JP2005240587A - Exhaust emission control device of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively reduce particulates and NOx even immediately after the regeneration of an exhaust gas trap. <P>SOLUTION: This exhaust emission control device of a diesel engine comprises an exhaust gas recirculation means recirculating a part of the exhaust gases into an intake air, an adsorbing type NOx catalyst 13 adsorbing NOx in a lean atmosphere and releasing and reducing NOx adsorbed in a rich atmosphere, and the exhaust gas trap 14 collecting particulates in the exhaust gases. When the collected amount of the particulates by the exhaust gas trap 14 reaches a prescribed value, the exhaust gas trap 14 is regenerated. During a prescribed period after the regeneration of the exhaust gas trap 14, the recirculated amount of the exhaust gases is reduced and the sucked amount of air is reduced to a predetermined amount. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an improvement in an exhaust emission control device for a diesel engine.

  Patent Document 1 discloses that exhaust gas recirculation is performed to reduce NOx discharged from a diesel engine, and that particulates (PM) contained in the exhaust gas are collected by an exhaust trap.

  By increasing the exhaust gas recirculation rate, the NOx reduction effect increases, but on the other hand, the particulates in the exhaust gas tend to increase. Therefore, the particulates are collected by the exhaust trap, and the collected particulates are supplemented. When the collection amount reaches a predetermined value, for example, the fuel injection amount is temporarily increased to raise the exhaust temperature, and the exhaust trap is regenerated.

NOx is relatively reduced by exhaust gas recirculation, but in order to further reduce the NOx emission level, NOx in the exhaust is adsorbed during operation with lean air-fuel ratio, and NOx is released and reduced in a rich atmosphere. May have a catalyst. When the amount of NOx adsorbed in the lean atmosphere reaches a certain amount, rich spike is performed, and NOx is released and reduced in the NOx catalyst.
JP-A-5-133286

  Incidentally, as described above, it is known that when the exhaust trap regeneration process for removing the collected particulates by combustion is performed, the particulate collection efficiency decreases for a while after the regeneration. Therefore, immediately after regeneration of the exhaust trap, the exhaust gas recirculation rate is reduced so that the particulates in the exhaust gas do not increase.

  However, as the exhaust gas recirculation rate decreases, the amount of NOx discharged increases during this period, and therefore the amount of NOx that must be treated with the NOx catalyst increases. However, by reducing the exhaust gas recirculation rate, the intake air amount (fresh air amount) is relatively increased and the exhaust temperature also rises. This tends to lower the NOx purification efficiency of the NOx catalyst, and therefore. There has been a problem that NOx cannot be effectively reduced immediately after regeneration of the exhaust trap.

  Accordingly, an object of the present invention is to effectively reduce particulates and NOx even immediately after regeneration of an exhaust trap.

  The present invention relates to an exhaust gas recirculation means for recirculating a part of exhaust gas into intake air in an diesel engine, and an adsorption type installed in an exhaust passage for adsorbing NOx in a lean atmosphere and releasing / reducing NOx adsorbed in a rich atmosphere. NOx catalyst, an exhaust trap installed in the exhaust passage and collecting particulates in the exhaust, and when the particulate collection amount in the exhaust trap reaches a predetermined value, the exhaust trap is regenerated. After regeneration of the exhaust trap, Control means for reducing the exhaust gas recirculation amount and reducing the intake air amount to a predetermined amount during the predetermined period.

  Immediately after regenerating the exhaust trap, the particulate collection efficiency decreases. During this time, the exhaust gas recirculation rate is decreased, the particulates in the exhaust gas itself are decreased, and the increase in NOx due to the decrease in the exhaust gas recirculation rate is not. By reducing the intake air amount, it is possible to efficiently purify NOx while maintaining the high purification efficiency of the NOx catalyst, in which the purification efficiency is good in a region where both the intake air amount and the exhaust temperature are lowered. . That is, particulates and NOx can be effectively reduced even immediately after regeneration of the exhaust trap.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

  First, the overall configuration will be described with reference to FIG. 1. Reference numeral 1 denotes a diesel engine main body, and high-pressure fuel is directly applied to a fuel injection valve 2 of each cylinder by a common rail fuel injection device 3. Supplied. Each fuel injection valve 2 opens and closes in response to an injection signal from an engine control unit (ECU) 10 to inject high-pressure fuel into the cylinder. The ECU 10 also performs various controls as will be described later.

  An intake passage 5 is connected to an intake collector 4 connected to each intake port of the diesel engine body 1, and a compressor 6 a of a variable nozzle type turbocharger 6 for supercharging from the upstream side is connected to the intake passage 5. An intercooler 7 for cooling the air and an intake throttle valve 8 for controlling the intake air amount are installed.

  Further, from the upstream side of the exhaust passage 11, the turbine 6 b of the turbocharger 6, the oxidation catalyst 12 that oxidizes unburned components in the exhaust, NOx in the exhaust during the lean operation is adsorbed, and is adsorbed by a rich spike. An adsorption-type NOx catalyst 13 that releases and reduces the NOx that has been exhausted and an exhaust trap (DPF) 14 that collects particulates (PM) in the exhaust gas are sequentially arranged.

  In addition, an exhaust gas recirculation passage 21 that branches from the exhaust passage 11 upstream of the turbine 6b and is connected to the intake collector 4 is provided, and an exhaust gas recirculation control valve 22 is installed in the exhaust gas recirculation passage 21 according to operating conditions. The amount of exhaust gas recirculated during intake is controlled.

  The ECU 10 detects an engine speed sensor 31 for detecting the engine speed, an accelerator position sensor 32 for detecting an accelerator pedal position, and an exhaust pressure between the NOx catalyst 13 and the DPF 14 in the exhaust passage 11. Detection signals from an exhaust pressure sensor 33, an exhaust air / fuel ratio sensor 34 for detecting an exhaust air / fuel ratio downstream of the DPF 14, a temperature sensor 35 for the DPF 14, a temperature sensor 36 for the NOx catalyst 13 and the like are input, and based on these signals, the turbo A signal for controlling the opening of the variable nozzle vane of the charger 6, a signal for controlling the opening of the exhaust gas recirculation control valve 22, a signal for controlling the opening of the intake throttle valve 8, and the fuel injection The signal for controlling the fuel injection amount by the valve 2 and the rich spike timing of the NOx catalyst 13 are judged to perform the rich spike control. A signal for operating the fuel injection valve 2 and a signal for operating the fuel injection valve 2 for determining the regeneration timing of the DPF 14 and supplying the fuel necessary for increasing the exhaust temperature for regeneration are calculated and output. To do.

  Further, after the regeneration of the DPF 14, the ECU 10 adjusts the opening degree of the exhaust gas recirculation control valve 22 for a predetermined period after the regeneration in order to reduce the PM emission amount as the PM collection efficiency by the DPF 14 decreases. In order to reduce the exhaust gas recirculation amount, on the other hand, in order to prevent a decrease in the purification efficiency of the NOx catalyst 13 due to a relative increase in the intake air amount and an increase in the exhaust temperature, the opening degree of the intake throttle valve 8 is reduced. By controlling the throttle or the opening of the variable nozzle vane of the turbocharger 6 as necessary to reduce the intake air amount, it is possible to effectively reduce the PM emission amount without deteriorating the fuel consumption.

  Hereinafter, the above-described control executed by the ECU 10 will be described with reference to the flowchart of FIG.

  First, in FIG. 2, in step S1, the engine operating state is determined based on signals from the rotation speed sensor 31, accelerator opening sensor 32, exhaust pressure sensor 33, exhaust air / fuel ratio sensor 34, DPF temperature sensor 35, NOx catalyst temperature sensor 36, and the like. Based on these values, the NOx adsorption amount adsorbed on the NOx catalyst 13 in step S2 is obtained by calculation. This calculation method is a method of adding the NOx adsorption amount every time it travels an integrated value of the engine speed or a predetermined distance, as described in, for example, page 6 of Japanese Patent Publication No. 2600492. Also good.

  In step S3, the amount of sulfur deposited on the NOx catalyst 13 is calculated. Here, the amount of accumulated sulfur can be estimated from the integrated value of the engine speed according to the above publication.

  In step S4, the particulate collection amount to the DPF 14 is calculated. The particulate collection amount can be predicted by, for example, detecting the exhaust pressure on the inlet side of the DPF 14 with the exhaust pressure sensor 33, and the exhaust pressure of the DPF 14 relatively increases as the particulate collection amount increases. It is also possible to estimate the particulate collection amount by combining the travel distance from the previous regeneration of the DPF 14, the engine speed and the exhaust pressure.

  In step S5, it is determined whether the DPF 14 is in the regeneration mode. The regeneration mode is performed when the collected amount of the particulate accumulated in the DPF 14 reaches a predetermined amount, and the collected particulate is burned and removed by raising the exhaust gas temperature. During the playback mode, the playback request flag reg = 1, and the playback mode is executed according to the flowchart of FIG. The playback mode will be described later.

  In step S6, it is determined whether or not the sulfur poisoning release mode during regeneration of the NOx catalyst is in progress. In the sulfur poisoning release mode, the sulfur poisoning release request flag desul is set (desul flag = 1), so that sulfur is removed by combustion according to the flowchart of FIG. 4 as will be described later.

  In step S7, it is determined whether or not the NOx catalyst 13 is in the rich spike mode. The rich spike is performed when the amount of NOx accumulated on the NOx catalyst 13 at the time of lean operation reaches a predetermined value, and the NOx adsorbed and held on the NOx catalyst 13 is released due to the enrichment of the air-fuel ratio and is simultaneously reduced. The When the NOx catalyst regeneration request (rich spike request) sp flag is set, rich spike control is performed according to the flowchart of FIG. 5 described later.

  In step S8, it is determined whether the DPF 14 is being regenerated and the melt prevention mode is in effect when the NOx catalyst 13 is released from sulfur poisoning. In the melting prevention mode, the melting prevention request flag reg is reached, and the melting prevention mode is executed according to the flowchart of FIG.

  In step S9, it is determined whether or not the amount of particulate (PM) accumulated in the DPF 14 has reached a predetermined amount PM and the regeneration time of the DPF 14 has come. The determination value PM1 is set, for example, as a threshold value of exhaust pressure shown in FIG. 11, and is determined based on the fuel injection amount Q (accelerator opening degree) and the engine speed Ne at that time. When it exceeds, the regeneration time is determined (the threshold value increases as Q and Ne increase, respectively). However, separately from this, the regeneration time may be determined when the travel distance from the previous regeneration exceeds a predetermined value and exceeds the exhaust pressure threshold. If it is determined that the regeneration time is reached, the process proceeds to step S501 in the flowchart of FIG. 7, and the regeneration request flag reg flag = 1 is set and a regeneration request for the DPF 14 is issued.

  In step S10, the particulate collection amount collected by the DPF 14 reaches the predetermined value PM2, the target exhaust gas recirculation rate (EGR rate) reduction mode is changed to the normal EGR rate mode, and the intake air amount restriction control is performed. It is determined whether it is time to cancel. During a predetermined period immediately after the regeneration of the DPF 14, the particulate collection efficiency decreases. During this period, the exhaust gas recirculation rate is reduced to reduce the particulate discharge amount. As the exhaust gas temperature increases and the exhaust gas temperature rises, the purification efficiency of the NOx catalyst 13 decreases. Therefore, in order to prevent this, the intake air amount is limited.

  The determination as to whether or not the particulate collection amount has reached a predetermined value PM2 is set, for example, as the exhaust pressure threshold value shown in FIG. 12, and the fuel injection amount Q (accelerator opening) and engine rotation at that time are set. When the exhaust pressure threshold determined based on the number Ne is exceeded, it is determined that the EGR rate is to be changed. The exhaust pressure threshold value corresponding to the predetermined value PM2 is such that the particulate collection is resumed from the state immediately after the DPF 14 is regenerated, and the particulate collection efficiency is increased due to some particulate collection. This corresponds to the exhaust pressure upstream of the DPF 14 when returning to the normal state (see FIG. 20), which is naturally much smaller than the PM1.

  In this case, according to the flowchart of FIG. 8, the lowegr flag = 0, which will be described later, is set in step S601, the EGR rate is returned to the normal value in step S602, and the intake air amount restriction control is canceled in step S603.

  Next, returning to FIG. 2, in step S11, it is determined whether or not the amount of sulfur accumulated on the NOx catalyst 13 has reached the predetermined value SNM1 and the poisoning release time has come. When the poisoning amount reaches a predetermined value, a poisoning release request is issued with the sulfur poisoning release request flag desul = 1 in step S701 according to the flowchart of FIG.

  In step S12, it is determined whether the NOx amount adsorbed on the NOx catalyst 13 has reached a predetermined value NOx1 and NOx regeneration is necessary. When NOx regeneration, that is, when the air-fuel ratio is temporarily rich and NOx is released from the NOx catalyst 13 and the reduction process is reached, the NOx regeneration request flag sp = 1 is set in step S801 according to the flowchart of FIG. Make a request for a rich spike.

  Next, the case where the regeneration request flag reg flag = 1 is reached in step S5 of FIG. 2 and the DPF 14 is regenerated when the particulate collection amount reaches a predetermined value will be described with reference to FIG.

  In step S101, the exhaust (excess air ratio) λ is controlled to a target value necessary for regeneration of the DPF 14. This exhaust λ is also shown in FIG. 15, but becomes smaller as the amount of accumulated particulates increases. The target exhaust λ is controlled by adjusting the opening of the intake throttle valve 8, and as shown in FIG. 13, the target intake air amount (intake air amount) when λ = 1 is the fuel injection amount Q. The larger the rotation speed Ne and the engine rotation Ne, the larger.

  In step S102, it is determined whether or not the temperature of the regenerating DPF 14 is equal to or higher than the target upper limit value T1, and if it exceeds the upper limit value, the process proceeds to step S112 and the fuel post-injection amount is decreased by a predetermined amount. Lower.

  If the upper limit value is not exceeded, it is determined in step S103 whether the temperature of the DPF 14 is higher than the target lower limit value T2, and if it is less than the lower limit value, the process proceeds to step S111 and the fuel post injection amount is set to a predetermined amount. Just increase the amount and raise the temperature. As shown in FIG. 16, the unit injection amount of the post injection is determined according to the fuel injection amount (main injection amount) and the engine speed at that time.

  On the other hand, when the temperature of the DPF 14 falls between the upper limit value and the lower limit value, the process proceeds to step S104, and it is determined whether the reference time tdpfreg has elapsed from the first post-injection t1. . When the reference time elapses, the particulates collected in the DPF 14 are reliably burned and removed.

  When the reference time has elapsed, it is determined that the regeneration has ended, the process proceeds to step S105, the post injection is stopped, and the heating of the DPF 14 is stopped. In step S106, since the reproduction mode is completed, the reg flag = 0 is set.

  In step S107, although the regeneration mode is finished, if the exhaust λ is suddenly increased when the particulate unburned residue is in the DPF 14, the particulate may burn at a stretch in the DPF 14 and may be melted. In order to enter the melting prevention mode of the DPF 14, the rec flag = 1 is set.

  In step S108, immediately after the regeneration of the DPF 14, the particulate collection efficiency by the DPF 14 decreases as shown in FIG. 20, so that the target exhaust gas recirculation rate is decreased as shown in FIG. However, the generation of particulates itself is suppressed. In FIG. 17, the solid line is the normal recirculation rate characteristic line during normal exhaust gas recirculation, and the dotted line is the constant recirculation characteristic line when exhaust gas recirculation is reduced. It is.

  In step S109, in order to maintain the high purification efficiency of the NOx catalyst 13 as shown in FIG. 21, the opening of the variable nozzle of the turbocharger 6 is opened as shown in FIG. Decrease to In FIG. 18, the solid line is the variable nozzle opening during normal operation, and the dotted line is the characteristic line of the variable nozzle opening when exhaust gas recirculation is reduced. The larger the number in the figure, the larger the nozzle opening. Decrease. The target intake air amount can also be reduced by reducing the opening of the intake throttle valve 8 as shown in FIG.

  The target intake air amount is set so that the purification efficiency of the NOx catalyst 13 shown in FIG. 21 is high, but the target intake air amount is corrected based on the actual temperature of the NOx catalyst 13. For example, when the catalyst temperature at that time is high, the amount of decrease in the intake air amount is increased. On the other hand, when the catalyst temperature is not so high, the amount of decrease in the intake air amount is decreased.

  In step S110, the target exhaust gas recirculation rate is decreased and the mode is shifted to a mode for increasing the purification efficiency of the NOx catalyst 13, so that the lowegr flag = 1 is set until the particulate collection efficiency of the DPF 14 returns to the normal state after the regeneration of the DPF 14. Maintains a low exhaust gas recirculation rate and a low intake air amount mode.

  With reference to FIG. 4, the sulfur poisoning release mode after step S <b> 6 in FIG. 2 will be described.

  In step S201, since the amount of sulfur deposited on the NOx catalyst 13 has reached a predetermined amount, the exhaust λ is controlled to stoichiometric (exhaust λ = 1). The opening degree of the intake throttle valve 8 is adjusted so that the target air amount shown in FIG.

  In step S202, it is determined whether the temperature of the NOx catalyst 13 is higher than a predetermined value T3. For example, when a Ba-based adsorption type NOx catalyst is provided, in order to release sulfur poisoning, it is necessary to set the temperature to 600 ° C. or higher in a rich to stoichiometric atmosphere. Therefore, the predetermined value T3 is set to 600 ° C. or higher. If the catalyst temperature is lower than the predetermined value, the process proceeds to step S209 to perform post injection by a predetermined amount to increase the temperature. However, although the exhaust λ varies due to the post-injection, the target exhaust λ and the target catalyst temperature (catalyst bed temperature) are obtained by adjusting the intake air amount again in step S201.

  When the catalyst temperature is equal to or higher than the predetermined value T3, it is determined whether or not a predetermined time tdesul has elapsed in step S203, and the sulfur poisoning release is executed until it elapses.

  When the predetermined time tdesul elapses, it is determined that the sulfur poisoning has been cancelled, and the stoichiometric operation is canceled in step S204. In step S205, although the sulfur poisoning release mode is finished, if the exhaust λ is suddenly increased under such high-temperature exhaust conditions (λ> 1), the particulates accumulated in the DPF 14 are burned at once. Since the DPF 14 may be melted, a rec flag is set to shift to the melt prevention mode.

  In step S206, since the sulfur poisoning release mode is completed, the desul flag is set to flag dusel = 0. In step S207, the sulfur poisoning release mode is also completed, so the sulfur accumulation amount on the NOx catalyst 13 is reset to zero. In step S208, the sulfur poisoning release is performed, and during this time, the NOx catalyst 13 is exposed to the stoichiometric air-fuel ratio, so that NOx regeneration (rich spike) is performed. However, NOx regeneration is also performed at the same time by releasing sulfur poisoning. Therefore, the flag sp = 0 as the NOx catalyst regeneration request flag is set.

  The NOx catalyst regeneration (rich spike) control mode after step S7 in FIG. 2 will be described with reference to FIG.

  In step S301, exhaust λ is at least stoichiometric or richer than this in order to release and reduce NOx adsorbed to the NOx catalyst 13. For this purpose, the fuel injection amount is temporarily increased or the intake amount is reduced. In step S302, it is determined whether the rich spike time has elapsed by a predetermined time tspike. If the predetermined time has elapsed, the rich spike is canceled in step S303, the flag sp = 0 is set, and the rich spike mode is terminated. Let

  The melt damage prevention mode of the DPF 14 in step S8 and subsequent steps in FIG. 2 will be described with reference to FIG.

  In step S401, the temperature of the DPF 14 is detected. In step S402, immediately after regeneration of the DPF 14 or immediately after high-load operation, the temperature of the DPF 14 is very high, so that the exhaust λ suddenly increases, such as when there is unburned particulates in the DPF 14. These may burn at once and the DPF 14 may be melted, so that the exhaust λ is controlled to λ <1.4, for example. As the target air amount at that time, the opening degree of the intake throttle valve 8 is feedback-controlled based on the output of the exhaust air-fuel ratio sensor 34 provided downstream of the DPF 14 so that the air amount as shown in FIG. .

  In step S403, it is determined whether or not the temperature of the DPF 14 is lower than a temperature T4 at which there is no possibility of sudden oxidation of particulates. If it becomes lower than T4, even if the oxygen concentration in the exhaust gas becomes the same as the atmosphere, it is possible to avoid melting of the DPF 14.

  In step S404, since there is no risk of melting of the DPF 14, the control of the exhaust λ is stopped. In step S405, the rec flag = 0 which is a melting prevention flag is set, and a series of control is finished.

  Next, the overall operation will be described.

  When exhaust gas from a diesel engine passes through the oxidation catalyst 12, unburned components in the exhaust gas are oxidized and removed. When the exhaust air-fuel ratio is lean in the adsorption NOx catalyst 13 downstream of the exhaust gas, NOx in the exhaust gas is adsorbed. Removed. Note that, depending on the operation state, when the exhaust air-fuel ratio is stoichiometric or rich such as at high load, NOx adsorbed on the NOx catalyst 13 is released from the catalyst and simultaneously reduced. When there is a time interval during which the exhaust air-fuel ratio becomes rich and the amount of NOx adsorbed to the NOx catalyst 13 reaches a predetermined value, the air-fuel ratio is temporarily enriched by a rich spike, whereby the NOx catalyst 13 The adsorbed NOx is released / reduced from the catalyst, that is, the catalyst is regenerated.

  Further, the particulates contained in the exhaust gas are collected by the downstream DPF 14 and are prevented from being released to the outside. When the particulate collection amount in the DPF 14 reaches a predetermined value, the exhaust particulate temperature is increased by post injection or the like, and the particulate collection is burned and removed, that is, the DPF 14 is regenerated.

  As shown in FIG. 20, when the particulate collection amount disappears due to regeneration of the DPF 14, the particulate collection efficiency of the DPF 14 decreases until the particulate collection amount is accumulated to some extent. During this time, the rate at which the particulates in the exhaust are directly released to the outside increases. The amount of particulate generation is affected by the exhaust gas recirculation rate. When the exhaust gas recirculation rate is increased to increase the NOx reduction amount, the particulate generation amount also increases.

  Therefore, immediately after the regeneration of the DPF 14, the exhaust gas recirculation rate is decreased from the normal state for a while, thereby reducing the particulate generation amount itself and compensating for the decrease in the collection efficiency in the DPF 14.

  On the other hand, the amount of NOx generated relatively increases due to the decrease in the exhaust gas recirculation rate. This is dealt with by increasing the NOx purification efficiency of the NOx catalyst 13.

  As shown in FIG. 21, the purification efficiency of the NOx catalyst 13 shows the highest value in the region where the intake air amount is small and the catalyst temperature is low. When the exhaust gas recirculation rate is decreased, the amount of intake air is relatively increased by that amount, and the exhaust gas temperature is also increased by an amount corresponding to good combustion. That is, when the exhaust gas recirculation rate is decreased, the purification efficiency of the NOx catalyst 13 is lowered, and the processing of NOx in the exhaust gas is deteriorated accordingly.

  Therefore, in this state, the variable nozzle opening of the turbocharger 6 is relatively increased to reduce the supercharging amount, and further, the opening of the intake throttle valve 8 is throttled from the fully open position to a target intake air amount. . As a result, the exhaust temperature decreases with the intake air amount, and it becomes possible to operate in a region where the purification efficiency of the NOx catalyst 13 is high, and the NOx catalyst 13 effectively increases the NOx accompanying the decrease in the exhaust gas recirculation rate. Can be processed.

  Note that the intake air amount is reduced within a range in which the exhaust air-fuel ratio (exhaust λ) maintains lean, so that the NOx adsorption capability of the NOx catalyst 13 can be maintained satisfactorily.

  The low exhaust gas recirculation and low intake air amount control is terminated when it is determined that the DPF 14 has returned to the normal state when the particulate collection amount in the DPF 14 reaches a predetermined value (PM2).

  As described above, according to the present embodiment, the particulate collection efficiency decreases immediately after the DPF 14 is regenerated, but during this period, the exhaust gas recirculation rate is decreased, the particulates themselves in the exhaust gas are decreased, and the exhaust gas recirculation is reduced. The amount of intake air was reduced to increase NOx due to the decrease in rate. For this reason, it is possible to efficiently purify NOx even under low exhaust gas recirculation by utilizing the characteristics of the NOx catalyst 13 that provides good purification efficiency in a region where both the intake air amount and the exhaust temperature decrease. Immediately after the reproduction, the particulates and NOx can be reduced.

  The reduction of the intake air amount can be realized easily and accurately by reducing the opening degree of the intake throttle valve 8 from the fully opened state, and can also be realized by relatively increasing the variable nozzle opening degree of the turbocharger 6.

  In addition, the reduction target of the intake air amount is determined according to the temperature of the NOx catalyst 13, so that a decrease in engine combustion efficiency can be suppressed to a minimum while maintaining good catalyst purification efficiency.

  The exhaust emission control device of the present invention can be applied to diesel engines for vehicles and the like.

It is a block diagram which shows embodiment of this invention. It is a flowchart which similarly shows the control content. It is a flowchart which similarly shows the control content. It is a flowchart which similarly shows the control content. It is a flowchart which similarly shows the control content. It is a flowchart which similarly shows the control content. It is a flowchart which similarly shows the control content. It is a flowchart which similarly shows the control content. It is a flowchart which similarly shows the control content. It is a flowchart which similarly shows the control content. It is a characteristic view of DPF regeneration time determination. It is a characteristic view of the exhaust gas recirculation rate decrease mode release determination. FIG. 6 is a characteristic diagram of a target intake air amount at which exhaust λ = 1. FIG. 5 is a characteristic diagram of a target intake air amount for preventing DPF melting damage. FIG. 6 is a characteristic diagram of exhaust λ during DPF regeneration. It is a characteristic view of the post injection for exhaust gas temperature rising. It is a characteristic view of the target exhaust gas recirculation rate when the exhaust gas recirculation rate is decreased. It is a characteristic view of the variable nozzle opening degree of the turbocharger when the exhaust gas recirculation rate decreases. It is a characteristic view of the intake throttle valve opening. It is a characteristic figure of the particulate collection efficiency of DPF. It is a characteristic view of the purification efficiency of the NOx catalyst.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine body 2 Fuel injection valve 5 Intake passage 6 Turbocharger 8 Intake throttle valve 10 Control unit 11 Exhaust passage 13 Adsorption type NOx catalyst 14 Exhaust trap (DPF)
21 Exhaust gas recirculation passage 22 Exhaust gas recirculation control valve

Claims (5)

In diesel engines,
Exhaust gas recirculation means for recirculating part of the exhaust gas into the intake air;
An adsorption-type NOx catalyst that is installed in the exhaust passage, adsorbs NOx in a lean atmosphere, and releases and reduces NOx adsorbed in a rich atmosphere;
An exhaust trap installed in the exhaust passage to collect particulates in the exhaust;
When the particulate collection amount to the exhaust trap reaches a predetermined value, the exhaust trap is regenerated. After regeneration of the exhaust trap, the exhaust gas recirculation amount is reduced and the intake air amount is reduced to a predetermined amount after a predetermined period. Control means to reduce,
An exhaust emission control device for a diesel engine, comprising:   The exhaust gas purification device for a diesel engine according to claim 1, wherein the reduction of the intake air amount is performed by reducing the opening of an intake throttle valve provided in the intake passage.   The exhaust gas purification device for a diesel engine according to claim 1, wherein the reduction of the intake air amount is performed by increasing a variable nozzle opening of a turbocharger that supercharges intake air.   2. The diesel engine according to claim 1, wherein the reduction of the intake air amount is performed by simultaneously controlling an opening of an intake throttle valve provided in an intake passage and a variable nozzle opening of a turbocharger that supercharges intake air. Exhaust purification equipment.   The exhaust emission control device for a diesel engine according to any one of claims 1 to 4, wherein the amount of intake air to be reduced is determined based on a temperature of the NOx catalyst.

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