JP3846355B2 - 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 exhaust gas flowing in when the 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 stored and reduced_XNO to reduce the amount of_XThe catalyst is arranged in an annular branch passage that branches off from the engine exhaust passage and extends annularly and then returns to the engine exhaust passage. At this time, the exhaust gas is guided to one end of the annular branch passage, and then the other end of the annular branch passage is annularly branched. The exhaust gas is allowed to flow into the engine exhaust passage downstream of one end of the passage, or the exhaust gas is led to the other end of the annular branch passage, and at this time, from one end of the annular branch passage to the other end of the annular branch passage. Also known is an exhaust purification device for an internal combustion engine provided with a switching valve for switching whether exhaust gas flows out into a downstream engine exhaust passage (see JP-A-2001-27114). In the present specification, the ratio of the air supplied to the exhaust passage upstream of a certain position of the exhaust passage, the combustion chamber, and the intake passage and the hydrocarbon HC and carbon monoxide CO is determined by the ratio of the exhaust gas at that position. This is called the air-fuel ratio.
[0003]
By the way, NO_XNO that the catalyst can store_XAmount is limited, so NO_XNO stored in the catalyst_XNO when the amount exceeds the allowable amount_XReduce the air-fuel ratio of the exhaust gas flowing into the catalyst and NO_XSupply the reducing agent to the catalyst, thereby NO_XNO stored in the catalyst_XThe amount of need to be reduced. Therefore, in the above publication, the air-fuel ratio of the air-fuel mixture combusted by the internal combustion engine is temporarily switched to the stoichiometric air-fuel ratio or the rich air-fuel ratio.
[0004]
[Problems to be solved by the invention]
NO_XReduce the air-fuel ratio of the exhaust gas flowing into the catalyst and NO_XVarious methods are known for supplying a reducing agent to a catalyst, such as a switching valve and NO._XNO in the annular branch passage between the catalysts_XIt is also possible to arrange a reducing agent supply valve for supplying the reducing agent to the catalyst.
[0005]
However, when this is done, the reducing agent supply valve is set to NO._XIn some cases, the catalyst cannot be sufficiently separated. In this case, the reducing agent supplied from the reducing agent supply valve and the exhaust gas cannot be sufficiently mixed._XReducing agent cannot be supplied to the entire catalyst, so NO_XNO over the entire catalyst_XThere is a problem that it cannot be used effectively for purification.
[0006]
Therefore, the object of the present invention is NO._XNO over the entire catalyst_XAn object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can be used effectively for purification.
[0007]
[Means for Solving the Problems]
  In order to solve the above-described problem, according to the first invention, the NO in the exhaust gas flowing in when the air-fuel ratio of the flowing exhaust gas is lean._XNO when storing the reducing agent in the exhaust gas when the air-fuel ratio of the exhaust gas flowing in decreases_XNO is stored and reduced_XNO to reduce the amount of_XThe catalyst is arranged in an annular branch passage that branches off from the engine exhaust passage and extends annularly and then returns to the engine exhaust passage. At this time, the exhaust gas is guided to one end of the annular branch passage, and then the other end of the annular branch passage is annularly branched. The forward flow position where the exhaust gas flows into the engine exhaust passage downstream from one end of the passage, and the exhaust gas is guided to the other end of the annular branch passage while downstream from the other end of the annular branch passage. A switching valve capable of switching between a reverse flow position where exhaust gas flows out into the engine exhaust passage., NO_XReducing agent supply valve for supplying reducing agent to the catalystSwitching valve and NO _X Between the catalystsIn an exhaust gas purification apparatus for an internal combustion engine arranged in an annular branch passage, a plurality of reducing agent supply valves are provided, and these reducing agent supply valves are set to NO._XA face-to-face arrangement on one end of the catalystWhen the switching valve is switched from the forward flow position to the reverse flow position or vice versa, the amount of exhaust gas flowing through the annular branch passage is temporarily reduced, and the amount of exhaust gas bypassing the annular branch passage is increased accordingly. The switching valve is switched from the forward flow position to the reverse flow position or vice versa, so that NO _X NO facing each other from the reducing agent supply valve when the amount of exhaust gas flowing through the catalyst portion is reduced _X While supplying a reducing agent to the catalyst part, NO _X When the amount of exhaust gas flowing through the catalyst portion becomes a small amount, _X Reducing agent supply timing is set for each reducing agent supply valve so that the reducing agent is supplied to the catalyst part.is doing.
[0008]
Further, according to the second invention, in the first invention, NO is generated by spraying the reducing agent formed by the reducing agent supply valve._XThe reducing agent supply valves are respectively positioned so that almost the entire one end face of the catalyst is covered.
[0011]
  Also,3According to the second invention, in the first invention, NO_XA plurality of NOs in which the catalyst is arranged in parallel in the annular branch passage_XIt is composed of a catalyst, and each of a plurality of reducing agent supply valves has a corresponding NO._XIt is arranged to face one end face of the catalyst.
[0014]
  Also,4According to the second invention, in the first invention, NO_XA catalyst is supported on a particulate filter for collecting fine particles contained in the exhaust gas.
According to the fifth aspect, in the fourth aspect, the switching valve is switched from the forward flow position to the reverse flow position or vice versa when the amount of fine particles deposited on the particulate filter exceeds the allowable amount.
[0015]
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.
[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 Is an exhaust valve, and 10 is an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13. A throttle valve 17 driven by a step motor 16 is disposed in the intake duct 13, and a cooling device 18 for cooling intake air flowing through the intake duct 13 is disposed around the intake duct 13. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 18 and the intake air is cooled by the engine cooling water.
[0017]
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.
[0018]
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.
[0019]
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 69f and 69r denote one end face and the other end face of the particulate filter 69, respectively.
[0020]
The particulate filter 69 as shown in FIG. 2 (A) showing a partial longitudinal sectional view of the catalytic converter 22 including one end face of the particulate filter 69 and FIG. 2 (B) showing a partial transverse sectional view of the catalytic converter 22. 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 have one end opened and the other end closed by a non-breathable sealing material 72, and the other end opened and one end closed by a non-breathable sealing material 73. The exhaust gas passage 71 is provided. 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.
[0021]
As will be described later, NO on the particulate filter 69._XA catalyst 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. Additional catalyst, eg additional NO_XA catalyst 76 is accommodated.
[0022]
Further, the annular exhaust pipe 67 between the inflow / outflow port 65 of the switching valve 61 and the particulate filter 69 is an electrically controlled reducing agent supply valve 77a, 77b for intermittently supplying the reducing agent to the particulate filter 69. Is attached. Here, assuming that the particulate filter 69 includes a filter part FPA and a filter part FPB arranged in parallel in the annular exhaust pipe 67, a reducing agent supply valve 77a is provided for the filter part FPA. A reducing agent supply valve 77b is provided for the partial FPB. These reducing agent supply valves 77a and 77b are arranged to face one end face 69f of the particulate filter 69, respectively. The reducing agent supply valves 77a and 77b are supplied with a reducing agent from an electrically controlled reducing agent pump 78, respectively. In addition to liquid or gaseous hydrocarbons, hydrogen, urea, or the like can be used as the reducing agent. However, in the embodiment according to the present invention, fuel, that is, light oil, is used as the reducing agent.
[0023]
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. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 26, and the EGR gas is cooled by the engine cooling water.
[0024]
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.
[0025]
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 are connected. It comprises. The output signal of the fuel pressure sensor 29 is input to the input port 45 via the corresponding AD converter 47. Further, temperature sensors 48a and 48b for generating output voltages proportional to the temperatures of the filter part FPA and the filter part FPB are attached to the filter part FPA and the filter part FPB of the particulate filter 69, respectively. Are respectively input to the input ports 45 through the corresponding AD converters 47. Further, 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. The Further, the input port 45 is connected with a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, 30 °.
[0026]
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 77a, 77b and a reducing agent pump 78, respectively.
[0027]
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, all the exhaust gas discharged from the internal combustion engine flows into the annular exhaust pipe 67 sequentially through the inflow port 62 and the inflow / outflow port 65 as shown by the solid arrows in FIG. It flows into the particulate filter 69 through the one end surface 69f, flows out of the particulate filter 69 through the other end surface 69r, and then flows out into the exhaust gas exhaust outlet pipe 64 through the inflow / outflow port 66 and the outflow port 63 sequentially.
[0028]
On the other hand, when the switching valve 61 is positioned at a position indicated by a 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 discharged from the internal combustion engine flows into the annular exhaust pipe 67 sequentially through the inflow port 62 and the inflow / outflow port 66 as shown by the broken arrows in FIG. It flows into the particulate filter 69 through the other end surface 69r, flows out from the particulate filter 69 through the one end surface 69f, and then flows out into the exhaust gas discharge pipe 64 through the inflow / outflow port 65 and the outflow port 63 sequentially.
[0029]
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. Hereinafter, the flow of exhaust gas indicated by a solid line in FIG. 3B is referred to as forward flow, and the flow of exhaust gas indicated by a broken line is referred to as reverse flow. In addition, the position of the switching valve 61 indicated by a solid line in FIG. 3B 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.
[0030]
The exhaust gas that has flowed into the exhaust gas discharge pipe 64 through the outflow port 66 then passes through the additional catalyst 76 along the outer peripheral surface of the annular exhaust pipe 67 as shown in FIGS. 3 (A) and 3 (B). After proceeding, it flows out into the exhaust pipe 23.
[0031]
Explaining the flow of the exhaust gas in the particulate filter 69, during forward flow, the exhaust gas flows into the particulate filter 69 through the one end surface 69f and flows out of the particulate filter 69 through the other end surface 69r. At this time, the exhaust gas flows into the exhaust gas passage 70 opened in the one end face 69f, and then flows into the adjacent exhaust gas outflow passage 71 through the surrounding partition wall 74. On the other hand, during the reverse flow, the exhaust gas flows into the particulate filter 69 through the other end surface 69r and flows out of the particulate filter 69 through the one end surface 69f. At this time, the exhaust gas flows into the exhaust gas passage 71 opened in the other end surface 69r, and then flows into the adjacent exhaust gas outflow passage 70 through the surrounding partition wall 74.
[0032]
As shown in FIG. 4, NO is formed on both side surfaces of the partition wall 74 of the particulate filter 69 and on the inner wall surface of the pore._XEach catalyst 80 is supported. This NO_XThe catalyst is, for example, alumina as a carrier, and on this carrier, for example, alkali metal such as potassium K, sodium Na, lithium Li, cesium Cs, alkaline earth such as barium Ba, calcium Ca, lanthanum La, yttrium Y, etc. At least one selected from rare earths and a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir are supported. Additional NO_XThe catalyst 76 is similarly configured.
[0033]
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 stored and reduced_XAccumulation and reduction action to reduce the amount of.
[0034]
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.
[0035]
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 is O on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂). 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.
[0036]
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 ⁻→ NO₂) And thus NO_XNitrate ion NO in the catalyst₃ ⁻Is NO₂NO in the form of_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.₂NO when no longer exists_XNO from catalyst to next₂Is released and reduced, NO_XNO stored in the catalyst_XThe amount of is gradually reduced.
[0037]
NO without forming nitrate_XStore NO_XNO without releasing_XIt is also possible to reduce
[0038]
As described above, the exhaust gas passes through the particulate filter 69 regardless of whether it is forward flow or reverse flow. At this time, fine particles mainly composed of carbon solid contained in the exhaust gas are collected on the particulate filter 69. Is done. 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 has an oxidizing action, if the temperature of the particulate filter 69 is maintained at a temperature at which the particulates can be oxidized, for example, 250 ° C. or more, the particulates are oxidized on the particulate filter 69 and removed. .
[0039]
However, when the temperature of the particulate filter 69 is not maintained at a temperature at which particulates can be oxidized, or when the amount of particulates flowing into the particulate filter 69 per unit time becomes considerably large, the particulates deposited on the particulate filter 69 will not be retained. The amount gradually increases and the pressure loss of the particulate filter 69 increases.
[0040]
Therefore, in the embodiment according to the present invention, for example, when the amount of deposited fine particles on the particulate filter 69 exceeds the allowable maximum amount, the switching valve 61 is switched from the forward flow position to the reverse flow position or vice versa and flows into the particulate filter 69. A temperature rise control is performed in which the temperature of the particulate filter 69 is increased to 600 ° C. or higher while the air-fuel ratio of the exhaust gas is maintained lean, and then maintained at 600 ° C. or higher. When this temperature increase control is performed, the fine particles deposited on the particulate filter 69 are ignited and burned and removed. In this case, since the flow of the exhaust gas is reversed, the ash formed by burning the fine particles is easily removed from the particulate filter 69.
[0041]
There are various methods for raising the temperature of the particulate filter 69. For example, an electric heater is arranged on the end face of the particulate filter 69 and the exhaust gas flowing into the particulate filter 69 or the particulate filter 69 is heated by the electric heater, or fuel is supplied into the exhaust passage upstream of the particulate filter 69. There are a method of heating the particulate filter 69 by burning this fuel and a method of raising the temperature of the particulate filter 69 by raising the temperature of the exhaust gas discharged from the internal combustion engine.
[0042]
On the other hand, as described above, since the air-fuel ratio of the exhaust gas flowing into the particulate filter 69 is maintained lean, NO in the exhaust gas_XIs NO_XStored in the catalyst, NO_XNO accumulated in catalyst_XThe amount increases gradually.
[0043]
In an embodiment according to the invention, for example NO_XNO accumulated in catalyst_XNO when the amount exceeds the allowable amount_XNO stored in the catalyst_XNO_XNO accumulated in catalyst_XFrom the reducing agent supply valves 77a and 77b to reduce the amount of NO_XA reducing agent is temporarily supplied to the catalyst. In this case, NO_XThe air-fuel ratio of the exhaust gas flowing into the catalyst is temporarily switched to rich.
[0044]
When the reducing agent is to be supplied from the reducing agent supply valves 77a and 77b, the switching valve 61 is temporarily held at the weak forward flow position indicated by the solid line in FIG. When the switching valve 61 is held in this weak forward flow position, most of the exhaust gas discharged from the internal combustion engine is directly discharged from the inflow port 62 through the outflow port 63 as shown by the arrow in FIG. It flows out into the pipe 64, and the remaining slight constant amount of exhaust gas flows into the annular exhaust pipe 67 through the inflow / outflow port 65, and then passes through the particulate filter 69. That is, when the switching valve 61 is held at the weak forward flow position, the amount of exhaust gas flowing into the particulate filter 69 is reduced compared to when the switching valve 61 is held at the forward flow position or the reverse flow position. For this reason, 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.
[0045]
When the switching valve 61 is held at the bypass position indicated by the broken line in FIG. 5, almost all exhaust gas discharged from the internal combustion engine directly enters the exhaust gas discharge pipe 64 from the inflow port 62 through the outflow port 63. In other words, the particulate filter 69 is bypassed. The weak forward flow position described above is a position slightly moved from the bypass position toward the forward flow position.
[0046]
As described above, the reducing agent supply valves 77a and 77b are arranged so as to face the one end surface 69f of the particulate filter 69. Therefore, when the reducing agent is supplied from the reducing agent supply valves 77a and 77b, as shown in FIG. Sprays Ra and Rb of the reducing agent toward the one end surface 69f of the particulate filter 69 are formed. This reducing agent flows into the particulate filter 69 through the one end face 69f, and NO is generated by the forward exhaust gas._XIt is diffused throughout the catalyst. In this case, generally speaking, the reducing agent is supplied from the reducing agent supply valve 77a to the filter portion FPA, and the reducing agent is supplied from the reducing agent supply valve 77b to the filter portion FPB.
[0047]
The reducing agent supplied from the reducing agent supply valves 77a and 77b reaches the particulate filter 69 with its penetrating force, and is not necessarily sufficiently mixed with the exhaust gas before flowing into the particulate filter 69. However, in the embodiment according to the present invention, as shown in FIG. 5, the reducing agent supply valves 77a and 77b are positioned so that the entire one end surface 69f of the particulate filter 69 is covered with the reducing agent sprays Ra and Rb. Therefore, the reducing agent should be NO_XIt becomes possible to supply the entire catalyst.
[0048]
NO_XWhen the reducing agent is to be supplied to the catalyst, as shown in FIG. 6, a reducing agent in an amount of QR is supplied intermittently at a time interval INT from each of the reducing agent supply valves 77a and 77b. The
[0049]
Here, as the filter partial temperatures TFA and TFB become higher, NO_XThe reaction rate of the reducing agent on the catalyst is increased. This causes the reducing agent to react quickly with oxygen, i.e. NO._XThe amount of reducing agent used for the reducing action of is reduced. Therefore, in the embodiment according to the present invention, as indicated by the curve A in FIG. 7A, the reducing agent supply amount QR of the reducing agent supply valve 77a increases as the filter partial temperature TFA increases, and FIG. ), The reducing agent supply amount QR of the reducing agent supply valve 77b increases as the filter partial temperature TFB increases as indicated by the curve B. Further, as indicated by the curve A in FIG. 7B, the time interval INT of the reducing agent supply valve 77a decreases as the filter partial temperature TFA increases, and as indicated by the curve B in FIG. 7B. As the filter partial temperature TFB increases, the time interval INT of the reducing agent supply valve 77b decreases.
[0050]
On the other hand, the radius of curvature of the axis of the annular exhaust pipe 67 passing through the filter portion FPB is larger than the radius of curvature of the axis of the annular exhaust pipe 67 passing through the filter portion FPA. The axis of the annular exhaust pipe 67 facing the end faces 69f and 69r of the 69 changes its direction almost at right angles immediately before these end faces 69f and 69r. In this case, the amount or flow rate of the exhaust gas that passes through the filter portion FPB is larger than the amount or flow rate of the exhaust gas that passes through the filter portion FPA, and therefore the residence time of the reducing agent in the filter portion FPB is reduced. The residence time is shorter.
[0051]
Therefore, in the embodiment according to the present invention, as shown in FIGS. 7A and 7B, the reducing agent supply amount QR in the reducing agent supply valve 77b is larger than the reducing agent supply amount QR in the reducing agent supply valve 77a. The time interval INT in the reducing agent supply valve 77b is made smaller than the time interval INT in the reducing agent supply valve 77a.
[0052]
Therefore, generally speaking, the temperatures of the filter parts FPA and FPB corresponding to the reducing agent supply actions such as the reducing agent supply amount and the reducing agent supply timing in the reducing agent supply valves 77a and 77b, respectively, or the corresponding filter parts respectively. This means that the values are set based on the amount of exhaust gas flowing through the FPA and FPB. Alternatively, it can be seen that the reducing agent supply actions of the reducing agent supply valves 77a and 77b are different from each other. In this way, excess or deficiency does not occur in the reducing agent supplied to the filter portions FPA and FPB.
[0053]
Then for example NO_XNO accumulated in catalyst_XWhen the amount becomes almost zero, the reducing agent supply action from the reducing agent supply valves 77a and 77b is stopped.
[0054]
FIG. 8 shows a routine for executing the above-described reducing agent supply control. This routine is executed by interruption every predetermined time.
[0055]
Referring to FIG. 8, first, at step 100, the reducing agent supply valves 77a and 77b are controlled to NO._XIt is determined whether or not the reducing agent should be supplied to the catalyst. NO from the reducing agent supply valves 77a and 77b_XWhen the reducing agent is to be supplied to the catalyst, the routine proceeds to step 101 where the switching valve 61 is switched to the weak forward flow position shown in FIG. In the subsequent step 102, the reducing agent supply amount QR and the supply time interval INT in the reducing agent supply valves 77a and 77b are calculated from the map of FIG. In the subsequent step 103, a reducing agent is supplied in accordance with these QR and INT. In the following step 104, it is determined whether or not the reducing agent supply operation should be stopped. When the reducing agent supply action is to be continued, the processing cycle is terminated, and when the reducing agent supply action is to be stopped, the routine proceeds to step 105 where the reducing agent supply action is stopped. In the subsequent step 106, the switching valve 61 is returned to the position before the reducing agent supply operation is started.
[0056]
In the embodiments described so far, NO_XNO accumulated in catalyst_XWhen the reducing agent is supplied from the reducing agent supply valves 77a and 77b in order to reduce the amount, the switching valve 61 is temporarily held at the weak forward flow position. However, in this case, a large amount of exhaust gas does not pass through the particulate filter 69, so that the fine particles contained in the large amount of exhaust gas cannot be collected.
[0057]
Therefore, in another embodiment according to the present invention, the reducing agent is supplied from the reducing agent supply valves 77a and 77b when the switching valve 61 is switched from the backflow position to the forward flow position. In this way, NO_XNO accumulated in catalyst_XThere is no need to hold the switching valve 61 in the weak forward flow position in order to reduce the amount.
[0058]
FIG. 9 shows the flow rate of the exhaust gas flowing through the filter parts FPA and FPB of the particulate filter 69 when the switching valve 61 is switched from the backflow position to the forward flow position. In FIG. The flow rate of the exhaust gas passing through the FPA, and the curve B shows the flow rate of the exhaust gas passing through the filter portion FPB.
[0059]
In FIG. 9, an arrow X represents a time when a signal for switching the switching valve 61 from the backflow position to the forward flow position is issued to the switching valve driving step motor 60, and when this signal is issued, the switching valve 61 is moved to the backflow position. To the forward flow position. As a result, as shown in FIG. 9, the exhaust gas flow rate in the reverse flow direction gradually decreases, and once it becomes zero, the exhaust gas flow rate in the forward flow direction gradually increases.
[0060]
As described above, when the switching valve 61 is switched from the backflow position to the forward flow position, the flow rate of the exhaust gas flowing through the filter portions FPA and FPB temporarily decreases._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. Further, if a reducing agent is supplied when a small amount of exhaust gas is flowing in the forward flow direction, the reducing agent supplied from the reducing agent supply valves 77a and 77b becomes NO by this exhaust gas._XAs described above, it is diffused throughout the catalyst.
[0061]
Therefore, in another embodiment according to the present invention, the reducing agent is supplied from the reducing agent supply valves 77a and 77b when the flow rate of the exhaust gas flowing in the forward flow direction in the filter portions FPA and FPB becomes a slight constant amount Q0. I am doing so. That is, in the example shown in FIG. 9, when the time indicated by the arrow YA is reached, the reducing agent is injected from the reducing agent supply valve 77a only once, for example, and when the time indicated by the arrow YB is reached, the reducing agent is supplied from the reducing agent supply valve 77b. Is injected only once, for example.
[0062]
The time required for the flow rate of the exhaust gas flowing in the forward flow direction in the filter portions FPA and FPB to become the above-mentioned Q0 after the signal for switching the switching valve 61 from the reverse flow position to the forward flow position is generated is the unit time from the internal combustion engine. As the amount of exhaust gas exhausted per hit increases, the amount of exhaust gas decreases, and the amount of exhaust gas increases as the engine load L represented by the amount of depression of the accelerator pedal increases. Therefore, in another embodiment according to the present invention, as shown by a curve A in FIG. 10B, the standby time SBT in the reducing agent supply valve 77a becomes shorter as the engine load L becomes higher, and FIG. As shown by the curve B, the standby time SBT in the reducing agent supply valve 77b is shortened as the engine load L increases, and the standby time after the signal for switching the switching valve 61 from the reverse flow position to the forward flow position is generated. When only SBT has elapsed, the reducing agent is supplied from the reducing agent supply valves 77a and 77b.
[0063]
Further, as shown in FIG. 9, after the signal for switching the switching valve 61 from the backflow position to the forward flow position is issued, the flow rate of the exhaust gas flowing in the forward flow direction in the filter portion FPA becomes Q0 described above. The time required is longer than the time required until the flow rate of the exhaust gas flowing in the forward flow direction in the filter portion FPB becomes Q0 after the signal for switching the switching valve 61 from the reverse flow position to the forward flow position is issued. . Therefore, in another embodiment according to the present invention, as shown in FIG. 10B, the standby time SBT in the reducing agent supply valve 77a is longer than the standby time SBT in the reducing agent supply valve 77b.
[0064]
On the other hand, NO increases as the engine load L increases._XThe residence time of the reducing agent in the catalyst is shortened. Therefore, in another embodiment according to the present invention, the reducing agent supply amount QR in the reducing agent supply valve 77a increases as the engine load L increases as shown by the curve A in FIG. As indicated by curve B in A), the reducing agent supply amount QR in the reducing agent supply valve 77b increases as the engine load L increases.
[0065]
Furthermore, as described above, the retention time of the reducing agent in the filter portion FPB is shorter than the retention time of the reducing agent in the filter portion FPA. Therefore, as shown in FIG. 10A, the reducing agent supply amount QR in the reducing agent supply valve 77b is made larger than the reducing agent supply amount QR in the reducing agent supply valve 77a.
[0066]
FIG. 11 shows a routine for executing the reducing agent supply control according to another embodiment described above. This routine is executed by interruption every predetermined time.
[0067]
Referring to FIG. 11, first, at step 110, the reducing agent supply valves 77a and 77b are controlled to NO._XIt is determined whether or not the reducing agent should be supplied to the catalyst. NO from the reducing agent supply valves 77a and 77b_XWhen the reducing agent should be supplied to the catalyst, the routine proceeds to step 111 where it is determined whether or not the position of the switching valve 61 should be switched from the backflow position to the forward flow position. When the position of the switching valve 61 is not to be switched from the backflow position to the forward flow position, the processing cycle is terminated. When the position of the switching valve 61 is to be switched from the backflow position to the forward flow position, the routine proceeds to step 112 where the reducing agent supply amount QR and standby The time SBT is calculated from the map of FIG. In the following step 113, the reducing agent is supplied according to these QR and SBT.
[0068]
Note that the reducing agent may be supplied when the switching valve 61 is switched from the forward flow position to the reverse flow position. However, in this case, the reducing agent supplied from the reducing agent supply valves 77a and 77b is NO._XThere is a risk of returning to the annular exhaust pipe 67 before reaching the catalyst.
[0069]
FIG. 12 shows still another embodiment according to the present invention. In the embodiment shown in FIG. 12, the particulate filter 69 is composed of a plurality of, for example, three particulate filters 69a, 69b, 69c arranged in parallel with each other. That is, three filter housing chambers 68a, 68b, 68c arranged in parallel with each other in the annular exhaust pipe 67 are formed, and the particulate filters 69a, 69b are respectively provided in the corresponding filter housing chambers 68a, 68b, 68c. , 69c. In addition, three reducing agent supply valves 77a, 77b, 77c are attached to the annular exhaust pipe 67, and these reducing agent supply valves 77a, 77b, 77c are respectively one end faces 69af, 69bf, 69cf of the corresponding particulate filters. It is arranged facing each other.
[0070]
Here, the reducing agent supply valves 77a, 77b, and 77c are positioned so that the entire one end faces 69af, 69bf, and 69cf of the corresponding particulate filter are covered by the reducing agent spray from the reducing agent supply valves 77a, 77b, and 77c, respectively. Has been. Therefore, in this case also, the reducing agent is NO._XIt becomes possible to supply the entire catalyst.
[0071]
Also in the embodiment shown in FIG. 12, the reducing agent supply action of the reducing agent supply valves 77a, 77b, 77c is the temperature of the corresponding particulate filter 69a, 69b, 69c, or the corresponding particulate filter 69a, 69b, 69c. Each is set based on the amount of exhaust gas flowing through.
[0072]
In the embodiment shown in FIG. 2, the cross section of the particulate filter 69 is elliptical, whereas in the embodiment shown in FIG. 12, the cross sections of the particulate filters 69a, 69b, 69c are circular. . As a result, the exhaust gas easily flows uniformly through the particulate filters 69a, 69b, and 69c, and therefore, the reducing agent is easily supplied uniformly. Further, the capacity of the individual particulate filters 69a, 69b, 69c can be reduced, and therefore the space required for mounting the catalytic converter 22 can be reduced. Further, a plurality of catalytic converters 22 can be arranged in series. In this way, it is NO whether it is forward or backward._XA reducing agent can be supplied to the catalyst, and NO_XIt becomes possible to easily supply the reducing agent to the entire catalyst.
[0073]
In the embodiments described so far, the reducing agent supply valve is arranged so as to face only one end face of the particulate filter. However, the reducing agent supply valve can also be arranged so as to face both end faces of the particulate filter.
[0074]
Also, in the embodiments described so far, NO_XNO accumulated in catalyst_XNO from the reducing agent supply valve to reduce the amount_XThe present invention is applied when supplying a reducing agent to a catalyst. However, NO_XAccumulated SO in catalyst_XNO from the reducing agent supply valve to reduce the amount_XThe present invention is also applied when a reducing agent is supplied to the catalyst or when the reducing agent is supplied from the reducing agent supply valve to the particulate filter in order to perform temperature rise control to oxidize and remove the deposited fine particles on the particulate filter 69. Can be applied.
[0075]
Where NO_XAccumulated SO in catalyst_XNO from the reducing agent supply valve to reduce the amount_XThe case where the reducing agent is supplied to the catalyst will be described in a little more detail. In the exhaust gas, sulfur content is SO_XIs included in the form of NO_XNO in the catalyst_XNot only SO_XCan also be stored. This SO_XNO_XThe accumulation mechanism in the catalyst is NO_XThis is considered to be the same as the accumulation mechanism. That is, when the case where platinum Pt and barium Ba are supported on a carrier is simply described as an example, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst is lean, as described above, oxygen O₂Is O₂ ⁻Or O^2-Attached to the surface of platinum Pt in the form of SO₂Is O on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with SO₃It becomes. The generated SO₃NO is being oxidized on platinum Pt_XIt is absorbed in the catalyst and binds to barium oxide BaO, while sulfate ion SO₄ ⁻NO in the form of_XIt diffuses into the catalyst. This sulfate ion SO₄ ⁻Then barium ion Ba⁺Combined with sulfate BaSO₄Is generated.
[0076]
This sulfate BaSO₄Is difficult to decompose, NO_XEven if the air-fuel ratio of the exhaust gas flowing into the catalyst is simply rich, NO_XSulfate BaSO in the catalyst₄The amount of does not decrease. For this reason, as time passes, NO_XSulfate BaSO in the catalyst₄The amount of NO increases, resulting in NO_XNO that the catalyst can store_XThe amount of will decrease.
[0077]
However, NO_XNO while maintaining the catalyst temperature above 550 ° C_XIf the air-fuel ratio of the exhaust gas flowing into the catalyst is rich or stoichiometric, NO_XSulfate BaSO in the catalyst₄Decomposes into SO₃NO in the form of_XReleased from the catalyst. This released SO₃If exhaust gas contains a reducing agent, ie, HC or CO, it reacts with HC and CO to react with SO.₂To be reduced. In this way NO_XSO stored in the catalyst_XThe amount of NO decreases gradually, at this time NO_XFrom catalyst to SO_XIs SO₃It will not leak out.
[0078]
So, for example, NO_XAccumulated SO in catalyst_XNO when the amount exceeds the allowable amount_XTo increase the temperature of the catalyst to 550 ° C and then maintain it above 550 ° C, and NO_XAccumulated SO in catalyst_XFrom the reducing agent supply valves 77a and 77b to reduce the amount of NO_XA reducing agent can be temporarily supplied to the catalyst. In this case, NO_XThe air-fuel ratio of the exhaust gas flowing into the catalyst is temporarily switched to rich.
[0079]
【The invention's effect】
NO_XReducing agent can be supplied to the entire catalyst, so NO_XNO over the entire catalyst_XIt can be used effectively for purification.
[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 diagram for explaining the flow of exhaust gas in a normal state.
FIG. 4 is a partial enlarged cross-sectional view of a partition wall of a particulate filter.
FIG. 5 is a view for explaining a reducing agent supply operation;
FIG. 6 is a view for explaining a reducing agent supply operation.
FIG. 7 is a diagram showing a reducing agent supply amount and a time interval.
FIG. 8 is a flowchart for executing reducing agent supply control;
FIG. 9 is a diagram showing an exhaust gas flow rate in a filter portion.
FIG. 10 is a diagram showing a reducing agent supply amount and a delay time.
FIG. 11 is a flowchart for executing reducing agent supply control;
FIG. 12 is a view showing the structure of a catalytic converter according to still another embodiment of the present invention.
[Explanation of symbols]
1 ... Engine body
20a ... exhaust pipe
22 ... Catalytic converter
61 ... Switching valve
67 ... Annular exhaust pipe
65, 66 ... Inflow / outflow port
69 ... Particulate filter
69f: One end face of the particulate filter
77a, 77b ... reducing agent supply valve
80 ... NO_Xcatalyst
Ra, Rb ... Reducing agent spray

Claims (5)

Stores NO _X in the exhaust gas flowing in when the air-fuel ratio of the inflowing exhaust gas is lean, and stores that reducing agent is contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas decreases An NO _X catalyst that reduces the amount of NO _X stored by reducing NO _X is disposed in an annular branch passage that branches from the engine exhaust passage and extends in an annular shape and then returns to the engine exhaust passage, and the exhaust gas is annular While leading to one end of the branch passage, the forward flow position where the exhaust gas flows out from the other end of the annular branch passage into the engine exhaust passage downstream of one end of the annular branch passage, and the exhaust gas is guided to the other end of the annular branch passage. in this case comprises a switching valve that can switch between one end backflow position where the exhaust gas flows out into the downstream of the exhaust passage than the other end of the annular branch passages from the annular branch passage while reducing the N O _X catalyst Return to supply agent The agent feed valve in the exhaust purification system of an internal combustion engine arranged in an annular branch passage between the switching valve and the NO _X catalyst, comprising a plurality of reducing agent supply valve, these reducing agent supply valve to one end face of the NO _X catalyst When face-to-face and the switching valve is switched from the forward flow position to the reverse flow position or vice versa, the amount of exhaust gas flowing through the annular branch passage temporarily decreases and the amount of exhaust gas that bypasses the annular branch passage accordingly There adapted to increase, respectively, from the reducing agent feed valve when the amount of exhaust gas switching valve is switched to or vice versa backflow position from the forward flow position thereby flowing in the NO _X catalyst portion is reduced supplies a reducing agent to the NO _X catalyst portion facing the reducing agent is supplied thereto NO _X catalyst portion when the amount of exhaust gas flowing through the NO _X catalyst portion becomes small amount, respectively As such, an exhaust purifying apparatus for an internal combustion engine which sets the reducing agent supply timing for each reducing agent supply valve. An exhaust purification system of an internal combustion engine according to claim 1, substantially the entire is positioned respectively a reducing agent feed valve so as to be covered in one end face of the NO _X catalyst by spraying the reducing agent formed by the reducing agent feed valve. The NO _X catalyst is composed of a plurality of NO _X catalysts arranged in parallel with each other in the annular branch passage, and the plurality of reducing agent supply valves are arranged facing one end surface of the corresponding NO _X catalyst. Exhaust gas purification device for internal combustion engine. The exhaust purification device for an internal combustion engine according to claim 1, wherein the NO _X catalyst is supported on a particulate filter for collecting particulates contained in the exhaust gas . The exhaust emission control device for an internal combustion engine according to claim 4 , wherein the switching valve is switched from the forward flow position to the reverse flow position or vice versa when the amount of fine particles accumulated on the particulate filter exceeds an allowable amount .

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