JP2009150271A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure a catalyst floor temperature of an NOx reduction catalyst when an accelerator is set at off, a cylinder fuel injection amount is reduced to zero, and the operation such as an idle operation is transferred to a light load area. <P>SOLUTION: This exhaust emission control device of an internal combustion engine having the NOx reduction catalyst comprises: a variable nozzle turbocharger; an after-turbo oxidation catalyst; and a fuel adding valve. The after-turbo oxidation catalyst is disposed immediately after the variable nozzle turbocharger and on the upstream side of the NOx reduction catalyst. The fuel adding valve configures the exhaust emission control device of the internal combustion engine disposed in an exhaust manifold, and controls the nozzle opening of the variable nozzle turbocharger to the excessive restriction side. The addition of the fuel from the fuel adding valve, a post-fuel injection by the fuel injection valve, or the recirculation of exhaust gas is also performed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  In an internal combustion engine that includes a NOx reduction catalyst for purifying NOx contained in exhaust gas, adds fuel as a reducing agent, and performs NOx reduction purification, the catalyst bed temperature is raised to a certain temperature or higher. It is necessary to warm. For example, in the exhaust purification device of Patent Document 1, in the operation region of the internal combustion engine, the exhaust gas recirculation (EGR) amount is controlled, or the pilot injection or the post injection by the fuel injection valve is controlled to control the exhaust temperature. A technique for adding fuel as a reducing agent upstream of a NOx reduction catalyst is disclosed. However, the exhaust purification device of Patent Document 1 further includes means for determining the catalyst bed temperature, and when this temperature falls below a predetermined value, the fuel addition is stopped.

JP 2003-120392 A

  That is, in the exhaust gas purification apparatus of Patent Document 1, when the accelerator is turned off and the in-cylinder fuel injection amount becomes zero, the exhaust gas temperature decreases, so when shifting from the accelerator off state to a light load region such as idle operation. In addition, the catalyst bed temperature of the NOx reduction catalyst has already decreased, and the fuel addition must be stopped. In the light load region, the exhaust temperature is aimed to increase through low-temperature combustion based on exhaust gas recirculation control. However, the catalyst activation temperature has already decreased, and HC and CO emissions required for catalyst activation. Therefore, the combustion of the HC and CO with the NOx reduction catalyst does not continue, and there is a problem that white smoke is generated.

  Therefore, in order to reduce NOx in the exhaust gas, the accelerator is turned off to prevent a decrease in the catalyst bed temperature of the NOx reduction catalyst when the in-cylinder fuel injection amount becomes zero. Ensuring the catalyst bed temperature of the NOx reduction catalyst when shifting to the load region becomes an issue.

  According to the first aspect of the present invention, there is provided an exhaust purification device for an internal combustion engine including a NOx reduction catalyst, comprising a variable nozzle turbocharger, an after turbo oxidation catalyst, and a fuel addition valve, and the after turbo oxidation catalyst. Is provided immediately after the variable nozzle turbocharger and upstream of the NOx reduction catalyst, and the fuel addition valve is disposed in the exhaust manifold.

  That is, in the first aspect of the invention, the after-turbo oxidation catalyst (ATC) is disposed upstream of the NOx reduction catalyst, and the fuel is added by the fuel addition valve upstream of the after-turbo oxidation catalyst. HC and CO can be supplied. Therefore, by burning HC and CO with the after-turbo oxidation catalyst, when the accelerator is turned off and the in-cylinder fuel injection amount becomes zero, the exhaust gas temperature at the after-turbo oxidation catalyst outlet can be kept high. Therefore, the temperature of the gas flowing into the NOx reduction catalyst rises, and the catalyst bed temperature of the NOx reduction catalyst when shifting to a light load region such as idle operation can be ensured. The fuel addition upstream of the after-turbo oxidation catalyst may be performed by exhaust gas recirculation, post-injection by a fuel injection valve, or the like.

  According to the invention described in claim 2, when the accelerator is turned off and the in-cylinder fuel injection amount becomes zero, the nozzle opening of the variable nozzle turbocharger is controlled to the over-throttle side. An internal combustion engine exhaust gas purification apparatus is provided.

  That is, according to the second aspect of the present invention, when the accelerator is turned off and the in-cylinder fuel injection amount becomes zero, the intake air that has cooled is prevented from flowing into the after-turbo oxidation catalyst, and the temperature of the after-turbo oxidation catalyst is reduced. Is maintained in the vicinity of the catalyst activation temperature, and HC and CO in the exhaust gas are burned by the after-turbo oxidation catalyst. Therefore, when the accelerator is turned off and the in-cylinder fuel injection amount becomes zero, the exhaust gas temperature at the outlet of the after-turbo oxidation catalyst can be maintained high, so that the temperature of the gas flowing into the NOx reduction catalyst rises and When shifting to the light load region, the catalyst bed temperature of the NOx reduction catalyst can be ensured. Instead of controlling the nozzle opening of the variable nozzle turbocharger to the excessive throttle side, the exhaust throttle valve downstream of the NOx reduction catalyst may be controlled to the throttle side.

  According to the third aspect of the present invention, when the accelerator is turned off and the in-cylinder fuel injection amount becomes zero, the fuel addition from the fuel addition valve or the post fuel injection by the fuel injection valve or the exhaust re-injection is further performed. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein fuel is supplied by circulation and fuel is burned by an after-turbo oxidation catalyst.

  That is, according to the third aspect of the present invention, when the accelerator is turned off and the in-cylinder fuel injection amount becomes zero, the NOx reduction catalyst is conventionally only obtained by the post fuel injection by the fuel injection valve or the fuel addition from the fuel addition valve. Was not activated, and there was a problem of increased white smoke. However, fuel was added upstream of the after-turbo oxidation catalyst and HC and CO were burned in the after-turbo oxidation catalyst. When the injection amount becomes zero, the exhaust gas temperature at the outlet of the after-turbo oxidation catalyst until the transition to the idling operation can be maintained high, so that the gas temperature flowing into the NOx reduction catalyst rises, and the light load region such as idling operation The catalyst bed temperature of the NOx reduction catalyst in can be ensured. The supply of HC and CO to the after-turbo oxidation catalyst may be performed by post fuel injection by a fuel injection valve or exhaust gas recirculation.

  According to the invention described in claim 4, when the temperature of the after-turbo oxidation catalyst reaches the catalyst activation temperature, the internal opening engine of the variable nozzle turbocharger is controlled to the open side. An exhaust gas purification apparatus is provided.

  That is, in the invention of claim 4, once the temperature of the after-turbo oxidation catalyst reaches the activation temperature and further the supply of fuel combusted in the after-turbo oxidation catalyst is continued, the after-turbo oxidation catalyst may be deactivated. Therefore, the nozzle opening degree of the variable nozzle turbocharger can be controlled to the open side, and deterioration of fuel consumption due to over-throttle can be avoided.

  According to the fifth aspect of the present invention, there is provided an exhaust purification device for an internal combustion engine including a NOx reduction catalyst, comprising a variable nozzle turbocharger, an after turbo oxidation catalyst, and a fuel addition valve, and the after turbo oxidation catalyst. Is located immediately after the variable nozzle turbocharger and upstream of the NOx reduction catalyst, the fuel addition valve is located downstream of the after-turbo oxidation catalyst and upstream of the NOx reduction catalyst, the accelerator is turned off, and the in-cylinder When the fuel injection amount becomes zero, the nozzle opening of the variable nozzle turbocharger is controlled to the over-throttle side, and further fuel is supplied to the after-turbo oxidation catalyst by post fuel injection by the fuel injection valve or exhaust gas recirculation. An exhaust gas purification device for an internal combustion engine is provided, in which the reducing agent fuel is added to the NOx reduction catalyst by adding fuel from a fuel addition valve.

  That is, when the control of claim 3 is performed, in the configuration of claim 1, the added fuel burns in the after-turbo oxidation catalyst disposed upstream of the NOx reduction catalyst, and the fuel to the NOx reduction catalyst Therefore, in the invention of claim 5, the fuel addition valve is arranged downstream of the after-turbo oxidation catalyst and upstream of the NOx reduction catalyst, and the after-turbo oxidation is performed. Ensuring the activity of the catalyst is ensured by combustion by post-injection of fuel from the fuel injection valve or fuel supply by exhaust gas recirculation, and NOx reducing agent fuel addition is controlled by the fuel addition valve. As a result, it is possible to achieve both the effect of ensuring the activity of the after-turbo oxidation catalyst and increasing the NOx reduction efficiency. Further, it is not necessary to limit the amount of fuel added in order to avoid overheating of the after-turbo oxidation catalyst.

  According to the invention described in each claim, when the accelerator is turned off and the in-cylinder fuel injection amount becomes zero, it is possible to prevent the catalyst bed temperature of the NOx reduction catalyst from being lowered, and in a light load region such as idle operation. The catalyst bed temperature of the NOx reduction catalyst in the case of transition can be ensured, and there is a common effect that NOx reduction in the exhaust gas can be promoted.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that, in the plurality of attached drawings, the same or corresponding members or devices are denoted by the same reference numerals.

  FIG. 1 is a diagram illustrating an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention. The internal combustion engine 10 includes a NOx reduction catalyst 13 downstream thereof to reduce and purify exhaust from the internal combustion engine 10. The internal combustion engine 10 is disposed downstream of the exhaust manifold 12 and upstream of the NOx reduction catalyst 13. The variable nozzle turbocharger 2 drives the turbine by exhaust and pumps intake air, and the NOx reduction catalyst immediately after the variable nozzle turbocharger 2. 13 is provided with an after-turbo oxidation catalyst 14 disposed upstream of 13 and a fuel addition valve 16 disposed in the exhaust manifold 12 for adding fuel to the exhaust. The internal combustion engine 10 includes an EGR cooler 3 and an EGR valve 7 for performing exhaust gas recirculation (EGR), and a common rail fuel injection valve 11.

FIG. 2 is a flowchart for explaining an embodiment of the control of the exhaust emission control device shown in FIG. In step 100, from the engine ECU, the engine speed NE (rpm), the accelerator opening ACCP (%), the fuel injection amount Qfin (mm ³ / sec), the nozzle opening pvnfin (%) of the variable nozzle turbocharger, the after turbo The oxidation catalyst temperature Tatc (° C.) is read. In step 200, it is determined whether or not the fuel injection amount is zero in the accelerator off state. If the fuel injection amount is zero in the accelerator off state, the process proceeds to step 300 and the nozzle opening of the variable nozzle turbocharger is determined. Is controlled to the over-throttle side to prevent the cooled intake air from flowing into the after-turbo oxidation catalyst. In this case, instead of controlling the nozzle opening degree of the variable nozzle turbocharger to the excessive throttle side, an exhaust throttle valve (not shown) downstream of the NOx reduction catalyst may be controlled to the throttle side. Further, the process proceeds to step 400, where the fuel addition signal exqfin is turned on and fuel addition is started. That is, HC and CO are burned with an after-turbo oxidation catalyst. Therefore, since the exhaust gas temperature at the outlet of the after-turbo oxidation catalyst can be maintained high, the temperature of the gas flowing into the NOx reduction catalyst increases. The supply of HC and CO to the after-turbo oxidation catalyst may be performed by post fuel injection by a fuel injection valve or exhaust gas recirculation. Proceeding to step 500, if the after-turbo oxidation catalyst temperature is equal to or higher than the activation temperature α, proceeding to step 600, the fuel addition signal exqfin is turned off and fuel addition is stopped. Further, the process proceeds to step 700, where the nozzle opening of the variable nozzle turbocharger is controlled to the open side, and set to the target value pvntrg for normal control. On the other hand, when the after-turbo oxidation catalyst temperature is lower than the activation temperature α in step 500, the process returns to step 200, and it is determined again whether the fuel injection amount is zero in the accelerator-off state. When the injection amount is zero, the nozzle opening of the variable nozzle turbocharger is further controlled to the over-throttle side.

  In this way, when the fuel injection amount is zero in the accelerator off state, the catalyst bed temperature of the NOx reduction catalyst can be ensured, and therefore the catalyst bed of the NOx reduction catalyst in the light load region such as the idling operation thereafter. The temperature can be secured.

  FIG. 3 is a diagram for explaining another embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention. 4 differs from FIG. 2 in that the fuel addition valve 16 is disposed downstream of the after-turbo oxidation catalyst 14 and upstream of the NOx reduction catalyst 13.

  FIG. 4 is a flowchart illustrating an embodiment of control of the exhaust purification device shown in FIG. In this control, Step 100 to Step 400 are the same as those in FIG. 2, but the fuel addition signal exqfin is turned on in Step 400 and fuel addition is started. The signal expost is turned on. That is, the fuel from the fuel addition valve 16 is used as a reducing agent in the NOx reduction catalyst 13, and the after-turbo oxidation catalyst 14 burns fuel from the fuel injection valve by post injection or fuel in the exhaust by exhaust gas recirculation. The temperature of the after-turbo oxidation catalyst is increased. Proceeding to step 500, if the after-turbo oxidation catalyst temperature is equal to or higher than the activation temperature α, proceeding to step 600, turning off the fuel addition signal exqfin, stopping the fuel addition, and further, in step 610, the post injection permission signal Turn off the post and stop post-injection. Other flows are the same as those in FIG.

  Therefore, in the embodiment shown in FIGS. 1 and 2, the added fuel is burned by the after-turbo oxidation catalyst disposed upstream of the NOx reduction catalyst, the supply of fuel to the NOx reduction catalyst is insufficient, and the NOx reduction is performed. While the efficiency may be reduced, in the embodiment of FIGS. 3 and 4, the supply of fuel to the NOx reduction catalyst is ensured, and both the effect of ensuring the activity of the after-turbo oxidation catalyst and increasing the NOx reduction efficiency are achieved. Can be advantageous. There is also an advantage that it is not necessary to limit the amount of fuel added to avoid overheating of the after-turbo oxidation catalyst.

It is a figure explaining the schematic structure of embodiment at the time of applying the present invention to the exhaust gas purification device of an internal-combustion engine. It is a flowchart explaining the schematic structure of embodiment at the time of applying this invention to the exhaust gas purification apparatus of an internal combustion engine. It is a figure explaining the schematic structure of other embodiment at the time of applying this invention to the exhaust gas purification apparatus of an internal combustion engine. It is a flowchart explaining schematic structure of other embodiment at the time of applying this invention to the exhaust gas purification apparatus of an internal combustion engine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Air cleaner 2 Variable nozzle turbocharger 3 EGR cooler 4 Intake bypass valve 5 Intercooler 6 Intake throttle valve 7 EGR valve 8 Intake manifold 9 Common rail 10 Internal combustion engine body 11 Fuel injection valve 12 Exhaust manifold 13 NOx reduction catalyst 14 ATC
15 Exhaust temperature sensor 16 Fuel addition valve

Claims (5)

An exhaust purification device for an internal combustion engine including a NOx reduction catalyst,
Variable nozzle turbocharger,
An after-turbo oxidation catalyst,
A fuel addition valve,
The after-turbo oxidation catalyst is disposed immediately after the variable nozzle turbocharger and upstream of the NOx reduction catalyst;
The fuel addition valve is disposed in the exhaust manifold;
An exhaust purification device for an internal combustion engine. When the accelerator is turned off and the in-cylinder fuel injection amount becomes zero, the nozzle opening of the variable nozzle turbocharger is controlled to the over-throttle side,
The exhaust emission control device for an internal combustion engine according to claim 1. When the accelerator is turned off and the in-cylinder fuel injection amount becomes zero, fuel addition from the fuel addition valve or fuel supply by post fuel injection by the fuel injection valve or exhaust recirculation is performed,
Burning the fuel with the after-turbo oxidation catalyst;
The exhaust emission control device for an internal combustion engine according to claim 2.   The exhaust purification device of an internal combustion engine according to claim 3, wherein when the temperature of the after-turbo oxidation catalyst reaches a catalyst activation temperature, the nozzle opening degree of the variable nozzle turbocharger is controlled to the open side. An exhaust purification device for an internal combustion engine including a NOx reduction catalyst,
Variable nozzle turbocharger,
An after-turbo oxidation catalyst,
A fuel addition valve,
The after-turbo oxidation catalyst is disposed immediately after the variable nozzle turbocharger and upstream of the NOx reduction catalyst;
The fuel addition valve is disposed downstream of the after-turbo oxidation catalyst and upstream of the NOx reduction catalyst;
When the accelerator is turned off and the in-cylinder fuel injection amount becomes zero,
Control the nozzle opening of the variable nozzle turbocharger to the over-throttle side,
Furthermore, fuel is supplied to the after-turbo oxidation catalyst by post fuel injection or exhaust gas recirculation by a fuel injection valve, and reductant fuel is added to the NOx reduction catalyst by adding fuel from the fuel addition valve.
An exhaust purification device for an internal combustion engine.

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