JP2008128213A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

An exhaust emission control device for an internal combustion engine is provided that can increase the setting accuracy of a reducing agent supply amount during rich spike control without being affected by TWC degradation.
And A TWC7 provided upstream of the exhaust passage, and LNC9 provided on the downstream side, and estimating means _the amount of NO _X adsorbed in the TWC, the estimation of the amount of reducing agent consumed by TWC An exhaust gas purification device for an internal combustion engine having means,
And correcting means for correcting the amount of reducing agent supplied to the LNC in consideration of the increase and decrease of the NO _X adsorption capacity and / or reducing agent consumption TWC, first learning of changes in the reducing agent consumption amount due to deterioration of the TWC a correction unit, and shall make a second learning correction means on the change of the NO _X adsorption amount and / or NO _X reduction performance due to deterioration of the TWC.
[Selection] Figure 3

Description

The present invention relates to an exhaust purifying apparatus for an internal combustion engine, and particularly relates to an exhaust purification device of an internal combustion engine and more to further improve the exhaust gas purification capacity by cooperation with the three-way catalyst and a lean NO _X catalyst.

An internal combustion engine (for example, a diesel engine) that performs lean combustion has a large amount of NO _X (nitrogen oxide) emissions, and therefore, a lean NO _X catalyst (hereinafter referred to as LNC) that performs a detoxifying process may be provided. is there. In this LNC, so the _the NO _X storage amount increases its acquisition performance is lowered, timely, the air-fuel ratio of the exhaust gas in order to perform the release and reduction process occluded NO _X (hereinafter, referred to as the exhaust A / F ) Is intermittently performed to perform rich spike control.

As technology for this rich spike control, the reducing agent supply amount is estimated from the output of the O ₂ sensor installed upstream of the LNC and the space velocity of the exhaust gas flowing into the LNC, and the estimated reducing agent supply amount is captured by the LNC. technique so as to end the rich-spike control is known at the time of exceeding the reducing agent necessary amount calculated beforehand corresponding to the amount of NO _X is (see Patent Document 1).

On the other hand, a recent diesel engine has a three-way catalyst (hereinafter referred to as “three-way catalyst”) for detoxifying CO (carbon monoxide), HC (hydrocarbon), and NO _X in order to further purify harmful components in exhaust gas. , Indicated as TWC) on the upstream side of the LNC. The TWC, there are oxidative capacity and reduced capacity, an oxygen adsorbent (hereinafter referred to as OSC) provided with a, also has a release-reduction action of absorption and absorbing NO _X of the NO _X by the same mechanism as LNC .

In such an exhaust purification device in which the TWC and the LNC are connected in series, a part of the reducing agent (unburned component) supplied during the rich spike control is consumed by the OSC provided in the TWC, It consumed by NO _X treatment TWC itself. Therefore, it is necessary to consider the amount of reducing agent consumed in the TWC in setting the reducing agent supply amount (rich operation duration) to the LNC.
JP 2006-207487 A

However, the reducing agent consumption by TWC because changes due to deterioration of the oxygen adsorption capacity of degradation and OSC of the NO _X capacity of TWC itself, when the rich spike control of LNC without considering the change, for example TWC and the consumption of the reducing agent in is insufficient NO _X treatment at large, the LNC unexpectedly, the excess CO consumption of the reducing agent from the small and LNC unexpectedly in TWC, HC flows out Become. That is, an error occurs in the end determination of the rich spike control in the LNC due to the deterioration of the TWC, leading to deterioration of exhaust emission and fuel consumption.

  The present invention has been devised in view of such problems of the prior art, and its main purpose is to increase the setting accuracy of the reducing agent supply amount during rich spike control without being affected by TWC degradation. An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine.

In order to solve such a problem, according to the present invention, a first catalyst (for example, TWC7) having at least a reduction function provided on the upstream side of the exhaust passage and an exhaust A / F provided on the downstream side are lean. a second catalyst which adsorbs to and reduced and purified NO _X adsorbed in the rich state NO _X in the state (e.g. LNC 9), and _the amount of NO _X estimating component is captured in a first catalyst in a first catalyst in the exhaust purification system of an internal combustion engine having a reducing agent amount estimating means being drain in, supplied to the second catalyst in consideration of the increase and decrease of the NO _X absorbent capacity and / or reducing agent consumption amount of the first catalyst Correction means for correcting the amount of reducing agent, learning correction means for a change in the amount of reducing agent consumed due to deterioration of the first catalyst, NO _X absorption capacity and / or NO _X reduction performance due to deterioration of the first catalyst Learning correction means for change It was assumed to be example.

According to the present invention, taking into account that the amount of reducing agent consumed by the first catalyst and the amount of NO _x adsorbed on the first catalyst change as the first catalyst deteriorates. Since the supply amount of the reducing agent during the rich spike control can be set, it is possible to optimally set the supply amount of the reducing agent, which has a great effect on suppressing exhaust emission and deterioration of fuel consumption. it can.

  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 for removing (PM), as well as capture the NO _X in the exhaust gas when the oxygen concentration is high (lean), (often unburned fuel as a rich / reducing agent) oxygen concentration is low when An exhaust purification device 10 is connected, in which LNC 9 (second catalyst) for releasing / reducing NO _X occluded therein is connected in this order from the upstream along the flow of exhaust.

  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 exhaust purification apparatus 10 provided in the engine E is evacuated by reducing to release and reduced the NO _X occluded in the TWC7 or LNC 9, the intake air amount with increasing e.g. fuel injection amount A / It is necessary to perform rich spike control to enrich F temporarily in a timely manner.

  This rich spike control is performed as follows.

First, during operation of the engine, by searching a map set in advance based on the absolute pressure of the crank shaft rotational speed and the intake passage, constantly seeking and integrating the NO _X emissions per unit time, so far An estimated value of the amount of NO _X absorbed by the LNC 9 is calculated. And this _the NO _X storage amount, if reached absorbent capacity value of LNC9 set in advance, performing the rich spike control is determined that _the NO _X storage amount of LNC9 is saturated. As a result, the unburned components in the exhaust gas flowing into the LNC 9 serve as a reducing agent, and NO _X stored in the LNC 9 is reduced, and the NO _X trapping performance of the LNC 9 is restored.

During the execution of rich spike control, the exhaust A / F is monitored by comparing the outputs of the O ₂ sensors 27U and 27L provided on the upstream side and the downstream side of the TWC 7 so that a predetermined reducing atmosphere is maintained. The fuel injection amount and the intake air amount are feedback controlled, and the reducing agent supply amount is integrated. This reducing agent supply amount is obtained, for example, by multiplying the value obtained by subtracting the actual exhaust A / F obtained from the output of the upstream O ₂ sensor 27U from 14.7 representing the theoretical air-fuel ratio by the space velocity of the exhaust gas. can get.

If the integrated value of the reducing agent supply amount reaches the amount required to reduce all NO _X stored in the LNC 9, it is determined that the NO _X absorption capacity of the LNC 9 has been restored and the rich spike control is terminated. Let

Here, the amount of reducing agent to be supplied to the LNC 9 is set in consideration of the amount of reducing agent consumed in the TWC 7. Therefore, if the amount of reducing agent consumed in TWC 7 changes due to aging of TWC 7 or the like, the amount of reducing agent actually supplied to LNC 9 changes. The reducing agent is consumed in this TWC7, the amount consumed by the process of TWC7 itself NO _X, there is a minute consumed by OSC. Therefore, in the present invention, it is assumed that monitor the change in the oxygen adsorption capacity of the NO _X processing power and OSC of TWC7, it corrects the reducing agent required amount during the rich spike control according to the change.
<OSC learning>

NO _X accumulated value (is _the NO _X storage amount of TWC7 0) is generally 0 to exhaust A / F rich when the output difference between the _{O 2} sensor 27L provided in the _{O 2} sensor 27U and downstream provided upstream of TWC7 (See FIG. 3). If the amount of oxygen adsorbed by the OSC in the TWC 7 is large, the reducing agent is consumed (oxidized) by the oxygen released from the OSC. Therefore, the exhaust A / F value is the output value of the O ₂ sensor 27L on the downstream side of the TWC 7. (The broken line in FIG. 3) is leaner than the output value (solid line in FIG. 3) of the upstream O ₂ sensor 27U. That is, the degree of deterioration of the oxygen adsorption capacity of the OSC can be determined from the degree of difference between the exhaust A / F upstream and downstream of the TWC 7 when NO _X is not captured by the TWC 7, and the correction coefficient is determined according to the degree of deterioration. Determine.
<Adsorbed NO _X learning>

After learning the degree of deterioration of the OSC, it corrects the relation value between the integrated value of the NO _X absorption amount of the reducing agent amount and LNC consumed during the rich spike control.

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 graph which shows notionally exhaust A / F change before and after TWC.

Explanation of symbols

7 TWC
9 LNC

Claims (1)

Reducing a first catalyst having at least reducing function provided on the upstream side of the exhaust passage, the NO _X adsorbed in and rich state adsorbs NO _X in the lean state exhaust air-fuel ratio provided on the downstream side purification in the exhaust purification system of an internal combustion engine having a second catalyst, and estimating means _the amount of NO _X trapped in the first catalyst and the reducing agent amount estimation means is consumed in the first catalyst There,
Correction means for correcting the amount of reducing agent supplied to the second catalyst in consideration of increase / decrease in NO _X absorption capacity and / or reducing agent consumption of the first catalyst;
Learning correction means relating to a change in the reducing agent consumption accompanying the deterioration of the first catalyst;
An exhaust gas purification apparatus for an internal combustion engine, comprising: a learning correction means for a change in NO _X absorption capacity and / or NO _X reduction performance accompanying the deterioration of the first catalyst.

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