JP4265177B2 - 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]
NO in the exhaust gas flowing in when the air-fuel ratio of the exhaust gas flowing into the exhaust passage of the internal combustion engine where the combustion is continuously performed under the lean 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_XPlace catalyst and NO_XNO in the catalyst_XNO_XNO stored in the catalyst_XNO to reduce the amount of_XThe reducing agent supply valve that temporarily supplies the reducing agent to the catalyst is_XNO in the exhaust passage upstream of the catalyst_XBy providing a bypass passage that bypasses the catalyst and changing the amount of exhaust gas flowing into the bypass passage according to the engine operating state, NO_XThe amount of exhaust gas flowing into the catalyst is changed according to the engine operating state, and the amount of exhaust gas flowing into the bypass passage is temporarily increased to reduce NO._XWhen the amount of exhaust gas flowing into the catalyst temporarily decreases, NO is reduced from the reducing agent supply valve._X2. Description of the Related Art An exhaust gas purification apparatus for an internal combustion engine in which a reducing agent is used as a catalyst is known (see Patent Document 1).
[0003]
In this way, the exhaust gas is prevented from flowing into the bypass passage, and almost all the exhaust gas is NO._XCompared to the case of supplying the reducing agent when flowing into the catalyst, NO_XIt is possible to reduce the amount of reducing agent required to make the air-fuel ratio of the exhaust gas flowing into the catalyst rich.
[0004]
[Patent Document 1]
JP 2001-317338 A
[0005]
[Problems to be solved by the invention]
NO_XThe reducing agent supplied into the catalyst is NO_XNO in the catalyst_XBecause it reacts exothermically with oxygen, NO_XNO in the catalyst_XNO_XNO accumulated in catalyst_XNO by reducing the amount_XThe temperature of the catalyst can be raised or NO_XIt is possible to prevent the temperature of the catalyst from decreasing.
[0006]
However, as mentioned above, NO_XWhen the amount of reducing agent supplied into the catalyst is reduced, NO_XThe temperature of the catalyst cannot be raised or NO_XIt becomes impossible to prevent the temperature of the catalyst from decreasing, and as a result NO_XThe catalyst cannot be activated quickly or NO_XThere is a problem that the activity of the catalyst may be lost.
[0007]
Therefore, the object of the present invention is NO._XActivate catalyst quickly or NO_XAn object of the present invention is to provide an exhaust purification device for an internal combustion engine that can maintain the activity of a catalyst high.
[0008]
[Means for Solving the Problems]
  In order to solve the above-described problem, according to a first aspect of the present invention, when the air-fuel ratio of the exhaust gas flowing into the exhaust passage of the internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio is lean, the fuel flows into the exhaust passage. NO in exhaust gas_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_XPlace catalyst and NO_XNO in the catalyst_XNO_XNO stored in the catalyst_XNO to reduce the amount of_XThe reducing agent supply means for temporarily supplying the reducing agent to the catalyst is NO_XIn an exhaust gas purification apparatus for an internal combustion engine disposed in an exhaust passage upstream of the catalyst, NO_XBy providing a bypass passage that bypasses the catalyst and changing the amount of exhaust gas flowing into the bypass passage, NO_XThe amount of exhaust gas flowing into the catalyst is changed,NO _X Compared to when the temperature of the catalyst is low, the NO from the reducing agent supply means _X NO when supplying reducing agent to catalyst _X An exhaust gas purification apparatus for an internal combustion engine in which the amount of exhaust gas flowing into the catalyst is increased. Almost all exhaust gas is prevented from flowing into the bypass passage. _X NO flows from the reducing agent supply means when flowing into the catalyst. _X After supplying the reducing agent to the catalyst and the elapsed time from the start of the internal combustion engine exceeds the set time, a part of the exhaust gas flows into the bypass passage and NO. _X When the amount of exhaust gas flowing into the catalyst is reduced, NO is supplied from the reducing agent supply means. _X To supply a reducing agent to the catalystis doing.
[0009]
  According to the second invention, in the first invention,NO _X The temperature of the catalyst is NO _X NO when the temperature drops below the lower purification temperature _X NO of catalyst _X The purifying capacity decreases beyond the allowable lower limit value, and the set time is NO after the internal combustion engine is started. _X The temperature of the catalyst is NO _X Set to the time required to reach the lower purification temperature limitis doing.
[0010]
  Also, according to the third invention, No.1OcularIn the invention,The NO on the particulate filter for collecting particulates contained in the inflowing exhaust gas _X Catalyst is supported, NO _X NO when the temperature of the catalyst falls below the lower limit temperature _X The fine particle oxidation ability of the catalyst falls below the allowable lower limit, and the set time is set to NO after the internal combustion engine is started. _X Set to the time required for the catalyst temperature to reach the lower limit temperature of particulate oxidation abilityis doing.
[0011]
  According to the fourth invention,1In the second invention,Exhaust gas is NO _X A forward flow position for guiding the exhaust gas so that it flows into the catalyst from one end face, flows in the forward flow direction and then flows out from the other end face, and the exhaust gas is NO. _X A switching valve is provided that can switch between a backflow position that guides exhaust gas so that the exhaust gas flows into the catalyst from the other end face, flows in the backflow direction, and then flows out from the one end face. When switching to the reverse or vice versa, the amount of exhaust gas flowing into the bypass passage gradually increases and NO is increased accordingly. _X The amount of exhaust gas flowing into the catalyst gradually decreases, and then NO _X NO after the direction of exhaust gas flow in the catalyst is reversed _X The amount of exhaust gas flowing into the catalyst is gradually increased, and the amount of exhaust gas flowing into the bypass passage is gradually decreased by that amount. _X The reducing agent supply means is provided in an exhaust passage located upstream of the catalyst..
[0012]
  According to the fifth invention, in the fourth invention,When the elapsed time from the start of the internal combustion engine is shorter than a predetermined set time, NO is supplied from the reducing agent supply means when the switching valve is held in the forward flow position. _X After the reducing agent is supplied into the catalyst and the elapsed time from the start of the internal combustion engine exceeds the set time, the switching valve is switched from the forward flow position to the reverse flow position or vice versa. NO _X To supply a reducing agent in the catalystis doing.
[0013]
  To solve the above problemsAccording to the sixth inventionFor example, NO in the exhaust gas flowing into the exhaust passage of the internal combustion engine where the combustion is continuously performed under the lean air-fuel ratio when the air-fuel ratio of the exhaust gas flowing in is lean. _X NO when storing the reducing agent in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in decreases _X NO is being reduced and stored _X NO decreases in quantity _X Place catalyst and NO _X NO in the catalyst _X NO _X NO stored in the catalyst _X NO to reduce the amount of _X The reducing agent supply means for temporarily supplying the reducing agent to the catalyst is NO _X In an exhaust gas purification apparatus for an internal combustion engine disposed in an exhaust passage upstream of the catalyst, NO _X By providing a bypass passage that bypasses the catalyst and changing the amount of exhaust gas flowing into the bypass passage, NO _X The amount of exhaust gas flowing into the catalyst is changed, and NO is supplied from the reducing agent supply means. _X NO when the reducing agent is supplied to the catalyst _X The amount of exhaust gas flowing into the catalyst is NO _X Depending on the temperature of the catalyst, the exhaust gas is NO _X A forward flow position for guiding the exhaust gas so that it flows into the catalyst from one end face, flows in the forward flow direction and then flows out from the other end face, and the exhaust gas is NO. _X A switching valve is provided that can switch between a backflow position that guides exhaust gas so that the exhaust gas flows into the catalyst from the other end face, flows in the backflow direction, and then flows out from the one end face. When switching to the reverse or vice versa, the amount of exhaust gas flowing into the bypass passage gradually increases and NO is increased accordingly. _X The amount of exhaust gas flowing into the catalyst gradually decreases, and then NO _X NO after the direction of exhaust gas flow in the catalyst is reversed _X The amount of exhaust gas flowing into the catalyst is gradually increased, and the amount of exhaust gas flowing into the bypass passage is gradually decreased by that amount. _X The reducing agent supply means is provided in the exhaust passage located upstream of the catalyst, and when the switching valve is held at the forward flow position, NO is supplied from the reducing agent supply means. _X NO is supplied from the reducing agent supply means during a transient when the reducing agent is supplied into the catalyst or the switching valve is switched from the forward flow position to the reverse flow position or vice versa. _X Whether to supply the reducing agent into the catalyst, NO _X Switch according to the temperature of the catalystis doing.
[0014]
  According to the seventh invention,6In the second invention,NO _X When the temperature of the catalyst is lower than a predetermined set temperature, NO is supplied from the reducing agent supply means when the switching valve is held in the forward flow position. _X Supply the reducing agent to the catalyst, NO _X When the temperature of the catalyst is higher than the set temperature, NO is reduced from the reducing agent supply means during the transition when the switching valve is switched from the forward flow position to the reverse flow position or vice versa. _X To supply a reducing agent to the catalystis doing.
[0015]
  According to the eighth invention7In the second invention,NO _X The temperature of the catalyst is NO _X NO when the temperature drops below the lower purification temperature _X NO of catalyst _X The purifying capacity decreases beyond the allowable lower limit, and the set temperature is set to NO. _X NO of catalyst _X The lower limit temperature is set..
[0016]
  According to the ninth invention,7In the second invention,The NO on the particulate filter for collecting particulates contained in the inflowing exhaust gas _X Catalyst is supported, NO _X NO when the temperature of the catalyst falls below the lower limit temperature _X The fine particle oxidation ability of the catalyst is lowered beyond the allowable lower limit, and the set temperature is set to NO. _X Set to the minimum particle oxidation capacity minimum temperature of the catalystis doing.
[0017]
  According to the tenth invention6In the second invention,When the elapsed time from the start of the internal combustion engine is shorter than a predetermined set time, NO is supplied from the reducing agent supply means when the switching valve is held in the forward flow position. _X After supplying the reducing agent to the catalyst and the elapsed time from the start of the internal combustion engine has exceeded the set time, the switching valve is switched from the forward flow position to the reverse flow position or vice versa. _X To supply a reducing agent to the catalystis doing.
[0018]
  To solve the above problemsAccording to the eleventh inventionFor example, NO in the exhaust gas flowing into the exhaust passage of the internal combustion engine where the combustion is continuously performed under the lean air-fuel ratio when the air-fuel ratio of the exhaust gas flowing in is lean. _X NO when storing the reducing agent in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in decreases _X NO is being reduced and stored _X NO decreases in quantity _X Place catalyst and NO _X NO in the catalyst _X NO _X NO stored in the catalyst _X NO to reduce the amount of _X The reducing agent supply means for temporarily supplying the reducing agent to the catalyst is NO _X In an exhaust gas purification apparatus for an internal combustion engine disposed in an exhaust passage upstream of the catalyst, NO _X By providing a bypass passage that bypasses the catalyst and changing the amount of exhaust gas flowing into the bypass passage, NO _X The amount of exhaust gas flowing into the catalyst is changed, and NO is supplied from the reducing agent supply means. _X NO when the reducing agent is supplied to the catalyst _X The amount of exhaust gas flowing into the catalyst is NO _X Depending on the temperature of the catalyst, the exhaust gas is NO _X A forward flow position for guiding the exhaust gas so that it flows into the catalyst from one end face, flows in the forward flow direction and then flows out from the other end face, and the exhaust gas is NO. _X A switching valve is provided that can switch between a backflow position that guides exhaust gas so that the exhaust gas flows into the catalyst from the other end face, flows in the backflow direction, and then flows out from the one end face. When switching to the reverse or vice versa, the amount of exhaust gas flowing into the bypass passage gradually increases and NO is increased accordingly. _X The amount of exhaust gas flowing into the catalyst gradually decreases, and then NO _X NO after the direction of exhaust gas flow in the catalyst is reversed _X The amount of exhaust gas flowing into the catalyst is gradually increased, and the amount of exhaust gas flowing into the bypass passage is gradually decreased by that amount. _X The reducing agent supply means is provided in the exhaust passage located upstream of the catalyst, and NO is supplied from the reducing agent supply means during a transient when the switching valve is switched from the forward flow position to the reverse flow position or vice versa. _X While supplying the reducing agent to the catalyst, the time interval from the reference time until the reducing agent is supplied is NO. _X Set according to the temperature of the catalysting.
[0019]
  According to the twelfth invention,6 or 11In the second invention,NO _X Compared to when the temperature of the catalyst is low, the NO from the reducing agent supply means _X NO when supplying reducing agent to catalyst _X To increase the amount of exhaust gas flowing into the catalystis doing.
[0020]
  According to the thirteenth invention,1,6,11,12The second inventionAny one ofInNO from the reducing agent supply means _X NO when supplying reducing agent to catalyst _X Compared to when the amount of exhaust gas flowing into the catalyst is large, the NO from the reducing agent supply means _X To increase the amount of reducing agent supplied to the catalystis doing.
[0021]
  According to the 14th invention1,6,11The second inventionAny one ofInNO by changing the amount of exhaust gas flowing into the bypass passage according to the engine operating state _X The amount of exhaust gas flowing into the catalyst is changed according to the engine operating state.
  According to the fifteenth invention, in any one of the first, sixth and eleventh inventions, an additional NO is added in the bypass passage. _X Place catalyst and add NO _X Additional reducing agent supply means for supplying reducing agent to the catalyst is connected to the inflow end of the bypass passage and additional NO. _X Place in the bypass passage between the catalysts and add NO _X NO in the catalyst _X Reduce NO and add NO _X NO stored in the catalyst _X Additional NO from additional reducing agent supply means to reduce the amount of _X While temporarily supplying the reducing agent to the catalyst, at this time additional NO _X The amount of exhaust gas flowing into the catalyst _X It is made different depending on the temperature of the catalyst.
[0022]
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.
[0023]
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 an outlet of a compressor 15 of an exhaust turbocharger 14 via an intake duct 13. The tube 15a is connected. 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.
[0024]
On the other hand, the exhaust port 10 is connected to an exhaust turbine 21 of an exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20, and an outlet of the exhaust turbine 21 is connected to a catalytic converter 22 via an exhaust pipe 20a.
[0025]
Referring to FIG. 2 together with FIG. 1, the catalytic converter 22 includes a switching valve 61 driven by a step motor 60, and an outlet of the exhaust pipe 20 a is connected to an inflow port 62 of the switching valve 61. An exhaust gas discharge pipe 64 of the catalytic converter 22 is connected to the outflow port 63 of the switching valve 61 facing the inflow port 62. The switching valve 61 further has a pair of inflow / outflow ports 65, 66 facing each other on both sides of a straight line connecting the inflow port 62 and the outflow port 63, and the inflow / outflow ports 65, 66 have an annular shape of the catalytic converter 22. Both ends of the exhaust pipe 67 are connected. The exhaust pipe 23 is connected to the outlet of the exhaust gas discharge pipe 64.
[0026]
The annular exhaust pipe 67 extends through the exhaust gas exhaust pipe 64, and a filter housing chamber 68 is formed in a portion of the annular exhaust pipe 67 located in the exhaust gas exhaust pipe 64. A particulate filter 69 for collecting fine particles in the exhaust gas is housed in the filter housing chamber 68. In FIG. 2, reference numerals 69a and 69b denote one end face and the other end face of the particulate filter 69, respectively.
[0027]
As shown in FIG. 2A showing a partial longitudinal sectional view of the catalytic converter 22 including the one end face 69a of the particulate filter 69 and FIG. 2B showing a partial transverse sectional view of the catalytic converter 22, The filter 69 has a honeycomb structure and includes a plurality of exhaust gas passages 70 and 71 extending in parallel with each other. These exhaust gas passages are constituted by an exhaust gas passage 70 having one end opened and the other end closed by a sealing material 72, and an exhaust gas passage 71 having the other end opened and one end closed by a sealing material 73. Is done. Note that the hatched portion in FIG. 2A shows the sealing material 73. The exhaust gas passages 70 and 71 are alternately arranged via thin partition walls 74 formed of a porous material such as cordierite. In other words, the exhaust gas passages 70 and 71 are arranged such that each exhaust gas passage 70 is surrounded by four exhaust gas passages 71 and each exhaust gas passage 71 is surrounded by four exhaust gas passages 70.
[0028]
As will be described later, NO on the particulate filter 69._XA catalyst 81 is supported. On the other hand, a catalyst storage chamber 75 is formed in the exhaust gas discharge pipe 64 between the outflow port 63 of the switching valve 61 and the portion through which the annular exhaust pipe 67 penetrates. An auxiliary catalyst 76 having an oxidizing ability carried on a substrate having a honeycomb structure is accommodated. In this case, NO_XThe air-fuel ratio of the exhaust gas flowing into the catalyst 81 matches the air-fuel ratio of the exhaust gas flowing into the particulate filter 69, and NO_XThe temperature of the catalyst 81 also matches the temperature of the particulate filter 69.
[0029]
Also, the inflow / outflow port 65 of the switching valve 61 and the NO_XThe annular exhaust pipe 67 between the catalysts 81 has NO._XAn electrically controlled reducing agent supply valve 77 for supplying a reducing agent to the catalyst 81 is attached. A reducing agent is supplied to the reducing agent supply valve 77 from an electrically controlled reducing agent pump 78. In the embodiment according to the present invention, the fuel of the internal combustion engine, that is, light oil, is used as the reducing agent. In the embodiment according to the present invention, the inflow / outflow port 66 and the NO._XA reducing agent supply valve is not disposed in the annular exhaust pipe 67 between the catalysts 81.
[0030]
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.
[0031]
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.
[0032]
  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 intake pipe 15a has a mass flow rate of intake air.TheAn air flow meter 49 for detecting is attached, and a pressure sensor 50 for detecting a pressure in the exhaust pipe 20a, that is, an engine back pressure, is attached to the exhaust pipe 20a. In addition, a temperature sensor 51 for detecting the temperature of the particulate filter 69 is attached to, for example, the central portion of the particulate filter 69, and a load that generates an output voltage proportional to the depression amount of the accelerator pedal 52 is generated in the accelerator pedal 52. A sensor 53 is connected. The depression amount L of the accelerator pedal 52 represents a required load. Output signals of the fuel pressure sensor 29, the air flow meter 49, the pressure sensor 50, the temperature sensor 51, and the load sensor 53 are input to the input port 45 via the corresponding AD converters 47, respectively. 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.
[0033]
  On the other hand, the output port 46 is connected through a corresponding drive circuit 48 to the fuel injection valve 6, the throttle valve driving step motor 16, the EGR control valve 25, the fuel pump 28, the switching valve driving step motor 60, the reducing agent supply valve 77, And reductionAgentThese are respectively connected to the pumps 78, and these are controlled based on an output signal from the electronic control unit 40.
[0034]
The switching valve 61 is normally positioned at one of a position indicated by a solid line and a position indicated by a broken line in FIG. When the switching valve 61 is positioned at the position indicated by the solid line in FIG. 3B, the inflow port 62 communicates with the inflow / outflow port 65 while the communication between the outflow port 63 and the inflow / outflow port 66 is blocked by the switching valve 61. The outflow port 63 is communicated with the inflow / outflow port 66 by the switching valve 61. As a result, as shown by the solid arrows in FIG. 3B, all the exhaust gas flowing through the exhaust pipe 20a flows into the annular exhaust pipe 67 through the inflow port 62 and the inflow / outflow port 65 in sequence, Next, after passing through the particulate filter 69, it flows into the exhaust gas discharge pipe 64 through the inflow / outflow port 66 and the outflow port 63 in order.
[0035]
On the other hand, when the switching valve 61 is positioned at the position indicated by the broken line in FIG. 3B, the inflow port 62 is inflow / outflow while the communication between the outflow port 63 and the inflow / outflow port 65 is blocked by the switching valve 61. The outflow port 63 is communicated with the inflow / outflow port 65 by the switching valve 61. As a result, all the exhaust gas flowing through the exhaust pipe 20a flows into the annular exhaust pipe 67 through the inflow port 62 and the inflow / outflow port 66 in sequence as shown by the broken arrows in FIG. Next, after passing through the particulate filter 69, it flows into the exhaust gas discharge pipe 64 through the inflow / outflow port 65 and the outflow port 63 in order.
[0036]
By switching the position of the switching valve 61 in this way, the flow of exhaust gas in the annular exhaust pipe 67 is reversed. In other words, the exhaust gas is NO_XIt flows into the catalyst 81 through its one end face, and NO_XExhaust gas is guided to flow out from the catalyst 81 through the other end face, or NO_XIt flows into the catalyst 81 through the other end face and NO._XIt is possible to switch whether to guide the exhaust gas so as to flow out from the catalyst 81 through one end face thereof. Hereinafter, the exhaust gas flow indicated by the solid line in FIG. 3B is referred to as forward flow, and the exhaust gas flow indicated by the broken line is referred to as reverse flow. 3B, the position of the switching valve 61 indicated by a solid line is referred to as a forward flow position, and the position of the switching valve 61 indicated by a broken line is referred to as a backflow position.
[0037]
The exhaust gas that has flowed into the exhaust gas discharge pipe 64 through the outflow port 66 then passes through the catalyst 76 and travels along the outer peripheral surface of the annular exhaust pipe 67 as shown in FIGS. After that, it flows out into the exhaust pipe 23.
[0038]
Explaining the flow of exhaust gas in the particulate filter 69, during forward flow, the exhaust gas flows into the particulate filter 69 through the one end surface 69a and flows out of the particulate filter 69 through the other end surface 69b. At this time, the exhaust gas flows into the exhaust gas passage 70 opened in the one end surface 69 a, and then flows into the adjacent exhaust gas passage 71 through the surrounding partition wall 74. On the other hand, during reverse flow, the exhaust gas flows into the particulate filter 69 via the other end surface 69b and flows out of the particulate filter 69 via the one end surface 69a. At this time, the exhaust gas flows into the exhaust gas passage 71 opened in the other end face 69b, and then flows into the adjacent exhaust gas passage 70 through the surrounding partition wall 74.
[0039]
Here, the particulate filter 69 is disposed substantially at the center of the annular exhaust pipe 67, that is, the distance from the inflow port 62 of the switching valve 61 to the particulate filter 69 and the distance from the particulate filter 69 to the outflow port 63. The distance hardly changes between when the switching valve 61 is in the forward flow position and when it is in the reverse flow position.
[0040]
On the partition wall 74 of the particulate filter 69, that is, on both side surfaces of the partition wall 74 and the inner wall surface of the pore, as shown in FIG._XEach catalyst 81 is supported. This NO_XThe catalyst 81 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 are supported 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.
[0041]
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.
[0042]
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 support.
[0043]
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.
[0044]
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_XIf the exhaust gas contains a reducing agent, that is, HC or CO, it can be reduced by reacting with the HC and CO. 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.
[0045]
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
[0046]
Meanwhile, in the embodiment according to the present invention, the auxiliary catalyst 76 is formed from a noble metal catalyst containing noble metal such as platinum Pt without containing alkali metal, alkaline earth, and rare earth. However, the auxiliary catalyst 76 is the NO described above._XYou may form from a catalyst.
[0047]
By the way, in the embodiment according to the present invention, the switching valve 61 is switched from the forward flow position to the reverse flow position or vice versa according to the engine operating state, specifically, for example, when the required load L becomes zero. This is due to the following reason.
[0048]
FIG. 5 shows NO when the switching valve 61 is switched._XA time-dependent change in the amount QE of the exhaust gas flowing in the forward flow direction into the catalyst 81 is shown. In FIG. 5, an arrow X indicates a time when a signal to switch the switching valve 61 is generated, a solid line indicates a case where the switching valve 61 is switched from the backflow position to the forward flow position, and a broken line indicates that the switching valve 61 is switched. The case where it can switch from a forward flow position to a backflow position is shown. NO_XThe exhaust gas amount QE is a positive value when the direction of the exhaust gas flowing into the catalyst 81 is a forward flow direction, and is a negative value when the direction is a reverse flow direction. Further, in the example shown in FIG. 5, the exhaust gas amount QE when the switching valve 61 is in the forward flow position is represented by 100, and the exhaust gas amount QE when it is in the reverse flow position is represented by -100. .
[0049]
A case where the switching valve 61 is switched from the backflow position to the forward flow position will be described as an example. When the switching valve 61 is displaced from the backflow position toward the forward flow position, the inflow port 62 is directly connected not only to the inflow / outflow port 65 but also to the outflow port 63, so that the exhaust gas flowing into the inflow port 62 Part of is NO_XThe catalyst 81 is bypassed. As the switching valve 61 moves toward the forward flow position, NO_XThe amount of exhaust gas that bypasses the catalyst 81 gradually increases, and NO is increased accordingly._XThe amount QE of the exhaust gas that flows into the catalyst 81 in the reverse flow direction gradually decreases. Then NO_XAfter the amount of exhaust gas QE flowing into the catalyst 81 once becomes zero, NO_XThe direction of the exhaust gas flow in the catalyst 81 is reversed, and NO_XThe amount QE of exhaust gas flowing into the catalyst 81 in the forward flow direction gradually increases, and NO is correspondingly increased._XThe amount of exhaust gas that bypasses the catalyst 81 gradually decreases. The same applies when the switching valve 61 is switched from the forward flow position to the reverse flow position. In this way, the exhaust gas flow path from the inflow port 62 to the outflow port 63 of the switching valve 61 can act as a bypass passage that bypasses the particulate filter 69.
[0050]
Therefore, when the switching valve 61 is switched from the forward flow position to the reverse flow position or vice versa, the exhaust gas temporarily becomes NO._XThe catalyst 81 is bypassed. Therefore, in an embodiment according to the present invention, NO_XThe switching valve 61 is switched when the required load L is zero so that the amount of exhaust gas that bypasses the catalyst 81 is as small as possible. As a result, the particulate filter 69 and NO_XFine particles bypassing the catalyst 81 and NO_XThe amount of can be reduced.
[0051]
As described above, the exhaust gas passes through the particulate filter 69 regardless of whether the switching valve 61 is in the forward flow position or the reverse flow position. Further, the internal combustion engine shown in FIG. 1 is continuously combusted under a lean air-fuel ratio, and therefore, the air-fuel ratio of the exhaust gas flowing into the particulate filter 69 is maintained lean. As a result, NO in the exhaust gas_XIs NO on the particulate filter 69_XIt is stored in the catalyst 81.
[0052]
NO over time_XNO accumulated in catalyst 81_XThe amount increases gradually. Therefore, in an embodiment according to the present invention, NO_XNO accumulated in catalyst 81_XNO when the amount exceeds the allowable amount_XNO stored in catalyst 81_XNO_XNO accumulated in catalyst 81_XNO to reduce the amount_XFrom the reducing agent supply valve 77, NO is reduced so that the air-fuel ratio of the exhaust gas flowing into the catalyst 81 becomes temporarily rich._XA reducing agent supply operation for temporarily supplying a reducing agent to the catalyst 81 is performed. Accumulated NO_XThe amount can be determined based on the engine operating state, for example.
[0053]
On the other hand, fine particles mainly composed of carbon contained in the exhaust gas are collected on the particulate filter 69. That is, schematically, fine particles are collected on the side surface and the pores of the partition wall 74 on the exhaust gas passage 70 side in the forward flow, and on the side surface and the pores of the partition wall 74 on the exhaust gas passage 71 side in the reverse flow. Fine particles are collected. The internal combustion engine shown in FIG. 1 continues to burn under a lean air-fuel ratio, and NO_XSince the catalyst 81 has an oxidizing ability, if the temperature of the particulate filter 69 is maintained at a temperature at which particulates can be oxidized, for example, 250 ° C. or more, the particulates are oxidized on the particulate filter 69 and removed. The
[0054]
In this case, the above-mentioned NO_XNO of catalyst 81_XAccording to the accumulation and reduction mechanism of NO_XNO in catalyst 81_XNO is also stored when_XActive oxygen is also generated when is released. This active oxygen is oxygen O₂Therefore, the fine particles deposited on the particulate filter 69 are rapidly oxidized. That is, NO on the particulate filter 69._XWhen the catalyst 81 is supported, fine particles deposited on the particulate filter 69 are oxidized regardless of whether the air-fuel ratio of the exhaust gas flowing into the particulate filter 69 is lean or rich. In this way, the fine particles are continuously oxidized.
[0055]
Where NO_XNO in the catalyst 81_XNO_XNO accumulated in catalyst 81_XThe reducing agent supply operation for reducing the amount will be described in detail with reference to FIG.
[0056]
In the embodiment according to the present invention, as shown by the arrow Y1 in FIG._XEven if the amount QN exceeds the first allowable amount QN1, the reducing agent supply action is not immediately performed, and then when the required load L becomes zero and the switching valve 61 is switched as shown by the arrow Y2, the reducing agent supply is performed. The action is performed. As a result, the exhaust gas air-fuel ratio AFN is temporarily switched to rich as shown in FIG._XThe quantity QN is reduced to eg zero.
[0057]
Next, as shown by the arrow Y3 in FIG. 6, when the required load L becomes zero again, the switching valve 61 is switched, but at this time, the accumulated NO_XSince the amount QN is smaller than the first allowable amount QN1, the reducing agent supply action is not performed. Next, as shown by arrow Y4 in FIG._XEven if the amount QN again exceeds the first allowable amount QN1, the reducing agent supply action is not immediately performed, and therefore, the accumulated NO_XThe quantity QN increases gradually.
[0058]
Next, as shown by arrow Y5, the accumulated NO_XWhen the amount QN is larger than the second allowable amount QN2 (> QN1), the reducing agent supply operation is performed even if the required load L is not zero. As a result, NO_XCatalyst 81 is NO_XIs prevented from saturating.
[0059]
NO like this_XNO accumulated in catalyst 81_XWhen the amount QN is larger than the first allowable amount QN1 and smaller than the second allowable amount QN2, the reducing agent supply action is performed when the switching valve 61 is switched as shown by the arrow Y2 in FIG.
[0060]
In each embodiment according to the present invention, when this reducing agent supply action is performed, NO_XThe amount of exhaust gas flowing into the catalyst is NO_XThe temperature varies depending on the temperature T of the catalyst 81. Next, first to fourth embodiments according to the present invention will be sequentially described.
[0061]
In the first embodiment according to the present invention, the transient supply in which the reducing agent supply operation is performed during the transition when the switching valve 61 is switched and the forward flow supply in which the reducing agent supply operation is performed when the switching valve 61 is in the forward flow position are NO._XIt is selectively switched according to the temperature T of the catalyst 81.
[0062]
First, transient supply will be described. As described above with reference to FIG. 5, when the switching valve 61 is switched,_XThe amount QE of exhaust gas flowing into the catalyst 81 temporarily decreases. Therefore, if the reducing agent supply action is performed at this time, NO_XIt is possible to reduce the amount of reducing agent required to switch the air-fuel ratio AFN of the exhaust gas flowing into the catalyst 81 to rich. At this time, NO_XSince the space velocity of the exhaust gas in the catalyst 81 decreases, NO_XThe residence time of the reducing agent in the catalyst 81 becomes longer, and therefore the reducing agent can be used effectively. This is the concept of transient supply.
[0063]
More specifically, when the switching valve 61 is switched from the backflow position to the forward flow position, as indicated by an arrow RT in FIG._XWhile the amount QE of the exhaust gas flowing into the catalyst 81 once increases to zero, the reducing agent supply operation is performed. In this case, the time interval from the reference time, for example, the time X when the signal for switching the switching valve 61 is issued to the time when the reducing agent supply operation is performed is represented by tRF. On the other hand, when the switching valve 61 is switched from the forward flow position to the reverse flow position, as indicated by an arrow RT in FIG._XThe reducing agent is supplied while the amount QE of the exhaust gas flowing in the forward direction into the catalyst 81 is decreasing. The time interval in this case is represented by tFR. In this way, part of the exhaust gas is NO_XThe reducing agent supply operation is performed while flowing into the catalyst 81.
[0064]
On the other hand, in the forward flow supply, the reducing agent supply operation is performed when the switching valve 61 is in the forward flow position. That is, when the switching valve 61 is switched from the backflow position to the forward flow position, as shown by the arrow RF in FIG. 7A, the reducing agent is supplied after the switching valve 61 is switched to the forward flow position. On the other hand, when the switching valve 61 is switched from the forward flow position to the reverse flow position, the reducing agent supply action is performed before the switching valve 61 is switched to the reverse flow position, as indicated by an arrow RF in FIG. . In this way, almost all exhaust gas is NO._XThe reducing agent supply operation is performed while flowing into the catalyst 81.
[0065]
In the example shown in FIG. 7, when transient supply is performed, NO is applied when the reducing agent supply operation is performed._XThe amount QE of the exhaust gas flowing into the catalyst 81 is a small QET._XFor example, the reducing agent supply amount QR necessary for setting the air-fuel ratio of the exhaust gas flowing into the catalyst 81 to a constant rich air-fuel ratio is set to a relatively small QRT. On the other hand, when the forward supply is performed, NO is applied when the reducing agent supply operation is performed._XThe amount QE of the exhaust gas flowing into the catalyst 81 is a large QEF, and the reducing agent supply amount QR in this case is set to a relatively large QRF (> QRT).
[0066]
As I mentioned at the beginning, NO_XThe reducing agent supplied into the catalyst 81 is NO._XNO in catalyst 81_XAnd exothermic reaction with oxygen, the amount of heat generated at this time is NO when the reducing agent supply action is performed._XThe amount of exhaust gas QE and NO flowing into the catalyst 81_XIt depends on the amount QR of the reducing agent supplied to the catalyst 81, that is, the amount of heat generation increases as QE and QR increase.
[0067]
Therefore, if forward flow supply is performed rather than transient supply, NO_XThe temperature T of the catalyst 81 can be raised or NO_XIt is possible to prevent the temperature T of the catalyst 81 from decreasing.
[0068]
Therefore, in the first embodiment according to the present invention, NO is used._XWhen the temperature T of the catalyst 81 is lower than a predetermined set temperature TS, the forward flow is supplied, and NO_XWhen the temperature T of the catalyst 81 is higher than the set temperature TS, transient supply is performed.
[0069]
Generally speaking, NO_XCompared to when the temperature T of the catalyst 81 is low, the NO is reduced when the reducing agent supply action is performed._XThis means that the amount QE of exhaust gas flowing in the forward direction into the catalyst 81 is increased.
[0070]
FIG. 8A shows NO._XNO of catalyst 81_XIndicates purifying ability, ie NO_XThe temperature T of the catalyst 81 is NO._XWhen the temperature drops below the lower purification temperature limit TLN, NO_XNO of catalyst 81_XThe purification capacity falls beyond the allowable lower limit value ALN. Accordingly, the set temperature TS described above is set to this NO._XIf the purification capacity lower limit temperature TLN is set, NO_XNO of catalyst 81_XThe purifying ability can be quickly increased to the allowable lower limit value ALN or higher, or can be maintained to the allowable lower limit value ALN or higher.
[0071]
FIG. 8B shows NO._XIt shows the particulate oxidation ability of the catalyst 81, ie NO_XWhen the temperature T of the catalyst 81 falls below the lower limit temperature TLPM for particulate oxidation ability, NO_XThe fine particle oxidation ability of the catalyst 81 decreases beyond the allowable lower limit ALPM. Therefore, if the set temperature TS described above is set to the fine particle oxidation ability lower limit temperature TLPM, NO._XThe fine particle oxidation ability of the catalyst 81 can be quickly increased to the allowable lower limit ALPM or higher, or can be maintained to the allowable lower limit ALPM or higher.
[0072]
On the other hand, from the opposite perspective, if transient supply is performed rather than forward flow supply, NO_XThe temperature rise of the catalyst 81 can be suppressed. That is, as shown in FIG._XThe temperature T of the catalyst 81 is NO._XWhen the temperature rises above the upper purification temperature limit TUN, NO_XNO of catalyst 81_XThe purification capacity falls beyond the allowable lower limit value ALN. Accordingly, the set temperature TS described above is set to this NO._XIf the purifying capacity upper limit temperature TUN is set, NO_XNO of catalyst 81_XThe purifying ability can be maintained above the allowable lower limit value ALN.
[0073]
FIG. 9 shows an exhaust purification control routine for executing the above-described embodiment according to the present invention. This routine is executed by interruption every predetermined time.
[0074]
Referring to FIG. 9, first, in step 100, it is determined whether or not the required load L has become zero, that is, whether or not the switching valve 61 should be switched from the forward flow position to the reverse flow position or vice versa. When the required load L becomes zero, the routine proceeds to step 101 where NO_XNO accumulated in catalyst 81_XIt is determined whether or not the amount QN is larger than the first allowable amount QN1. When QN ≦ QN1, the routine proceeds to step 102 where the switching valve 61 is switched and the reducing agent supply action is not performed.
[0075]
On the other hand, when QN> QN1, the routine proceeds to step 103 where a reducing agent supply control routine is executed. The reducing agent supply control routine of the first embodiment according to the present invention is shown in FIG.
[0076]
Referring to FIG. 10, first, in step 120, NO._XIt is determined whether or not the temperature T of the catalyst 81 is lower than the set temperature TS. When T <TS, the routine proceeds to step 121 where the reducing agent supply amount QR is set to a relatively large QRF. In the subsequent step 122, the switching valve 61 is switched and the forward flow is supplied. That is, when the switching valve 61 is in the backflow position, the switching valve 61 is switched to the forward flow position, and then the reducing agent is supplied by QR. When the switching valve 61 is in the forward flow position, the reducing agent is supplied by QR, and then the switching valve 61 is switched to the forward flow position.
[0077]
On the other hand, when T ≧ TS, the routine proceeds to step 123 where the reducing agent supply amount QR is set to a relatively small QRT. In the following step 124, the switching valve 61 is switched and transient supply is performed. That is, the reducing agent supply operation is performed at the time when the switching valve 61 is switched.
[0078]
Referring to FIG. 9 again, when the required load L is not zero, the routine proceeds from step 100 to step 104, where the accumulated NO_XIt is determined whether or not the amount QN is larger than the second allowable amount QN2. When QN ≦ QN2, the processing cycle is terminated. When QN> QN2, the routine proceeds to step 105 where it is determined whether or not the switching valve 61 is currently in the forward flow position. When the switching valve 61 is currently in the forward flow position, the routine proceeds to step 106 where the reducing agent supply amount QR is calculated, and then the routine proceeds to step 107 where forward flow supply is performed. On the other hand, when the switching valve 61 is currently in the backflow position, the routine proceeds to step 108 where the reducing agent supply amount QR is calculated, and then the routine proceeds to step 109 where transient supply is performed.
[0079]
That is, when the process proceeds from step 104 to step 105, it is not the time to switch the switching valve 61. Therefore, when the switching valve 61 is in the forward flow position, the forward flow is supplied. At this time, since a relatively large amount of exhaust gas is discharged from the internal combustion engine, when the switching valve 61 is in the backflow position, transient supply with a small reducing agent supply amount QR is performed. In step 106 and step 108, for example, the reducing agent supply amount QR is calculated based on the intake air amount.
[0080]
Next, a second embodiment according to the present invention will be described.
[0081]
NO when the elapsed time tD from the start of the engine is relatively short_XNO when the temperature T of the catalyst 81 is low and the elapsed time tD is long._XThe temperature T of the catalyst 81 increases. Therefore, if the forward flow is supplied when the elapsed time tD is short, NO_XThe temperature T of the catalyst 81 can be quickly raised.
[0082]
In the second embodiment according to the present invention, when the elapsed time tD is shorter than the predetermined set time tDS, the forward flow is supplied, and after the elapsed time tD becomes longer than the set time tDS, the transient supply is performed. Yes. In addition, since the engine was started, NO_XThe temperature T of the catalyst 81 is equal to the NO described above with reference to FIG._XIt is also possible to obtain the required time until the lower limit temperature TLN for purification ability or the lower limit temperature TLPM for fine particle oxidation is obtained in advance by experiment, and this required time can be set as the set time tDS.
[0083]
FIG. 11 shows a reducing agent supply control routine of the second embodiment according to the present invention. This routine is executed in step 103 of FIG.
[0084]
Referring to FIG. 11, first, at step 140, it is judged if an elapsed time tD after the engine is started is shorter than a set time tDS. When tD <tDS, the routine proceeds to step 141 where the reducing agent supply amount QR is set to a relatively large QRF. In the subsequent step 142, the switching valve 61 is switched and forward flow supply is performed. On the other hand, when tD ≧ tDS, the routine proceeds to step 143 where the reducing agent supply amount QR is set to a relatively small QRT. In the following step 144, the switching valve 61 is switched and transient supply is performed.
[0085]
Next, a third embodiment according to the present invention will be described. In the third embodiment, the transient supply described above is performed, and the forward flow supply is not performed.
[0086]
In transient supply, NO is applied when the reducing agent supply action is performed._XThe amount QET of the exhaust gas flowing into the catalyst 81 depends on the reference time, for example, the time interval tRF, tFR from the time X when the signal for switching the switching valve 61 is issued until the reducing agent supply operation is performed. That is, when the switching valve 61 is switched from the backflow position to the forward flow position, as shown in FIG. 12A, the exhaust gas amount QET decreases as the time interval tRF becomes shorter, as shown in FIG. Thus, when the time interval tRF becomes longer, the exhaust gas amount QET increases. When the switching valve 61 is switched from the forward flow position to the reverse flow position, the exhaust gas amount QET increases as the time interval tFR decreases, and the exhaust gas amount QET decreases as the time interval tFR increases.
[0087]
Therefore, in the third embodiment according to the present invention, the time intervals tRF and tFR are set to NO._XThe temperature is set according to the temperature T of the catalyst 81. Specifically, as shown in FIG. 13, the time interval tRF when the switching valve 61 is switched from the backflow position to the forward flow position is NO._XThe time interval tFR when the switching valve 61 is switched from the forward flow position to the reverse flow position is NO as the temperature T of the catalyst 81 decreases._XThe temperature is shortened as the temperature T of the catalyst 81 decreases.
[0088]
FIG. 14 shows the reducing agent supply amount QR in this case. That is, as shown in FIG. 14A, the reducing agent supply amount QR increases as the time interval tRF becomes longer, and as shown in FIG. 14B, the reducing agent supply amount QR decreases as the time interval tFR becomes shorter. Will increase. Therefore, when the reducing agent supply action is performed, NO_XAs the amount QET of the exhaust gas flowing into the catalyst 81 increases, the reducing agent supply amount QR increases.
[0089]
FIG. 15 shows the reducing agent supply control routine of the third embodiment according to the present invention. This routine is executed in step 103 of FIG.
[0090]
Referring to FIG. 15, first, at step 160, the time interval tFR or tRF is calculated from the map of FIG. 13 according to the current position of the switching valve 61. In the following step 161, the reducing agent supply amount QR is calculated from the map of FIG. In the following step 162, the switching valve 61 is switched and transient supply is performed. That is, the reducing agent is supplied by the reducing agent supply amount QR when the time intervals tFR and tRF have elapsed from the timing X when the signal for switching the switching valve 61 is issued.
[0091]
Next, a fourth embodiment according to the present invention will be described.
[0092]
In the transient supply described so far, the switching valve 61 is continuously switched from the forward flow position to the reverse flow position or vice versa, and the reducing agent supply action is performed in the middle thereof.
[0093]
In contrast, in the fourth embodiment according to the present invention, the weak forward flow supply that performs the reducing agent supply operation when the switching valve 61 is temporarily held at the weak forward flow position and the switching valve 61 is held at the weak forward flow position. Is done. When the switching valve 61 is held at the weak forward flow position, most of the exhaust gas flows out from the inflow port 62 directly into the exhaust gas discharge pipe 64 through the outflow port 63 as shown by an arrow in FIG. NO_XThe catalyst 81 is bypassed, and a small amount of the remaining exhaust gas flows into the annular exhaust pipe 67 via the inflow / outflow port 65, and then NO._XThe catalyst 81 flows in the forward flow direction. This weak forward flow supply will be described in detail with reference to FIG.
[0094]
FIG. 17 shows the position VP and NO of the switching valve 61 when the weak forward flow supply is performed._XFIG. 6 is a view showing the change over time in the amount QE of exhaust gas flowing in the forward flow direction into the catalyst 81 in the same manner as FIG. 5.
[0095]
Further, the switching valve position VP is a reference position, for example, almost all exhaust gas is NO._XThe position of the switching valve 61 with respect to the entire bypass position that bypasses the catalyst 81 is shown. When the switching valve 61 is between the entire bypass position and the forward flow position, the switching valve position VP becomes a positive value and approaches the forward flow position from the entire bypass position. As it grows. Further, when the switching valve 61 is between the total bypass position and the backflow position, the switching valve position VP becomes a negative value and becomes smaller as the backflow position is approached from the total bypass position.
[0096]
When the switching valve 61 is switched from the backflow position to the forward flow position, for example, as shown in FIG. 17, the switching valve 61 is moved from the backflow position to the weak forward flow position WF and temporarily held at the weak forward flow position WF. Then, it is moved to the forward position which is the target position. As a result, NO_XA slight amount QE of the exhaust gas flowing into the catalyst 81 is temporarily held at QEWF, and at this time, a reducing agent supply operation is performed as indicated by an arrow R. In this case, the time interval from the time X when the signal for switching the switching valve 61 is issued until the reducing agent supply operation is performed is represented by tWF. The same applies when the switching valve 61 is switched from the forward flow position to the reverse flow position.
[0097]
NO when the reducing agent supply action is performed_XThe amount QEWF of the exhaust gas flowing into the catalyst 81 depends on the weak forward flow position WF, that is, the exhaust gas amount QEWF decreases as the weak forward flow position WF decreases. FIG. 18A shows the case where the weak forward flow position WF is small, and FIG. 18B shows the case where the weak forward flow position WF is large.
[0098]
Therefore, in the fourth embodiment according to the present invention, the weak forward flow position WF is set to NO._XThe temperature is set according to the temperature T of the catalyst 81. Specifically, as shown in FIG. 19, the weak forward flow position WF is NO._XThe temperature is increased as the temperature T of the catalyst 81 decreases.
[0099]
As shown in FIG. 20, the reducing agent supply amount QR in this case increases as the weak forward flow position WF increases. Therefore, when the reducing agent supply action is performed, NO_XAs the amount QEWF of the exhaust gas flowing into the catalyst 81 increases, the reducing agent supply amount QR increases.
[0100]
FIG. 21 shows the reducing agent supply control routine of the fourth embodiment according to the present invention. This routine is executed in step 103 of FIG.
[0101]
Referring to FIG. 21, first, at step 180, the weak forward flow position WF is calculated from the map of FIG. In the subsequent step 181, the reducing agent supply amount QR is calculated from the map of FIG. In the subsequent step 182, the switching valve 61 is switched and weak forward flow supply is performed. That is, the switching valve 61 is temporarily held at the weak forward flow position WF, and at this time, the reducing agent is supplied by the reducing agent supply amount QR.
[0102]
Each of the embodiments according to the present invention described so far can also be applied to the internal combustion engine shown in FIGS.
[0103]
In the internal combustion engine shown in FIG. 22, a casing 168 is connected to the outlet of the exhaust pipe 20 a, the casing 168 is connected to the casing 175 through the exhaust pipe 20 c, and the casing 175 is connected to the exhaust pipe 23. These casings 168 and 175 have NO inside_XThe particulate filter 69 carrying the catalyst 81 and the auxiliary catalyst 76 are accommodated.
[0104]
A bypass pipe 185 is branched from the exhaust pipe 20a, and an outflow end of the bypass pipe 185 opens to the exhaust pipe 20c. In addition, a switching valve 161 controlled by an electronic control unit (not shown) is disposed in a portion of the exhaust pipe 20a where the inflow end of the bypass pipe 185 is open. Further, a reducing agent supply valve 77 is disposed in the exhaust pipe 20 a between the inflow end of the bypass pipe 185 and the particulate filter 69.
[0105]
The switching valve 161 is normally held at the normal position shown by the solid line in FIG. When the switching valve 161 is held in this normal position, the bypass pipe 185 is shut off, and almost all the exhaust gas flowing into the exhaust pipe 20a is guided into the particulate filter 69. Therefore, the normal position of the switching valve 161 corresponds to the forward flow position or the reverse flow position of the switching valve 61 in the internal combustion engine of FIG.
[0106]
When the switching valve 161 is held at the weak flow position indicated by the alternate long and short dash line in FIG. 23, a small part of the exhaust gas flowing into the exhaust pipe 20a is guided into the particulate filter 69 and the remaining exhaust gas is bypassed. Guided into tube 185. Therefore, the weak flow position of the switching valve 161 corresponds to the weak forward flow position of the switching valve 61 in the internal combustion engine of FIG. If the switching valve 161 is held at the bypass position indicated by the broken line in FIG. 23, the bypass pipe 185 is opened, and almost all exhaust gas flowing into the exhaust pipe 20a bypasses the particulate filter 69. Therefore, the bypass position of the switching valve 161 corresponds to the entire bypass position of the switching valve 61 in the internal combustion engine of FIG.
[0107]
In this case, for example, NO_XWhen the temperature T of the catalyst 81 is low, the reducing agent is supplied when the switching valve 161 is in the normal position, and NO_XWhen the temperature T of the catalyst 81 is high, the reducing agent supply operation can be performed during a transition in which the switching valve 161 is switched from the normal position to the bypass position or vice versa.
[0108]
On the other hand, in the internal combustion engine shown in FIG. 24, the exhaust pipe 20a is formed of a Y-shaped pipe having a pair of branch pipes 91 ′ and 91 ″, and casings 68 ′ and 68 ″ are connected to the outlets of the branch pipes, respectively. The The casings 68 'and 68 "are connected to the branch pipes 92' and 92" of the exhaust pipe 20c, and are connected to the casing 175 via the exhaust pipe 20c. The casing 175 is connected to the exhaust pipe 23. First and second particulate filters 69 ′ and 69 ″ are accommodated in the casings 68 ′ and 68 ″, respectively, and an auxiliary catalyst 76 is accommodated in the casing 175. It should be noted that the first and second NO filters are respectively provided on the first and second particulate filters 69 'and 69 "._XCatalysts 81 'and 81 "are supported.
[0109]
In the branch pipe of the exhaust pipe 20c, first and second switching valves 61 ′ and 61 ″ driven by a common actuator 260 are respectively arranged. In the branch pipe of the exhaust pipe 20a, the first and second switches are arranged. The reducing agent supply valves 77 ′ and 77 ″ are respectively arranged. The actuator 260 and the reducing agent supply valves 77 'and 77 "are controlled by an electronic control unit (not shown).
[0110]
The switching valves 61 ′ and 61 ″ are normally held at the first normal position indicated by a solid line in FIG. 25A or the second normal position indicated by a broken line. 1, the first switching valve 61 ′ is held in the fully open position, and the second switching valve 61 ″ is held in the fully closed position. Therefore, the solid line arrow in FIG. As shown, almost all the exhaust gas flowing into the exhaust pipe 20a is the first NO._XIt is led into the catalyst 69 '. On the other hand, when the switching valves 61 ′ and 61 ″ are held in the second normal position, the first switching valve 61 ′ is held in the fully closed position, and the second switching valve 61 ″ is held in the fully open position. Therefore, as shown by the broken arrow in FIG. 25A, almost all the exhaust gas flowing into the exhaust pipe 20a is second NO._XAccordingly, the first and second normal positions of the switching valves 61 'and 61 "correspond to the normal position or the bypass position of the switching valve 161 in the internal combustion engine of FIG.
[0111]
When the switching valves 61 ′ and 61 ″ are held at the first weak flow position indicated by the solid line in FIG. 25B, a small part of the exhaust gas that has flowed into the exhaust pipe 20 a becomes the first NO._XThe remaining exhaust gas guided into the catalyst 81 'is second NO._XOn the other hand, when the switching valves 61 ′ and 61 ″ are held at the second weak flow position shown by the broken line in FIG. 25B, the exhaust gas flowing into the exhaust pipe 20a is guided. A small part is the second NO_XThe remaining exhaust gas introduced into the catalyst 81 "is the first NO._XIt is led into the catalyst 81 '. Thus, the weak flow positions of the switching valves 61 'and 61 "correspond to the weak forward flow positions of the switching valve 61 in the internal combustion engine of FIG.
[0112]
In this case, the first NO_XLooking at the catalyst 81 ', for example, the first NO_XWhen the temperature of the catalyst 81 'is low, when the switching valves 61' and 61 "are in the first normal position, the reducing agent supply action is performed, and the first NO_XWhen the temperature of the catalyst 81 ′ is high, the reducing valve 61 ′, 61 ″ can perform a reducing agent supply operation during a transition in which the switching valve 61 ′, 61 ″ is switched from the first normal position to the second normal position or vice versa. NO_XLooking at the catalyst 81 ", for example, the second NO_XWhen the temperature of the catalyst 81 "is low, the reducing valve supply action is performed when the switching valves 61 'and 61" are in the second normal position, and the second NO._XWhen the temperature of the catalyst 81 "is high, the reducing valve 61 ', 61" can perform a reducing agent supply operation during a transition in which the switching valve 61', 61 "is switched from the first normal position to the second normal position or vice versa.
[0113]
Therefore, generally speaking, NO in the exhaust passage_XPlace catalyst and NO_XA reducing agent supply valve is disposed in the exhaust passage upstream of the catalyst, and is branched from the exhaust passage upstream of the reducing agent supply valve to reduce the reducing agent supply valve._XBy providing a bypass passage that bypasses the catalyst and controlling the amount of exhaust gas flowing through the bypass passage, NO_XThis means that a switching valve is provided for controlling the amount of exhaust gas flowing through the catalyst.
[0114]
In addition, in the internal combustion engine shown in FIG._XNO flows into the catalyst through its one end face_XGuide the exhaust gas to flow out from the catalyst through the other end face, or NO_XNO flows into the catalyst through the other end face_XThat is, whether the exhaust gas is guided so as to flow out from the catalyst through one end face thereof is switched.
[0115]
In the internal combustion engine shown in FIG. 24, for example, when focusing on the exhaust passage portion from the branch pipe 91 'of the exhaust pipe 20a to the branch pipe 92' of the exhaust pipe 20c, the branch pipe 91 "to the exhaust pipe 20c of the exhaust pipe 20a. It can also be seen that the part of the exhaust passage up to the branch pipe 92 "acts as a bypass passage. In this case, the second reducing agent supply valve 77 ", the second particulate filter 69", the second NO_XEach of the catalysts 81 "has an additional reducing agent supply valve, an additional particulate filter and an additional NO disposed in the bypass passage._XThat is, it constitutes a catalyst.
[0116]
【The invention's effect】
NO_XActivate catalyst quickly or NO_XThe activity of the catalyst can be kept high.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
FIG. 2 is a diagram showing a structure of a catalytic converter.
FIG. 3 is a view for explaining the flow of exhaust gas when the switching valve is in a forward flow position or a reverse flow position.
FIG. 4 is a partial enlarged cross-sectional view of a partition wall of a particulate filter.
FIG. 5: NO when the switching valve is switched_XIt is a diagram which shows a time-dependent change of the exhaust gas QE which flows in in a catalyst.
FIG. 6 is a view for explaining a reducing agent supply operation.
FIG. 7 is a diagram similar to FIG. 5 for explaining the first embodiment according to the present invention.
FIG. 8 NO_XIt is a diagram which shows the characteristic of a catalyst.
FIG. 9 is a flowchart showing an exhaust purification control routine.
FIG. 10 is a flowchart showing a reducing agent supply control routine of the first embodiment according to the present invention.
FIG. 11 is a flowchart showing a reducing agent supply control routine of a second embodiment according to the present invention.
FIG. 12 is a diagram similar to FIG. 5 for explaining a third embodiment according to the present invention.
FIG. 13 is a diagram showing time intervals tRF and tFR.
FIG. 14 is a diagram showing a reducing agent supply amount QR.
FIG. 15 is a flowchart showing a reducing agent supply control routine of a third embodiment according to the present invention.
FIG. 16 is a view for explaining the flow of exhaust gas when the switching valve is in a weak forward flow position.
FIG. 17 is a diagram for explaining a fourth embodiment according to the present invention.
FIG. 18 is a diagram for explaining a fourth embodiment according to the present invention.
FIG. 19 is a diagram showing a weak forward flow position WF.
FIG. 20 is a diagram showing a reducing agent supply amount QR.
FIG. 21 is a flowchart showing a reducing agent supply control routine according to a fourth embodiment of the present invention.
FIG. 22 is a diagram showing another internal combustion engine to which the present invention is applicable.
23 is a view for explaining the position of a switching valve of the internal combustion engine shown in FIG. 22. FIG.
FIG. 24 is a view showing another internal combustion engine to which the present invention is applicable.
25 is a view for explaining the position of a switching valve of the internal combustion engine shown in FIG. 24. FIG.
[Explanation of symbols]
1 ... Engine body
20a ... exhaust pipe
51. Temperature sensor
61 ... Switching valve
69 ... Particulate filter
77 ... Reducing agent supply valve
81 ... NO_Xcatalyst

Claims (15)

In the exhaust passage of the internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio, NO _X in the exhaust gas flowing in when the air-fuel ratio of the inflowing exhaust gas is lean is stored, and the inflowing exhaust gas When the air-fuel ratio is reduced, a NO _X catalyst that reduces the amount of NO _X stored by reducing the stored NO _X when the reducing agent is contained in the exhaust gas is disposed, and the NO _X catalyst in the NO _X catalyst is disposed. temporarily supplying the reducing agent supply means of the reducing agent to the NO _X catalyst to reduce the amount of the NO _X that the reduction of NO _X is stored in the NO _X catalyst, in the exhaust passage of the NO _X catalyst upstream In the exhaust gas purification apparatus for an internal combustion engine arranged, a bypass passage that bypasses the NO _X catalyst is provided, and the amount of exhaust gas flowing into the NO _X catalyst is changed by changing the amount of exhaust gas flowing into the bypass passage. As the amount changes It is, than when higher when the temperature of the NO _X catalyst is low, so much amount of the exhaust gas flowing into the NO _X catalyst when supplying a reducing agent from the reducing agent supply means to the NO _X catalyst When the elapsed time from the start of the internal combustion engine is shorter than a predetermined set time, the exhaust gas is prevented from flowing into the bypass passage and almost all after the reducing agent supplied from the reducing agent supply means to the NO _X catalyst, the amount of time elapsed since the startup of the internal combustion engine exceeds a set time when the exhaust gas flows into the NO _X catalyst, the exhaust gas one part exhaust purification device of an internal combustion engine so as to supply the reducing agent from the reducing agent supply means to the NO _X catalyst when the amount of exhaust gas flowing into the NO _X catalyst to flow into the bypass passage is reduced . Temperature of the NO _X catalyst being adapted to NO _X purification performance of the NO _X catalyst when reduced beyond the NO _X purification performance limit temperature decreases beyond the allowable lower limit value, the set time is started internal combustion engine 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the time required for the temperature of the NO _X catalyst to reach the NO _X purification capacity lower limit temperature is set . The NO _X catalyst are supported on a particulate filter for trapping particulate contained in the exhaust gas flowing, of the NO _X catalyst when the temperature of the NO _X catalyst is reduced over the particulate oxidation ability minimum temperature claims particulate oxidation ability is controlled so as to decrease beyond the allowable lower limit value was set to the required time of the setting time since the startup of the internal combustion engine until the temperature of the NO _X catalyst is particulate oxidation ability minimum temperature Item 6. An exhaust emission control device for an internal combustion engine according to Item 1 . A forward flow position in which the exhaust gas guides the exhaust gas to flow out from the other end face after flowing in the inflow and forward flow direction from one end face in the NO _X catalyst, the exhaust gas flows from the other end face in the NO _X catalyst backflow A switching valve that can switch between a backflow position that guides exhaust gas so as to flow out from one end face after flowing in the direction, and the switching valve is switched from the forward flow position to the reverse flow position or vice versa by an amount gradually increases correspondingly of the exhaust gas flowing in the bypass passage NO _X amount of exhaust gas flowing into the catalyst decreases gradually, then NO after the orientation of the exhaust gas flow in the NO _X catalyst is reversed the amount of the exhaust gas amount of the exhaust gas flowing into the _X catalyst flows gradually increased bypass passage is correspondingly adapted to decrease gradually, the exhaust gas flow in the forward flow direction An exhaust purification system of an internal combustion engine according to claim 1, wherein the reducing agent supply means into the exhaust passage located in the NO _X catalyst upstream is provided. When shorter than the set time the elapsed time reaches a predetermined from being started internal combustion engine supplies the reducing agent from the reducing agent supply means into the NO _X catalyst when the selector valve is held in the forward flow position, after the elapsed time from the startup of the internal combustion engine exceeds a set time, supplying the reducing agent from the reducing agent supply means during a transient switching valve is switched to or vice versa backflow position from the forward flow position in NO _X catalyst The exhaust emission control device for an internal combustion engine according to claim 4, wherein the exhaust gas purification device is configured as described above . In the exhaust passage of the internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio, NO _X in the exhaust gas flowing in when the air-fuel ratio of the inflowing exhaust gas is lean is stored, and the inflowing exhaust gas When the air-fuel ratio is reduced, a NO _X catalyst that reduces the amount of NO _X stored by reducing the stored NO _X when the reducing agent is contained in the exhaust gas is disposed, and the NO _X catalyst in the NO _X catalyst is disposed . temporarily supplying the reducing agent supply means of the reducing agent to the NO _X catalyst to reduce the amount of the NO _X that the reduction of NO _X is stored in the NO _X catalyst, in the exhaust passage of the NO _X catalyst upstream in the exhaust purification apparatus arranged an internal combustion engine, both the bypass passage bypassing the NO _X catalyst is provided, the exhaust gas flowing into the NO _X catalyst by the amount of the exhaust gas flowing into the bypass passage is changed As the amount of changes It is, the amount of exhaust gas flowing into the NO _X catalyst when the reducing agent is supplied from the reducing agent supply means to the NO _X catalyst is made different depending on the temperature of the NO _X catalyst, the exhaust gas is NO _X a forward flow position for guiding the exhaust gas to flow out from the other end face after flowing in the inflow and forward flow direction from one end face in the catalyst after the exhaust gas has flowed into the inflow and backflow direction from the other end face in the NO _X catalyst A switching valve that can switch between a backflow position that guides exhaust gas so as to flow out from one end face thereof, and when the switching valve is switched from the forward flow position to the backflow position or vice versa, the amount of the exhaust gas amount of the exhaust gas flowing flows only into the NO _X catalyst gradually increased correspondingly decreases gradually, then NO _X catalyst after the orientation of the exhaust gas flow is reversed in the NO _X catalyst The amount of the exhaust gas amount of the exhaust gas flowing into the medium flows only in the bypass passage gradually increased correspondingly and is adapted to decrease gradually, located in the NO _X catalyst upstream with respect to the exhaust gas flow in the forward flow direction into the exhaust passage and the is provided a reducing agent feeding means, or the switching valve to supply the reducing agent from the reducing agent supply means into the NO _X catalyst when held in the forward flow position, the switching valve from the forward flow position or to supply the reducing agent from the reducing agent supply means during a transient is switched to the reverse flow position or vice versa in the NO _X catalyst, exhaust gas purification apparatus for an internal combustion engine to switch in accordance with the temperature of the NO _X catalyst. When the temperature of the NO _X catalyst is lower than a predetermined set temperature, the reducing agent is supplied from the reducing agent supply means to the NO _X catalyst when the switching valve is held in the forward flow position, and the temperature of the NO _X catalyst is when higher than the set temperature, the switching valve of an internal combustion engine according to claim 6 which is adapted to supply the reducing agent to the NO _X catalyst from a reducing agent supply means during a transient is switched on or vice versa backflow position from the forward flow position Exhaust purification device. Temperature of the NO _X catalyst has become NO _X purification performance of the NO _X catalyst when reduced beyond the NO _X purification performance limit temperature decreases beyond the allowable lower limit value, the setting temperature of the NO _X catalyst NO _X The exhaust gas purification apparatus for an internal combustion engine according to claim 7, wherein the exhaust gas purification apparatus is set to a lower purification temperature lower limit temperature . The NO _X catalyst are supported on a particulate filter for trapping particulate contained in the exhaust gas flowing, of the NO _X catalyst when the temperature of the NO _X catalyst is reduced over the particulate oxidation ability minimum temperature particulate oxidation ability is controlled so as to decrease beyond the allowable lower limit value, the exhaust purification system of an internal combustion engine according to claim 7 which sets the set temperature to particulate oxidation ability minimum temperature of the NO _X catalyst. When shorter than the set time the elapsed time reaches a predetermined from being started internal combustion engine, the reducing agent supplied from the reducing agent supply means to the NO _X catalyst when the selector valve is held in the forward flow position, the internal combustion after the engine is the amount of time elapsed since the start exceeds the set time, so that the switching valve to supply the reducing agent to the NO _X catalyst from a reducing agent supply means during a transient is switched on or vice versa backflow position from the forward flow position The exhaust emission control device for an internal combustion engine according to claim 6 . In the exhaust passage of the internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio, NO _X in the exhaust gas flowing in when the air-fuel ratio of the inflowing exhaust gas is lean is stored, and the inflowing exhaust gas When the air-fuel ratio is reduced, a NO _X catalyst that reduces the amount of NO _X stored by reducing the stored NO _X when the reducing agent is contained in the exhaust gas is disposed, and the NO _X catalyst in the NO _X catalyst is disposed . temporarily supplying the reducing agent supply means of the reducing agent to the NO _X catalyst to reduce the amount of the NO _X that the reduction of NO _X is stored in the NO _X catalyst, in the exhaust passage of the NO _X catalyst upstream In the exhaust gas purification apparatus for an internal combustion engine arranged, a bypass passage that bypasses the NO _X catalyst is provided, and the amount of exhaust gas flowing into the NO _X catalyst is changed by changing the amount of exhaust gas flowing into the bypass passage. As the amount changes It is, the amount of exhaust gas flowing into the NO _X catalyst when the reducing agent is supplied from the reducing agent supply means to the NO _X catalyst is made different depending on the temperature of the NO _X catalyst, the exhaust gas is NO _X a forward flow position for guiding the exhaust gas to flow out from the other end face after flowing in the inflow and forward flow direction from one end face in the catalyst after the exhaust gas has flowed into the inflow and backflow direction from the other end face in the NO _X catalyst A switching valve that can switch between a backflow position that guides exhaust gas so as to flow out from one end face thereof, and when the switching valve is switched from the forward flow position to the backflow position or vice versa, the amount of the exhaust gas amount of the exhaust gas flowing flows only into the NO _X catalyst gradually increased correspondingly decreases gradually, then NO _X catalyst after the orientation of the exhaust gas flow is reversed in the NO _X catalyst The amount of the exhaust gas amount of the exhaust gas flowing into the medium flows only in the bypass passage gradually increased correspondingly and is adapted to decrease gradually, located in the NO _X catalyst upstream with respect to the exhaust gas flow in the forward flow direction is provided with the reducing agent supply means into the exhaust passage, the switching valve to supply the reducing agent to the NO _X catalyst from a reducing agent supply means during a transient is switched on or vice versa backflow position from the forward flow position, the reference timing exhaust purifying apparatus for an internal combustion engine a time interval until the reducing agent is supplied and set according to the temperature of the NO _X catalyst from. Than when higher when the temperature of the NO _X catalyst is low, claims and as the amount of exhaust gas flowing into the NO _X catalyst increases when supplying a reducing agent from the reducing agent supply means to the NO _X catalyst 6 Or the exhaust gas purification apparatus for an internal combustion engine according to 11 . Than when less when the amount of exhaust gas flowing into the NO _X catalyst is often when supplying a reducing agent from the reducing agent supply means to the NO _X catalyst, reducing agent supplied to the NO _X catalyst from a reducing agent supply means The exhaust gas purification device for an internal combustion engine according to any one of claims 1, 6, 11, and 12, wherein the amount of the internal combustion engine is increased . Claim the amount of exhaust gas flowing into the NO _X catalyst by the amount of the exhaust gas flowing into the bypass passage is changed in accordance with the engine operating state is adapted to be changed in accordance with the engine operating condition The exhaust emission control device for an internal combustion engine according to any one of 1, 6 and 11 . Additional NO in the bypass passage _X Place catalyst and add NO _X Additional reducing agent supply means for supplying reducing agent to the catalyst is connected to the inflow end of the bypass passage and additional NO. _X Place in the bypass passage between the catalysts and add NO _X NO in the catalyst _X Reduce NO and add NO _X NO stored in the catalyst _X Additional NO from additional reducing agent supply means to reduce the amount of _X While temporarily supplying the reducing agent to the catalyst, at this time additional NO _X The amount of exhaust gas flowing into the catalyst _X The exhaust emission control device for an internal combustion engine according to any one of claims 1, 6, and 11, wherein the exhaust gas purification device differs according to the temperature of the catalyst.

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