JP3922408B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that purifies nitrogen oxides (hereinafter referred to as “NOx”) contained in the exhaust gas of the internal combustion engine with a plurality of catalysts.
[0002]
[Prior art]
In recent years, as disclosed in JP-A-4-214919, it has been proposed to arrange a plurality of catalysts in series in an exhaust pipe of an internal combustion engine in order to increase exhaust purification efficiency. Further, in order to purify NOx in exhaust gas in an oxygen-excess atmosphere such as a diesel engine, it is necessary to supply a hydrocarbon such as fuel (hereinafter referred to as “HC”) as a NOx reducing agent to the catalyst.
[0003]
As shown in FIG. 2, the reaction amount of HC in the catalyst increases with an increase in the catalyst temperature (B in FIG. 2). When the catalyst temperature is high, the reaction amount of HC becomes almost 100% (C in FIG. 2). . Therefore, when supplying HC from the uppermost stream of the catalyst arranged in series, if the temperature of the catalyst arranged on the upstream side is high, almost all of the supplied HC reacts with the upstream catalyst, and downstream. HC cannot be supplied to the catalyst on the side. For this reason, there is a problem that the downstream catalyst cannot purify NOx and a high NOx purification rate cannot be obtained.
[0004]
In order to solve this problem, Japanese Patent Laid-Open No. 4-214919 discloses that a plurality of HC supply devices are provided upstream of a plurality of catalysts installed in series, and HC is separately supplied to each catalyst. Like to do. Thereby, by supplying HC to all the plurality of catalysts, a high NOx purification rate is obtained.
[0005]
[Problems to be solved by the invention]
However, in the configuration of the above publication, since one HC supply device is required for each of the plurality of catalysts, the configuration becomes complicated and the cost is increased, and the device is increased in size, so that the vehicle is actually mounted. There is a problem that it becomes difficult.
[0006]
The present invention has been made in view of such circumstances. Therefore, the object of the present invention is to make it possible to supply HC to all of a plurality of catalysts with a simple structure and to efficiently purify NOx. An object of the present invention is to provide an exhaust emission control device for an engine.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the exhaust gas purification apparatus for an internal combustion engine of claim 1 of the present invention, a plurality of catalysts are installed in series in the exhaust passage, and the fuel injection control means is connected to the fuel injection means of each cylinder. On the other hand, a main injection command for generating engine output is output near the compression top dead center, and at the same time, post-injection for supplying HC to the catalyst in the expansion stroke or exhaust stroke of the engine to the fuel injection means of at least one cylinder Outputs a command. In this case, the active state of the catalyst (hereinafter referred to as “upstream catalyst”) arranged upstream of the most downstream catalyst among the plurality of catalysts is determined by the upstream catalyst active state determination means, and the upstream catalyst The post-injection timing is corrected by the post-injection timing correcting means in accordance with the active state of. Thus, the amount of HC that reacts with the upstream catalyst is controlled so that the HC supplied by the post injection reaches the downstream catalyst.
[0008]
Here, the reason why the amount of HC that reacts with the upstream catalyst can be controlled by correcting the post-injection timing will be described. The post-injected fuel (diesel oil) has a high boiling point HC, which is reformed (pyrolyzed) by the combustion heat in the cylinder and changes to a low boiling point HC. The higher the quality), the easier it is to react on the catalyst. As shown in FIG. 3, the degree of reforming of the post-injected fuel (HC) changes depending on the temperature in the cylinder at the time of post-injection, and the temperature in the cylinder at the time of post-injection changes depending on the post-injection time. Can change the degree of reforming of the post-injected fuel (HC).
[0009]
As described above, since the reactivity of HC changes due to the change in the reforming degree of the post-injected fuel, it is possible to control the amount of HC that reacts with the upstream catalyst. For this reason, by correcting the post-injection timing according to the active state of the upstream catalyst, HC can be distributed to the downstream catalyst, and NOx is efficiently purified by using all of the plurality of catalysts effectively. And a high NOx purification rate can be obtained. In addition, since HC is supplied to a plurality of catalysts by post-injection, it is not necessary to provide the same number of HC supply devices as the number of catalysts as in the above-mentioned known example, the configuration of the device can be simplified, and the device can be downsized. The cost can be reduced and the vehicle can be easily mounted.
[0010]
In this case, as in claim 2, the lower the upstream catalyst active state determined by the upstream catalyst active state determining means, the more the post-injection timing is corrected, and the higher the upstream catalyst active state, It may be configured to correct the injection timing by retarding the angle. That is, when the upstream catalyst temperature is high and the active state is high (C in FIG. 2), if the post-injection timing is retarded, the temperature in the cylinder at the time of post-injection becomes low. Can be supplied from the upstream side of the catalyst. Since high boiling point HC has low reactivity and does not react very much even at high temperatures, even if the temperature of the upstream catalyst is high and the active state is high, it is possible to suppress the amount of HC reaction there, and HC is also applied to the downstream catalyst. Can be spread.
[0011]
On the other hand, when the temperature of the upstream catalyst is low and the active state is low (the low temperature side of A and B in FIG. 2), if the post injection timing is corrected to advance, the temperature in the cylinder at the time of post injection becomes high. The degree of reforming of HC is large (the number of carbon atoms is small), and HC with a high proportion of low boiling point HC can be supplied from the upstream side of the catalyst. Since the low boiling point HC is highly reactive and reacts even at a relatively low temperature, even if the temperature of the upstream catalyst is low and the active state is low, it is possible to purify NOx. Further, since the purification rate of HC in the catalyst is relatively low at a low temperature (the low temperature side of A and B in FIG. 2), HC that has not reacted with the upstream catalyst is supplied to the downstream catalyst. As a result, NOx can be efficiently purified by effectively using a plurality of catalysts, and a high NOx purification rate can be obtained.
[0012]
According to a third aspect of the present invention, the main exhaust passage and the bypass exhaust passage having the HC adsorbent are provided in parallel between the plurality of catalysts arranged in series in the exhaust passage, and upstream of the parallel passage. The active state of the arranged catalyst may be determined by the upstream side catalyst active state determination means, and both the exhaust passages may be switched by the exhaust passage switching means according to the determination result. By doing this, even when the upstream catalyst is in a high active state and the post-injected HC reacts entirely with the upstream catalyst, by switching the exhaust flow to the bypass exhaust passage having the HC adsorbent, The HC that has been adsorbed on the HC adsorbent so far can be desorbed and supplied to the downstream catalyst. Therefore, even if the active state of the upstream catalyst becomes high, HC can be supplied to the downstream catalyst, all the catalysts can be used effectively, and a high NOx purification rate can be obtained.
[0013]
In this case, the claim 5 As described above, the exhaust passage switching means may be switched depending on whether the activation state of the upstream catalyst is within a predetermined range (B in FIG. 2) where the NOx purification rate is high. For example, when the activation state of the upstream catalyst is lower than a predetermined range (A in FIG. 2), the HC purification rate is low, and thus the supplied HC passes through the upstream catalyst without being reacted. Therefore, in this state, exhaust gas is caused to flow to the bypass exhaust passage side, and the HC that has passed through is adsorbed by the HC adsorbent. In other words, when the upstream catalyst activity state is lower than the predetermined range, it is estimated that the downstream catalyst activity state is also lower than the predetermined range, and the HC in the exhaust gas that has passed through the upstream catalyst is placed in the bypass exhaust passage. By adsorbing with HC adsorbent, HC is stored for the subsequent purification of NOx. As a result, the post-injection amount can be reduced, and HC can be prevented from passing through the downstream catalyst and discharged into the atmosphere, so that the amount of HC discharged into the atmosphere can be greatly reduced.
[0014]
In addition, when the activation state of the upstream catalyst is within a predetermined range (B in FIG. 2), a part of the supplied HC passes through the upstream catalyst without being reacted, but the exhaust temperature is relatively high. Further, the temperature of the downstream catalyst becomes high, and the downstream catalyst can also purify NOx. Therefore, in this state, by switching the exhaust flow to the main exhaust passage side and supplying the HC that has passed through the upstream catalyst to the downstream catalyst through the main exhaust passage, the downstream catalyst can also purify NOx. .
[0015]
Further, when the activation state of the upstream side catalyst is higher than the predetermined range (C in FIG. 2), the HC purification rate in the upstream side catalyst is almost 100%. It reacts with the catalyst and is not supplied to the downstream catalyst. Therefore, in this state, high temperature exhaust gas is flowed to the bypass exhaust passage side to raise the temperature of the HC adsorbent, thereby desorbing the HC that has been adsorbed on the HC adsorbent so far, and the downstream catalyst. And the NOx is purified by the downstream catalyst.
[0016]
In this way, if the exhaust passage is switched depending on whether or not the active state of the upstream catalyst is within a predetermined range (B in FIG. 2), even if the active state of the upstream catalyst changes, the downstream catalyst is changed. HC can be reliably supplied, and a high NOx purification rate can be obtained by using all the catalysts effectively.
[0017]
Claims 3 As described above, in addition to the active state of the upstream catalyst, the active state of the downstream catalyst may be determined, and the exhaust passage switching means may be switched as follows based on both.
[0018]
(1) When the active state of the upstream catalyst is lower than the predetermined range (A in FIG. 2)
In this case, unreacted HC in the upstream catalyst passes through the upstream catalyst. At that time, when the active state of the downstream catalyst is within a predetermined range (B in FIG. 2) and a high NOx purification rate is obtained in the downstream catalyst, the exhaust is flowed to the main exhaust passage and HC is directly downstream Supply to catalyst to purify NOx. On the other hand, when the active state of the downstream catalyst is not within the predetermined range (A and C in FIG. 2) and the high NOx purification rate cannot be obtained in the downstream catalyst, HC cannot be effectively used in the downstream catalyst. The exhaust gas is caused to flow into the bypass exhaust passage, and the HC in the exhaust gas is adsorbed by the HC adsorbent.
[0019]
(2) When the active state of the upstream catalyst is within a predetermined range (B in FIG. 2)
In this case, since most of the supplied HC reacts with the upstream catalyst, even if the activity state of the downstream catalyst is within the predetermined range (B in FIG. 2), the downstream catalyst has insufficient HC. The NOx purification rate decreases. Therefore, in this case, the exhaust is allowed to flow to the bypass exhaust passage. As a result, a relatively high temperature exhaust gas passes through the HC adsorbent, so that the HC that has been adsorbed by the HC adsorbent so far is desorbed and supplied to the downstream catalyst. A sufficient amount of HC is supplied to purify NOx. On the other hand, when the active state of the downstream catalyst is not within the predetermined range (A and C in FIG. 2) and a high NOx purification rate cannot be obtained in the downstream catalyst, HC cannot be effectively used in the downstream catalyst. Therefore, by letting the exhaust gas flow into the main exhaust passage, HC desorption from the HC adsorbent in the bypass exhaust passage is prevented.
[0020]
(3) When the active state of the upstream catalyst is higher than the predetermined range (C in FIG. 2)
In this case, since almost all of the supplied HC reacts with the upstream catalyst, whether the activity state of the downstream catalyst is within the predetermined range as in the case where the activity state of the upstream catalyst is within the predetermined range. The exhaust passage is switched depending on whether or not.
[0021]
As described above, by switching the exhaust passage according to the active state of the upstream catalyst and the active state of the downstream catalyst, the HC supplied by the post-injection can be used very efficiently in each of the plurality of catalysts, and the NOx purification rate can be increased. Can be increased.
[0022]
By the way, when the time for flowing the exhaust gas to the main exhaust passage becomes long, the temperature of the HC adsorbent in the bypass exhaust passage decreases due to heat dissipation. If the exhaust flow is suddenly switched from the main exhaust passage to the bypass exhaust passage in this state, the exhaust passes through the cooled HC adsorbent, so that the exhaust temperature decreases. Therefore, the temperature of the downstream side catalyst may decrease, and the NOx purification rate may decrease.
[0023]
As a countermeasure, the claims 4 As described above, when switching the flow of exhaust from the main exhaust passage to the bypass exhaust passage, the operation of alternately switching the exhaust passage switching means between the bypass exhaust passage side and the main exhaust passage side is repeated for a while. Also good. In this way, when the flow of the exhaust gas is switched from the main exhaust passage to the bypass exhaust passage, the high-temperature exhaust gas is intermittently supplied to the downstream catalyst through the main exhaust passage for a while. The rapid temperature drop of the side catalyst can be prevented, and NOx can be purified at a high purification rate even immediately after switching the exhaust passage even at the downstream side catalyst.
[0024]
In this case, the claim 6 As described above, when the exhaust flow is switched from the main exhaust passage to the bypass exhaust passage, at least one of the switching frequency of the exhaust passage switching means and the time ratio of the switching interval is changed according to the change speed of the active state of the upstream catalyst. You may make it let it. In other words, the more the change in the active state of the upstream catalyst is more gradual (that is, the more the change in exhaust temperature is), the more sudden the exhaust flow is switched from the main exhaust passage to the bypass exhaust passage, the more the catalyst flows into the downstream catalyst. The reduction in the NOx purification rate due to the temperature drop of the exhaust gas is likely to increase. In this case, the switching frequency of the exhaust passage switching means is increased to shorten the time interval for supplying the low temperature exhaust gas from the bypass exhaust passage side to the downstream catalyst, or the exhaust gas flowing through the main exhaust passage side. If the time ratio of the switching interval is changed so as to increase the ratio, the temperature decrease of the exhaust gas flowing into the downstream catalyst can be suppressed, and the decrease in the NOx purification rate of the downstream catalyst can be prevented more reliably. .
[0025]
Claims 7 As described above, an HC adsorbent may be provided for each of a plurality of catalysts installed in series, and the HC adsorbing capacity thereof may be increased as the HC adsorbent on the downstream side. That is, when the catalyst is highly active, among the catalysts installed in series, HC is mainly supplied to the upstream catalyst by post-injection, while the downstream catalyst is mainly adsorbed in advance by the HC adsorption means. HC is supplied by desorbing the HC. As a result, even when there is a situation where the HC supplied by post-injection is consumed by the upstream catalyst and hardly reaches the downstream catalyst when the catalyst is highly active, the HC is desorbed from the HC adsorbing means and the downstream side Since HC can be supplied to the catalyst, it is possible to prevent the downstream catalyst from becoming deficient due to insufficient HC when the catalyst is highly active, which is extremely effective in improving the purification rate.
[0026]
In this case, if the HC adsorption capacity of the upstream HC adsorption means is increased, most of the HC supplied by the post-injection is adsorbed by the upstream HC adsorption means, and the amount of HC reaching the downstream HC adsorption means is small. turn into. Therefore, the claim 7 Then, by configuring the HC adsorption capacity of the HC adsorption means to be larger on the downstream side than on the upstream side, the HC supplied by the post-injection can be sufficiently distributed to the downstream side, A sufficient amount of HC is adsorbed by both HC adsorption means on the downstream side. After that, when the active state of the catalyst becomes high, HC is desorbed from each HC adsorbing means and is also supplied to the downstream catalyst, so the downstream catalyst is also used as effectively as the upstream catalyst Thus, NOx can be purified, and the NOx purification rate can be greatly improved.
[0027]
Further claims 7 Thus, the upstream catalyst activity state determining means determines the active state of a catalyst installed upstream of the most downstream catalyst (hereinafter referred to as “upstream catalyst”) among the plurality of catalysts, and the upstream catalyst The post-injection command may be output only for a predetermined period when the active state is low and the NOx purification rate in the upstream catalyst is low. That is, when the active state of the upstream catalyst is low and the NOx purification rate is low, HC is adsorbed by the HC adsorbing means of the upstream catalyst and the downstream catalyst, and the HC is adsorbed from each HC adsorbing means when the catalyst is highly active thereafter. The aim is to improve the NOx purification rate by desorption. However, since the amount of HC adsorbed by the HC adsorbing means is finite, excessive HC supply does not lead to an improvement in the NOx purification rate, leading to deterioration in fuel consumption. Therefore, after the post-injection is performed only for a predetermined period and after the effective HC amount is adsorbed, the post-injection is stopped, thereby minimizing the fuel consumption by the post-injection and satisfying the demand for low fuel consumption.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment (1)]
Hereinafter, an embodiment (1) in which the present invention is applied to a diesel engine will be described with reference to FIGS.
[0029]
First, the overall configuration of the engine control system will be described with reference to FIG. The intake air sucked through the intake pipe 11 is sucked through the intake manifold 13 into each cylinder of the diesel engine 10 which is an internal combustion engine. A solenoid valve type fuel injection valve 14 (fuel injection means) is attached to each cylinder of the diesel engine 10, and fuel accumulated at a high pressure from a high pressure fuel pump 15 is distributed to each fuel injection valve 14 through a common rail 16. Is done. A fuel pressure sensor 12 that detects the pressure of fuel distributed to the fuel injection valve 14 (common rail fuel pressure) is attached to the common rail 16.
[0030]
As shown in FIG. 4, the fuel injection valve 14 performs main injection for generating engine output in the vicinity of compression top dead center, and prior to this main injection, performs pilot injection to inject a small amount of fuel. When the fuel is ignited, the main injection is performed to reduce the premixed combustion in the early stage of combustion and reduce the NOx emission amount. Further, the fuel injection valve 14 of at least one cylinder performs post-injection for supplying HC to NOx catalysts 20 and 21 described later in the expansion stroke or the exhaust stroke.
[0031]
Exhaust gas discharged from each cylinder of the diesel engine 10 is discharged to one exhaust pipe 18 (exhaust passage) through the exhaust manifold 17, and two NOx catalysts 19, 20 are disposed in the middle of the exhaust pipe 18. They are arranged in series. Each NOx catalyst 19, 20 has a catalyst component (for example, Cu-zeolite, Pt-zeolite, etc.) capable of reducing and purifying NOx in the presence of a reducing agent (HC) even in an oxygen-rich atmosphere on the surface of a ceramic or metal carrier. It is supported.
[0032]
In this case, the supported zeolite serves as a hydrocarbon adsorbing means that adsorbs HC in the exhaust gas at a low temperature (eg, 200 ° C. or less) and desorbs the adsorbed HC at a high temperature (eg, 200 ° C. or more), The greater the amount of zeolite, the greater the HC adsorption capacity. In the present embodiment (1), the amount of zeolite in the downstream NOx catalyst 20 is increased (for example, 1.5 times) and supported as compared with the upstream NOx catalyst 19.
[0033]
As shown in FIG. 2, the NOx purification characteristics of the NOx catalysts 19 and 20 have a high NOx purification rate in the predetermined temperature range B, and the NOx purification rate extremely decreases in the other temperature ranges A and C. Further, in the HC purification characteristics of the NOx catalysts 19 and 20, in the low temperature region A, HC passes through with little reaction. Further, in the predetermined temperature range B where the NOx purification rate becomes high, the HC purification rate becomes higher as the temperature becomes higher, and in the high temperature region C, the HC purification rate becomes almost 100%.
[0034]
An exhaust temperature sensor 21 is installed between the two NOx catalysts 19 and 20. The exhaust gas temperature sensor 21 serves as upstream side catalyst active state determination means for determining the active state (catalyst temperature) of the upstream side NOx catalyst 19 by detecting the outflow gas temperature of the upstream side NOx catalyst 19.
[0035]
An output signal of the exhaust temperature sensor 21 is input to an engine electronic control circuit (hereinafter referred to as “ECU”) 22. The ECU 22 reads output signals from the engine speed sensor 23, the accelerator sensor 24, etc., detects the operating state of the diesel engine 10, calculates the injection amount and injection timing of pilot injection, main injection, and post-injection, and claims And the post-injection timing according to the exhaust temperature detected by the exhaust temperature sensor 21, that is, the temperature of the upstream NOx catalyst 19 (hereinafter referred to as "upstream catalyst temperature"). to correct.
[0036]
In this case, when the upstream catalyst temperature is low (A in FIG. 2), post-injection is performed for a predetermined period. That is, HC that is sufficiently gasified by post-injecting fuel into the cylinder having a high temperature is supplied to the NOx catalysts 19 and 20. The HC hardly reacts with the upstream NOx catalyst 19 having low activity, and a part of the HC is adsorbed to the HC adsorption means (zeolite) of the upstream NOx catalyst 19, but the adsorption amount is small because it is gasified. , Most of them reach the HC adsorption means of the downstream side NOx catalyst 20. Since the HC adsorption means of the downstream side NOx catalyst 20 has a large HC adsorption capacity, most of the reached HC is adsorbed there. The HC adsorbed by the HC adsorbing means of the downstream side NOx catalyst 20 is desorbed and supplied to the downstream side NOx catalyst 20 when the catalyst is subsequently activated, and is effectively used for NOx purification. At that time, there is an upper limit on the amount of HC adsorbed by the HC adsorbing means, and a large amount of post-injection over a long period of time leads to deterioration of fuel consumption.
[0037]
On the other hand, when the upstream side catalyst temperature is relatively high (B and C in FIG. 2), the post-injection timing is retarded as the upstream side catalyst temperature is lower. That is, when the upstream side catalyst temperature is high, almost all of the supplied HC reacts with the upstream side NOx catalyst 19, so that the HC does not reach the downstream side NOx catalyst 20, and the downstream side NOx catalyst 20 purifies NOx. It becomes impossible.
[0038]
In order to prevent this, when the upstream catalyst temperature is high, the post-injection timing is retarded to lower the temperature in the cylinder at the time of post-injection, thereby reducing the degree of reforming of HC and increasing the high boiling point. HC having a high HC ratio is supplied to both NOx catalysts 19 and 20. Since high boiling point HC has low reactivity and does not react very much even at high temperature, it becomes possible to suppress the amount of HC reaction in the upstream NOx catalyst 19 even if the upstream catalyst temperature is high and the active state is high. HC can also be supplied to the NOx catalyst 20.
[0039]
On the other hand, when the upstream catalyst temperature is relatively low (B in FIG. 2, particularly the low temperature side), the post-injection timing is advanced to increase the temperature in the cylinder at the time of post-injection, thereby improving the HC. The quality is increased, and HC having a high proportion of low-boiling HC is supplied to both NOx catalysts 19 and 20. Since the low boiling point HC has high reactivity and reacts even at a relatively low temperature, it is possible to purify NOx even if the upstream catalyst temperature is low and the active state is low. Further, since the HC purification rate is relatively low at a low temperature (B in FIG. 2, particularly the low temperature side), HC that has not reacted with the upstream NOx catalyst 19 is supplied to the downstream NOx catalyst 20. Thereby, NOx can be efficiently purified by effectively using the two NOx catalysts 19 and 20 on the upstream side and the downstream side, and a high NOx purification rate can be obtained.
[0040]
The NOx purification control described above is executed by a post injection timing correction program shown in FIG. The program is executed by the ECU 22 at predetermined time intervals (for example, every second) and serves as post injection timing correction means in the claims. When this program is started, first, in step 101, the output signal of the exhaust temperature sensor 21 is read. In this case, since the exhaust temperature sensor 21 is provided downstream of the upstream NOx catalyst 19, the temperature detected by the exhaust temperature sensor 21 is the outflow gas temperature of the upstream NOx catalyst 19, and consequently the upstream NOx catalyst 19. Is the upstream catalyst temperature T representing the active state of
[0041]
In the next step 102, it is determined whether the region including the upstream catalyst temperature T corresponds to any of A, B, and C in FIG. For example, if the upstream catalyst temperature T is 200 ° C. or lower, it is determined as A, if the upstream catalyst temperature T is 200 to 300 ° C., it is determined as B, and if the upstream catalyst temperature T is 300 ° C. or higher, it is determined as C. .
[0042]
If the region determined in step 102 is A, post-injection is performed in step 103. The post-injection time at this time is set to a time when the post-injected fuel does not burn in the cylinder, and is determined by the ECU 22 based on the output of each sensor. After starting the post-injection in step 103, it is determined in step 104 whether or not a predetermined time has elapsed. If not, the process waits until it elapses. Cancel. The predetermined time in this case is determined by the ECU 22 based on, for example, the saturated adsorption amount in the HC adsorption means, the engine operating conditions, the post-injection amount, and the like. Moreover, it is good also as a fixed value simply.
[0043]
On the other hand, if the region determined in step 102 is B or C, the process proceeds to step 106, and the upstream catalyst temperature T is compared with the set temperature T1. Here, the set temperature T1 is a temperature at which the NOx purification rate reaches a peak in B of FIG. 2, and is set to, for example, 250 to 500 ° C. If the upstream catalyst temperature T is higher than the set temperature T1, the routine proceeds to step 107, where the post-injection timing is delayed by a map or the like according to the upstream catalyst temperature T, and corrected in the next step 108. Post-injection is performed at the injection timing. As shown in FIG. 6, the correction amount of the post-injection timing at that time increases the retard amount as the upstream catalyst temperature T increases. As a result, the higher the upstream side catalyst temperature T is, the smaller the degree of reforming of HC and the lower the reactivity of HC are obtained. As shown in FIG. 7, the reduction amount due to the HC reaction in the upstream side NOx catalyst 19 is reduced. A sufficient amount of HC can be supplied to the downstream side NOx catalyst 20 as well. As a result, the downstream NOx catalyst 20 can sufficiently purify NOx, and a high NOx purification rate can be obtained.
[0044]
On the other hand, if the upstream catalyst temperature T is equal to or lower than the set temperature T1, the routine proceeds to step 109, where the post-injection timing is corrected by a map or the like according to the upstream catalyst temperature, and the post-injection timing corrected in the following step 108. After injection is carried out. As shown in FIG. 6, the correction amount of the post-injection timing at that time increases the advance amount as the upstream catalyst temperature T is lower. Thereby, as the upstream catalyst temperature T is lower, the degree of reforming of HC is increased to obtain HC having higher reactivity, so that both the upstream and downstream NOx catalysts 19, 20 can be connected as shown in FIG. Effectively used, NOx can be purified efficiently, and a high NOx purification rate can be obtained.
[0045]
In the embodiment (1) described above, the post-injection timing is continuously corrected according to the upstream catalyst temperature according to the map of FIG. 6, but the correction amount of the post-injection timing is set according to the upstream catalyst temperature. It is also possible to switch to a plurality of stages. Further, since the temperature in the cylinder is different depending on the engine operating conditions (engine speed and load) even if the crank angle is the same, the post-injection timing and the correction amount of the post-injection timing may be varied depending on the engine operating conditions. good.
[0046]
Further, in the present embodiment (1), the exhaust gas temperature sensor 21 provided downstream of the upstream NOx catalyst 19 detects the outflow gas temperature of the upstream NOx catalyst 19 so that the upstream NOx catalyst 19 is activated (upstream). However, instead of this, the inflow gas temperature and the outflow gas temperature of the upstream NOx catalyst 19 are detected, and the activation state (upstream catalyst temperature) of the upstream NOx catalyst 19 is determined from both of them. It may be estimated. At that time, the inflow gas temperature of the upstream NOx catalyst 19 may be calculated from the engine operating conditions. Further, a temperature sensor may be provided in the upstream NOx catalyst 19 itself so as to directly detect the active state (upstream catalyst temperature) of the upstream NOx catalyst 19.
[0047]
In the present embodiment (1), two NOx catalysts are provided in series in the exhaust pipe 18, but three or more NOx catalysts may be provided in series.
[0048]
[Embodiment (2)]
FIG. 9 shows the configuration of the embodiment (2) of the present invention. Hereinafter, only different portions from the embodiment (1) shown in FIG. 1 will be described.
[0049]
In the present embodiment (2), an HC adsorbent 40 is installed as an HC adsorbing means between the upstream catalyst 19 and the downstream catalyst 20. That is, in the embodiment (1), the HC adsorption means in the downstream catalyst 20 is composed only of the zeolite layer supported on the downstream catalyst 20, but in this embodiment (2), the HC adsorption means of the downstream catalyst 20 is used. In order to further increase the amount of HC adsorbed in HC, an HC adsorbent 40 is installed. This HC adsorbent 40 is a material in which a porous material such as zeolite is supported on the surface of a carrier such as ceramic or metal, adsorbs HC in the exhaust at a low temperature (for example, 200 ° C. or less), and at a high temperature ( For example, HC adsorbed at 200 ° C. or higher is desorbed.
[0050]
By controlling the embodiment (2) having the above configuration in the same manner as the embodiment (1), it is possible to obtain an effect equal to or greater than that described in the embodiment (1).
A plurality of the NOx catalysts 19 and 20 and the HC adsorbent 40 may be accommodated in the same case.
[0051]
[Embodiment (3)]
The embodiment (3) of the present invention will be described below with reference to FIGS. In this embodiment (3), the main exhaust passage 31 and the bypass exhaust passage 32 are provided in parallel between the two NOx catalysts 19, 20 arranged in series with the exhaust pipe 18, and in the middle of the bypass exhaust passage 32. An HC adsorbent 33 that adsorbs HC in the exhaust is disposed. This HC adsorbent 33 is a material in which a porous material such as zeolite is supported on the surface of a carrier such as ceramic or metal, adsorbs HC in the exhaust at a low temperature (eg, 200 ° C. or less), and at a high temperature HC adsorbed on (for example, 200 ° C. or higher) is desorbed.
[0052]
On the other hand, an exhaust passage switching valve 34 is provided at an upstream branch portion between the main exhaust passage 31 and the bypass exhaust passage 32, and the exhaust flow is changed by switching the exhaust passage switching valve 34. Is selectively switched to one of the above. The exhaust passage switching valve 34 is controlled by the ECU 22 using a motor or negative pressure as a drive source. Between the upstream NOx catalyst 19 and the exhaust passage switching valve 34, an exhaust temperature sensor 21 (upstream catalyst active state determination means) is installed. Other system configurations are the same as those of the above-described embodiment (1).
[0053]
In the present embodiment (3), as in the embodiment (3), HC as a reducing agent is supplied to the NOx catalysts 19 and 20 in the expansion stroke or exhaust stroke after the main fuel injection for generating engine output. In this case, the flow of exhaust gas is selectively sent to either the main exhaust passage 31 or the bypass exhaust passage 32 in accordance with the active state of the upstream NOx catalyst 19 (upstream catalyst temperature). Switch.
[0054]
That is, when the upstream catalyst temperature (active state) is lower than the predetermined range (A in FIG. 2), since the HC purification rate is low, the supplied HC passes through the upstream NOx catalyst 19 without being reacted. End up. Therefore, in this state, the exhaust is caused to flow toward the bypass exhaust passage 32 so that the HC that has passed through is adsorbed by the HC adsorbent 33. In other words, when the activation state of the upstream NOx catalyst 19 is lower than the predetermined range, it is estimated that the activation state of the downstream NOx catalyst 20 is also lower than the predetermined range, and the HC in the exhaust gas passing through the upstream NOx catalyst 19 is estimated. Is adsorbed by the HC adsorbent 33 in the bypass exhaust passage 32 to store HC for subsequent purification of NOx. In particular, HC obtained by the post-injection of the common rail diesel engine is sufficiently gasified, so that it easily passes through the upstream NOx catalyst 19. Therefore, if this HC is adsorbed on the HC adsorbent 33, the effect of effective use of HC and reduction of HC emission amount is great.
[0055]
When the activation state of the upstream NOx catalyst 19 is within a predetermined range (B in FIG. 2), a part of the supplied HC passes through the upstream NOx catalyst 19 without being reacted, but the exhaust temperature is Since the temperature is relatively high, the temperature of the downstream NOx catalyst 20 also becomes high, and the downstream NOx catalyst 20 can also purify NOx. Therefore, in this state, the flow of the exhaust gas is switched to the main exhaust passage 31 side, and the HC that has passed through the upstream NOx catalyst 19 is supplied to the downstream NOx catalyst 20 through the main exhaust passage 31, so that the downstream NOx catalyst 20 But it purifies NOx.
[0056]
When the activation state of the upstream NOx catalyst 19 is higher than the predetermined range (C in FIG. 2), the HC purification rate in the upstream NOx catalyst 19 is almost 100%. , All react with the upstream NOx catalyst 19 and are not supplied to the downstream NOx catalyst 20. Therefore, in this state, high-temperature exhaust is caused to flow toward the bypass exhaust passage 32 to raise the temperature of the HC adsorbent 33, thereby desorbing the HC that has been adsorbed on the HC adsorbent 33 so far. The downstream NOx catalyst 20 is supplied and the downstream NOx catalyst 20 purifies NOx.
[0057]
The NOx purification control described above is executed by the exhaust passage switching control program shown in FIG. This program is executed by the ECU 22 every predetermined time (for example, every second), and serves as a control means in the claims. When this program is started, first, in step 201, the upstream catalyst temperature T detected by the exhaust temperature sensor 21 (the active state of the upstream NOx catalyst 19) is read. In the next step 202, this upstream catalyst temperature is read. It is determined whether the active state region including T corresponds to any of A, B, and C in FIG. For example, if the upstream catalyst temperature T is 200 ° C. or lower, it is determined as A, if the upstream catalyst temperature T is 200 to 300 ° C., it is determined as B, and if the upstream catalyst temperature T is 300 ° C. or higher, it is determined as C. .
[0058]
If the region determined in step 202 is A or C, the process proceeds to step 203, and the exhaust passage switching valve 34 is switched to allow exhaust to flow to the bypass exhaust passage 32 side. That is, in the region A where the upstream catalyst temperature T is low, HC passes through the upstream NOx catalyst 19 without being reacted, and the downstream NOx catalyst 20 is also in a low activity state with a low temperature. The exhaust gas flowing out from the exhaust gas 19 is caused to flow through the HC adsorbent 33 in the bypass exhaust passage 32 so that the HC in the exhaust is adsorbed by the HC adsorbent 33. Further, in the region C where the upstream catalyst temperature T is high, all of the supplied HC reacts with the upstream NOx catalyst 19, so that the high temperature exhaust gas flows to the bypass exhaust passage 32 side and the temperature of the HC adsorbent 33 is increased. , The HC adsorbed by the HC adsorbent 33 until then is desorbed and supplied to the downstream NOx catalyst 20, and the downstream NOx catalyst 20 purifies NOx.
[0059]
On the other hand, if the region determined in step 202 is B, the process proceeds to step 204, and the exhaust passage switching valve 34 is switched so that the exhaust flows to the main exhaust passage 31 side. That is, in the region B, a part of the supplied HC passes through the upstream NOx catalyst 19 without being reacted, but the downstream NOx catalyst 20 is also in a state capable of purifying NOx, so that the flow of the exhaust is changed to the main exhaust. By switching to the passage 31 side and supplying HC that has passed through the upstream side NOx catalyst 19 to the downstream side NOx catalyst 20, the downstream side NOx catalyst 20 also purifies NOx.
[0060]
In the exhaust passage switching control described above, for example, as shown in FIG. 12, when the active state (upstream catalyst temperature) of the upstream NOx catalyst 19 changes in the order of A → B → C, the first low-temperature region A Then, the exhaust is caused to flow toward the bypass exhaust passage 32, and the HC that has passed is adsorbed by the HC adsorbent 33. Thereafter, in the region B, the flow of the exhaust gas is switched to the main exhaust passage 31 side, and the HC that has passed through the upstream NOx catalyst 19 is supplied to the downstream NOx catalyst 20 through the main exhaust passage 31. Thereby, NOx is purified by both the upstream NOx catalyst 19 and the downstream NOx catalyst 20. At this time, the HC adsorbed on the HC adsorbent 33 in the previous region A is retained.
[0061]
Thereafter, in the high temperature region C, the exhaust gas is flowed to the bypass exhaust passage 32 side, and the temperature of the HC adsorbent 33 is increased, so that the HC adsorbed by the HC adsorbent 33 until then is desorbed. To the downstream NOx catalyst 20 and the downstream NOx catalyst 20 purifies NOx. At this time, conventionally, the amount of HC supplied to the downstream side NOx catalyst 20 is insufficient, and the downstream side NOx catalyst 20 could hardly purify NOx. However, in this embodiment (3), HC is removed from the HC adsorbent 33. Since it can be supplied to the downstream NOx catalyst 20, NOx can be purified by the downstream NOx catalyst 20, and the NOx purification rate can be improved as compared with the conventional case.
[0062]
According to the embodiment (3) described above, the exhaust passage is switched in accordance with the activation state (upstream catalyst temperature) of the upstream NOx catalyst 19, so that even if the activation state of the upstream NOx catalyst 19 is high, the downstream side HC can be reliably supplied to the NOx catalyst 20, and a high NOx purification rate can be obtained by effectively using the two upstream and downstream NOx catalysts 19,20. In addition, when the upstream NOx catalyst 19 is in a low temperature state where NOx cannot be purified with high efficiency, the HC in the exhaust gas that has passed through the upstream NOx catalyst 19 is adsorbed by the HC adsorbent 33 and the subsequent NOx purification. Since HC can be stored in the exhaust gas, the post-injection amount can be reduced, fuel consumption can be reduced, and HC can be prevented from passing through the downstream side NOx catalyst 20 and discharged into the atmosphere. Can be greatly reduced.
[0063]
In this embodiment (3), the post-injection of the fuel injection valve 14 is used as the reducing agent supply means for supplying the reducing agent (HC) to the NOx catalyst. It may be attached to the exhaust pipe 18 upstream of the NOx catalyst 19 and HC may be supplied into the exhaust pipe 18 from this HC supply nozzle. Also in the present embodiment (3), three or more NOx catalysts may be provided in series in the exhaust pipe.
[0064]
[Embodiment (4)]
In the embodiment (4) of the present invention shown in FIGS. 13 and 14, in addition to the system configuration of the embodiment (3), an exhaust gas temperature sensor as a downstream side catalyst active state determination means is provided downstream of the downstream side NOx catalyst 20. 35 is provided. Other system configurations are the same as those in the embodiment (3).
[0065]
In the present embodiment (4), the ECU 22 controls the exhaust passage switching valve 34 as follows based on the output signals of the two upstream and downstream exhaust temperature sensors 21 and 35.
[0066]
(1) The control method when the active state of the upstream NOx catalyst 19 is lower than the predetermined range (A in FIG. 2) is as follows.
In this case, unreacted HC in the upstream NOx catalyst 19 passes through the upstream NOx catalyst 19. At that time, if the active state of the downstream NOx catalyst 20 is within a predetermined range (B in FIG. 2) and a high NOx purification rate can be obtained with the downstream NOx catalyst 20, the exhaust flows through the main exhaust passage 31, HC is directly supplied to the downstream NOx catalyst 20 to purify NOx. On the other hand, when the activation state of the downstream NOx catalyst 20 is not within the predetermined range (A and C in FIG. 2) and the high NOx purification rate cannot be obtained with the downstream NOx catalyst 20, the downstream NOx catalyst 20 performs HC. Therefore, exhaust gas is allowed to flow through the bypass exhaust passage 32 and HC is adsorbed by the HC adsorbent 33.
[0067]
(2) The control method when the activation state of the upstream NOx catalyst 19 is within the predetermined range (B in FIG. 2) is as follows.
In this case, since most of the supplied HC reacts with the upstream NOx catalyst 19, even if the activation state of the downstream NOx catalyst 20 is within a predetermined range (B in FIG. 2), the downstream NOx catalyst 20 HC is insufficient and the NOx purification rate decreases. Therefore, in this case, the exhaust gas is caused to flow through the bypass exhaust passage 32. As a result, the relatively high temperature exhaust gas passes through the HC adsorbent 33, so that the HC that has been adsorbed by the HC adsorbent 33 so far is desorbed and supplied to the downstream NOx catalyst 20. For this reason, a sufficient amount of HC is also supplied to the downstream NOx catalyst 20 to purify NOx. On the other hand, if the downstream NOx catalyst 20 is not within the predetermined range (A and C in FIG. 2) and the downstream NOx catalyst 20 cannot obtain a high NOx purification rate, the downstream NOx catalyst 20 Since HC cannot be used effectively, the exhaust is allowed to flow through the main exhaust passage 31 to prevent HC from being desorbed from the HC adsorbent 33 in the bypass exhaust passage 32.
[0068]
(3) The control method when the active state of the upstream NOx catalyst 19 is higher than the predetermined range (C in FIG. 2) is as follows.
In this case, since almost all of the supplied HC reacts with the upstream NOx catalyst 19, the active state of the downstream NOx catalyst 20 is the same as when the upstream NOx catalyst 19 is within the predetermined range. The exhaust passage is switched depending on whether it is within a predetermined range.
[0069]
The NOx purification control described above is executed by the ECU 22 at predetermined time intervals (for example, every second) according to the exhaust passage switching control program of FIG. When this program is started, first, in step 301, the upstream side catalyst temperature Ta (active state of the upstream side NOx catalyst 19) detected by the two exhaust temperature sensors 21 and 35 and the downstream side catalyst temperature Tb (downstream side NOx). The active state of the catalyst 20) is read. Thereafter, in step 302, it is determined whether or not the upstream catalyst temperature Ta is included in the region A.
[0070]
When the upstream catalyst temperature Ta is included in the region A (that is, when the activation state of the upstream NOx catalyst 19 is low), the process proceeds to step 303 to determine whether or not the downstream catalyst temperature Tb is included in the region B. To do. When the downstream catalyst temperature Tb is included in the region B, the active state of the downstream NOx catalyst 20 is within a predetermined range, and the NOx purification rate of the downstream NOx catalyst 20 is high. The passage switching valve 34 is switched to allow the exhaust to flow toward the main exhaust passage 31, and HC that has passed through the upstream NOx catalyst 19 without being reacted is supplied to the downstream NOx catalyst 20.
[0071]
On the other hand, if it is determined in step 303 that the downstream catalyst temperature Tb is not included in the region B, the activation state of the downstream NOx catalyst 20 is not within the predetermined range, and the NOx purification rate of the downstream NOx catalyst 20 is Therefore, from the viewpoint of effective use of HC, the process proceeds to Step 305, where the exhaust passage switching valve 34 is switched to flow exhaust to the bypass exhaust passage 32 side, and the HC that has passed through the upstream side NOx catalyst 19 is adsorbed by HC. Adsorbed to the material 33.
[0072]
If it is determined in step 302 described above that the upstream catalyst temperature Ta is not included in the region A, the upstream NOx catalyst 19 is activated, so that the HC passing through the upstream NOx catalyst 19 is relatively Few. In this case, the process proceeds to step 304 to determine whether or not the downstream catalyst temperature Tb is included in the region B. If included in the region B, the activation state of the downstream NOx catalyst 20 is within a predetermined range. Yes, since the NOx purification rate of the downstream side NOx catalyst 20 is high, the routine proceeds to step 305, where the exhaust passage switching valve 34 is switched so that the exhaust flows to the bypass exhaust passage 32 side. As a result, high-temperature exhaust gas is caused to flow toward the bypass exhaust passage 32 to raise the temperature of the HC adsorbent 33, thereby desorbing the HC that has been adsorbed by the HC adsorbent 33 so far and downstream NOx. The catalyst is supplied to the catalyst 20 and the downstream NOx catalyst 20 purifies NOx.
[0073]
On the other hand, when it is determined in step 304 that the downstream catalyst temperature Tb is not included in the region B, the activation state of the downstream NOx catalyst 20 is not within the predetermined range, and the NOx purification rate of the downstream NOx catalyst 20 is Since it is not so high, from the viewpoint of effective use of HC, the process proceeds to step 306, where the exhaust passage switching valve 34 is switched to flow the exhaust to the main exhaust passage 31 side, and HC desorption from the HC adsorbent 33 is stopped. .
[0074]
In the embodiment (4) described above, in addition to the upstream catalyst temperature Ta (the active state of the upstream NOx catalyst 19), the downstream catalyst temperature Tb (the active state of the downstream NOx catalyst 20) is also detected. Since the exhaust passage is switched according to the result, the exhaust passage is switched more appropriately than in the case of switching the exhaust passage based only on the upstream side catalyst temperature as in the embodiment (3). This can further reduce the fuel consumption and increase the NOx purification rate.
[0075]
In this embodiment (4) as well, as a reducing agent supply means for supplying a reducing agent (HC) to the NOx catalyst, an HC supply nozzle may be connected upstream of the upstream NOx catalyst instead of post-injection. Alternatively, three or more NOx catalysts may be provided in series in the exhaust pipe.
[0076]
[Embodiment (5)]
In the embodiment (5) of the present invention shown in FIGS. 15 to 17, when the exhaust flow is switched from the main exhaust passage 31 to the bypass exhaust passage 32 in the same system configuration as the embodiment (3) shown in FIG. The operation of alternately switching the exhaust passage switching valve 34 between the bypass exhaust passage 32 side and the main exhaust passage 31 side is repeated for a predetermined time or a predetermined number of times. Other configurations are the same as those in FIG.
[0077]
That is, when the time for flowing the exhaust gas to the main exhaust passage 31 becomes longer, the temperature of the HC adsorbent 33 in the bypass exhaust passage 32 decreases due to heat dissipation. In this state, if the flow of exhaust gas is suddenly switched from the main exhaust passage 31 to the bypass exhaust passage 32 side, the exhaust gas passes through the cooled HC adsorbent 33, so that the exhaust temperature decreases. For this reason, the temperature of the downstream NOx catalyst 20 may decrease, and the NOx purification rate may decrease.
[0078]
In the present embodiment (5), in order to prevent this, when switching the exhaust flow from the main exhaust passage 31 to the bypass exhaust passage 32, the exhaust passage switching valve 34 is connected to the bypass exhaust passage 32 side and the main exhaust passage 31 side. By repeating the operation of alternately switching to a predetermined time or a predetermined number of times, a rapid temperature drop of the downstream side NOx catalyst 20 is prevented. Further, at the time of switching the exhaust passage, the switching frequency f of the exhaust passage switching valve 34 is increased as the change rate of the active state (upstream catalyst temperature) of the upstream NOx catalyst 19 is smaller.
[0079]
That is, when the exhaust gas temperature changes more gradually and the change in the active state of the upstream NOx catalyst 19 is smaller, the exhaust flow suddenly switches from the main exhaust passage 31 to the bypass exhaust passage 32 and flows into the downstream NOx catalyst 20. The reduction in the NOx purification rate due to the temperature drop of the exhaust gas is likely to increase. As a countermeasure, when the switching frequency f of the exhaust passage switching valve 34 is increased, the time interval for supplying low-temperature exhaust gas from the bypass exhaust passage 32 side to the downstream NOx catalyst 20 is shortened, and the temperature change of the downstream NOx catalyst 20 is reduced. Therefore, it is possible to prevent a reduction in the NOx purification rate due to a decrease in exhaust gas temperature.
[0080]
The NOx purification control described above is executed by the ECU 22 at predetermined time intervals (for example, every second) according to the exhaust passage switching control program of FIG. When this program is started, first, in step 401, the upstream catalyst temperature T (active state of the upstream NOx catalyst 19) detected by the exhaust temperature sensor 21 is read. In the next step 402, this upstream catalyst temperature is read. It is determined whether the active state region including T corresponds to any of A, B, and C in FIG.
[0081]
If the region determined in step 402 is A or C, the process proceeds to step 403, where the change rate of the upstream catalyst temperature T is calculated by subtracting the current temperature T from the previous temperature T, for example. Based on the change rate of the upstream catalyst temperature T, the switching frequency f of the exhaust passage switching valve 34 is calculated from a map. As shown in FIG. 16, the map of the switching frequency f is determined by using the change rate of the upstream catalyst temperature T as a parameter, and is set so that the change frequency f increases as the change rate of the upstream catalyst temperature T decreases. ing.
[0082]
After calculating the switching frequency f, the process proceeds to step 404, and when the exhaust flow is switched from the main exhaust passage 31 to the bypass exhaust passage 32, the exhaust passage switching valve 34 is set to the bypass exhaust passage 32 side and the main exhaust passage 31 at the switching frequency f. The operation of switching alternately to the side is repeated for a predetermined time or a predetermined number of times. On the other hand, if the region determined in step 402 is B, the process proceeds to step 405, and the exhaust passage switching valve 34 is switched to allow the exhaust to flow to the main exhaust passage 31 side.
[0083]
In the exhaust passage switching control described above, for example, as shown in FIG. 17, when the active state (upstream catalyst temperature) of the upstream NOx catalyst 19 changes in the order of A → B → C, the region of A → B is The same control as in the embodiment (3) is performed. Thereafter, at time X when the activation state of the upstream NOx catalyst 19 changes from B to C, the exhaust passage is switched from the main exhaust passage 31 side to the bypass exhaust passage 32 side. Since the exhaust gas passes through the HC adsorbent 33 cooled by the heat release, the exhaust gas temperature decreases, so that the temperature of the downstream NOx catalyst 20 decreases and the NOx purification rate decreases.
[0084]
On the other hand, in the present embodiment (5), when switching the exhaust passage from the main exhaust passage 31 side to the bypass exhaust passage 32 side, the exhaust passage switching valve 34 is switched at the switching frequency f, thereby intermittently discharging the high-temperature exhaust. Therefore, the downstream NOx catalyst 20 can be supplied from the main exhaust passage 31 side to the downstream NOx catalyst 20, and a rapid temperature drop of the downstream NOx catalyst 20 can be prevented. A purification rate can be obtained.
[0085]
In the present embodiment (5), the switching frequency is changed in accordance with the changing speed of the active state (upstream catalyst temperature) of the upstream NOx catalyst 19, but the switching frequency is constant and the time ratio (duty ratio) of the switching interval is changed. Of course, both the switching frequency and the time ratio of the switching interval may be changed. In this case, the time ratio of the switching interval may be changed so that the ratio of the exhaust flowing through the main exhaust passage 31 increases as the change rate of the activation state of the upstream NOx catalyst 19 decreases.
[0086]
Alternatively, at the time of switching the exhaust passage, instead of switching the exhaust passage switching valve 34 at the switching frequency f, the exhaust passage switching valve 34 is held at an intermediate position, and the opening degree thereof depends on the active state of the upstream NOx catalyst 19. Even if the control is performed, the same effect can be obtained.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an entire engine control system showing an embodiment (1) of the present invention.
FIG. 2 is a graph showing the relationship between catalyst temperature and purification rate
FIG. 3 is a graph showing the relationship between post-injection timing, cylinder internal temperature, and HC reforming degree.
FIG. 4 is a time chart showing the relationship between pilot injection, main injection, and post-injection.
FIG. 5 is a flowchart showing a process flow of a post-injection timing control program.
FIG. 6 is a graph showing the relationship between upstream catalyst temperature T and post-injection timing.
FIG. 7 is a graph showing the distribution of the HC amount and NOx amount in the exhaust when the upstream catalyst temperature T> the set temperature T1.
FIG. 8 is a graph showing the distribution of the HC amount and NOx amount in the exhaust when the upstream catalyst temperature T ≦ the set temperature T1.
FIG. 9 is a block diagram of the entire engine control system showing the embodiment (2) of the present invention.
FIG. 10 is a configuration diagram of the entire engine control system showing the embodiment (3) of the present invention.
FIG. 11 is a flowchart showing a processing flow of an exhaust passage switching control program according to the embodiment (3) of the present invention.
FIG. 12 is a time chart showing the behavior of the exhaust passage switching control according to the embodiment (3) of the present invention.
FIG. 13 is a block diagram of the entire engine control system showing the embodiment (4) of the present invention.
FIG. 14 is a flowchart showing the flow of processing of an exhaust passage switching control program according to the embodiment (4) of the present invention.
FIG. 15 is a flowchart showing a processing flow of an exhaust passage switching control program according to the embodiment (5) of the present invention.
FIG. 16 is a diagram conceptually showing a map of the switching frequency of the exhaust passage switching valve using the change rate of the upstream catalyst temperature as a parameter.
FIG. 17 is a time chart showing the behavior of the exhaust passage switching control according to the embodiment (5) of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Diesel engine (internal combustion engine), 11 ... Intake pipe, 14 ... Fuel injection valve (fuel injection means, reducing agent supply means), 15 ... High-pressure fuel pump, 18 ... Exhaust pipe (exhaust passage), 19 ... Upstream NOx Catalyst (catalyst), 20 ... downstream side NOx catalyst (catalyst), 21 ... exhaust gas temperature sensor (upstream side catalyst active state determination means), 22 ... ECU (fuel injection control means, post-injection timing correction means, control means), 23 ... engine speed sensor, 31 ... main exhaust passage, 32 ... bypass exhaust passage, 33 ... HC adsorbent, 34 ... exhaust passage switching valve (exhaust passage switching means), 35 ... exhaust temperature sensor (downstream catalyst active state judging means) ), 40 ... HC adsorbent (HC adsorbing means).

Claims (7)

A fuel injection means is provided for each cylinder of the internal combustion engine, and a plurality of catalysts for reducing and purifying nitrogen oxides in the exhaust gas are installed in series in the exhaust passage of the internal combustion engine. A main injection command for generating engine output in the vicinity of the compression top dead center and a post-injection command for supplying hydrocarbons to the catalyst in the expansion stroke or exhaust stroke of the engine to the fuel injection means of at least one cylinder In an exhaust gas purification apparatus for an internal combustion engine provided with a fuel injection control means for outputting
An upstream catalyst active state determining means for determining an active state of a catalyst (hereinafter referred to as “upstream catalyst”) disposed upstream of the most downstream catalyst among the plurality of catalysts;
The fuel injection control means includes post-injection timing correction means for correcting a post-injection timing in the post-injection command in accordance with the active state of the upstream catalyst determined by the upstream catalyst active state determination means. An exhaust purification device for an internal combustion engine.   The post-injection timing correction means corrects the advance of the post-injection timing as the upstream catalyst activation state determined by the upstream catalyst activation state determination means is low, and the upstream catalyst activation state is high. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the post-injection timing is corrected for delay. A plurality of catalysts arranged in series in the exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in the exhaust; and
Reducing agent supply means for supplying a nitrogen oxide reducing agent to the catalyst;
A main exhaust passage and a bypass exhaust passage formed in parallel between the plurality of catalysts;
A hydrocarbon adsorbent that is provided in the bypass exhaust passage, adsorbs hydrocarbons in exhaust at low temperatures, and desorbs hydrocarbons adsorbed at high temperatures;
Exhaust passage switching means for selectively switching the flow of exhaust to either the main exhaust passage or the bypass exhaust passage;
Upstream side catalyst active state determining means for determining an active state of a catalyst (hereinafter referred to as “upstream side catalyst”) disposed upstream of a parallel passage of the main exhaust passage and the bypass exhaust passage;
Whether the active state of the catalyst (hereinafter referred to as “downstream catalyst”) disposed downstream of the downstream side joining portion between the main exhaust passage and the bypass exhaust passage is within a predetermined range in which the nitrogen oxide purification rate is high. Downstream catalytic activity state determining means for determining whether or not,
Control for controlling the switching position of the exhaust passage switching means based on the active state of the upstream catalyst and the active state of the downstream catalyst determined by the upstream catalyst active state determining means and the downstream catalyst active state determining means and means,
The control means includes
When it is determined that the activation state of the upstream catalyst is lower than a predetermined range in which the nitrogen oxide purification rate is high and the activation state of the downstream catalyst is out of the predetermined range, exhaust gas is allowed to flow through the bypass exhaust passage. Switching the exhaust passage switching means,
The exhaust passage switching means is configured to cause the exhaust to flow into the main exhaust passage when it is determined that the active state of the upstream catalyst is lower than the predetermined range and the active state of the downstream catalyst is within the predetermined range. Switch
When it is determined that the active state of the upstream catalyst is within or higher than the predetermined range and the active state of the downstream catalyst is out of the predetermined range, the exhaust is caused to flow through the main exhaust passage. Switch the exhaust passage switching means,
The exhaust gas is caused to flow through the bypass exhaust passage when it is determined that the active state of the upstream catalyst is within or higher than the predetermined range and the active state of the downstream catalyst is within the predetermined range. An exhaust emission control device for an internal combustion engine, wherein the passage switching means is switched . A plurality of catalysts arranged in series in the exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in the exhaust; and
Reducing agent supply means for supplying a nitrogen oxide reducing agent to the catalyst;
A main exhaust passage and a bypass exhaust passage formed in parallel between the plurality of catalysts;
A hydrocarbon adsorbent that is provided in the bypass exhaust passage, adsorbs hydrocarbons in exhaust at low temperatures, and desorbs hydrocarbons adsorbed at high temperatures;
Exhaust passage switching means for selectively switching the flow of exhaust to either the main exhaust passage or the bypass exhaust passage;
Upstream side catalyst active state determining means for determining an active state of a catalyst (hereinafter referred to as “upstream side catalyst”) disposed upstream of a parallel passage of the main exhaust passage and the bypass exhaust passage;
Control means for controlling the switching position of the exhaust passage switching means based on the active state of the upstream catalyst determined by the upstream catalyst active state determination means;
With
The control means switches the exhaust passage switching means alternately between the bypass exhaust passage side and the main exhaust passage side for a while when the exhaust flow is switched from the main exhaust passage to the bypass exhaust passage. exhaust gas purification apparatus for an internal combustion engine you and repeating the operation. The upstream side catalyst active state determining means determines whether the active state of the upstream side catalyst is within a predetermined range with a high nitrogen oxide purification rate,
The control means switches the exhaust passage switching means so that the exhaust flows into the main exhaust passage when it is determined that the active state of the upstream catalyst is within the predetermined range, and the active state of the upstream catalyst is 5. The exhaust emission control device for an internal combustion engine according to claim 4 , wherein the exhaust passage switching means is switched so that the exhaust flows through the bypass exhaust passage when it is determined that the exhaust gas is out of the predetermined range. Means for determining the change rate of the activation state of the upstream catalyst determined by the upstream catalyst activation state determination unit;
The control means, when switching the flow of exhaust from the main exhaust passage to the bypass exhaust passage, the ratio of the switching frequency of the exhaust passage switching means and the time ratio of the switching interval according to the change rate of the active state of the upstream catalyst 6. The exhaust gas purification apparatus for an internal combustion engine according to claim 3 , wherein at least one of them is changed. A fuel injection means is provided for each cylinder of the internal combustion engine, and a plurality of catalysts for reducing and purifying nitrogen oxides in the exhaust gas are installed in series in the exhaust passage of the internal combustion engine. A main injection command for generating engine output in the vicinity of the compression top dead center and a post-injection command for supplying hydrocarbons to the catalyst in the expansion stroke or exhaust stroke of the engine to the fuel injection means of at least one cylinder And an upstream catalyst active state determination for determining an active state of a catalyst (hereinafter referred to as an “upstream catalyst”) installed upstream of the most downstream catalyst among the plurality of catalysts. An exhaust gas purification apparatus for an internal combustion engine comprising means ,
The plurality of catalysts each have hydrocarbon adsorption means for adsorbing hydrocarbons in exhaust at low temperatures and desorbing hydrocarbons adsorbed at high temperatures, and the plurality of hydrocarbon adsorption means have hydrocarbon adsorption capacity. It is configured so that the downstream one is larger than the upstream one ,
The fuel injection control means outputs a post-injection command only for a predetermined period when the upstream catalyst active state determined by the upstream catalyst active state determination means is lower than a predetermined range in which the nitrogen oxide purification rate is high. exhaust gas purification apparatus for an internal combustion engine you characterized by.

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