JP2008128212A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of highly efficiently performing DPF regeneration and a sulfur purge, without deteriorating fuel economy. <P>SOLUTION: This exhaust emission control device 10 of the internal combustion engine is formed by arranging a TWC 7, a DPF 8 and an LNC 9 in a row in this order from the upstream side in an exhaust passage, and has a DPF regenerating means and a sulfur purge means of the TWC and the LNC. The sulfur purge is performed in parallel to the DPF regeneration. A target value of the exhaust air-fuel ratio is alternately switched to the lean side and the rich side in a state of setting at least any of the TWC and the LNC to the predetermined temperature or more. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention includes an internal combustion engine that includes a means for removing sulfur adsorbed by a catalyst device that purifies exhaust gas from an internal combustion engine, and a means for performing regeneration processing of a filter device that captures particulate matter (PM). The present invention relates to an exhaust purification device.

In order to detoxify CO (carbon monoxide), HC (hydrocarbon), and NO _x (nitrogen oxide) discharged from the combustion chamber of an automobile internal combustion engine, a three-way is provided in the exhaust passage of the internal combustion engine. A catalyst (hereinafter referred to as TWC) is provided. This TWC is mainly adapted to the combustion state at the stoichiometric air-fuel ratio (hereinafter referred to as stoichiometric), and particularly an internal combustion engine (for example, a diesel engine) that performs lean combustion has a large NO _X emission amount. A lean NO _X catalyst (hereinafter referred to as LNC) for detoxification may be provided downstream of the TWC.

  In addition, particulate matter (Particulate Matter: hereinafter referred to as PM) is generated in the diesel engine, so a DPF (Diesel Particulate Filter) that captures the particulate matter is installed downstream of the TWC and upstream of the LNC. Yes. When the amount of accumulated PM on the DPF increases, back pressure increases (decreases in output) due to clogging. Therefore, the PM is forcibly reburned and removed at a proper time (hereinafter referred to as DPF regeneration). Need to do. In order to perform this DPF regeneration, it is necessary that the temperature of the exhaust gas is higher than a predetermined value and the air-fuel ratio (hereinafter referred to as exhaust A / F) is higher than a predetermined value (hereinafter referred to as lean). Yes (see Patent Document 1).

On the other hand, since the fuel contains sulfur, SO _X (sulfur oxide) and H ₂ S (hydrogen sulfide) are also discharged. State in which these sulfur is absorbed in the TWC or LNC (or less, S referred to as poisoning) becomes, because these of the NO _X purification performance is lowered, must be released in a timely manner harmless absorbed sulfur is there. In order to perform this sulfur release process (hereinafter referred to as sulfur purge), the temperature of the exhaust gas flowing into the TWC or LNC is higher than a predetermined value, and the exhaust A / F is lower than a predetermined value (hereinafter, referred to as “sulfur purge”). (Referred to Patent Document 2).
JP 2000-161044 A JP 2003-120373 A

  In other words, both DPF regeneration and sulfur purge must be performed at high temperatures, but DPF regeneration must be performed in a lean atmosphere, and sulfur purge must be performed in a different combustion state in a rich atmosphere. Processing was done individually. Since these processes are performed by forcibly changing the combustion state in the normal operation for the process, the sulfur purge particularly in a rich atmosphere has a disadvantage that the fuel consumption deteriorates if the process time is prolonged.

  The present invention was devised to solve such problems of the prior art, and its main purpose is an internal combustion engine capable of executing DPF regeneration and sulfur purge with high efficiency without causing deterioration of fuel consumption. An object of the present invention is to provide an exhaust purification device.

To solve such problems, claim 1 of the present invention, the first catalyst having at least reducing function (e.g. TWC7), and DPF 8, and the exhaust A / F adsorbs NO _X in the lean state rich in the exhaust purification apparatus 10 of the second catalyst (e.g. LNC 9) and the internal combustion engine formed by arrayed in this order from the upstream in the exhaust passage to reduce and purify the NO _X adsorbed in the state, the DPF regeneration means, the first catalyst In addition, a sulfur purge means for the second catalyst is provided, and the sulfur purge is performed in parallel with the DPF regeneration.
Particularly, the invention of claim 2 is characterized in that the target value of the exhaust A / F is alternately switched between the lean side and the rich side in a state where at least one of the first catalyst and the second catalyst is equal to or higher than a predetermined temperature. To do.

According to the present invention, the sulfur purge of the first catalyst and the second catalyst disposed downstream thereof can be performed in a short time in a high temperature / rich atmosphere in synchronization with the DPF regeneration. first catalyst and NO _X purification performance of the second catalyst while suppressing to a minimum the adverse spans can be prevented from being deteriorated. In particular, sulfur purge, when performed alone, causes a deterioration in fuel consumption. Parallel processing can shorten processing time, and the progress of both processes becomes average. Even if the process is interrupted for the reason, the functions of the DPF, the first catalyst, and the second catalyst are not impaired.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a basic configuration diagram of an internal combustion engine E to which the present invention is applied. The internal combustion engine (diesel engine) E has a mechanical structure itself that is not different from that of a known one, and includes a turbocharger 1 with a supercharging pressure variable mechanism. A passage 2 is connected, and an exhaust passage 3 is connected to the turbine side of the turbocharger 1. An air cleaner 4 is connected to the upstream end of the intake passage 2, and an intake control valve 5 for adjusting the flow rate of fresh air flowing into the combustion chamber at an appropriate position of the intake passage 2, and flows in a low rotation speed / low load operation region. A swirl control valve 6 is provided for reducing the cross-sectional area of the road and increasing the intake air flow velocity. Further, on the downstream side of the supercharger 1 in the exhaust passage 3, a TWC 7 (first catalyst) that oxidizes HC and CO in the exhaust and reduces NO _X under a stoichiometric atmosphere, and particulate matter such as soot A filter (DPF) 8 that removes (PM) and captures NO _X in the exhaust when the oxygen concentration is high (lean), and releases and reduces the stored NO _X when the oxygen concentration is low (rich) An exhaust purification device 10 is connected, which is connected to the LNC 9 (second catalyst) in this order from the upstream along the exhaust flow.

  The swirl control valve 6 and the portion immediately after the combustion chamber in the exhaust passage 3 are connected to each other via an exhaust recirculation (hereinafter referred to as EGR) passage 11. The EGR passage 11 includes a cooler passage 11a and a bypass passage 11b branched via a switching valve 12, and an EGR control valve 13 for adjusting the EGR flow rate flowing into the combustion chamber is provided at the junction. .

  The cylinder head of the internal combustion engine E is provided with a fuel injection valve 14 with its tip facing the combustion chamber. The fuel injection valve 14 is connected to a common rail 15 that stores fuel in a predetermined high pressure state, and a fuel pump 17 that is driven by a crankshaft and pumps fuel from the fuel tank 16 is connected to the common rail 15.

  These turbocharger 1 supercharging pressure variable mechanism 19, intake control valve 5, EGR passage switching valve 12 and EGR control valve 13, fuel injection valve 14, fuel pump 17... (Referred to as FIG. 2).

On the other hand, as shown in FIG. 2, the ECU 18 includes an intake valve opening sensor 20, a crankshaft rotation speed sensor 21, an intake flow rate sensor 22, a supercharging pressure sensor 23, and an EGR valve disposed at predetermined locations of the internal combustion engine E. Output signals from the opening sensor 24, the common rail pressure sensor 25, the accelerator pedal operation amount sensor 26, the O ₂ sensors 27U and 27L, the NO _X sensors 28U and 28L, the TWC temperature sensor 29, the LNC temperature sensor 30, and so on are input. Has been.

  In the memory of the ECU 18, a map is set in which control target values for each control object including the optimum fuel injection amount obtained in advance by a bench test or the like according to the crankshaft rotation speed and the required torque (accelerator pedal operation amount) are set. Thus, each part is controlled so that an optimal combustion state is obtained in accordance with the load state of the internal combustion engine E.

  In the internal combustion engine E, it is necessary to perform a DPF regeneration process for removing PM accumulated in the DPF 8 and a sulfur purge process for removing sulfur stored in the TWC 7 or LNC 9 in a timely manner. Among these, sulfur purge is carried out in a rich atmosphere that lasts for a relatively long time, so that the amount of PM generated in the exhaust gas increases, but in general, the frequency is lower than that of DPF regeneration. Therefore, in the present invention, when performing DPF regeneration under a lean atmosphere, intermittent rich control is performed at the same time so that sulfur purge is performed in parallel with DPF regeneration.

  Next, DPF regeneration and sulfur purge processing procedures according to the present invention will be described with reference to FIG. First, the engine load situation, fuel supply amount, etc. are constantly monitored to estimate the PM generation amount, and it is determined whether or not the PM accumulation amount of the DPF 8 obtained by integrating the amount has reached a predetermined threshold value. (Step 1).

  If this value is equal to or less than the predetermined value (No at Step 1 :), it is determined that the DPF regeneration process is not yet required, and this process is terminated. When it is determined that the predetermined value has been reached (step 1: affirmative), it is determined whether or not the temperature of the TWC 7 has reached the predetermined value (step 2). 2: No), for example, temperature increase processing by post injection or the like is performed (step 3). If it is determined that the predetermined value has been reached (step 2: affirmative), the DPF regeneration time is calculated with reference to the processing time table (FIG. 4) in which the relationship between the PM accumulation amount and the regeneration time is set. (Step 4).

  At the same time, an integrated value of the S poison amount is estimated from the travel distance, travel time, fuel consumption, oxygen concentration, etc., and a processing time table (FIG. 5) in which the relationship between the S poison amount and the regeneration time is set. Refer to and calculate the time required for sulfur purge (step 5).

  The operation switching time between the rich timer and the lean timer is set from both processing times (step 6), and the rich and lean operations at a predetermined high temperature state are alternately repeated (step 7).

  This process is repeated until it is determined in step 8 that the timer has finished counting.

Since the diesel engine is lean in steady operation, PM trapped in the DPF 8 can be reburned also by active oxygen generated when NO _X is trapped in the TWC 7 under a high temperature lean atmosphere. The PM by active oxygen generated during the rich spike control performed for of the NO _X purification is afterburning. That is, DPF regeneration can be processed over a wide operating range.

  On the other hand, the sulfur purge is performed in a high temperature rich atmosphere, but the temperature of the supercharger is too high in the high load region, and the temperature is insufficient in the low load region. That is, the optimum load area for processing is limited to some extent (see FIG. 6).

  As described above, since the progress of sulfur purge and DPF regeneration is greatly influenced by the operating state, the switching time distribution between the rich timer and the lean timer is appropriately determined according to the degree of achievement with respect to the time required for the entire processing. It is possible to correct it.

  That is, since the sulfur purgeable area is narrower than the DPF recyclable area, it is preferable to prioritize sulfur purge in an operation state in which start / stop is repeated in an urban area.

  Further, since sulfur purge cannot be performed in an excessively low load region or an excessively high load region, only the DPF regeneration process is necessarily executed.

  And when traveling in a state where sulfur purge is always possible, such as high-speed constant speed traveling, simply calculate the shortest processing time corresponding to the amount of PM deposition and S poisoning, and switch the processing time distribution with a timer Just do it.

As described above, the DPF regeneration and the sulfur purge are performed in parallel by switching between the rich timer and the lean timer, so that they are always processed on average, and the PM capturing ability of the DPF 8 and the NOC of the TWC 7 and the LNC 9 are always processed. _X capture capability can be maintained at a high level.

1 is an overall configuration diagram of an internal combustion engine to which the present invention is applied. It is a block diagram of a control device to which the present invention is applied. It is a flowchart in connection with this invention process. It is the processing time table which set the relationship between PM deposition amount and regeneration time. It is the processing time table which set the relationship between S poison amount and reproduction | regeneration time. It is a distribution map of the optimal operation area | region for each process.

Explanation of symbols

7 TWC
8 DPF
9 LNC

Claims (2)

An exhaust passage includes at least a first catalyst having a reduction function, a particulate matter trapping filter, and a second catalyst that adsorbs NO _X when the exhaust air-fuel ratio is lean and reduces and purifies NO _X adsorbed when rich. An exhaust purification device for an internal combustion engine arranged in this order from the upstream,
The particulate matter trapping filter regeneration processing means, and the sulfur poisoning recovery processing means of the first catalyst and the second catalyst, wherein the sulfur poisoning recovery processing is the regeneration of the particulate matter trapping filter. A control apparatus for an internal combustion engine, which is performed in parallel with the processing.   2. The exhaust air / fuel ratio target value is alternately switched between a lean side and a rich side in a state where at least one of the first catalyst and the second catalyst is equal to or higher than a predetermined temperature. Control device for internal combustion engine.

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