JP2013024210A - Exhaust post-processing device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device suppressing HC discharged to the downstream of an NOtrap catalyst even in a layout provided with a filter on the upstream side of an exhaust channel and the NOtrap catalyst on the downstream side of the exhaust channel.SOLUTION: In an exhaust post-processing device for a diesel engine provided with the filter (13) on the upstream side of the exhaust channel and the NOtrap catalyst (15) on the downstream side of the exhaust channel and executing a rich spike process making an excess air ratio of exhaust basic target excess air ratio, the excess air ratio equivalent to or less than a theoretical air-fuel ratio being made the basic target excess air ratio, when regeneration timing of the NOtrap catalyst (15) comes, provided is an excess air ratio correction means (53) correcting the basic target excess air ratio in the rich spike process to the increasing side in the operation range in which SOF is generated comparatively much.

Description

  The present invention relates to an exhaust aftertreatment device for a diesel engine.

  Some have a filter that collects particulates in exhaust gas flowing in upstream of the exhaust passage and a NOx catalyst (NOx adsorption catalyst and NOx storage catalyst) downstream of the exhaust passage (see Patent Document 1).

JP 2008-298024 A

  By the way, the NOx in the exhaust flowing in when the excess air ratio of the exhaust is larger than the value corresponding to the theoretical air-fuel ratio is trapped, and the NOx trapped when the equivalent ratio air excess ratio of the exhaust is more than the value corresponding to the theoretical air-fuel ratio. There are NOx trap catalysts that desorb and purify. In the case of a layout that does not include a filter upstream of the NOx trap catalyst, the post-injection amount is set so that the basic target air excess ratio during the rich spike process can be obtained, so that the NOx trap catalyst has a reduced amount. Can supply without shortage.

  On the other hand, the inventor is examining an exhaust aftertreatment device having a layout in which a filter is provided on the upstream side of the NOx trap catalyst. In the case of this layout as well, when the above rich spike processing is applied as it is, the amount of HC discharged downstream of the NOx trap catalyst 15 is larger than that in the case of a layout that does not include a filter upstream of the NOx trap catalyst. I knew it would be.

  Accordingly, the present invention provides an exhaust aftertreatment device capable of suppressing HC discharged downstream of the NOx trap catalyst even in a layout in which a filter is provided upstream of the exhaust passage and a NOx trap catalyst is provided downstream of the exhaust passage. For the purpose.

  In the exhaust aftertreatment device for a diesel engine according to the present invention, a filter for collecting particulates composed of dry soot and SOF present in inflowing exhaust gas is disposed upstream of the exhaust passage, and the excess air ratio of the exhaust corresponds to the stoichiometric air fuel ratio. NOx trapping catalyst that traps NOx in the exhaust that flows in when the exhaust gas is larger than the above value, and desorbs and purifies NOx trapped when the excess air ratio of the exhaust is equal to or higher than the theoretical air-fuel ratio is disposed downstream of the exhaust passage. In addition, when the regeneration timing of the NOx trap catalyst is reached, a rich spike process is performed so that the basic target air excess ratio is obtained by setting the air excess ratio equal to or less than the value corresponding to the theoretical air-fuel ratio as the basic target air excess ratio. In an operation region where a relatively large amount of SOF is generated, there is provided an excess air ratio correction means for correcting the basic target excess air ratio during the rich spike process to the increase side.

  According to the present invention, in consideration of the fact that SOF desorbed from the filter during the rich spike process flows into the NOx trap catalyst in the operating region where a relatively large amount of SOF is generated, the basic target air during the rich spike process is anticipated. Since the excess rate is corrected to the increase side, excessive supply of the reducing agent amount to the NOx trap catalyst is prevented even in the layout in which the filter is provided upstream of the exhaust passage and the NOx trap catalyst is provided downstream of the exhaust passage. It is possible to reduce HC discharged downstream of the NOx trap catalyst.

1 is a schematic configuration diagram of an exhaust aftertreatment device for a diesel engine according to a first embodiment of the present invention. It is a block diagram of a SOF adsorption amount calculation unit and a post injection amount calculation unit. It is a characteristic view of the amount of basic engine out SOF. It is a characteristic view of the water temperature correction coefficient with respect to the cooling water temperature. It is a characteristic view of the purification correction coefficient with respect to the oxidation catalyst temperature. It is a characteristic figure of SOF adsorption capacity to dry soot amount. It is a characteristic figure of SOF adsorption capacity to filter temperature. It is a characteristic view of the SOF desorption amount with respect to the actual excess air ratio. It is a characteristic view of SOF desorption amount with respect to filter temperature. It is a characteristic view of the amount of SOF desorption with respect to the volume velocity of exhaust. It is a characteristic view of the amount of HC desorption with respect to the amount of SOF adsorption. It is a characteristic view of the amount of HC desorption with respect to the filter temperature. It is a characteristic view of the air excess ratio correction amount with respect to the HC desorption amount. It is a characteristic view of the air excess ratio correction amount with respect to the fuel injection amount. It is a characteristic view of the air excess ratio correction amount with respect to the cylinder intake air amount. It is a characteristic view of the air excess ratio correction amount with respect to the engine rotation speed. FIG. 6 is a characteristic diagram of a post injection amount. It is a block diagram of an excess air ratio correction amount calculation unit. It is a timing chart which shows change of HC concentration of a 1st embodiment by contrast with a comparative example.

  Embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an exhaust aftertreatment device for a diesel engine according to a first embodiment of the present invention. In FIG. 1, an intake passage 2 of a diesel engine 1 is provided with an intake compressor of a variable nozzle type turbocharger 3. The intake air is supercharged by the intake compressor, cooled by the intercooler 4, passes through the normally open throttle valve 5, and then flows into the cylinder of each cylinder through the collector 6. The fuel is increased in pressure by the common rail type fuel injection device, that is, by the high pressure fuel pump 7, sent to the common rail 8, and directly injected from the fuel injection valve 9 of each cylinder into the cylinder. The air flowing into the cylinder and the injected fuel are combusted by compression ignition here, and the exhaust gas flows out to the exhaust passage 10.

  Part of the exhaust gas flowing into the exhaust passage 10 is recirculated to the intake side via the EGR valve 12 through the EGR passage 11 as EGR gas. The remainder of the exhaust passes through the exhaust turbine of the variable nozzle type turbocharger 3 and drives the exhaust turbine.

  The engine control unit 21 receives signals of an accelerator opening (accelerator pedal depression amount) ACC from the accelerator sensor 22 and an engine rotational speed Ne from the crank angle sensor 23. The control unit 21 calculates the fuel injection timing and the fuel injection amount of the main injection based on the engine load (accelerator opening degree and the like) and the engine rotational speed Ne, and sends a valve opening command signal corresponding thereto to the fuel injection valve 9. Output to. Further, the engine control unit 21 performs EGR control and supercharging pressure control in a coordinated manner so that the target EGR rate and the target intake air amount can be obtained. The engine control unit 21 is constituted by a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface).

  A filter (DPF) 13 that collects particulates in the exhaust is disposed downstream of the exhaust turbine in the exhaust passage 10. When the particulate accumulation amount of the filter 13 reaches a predetermined value (threshold value), the engine control unit 21 regenerates the filter 13. For example, by performing post-injection in the expansion stroke or exhaust stroke immediately after the main injection, the exhaust is raised to the temperature at which the particulates burn, the filter 13 is regenerated, and the particulates deposited on the filter 13 are removed by combustion. Then, the filter 13 is regenerated. In order to obtain the target regeneration temperature, the post-injection amount and post-injection timing are determined in advance according to the engine load and rotational speed (operating conditions), and in accordance with the engine load and rotational speed at that time. The post injection is performed so that the post injection amount and the post injection timing are obtained.

  In order to perform complete regeneration in which all of the particulates accumulated on the filter 13 are burned and removed, it is necessary to raise the particulate combustion temperature as much as possible within a range not exceeding the allowable temperature of the filter 13 during regeneration processing. It becomes. For this reason, in this embodiment, an oxidation catalyst (noble metal) 14 is disposed upstream of the filter 13. The oxidation catalyst 14 burns exhaust components (HC, CO) flowing in by post-injection for regeneration processing of the filter 13 to raise the temperature of the exhaust gas and promote the combustion of particulates in the filter 13. The carrier constituting the filter 13 may be coated with an oxidation catalyst. At this time, the oxidation reaction at the time of burning the particulates can be promoted, the bed temperature of the filter 13 can be substantially increased, and the burning of the particulates in the filter 13 can be promoted.

  The catalyst is not limited to the oxidation catalyst 14. Any catalyst having an oxidation function can be replaced with an oxidation catalyst. FIG. 1 shows a case where a three-way catalyst (TWC) is employed as the oxidation catalyst 14.

  Downstream of the filter 13 is a NOx trap that traps (for example, adsorbs) NOx in the exhaust in an oxygen atmosphere, desorbs the NOx trapped in the reducing atmosphere, and reduces and purifies using HC in the exhaust as a reducing agent. A catalyst (LNT) 15 is provided. The oxygen atmosphere is obtained when the exhaust air excess ratio is larger than 1.0 (a value corresponding to the theoretical air-fuel ratio). On the other hand, the reducing atmosphere is obtained when the exhaust air excess ratio is 1.0 or less.

  When the NOx accumulation amount of the NOx trap catalyst 15 reaches a predetermined value (threshold value), the engine control unit 21 performs rich spike processing to switch the exhaust gas flowing through the NOx trap catalyst 15 from the oxygen atmosphere to the reducing atmosphere. In this rich spike processing, post-injection is performed in the expansion stroke or exhaust stroke immediately after the main injection, the amount of unburned HC discharged to the exhaust passage 10 is increased, and this HC is used as a reducing agent to the NOx trap catalyst 15. Is to supply.

  Since the diesel engine 1 is operated at an excess air ratio (air-fuel ratio leaner than the theoretical air-fuel ratio) larger than 1.0 (value corresponding to the theoretical air-fuel ratio) during normal operation, the addition of post-injection alone The excess air ratio of the exhaust cannot be switched to 1.0. Therefore, the amount of intake air flowing into the cylinder (hereinafter referred to as “cylinder intake air amount”) Qac is reduced by closing the throttle valve 5 in the fully open position during normal operation during the rich spike process. As a result, the excess air ratio of the exhaust gas is switched to 1.0. That is, the post injection amount and the throttle valve opening (intake air amount) so that the excess air ratio determined by the total fuel injection amount Qfuel of the main injection amount and the post injection amount and the cylinder intake air amount Qac is 1.0. ). Here, if the throttle valve opening during the rich spike process is determined, the post injection amount is uniquely determined.

  Further, the NOx amount per predetermined time trapped by the NOx trap catalyst 15 is calculated every predetermined time (fixed period), and the NOx amount per predetermined time is added (integrated) to be accumulated on the NOx trap catalyst 15. The amount of NOx deposited is calculated. This NOx accumulation amount is compared with a predetermined threshold value, and when the NOx accumulation amount becomes equal to or greater than the threshold value (when the regeneration timing of the NOx trap catalyst 15 is reached), post injection (rich spike processing) is executed. . The NOx accumulation amount to be reduced and purified is basically the same as the threshold value. Therefore, a post injection amount suitable for reducing and purifying all the NOx accumulation amount equal to the threshold value under the target excess air ratio of 1.0 is also determined in advance.

  In this way, during normal operation in which the excess air ratio of the exhaust gas exceeds 1.0, when the NOx accumulation amount exceeds the threshold value, the throttle valve opening is changed from the fully open state to the predetermined throttle valve opening. In addition to switching (throttle throttling), post-injection is started. When the post-injection period has elapsed, post-injection is terminated and the throttle valve 5 is returned to the fully open position.

  When the layout does not include the filter 13 on the upstream side of the NOx trap catalyst 15, the post injection amount is set so that the basic target excess air ratio tλ0 (= 1.0) during the rich spike process can be obtained. Therefore, the amount of reduction to the NOx trap catalyst 15 is supplied without excess or deficiency. Therefore, when the rich spike process is applied as it is even in the case of the layout including the filter 13 on the upstream side of the NOx trap catalyst 15, the amount of HC discharged downstream of the NOx trap catalyst 15 may increase. all right.

  As a result of analyzing the cause, the following has been found. That is, the particulates deposited on the filter 13 are composed of dry soot as carbon particles and an organic solvent-soluble component (hereinafter referred to as “SOF”) as mist-like HC. When operating in a low load range where the engine load is relatively small (or in a low temperature range where the combustion temperature in the cylinder is relatively low), the combustion temperature in the cylinder does not rise so much, so the engine load is relatively high. More SOF is generated than when operating in a region (or a high temperature region where the combustion temperature in the cylinder is relatively high). This SOF is collected by the filter 13 as described above. Then, when the NOx trap catalyst 15 is regenerated in a state where a relatively large amount of SOF is adsorbed on the filter 26 and post injection is performed, SOF is desorbed from the filter 13 and flows into the NOx trap catalyst 15 as HC. Has been understood.

  The amount of reducing agent (that is, the post injection amount) that should be supplied to the NOx trap catalyst 15 in the rich spike processing is determined in advance by the NOx accumulation amount. However, HC desorbed from the filter 13 during the rich spike process has not been considered. For this reason, the amount of reducing agent supplied to the NOx trap catalyst 15 becomes excessive by the amount of HC (reducing agent) supplied from the filter 13 to the NOx trap catalyst 15. As a result, the excess HC that is not used for NOx reduction by the NOx trap catalyst 15 is discharged directly downstream of the NOx trap catalyst 15.

  Therefore, in the first embodiment, an excess air ratio correcting unit that corrects the basic target excess air ratio during the rich spike process to the increasing side in an operation region where a relatively large amount of SOF is generated is provided.

  In the rich spike processing of the present embodiment, post injection is performed after main injection, and HC as a reducing agent is supplied to the NOx trap catalyst 15 by this post injection, whereby the excess air ratio of the exhaust is the basic target excess air ratio. It is assumed that the value is 1.0 (value corresponding to the theoretical air-fuel ratio). For this reason, by correcting the post injection amount to the decreasing side according to the amount of HC desorbed from the filter 13 during the rich spike processing, the target excess air ratio during the rich spike processing is set to a value larger than 1.0. to correct.

  This control performed by the engine control unit 21 will be described in detail with reference to the block diagram of FIG.

  2, a block diagram of the post injection amount calculation unit 50 is shown in the upper part of FIG. 2, and a block diagram of the SOF adsorption amount calculation unit 30 is shown in the lower part of FIG. The description will start from the lower block diagram of FIG.

  Now, for the sake of simplicity, a mode for operating with a target excess air ratio greater than 1.0 (normal operation mode), a mode for performing rich spike processing (rich spike mode), and a mode for regenerating the filter 13 ( Let us consider a case where there are only three modes (filter regeneration mode). Further, it is assumed that the filter regeneration mode is not executed immediately before the rich spike mode.

  The SOF adsorption amount calculation unit 30 includes a basic engine out SOF amount calculation unit 31, a water temperature correction coefficient calculation unit 32, a multiplication unit 33, a purification correction coefficient calculation unit 34, a multiplication unit 35, a basic SOF adsorption amount calculation unit 36, and an SOF adsorption capacity. The calculation unit 38 and the SOF desorption amount calculation unit 40 are included. Then, the SOF adsorption amount calculation unit 30 calculates the SOF adsorption amount of the filter 13 at a constant period (for example, every 10 ms) in the normal operation mode.

  First, the basic engine out SOF amount calculation unit 31 refers to a map having the contents shown in FIG. 3 based on the engine rotational speed Ne [rpm] and the target engine torque Trq [Nm], thereby engine out (exhaust passage 10 inlet). The SOF amount per predetermined time (per 10 ms) is calculated as the basic engine out SOF amount [mg / s].

  As shown in FIG. 3, the basic engine out SOF amount is a value that decreases as the target engine torque Trq increases when the engine speed Ne is constant. This is because a large amount of SOF is generated on the side where the combustion temperature in the cylinder is relatively low, and as the target engine torque Trq increases, so much fuel is supplied and the combustion temperature in the cylinder becomes high. This is because the amount of occurrence of is reduced. Further, it has little sensitivity to the engine speed Ne. That is, when the target engine torque Trq is constant, the basic engine out SOF amount is a value that slightly decreases as the engine speed Ne increases. Thus, relatively more SOF is generated in the low load region where the engine load is relatively small than on the high load side where the engine load is relatively large.

  The target engine torque Trq is basically calculated by searching a predetermined map, for example, from the accelerator opening degree ACC detected by the accelerator sensor 22 and the engine rotational speed Ne detected by the crank angle sensor 23. You can do it.

The water temperature correction coefficient calculation unit 32 calculates a water temperature correction coefficient Ktw [anonymous number] by searching a table having the contents shown in FIG. 4 from the cooling water temperature TW [° C.] detected by the water temperature sensor 24. The multiplication unit 33 multiplies the basic engine out SOF amount by the water temperature correction coefficient Ktw to calculate the engine out SOF amount [mg / s]. In other words,
Engine out SOF amount = Basic engine out SOF amount × Ktw
... (1)
The engine out SOF amount is calculated by the following formula.

  The purpose of introducing the water temperature correction coefficient Ktw as in the equation (1) is that the SOF in the cylinder is more generated as the cooling water temperature TW is relatively lower, and the increased SOF is deposited on the filter 13. This is because the amount of SOF increases.

  As shown in FIG. 4, the water temperature correction coefficient Ktw is 1.0 when the cooling water temperature TW is the predetermined value TW0, and is a value that is larger than 1.0 as the cooling water temperature TW decreases in the temperature range below the predetermined value TW0. . This is because when the cooling water temperature TW is relatively low in the temperature range below the predetermined value TW0, the combustion temperature in the cylinder is relatively lower than when the cooling water temperature TW is relatively high. This is because many occur.

The purification correction coefficient calculation unit 34 calculates a purification correction coefficient Ktwc [anonymous number] by searching a table having the content in FIG. 5 from the temperature TWCtemp [° C.] of the oxidation catalyst 14. The multiplication unit 35 multiplies the purification correction coefficient Ktwc by the engine out SOF amount to calculate the filter inflow SOF amount [mg / s]. In other words,
Filter inflow SOF amount = Engine out SOF amount × Ktwc (2)
The filter inflow SOF amount is calculated by the following formula.

  The purpose of introducing the purification correction coefficient Ktwc as in equation (2) is as follows. That is, a part of the SOF generated in the cylinder and flowing into the exhaust passage 10 is oxidized by the oxidation catalyst 14 and disappears. This is because the amount of SOF deposited on the filter 13 is reduced by the amount of SOF that is oxidized by the oxidation catalyst 14 and disappears.

  As shown in FIG. 5, the purification correction coefficient Ktwc becomes 1.0 when the oxidation catalyst temperature TWCtemp is equal to or lower than a predetermined value TWC0. This is because the oxidation catalyst 14 is not activated in the temperature range below the predetermined value TWC0, and the SOF does not oxidize even if it passes through the oxidation catalyst 14.

  On the other hand, in the temperature range exceeding the predetermined value TWC0, the purification correction coefficient Ktwc is a value that decreases as the oxidation catalyst temperature TWCtemp increases. This is because, in the temperature range exceeding the predetermined value TWC0 at which the oxidation catalyst 14 is activated, the higher the oxidation catalyst temperature TWCtemp, the more purified (oxidized) the inflowing SOF, and accordingly, the amount of SOF deposited on the filter 13 is reduced accordingly. It is to become. The oxidation catalyst temperature TWCtemp is detected by a temperature sensor 25 provided on the oxidation catalyst 14.

The basic SOF adsorption amount calculation unit 36 calculates the basic SOF adsorption amount [mg] of the filter 13 by adding this filter inflow SOF amount to the basic SOF adsorption amount [mg] accumulated in the filter 13 until the previous time. To do. In other words,
Basic SOF adsorption amount = Basic SOF adsorption amount (previous) + Filter inflow SOF amount
... (3)
However, basic SOF adsorption amount (previous); basic SOF adsorption amount up to the previous time,
The basic SOF adsorption amount of the filter 13 is calculated by the following equation. The expression (3) calculates the basic SOF adsorption amount of the filter 13 by adding the SOF amount flowing into the filter 13 at a constant period. The reason for “basic” is to distinguish it from the amount of SOF adsorption that has passed through the subtractor 41.

  Since the SOF accumulated in the filter 13 disappears due to the regeneration process of the filter 13, the basic SOF adsorption amount (previous) on the right side of the equation (3) is reset to zero immediately after the end of the filter regeneration mode. The previous value holding unit 37 holds the basic SOF adsorption amount (previous) on the right side of the equation (3).

  The SOF adsorption capacity calculation unit 38 searches for a predetermined map from the dry soot amount msoot [mg] accumulated on the filter 13 and the filter temperature DPFtemp detected by the temperature sensor 26 to thereby obtain the SOF adsorption capacity [mg] of the filter 13. Is calculated. The minimum side selection unit 39 compares the SOF adsorption capacity calculated by the SOF adsorption capacity calculation unit 38 with the basic SOF adsorption amount calculated by the basic SOF adsorption amount calculation unit 36, and selects and outputs a smaller value side. To do. That is, if the basic SOF adsorption amount is less than or equal to the SOF adsorption capacity, the basic SOF adsorption amount is output, and if the basic SOF adsorption amount exceeds the SOF adsorption capacity, the SOF adsorption capacity is output.

  As described above, the value (calculated value) calculated by the basic SOF adsorption amount calculation unit 36 is limited by the SOF adsorption capacity because the SOF adsorption amount that can be actually accumulated on the filter 13 is the basic SOF adsorption amount that is the calculated value. This is because the maximum value (that is, the SOF adsorption capacity) may be exceeded. There is a limit to the amount of SOF that can be actually deposited on the filter 13, and this limit value depends on the dry soot amount msot [mg] deposited on the filter 13 and the filter temperature DPFtemp.

  The characteristics of the SOF adsorption capacity of the filter 13 are specifically shown in FIGS. As shown in FIG. 6, the SOF adsorption capacity of the filter 13 is a value that increases as the amount of dry soot msoot deposited on the filter 13 increases when the filter temperature DPFtemp is constant. This is because the SOF in the exhaust often adheres to the dry soot and drifts in the exhaust passage 10 rather than drifting in the exhaust passage 10 alone. Therefore, the larger the amount of dry soot msout deposited on the filter 13 is, the larger the filter 13 is. This is because the amount of SOF that can be adsorbed on the substrate increases.

  Further, as shown in FIG. 7, the SOF adsorption capacity of the filter 13 is a value that decreases as the filter temperature DPFtemp increases when the amount of dry soot msoot deposited on the filter 13 is constant. This is because the SOF desorbed from the filter 13 increases as the filter temperature DPFtemp increases, and the amount of SOF that can be adsorbed by the filter 13 decreases accordingly.

  A known calculation method (see Japanese Patent Application Laid-Open No. 7-34857) may be used for calculating the dry soot amount msoot.

Up to this point, attention has been paid to the side on which SOF accumulates on the filter 13 in the normal operation mode. On the other hand, SOF is easily detached from the filter 13 when the filter temperature DPFtemp becomes relatively high, unlike the dry soot. The SOF desorption amount calculation unit 40 calculates the amount of desorbed SOF in the normal operation mode. That is, in the SOF desorption amount calculation unit 40, in the normal operation mode, based on the actual excess air ratio rλ [anonymous number] of the exhaust, the filter temperature DPFtemp, and the volume velocity SV [m ³ / s] of the exhaust flowing through the filter 13. The SOF desorption amount [mg] from the filter 13 is calculated. The subtraction unit 41 calculates a value obtained by subtracting the SOF desorption amount from the output [mg] from the minimum side selection unit 38 as the SOF adsorption amount [mg] of the filter 13. That is, SOF adsorption amount = minimum side selection unit output−SOF desorption amount (4)
The SOF adsorption amount of the filter 13 is calculated by the following equation.

  The characteristics of the SOF desorption amount from the filter 13 in the normal operation mode are specifically shown in FIG. 8, FIG. 9, and FIG. As shown in FIG. 8, the SOF desorption amount from the filter 13 in the normal operation mode increases as the actual exhaust air excess ratio rλ decreases when the filter temperature DPFtemp and the exhaust volume velocity SV are constant. It is. This is because when the actual excess air ratio rλ is relatively small, the combustion temperature in the cylinder becomes higher than when the actual excess air ratio rλ is relatively large, and the exhaust temperature rises. This is because it becomes easy to desorb. The actual excess air ratio rλ may be obtained from an actual air-fuel ratio detected by an air-fuel ratio sensor 27 provided upstream of the oxidation catalyst 14, for example. A value obtained by dividing the actual air-fuel ratio by the theoretical air-fuel ratio is the actual excess air ratio rλ.

  As shown in FIG. 9, the SOF desorption amount from the filter 13 in the normal operation mode is such that the filter temperature DPFtemp is a predetermined value 1 (for example, 100 ° C.) when the actual excess air ratio rλ and the exhaust volume velocity SV are constant. Degree) to a predetermined value 2 (for example, about 250 ° C.). This is because SOF is actively desorbed from the filter 13 when the filter temperature DPFtemp exceeds the predetermined value 1. The reason why the SOF desorption amount from the filter 13 decreases in the region where the filter temperature DPFtemp exceeds the predetermined value 2 is that no SOF remains in the filter 13.

  As shown in FIG. 10, the SOF desorption amount from the filter 13 in the normal operation mode is a value that increases as the exhaust volume velocity SV increases when the actual excess air ratio rλ and the filter temperature DPFtemp are constant. . This is because when the volumetric velocity SV of the exhaust gas is relatively large, the amount of SOF that is blown away by the exhaust flow and desorbed from the filter 13 is relatively larger than when the volume SV of the exhaust gas is relatively small. . Since the exhaust volume velocity SV increases as the engine 1 becomes higher in load, the accelerator opening ACC, the fuel injection amount Qfuel, and the target engine torque Trq can be used in place of the exhaust volume flow SV.

  The maximum side selection unit 42 compares zero [mg] with the SOF adsorption amount from the subtraction unit 41 and outputs the larger side. This is to prevent the SOF adsorption amount from being calculated as a negative value.

  The SOF adsorption amount of the filter 13 in the normal operation mode calculated in this way is input to the post injection amount calculation unit 50 in the upper part of FIG.

  2, the post injection amount calculation unit 50 includes an HC desorption amount calculation unit 51, an excess air ratio correction amount calculation unit 52, an excess air ratio correction unit 53, and a post injection amount calculation unit 54. . The post injection amount calculation unit 50 works at the timing when the normal operation mode is switched to the rich spike mode.

  The HC desorption amount calculation unit 51 searches a predetermined map from the SOF adsorption amount of the filter 13 and the filter temperature DPFtemp to obtain the SOF desorption amount from the filter 13 at the time of rich spike processing. Calculated as desorption amount [mg].

  The HC desorption amount calculation unit 51 (HC desorption amount calculation means) is the same as the HC desorption amount calculation unit 40 in that the SOF desorption amount from the filter 13 is calculated. However, the SOF desorption amount calculation unit 40 calculates the SOF desorption amount from the filter 13 in the normal operation mode, whereas the HC desorption amount calculation unit 51 switches to the rich spike mode (when the rich spike process starts). ) In that the amount of SOF desorption from the filter 13 is calculated. Here, since HC supplied from the filter to the NOx trap catalyst during the rich spike process is a problem, it is necessary during the rich spike process separately from the SOF desorption amount calculation unit 40 required during the normal operation mode. An HC desorption amount calculation unit 51 is provided.

  The characteristics of the HC desorption amount of the filter 13 during the rich spike process are specifically shown in FIGS. As shown in FIG. 11, the HC desorption amount of the filter 13 is large when the filter temperature DPFtemp at the time of switching to the rich spike mode is a constant condition, and the SOF adsorption amount of the filter 13 at the time of switching to the rich spike mode is large. It is a value that becomes larger. This is because the HC desorption amount of the filter 13 during the rich spike process increases as the SOF adsorption amount of the filter 13 during the switching to the rich spike mode increases.

  The reason why the HC desorption amount of the filter 13 during the rich spike process increases as the SOF adsorption amount of the filter 13 at the time of switching to the rich spike mode increases is considered to be due to physical adsorption of the HC to the filter 13. I don't really understand. However, according to the experimental results, the larger the SOF adsorption amount of the filter 13 at the time of switching to the rich spike mode, the greater the HC desorption amount of the filter 13 at the time of rich spike processing. FIG. 11 shows the results of this experiment.

  As shown in FIG. 12, the HC desorption amount of the filter 13 is such that the filter temperature DPFtemp when switching to the rich spike mode is predetermined when the SOF adsorption amount of the filter 13 when switching to the rich spike mode is constant. It is a value that increases in a range from a value 1 (for example, about 100 ° C.) to a predetermined value 2 (for example, about 250 ° C.). This is because SOF actively desorbs from the filter 13 when the filter temperature DPFtemp at the time of switching to the rich spike mode exceeds the predetermined value 1. The reason why the SOF desorption amount decreases in the region where the filter temperature DPFtemp at the time of switching to the rich spike mode exceeds the predetermined value 2 is that no SOF remains in the filter 13. The characteristics of FIG. 12 are the same as the characteristics of FIG.

The excess air ratio correction amount calculation unit 52 calculates the excess air ratio correction amount Δλ based on the HC desorption amount of the filter 13 during the rich spike process and the operating point when switching to the rich spike mode (at the start of the rich spike process). [Anonymous] is calculated. The excess air ratio correction unit 53 (excess air ratio correction means) adds this excess air ratio correction amount Δλ to the basic target excess air ratio tλ0 [anonymous number] at the time of the rich spike process to increase the target air excess at the time of the rich spike process. The rate tλ [anonymous number] is calculated. In other words,
tλ = tλ0 + Δλ (5)
The target excess air ratio tλ at the time of rich spike processing is calculated by the following formula. The basic target excess air ratio rλ0 at the time of rich spike processing on the right side of the equation (5) is 1.0 (value corresponding to the theoretical air-fuel ratio). The basic target excess air ratio tλ0 is a target excess air ratio at the time of rich spike processing in a layout in which the filter 13 is not provided on the upstream side of the NOx trap catalyst 15.

  As shown in FIG. 13, the excess air ratio correction amount Δλ is the HC desorption of the filter 13 during the rich spike process when the conforming point engine speed Nemat, the conforming point fuel injection amount Qfmat, and the conforming point cylinder intake air amount Qacat. The quantity is zero and zero. Further, the excess air ratio correction amount Δλ increases as the HC desorption amount of the filter 13 during the rich spike processing increases with a positive value.

  When the excess air ratio correction amount Δλ is calculated as a positive value, the target excess air ratio tλ becomes larger than 1.0. That is, the post-injection amount for performing the rich spike process is corrected to the decrease side as compared with the case where the excess air ratio correction amount Δλ is zero. The reason why the excess air ratio correction amount Δλ is increased by a positive value as the HC desorption amount of the filter 13 at the time of rich spike processing increases by a positive value is as follows. That is, since the HC desorption amount of the filter 13 is excessively supplied to the NOx trap catalyst 15 as a reducing agent during the rich spike processing, this extra reducing agent is subtracted from the reducing agent by post injection. is there.

  As described above, regarding the HC desorption amount of the filter 13 during the rich spike processing, the excess air ratio correction amount Δλ is a value for correcting the excess air ratio of the exhaust from 1.0 to the increase side. In other words, the target excess air ratio tλ at the time of the rich spike process is not a value that is corrected to a decrease side from 1.0.

  “Fit point fuel injection amount Qfmat” is the fuel injection amount Qfuel at the fit point, “Fit point cylinder intake air amount Qacat” is the cylinder intake air amount Qacat at the fit point, and “Fit point engine rotation speed Nemat” is fit. It is the engine speed at a point. If rich spike processing is performed at the matching point, an air-fuel mixture having a basic target excess air ratio tλ0 during rich spike processing can be obtained. That is, the “conformity point” is an engine operating point at which the basic target excess air ratio tλ0 during the rich spike process can be obtained in the layout without the filter 13 on the upstream side of the NOx trap catalyst 15.

  Here, when it is time to regenerate the NOx trap catalyst 15 in the normal operation mode, the engine operating point determined from the fuel injection amount Qfuel, the cylinder intake air amount Qac, and the engine rotational speed Ne is not always at the appropriate point. That is, in the case of a layout that does not include the filter 13 on the upstream side of the NOx trap catalyst 15, when the rich spike process is performed at an engine operation point that is out of the conformity point in the normal operation mode, the basic target excess air ratio during the rich spike process rλ0 may not be obtained.

  Therefore, in the present embodiment, the excess air ratio correction amount Δλ is also calculated according to the engine operating point at the time of switching to the rich spike mode (at the start of the rich spike process). This is because the basic target air excess ratio tλ0 at the time of rich spike processing even when the rich spike processing is performed at an engine operating point deviating from the matching point in the case of a layout without the filter 13 on the upstream side of the NOx trap catalyst 15. This is to obtain an air-fuel mixture. Here, the engine operating point at the time of switching to the rich spike mode is determined from the engine speed Ne, the fuel injection amount Qfuel, and the cylinder intake air amount Qac at the time of switching to the rich spike mode. Accordingly, the excess air ratio correction amount Δλ is also calculated in accordance with the fuel injection amount Qfuel, the cylinder intake air amount Qac, and the engine rotational speed Ne when switching to the rich spike mode.

  The characteristics of the excess air ratio correction amount Δλ based on the operating point (Ne, Qfuel, Qac) at the time of switching to the rich spike mode are specifically shown in FIG. 14, FIG. 15, and FIG.

  As shown in FIG. 14, the excess air ratio correction amount Δλ is such that the actual fuel injection amount Qfuel is when the engine speed Ne is the conforming point engine rotational speed Nemat and the cylinder intake air amount Qac is the conforming point cylinder intake air amount Qacmat. The value increases as the value increases outside the conforming point fuel injection amount Qfmat. This is because if the actual fuel injection amount Qfuel at the time of switching to the rich spike mode is larger than the conforming point fuel injection amount Qfmat, the actual fuel injection amount at the time of rich spike processing is increased by the increased fuel injection amount. Since the excess air ratio is smaller than the basic target excess air ratio tλ0 during the rich spike process, the actual excess air ratio during the rich spike process is returned to the basic target excess air ratio rλ0 during the rich spike process. is there.

  Further, as shown in FIG. 14, the excess air ratio correction amount Δλ is a value that becomes negative and increases as the actual fuel injection amount Qfuel becomes smaller than the matching point fuel injection amount Qfmat. If the actual fuel injection amount Qfuel at the time of switching to the rich spike mode is smaller than the compatible fuel injection amount Qfmat, the actual fuel injection amount at the time of rich spike processing is reduced by the amount of the smaller fuel injection amount. Since the excess air ratio becomes larger than the basic target excess air ratio tλ0 during the rich spike processing, the actual excess air ratio during the rich spike processing is returned to the basic target excess air ratio tλ0 during the rich spike processing. is there.

  As shown in FIG. 15, the excess air ratio correction amount Δλ corresponds to the actual cylinder intake air amount Qac when the engine speed Ne is the conforming point engine rotational speed Nemat and the fuel injection amount Qfuel is the conforming point fuel injection amount Qfmat. It is a value that becomes negative and larger as it becomes larger than the point cylinder intake air amount Qacmat. This is because when the actual cylinder intake air amount Qac at the time of switching to the rich spike mode is larger than the compatible cylinder intake air amount Qacmat, the amount of the increased cylinder air amount is at the time of rich spike processing. Therefore, the actual excess air ratio during the rich spike processing is returned to the basic target excess air ratio tλ0 during the rich spike processing. Because.

  Further, as shown in FIG. 15, the excess air ratio correction amount Δλ is a value that increases as the actual cylinder intake air amount Qac becomes smaller than the matching point cylinder intake air amount Qacmat and becomes larger. This is because, when the actual cylinder intake air amount Qac at the time of switching to the rich spike mode is smaller than the compatible point cylinder intake air amount Qacmat, the amount of the reduced cylinder air amount corresponds to the time of rich spike processing. Therefore, the actual excess air ratio during the rich spike process is returned to the basic target excess air ratio tλ0 during the rich spike process. Because.

  As shown in FIG. 16, when the fuel injection amount Qfuel is the conforming point fuel injection amount Qfmat and the cylinder intake air amount Qac is the conforming point cylinder intake air amount Qacmat, the actual engine speed Ne is It is a value that becomes positive and larger as it becomes larger than the matching point engine rotation speed Nemat. This is because if the actual engine speed Ne at the time of switching to the rich spike mode is larger than the conforming engine speed Nemat, the cylinder intake air amount is increased by the increased engine speed. Since the actual excess air ratio at the time of rich spike processing decreases and becomes smaller than the basic target excess air rate tλ0 at the time of rich spike processing, the actual excess air ratio at the time of rich spike processing becomes the basic target air at the time of rich spike processing. This is to return the excess rate to tλ0.

  Further, as shown in FIG. 16, the excess air ratio correction amount Δλ is a value that becomes negative and increases as the actual engine speed Ne becomes smaller than the matching point engine speed Nemat. This is because if the actual engine speed Ne at the time of switching to the rich spike mode is smaller than the conforming engine speed Nemat, the cylinder intake air amount increases by the reduced engine speed. Therefore, the actual excess air ratio at the time of rich spike processing becomes larger than the basic target excess air ratio tλ0 at the time of rich spike processing. Therefore, the actual excess air ratio at the time of rich spike processing becomes the basic target excess air at the time of rich spike processing. This is to return to the rate tλ0.

  Thus, regarding the parameters (Ne, Qfuel, Qac) other than the HC desorption amount of the filter 13, the excess air ratio correction amount Δλ is a value on the side where the excess air ratio is increased from 1.0, and the excess air ratio is 1. It can be any value on the side of decreasing from zero.

  As described above, the purpose of calculating the excess air ratio correction amount based on the HC desorption amount of the filter 13 during the rich spike process, and the excess air ratio correction amount based on the engine operating point at the time of switching to the rich spike mode. This is different from the purpose of calculating. That is, since the air excess rate correction amount Δλ includes two different purposes, it can be configured as an air excess rate separated for each purpose. For example, as shown in FIG. 18, the excess air ratio correction amount calculation unit 52 is replaced with a first excess air ratio correction amount calculation unit 52a, a second excess air ratio correction amount calculation unit 52b, and a third excess air ratio correction amount calculation. The unit 52c, the fourth excess air ratio correction amount calculation unit 52d, and the addition unit 52e.

  In the first excess air ratio correction amount calculation unit 52a, the excess air ratio that is a value for correcting the basic target excess air ratio during the rich spike processing to the increase side based on the HC desorption amount of the filter 13 during the rich spike processing. A correction amount (first excess air ratio correction amount) Δλ1 [nameless number] is calculated.

  In the second excess air ratio correction amount calculation unit 52b, based on the fuel injection amount Qfuel at the time of switching to the rich spike mode, when the layout does not include the filter 13 on the upstream side of the NOx trap catalyst 15, the rich spike processing time An excess air ratio correction amount (second excess air ratio correction amount) Δλ2 [anonymous number] for obtaining the basic target excess air ratio is calculated.

  Based on the cylinder intake air amount Qac when switching to the rich spike mode, the third excess air ratio correction amount calculation unit 52c performs the rich spike process in the case of a layout that does not include the filter 13 on the upstream side of the NOx trap catalyst 15. The excess air ratio correction amount (third excess air ratio correction amount) Δλ3 [anonymous number] for obtaining the basic target excess air ratio is calculated.

  In the fourth excess air ratio correction amount calculation unit 52d, based on the engine rotation speed Ne when switching to the rich spike mode, the layout without the filter 13 on the upstream side of the NOx trap catalyst 15 is used during the rich spike processing. An excess air ratio correction amount (fourth excess air ratio correction amount) Δλ4 [anonymous number] for obtaining the basic target excess air ratio is calculated.

  The adding unit 52e calculates a value obtained by adding the four excess air ratio correction amounts Δλ1 to Δλ4 as an excess air ratio correction amount Δλ (= Δλ1 + Δλ2 + Δλ3 + Δλ4).

  The fuel injection amount Qfuel at the time of switching to the rich spike mode is a value proportional to the engine target torque Trq at the time of switching to the rich spike mode. Therefore, the fuel injection amount Qfuel at the time of switching to the rich spike mode may be calculated in proportion to the engine target torque Trq at the time of switching to the rich spike mode.

  The cylinder intake air amount is obtained, for example, by performing a first-order lag process on the intake air amount Qa detected by the air flow meter 28 provided in the intake passage upstream of the throttle valve 5 (known). Therefore, the first-order lag processing value at the time of switching to the rich spike mode may be set as the cylinder intake air amount Qac at the time of switching to the rich spike mode.

  Returning to FIG. 2, the post injection amount calculation unit 54 searches the table having the contents shown in FIG. 17 from the target excess air ratio tλ (= tλ0 + Δλ) at the time of the rich spike processing thus calculated, thereby obtaining the post injection amount. Qpost is calculated.

  In FIG. 17, the post-injection amount at the basic target excess air ratio tλ0 during the rich spike process is defined as “basic post-injection amount Qpost0”. The post injection amount Qpost is a value that becomes smaller than the basic post injection amount Qpost0 as the target excess air ratio tλ at the time of rich spike processing becomes larger than the basic target excess air rate tλ0 at the time of rich spike processing. This is because when tλ becomes larger than tλ0, the post injection amount Qpost is made smaller than the basic post injection amount Qpost0 so that the excess air ratio of the exhaust gas becomes larger, so that tλ can be obtained.

  Further, as shown in FIG. 17, the post injection amount Qpost is a value that becomes larger than the basic post injection amount Qpost0 as the target excess air ratio tλ during the rich spike process becomes smaller than the basic target excess air ratio tλ0 during the rich spike process. is there. This is because, when tλ becomes smaller than tλ0, the post injection amount Qpost is made larger than the basic post injection amount Qpost0 so that the excess air ratio of the exhaust gas becomes smaller, so that tλ can be obtained.

  Since the post injection amount Qpost is determined by the fuel pressure of the common rail 8 and the post injection period, the post injection period is uniquely determined when the fuel pressure of the common rail 8 is determined. For this reason, the post injection period may be determined from the post injection amount Qpost and the common rail fuel pressure at that time.

  The rich spike processing unit 55 closes the throttle valve 5 to a predetermined opening when switching to the rich spike mode, and performs post injection using the post injection amount Qpost (or post injection period) calculated in this way. .

  Here, the effect of this embodiment is demonstrated.

  FIG. 19 shows how the HC concentration changes during the rich spike process in the operation region where SOF is generated relatively in comparison with the layout including the filter 13 on the upstream side of the NOx trap catalyst 15. Yes. Among these, the case where the excess air ratio correction at the time of rich spike processing of the present invention is not performed is shown as a comparative example in the upper part of FIG. Each is shown.

  In FIG. 19, the “required value” indicated by the broken line is a required value of the HC concentration necessary for regenerating the NOx trap catalyst 15. According to the present embodiment, the excess air ratio is corrected to the increase side by the amount of HC desorbed from the filter 13 during the rich spike process, so that the basic excess air ratio tλ0 during the rich spike process is obtained. . For this reason, as indicated by the solid line in the lower part of FIG. 19, the HC concentration at the filter outlet (NOx trap catalyst inlet) is below this required value. As a result, the HC concentration at the tail pipe outlet can be suppressed as shown by the two-dot chain line in the lower part of FIG.

  On the other hand, in the comparative example, the amount of HC desorbed and supplied from the filter 13 during the rich spike process is not considered. For this reason, the amount of HC desorbed from the filter 13 is excessively supplied, which exceeds the required value of the HC concentration at the filter outlet (NOx trap catalyst inlet) as shown by the solid line in the upper part of FIG. For this reason, HC corresponding to the area indicated by hatching in the upper part of FIG. 19 becomes excessively supplied and flows downstream of the NOx catalyst 15 without being used as a reducing agent in the NOx trap catalyst 15. As a result, as indicated by a two-dot chain line in the upper part of FIG. 19, the HC concentration at the tail pipe outlet is higher than that in the present embodiment.

  As described above, according to this embodiment, the filter 13 that collects particulates composed of dry soot and SOF present in the inflowing exhaust gas is disposed upstream of the exhaust passage 10, and the excess air ratio of the exhaust gas is the stoichiometric air-fuel ratio. A NOx trap catalyst 15 that traps NOx in the exhaust that flows in when it is larger than a considerable value, and desorbs and purifies the trapped NOx when the excess air ratio of the exhaust is equal to or greater than the theoretical air-fuel ratio, is provided in the exhaust passage 10. Provided downstream, when the NOx trap catalyst 15 is in the regeneration period, the excess air ratio equal to or less than the value corresponding to the theoretical air-fuel ratio is set as the basic target excess air ratio tλ0, and rich so that this basic target excess air ratio tλ0 is obtained. In a diesel engine exhaust aftertreatment device that performs spike processing, the basic target for rich spike processing in the operating range where a relatively large amount of SOF occurs Since the excess air ratio correcting means (53 in FIG. 2) for correcting the excess air ratio tλ0 to the increasing side is provided, a layout in which the filter 13 is provided upstream of the exhaust passage 10 and the NOx trap catalyst 15 is provided downstream of the exhaust passage 10 is provided. Even in this case, excessive supply of the reducing agent amount to the NOx trap catalyst 15 can be suppressed and HC discharged downstream of the NOx trap catalyst 15 can be reduced.

  According to the present embodiment, the operation region in which a relatively large amount of SOF is generated is a low temperature region in which the combustion temperature in the cylinder is relatively low or a low load region in which the engine load is relatively small. Even if the rich spike processing is performed in a low temperature range where the temperature is relatively low or a low load range where the engine load is relatively small, it is possible to suppress an excessive supply of the reducing agent amount to the NOx trap catalyst 15.

  According to the present embodiment, the excess air ratio correcting means is configured to adjust the SOF adsorption amount of the filter 13 when switching to the rich spike mode (when rich spike processing is started) and when switching to the rich spike mode (starting rich spike processing). HC desorption amount calculation unit 51 (HC desorption amount calculation means) for calculating the HC desorption amount of the filter 13 in the rich spike mode (during rich spike processing) based on the filter temperature DPFtemp at the time) The excess air ratio correction amount calculation unit 52 calculates the excess air ratio correction amount Δλ for correcting the basic target excess air ratio tλ0 during the rich spike processing to the increase side according to the HC desorption amount of the rich spike mode. (Excess air ratio correction amount calculating means), so that the SOF absorption of the filter 13 in the rich spike mode is provided. Regardless of the temperature DPFtemp of the filter 13 in the amount and the rich spike mode, it is possible to provide just enough to HC desorption amount of the filter 13 in the rich spike mode.

  According to the present embodiment, the excess air ratio correction amount calculation unit 52 (the excess air ratio correction amount calculation means) corrects the excess air ratio as the HC desorption amount of the filter 13 in the rich spike mode (during rich spike processing) increases. Since the amount is increased (see FIG. 13), the amount of reducing agent that is not excessive or insufficient can be supplied to the NOx trap catalyst 15 regardless of the HC desorption amount of the filter 13 in the rich spike mode.

  According to the present embodiment, the excess air ratio correction amount Δλ is calculated by the excess air ratio correction amount calculation unit 52 even in accordance with the engine operating point at the time of switching to the rich spike mode (when the rich spike process is started). Even if rich spike processing is performed at different engine operating points, the amount of reducing agent to the NOx trap catalyst 15 can be given without excess or deficiency.

  According to the present embodiment, the HC desorption amount of the filter 13 at the time of the rich spike process is a value that increases as the SOF adsorption amount of the filter 13 at the time of switching to the rich spike mode (at the start of the rich spike process) increases. Therefore (see FIG. 11), even if the SOF adsorption amount of the filter 13 at the time of switching to the rich spike mode is different, the HC desorption amount from the filter 13 at the time of the rich spike process can be given without excess or deficiency.

  According to the present embodiment, the SOF adsorption amount calculator 36 adds the SOF adsorption amount of the filter 13 to the SOF amount flowing into the filter 13 in the normal operation mode (not during the rich spike process) at a constant cycle. Since the subtraction unit 41 subtracts the SOF amount desorbed from the filter 13 at a constant period in the normal operation mode (not in the rich spike process), the SOF adsorption is performed every moment in the normal operation mode. The amount can be accurately grasped. For this reason, the excess air ratio correction can be appropriately performed no matter what timing in the normal operation mode the rich spike processing is started.

  According to the present embodiment, when the value obtained by adding the SOF amount flowing into the filter 13 at a constant period exceeds the SOF adsorption capacity of the filter 13 in the normal operation mode (not during the rich spike process), this SOF adsorption capacity. Therefore, the SOF adsorption amount that is not actually adsorbed by the filter 13 can be prevented from being calculated.

  According to the present embodiment, since the multiplication unit 35 calculates the SOF amount flowing into the filter 13 in the normal operation mode (not during the rich spike processing) based on the engine out SOF amount, the engine out SOF amount is Even if they are different, the SOF amount flowing into the filter 13 can be given without excess or deficiency.

  According to the present embodiment, the amount of SOF desorbed from the filter 13 during the normal operation mode (not during the rich spike process) is set to at least the actual excess air ratio rλ, the temperature DPFtemp of the filter 13, and the exhaust volume velocity SV. Since the SOF desorption amount calculation unit 40 calculates based on one, even if the actual excess air ratio rλ, the temperature DPFtemp of the filter 13 and the volume velocity SV of the exhaust gas are different, the SOF desorption amount calculation unit 40 desorbs from the filter 13 in the normal operation mode. The amount of SOF to be released can be given without excess or deficiency.

DESCRIPTION OF SYMBOLS 1 Engine 5 Throttle valve 9 Fuel injection valve 13 Filter 15 NOx trap catalyst 21 Engine control unit 30 SOF adsorption amount calculation part 50 Post injection amount calculation part 51 HC desorption amount calculation part (HC desorption amount calculation means)
52 Excess air ratio correction amount calculation unit (excess air ratio correction amount calculation means)
53 Excess air ratio correction unit (excess air ratio correction means)
54 Post injection amount calculation unit

Claims (10)

NOx in the exhaust gas flowing in when the excess air ratio of the exhaust gas is larger than the value corresponding to the stoichiometric air-fuel ratio, a filter that collects particulates composed of dry soot and SOF present in the flowing exhaust gas is disposed upstream of the exhaust passage. And a NOx trap catalyst that desorbs and purifies NOx trapped when the excess air ratio of the exhaust gas is equal to or higher than the theoretical air-fuel ratio, and is provided downstream of the exhaust passage.
When it is time to regenerate the NOx trap catalyst, the excess air ratio below the value corresponding to the stoichiometric air-fuel ratio is set as the basic target excess air ratio, and the diesel engine that performs rich spike processing to obtain this basic target excess air ratio is obtained. In the exhaust aftertreatment device,
An exhaust aftertreatment device for a diesel engine, comprising an excess air ratio correction means for correcting the basic target excess air ratio during the rich spike process to an increase side in an operating region where a relatively large amount of SOF is generated.   2. The diesel engine according to claim 1, wherein the operation region in which a relatively large amount of SOF is generated is a low temperature region in which the combustion temperature in the cylinder is relatively low or a low load region in which the engine load is relatively small. Engine exhaust aftertreatment device. The excess air ratio correcting means is
HC desorption amount calculating means for calculating the HC desorption amount of the filter during the rich spike processing based on the SOF adsorption amount of the filter at the start of the rich spike processing and the temperature of the filter at the start of the rich spike processing; ,
An excess air ratio correction amount calculation that calculates an excess air ratio correction amount for correcting the basic target excess air ratio during the rich spike processing to the increase side according to the calculated HC desorption amount during the rich spike processing. The exhaust aftertreatment device for a diesel engine according to claim 1, further comprising: means.   The after-exhaust of a diesel engine according to claim 3, wherein the excess air ratio correction amount calculation means increases the excess air ratio correction amount as the amount of HC desorption of the filter during the rich spike processing increases. Processing equipment.   The exhaust aftertreatment device for a diesel engine according to claim 3, wherein the excess air ratio correction amount is also calculated according to an engine operating point at the start of rich spike processing.   5. The diesel engine according to claim 3, wherein the HC desorption amount of the filter during the rich spike processing is a value that increases as the SOF adsorption amount of the filter at the start of the rich spike processing increases. Exhaust aftertreatment device.   The SOF adsorption amount of the filter is added at a constant cycle to the SOF amount flowing into the filter when not during the rich spike processing, and the SOF amount desorbed from the filter when not during the rich spike processing is constant. The exhaust aftertreatment device for a diesel engine according to claim 3, wherein the exhaust aftertreatment device is calculated by subtraction.   8. The method according to claim 7, wherein when the value obtained by adding the SOF amount flowing into the filter at a certain period when the rich spike processing is not performed exceeds the SOF adsorption capacity of the filter, the SOF adsorption capacity is limited. Diesel engine exhaust aftertreatment system.   The exhaust aftertreatment device for a diesel engine according to claim 7 or 8, wherein the SOF amount flowing into the filter when not during the rich spike processing is calculated based on the engine out SOF amount.   The amount of SOF desorbed from the filter when not during the rich spike processing is calculated based on at least one of an actual excess air ratio, a temperature of the filter, and a volume velocity of the exhaust gas. Diesel engine exhaust aftertreatment device.

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