe 20b, and an electrically controlled secondary air control valve 33 that is normally kept closed. Be placed.
[0021]
The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41 such as 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. Is provided. The output signal of the fuel pressure sensor 29 is input to the input port 45 via the corresponding AD converter 47. NO in the exhaust pipe 20b_XA temperature sensor 48 for detecting the temperature of the exhaust gas flowing out of the catalyst 22 is attached, and the output voltage of the temperature sensor 48 is input to the input port 45 via the corresponding AD converter 47. A load sensor 51 that generates an output voltage proportional to the amount of depression of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. You. Where NO_XThe temperature of the exhaust gas flowing out of the catalyst 22 is NO_XIt represents the temperature of the catalyst 22, and the depression amount of the accelerator pedal 50 represents the required load. Further, the input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. The CPU 44 calculates the engine speed based on the output pulse.
[0022]
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, the fuel pump 28, and the secondary air control valve 33 via the corresponding drive circuit 53, respectively.
[0023]
In the embodiment according to the present invention, the supply of fuel for obtaining the engine output is temporarily stopped during the engine deceleration operation. This will be briefly described with reference to a deceleration operation control routine shown in FIG.
[0024]
Referring to FIG. 2, first, in step 100, it is determined whether or not a flag XFC indicating that the fuel supply has been stopped is set (XFC = 1). Since the flag XFC is normally reset (XFC = 0), the routine proceeds to step 101, where it is determined whether or not the required load L is zero, that is, whether or not the engine is being decelerated. When L> 0, the processing cycle ends and fuel supply is continued. On the other hand, if L = 0, then the routine proceeds to step 102, where it is determined whether or not the engine speed N is higher than a first threshold value N1. When N ≦ N1, the processing cycle ends, and fuel supply is continued. On the other hand, if N> N1, then the routine proceeds to step 103, where the fuel supply is stopped. In the following step 104, the EGR control valve 25 is fully opened, and in the following step 105, the flag XFC is set (XFC = 1).
[0025]
When the flag XFC is set, the process proceeds from step 100 to step 106, where it is determined whether the required load L is greater than zero or the engine speed N is lower than a second threshold value N2 (<N1), that is, whether the engine It is determined whether or not the vehicle has not been decelerated or the engine speed N has become considerably low. When L = 0 and N ≧ N2, the processing cycle ends, and the fuel supply is continued and stopped. On the other hand, if L> 0 or N <N2, then the routine proceeds to step 107, where fuel supply is restarted. In the following step 108, the opening of the EGR control valve 25 is normally controlled. That is, the opening of the EGR control valve 25 is controlled in accordance with the engine operating state, for example, the required load L and the engine speed N. In the following step 109, the flag XFC is reset (XFC = 0).
[0026]
On the other hand, NO on both side surfaces of the partition wall of the particulate filter 22a and on the inner wall surface of the pores._XCatalysts 22 are respectively supported. This NO_XThe catalyst 22 is made of, for example, alumina as a carrier. On this carrier, for example, alkali metals such as potassium K, sodium Na, lithium Li, and cesium Cs, alkaline earths such as barium Ba and calcium Ca, lanthanum La, and yttrium Y And at least one selected from rare earth elements and a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir.
[0027]
NO_XThe catalyst is NO when the average air-fuel ratio of the inflowing exhaust gas is lean._XNO when the reducing agent is contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas decreases_XNO stored and reduced_XPerforms an accumulation reducing action to reduce the amount of
[0028]
NO_XThe detailed mechanism of the accumulation and reduction of the catalyst has not been fully elucidated. However, the mechanism currently considered is briefly described below, taking the case where platinum Pt and barium Ba are carried on a carrier as an example.
[0029]
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 exhaust gas flowing into the catalyst greatly increases, and the oxygen O₂Is O₂ ⁻Or O^2-On 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). NO generated next₂Is partially oxidized on platinum Pt while NO_XWhile being absorbed in the catalyst and binding to barium oxide BaO, nitrate ions NO₃ ⁻NO in the form of_XDiffusion into the catalyst. NO in this way_XIs NO_XStored in the catalyst.
[0030]
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 NO₂Is reduced and the reaction proceeds in the opposite direction (NO₃ ⁻→ NO + 2O^*) And thus NO_XNitrate ion NO in catalyst₃ ⁻Is NO in the form of NO_XReleased from the catalyst. This released NO_XIf the exhaust gas contains a reducing agent, that is, HC or CO, it reacts with these HC and CO to be reduced. Thus, NO on the surface of platinum Pt_XNO when no longer exists_XNO from catalyst to catalyst_XIs released and reduced, and NO_XNO stored in the catalyst_XGradually decreases.
[0031]
It should be noted that NO is formed without forming nitrate._XAnd store NO_XNO without releasing_XThere is also a view that it reduces Also, active oxygen O^*Focusing on, NO_XThe catalyst is NO_XOf active oxygen O along with the accumulation and release of oxygen^*It can also be regarded as an active oxygen generation catalyst that generates OH.
[0032]
On the other hand, the auxiliary catalyst 23 may be formed from any catalyst as long as it has oxidizing ability,_XIt can be formed from a catalyst, or can be formed from a noble metal catalyst carrying platinum Pt, for example, without having an accumulation reducing action. Further, the auxiliary catalyst 23 may be supported on the particulate filter.
[0033]
Now, in the embodiment according to the present invention, the internal combustion engine is continuously burning under a lean air-fuel ratio, and_XThe air-fuel ratio of the exhaust gas flowing into the catalyst 22 is kept lean. As a result, NO in the exhaust gas_XIs NO_XIt is stored in the catalyst 22.
[0034]
NO over time_XNO accumulated in the catalyst 22_XThe amount increases gradually. Therefore, in the embodiment according to the present invention, for example, NO_XNO accumulated in the catalyst 22_XNO when the amount exceeds the allowable amount_XNO stored in the catalyst 22_XIs reduced to NO_XNO accumulated in the 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.
[0035]
By the way, the sulfur content in the exhaust gas is SO_XIn the form of NO_XNO in the catalyst 22_XNot only SO_XIs also stored. This SO_XNO_XThe mechanism of accumulation in the catalyst 22 is NO_XIt is thought 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 briefly described as an example, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst 22 is lean, the oxygen O₂Is O₂ ⁻Or O^2-Is attached to the surface of platinum Pt in the form of₂Adheres to the surface of platinum Pt, and O₂ ⁻Or O^2-Reacts with SO₃It becomes. Then the generated SO₃Is further oxidized on platinum Pt_XThe sulfate ions SO are absorbed in the catalyst 22 and combined with barium oxide BaO.₄ ⁻NO in the form of_XIt diffuses into the catalyst 22. This sulfate ion SO₄ ⁻Is then barium ion Ba⁺Combined with sulfate BaSO₄Generate
[0036]
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 22₄Does not decrease. Therefore, as time passes, NO_XSulfate BaSO in catalyst 22₄Increases, resulting in NO_XNO that can be stored in the catalyst 22_XWill be reduced.
[0037]
However, NO_XWhile maintaining the temperature of the catalyst 22 at, for example, 600 ° C. or higher, NO_XWhen the average air-fuel ratio of the exhaust gas flowing into the catalyst 22 is set to the stoichiometric air-fuel ratio or rich, NO_XSulfate BaSO in catalyst 22₄Is decomposed into SO₃NO in the form of_XReleased from the catalyst 22. This released SO₃If the exhaust gas contains a reducing agent, that is, HC or CO, it reacts with these HC and CO and reacts with SO.₂It is reduced to. NO in this way_XSulfate BaSO in catalyst 22₄SO stored in the form of_XGradually decreases, and at this time NO_XFrom catalyst 22 to SO_XIs SO₃No spill in the form of
[0038]
Therefore, in the embodiment according to the present invention, for example, NO_XSO stored in catalyst 22_XIf the amount exceeds the allowable amount, NO_XSO stored in catalyst 22_XNO to reduce the amount_XWhile maintaining the temperature T of the catalyst 22 at the required temperature TS, for example, 600 ° C. or higher, NO_XThe accumulated SO that temporarily keeps the average air-fuel ratio of the exhaust gas flowing into the catalyst 22 rich_XThe amount decrease control is performed. Note that NO_XSO stored in catalyst 22_XWhether or not the amount exceeds the allowable amount can be determined, for example, based on the integrated value of the amount of fuel supplied from the fuel injection valve 6 and the amount of additional fuel.
[0039]
NO_XThere are various methods for raising the temperature T of the catalyst 22 to the required temperature TS or higher and maintaining it at the required temperature TS or higher. For example, NO_XAn electric heater is arranged at the upstream end of the catalyst 22, and the electric heater_XCatalyst 22 or NO_XA method for heating the exhaust gas flowing into the catalyst 22,_XThe fuel is secondarily injected into the exhaust passage upstream of the catalyst 22 to burn the fuel, thereby reducing the NO._XThe method of heating the catalyst 22 or the method of increasing the temperature of the exhaust gas discharged from the internal combustion engine to NO_XThere is a method of increasing the temperature of the catalyst 22.
[0040]
On the other hand, NO_XIn order to switch the average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 to the stoichiometric air-fuel ratio or rich, the average air-fuel ratio of the exhaust gas discharged from the combustion chamber 5 can be switched to the stoichiometric air-fuel ratio or rich, Or NO_XAdditional fuel or reductant may be injected secondary into the exhaust passage upstream of the catalyst 22. Here, in order to switch the average air-fuel ratio of the exhaust gas discharged from the combustion chamber 5 to the stoichiometric air-fuel ratio or rich, the average air-fuel ratio of the air-fuel mixture burned in the combustion chamber 5 is switched to the stoichiometric air-fuel ratio or rich. Alternatively, additional fuel may be injected during the expansion or exhaust stroke.
[0041]
In the embodiment according to the present invention, the air-fuel ratio of the exhaust gas discharged from the combustion chamber 5 is switched to rich by injecting additional fuel from the fuel injection valve 6 during the expansion stroke or the exhaust stroke, and thereby the NO._XThe average air-fuel ratio of the exhaust gas flowing into the catalyst 22 is switched to be rich.
[0042]
Whatever method is used, the accumulated SO_XIn order to reliably and quickly reduce the amount, as stated at the beginning, NO_XIt is preferable to make the average air-fuel ratio AFE of the exhaust gas as rich as possible in the catalyst 22. However, if the average air-fuel ratio AFE of the exhaust gas is made significantly rich, NO_XA large amount of HC, CO, H₂S may be discharged.
[0043]
Therefore, in the embodiment according to the present invention, NO_XAn auxiliary catalyst 23 is disposed downstream of the catalyst 22, and NO_XWhen the average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 is switched to rich, the secondary air is supplied to the auxiliary catalyst 23 so that the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 23 becomes lean. Supply these HC, CO, H₂S for example H₂O, CO₂, SO₂To oxidize.
[0044]
Next, a first embodiment according to the present invention shown in FIG. 1 will be described in detail with reference to FIG.
[0045]
In FIG. 3, the arrow X is, for example, NO_XSO stored in catalyst 22_XThis indicates when the amount exceeds the allowable amount. Accumulated SO_XIf the amount exceeds the allowable amount, NO_XThe temperature T of the catalyst 22 is raised to the required temperature TS or higher, and is maintained at the required temperature TS or higher. Next, as indicated by an arrow Y in FIG. 3, the required load L becomes zero, and at this time, the engine speed N is higher than the first threshold value N1, so that the fuel supply is stopped.
[0046]
NO when fuel supply is stopped_XThe average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 is switched to rich. When the fuel supply is stopped during the engine deceleration operation, the throttle opening DT is maintained at the small idle opening DTi, and the EGR control valve 25 is fully opened as described with reference to FIG. The amount of intake air at that time is considerably reduced. Therefore, it is possible to reduce the amount of additional fuel necessary for switching the average air-fuel ratio AFE of the exhaust gas to rich.
[0047]
NO_XWhen the average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 is switched to rich, the secondary air control valve 33 is opened. Even during the engine deceleration operation, the compressor 15 of the exhaust turbocharger 14 is operating, that is, the compressed air is discharged from the compressor 15 into the intake duct 13. Further, the flow path resistance in the cooling passage 18 is relatively high, so that the pressure in the intake duct 13 between the compressor 15 and the cooling device 18 is higher than the pressure in the exhaust pipe 20b. Therefore, at this time, if the secondary air control valve 33 is opened, the pressurized air in the intake duct 13 can be supplied to the auxiliary catalyst 23 as secondary air via the secondary air passage 31 and the secondary air supply nozzle 30. become.
[0048]
In this case, as shown in FIG. 3, the secondary air is supplied such that the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 23 becomes lean. As a result, NO_XSO stored in catalyst 22_XHC, CO, H discharged into the atmosphere, although the amount decreases reliably and quickly₂The amount of S has been reduced.
[0049]
Next, as shown by an arrow Z in FIG. 3, for example, when the engine speed N becomes equal to or less than the second threshold value N2 and fuel supply is restarted, NO_XThe average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 is returned to lean. At this time, the secondary air control valve 33 is closed, and the supply of the secondary air is stopped.
[0050]
Here, opening the secondary air control valve 33 and supplying the air in the intake duct 13 to the auxiliary catalyst 23 means that the amount of air supplied to the engine is reduced. However, in the first embodiment according to the present invention, since the secondary air is supplied from the intake duct 13 when the fuel supply is stopped, the combustion is not affected at all.
[0051]
FIG. 4 shows the storage SO of the first embodiment according to the present invention described above._X2 shows a routine for performing the amount decrease control. This routine is executed by interruption every predetermined set time.
[0052]
Referring to FIG. 4, first, at step 120, the accumulated SO_XIt is determined whether or not to execute the amount reduction control. In the embodiment according to the present invention, NO_XSO stored in catalyst 22_XAfter the amount exceeds the allowable amount, the accumulated SO_XUntil the amount reaches the lower limit amount, for example, zero, the accumulated SO_XIt is determined that the amount reduction control should be executed. Further, after the particulate oxidation control of the particulate filter 22b is completed, NO_XEven when the temperature T of the catalyst 22 is maintained at or above the required temperature TS, the accumulated SO_XIt is determined that the amount reduction control should be executed. Accumulated SO_XWhen the amount reduction control should not be executed, the process then proceeds to step 121, where the secondary air control valve 33 is closed or kept closed.
[0053]
In contrast, the accumulated SO_XWhen the amount reduction control is to be executed, the process proceeds from step 120 to step 122, and NO_XIt is determined whether the temperature T of the catalyst 22 is equal to or higher than the required temperature TS. If T <TS, then the routine proceeds to step 123, where NO_XTemperature raising control is performed to raise the temperature T of the catalyst 22 to the required temperature TS or higher and maintain it at the required temperature TS or higher. Next, the routine proceeds to step 121.
[0054]
Next, when T ≧ TS, the process proceeds from step 122 to step 124, where it is determined whether or not the flag XFC described with reference to FIG. 2 is set (XFC = 1). When the flag XFC is reset (XFC = 0), that is, when the fuel supply is not stopped, the process proceeds to step 121.
[0055]
On the other hand, when the flag XFC is set (XFC = 1), that is, when the fuel supply is stopped, the process proceeds from step 124 to step 125, and NO_XThe average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 is switched to and maintained rich. In the following step 126, the secondary air control valve 33 is opened. As a result, the air discharged from the compressor 15 is supplied to the auxiliary catalyst 23 as secondary air.
[0056]
In the first embodiment shown in FIG. 1, the inflow end of the secondary air passage 31 is opened in the intake duct 13 between the compressor 15 and the cooling device 18. It is possible to open the inflow end of the secondary air passage 31 into the intake duct 13 between the cooling passage 18 and the throttle valve 17, but in this case, the secondary air supply pressure is slightly reduced.
[0057]
FIG. 5 shows a second embodiment according to the present invention. The second embodiment is different from the first embodiment in that the inflow end of the secondary air passage 31 is opened in the intake duct 13 between the cooling device 18 and the throttle valve 17 in the intake duct 13 between the compressor 15 and the throttle valve 17. 1 is different from the first embodiment shown in FIG. Next, a second embodiment according to the present invention will be described in detail with reference to FIG.
[0058]
In FIG. 6, arrow X indicates, for example, NO._XSO stored in catalyst 22_XThis indicates when the amount exceeds the allowable amount. Accumulated SO_XIf the amount exceeds the allowable amount, NO_XThe temperature T of the catalyst 22 is raised to the required temperature TS or higher, and is maintained at the required temperature TS or higher. Next, as indicated by an arrow Y in FIG. 6, the required load L becomes zero, and at this time the engine speed N is higher than the first threshold value N1, so that the fuel supply is stopped.
[0059]
When the engine deceleration operation is started, NO_XThe average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 is switched to rich. During the engine deceleration operation, the throttle opening DT is maintained at the small idle opening DTi, and particularly when the fuel supply is stopped, the EGR control valve 25 is fully opened as described with reference to FIG. The intake air volume is considerably reduced. Therefore, it is possible to reduce the amount of additional fuel necessary for switching the average air-fuel ratio AFE of the exhaust gas to rich.
[0060]
NO_XWhen the average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 is switched to rich, the secondary air control valve 33 is opened. Further, at this time, the opening / closing drive of the throttle valve is intermittently performed in which the throttle valve 17 is opened at a high speed from the idle opening DTi to, for example, the maximum opening DTm, and is closed at a high speed to the idle opening DTi. In this manner, intake pulsation is forcibly formed in the intake duct 13 upstream of the throttle valve 17, and specifically, a positive pressure wave is formed in the throttle valve 17. This positive pressure wave reaches the secondary air supply nozzle 30 via the secondary air passage 31, and thus the secondary air is intermittently supplied to the auxiliary catalyst 23. Alternatively, an intake pulsation having a frequency corresponding to the flow path area and length of the secondary air passage 31 is also formed in the secondary air passage 31, whereby the secondary air is also intermittently supplied to the auxiliary catalyst 23. Is done.
[0061]
In this case, as shown in FIG. 6, the secondary air is supplied such that the average air-fuel ratio AFA of the exhaust gas flowing into the auxiliary catalyst 23 becomes lean. As a result, NO_XSO stored in catalyst 22_XHC, CO, H discharged into the atmosphere, although the amount decreases reliably and quickly₂The amount of S has been reduced.
[0062]
Further, a driving speed and a time interval in opening / closing driving of the throttle valve 17 are set so that the amount of air supplied into the combustion chamber 5 does not fluctuate, that is, even if opening / closing driving of the throttle valve 17 is performed, The throttle opening DT is substantially the same as the idle opening DTi. As a result, combustion is hardly affected, not only when fuel supply is stopped during engine deceleration operation, but also after fuel supply is restarted. In the example shown in FIG. 6, for example, even after the engine speed N becomes lower than the second threshold value N2 and fuel supply is restarted, NO_XThe average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 23 is continuously made rich, and the secondary air supply is continuously supplied to the auxiliary catalyst 23.
[0063]
Next, as shown by an arrow Z in FIG._XThe average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 is returned to lean. Further, at this time, the secondary air control valve 33 is closed, the opening / closing drive of the throttle valve 17 is also stopped, and therefore the supply of the secondary air is stopped.
[0064]
FIG. 7 shows the storage SO of the second embodiment according to the present invention described above._X2 shows a routine for performing the amount decrease control. This routine is executed by interruption every predetermined set time.
[0065]
Referring to FIG. 7, first, at step 140, the accumulated SO_XIt is determined whether or not to execute the amount reduction control. Accumulated SO_XWhen the amount reduction control should not be executed, the routine proceeds to step 141, where the secondary air control valve 33 is closed or kept closed. In contrast, the accumulated SO_XWhen the amount decrease control is to be executed, the process proceeds from step 140 to step 142, and NO_XIt is determined whether the temperature T of the catalyst 22 is equal to or higher than the required temperature TS. When T <TS, the process proceeds to step 143, and NO_XTemperature raising control is performed to raise the temperature T of the catalyst 22 to the required temperature TS or higher and maintain it at the required temperature TS or higher. Next, the routine proceeds to step 141.
[0066]
Next, when T ≧ TS, the process proceeds from step 142 to step 144, where it is determined whether the required load L is zero. If L> 0, that is, if it is not the engine deceleration operation, then the routine proceeds to step 141. On the other hand, when L = 0, that is, during the engine deceleration operation, the process proceeds from step 144 to step 145, and NO_XThe average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 is switched to and maintained rich. In the following step 146, the secondary air control valve 33 is opened, and in the following step 147, the throttle valve 17 is driven to open and close. As a result, the air discharged from the compressor 15 is supplied to the auxiliary catalyst 23 as secondary air.
[0067]
In the second embodiment shown in FIG. 5, the inflow end of the secondary air passage 31 is opened in the intake duct 13 between the cooling passage 18 and the throttle valve 17. It is possible to open the inflow end of the secondary air passage 31 into the intake duct 13 between the compressor 15 and the cooling device 18, but in this case, the secondary air supply pressure is slightly reduced.
[0068]
FIG. 8 shows a third embodiment according to the present invention.
[0069]
In the third embodiment, an air tank 34 for storing pressurized air is provided, and the inflow end of the secondary air passage 31 is connected to the air tank 34. A discharge port of a negative pressure pump 36 is connected to the air tank 34 via a check valve 35, and a suction port of the negative pressure pump 36 is connected to a negative pressure tank 38 via a check valve 37. The check valve 35 can flow only from the negative pressure pump 36 to the air tank 34, and the check valve 37 can flow only from the negative pressure tank 38 to the negative pressure pump 36.
[0070]
The negative pressure pump 36 is constituted by, for example, an engine-driven pump, and forms a negative pressure in the negative pressure tank 38. For example, a negative pressure chamber of a brake booster (not shown) is connected to the negative pressure tank 38 for storing the negative pressure, so that the brake booster is removed from the negative pressure tank 38 every time the brake is operated. Is supplied with a negative pressure.
[0071]
When the negative pressure in the negative pressure tank 38 is increased, air is discharged from the discharge port of the negative pressure pump 36, and the air is stored in the air tank 34. As a result, the air pressure in the air tank 34 gradually increases. When air is discharged from the discharge port of the negative pressure pump 36 together with the lubricating oil, an oil separator may be provided between the negative pressure pump 36 and the check valve 35.
[0072]
When the air pressure in the air tank 34 becomes sufficiently high, if the secondary air control valve 33 is opened, the pressurized air in the air tank 34 is assisted through the secondary air passage 31 and the secondary air supply nozzle 30. The catalyst 23 is supplied. In this case, the air tank 34 is independent of the intake passage and the exhaust passage, so that secondary air can be supplied to the auxiliary catalyst 23 at any timing as long as the air pressure is high. However, NO_XAs described above, it is preferable to change the average air-fuel ratio AFE of the exhaust gas to rich when the flow rate of the exhaust gas flowing into the catalyst 22 is small. Therefore, in the third embodiment according to the present invention, during the engine deceleration operation, While supplying secondary air to the auxiliary catalyst 23, NO_XThe average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 is maintained rich.
[0073]
FIG. 9 shows the stored SO of the third embodiment according to the present invention described above._X2 shows a routine for performing the amount decrease control. This routine is executed by interruption every predetermined set time.
[0074]
Referring to FIG. 9, first, at step 160, the accumulated SO_XIt is determined whether or not to execute the amount reduction control. Accumulated SO_XWhen the amount reduction control is not to be executed, the process then proceeds to step 161, where the secondary air control valve 33 is closed or kept closed. In contrast, the accumulated SO_XWhen the amount reduction control is to be executed, the process proceeds from step 160 to step 162, and NO_XIt is determined whether the temperature T of the catalyst 22 is equal to or higher than the required temperature TS. If T <TS, then the routine proceeds to step 163, where NO_XTemperature raising control is performed to raise the temperature T of the catalyst 22 to the required temperature TS or higher and maintain it at the required temperature TS or higher. Next, the routine proceeds to step 161.
[0075]
Next, when T ≧ TS, the process proceeds from step 162 to step 164, where it is determined whether the required load L is zero. When L> 0, that is, when it is not the engine deceleration operation, the routine proceeds to step 161. On the other hand, when L = 0, that is, during engine deceleration operation, the process proceeds from step 164 to step 165, and NO_XThe average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 is switched to rich and maintained. In the following step 166, the secondary air control valve 33 is opened. As a result, the pressurized air in the air tank 34 is supplied to the auxiliary catalyst 23 as secondary air.
[0076]
In each of the embodiments according to the present invention described above, NO_XThe accumulated SO of the catalyst 22_XNO to reduce volume_XThe case where the present invention is applied to make the average air-fuel ratio AFE of the exhaust gas flowing into the catalyst 22 rich is shown. However, NO_XNO stored in the catalyst 22_XNO stored and reduced_XThe present invention can also be applied when the average air-fuel ratio AFE of the exhaust gas is made rich to reduce the amount of the exhaust gas.
[0077]
【The invention's effect】
Secondary air can be supplied with a simple configuration.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
FIG. 2 is a flowchart for executing a control routine during deceleration operation.
FIG. 3 is a time chart for explaining a first embodiment according to the present invention.
FIG. 4 shows the storage SO of the first embodiment according to the present invention;_XIt is a flowchart for performing quantity reduction control.
FIG. 5 is an overall view of an internal combustion engine showing a second embodiment according to the present invention.
FIG. 6 is a time chart for explaining a second embodiment according to the present invention.
FIG. 7 shows a storage SO of a second embodiment according to the present invention;_XIt is a flowchart for performing quantity reduction control.
FIG. 8 is an overall view of an internal combustion engine showing a third embodiment according to the present invention.
FIG. 9 shows a third embodiment of the present invention;_XIt is a flowchart for performing quantity reduction control.
[Explanation of symbols]
1. Engine body
13. Intake duct
15 ... Compressor of exhaust turbocharger
17 ... Throttle valve
18. Cooling device
20a, 20b ... exhaust pipe
22 ... NO_Xcatalyst
23 ... Auxiliary catalyst
30 ... Secondary air supply nozzle
31 Secondary air passage
33 ... Secondary air control valve
34 ... Air tank
36 ... Negative pressure pump

Claims (8)

In an exhaust passage of an internal combustion engine air-fuel ratio of the mixture burned in the combustion chamber is maintained lean, stored the NO _X in the exhaust gas air-fuel ratio of the inflowing exhaust gas flows when the lean, flows with the air-fuel ratio of the exhaust gas is disposed a NO _X catalyst amount of the NO _X which the NO _X that accumulated to contain a reducing agent in the exhaust gas are stored by reduction decreases upon reduction, the In an exhaust gas purification device for an internal combustion engine in which an auxiliary catalyst having oxidizing ability is arranged in an exhaust passage downstream of a NO _X catalyst, a compressor of a supercharger is arranged in an intake passage, and an intake passage downstream of the compressor and a NO _X place the secondary air control valve in the secondary air passage is provided with the secondary air passage for exhausting communicate with each other a passage between the catalyst and co-catalyst, when the fuel supply stop during the decelerating operation of the engine, the NO _X catalyst Flow into That while maintaining the air-fuel ratio of the exhaust gas temporarily rich, the secondary air passage to the exhaust passage between the air NO _X catalyst and the auxiliary catalyst discharged from the compressor by opening the secondary air control valve An exhaust gas purification device for an internal combustion engine adapted to be supplied via an internal combustion engine. A cooling device for cooling air discharged from the compressor is disposed in an intake passage downstream of the compressor, and an inflow end of the secondary air passage is opened in an intake passage between the compressor and the cooling device. An exhaust purification device for an internal combustion engine according to claim 1. In an exhaust passage of an internal combustion engine air-fuel ratio of the mixture burned in the combustion chamber is maintained lean, stored the NO _X in the exhaust gas air-fuel ratio of the inflowing exhaust gas flows when the lean, flows with the air-fuel ratio of the exhaust gas is disposed a NO _X catalyst amount of the NO _X which the NO _X that accumulated to contain a reducing agent in the exhaust gas are stored by reduction decreases upon reduction, the In an exhaust gas purification apparatus for an internal combustion engine in which an auxiliary catalyst having oxidizing ability is disposed in an exhaust passage downstream of a NO _X catalyst, an exhaust passage upstream of a throttle valve and an exhaust passage between the NO _X catalyst and the auxiliary catalyst communicate with each other. the secondary air control valve in the secondary air passage is arranged provided with a following air passage, when less than the allowable maximum amount of flow is predetermined for the exhaust gas flowing through the exhaust passage, the NO _X catalyst Exhaust flowing into While the air-fuel ratio of gas and gas is kept rich temporarily, the throttle valve is temporarily opened and closed while the secondary air control valve is opened to forcibly generate intake pulsation in the intake passage upstream of the throttle valve. by allowed to exhaust purification device of an internal combustion engine so as to supply via the secondary air passage into the exhaust passage between the auxiliary air in the intake passage upstream a throttle valve and NO _X catalyst catalyst. A cooling device for cooling air discharged from the compressor is disposed in an intake passage between the compressor and the throttle valve. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein the exhaust gas purifying apparatus has an opening. In an exhaust passage of an internal combustion engine air-fuel ratio of the mixture burned in the combustion chamber is maintained lean, stored the NO _X in the exhaust gas air-fuel ratio of the inflowing exhaust gas flows when the lean, flows with the air-fuel ratio of the exhaust gas is disposed a NO _X catalyst amount of the NO _X which the NO _X that accumulated to contain a reducing agent in the exhaust gas are stored by reduction decreases upon reduction, the in the exhaust purification apparatus of the NO _X catalyst downstream of an internal combustion engine arranged an auxiliary catalyst having oxidizing ability in the exhaust passage, as well as comprising an air tank for storing compressed air, the air tank, via a secondary air control valve The secondary air control valve is opened while the air-fuel ratio of the exhaust gas flowing into the NO _X catalyst is temporarily rich while being connected to the exhaust passage between the NO _X catalyst and the auxiliary catalyst. pressurized air NO _X touch of An exhaust purification device for an internal combustion engine is supplied to the exhaust passage between the auxiliary catalyst. A negative pressure pump for generating a negative pressure in the negative pressure tank is provided, and when the negative pressure pump is operated, air discharged from the negative pressure pump is stored in the air tank. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 5. To reduce the amount of sulfur that is accumulated in the NO _X catalyst, NO _X claim and adapted to temporarily hold the rich air-fuel ratio of the exhaust gas flowing into the catalyst 1, 3, or 5 An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the secondary air is supplied such that the air-fuel ratio of the exhaust gas flowing into the auxiliary catalyst becomes lean.

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