JP2010265802A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine, accurately calculating a capture amount of SOx at a downstream part of a NOx catalyst during sulfur purging operation even when the NOx catalyst comprises upstream and downstream NOx catalysts separated from each other or even when capacity of the NOx catalyst is large. <P>SOLUTION: The exhaust emission control device of the internal combustion engine includes the upstream NOx catalyst 7 and the downstream NOx catalyst 8 separated from each other, and the sulfur purging operation is performed for desorbing SOx captured in the NOx catalysts 7, 8 (S4). An upstream part SOx desorption amount dQDeSOx1 is calculated (S26 in Fig.4, Fig.5), which is the desorption amount of SOx from the upstream NOx catalyst 7 during the sulfur purging operation, and based on the upstream part SOx desorption amount dQDeSOx1, a capture amount of SOx captured in the downstream NOx catalyst 8 is calculated as a downstream part SOx capture amount QSOx2 (S12 in Fig.3 (not shown), Fig.6). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine having a NOx catalyst for purifying exhaust gas, and more particularly to an exhaust gas purification apparatus that performs a sulfur purge operation for desorbing SOx trapped by the NOx catalyst.

  As a conventional exhaust gas purifying apparatus for this type of internal combustion engine, for example, one disclosed in Patent Document 1 is known. In this exhaust gas purification device, NOx in the exhaust gas discharged is captured by the NOx catalyst during normal lean operation. In addition, a rich operation for controlling the air-fuel ratio of the exhaust gas to the rich side is temporarily performed by adding fuel from a fuel addition valve provided in the exhaust passage, so that the NOx trapped by the NOx catalyst is reduced. While desorbing in the reduced state, the NOx trapping performance of the NOx catalyst is recovered.

  Further, in this exhaust gas purifying apparatus, sulfur purge operation for desorbing SOx (sulfur component) trapped by the NOx catalyst is performed, and as a result, it is reduced due to adhesion of SOx in fuel and engine oil. The NOx trapping performance of the NOx catalyst is restored. This sulfur purge operation increases the temperature of the exhaust gas by controlling the fuel injection timing to the retard side, and alternately controls the air-fuel ratio of the exhaust gas flowing into the NOx catalyst to the rich side and the lean side, Done. The end timing of the sulfur purge operation is determined based on the relationship between the execution time and a predetermined reference time set based on an experiment or the like.

JP 2005-139971 A

  When performing the sulfur purge operation as described above, it is very important to end the sulfur purge operation at an appropriate timing when the desorption of SOx from the NOx catalyst is completed. This is because the rich operation is performed during the sulfur purge operation. If the end timing is too late, fuel is wasted, causing fuel consumption deterioration and oil dilution, and raising the temperature of the NOx catalyst. This is because the long time promotes the thermal deterioration of the NOx catalyst. On the other hand, if the sulfur purge operation is terminated too early, a relatively large amount of SOx remains in the NOx catalyst, so that the NOx trapping performance of the NOx catalyst is not sufficiently recovered, and the exhaust gas characteristics are deteriorated. On the other hand, in the conventional exhaust gas purifying apparatus described above, the end timing of the sulfur purge operation is merely determined based on the relationship between the execution time of the sulfur purge operation and a predetermined reference time. I can't.

  In addition, as another conventional apparatus that executes the sulfur purge operation, the SOx inflow amount that flows into the NOx catalyst is calculated according to the operating state of the internal combustion engine, and the SOx removal that desorbs from the NOx catalyst during the sulfur purge operation is calculated. The separation amount is calculated according to the amount of reducing agent supplied to the NOx catalyst, and the SOx trapping amount of the NOx catalyst calculated by integrating the difference between the SOx inflow amount and the SOx desorption amount is a predetermined amount. It is also known that the sulfur purge operation is terminated when the value falls below the threshold value.

  In this conventional apparatus, it is assumed that the inflow and desorption of SOx are uniformly performed over the entire NOx catalyst. However, this assumption does not hold because the following phenomenon occurs particularly when the NOx catalyst is composed of an upstream NOx catalyst and a downstream NOx catalyst separated from each other. First, at the initial stage of the sulfur purge operation, a phenomenon occurs in which SOx desorbed from the upstream NOx catalyst is captured again by the downstream NOx catalyst. In the conventional apparatus, since such a phenomenon is not taken into consideration, the SOx inflow amount to the downstream NOx catalyst is easily calculated to be smaller than the actual amount.

  Second, during the sulfur purge operation, the downstream NOx catalyst has a phenomenon in which the desorption of SOx is delayed as compared with the upstream NOx catalyst. This is because the reducing agent in the exhaust gas is first consumed to desorb SOx in the upstream NOx catalyst, so that it takes time to supply sufficient reducing agent to the downstream NOx, and the downstream NOx This is because it takes time for the state of the catalyst, for example, the catalyst temperature or the like to be suitable for SOx desorption. As a result, as shown in FIG. 9, in the upstream NOx catalyst, the SOx desorption amount reaches a peak immediately after the start of the sulfur purge operation, whereas in the downstream NOx catalyst, the SOx desorption amount is delayed later. Reach the peak. In the conventional apparatus, since such a phenomenon is not taken into account, the SOx desorption amount of the downstream side NOx catalyst is easily calculated to be larger than the actual amount.

  As described above, in the conventional apparatus, during the sulfur purge operation, the SOx inflow amount of the downstream NOx catalyst is calculated to be small and the SOx desorption amount is calculated to be large. As a result, the SOx trapping amount of the downstream NOx catalyst is excessively small. It will be evaluated. For this reason, there is a tendency to end the sulfur purge operation early, and the above-described problem occurs when the end timing is too early. In addition, even when there is a single NOx catalyst, such a problem occurs when the capacity or the length of the exhaust passage is large, and the above phenomenon occurs between the upstream portion and the downstream portion of the NOx catalyst. Can occur as well.

  The present invention has been made to solve such a problem. In the case where the NOx catalyst is composed of the upstream and downstream NOx catalysts separated from each other, or in the case where the capacity of the NOx catalyst is large, etc. Another object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can accurately calculate the amount of SOx trapped in the downstream portion of the NOx catalyst during sulfur purge operation.

  In order to achieve this object, an exhaust gas purifying apparatus for an internal combustion engine according to the invention of claim 1 is provided in an exhaust passage (exhaust pipe 5 in the embodiment (hereinafter, the same in this section)) of the internal combustion engine, (Upstream side NOx catalyst 7, upstream part 27a of NOx catalyst 27) and downstream part (downstream side NOx catalyst 8, downstream part 27b of NOx catalyst 27) and capture NOx and SOx according to the oxygen concentration of exhaust gas or A desulfurized NOx catalyst and a sulfur purge control means (ECU2, step of FIG. 2) for performing a sulfur purge operation for desorbing SOx trapped by the NOx catalyst by supplying exhaust gas in a reducing atmosphere to the NOx catalyst 4) and SOx desorption for calculating the SOx desorption amount from the upstream portion of the NOx catalyst during the sulfur purge operation (upstream SOx desorption amount dQDeSOx1). Based on the amount calculation means (ECU 2, step 26 in FIG. 4, FIG. 5) and the calculated SOx desorption amount, the trapped amount of SOx trapped in the downstream portion of the NOx catalyst is set as the downstream portion SOx trap amount QSOx2. And a downstream SOx trapping amount calculating means (ECU 2, step 12 in FIG. 3, FIG. 6) for calculating.

  According to the exhaust gas purification apparatus for an internal combustion engine, the NOx catalyst has an upstream portion and a downstream portion, and a sulfur purge operation is performed to desorb SOx trapped by the NOx catalyst. As described above, when the NOx catalyst is separated and disposed, SOx desorbed from the upstream part of the NOx catalyst is trapped again in the downstream part at the initial stage of the sulfur purge operation. To do.

  According to the present invention, the amount of SOx desorbed from the upstream portion of the NOx catalyst during the sulfur purge operation is calculated and trapped in the downstream portion of the NOx catalyst based on the calculated amount of SOx desorbed. The downstream SOx trapping amount is calculated. Therefore, when the NOx catalyst is composed of upstream and downstream NOx catalysts separated from each other, or when the capacity of the NOx catalyst is large, SOx desorbed from the upstream part of the NOx catalyst is captured by the downstream part. Even when the phenomenon occurs, the downstream SOx trapping amount can be accurately calculated while reflecting this phenomenon.

  The invention according to claim 2 is the exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the state of the downstream portion of the NOx catalyst (the downstream portion SOx trapping amount QSOx2, the downstream catalyst temperature TCAT2, the degree of deterioration of the downstream NOx catalyst). Further includes catalyst state acquisition means (ECU2, FIG. 6, downstream catalyst temperature sensor 16, second and third air-fuel ratio sensors 13, 14) for acquiring DCATD2), and the downstream SOx trapping amount calculation means is acquired. The downstream portion SOx trapping amount QSOx2 is calculated according to the state of the downstream portion of the NOx catalyst.

  The degree to which the SOx desorbed from the upstream part of the NOx catalyst is captured by the downstream part and the degree to which the SOx is desorbed from the downstream part of the NOx catalyst are determined by the state of this downstream part, for example, the amount of SOx trapped in the downstream part, Changes according to temperature and degree of deterioration. According to said structure, while acquiring the state of the downstream part of a NOx catalyst, the downstream part SOx trapping amount is calculated according to the acquired state of the downstream part. Accordingly, the downstream SOx trapping amount can be calculated with higher accuracy while reflecting the SOx trapping degree and desorption degree in the downstream part according to the actual state of the downstream part.

  According to a third aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, the NOx catalyst is arranged in a state separated from each other along the exhaust passage, and the upstream side NOx catalyst 7 and the downstream side NOx catalyst 8. The upstream portion of the NOx catalyst is the upstream NOx catalyst 7, and the downstream portion of the NOx catalyst is the downstream NOx catalyst 8.

  According to this configuration, the NOx catalyst includes an upstream NOx catalyst and a downstream NOx catalyst separated from each other, the upstream NOx catalyst as an upstream portion of the NOx catalyst, and the downstream NOx catalyst as a downstream portion of the NOx catalyst, The invention according to claim 1 is applied. Therefore, the above-described operation of the invention according to claim 1 can be similarly obtained in the relationship between the upstream NOx catalyst and the downstream NOx catalyst. In this case, in particular, since the distance between the upstream portion and the downstream portion of the NOx catalyst is larger than that in the case of a single NOx catalyst, the state of the catalyst between the upstream portion and the downstream portion Since the state of the supplied exhaust gas is likely to vary greatly, the action according to the invention of claim 1 can be obtained very effectively.

  According to a fourth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, the upstream portion SOx trapping that calculates the SOx trapping amount trapped in the upstream portion of the NOx catalyst as the upstream portion SOx trapping amount QSOx1. Sulfur that determines the end timing of the sulfur purge operation based on the sum of the amount calculation means (ECU 2, step 11 in FIG. 3, FIG. 4) and the calculated upstream SOx trapping amount QSOx1 and downstream SOx trapping amount QSOx2. And purge end determining means (ECU 2, step 13 in FIG. 3, steps 5 and 6 in FIG. 2).

  According to this configuration, the SOx trapping amount trapped in the upstream portion of the NOx catalyst is calculated as the upstream portion SOx trapping amount, and based on the sum of the upstream portion SOx trapping amount and the downstream portion SOx trapping amount, Determine the end timing of the purge operation. Therefore, the sulfur purge operation can be terminated at an optimal timing based on the total SOx trapping amount of the upstream portion and the downstream portion of the NOx catalyst. In particular, unlike the prior art, the sulfur purge operation can be terminated at a timing when the SOx is sufficiently desorbed without underestimating the amount of SOx trapped in the downstream portion of the NOx catalyst during the sulfur purge operation. As a result, a large amount of SOx does not remain in the downstream portion of the NOx catalyst at the end of the sulfur purge operation, thereby reliably recovering NOx trapping performance as a whole NOx catalyst and maintaining good exhaust gas characteristics. Can do.

1 is a diagram schematically showing an exhaust gas purification apparatus according to a first embodiment of the present invention together with an internal combustion engine. It is a flowchart which shows the main flow of a sulfur purge control process. It is a flowchart which shows the calculation subroutine of the SOx trapping amount of the whole NOx catalyst. It is a flowchart which shows the calculation subroutine of the SOx trapping amount of an upstream NOx catalyst. It is a flowchart which shows the calculation subroutine of the SOx desorption amount from an upstream NOx catalyst. It is a flowchart which shows the calculation subroutine of the SOx trapping amount of a downstream NOx catalyst. It is a flowchart which shows the calculation subroutine of the SOx desorption amount from a downstream NOx catalyst. It is a figure which shows roughly the exhaust gas purification apparatus by 2nd Embodiment of this invention with an internal combustion engine. It is a figure which shows the desorption state of SOx in the upstream NOx catalyst and the downstream NOx catalyst during sulfur purge operation.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an exhaust gas purification apparatus 1 according to a first embodiment together with an internal combustion engine 3. The internal combustion engine (hereinafter referred to as “engine”) 3 is, for example, a four-cylinder diesel engine mounted on a vehicle (not shown).

  An intake pipe 4 and an exhaust pipe 5 are connected to each cylinder 3a of the engine 3 and a fuel injection valve (hereinafter referred to as “injector”) 6 is attached so as to face the combustion chamber 3b. The injector 6 is disposed on the top wall of the combustion chamber 3b and injects fuel supplied from a fuel tank (not shown) into the combustion chamber 3b. The fuel injection amount QINJ injected from the injector 6 is set by the ECU 2 described later, and is controlled by changing the valve opening time of the injector 6 by a control signal from the ECU 2.

  A crank angle sensor 10 is provided on the crankshaft 3 c of the engine 3. The crank angle sensor 10 includes a magnet rotor and an MRE pickup, and outputs a CRK signal and a TDC signal, which are pulse signals, to the ECU 2 as the crankshaft 3c rotates.

  The CRK signal is output every predetermined crank angle (for example, 30 °). The ECU 2 calculates the engine speed (hereinafter referred to as “engine speed”) NE of the engine 3 based on the CRK signal. The TDC signal is a signal indicating that the piston 3b in each cylinder 3a is at a predetermined crank angle position slightly ahead of the TDC position at the start of the intake stroke, and the engine 3 is 4 as in the present embodiment. In the case of a cylinder, it is output every 180 ° crank angle.

  An air flow sensor 11 is provided in the intake pipe 4. The air flow sensor 11 detects an intake air amount GAIR sucked into the cylinder 3 a via the intake pipe 4 and outputs a detection signal to the ECU 2.

  The exhaust pipe 5 is provided with an upstream NOx catalyst 7 and a downstream NOx catalyst 8 separated from each other. These NOx catalysts 7 and 8 have an oxygen storage capacity for capturing NOx in the exhaust gas and storing oxygen in the exhaust gas when the exhaust gas in the oxidizing atmosphere flows in. The NOx catalysts 7 and 8 reduce and purify NOx by releasing stored oxygen and reducing NOx in a reduced state when exhaust gas in a reducing atmosphere flows.

  The exhaust pipe 5 includes first to third air-fuel ratio sensors 12 to 14 on the upstream side of the upstream NOx catalyst 7, between the NOx catalysts 7 and 8, and on the downstream side of the downstream NOx catalyst 8, respectively. Is provided. These air-fuel ratio sensors 12 to 14 are composed of zirconia or the like, and linearly detect the oxygen concentration of the exhaust gas in a wide range of the air-fuel ratio of the air-fuel mixture supplied to the engine 3 from the rich region to the lean region. To do. These detection signals are output to the ECU 2.

  Based on the detection signals of the first to third air-fuel ratio sensors 12 to 14, the ECU 2 sets the air-fuel ratios of the exhaust gases at the respective installation positions (hereinafter referred to as “first to third exhaust gas air-fuel ratios”) AFEX1 to AFEX3, respectively. calculate. Here, the “air-fuel ratio of exhaust gas” refers to the weight ratio of air and combustible gas in the exhaust gas. For this reason, the air-fuel ratio of the exhaust gas increases when the exhaust gas is in an oxidizing atmosphere and decreases when it is in a reducing atmosphere.

  The upstream NOx catalyst 7 and the downstream NOx catalyst 8 are provided with an upstream catalyst temperature sensor 15 and a downstream catalyst temperature sensor 16, respectively. The catalyst temperature sensors 15 and 16 respectively detect the temperature of the upstream NOx catalyst 7 (hereinafter referred to as “upstream catalyst temperature”) TCAT1 and the temperature of the downstream NOx catalyst 8 (hereinafter referred to as “downstream catalyst temperature”) TCAT2. The detected signals are output to the ECU 2.

  Further, the ECU 2 outputs a detection signal representing an operation amount (hereinafter referred to as “accelerator opening”) AP of an accelerator pedal (not shown) of a vehicle equipped with the engine 3 from the accelerator opening sensor 17.

  The ECU 2 is composed of a microcomputer (all not shown) including a CPU, a RAM, a ROM, an I / O interface, and the like. The detection signals from the various sensors 10 to 17 described above are input to the CPU after A / D conversion and shaping by the I / O interface. The ECU 2 determines the operating state of the engine 3 according to these detection signals according to a control program stored in the ROM, and executes various controls according to the determined operating state.

  This control includes engine control including control of the fuel injection amount QINJ of the injector 6 and NOx trapped by the upstream and downstream NOx catalysts 7, 8 to release NOx of these NOx catalysts 7, 8. Regeneration control for recovering capture performance, sulfur purge for recovering NOx capture performance of these NOx catalysts 7, 8 by desorbing SOx captured by the upstream and downstream NOx catalysts 7, 8 Control etc. are included.

  In the present embodiment, the ECU 2 serves as the sulfur purge control means, the SOx desorption amount calculation means, the downstream portion SOx trapping amount calculation means, the catalyst state acquisition means, the upstream portion SOx trapping amount calculation means, and the sulfur purge end determination means. Equivalent to.

  FIG. 2 shows a main flow of the above-described sulfur purge control process. This process is executed every predetermined time. In this process, first, in step 1 (illustrated as “S1”, the same applies hereinafter), the SOx trapping amount QSOx is calculated. This SOx trapping amount QSOx includes SOx trapping amount trapped by the upstream NOx catalyst 7 (hereinafter referred to as “upstream SOx trapping amount”) QSOx1 and SOx trapping amount trapped by the downstream NOx catalyst 8 (hereinafter “ This is the sum of QSOx2 (referred to as downstream SOx trapping amount), that is, the total SOx trapping amount of the NOx catalyst. The calculation process will be described later.

  Next, it is determined whether or not the sulfur purge flag F_SOxPRG is “1” (step 2). If the answer is NO and the sulfur purge operation is not being performed, it is determined whether or not the SOx trapping amount QSOx calculated in step 1 is greater than a predetermined threshold value QREFS for determining the start of the sulfur purge operation (step 3). ). If the answer is NO and QSOx ≦ QREFS, this processing is terminated as it is.

  On the other hand, if the answer to step 3 is YES and the SOx trapping amount QSOx exceeds the threshold value QREFS, the sulfur purge flag F_SOxPRG is set to “1” (step 4), and the sulfur purge operation is started. In this sulfur purge operation, post-injection in which fuel is injected from the injector 6 at the initial stage of the exhaust stroke of the engine 3 is performed so that unburned fuel is discharged to the exhaust pipe 5 as a reducing agent, and the exhaust gas is controlled to a reducing atmosphere. Is done by. By this sulfur purge operation, the reducing agent in the exhaust gas is supplied to the upstream NOx catalyst 7 and the downstream NOx catalyst 8 in a high temperature state, so that the SOx trapped in the upstream and downstream NOx catalysts 7 and 8 is trapped. Reduced and eliminated.

  On the other hand, if the answer to step 2 is YES and the sulfur purge operation is being performed, it is determined whether or not the SOx trapping amount QSOx is smaller than a predetermined threshold value QREFE for determining the end of the sulfur purge operation (step 5). ). If the answer is NO and QSOx ≧ QREFE, the present process is terminated as it is, and the sulfur purge operation is continued.

  On the other hand, if the answer to step 5 is YES and the SOx trapping amount QSOx falls below the threshold value QREFE, the sulfur purge flag F_SOxPRG is set to “0” (step 6) to end the sulfur purge operation. The process ends.

  FIG. 3 shows a subroutine for calculating the SOx trapping amount QSOx executed in step 1 of FIG. In this process, the upstream SOx trapping amount QSOx1 is calculated (step 11), and the downstream SOx trapping amount QSOx2 is calculated (step 12). These calculation processes will be described later. Next, the sum of the calculated upstream SOx trapping amount QSOx1 and the downstream SOx trapping amount QSOx2 is calculated as the SOx trapping amount QSOx of the entire NOx catalyst (step 13), and this process ends.

  FIG. 4 shows a subroutine for calculating the upstream SOx trapping amount QSOx1. In this process, first, in step 21, the SOx inflow amount (hereinafter referred to as “upstream SOx inflow amount”) dQSOxIN1 to the upstream NOx catalyst 7 corresponding to the current processing cycle is calculated. This calculation is performed by searching a predetermined map (not shown) according to parameters representing the operating state of the engine 3, such as the engine speed NE and the fuel injection amount QINJ.

  Next, in steps 22 to 25, the upstream SOx adsorption amount dQSOxAD1 is calculated. The upstream SOx adsorption amount dQSOxAD1 represents the amount of SOx trapped by the upstream NOx catalyst 7 out of the SOx flowing into the upstream NOx catalyst 7 in the current processing cycle.

  First, at step 22, the SOx trapping amount correction coefficient KAQSOx1 for calculating the adsorption amount is calculated by searching a predetermined table according to the upstream portion SOx trapping amount QSOx1. Although not shown, in this table, the SOx trapping amount correction coefficient KAQSOx1 is set to a smaller value because the larger the upstream SOx trapping amount QSOx1 is, the more difficult it is to trap SOx.

  In step 23, a catalyst temperature correction coefficient KACATT1 for calculating the adsorption amount is calculated by searching a predetermined table in accordance with the upstream catalyst temperature TCAT1. Although not shown, in this table, the catalyst temperature correction coefficient KACATT1 is set to a larger value because SOx is more easily captured as the upstream catalyst temperature TCAT1 is higher.

  In step 24, a catalyst deterioration correction coefficient KACATD1 for calculating an adsorption amount is calculated by searching a predetermined table in accordance with the deterioration degree DCATD1 of the upstream NOx catalyst 7. Although not shown, in this table, the catalyst deterioration correction coefficient KACATD1 is set to a smaller value because SOx is less likely to be captured as the deterioration degree DCATTD1 is higher. The deterioration degree DCATD1 of the upstream NOx catalyst 7 depends on the degree of delay of the second exhaust gas air-fuel ratio AFEX2 with respect to the first exhaust gas air-fuel ratio AFEX1 detected during the regeneration control of the upstream and downstream NOx catalysts 7, 8. This is calculated based on the oxygen storage capacity of the upstream NOx catalyst 7 determined in this way.

In step 25, the upstream portion SOx adsorption amount dQSOxAD1 is calculated by multiplying the upstream portion SOx inflow amount dQSOxIN1 calculated in step 21 by the three correction coefficients calculated in steps 22 to 24 by the following equation (1). .
dQS0xAD1
= DQS0xIN1 x KAQSOx1 x KAATT1 x KACATD1
... (1)

  In step 26 following step 25, the SOx desorption amount (hereinafter referred to as “upstream SOx desorption amount”) dQDeSOx1 corresponding to the current processing cycle is calculated. The calculation process will be described later. Next, the difference between the upstream SOx adsorption amount dQSOxAD1 and the upstream SOx desorption amount dQDeSOx1 calculated in steps 25 and 26 is calculated as the SOx trapping amount dQSOx1 corresponding to the current processing cycle (step 27). Then, the upstream SOx trapping amount QSOx1 is calculated by adding the calculated SOx trapping amount dQSOx1 to the upstream SOx trapping amount QSOx1 calculated up to the previous time (step 28), and this process ends.

  FIG. 5 shows a subroutine for calculating the upstream portion SOx desorption amount dQDeSOx1 executed in step S26. In this process, first, in step 31, it is determined whether or not the sulfur purge flag F_SOxPRG is “1”. If the answer is NO and the sulfur purge operation is not being performed, the upstream SOx desorption amount dQDeSOx1 is set to a value of 0 (step 32), and this process is terminated.

  If the answer to step 31 is YES and the sulfur purge operation is being performed, the basic value dQDBASE1 of the upstream SOx desorption amount is calculated (step 33). The basic value dQDBASE1 is calculated by searching a predetermined map (not shown) according to the engine speed NE and the required torque PMCMD. The requested torque PMCMD is calculated according to the engine speed NE and the accelerator pedal opening AP.

  Next, the SOx trapping amount correction coefficient KDQSOx1 for calculating the desorption amount is calculated by searching a predetermined table according to the upstream portion SOx trapping amount QSOx1 (step 34). Although not shown, in this table, the SOx trapping amount correction coefficient KDQSOx1 is set to a larger value because the higher the upstream portion SOx trapping amount QSOx1, the easier the SOx desorption reaction at the upstream side NOx catalyst 7 is performed. Has been.

  Next, a catalyst temperature correction coefficient KDATT1 for calculating the desorption amount is calculated by searching a predetermined table according to the upstream catalyst temperature TCAT1 (step 35). Although not shown, in this table, the catalyst temperature correction coefficient KDATT1 is set to a larger value because the higher the upstream catalyst temperature TCAT1, the easier the SOx desorption reaction at the NOx catalyst 7 is performed.

  Next, a catalyst deterioration correction coefficient KDCATD1 for calculating the desorption amount is calculated by searching a predetermined table in accordance with the deterioration degree DCATD1 of the upstream NOx catalyst 7 (step 36). Although not shown, in this table, the catalyst deterioration correction coefficient KDCATD1 is set to a smaller value because the higher the degree of deterioration DCATTD1, the more difficult the SOx desorption reaction is performed in the upstream NOx catalyst 7.

  Next, an air-fuel ratio correction coefficient KDAFEX1 for calculating a desorption amount is calculated by searching a predetermined table according to the first exhaust gas air-fuel ratio AFEX1 (step 37). Although not shown, in this table, the air-fuel ratio correction coefficient KDAFEX1 indicates that the smaller the first exhaust gas air-fuel ratio AFEX1, the greater the amount of reducing agent in the exhaust gas flowing into the upstream NOx catalyst 7, and the SOx in the upstream NOx catalyst 7 This is set to a larger value because the elimination reaction of is facilitated.

Finally, the upstream portion SOx desorption amount dQDeSOx1 is calculated by multiplying the basic value dQDBASE1 calculated in step 33 by the four correction coefficients calculated in steps 34 to 37 by the following equation (2) (step 38). ), This process is terminated.
dQDeSOx1
= DQDBASE1 x KDQSOx1 x KDATT1 x KDCATD1
× KDAFEX1 (2)

FIG. 6 shows a subroutine for calculating the downstream SOx trapping amount QSOx2 executed in step 12 of FIG. In this process, first, in step 41, the upstream SOx inflow amount dQSOxIN1, the upstream SOx adsorption amount dQSOxAD1, and the upstream SOx desorption amount dQDeSOx1 calculated in steps 21, 25, and 26 of FIG. 3), the amount of SOx inflow into the downstream NOx catalyst 8 corresponding to the current processing cycle (hereinafter referred to as “downstream SOx inflow”) dQSOxIN2 is calculated.
dQS0xIN2
= DQSOxIN1-dQSOxAD1 + dQDeSOx1 (3)

  Here, (dQSOxIN1-dQSOxAD1) on the right side of the SOx that has flown into the upstream NOx catalyst 7 in the current processing cycle is not captured by the upstream NOx catalyst 7, but passed through (passed through) the SOx. Amount (hereinafter referred to as “upstream SOx passage amount”). As described above, the downstream portion SOx inflow amount dQSOxIN2 is calculated as a value obtained by adding the upstream portion SOx desorption amount dQDeSOx1 to the upstream portion SOx passage amount.

  The contents after step 42 of this process are basically the same as those after step 22 of the calculation process of the upstream SOx trapping amount QSOx1 in FIG. 4 and will be briefly described below. First, at step 42, the SOx trapping amount correction coefficient KAQSOx2 is calculated according to the downstream portion SOx trapping amount QSOx2, and at the next step 43, the catalyst temperature correction factor KACATT2 is calculated according to the downstream side catalyst temperature TCAT2. In step 44, the catalyst deterioration correction coefficient KACATD2 is calculated according to the deterioration degree DCATTD2 of the downstream NOx catalyst 8. The degree of deterioration DCATD2 of the downstream NOx catalyst 8 depends on the degree of delay of the third exhaust air / fuel ratio AFEX3 relative to the second exhaust air / fuel ratio AFEX2 detected during the regeneration control of the upstream and downstream NOx catalysts 7 and 8. It is calculated based on the obtained oxygen storage capacity of the downstream NOx catalyst 8 and the like.

  The correction coefficients KAQSOx2, KAATT2 and KACATD2 are calculated by searching respective predetermined tables (not shown). In addition, the tendency of setting the correction coefficient parameter in each table is the same as the tendency of the correction coefficients KAQSOx1, KAATT1 and KACATD1 described in relation to Steps 22 to 24 in FIG.

Next, in step 45, the downstream portion SOx adsorption amount dQSOxAD2 is calculated by multiplying the downstream portion SOx inflow amount dQSOxIN2 calculated in step 41 by the above three correction coefficients by the following equation (4).
dQS0xAD2
= DQSOxIN2 × KAQSOx2 × KACATT2 × KACATD2
... (4)
This downstream portion SOx adsorption amount dQSOxAD2 represents the amount of SOx trapped by the downstream NOx catalyst 8 out of the SOx flowing into the downstream NOx catalyst 8 in the current processing cycle.

  Next, at step 46, the SOx desorption amount (hereinafter referred to as “downstream SOx desorption amount”) dQDeSOx2 from the downstream NOx catalyst 8 corresponding to the current processing cycle is calculated. The calculation process will be described later. Next, the difference between the downstream SOx adsorption amount dQSOxAD2 and the downstream SOx desorption amount dQDeSOx2 calculated in steps 45 and 46 is calculated as the SOx trapping amount dQSOx2 corresponding to the current processing cycle (step 47). Then, by adding the calculated SOx trapping amount dQSOx2 to the downstream SOx trapping amount QSOx2 calculated so far, the downstream SOx trapping amount QSOx2 is calculated (step 48), and this processing is terminated.

  FIG. 7 shows a subroutine for calculating the downstream portion SOx desorption amount dQDeSOx2 executed in step 46 described above. The contents of this process are basically the same as the calculation process of the upstream SOx desorption amount dQDeSOx1 in FIG. 5 described above, and will be briefly described below. First, in step 51, it is determined whether or not the sulfur purge flag F_SOxPRG is “1”. If the answer is NO and the sulfur purge operation is not being performed, the downstream portion SOx desorption amount dQDeSOx2 is set to a value of 0 (step 52), and this processing is terminated.

  If the answer to step 51 is YES and the sulfur purge operation is being performed, a predetermined map (not shown) is searched for the basic value dQDBASE2 of the downstream SOx desorption amount according to the engine speed NE and the required torque PMCMD. (Step 53).

  In the next step 54, the SOx trapping amount correction coefficient KDQSOx2 is calculated according to the downstream portion SOx trapping amount QSOx2, and in step 55, the catalyst temperature correction factor KDATT2 is calculated according to the downstream catalyst temperature TCAT2. In step 56, the catalyst deterioration correction coefficient KDCATD2 is calculated in accordance with the degree of deterioration DCATTD2 of the downstream side NOx catalyst 8, and in step 57, the air-fuel ratio correction coefficient KDAFEX2 is calculated in accordance with the second exhaust gas air-fuel ratio AFEX2. To do.

  The correction coefficients KDQSOx2, KDATT2, KDCATD2, and KDAFEX2 are calculated by searching respective predetermined tables (not shown). In addition, the tendency of setting the correction coefficient parameters in each table is the same as the tendency of the correction coefficients KDQSOx1, KDATT1, KDCATD1, and KDAFEX1 described in relation to Steps 34 to 37 in FIG.

Finally, the downstream value SOx desorption amount dQDeSOx2 is calculated by multiplying the basic value dQDBASE2 calculated in step 53 by the four correction coefficients calculated in steps 54 to 57 by the following equation (5) (step 58). ), This process is terminated.
dQDeSOx2
= DQDBASE2 x KDQSOx2 x KDATT2 x KDCATD2
× KDAFEX2 (5)

  As described above, according to the present embodiment, the upstream SOx desorption amount dQDeSOx1, which is the SOx desorption amount from the upstream NOx catalyst 7 during the sulfur purge operation, is calculated (step 38). The upstream SOx desorption amount dQDeSOx1 flows into the upstream NOx catalyst 7 and is added to the upstream SOx passage amount (dQSOxIN1-dQSOxAD1), which is the amount of SOx that has passed through, to flow into the downstream NOx catalyst 8. The downstream SOx inflow amount dQDeSOxIN2 is calculated (step 41).

  Then, the downstream portion SOx adsorption amount dQSOxAD2 calculated based on the downstream portion SOx inflow amount dQDeSOxIN2 (step 45) and the downstream portion SOx desorption amount dQDeSOx2 (step 46), which is the SOx desorption amount from the downstream side NOx catalyst 8. Is calculated as the SOx trapping amount dQSOx2 corresponding to the current processing cycle (step 47), and by further integrating this, the downstream portion SOx trapping amount QSOx2 trapped in the downstream NOx catalyst 8 is calculated. To do.

  As described above, the downstream SOx trapping amount QSOx2 is calculated based on the upstream SOx desorption amount dQDeSOx1, so that the SOx desorbed from the upstream NOx catalyst 7 is trapped again by the downstream NOx catalyst 8. Even if this occurs, the downstream SOx trapping amount QSOx2 can be accurately calculated while reflecting this.

  Further, as parameters representing the state of the downstream NOx catalyst 8, the downstream SOx trapping amount QSOx2, the downstream catalyst temperature TCAT2, and the deterioration degree DCATD2 of the downstream NOx catalyst 8 are calculated or detected, and according to these parameters, The downstream portion SOx adsorption amount dQSOxAD2 and the downstream portion SOx desorption amount dQDeSOx2 are calculated (steps 45 and 58). Therefore, according to the actual state of the downstream NOx catalyst 8, the downstream SOx trapping amount QSOx2 can be calculated with higher accuracy while reflecting the trapping degree and desorption degree of the SOx in the downstream NOx catalyst 8.

  Further, in calculating the downstream portion SOx desorption amount dQDeSOx2, in addition to the parameter representing the state of the downstream NOx catalyst 8, the second exhaust gas air-fuel ratio which is the air-fuel ratio of the exhaust gas flowing into the downstream NOx catalyst 8 is calculated. AFEX2 is used. Therefore, the downstream portion SOx desorption amount dQDeSOx2 and thus the downstream portion SOx trapping amount QSOx2 can be calculated with higher accuracy.

  Further, the SOx trapping amount trapped by the upstream side NOx catalyst 7 is calculated as the upstream portion SOx trapping amount QSOx1 (FIG. 4), and the sum of the upstream portion SOx trapping amount QSOx1 and the downstream portion SOx trapping amount QSOx2 is calculated. When the value falls below the threshold value QREFE, the sulfur purge operation is terminated (steps 5, 6, and 13).

  Therefore, based on the total SOx trapping amount of the upstream and downstream NOx catalysts 7, 8, the sulfur purge operation can be terminated at an optimal timing. In particular, unlike the conventional case, the sulfur purge operation can be terminated at the timing when the SOx is sufficiently desorbed without underestimating the SOx trapping amount of the downstream NOx catalyst 8 during the sulfur purge operation. As a result, a large amount of SOx does not remain in the downstream NOx catalyst 8 at the end of the sulfur purge operation, thereby reliably recovering the NOx trapping performance of the upstream and downstream NOx catalysts 7, 8 and exhaust gas. Good characteristics can be maintained.

  Further, as in the present embodiment, particularly when the NOx catalyst is composed of the upstream NOx catalyst 7 and the downstream NOx catalyst 8 separated from each other, the upstream of the NOx catalyst is compared with the case where the NOx catalyst is single. Since the distance between the part and the downstream part is large, the state of the NOx catalyst and the state of the supplied exhaust gas are likely to greatly differ between the upstream part and the downstream part. Therefore, according to this embodiment, the effect described so far can be obtained very effectively.

  FIG. 8 shows an exhaust gas purification device 21 according to a second embodiment of the present invention. In the first embodiment described above, the NOx catalyst is composed of the upstream NOx 7 and the downstream NOx catalyst 8 separated from each other, whereas in this embodiment, the NOx catalyst has a length and capacity along the exhaust pipe 5. Is composed of a larger single NOx catalyst 27.

  In the present embodiment, for convenience of control, the NOx catalyst 27 is divided into the upstream portion 27a and the downstream portion 27b equally in the length direction of the exhaust pipe 5, and the divided upstream portion 27a and downstream portion 27b are divided. On the other hand, the present invention is applied in the same manner as the upstream and downstream NOx catalysts 7 and 8 in the first embodiment.

  For this reason, in this embodiment, the upstream side catalyst temperature sensor 15 and the downstream side catalyst temperature sensor 16 are provided in the upstream part 27a and the downstream part 27b of the NOx catalyst 27, respectively, and the boundary between the upstream part 27a and the downstream part 27b. A second air-fuel ratio sensor 13 is provided in the part. Other configurations are the same as those of the first embodiment, and the same reference numerals are given to the same components, and the detailed description thereof will be omitted. Therefore, also in this embodiment, the same effect as the first embodiment described above can be obtained.

  In addition, this invention can be implemented in various aspects, without being limited to the described embodiment. For example, in the embodiment, as parameters for calculating the upstream SOx adsorption amount dQSOxAD1 and the upstream SOx desorption amount dQDeSOx1, the upstream SOx trapping amount QSOx1, the upstream catalyst temperature TCAT1, and the deterioration degree DCATD1 of the upstream NOx catalyst 7 However, the calculation method is arbitrary, and other appropriate parameters can be used in addition to or in place of these parameters.

  The same applies to the parameters for calculating the downstream portion SOx adsorption amount dQSOxAD2 and the downstream portion SOx desorption amount dQDeSOx2. Furthermore, the method for calculating the downstream portion SOx trapping amount dQDeSOx based on the upstream portion SOx desorption amount dQDeSOx1 is not limited to the one shown in the embodiment, and any appropriate method can be adopted.

  In the embodiment, the sulfur purge operation for supplying exhaust gas in a reducing atmosphere to the NOx catalyst is performed by post injection in which fuel is injected from the injector 6. However, the present invention is not limited to this, and fuel or ammonia is reduced to the exhaust pipe 5. You may carry out by supplying directly as an agent.

  Furthermore, the embodiment is an example in which the present invention is applied to a diesel engine mounted on a vehicle. However, the present invention is not limited to this, and may be applied to various engines such as a gasoline engine. The present invention can also be applied to engines other than those for ships, for example, marine propulsion engine engines such as outboard motors having a crankshaft arranged vertically. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

1 Exhaust gas purification device 2 ECU (sulfur purge control means, SOx desorption amount calculation means, downstream SOx trapping amount calculation means, catalyst state acquisition means, upstream SOx trapping amount calculation means, sulfur purge end determination means)
3 Engine (Internal combustion engine)
5 Exhaust pipe (exhaust passage)
7 Upstream NOx catalyst (upstream part of NOx catalyst)
8 Downstream NOx catalyst (downstream part of NOx catalyst)
13 Second air-fuel ratio sensor (catalyst state acquisition means)
14 Third air-fuel ratio sensor (catalyst state acquisition means)
16 Downstream exhaust gas temperature sensor (catalyst state acquisition means)
21 Exhaust gas purification device 27 NOx catalyst 27a NOx catalyst upstream portion 27b NOx catalyst downstream portion dQDeSOx1 Upstream SOx desorption amount (SOx desorption amount from upstream portion)
QSOx1 upstream SOx trapping amount QSOx2 downstream SOx trapping amount (the state of the downstream portion of the NOx catalyst)
TCAT2 Downstream catalyst temperature (downstream of NOx catalyst)
DCATD2 Degree of deterioration of downstream NOx catalyst (state of downstream portion of NOx catalyst)

Claims (4)

A NOx catalyst provided in the exhaust passage of the internal combustion engine, having an upstream portion and a downstream portion, and capturing or desorbing NOx and SOx according to the oxygen concentration of the exhaust gas;
A sulfur purge control means for performing a sulfur purge operation for desorbing SOx trapped by the NOx catalyst by supplying exhaust gas in a reducing atmosphere to the NOx catalyst;
SOx desorption amount calculating means for calculating the amount of SOx desorption from the upstream portion of the NOx catalyst during the sulfur purge operation;
A downstream portion SOx trapping amount calculating means for calculating, as a downstream portion SOx trapping amount, a trapping amount of SOx trapped in the downstream portion of the NOx catalyst based on the calculated SOx desorption amount;
An exhaust gas purifying apparatus for an internal combustion engine, comprising: A catalyst state acquiring means for acquiring the state of the downstream portion of the NOx catalyst;
2. The exhaust gas of the internal combustion engine according to claim 1, wherein the downstream portion SOx trapping amount calculating unit calculates the downstream portion SOx trapping amount according to a state of the acquired downstream portion of the NOx catalyst. Purification equipment. The NOx catalyst includes an upstream NOx catalyst and a downstream NOx catalyst arranged in a state separated from each other along the exhaust passage,
The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the upstream portion of the NOx catalyst is the upstream NOx catalyst, and the downstream portion of the NOx catalyst is the downstream NOx catalyst. Upstream SOx trapping amount calculating means for calculating the SOx trapping amount trapped in the upstream portion of the NOx catalyst as an upstream SOx trapping amount;
The apparatus further comprises sulfur purge end determination means for determining an end timing of the sulfur purge operation based on a sum of the calculated upstream SOx trapping amount and the downstream SOx trapping amount. Item 2. An exhaust gas purification apparatus for an internal combustion engine according to Item 1.

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