JP4178851B2 - 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]
An exhaust emission control device equipped with a particulate filter (hereinafter referred to as a filter) capable of collecting particulates in exhaust gas discharged from a combustion chamber of an internal combustion engine and oxidizing and removing the collected particulates is a special feature. This is disclosed in Japanese Unexamined Patent Publication No. 2001-342821. In the exhaust emission control device described in the publication, exhaust gas can flow into the filter from one side, or flow into the filter from the opposite side. That is, the direction of the exhaust gas flowing into the filter can be reversed.
[0003]
Then, by reversing the direction of the exhaust gas flowing into the filter, the particulates collected in the filter flow in the filter and promote the oxidation action of the particulates in the filter. In the exhaust purification apparatus, the direction of the exhaust gas flowing into the filter is reversed when a condition for promoting the oxidation action of the particulates in the filter is satisfied.
[0004]
By the way, when the air-fuel ratio of the inflowing exhaust gas is lean, nitrogen oxides (NO in the exhaust gas)_X), And when the air-fuel ratio of the inflowing exhaust gas becomes rich, the NO_XNO can be reduced and purified with a reducing agent_XAn exhaust emission control device having a catalyst in an exhaust passage of an internal combustion engine is also known. In such an exhaust purification device, NO_XNO that the catalyst can hold_XThere is a limit to the amount of NO_XNO held by the catalyst_XAmount of NO (hereinafter referred to as NO_XWhen it reaches its upper limit, it is no longer NO._XThe catalyst is NO in the exhaust gas._XCan not hold, NO_XFlows out downstream of the exhaust gas purification device.
[0005]
Therefore, in such an exhaust purification device, NO_XIn order to suppress the outflow of exhaust gas downstream of the exhaust purification device, NO_XNO of catalyst_XBefore the holding amount reaches its upper limit, NO_XSupply rich air-fuel ratio exhaust gas to the catalyst, NO_XNO retained in the catalyst_XTo reduce and purify.
[0006]
[Problems to be solved by the invention]
Here, this NO._XWhen the catalyst is loaded, NO_XConditions for changing the direction of the exhaust gas flowing into the catalyst (ie, the filter), and NO_XThe condition for supplying exhaust gas having a rich air-fuel ratio to the catalyst (that is, the filter) may be satisfied at the same time. In this case, when the direction of the inflowing exhaust gas is switched, a part of the rich air-fuel ratio exhaust gas is NO._XThere is a problem that the catalyst flows out downstream of the exhaust purification device without passing through the catalyst (that is, the filter).
[0007]
These problems are generally related to NO as described above._XEquipped with a catalyst in the exhaust passage, NO_XThe direction of the exhaust gas flowing into the catalyst can be reversed and NO_XConditions for supplying exhaust gas with rich air-fuel ratio to the catalyst and NO_XThis is also a problem that occurs equally in an exhaust purification device in which the conditions for reversing the direction of the exhaust gas flowing into the catalyst are satisfied at the same time. Therefore, an object of the present invention is to provide a rich air-fuel ratio exhaust gas in such an exhaust purification device._XThe purpose is to suppress the downstream of the exhaust gas purification apparatus without passing through the catalyst.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, in the first invention, NO in exhaust gas discharged from an internal combustion engine._XNO to purify_XA catalyst is provided in the exhaust passage, and the NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst is lean, NO in the exhaust gas_XOn the other hand, when the air-fuel ratio of the exhaust gas flowing into it becomes rich, it is held NO_XIs further reduced and purified by a reducing agent, and further, enrichment means for enriching the air-fuel ratio of the exhaust gas is provided, and when the predetermined condition is satisfied, the enrichment means is operated to make NO_XIn an exhaust gas purification apparatus in which the air-fuel ratio of exhaust gas flowing into the catalyst is made rich, the exhaust gas is NO from one side._XNO flow from the other side and the forward flow mode to flow into the catalyst_XNO between the reverse flow mode to flow into the catalyst_XSwitching means for switching the inflow mode of the exhaust gas to the catalyst, and prohibiting the switching of the inflow mode by the switching means during the operation of the enrichment means, and in advance after the operation of the enrichment means is stopped The switching of the inflow mode by the switching means is prohibited over a predetermined switching prohibition period. Here, the enrichment means, the predetermined condition, and the switching means correspond to a fuel addition valve, a fuel injection valve, a rich requirement condition, and a switching valve, respectively, in the embodiments described later.
[0009]
In order to solve the above-mentioned problem, in the second invention, NO in exhaust gas discharged from the internal combustion engine._XNO to purify_XA catalyst is provided in the exhaust passage, and the NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst is lean, NO in the exhaust gas_XOn the other hand, when the air-fuel ratio of the exhaust gas flowing into it becomes rich, it is held NO_XIs further reduced and purified by a reducing agent, and further, enrichment means for enriching the air-fuel ratio of the exhaust gas is provided, and when the predetermined condition is satisfied, the enrichment means is operated to make NO_XIn an exhaust emission control device in which the air-fuel ratio of exhaust gas flowing into the catalyst is made rich, NO_XNO to bypass the catalyst_XNO from the exhaust passage upstream of the catalyst_XA bypass passage extending to the exhaust passage downstream of the catalyst, and NO_XSwitching means for switching an exhaust gas inflow mode between an inflow mode for flowing into the catalyst and an inflow mode for flowing exhaust gas into the bypass passage, and the inflow by the switching means during operation of the enrichment means In addition to prohibiting mode switching, switching of the inflow mode by the switching means is prohibited for a predetermined switching prohibition period even after the operation of the enrichment means is stopped. Here, the enrichment unit, the predetermined condition, and the switching unit correspond to a fuel addition valve, a fuel injection valve, a bypassable condition, and a switching valve, respectively, in the embodiments described later.
[0010]
In the third invention, in the first or second invention, almost all of the rich air-fuel ratio exhaust gas is NO after the operation of the enrichment means is stopped._XThe exhaust gas passage completion period until it passes through the catalyst is set as the switching prohibition period.
[0011]
In a fourth aspect, in the third aspect, the exhaust gas passage completion period is calculated based on at least one of the engine required load and the engine speed.
[0012]
According to a fifth aspect, in the third aspect, the internal combustion engine can burn fuel in the combustion chamber in a plurality of types of combustion modes, and the exhaust gas passage completion period is the engine required load for each combustion mode. And at least one of the engine speed.
[0013]
In a sixth aspect based on the third aspect, the exhaust gas passage completion period is calculated based on at least one of the temperature of the exhaust gas, the flow rate of the exhaust gas, and the pressure of the exhaust gas.
[0014]
In the seventh invention, in the third invention, the air-fuel ratio sensor capable of detecting the air-fuel ratio of the exhaust gas is NO._XAlmost all of the rich air-fuel ratio exhaust gas is detected when the air-fuel ratio sensor is disposed downstream of the catalyst and the air-fuel ratio sensor detects that the air-fuel ratio of the exhaust gas is no longer rich after the operation of the enrichment means is stopped._XIt is judged that the catalyst has passed.
[0015]
In the eighth invention, in the third invention, the air-fuel ratio sensor capable of detecting the air-fuel ratio of the exhaust gas is NO._XCatalyst upstream and NO_XIt is arranged downstream of the catalyst and NO after the operation of the enrichment means is stopped._XThe NO after the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor downstream of the catalyst is no longer rich_XThe air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor downstream of the catalyst is the above NO._XWhen the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor upstream of the catalyst is substantially equal, almost all of the rich air-fuel ratio exhaust gas is NO._XIt is judged that the catalyst has passed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to the drawings. FIG. 1 shows an internal combustion engine equipped with the exhaust emission control device of the present invention. The internal combustion engine shown in FIG. 1 is a compression ignition type internal combustion engine. In FIG. 1, 1 is an engine body, 2 is a combustion chamber, 3 is a fuel injection valve, 4 is an intake manifold, and 5 is an exhaust manifold. The fuel injection valve 3 is connected to a reservoir (so-called common rail) 6 for temporarily storing fuel from a fuel tank (not shown).
[0017]
The intake manifold 4 is connected to the outlet of the compressor 9 of the exhaust turbocharger 8 through the intake pipe 7. An intercooler 10 for cooling the air taken into the combustion chamber 2 is attached to the intake pipe 7. A throttle valve 11 driven by an electric motor (not shown) is disposed in the intake pipe 7 downstream of the intercooler 10 in order to control the amount of air taken into the combustion chamber 2. An intake pipe 12 is also attached to the inlet of the compressor 9. An air flow meter 13 for measuring the amount of air taken into the combustion chamber 2 is attached to the intake pipe 12.
[0018]
On the other hand, the exhaust manifold 5 is connected to an inlet portion of the turbine 15 of the exhaust turbocharger 8 through an exhaust pipe 14. An upstream air-fuel ratio sensor 16 for detecting the air-fuel ratio of the exhaust gas is attached to the exhaust pipe 14. The air-fuel ratio of the exhaust gas detected by the upstream air-fuel ratio sensor 16 is the ratio of the amount of fuel injected into the combustion chamber to the amount of air sucked into the combustion chamber.
[0019]
An exhaust pipe 17 is also attached to the outlet of the turbine 15. The exhaust pipe 17 is connected to the inlet of the exhaust purification device 18. The exhaust pipe 17 is provided with a fuel addition valve 19 for injecting fuel therein. The exhaust pipe 17 is provided with a temperature sensor 20 for detecting the temperature of the exhaust gas and a pressure sensor 21 for detecting the pressure of the exhaust gas. An exhaust pipe 22 is also attached to the outlet of the exhaust purification device 18. A downstream air-fuel ratio sensor 23 for detecting the air-fuel ratio of the exhaust gas is also attached to the exhaust pipe 22. The air-fuel ratio of the exhaust gas detected by the downstream air-fuel ratio sensor 23 is the amount of fuel injected into the combustion chamber and the amount of fuel injected from the fuel addition valve 19 with respect to the amount of air sucked into the combustion chamber. And the ratio of the total amount.
[0020]
The exhaust purification device 18 includes an exhaust pipe 24 that loops from the inlet portion and returns to the inlet portion, and an exhaust pipe (bypass passage) 25 that extends downstream from the inlet portion. In the exhaust pipe 24 having a loop shape, NO in the exhaust gas is present._XNO to purify_XA catalyst 32 is disposed. NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst 32 is lean, the catalyst 32 has NO in the exhaust gas._XIt is held by absorbing or adsorbing. On the other hand, NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst 32 becomes rich, the catalyst 32 holds NO._XIs reduced and purified by a reducing agent in the exhaust gas, specifically, hydrocarbon (fuel).
[0021]
Further, the exhaust purification device 18 has a switching valve 26 at its inlet. As shown in FIG. 2A, when the switching valve 26 is positioned at the first position, the exhaust gas flowing into the inlet portion is NO from one side._XIt is caused to flow into the catalyst 32. On the other hand, as shown in FIG. 2B, when the switching valve 26 is positioned at the second position, the exhaust gas flowing into the inlet is NO._XInstead of flowing into the catalyst 32, the catalyst 32 flows out downstream as it is. Further, as shown in FIG. 2 (C), when the switching valve 26 is positioned at the third position, the exhaust gas flowing into the inlet portion is NO from the other side._XIt is caused to flow into the catalyst 32.
[0022]
In this way, by switching the positioning position of the switching valve 26, the exhaust gas is reduced from one side to NO._XNO is allowed to flow into the catalyst 32 or exhaust gas is sent from the other side to NO._XThe exhaust gas is allowed to flow into the catalyst 32 or NO_XInstead of flowing into the catalyst 32, the exhaust gas purification device 18 can be directly discharged downstream. That is, by switching the positioning position of the switching valve 26 between the three positions described above, the NO_XThe inflow mode of the exhaust gas to the catalyst 32 can be switched.
[0023]
Hereinafter, the NO when the switching valve 26 is positioned at the position shown in FIG._XThe exhaust gas inflow mode to the catalyst 32 is referred to as a forward flow mode, and the NO when the switching valve 26 is positioned at the position shown in FIG._XThe exhaust gas inflow mode to the catalyst 32 is referred to as a reverse flow mode. The exhaust gas inflow mode to the exhaust pipe 25 when the switching valve 26 is positioned at the position shown in FIG. 2B is referred to as a bypass mode.
[0024]
An exhaust gas circulation (EGR) passage 27 for circulating the exhaust gas discharged from the combustion chamber 2 to the combustion chamber 2 again extends from the exhaust manifold 5 to the intake manifold 4. An EGR control valve 28 for controlling the amount of exhaust gas introduced into the combustion chamber 2 is attached to the EGR passage 27. Further, an EGR cooler 29 for cooling the exhaust gas is also attached to the EGR passage 27. Further, an oxidation catalyst 30 is disposed in the EGR passage 27 upstream of the EGR cooler 29. The oxidation catalyst 30 functions to oxidize and remove fuel (hydrocarbon) in the exhaust gas introduced into the EGR cooler 29 and the combustion chamber 2.
[0025]
By the way, in a compression ignition type internal combustion engine, fuel is usually burned under excess air, so the air-fuel ratio of the exhaust gas discharged from the combustion chamber 2 is usually lean. Further, in the combustion chamber 2, normally NO_XIn the exhaust gas exhausted from the combustion chamber 2, normally NO is_XIt is included. Therefore, NO_XThe catalyst 32 typically has a lean air-fuel ratio and NO._XExhaust gas containing will flow in. As described above, the lean air-fuel ratio exhaust gas is NO._XNO when flowing into the catalyst 32_XThe catalyst 32 is NO in the exhaust gas._XNormally NO_XNO retained in catalyst 32_XThe amount of continues to increase.
[0026]
However, NO_XNO that the catalyst 32 can hold_XSince there is a limit to the amount of NO, NO_XNO held by catalyst 32_XAmount of NO (hereinafter referred to as NO_XWhen it reaches its upper limit, it is no longer NO._XThe catalyst 32 is NO in the exhaust gas._XCan not hold, NO_XFlows out downstream of the exhaust gas purification device 18.
[0027]
Therefore, in the first embodiment, NO_XIn order to prevent the exhaust gas from flowing out downstream of the exhaust gas purification device 18_XNO of catalyst 32_XBefore the holding amount reaches the upper limit, fuel is injected from the fuel addition valve 19 so that the air-fuel ratio of the exhaust gas becomes rich. Specifically, in the first embodiment, NO_XNO of catalyst 32_XWhen a specific condition that the retained amount is smaller than the upper limit value but exceeds a value close to the upper limit value (hereinafter referred to as a rich request condition) is satisfied, fuel is injected from the fuel addition valve 19 to exhaust gas. The air-fuel ratio is made rich. According to this, NO_XSince rich air-fuel ratio exhaust gas flows into the catalyst 32, NO_XNO retained in catalyst 32_XIs reduced and purified by a reducing agent in exhaust gas, specifically, fuel (hydrocarbon) or carbon monoxide._XNO of catalyst 32_XThe holding amount is reduced. Therefore, after that, NO in the exhaust gas_XIs NO_XThe catalyst 32 is held.
[0028]
Of course, when fuel is injected from the fuel addition valve 19 in this way, the switching valve 26 is in the first position shown in FIG. 2 (A) or the second position shown in FIG. 2 (C). It is positioned at the position.
[0029]
By the way, in a compression ignition type internal combustion engine, fine particles mainly composed of carbon are usually generated. Therefore, the exhaust gas usually contains fine particles. NO of the first embodiment_XThe catalyst 32 also serves as a particulate filter for collecting such fine particles. That is, in the first embodiment, NO_XThe catalyst 32 is carried on the particulate filter. The structure of this particulate filter is shown in FIG. In the following description, NO_XThe catalyst and the particulate filter are denoted by reference numeral 25.
[0030]
3A is an end view of the particulate filter, and FIG. 3B is a longitudinal sectional view of the particulate filter. As shown in FIGS. 3A and 3B, the particulate filter (hereinafter referred to as a filter) 32 includes partition walls 54 having a honeycomb structure. A plurality of exhaust flow passages 50 and 51 extending in parallel with each other are formed by the partition walls 54. Of these exhaust flow passages, approximately half of the exhaust flow passages 50 are closed at their downstream ends by plugs 52. Hereinafter, these exhaust flow passages 50 are referred to as exhaust gas inflow passages. On the other hand, the remaining half of the exhaust flow passages 51 are closed at their upstream ends by plugs 53. Hereinafter, these exhaust flow passages 51 are referred to as exhaust outflow passages 51. Four exhaust gas outflow passages 51 are adjacent to the exhaust gas inflow passage 50. On the other hand, four exhaust gas inflow passages 50 are adjacent to the exhaust gas outflow passage 51.
[0031]
The exhaust gas flows into the exhaust gas inflow passage 50. Since the partition wall 54 is made of a porous material such as cordierite, the exhaust gas in the exhaust gas inflow passage 50 is adjacent through the pores of the partition wall 54 as indicated by arrows in FIG. It flows into the exhaust gas outflow passage 51. As described above, while the exhaust gas flows through the filter 32, the fine particles are collected on the front wall surface of the partition wall and the wall surface of the partition wall defining the pores.
[0032]
By the way, since the amount of fine particles that can be collected by the filter 32 is limited, when the amount of fine particles collected by the filter 32 (hereinafter referred to as fine particle collection amount) reaches the upper limit value, The filter 32 can no longer collect the particulates in the exhaust gas, and the particulates flow out downstream of the exhaust purification device 18. Further, when the amount of collected particulates of the filter 32 increases, the pressure loss due to the filter 32 increases.
[0033]
Therefore, in the first embodiment, in order to suppress an increase in pressure loss caused by the filter 32, the particulates collected by the filter 32 are continuously oxidized and removed within a short time. Specifically, in the first embodiment, a carrier layer made of alumina, for example, is formed in the filter 32 over the entire wall surfaces of the partition walls 54 and on the wall surfaces that define the pores of the partition walls 54. Then, a noble metal catalyst and an active oxygen generator are supported on the carrier layer, and the fine particles collected by the filter 32 are oxidized and removed by the active oxygen generated by the active oxygen generator and the catalytic action of the noble metal catalyst. Like to do.
[0034]
By the way, when the particulates collected by the filter 32 are caused to flow in the filter 32, the particulate oxidation action in the filter 32 is promoted. Therefore, in the first embodiment, in order to promote the particulate oxidation action in the filter 32, when a predetermined condition (hereinafter referred to as a particulate flow requirement condition) is satisfied, the position of the switching valve 26 is shown in FIG. By switching between the first position shown in FIG. 2 and the second position shown in FIG._XBy switching the inflow mode of the exhaust gas to the catalyst 32 between the forward flow mode and the reverse flow mode, the flow of the exhaust gas in the filter 32 is reversed, and the particulates collected in the filter 32 are caused to flow. Yes.
[0035]
In the first embodiment, the fine particle flow requirement condition is, for example, a condition that a predetermined time has elapsed or a condition that a pressure loss caused by the filter 32 exceeds a predetermined value.
[0036]
By the way, according to the above description, the above-described rich requirement condition and the fine particle flow requirement condition may be satisfied at the same time. In this case, while injecting fuel from the fuel addition valve 19, NO_XAssuming that the inflow mode of the exhaust gas to the catalyst 32 is switched between the forward flow mode and the reverse flow mode, a part of the fuel injected from the fuel addition valve 19 is NO during the bypass mode during the switching._XWithout passing through the catalyst 32, the exhaust gas purification device 18 flows out as it is.
[0037]
Therefore, in the first embodiment, in order to prevent the fuel from flowing out downstream of the exhaust purification device 18, when the rich requirement condition is satisfied, that is, the fuel is injected from the fuel addition valve 19. When the particulate flow requirement condition is satisfied, the switching of the position of the switching valve 26 is prohibited, and therefore NO_XSwitching of the exhaust gas inflow mode to the catalyst 32 is prohibited.
[0038]
By the way, even if the rich requirement condition is not satisfied and the fuel injection from the fuel addition valve 19 is stopped, all the exhaust gas having a rich air-fuel ratio by the fuel injected from the fuel addition valve 19 is NO._XIt does not pass through the catalyst 32. That is, when the fuel injection from the fuel addition valve 19 is stopped, the fuel addition valve 19_XRich air-fuel ratio exhaust gas remains in the exhaust passage to the catalyst 32. Here, when the fuel injection from the fuel addition valve 19 is stopped, the position of the switching valve 26 is switched._XWhen the inflow mode of the exhaust gas to the catalyst 32 is switched, a part of the rich air-fuel ratio exhaust gas remaining in the exhaust passage, that is, the fuel flows out downstream of the exhaust purification device 18.
[0039]
Therefore, in the first embodiment, in order to prevent the fuel from flowing out downstream of the exhaust purification device 18, even if the rich requirement condition is not satisfied and the fuel injection from the fuel addition valve 19 is stopped, The switching of the position of the switching valve 26 is prohibited until a predetermined period (hereinafter referred to as a switching prohibition period) elapses._XSwitching of the exhaust gas inflow mode to the catalyst 32 is prohibited.
[0040]
FIG. 4 shows a flowchart of a routine for executing control for prohibiting switching of the switching valve 26 according to the first embodiment. In the routine of FIG. 4, first, at step 10, it is judged if the rich request flag F is set (F = 1). The rich request flag F is a flag that is set when the rich request condition is satisfied, and is reset when the rich request condition is not satisfied. Therefore, when it is determined in step 10 that F = 1, the rich requirement condition is satisfied and the fuel is being injected from the fuel addition valve 19, so the routine proceeds to step 18. Then, switching of the switching valve 26 is prohibited, and then, in step 19, a switching prohibition flag Ff is set, and the routine ends. The switching prohibition flag Ff is a flag that is set when switching of the switching valve 26 is prohibited in step 18, and is reset when the switching prohibition of the switching valve 26 is canceled in step 15.
[0041]
By the way, when it is determined at step 10 that F = 0, the routine proceeds to step 11 where it is determined whether or not the switching prohibition flag Ff is set (Ff = 1). When it is determined in step 11 that Ff = 0, the routine ends. On the other hand, when it is determined at step 11 that Ff = 1, the routine proceeds to step 12 where the exhaust gas passage completion period Tp is calculated, then at step 13, the counter C is counted up, and then In step 14, it is determined whether or not the counter C has exceeded the switching prohibition period Tp (C> Tp).
[0042]
When it is determined in step 14 that C ≦ Tp, the routine returns to step 13, the counter C is incremented, and the routine returns to step 14 again. On the other hand, when it is determined in step 14 that C> Tp, the routine proceeds to step 15 where the switching prohibition of the switching valve 26 is released, and then in step 16, the switching prohibition flag Ff is reset, then In step 17, the counter C is cleared, and the routine ends.
[0043]
By the way, the switching prohibition period may be simply a predetermined period, but in order to more reliably suppress the fuel from flowing out downstream of the exhaust purification device 18, the first implementation is performed. In the embodiment, almost all of the rich air-fuel ratio exhaust gas is NO after the fuel injection from the fuel addition valve 19 is stopped._XA period until the catalyst 32 passes (hereinafter referred to as an exhaust gas passage completion period). In the first embodiment, the exhaust gas passage completion period Tp is obtained in advance based on the relationship between the load required for the internal combustion engine (hereinafter referred to as engine required load) L and the engine speed N, and is shown in FIG. Thus, it is stored in the form of a map, and the exhaust gas passage completion period is calculated from this map. Specifically, according to the first embodiment, the exhaust gas passage completion period is shorter as the engine required load is higher, and the exhaust gas passage completion period is shorter as the engine speed is higher.
[0044]
By the way, in the internal combustion engine of the present invention, when the amount of exhaust gas introduced into the combustion chamber 2 through the EGR passage 27 (hereinafter referred to as EGR gas amount) increases, the amount of fine particles generated in the combustion chamber 2 ( (Hereinafter referred to as the amount of fine particles generated) increases, and eventually reaches a peak. When the amount of EGR gas further increases, the temperature of the fuel in the combustion chamber and the surrounding gas becomes lower than the generation temperature of soot, and soot (fine particles) is hardly generated. In other words, if the fuel is burned while introducing an appropriate amount of exhaust gas into the combustion chamber 2 that is less than the amount of exhaust gas at which the amount of particulate generation reaches a peak, the amount of particulate generation can be suppressed to a low level. Even if the fuel is burned while introducing an appropriate amount of exhaust gas larger than the amount of exhaust gas having a peak into the combustion chamber 2, the amount of generated fine particles can be reduced.
[0045]
Furthermore, if the amount of EGR gas is small, the amount of air in the air-fuel mixture in the combustion chamber 2 is relatively large, so that the amount of fuel combustible in the combustion chamber 2 is large. Therefore, if the amount of EGR gas is small, a large output can be output from the internal combustion engine. On the other hand, if the amount of EGR gas is large, the amount of air in the air-fuel mixture in the combustion chamber 2 is relatively small, so the amount of fuel combustible in the combustion chamber 2 is small. Therefore, if the amount of EGR gas is large, the output that can be output from the internal combustion engine is small.
[0046]
In consideration of the relationship between the amount of EGR gas and the amount of generated fine particles, and the relationship between the amount of EGR gas and the output that can be output from the internal combustion engine, in the first embodiment, as shown in FIG. Is divided into two regions I and II based on the engine speed N and the required load L. When the engine operating state is in the first region I, a combustion mode (hereinafter, referred to as fuel combustion mode) in which fuel is combusted while introducing an appropriate amount of exhaust gas larger than the amount of exhaust gas at which the amount of generated fine particles reaches a peak. The fuel is burned in a low temperature combustion mode). On the other hand, when the engine operating state is in the second region II, a combustion mode in which fuel is combusted while introducing an appropriate amount of exhaust gas into the combustion chamber 2 that is smaller than the exhaust gas amount at which the amount of generated particulates reaches a peak (hereinafter referred to as a combustion mode). The fuel is burned in a normal combustion mode).
[0047]
The first region I is a region where the engine speed N is relatively small and the required load L is relatively low, and the second region II is the other region where the engine speed N is relatively large. Or it is an area where the required load L is relatively high.
[0048]
Incidentally, as described above, in the first embodiment, the exhaust gas passage completion period is calculated based on the engine required load and the engine speed, and it is assumed that the engine required load and the engine speed are the same. However, virtually all of the rich air-fuel ratio exhaust gas is NO_XThe period until passing through the catalyst 32 differs between when the fuel is burned in the low temperature combustion mode and when the fuel is burned in the normal combustion mode.
[0049]
Therefore, when the internal combustion engine is configured to burn combustion in the combustion chamber 2 in a plurality of types of fuel modes, the exhaust gas passage completion period is calculated according to the fuel combustion mode (that is, the combustion mode). Should. Therefore, in the present invention, the exhaust gas passage completion period is calculated based on the fuel injection amount from the fuel addition valve 19 and the engine speed for each fuel combustion mode.
[0050]
Here, in the first embodiment, a map as shown in FIG. 5 is prepared for each combustion mode such as the low temperature combustion mode and the normal combustion mode, and when the combustion mode is the low temperature combustion mode, the map for the low temperature combustion mode is prepared. The exhaust gas passage completion period is used to calculate the exhaust gas passage completion period. On the other hand, when the combustion mode is the normal combustion mode, the exhaust gas passage completion period is calculated using the normal combustion mode map. According to this, the calculated exhaust gas passage completion period is more accurately the true exhaust gas passage completion period.
[0051]
Of course, a correction coefficient for the exhaust gas passage completion period may be obtained for each combustion mode, and the exhaust gas passage completion period calculated based on the engine required load and the engine speed may be corrected with this correction coefficient.
[0052]
By the way, in the internal combustion engine of the present invention, fuel is injected from the fuel injection valve 3 in a fuel injection mode according to demand. For example, in the first embodiment, fuel is injected from the fuel injection valve 3 in the fuel injection mode shown in FIG. That is, as indicated by a symbol Qm in FIG. 7A, fuel is injected from the fuel injection valve 3 into the combustion chamber 2 at a timing immediately after the compression top dead center TDC. The fuel injected at this time is consumed mainly for driving the internal combustion engine.
[0053]
Further, in the first embodiment, when it is determined that the combustion of the fuel to be consumed for driving the internal combustion engine should be promoted, the fuel injection valve in the fuel injection mode shown in FIG. Fuel is injected from 3. That is, as indicated by the reference sign Qpi in FIG. 7B, a small amount of fuel is injected from the fuel injection valve 3 into the combustion chamber 2 at a timing immediately before the compression top dead center TDC. The fuel injected at this time is consumed mainly to promote the combustion of the fuel. Then, as shown by a symbol Qm in FIG. 7B, fuel for driving the internal combustion engine is injected from the fuel injection valve 3 into the combustion chamber 2 at a timing immediately after the compression top dead center TDC.
[0054]
Further, in the first embodiment, when it is determined that the temperature of the exhaust gas discharged from the combustion chamber 2 should be increased, the fuel injection valve 3 performs fuel injection in the fuel injection mode shown in FIG. Is injected. That is, as indicated by the symbol Qpo in FIG. 7C, fuel for driving the internal combustion engine is injected from the fuel injection valve 3 into the combustion chamber 2 at a timing immediately after the compression top dead center TDC. After that, as indicated by the symbol Qpo in FIG. 7C, a small amount of fuel is injected from the fuel injection valve 3 into the combustion chamber 2 at the timing immediately before the expansion bottom dead center BDC, that is, at the later stage of the expansion stroke. Is done. The fuel injected at the later stage of the expansion stroke is consumed mainly for increasing the temperature of the exhaust gas.
[0055]
By the way, as described above, in the first embodiment, the exhaust gas passage completion period is calculated based on the engine required load and the engine speed, but even if these engine required load and the engine speed are the same. In fact, almost all of the rich air-fuel ratio exhaust gas is NO_XThe period until passing through the catalyst 32 is different for each fuel injection mode.
[0056]
Therefore, when the internal combustion engine is configured to inject fuel from the fuel injection valve 3 in a plurality of types of fuel injection modes, the exhaust gas passage completion period is calculated according to the fuel injection mode (that is, the fuel injection mode). Should. Therefore, in the present invention, the exhaust gas passage completion period is calculated on the basis of the engine required load and the engine speed for each fuel injection mode. Here, in the first embodiment, a map as shown in FIG. 5 is prepared for each fuel injection mode such as FIGS. 7A to 7C, and the exhaust gas is used using the map for each fuel injection mode. The passage completion period is calculated. According to this, the calculated exhaust gas passage completion period becomes the true exhaust gas passage completion period more accurately.
[0057]
Of course, a correction coefficient for the exhaust gas passage completion period may be obtained for each fuel injection mode, and the exhaust gas passage completion period calculated based on the engine required load and the engine speed may be corrected with this correction coefficient. .
[0058]
Incidentally, as described above, in the first embodiment, the exhaust gas passage completion period is calculated based on the engine required load and the engine speed, and it is assumed that the engine required load and the engine speed are the same. However, virtually all of the rich air-fuel ratio exhaust gas is NO_XThe period until passing through the catalyst 32 varies depending on the fuel injection amount from the fuel addition valve 19 and the air-fuel ratio of the air-fuel mixture in the combustion chamber 2. Therefore, in the first embodiment, the exhaust gas passage completion period calculated from the map shown in FIG. 5 is corrected in accordance with the fuel injection amount from the fuel addition valve 19 and the air-fuel ratio of the air-fuel mixture in the combustion chamber 2. I have to.
[0059]
Specifically, for example, in the first embodiment, the larger the fuel injection amount from the fuel addition valve 19, the longer the exhaust gas passage completion period calculated so as to be longer, and the mixture in the combustion chamber 2 is corrected. The exhaust gas passage completion period calculated as the air-fuel ratio of the engine becomes smaller is corrected so as to become longer. According to this, the calculated exhaust gas passage completion period is more accurately the true exhaust gas passage completion period.
[0060]
By the way, in the first embodiment, the exhaust gas passage completion period is calculated based on the engine required load and the engine speed, but in addition to this, the temperature of the exhaust gas, the flow rate of the exhaust gas, and the exhaust gas The exhaust gas passage completion period can also be calculated based on the pressure.
[0061]
Therefore, in the second embodiment, the exhaust gas passage completion period is calculated based on the exhaust gas temperature, the exhaust gas flow rate, and the exhaust gas pressure. Specifically, the exhaust gas passage completion period is Tp, the volume of the exhaust passage from the fuel addition valve 19 to the downstream end face of the filter 32 is Vo, the temperature of the exhaust gas is Tex, the flow rate of the exhaust gas is Gex, and the pressure of the exhaust gas Is Pex and the gas constant of the exhaust gas is Rex, the exhaust gas passage completion period is calculated by the equation Tp = Vo / (Gex × Tex × Rex / Pex).
[0062]
In the second embodiment, similarly to the first embodiment, the exhaust gas passage completion period thus calculated is set to the combustion mode, the fuel injection mode, the fuel injection amount from the fuel addition valve 19, the inside of the combustion chamber 2. You may make it correct | amend by the air fuel ratio of an air-fuel | gaseous mixture. Further, the flow rate of the exhaust gas can be calculated based on the output from the air flow meter 13 and the fuel injection amount.
[0063]
By the way, almost all of the rich air-fuel ratio exhaust gas is NO._XThe passage through the catalyst 32 can also be detected using an air-fuel ratio sensor. In other words, the exhaust gas passage completion period can be calculated using the air-fuel ratio sensor. Therefore, in the third embodiment, almost all of the rich air-fuel ratio exhaust gas is NO by using the air-fuel ratio sensor as follows._XThe passage of the catalyst 32 is detected, and the exhaust gas passage completion period is set up to this time.
[0064]
That is, in the third embodiment, NO_XThe output from the downstream air-fuel ratio sensor 23 arranged downstream of the catalyst 32 is monitored, and after the fuel injection from the fuel addition valve 19 is stopped, the exhaust gas empty detected by the downstream air-fuel ratio sensor 23 is stopped. When the fuel ratio is no longer rich, almost all of the rich air-fuel ratio exhaust gas is NO._XIt is determined that the catalyst 32 has passed, and the exhaust gas passage completion period is determined until this time.
[0065]
In the fourth embodiment, almost all of the rich air-fuel ratio exhaust gas is NO by using the air-fuel ratio sensor as follows._XThe passage of the catalyst 32 is detected, and the exhaust gas passage completion period is set up to this time. That is, in the fourth embodiment, NO_XAn output from the upstream air-fuel ratio sensor 16 disposed upstream of the catalyst 32, and NO_XThe output from the downstream air-fuel ratio sensor 23 arranged downstream of the catalyst 32 is monitored, and after the fuel injection from the fuel addition valve 19 is stopped, the exhaust gas empty detected by the downstream air-fuel ratio sensor 23 is stopped. Since the air-fuel ratio of the exhaust gas detected by the downstream-side air-fuel ratio sensor 23 and the air-fuel ratio of the exhaust gas detected by the upstream-side air-fuel ratio sensor 26 are substantially equal after the fuel ratio is no longer rich. Almost all rich air-fuel ratio exhaust gas is NO_XIt is determined that the catalyst 32 has passed, and the exhaust gas passage completion period is determined until this time.
[0066]
FIG. 8 is a time chart showing the operation of the fuel addition valve according to the fourth embodiment. FIG. 8A shows an operation signal for the fuel addition valve. When this operation signal is turned on, fuel is injected from the fuel addition valve. When this operation signal is turned off, fuel injection from the fuel addition valve is stopped. Indicates. FIG. 8B shows the transition of the air-fuel ratio of the exhaust gas, the chain line X is the transition of the air-fuel ratio of the exhaust gas detected by the upstream air-fuel ratio sensor, and the solid line Y is detected by the downstream air-fuel ratio sensor. It is a transition of the air-fuel ratio of exhaust gas. FIG. 8C shows the time.
[0067]
When the rich request condition is satisfied at time t0, the operation signal for the fuel addition valve is turned ON. Then, the air-fuel ratio of the exhaust gas detected by the downstream-side air-fuel ratio sensor, that is, the air-fuel ratio Y of the exhaust gas downstream of the filter becomes small with a slight delay, and eventually becomes rich. When the rich requirement condition is not satisfied at time t1, the operation signal for the fuel addition valve is turned off. Then, the air-fuel ratio Y of the exhaust gas downstream of the filter becomes slightly delayed and eventually becomes lean. At time t3, the air-fuel ratio X of the exhaust gas detected by the upstream air-fuel ratio sensor is substantially equal to the air-fuel ratio Y of the exhaust gas downstream of the filter.
[0068]
Thereafter, similarly, the rich request condition is satisfied at time t4, the rich condition is not satisfied at time t5, the rich request condition is satisfied at time t8, the rich condition is not satisfied at time t9, and the rich condition is satisfied at time t12. At time t13, the rich condition is not satisfied.
[0069]
Now, according to the fourth embodiment, in FIG. 8, the period A is a period during which fuel is injected from the fuel addition valve, and therefore switching of the position of the switching valve 26 is prohibited. Further, according to the fourth embodiment, in FIG. 8, the period Tp is substantially equal to the air-fuel ratio of the exhaust gas detected by the upstream air-fuel ratio sensor after the air-fuel ratio of the exhaust gas downstream of the filter once becomes rich. Since this is a period during which no change is made, that is, the switching prohibition period (exhaust gas passage completion period), switching of the position of the switching valve 26 is also prohibited here. Therefore, in FIG. 8, the period B is a period during which the switching of the position of the switching valve 26 is permitted.
[0070]
By the way, according to the above-described embodiment, when the rich request condition is satisfied with a relatively short time interval, the period during which the switching of the switching valve 26 is prohibited may be continuous and may become very long. In this case, since the position of the switching valve 26 cannot be switched further, there is a problem that the particulate oxidation action of the filter 32 is not promoted. Therefore, in the above-described embodiment, when the total period during which the switching of the switching valve 26 is prohibited exceeds the allowable upper limit value, the fuel injection from the fuel addition valve 19 is forcibly prohibited, and then the exhaust gas passes. The position of the switching valve 26 may be switched when the completion period has elapsed, and then fuel injection from the fuel addition valve 19 may be resumed.
[0071]
In the above-described embodiment, by increasing the amount of fuel injected from the fuel injection valve 3 into the combustion chamber 2 instead of injecting fuel from the fuel addition valve 19 when the rich requirement condition is satisfied, The air-fuel ratio of the exhaust gas may be made rich.
[0072]
NO_XWhen the air-fuel ratio of the exhaust gas flowing into the catalyst 32 is lean, the catalyst 32 is sulfur oxide (SO_X). And NO_XSO retained by the catalyst 32_XWhen the amount of increases, NO_XNO that the catalyst 32 can hold_XThe amount of will decrease. Where NO_XNO while keeping the temperature of the catalyst 32 relatively high_XIf the air-fuel ratio of the exhaust gas flowing into the catalyst 32 is made rich, NO_XSO retained in the catalyst 32_XIs NO_XIt has been found to be removed from the catalyst 32.
[0073]
Therefore, in the above-described embodiment, NO_XSO of catalyst 32_XThe rich request condition may be satisfied when the holding amount exceeds a predetermined amount. According to this, NO_XSO of catalyst 32_XWhen the holding amount increases, NO_XSince the rich air-fuel ratio exhaust gas is supplied to the catalyst 32, NO_XFrom catalyst 32 to SO_XWill be removed. Of course, at this time, NO_XSome measure is taken to keep the temperature of the catalyst 32 relatively high.
[0074]
Further, as the temperature of the filter 32 is higher, the amount of fine particles oxidized and removed per unit time in the filter 32 increases. Here, when the rich air-fuel ratio exhaust gas flows into the filter 32, hydrocarbons in the exhaust gas are oxidized by the filter 32, and the temperature of the filter 32 rises. Therefore, in the above-described embodiment, in order to maintain a large amount of fine particles that are oxidized and removed per unit time in the filter 32, the amount of fine particles that can be oxidized and removed per unit time in the filter 32 is a predetermined lower limit value. The rich requirement condition may be satisfied when the value is less than.
[0075]
In the filter 32, fine particles are continuously oxidized and removed. However, if the amount of fine particles discharged from the combustion chamber 2 is large, a relatively large amount of fine particles temporarily accumulate on the filter 32. The fine particles once deposited are difficult to be removed by oxidation. Here, if a rich air-fuel ratio exhaust gas is supplied to the filter 32, fine particles deposited on the filter 32 can be oxidized and removed all at once using hydrocarbons in the exhaust gas as a reducing agent. Therefore, in the above-described embodiment, the rich request condition may be satisfied when the amount of fine particles accumulated on the filter 32 exceeds a predetermined upper limit value.
[0076]
By the way, instead of the exhaust purification apparatus in the above-described embodiment, the present invention can be applied even when the exhaust purification apparatus of the fifth embodiment shown in FIG. 9 is adopted. In the exhaust purification device 18 shown in FIG._XA catalyst 32 is disposed. NO_XNO from the exhaust passage upstream of the catalyst 32_XNO to the exhaust passage downstream of the catalyst 32_XA bypass passage 31 that bypasses the catalyst 32 extends. In the branch portion between the exhaust passage and the bypass passage 31, the exhaust gas is NO._XA switching valve 26 for switching whether to flow into the catalyst 32 or to flow exhaust gas into the bypass passage is disposed.
[0077]
That is, when the switching valve 26 is positioned at the position shown in FIG._XIt flows into the catalyst 32. On the other hand, the exhaust gas flows into the bypass passage 31 when the switching valve 26 is positioned at the position shown in FIG. For example, NO in exhaust gas_XNO is included in the exhaust gas because it does not contain_XEven if the exhaust gas is allowed to flow downstream of the exhaust gas purification device 18 without passing through the catalyst 32, the exhaust emission does not deteriorate, and the exhaust gas is reduced to NO._XIf the exhaust gas is discharged downstream of the exhaust purification device 18 without passing through the catalyst 32, NO_XWhen it is preferable because the pressure loss caused by the catalyst 32 is reduced, the switching valve 26 is positioned at the position shown in FIG.
[0078]
As described above, when the condition for allowing the exhaust gas to flow into the bypass passage 31 (hereinafter referred to as a bypassable condition) is satisfied, in the fifth embodiment, the position of the switching valve 26 is shown in FIG. The position is switched to the position shown in FIG. 9B (hereinafter referred to as a bypass position). However, as in the above-described embodiment, when the bypass enabling condition is satisfied while the rich requirement condition is satisfied, if the position of the switching valve 26 is switched to the bypass position, the rich air-fuel ratio exhaust gas is changed. NO_XWithout passing through the catalyst 32, the exhaust gas will flow downstream. Therefore, in the fifth embodiment, as in the above-described embodiment, even if the bypass enabling condition is satisfied while the rich request condition is satisfied, the switching of the position of the switching valve 26 is prohibited.
[0079]
By the way, even if the rich requirement condition is not satisfied and the fuel injection from the fuel addition valve 19 is stopped, all the exhaust gas having a rich air-fuel ratio by the fuel injected from the fuel addition valve 19 is NO._XIt does not pass through the catalyst 32. Therefore, in the fifth embodiment, as in the above-described embodiment, even if the rich requirement condition is not satisfied and the fuel injection from the fuel addition valve 19 is stopped, the switching valve is not used until the switching prohibition period elapses. The switching of the position 26 is prohibited.
[0080]
Other configurations of the fifth embodiment, such as setting of a switching prohibition period, are the same as the configurations in the above-described embodiment, and thus description thereof is omitted. Of course, as in the embodiment described above, NO_XCatalyst 32 is NO_XA particulate filter supporting a catalyst may be used.
[0081]
Finally, the fine particle oxidation action of the filter 32 will be described in detail. In the filter 32 of the present invention, platinum (Pt) is used as the noble metal catalyst. On the other hand, as the active oxygen generator, alkali metals such as potassium (K), sodium (Na), lithium (Li), cesium (Cs), rubidium (Rb), barium (Ba), calcium (Ca), strontium Alkaline earth metals such as (Sr), rare earths such as lanthanum (La), yttrium (Y), cerium (Ce), transition metals such as iron (Fe), and carbon groups such as tin (Sn) At least one selected from elements is used.
[0082]
The active oxygen generator generates active oxygen by holding oxygen by absorption when excess oxygen exists in the surroundings and releasing the held oxygen in the form of active oxygen when the surrounding oxygen concentration decreases. Next, the active oxygen generating action of the active oxygen generator will be described by taking as an example the case where platinum and potassium are supported on a carrier, but other noble metals, alkali metals, alkaline earth metals, rare earths, and transition metals are used. However, the same active oxygen generating action is performed.
[0083]
As described above, the air-fuel ratio of the exhaust gas discharged from the compression ignition type internal combustion engine is lean. Therefore, the exhaust gas flowing into the filter 32 contains a large amount of excess air. Further, NO is generated in the combustion chamber 2 of the compression ignition type internal combustion engine. Therefore, NO is contained in the exhaust gas. Therefore, the exhaust gas containing excess oxygen and NO flows into the exhaust gas inflow passage 50 of the filter 32.
[0084]
FIGS. 10A and 10B schematically show enlarged views of the surface of the carrier layer formed on the partition wall 54. In FIGS. 10A and 10B, 60 indicates platinum particles, and 61 indicates an active oxygen generator containing potassium.
[0085]
When the exhaust gas flows into the exhaust gas inflow passage 50 of the filter 32, as shown in FIG. 10A, oxygen (O₂) Is O₂ ^-Or O^2-It adheres to the surface of platinum in the form of NO in exhaust gas is these O₂ ^-Or O^2-Reacts with NO₂It becomes. NO generated in this way₂A part of is oxidized and retained on the active oxygen generator 61 while being oxidized on platinum, and as shown in FIG. 10 (A), nitrate ions (NO) while binding to potassium (K)._Three ^-) In the form of active oxygen generator 61 and potassium nitrate (KNO)._Three) Is generated. That is, oxygen in the exhaust gas is potassium nitrate (KNO_Three) Is retained in the active oxygen generator 61 by absorption.
[0086]
Here, fine particles mainly made of carbon (C) are generated in the combustion chamber 2. Therefore, these fine particles are contained in the exhaust gas. These fine particles contained in the exhaust gas are indicated by 62 in FIG. 10B when the exhaust gas flows through the exhaust gas inflow passage 50 or when passing through the pores of the partition wall 54. Thus, it contacts and adheres on the surface of the active oxygen generating agent 61.
[0087]
When the fine particles 62 adhere to the surface of the active oxygen generating agent 61 in this way, the oxygen concentration decreases at the contact surface between the fine particles 62 and the active oxygen generating agent 61. That is, the oxygen concentration around the active oxygen generator 61 decreases. When the oxygen concentration is lowered, a difference in concentration occurs between the active oxygen generator 61 having a high oxygen concentration, and thus oxygen in the active oxygen generator 61 is brought into contact with the fine particles 62 and the active oxygen generator 61. Try to move towards. As a result, potassium nitrate (KNO) formed in the active oxygen generator 61_Three) Is decomposed into potassium (K), oxygen (O) and NO, and oxygen (O) is directed to the contact surface between the fine particles 62 and the active oxygen generator 61, while NO is released from the active oxygen generator 61. Released to the outside.
[0088]
Here, since the oxygen toward the contact surface between the fine particles 62 and the active oxygen generating agent 61 is oxygen decomposed from a compound such as potassium nitrate, it has unpaired electrons, and therefore active oxygen having extremely high reactivity. It has become. Thus, the active oxygen generator 61 generates active oxygen. Note that NO released to the outside is oxidized on the downstream platinum and is held in the active oxygen generator 61 again.
[0089]
The active oxygen generated by the active oxygen generator 61 is consumed to oxidize and remove the fine particles adhering thereto. That is, the fine particles collected by the filter 32 are oxidized and removed by the active oxygen generated by the active oxygen generator 61.
[0090]
As described above, in the present invention, the fine particles collected by the filter 32 are oxidized and removed by the reactive oxygen having high reactivity without generating a luminous flame. If the fine particles are removed by oxidation without generating a bright flame in this way, the temperature of the filter 32 will not be excessively increased, and therefore the filter 32 will not be thermally deteriorated.
[0091]
Furthermore, since active oxygen used for oxidizing and removing fine particles has high reactivity, the fine particles are oxidized and removed even if the temperature of the filter 32 is relatively low. That is, the temperature of the exhaust gas discharged from the compression ignition internal combustion engine is relatively low, and therefore, the temperature of the filter 32 is often relatively low. According to the present invention, the temperature of the filter 32 is increased. Even if the special process is not performed, the particulates collected by the filter 32 are continuously removed by oxidation.
[0092]
Note that the active oxygen generator 61 is NO when there is excess oxygen in the surroundings._XIs retained in the form of nitrate ions, resulting in oxygen retention. That is, the active oxygen generator 61 is NO when excess oxygen is present in the surroundings._XHold by absorption. On the other hand, the active oxygen generator 61 is held in the form of nitrate ions when the surrounding oxygen concentration is lowered._XTo release active oxygen. That is, the active oxygen generator 61 is NO when the surrounding oxygen concentration is lowered._XTo release. Therefore, the active oxygen generator 61 of the present invention is NO._XAlso functions as a retention agent.
[0093]
Here, the case where the oxygen concentration around the active oxygen generating agent 61 is reduced means that, as described above, the surrounding atmosphere is a lean atmosphere, but in addition to the case where fine particles adhere to the active oxygen generating agent 61, the filter 32. In some cases, the air-fuel ratio of the exhaust gas flowing into the engine becomes rich and the surrounding atmosphere becomes rich.
[0094]
The ambient atmosphere is a rich atmosphere, but the NO released when the oxygen concentration around the active oxygen generator 61 decreases due to the fine particles adhering to the active oxygen generator 61._XAs described above, the active oxygen generator 61 is again held by absorption. On the other hand, the NO released when the air-fuel ratio of the exhaust gas flowing into the filter 32 becomes rich and the surrounding atmosphere becomes rich._XIs reduced and purified by hydrocarbons in the exhaust gas by the action of platinum. In other words, if the operation of the internal combustion engine is controlled so that the rich air-fuel ratio exhaust gas is discharged from the internal combustion engine, the NO held in the active oxygen generator 61_XCan be reduced and purified. Therefore, the filter 32 of the present invention is NO NO consisting of the active oxygen generator 61 and platinum._XA catalyst is provided.
[0095]
【The invention's effect】
According to the present invention, since the switching of the inflow mode by the switching means is prohibited during the operation of the enrichment means, the rich air-fuel ratio exhaust gas is NO during the operation of the enrichment means._XOutflow to the exhaust gas purification device downstream without passing through the catalyst is suppressed. Further, according to the present invention, even after the operation of the enrichment means is stopped, the switching of the inflow mode by the switching means is prohibited for a predetermined switching prohibition period. Even after the exhaust gas with rich air-fuel ratio is NO_XOutflow to the exhaust gas purification device downstream without passing through the catalyst is suppressed.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine provided with an exhaust purification device of the present invention.
FIG. 2 is a view for explaining an operation mode of the exhaust purification apparatus of the present invention.
FIG. 3 is a diagram showing a particulate filter.
FIG. 4 is a diagram illustrating a routine for executing switching prohibition control of the switching valve according to the first embodiment.
FIG. 5 is a diagram showing a map for calculating an exhaust gas passage completion period.
FIG. 6 shows a map used to determine the combustion mode.
FIG. 7 is a view for explaining a fuel injection mode of the first embodiment.
FIG. 8 is a time chart showing the operation of the fuel addition valve according to the fourth embodiment.
FIG. 9 is a view showing an exhaust emission control device of a fifth embodiment.
FIG. 10 is a view for explaining the particulate oxidation action in the particulate filter.
[Explanation of symbols]
1 ... Engine body
2 ... Combustion chamber
3 ... Fuel injection valve
4 ... Intake manifold
5 ... Exhaust manifold
16. Air-fuel ratio sensor
18 ... Exhaust gas purification device
19 ... Fuel addition valve
23 ... Air-fuel ratio sensor
26 ... switching valve
27 ... EGR passage
31 ... Bypass passage
32 ... NO_XCatalyst (Particulate filter)

Claims (8)

An NO _x catalyst for purifying NO _x in the exhaust gas discharged from the internal combustion engine is provided in the exhaust passage, and when the air-fuel ratio of the exhaust gas flowing into the NO _x catalyst is lean, holding the NO _X, whereas the air-fuel ratio of the exhaust gas flowing into the can reduced and purified by the reducing agent NO _X held with a rich, further to the air-fuel ratio of the exhaust gas rich of comprising the enrichment means, in the exhaust purification apparatus that is a rich air-fuel ratio of the exhaust gas flowing into the NO _X catalyst by actuating the enrichment means when a predetermined condition is satisfied, the exhaust gas switching to a forward flow mode with the exhaust gas to flow from one side to the NO _X catalyst between the other side of the reverse flow mode in which flow to the NO _X catalyst switching the inflow mode of the exhaust gas to the NO _X catalyst And the switching means prohibits the switching of the inflow mode during the operation of the enrichment means, and the inflow by the switching means for a predetermined switching prohibition period even after the operation of the enrichment means is stopped. An exhaust emission control device characterized by prohibiting mode switching. An NO _x catalyst for purifying NO _x in the exhaust gas discharged from the internal combustion engine is provided in the exhaust passage, and when the air-fuel ratio of the exhaust gas flowing into the NO _x catalyst is lean, holding the NO _X, whereas the air-fuel ratio of the exhaust gas flowing into the can reduced and purified by the reducing agent NO _X held with a rich, further to the air-fuel ratio of the exhaust gas rich of comprising the enrichment means, in the exhaust purification apparatus that is a rich air-fuel ratio of the exhaust gas flowing into the NO _X catalyst by actuating the enrichment means when a predetermined condition is satisfied, NO _X catalyst a bypass passage extending from the exhaust passage of the NO _X catalyst upstream to NO _X catalyst downstream of the exhaust passage so as to bypass the bypass passage inflow mode and the exhaust gas flowing the exhaust gas to the NO _X catalyst Switching means for switching the exhaust gas inflow mode between the inflow mode and the inflow mode to be introduced, and during the operation of the enrichment means, switching of the inflow mode by the switch means is prohibited, and the enrichment means An exhaust emission control device characterized in that switching of the inflow mode by the switching means is prohibited for a predetermined switching prohibition period even after the operation is stopped. An exhaust gas passage completion period from when the operation of the enrichment means is stopped until almost all of the rich air-fuel ratio exhaust gas passes through the NO _x catalyst is set as the switching prohibition period. Item 3. The exhaust emission control device according to Item 1 or 2. The exhaust emission control device according to claim 3, wherein the exhaust gas passage completion period is calculated based on at least one of an engine required load and an engine speed. The internal combustion engine can burn fuel in the combustion chamber in a plurality of types of combustion modes, and the exhaust gas passage completion period is based on at least one of the engine required load and the engine speed for each combustion mode. The exhaust emission control device according to claim 3, wherein the exhaust purification device is calculated. The exhaust emission control device according to claim 3, wherein the exhaust gas passage completion period is calculated based on at least one of an exhaust gas temperature, an exhaust gas flow rate, and an exhaust gas pressure. Air-fuel ratio sensor capable of detecting the air-fuel ratio of the exhaust gas is arranged in the NO _X catalyst downstream air-fuel ratio of the exhaust gas by the air-fuel ratio sensor after the deactivation of the enrichment means is detected to have disappeared rich Accordingly, it is determined that almost all of the rich air-fuel ratio exhaust gas has passed through the NO _x catalyst. Exhaust gas air-fuel ratio sensor capable of detecting the air-fuel ratio of the exhaust gas is arranged in the NO _X catalyst upstream and NO _X catalyst downstream, which is detected by the air-fuel ratio sensor of the NO _X catalyst downstream after deactivation enrichment means The air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor downstream of the NO _x catalyst after the gas air-fuel ratio is no longer rich is substantially equal to the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor upstream of the NO _x catalyst. 4. The exhaust emission control device according to claim 3, wherein it is determined that almost all of the rich air-fuel ratio exhaust gas has passed through the NO _x catalyst.

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