JPH11117786A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] SOx respectively interposed in a plurality of exhaust passages
Without thermally damaging the catalyst or three-way catalyst,
Provided is an exhaust gas purifying apparatus for an internal combustion engine capable of regenerating a NOx catalyst by efficiently releasing a sulfur component from a NOx catalyst provided on a downstream side of a collecting portion in which the exhaust passages are integrated. SOLUTION: NO caused by sulfur component in exhaust gas
x When the deterioration of the catalyst is detected, the internal combustion engine is operated in a rich manner, and the operating conditions for each cylinder group of the internal combustion engine, for example, the ignition timing are individually controlled in accordance with the temperature state of each catalyst, and the excess catalyst of the upstream side catalyst is controlled. The catalyst temperature is made substantially equal while preventing the temperature from rising, and the temperature of the NOx catalyst is sufficiently increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a fuel cell system, comprising: a plurality of exhaust passages provided for each of a plurality of cylinder groups; The sulfur component is released from the NOx catalyst provided on the downstream side of the collecting section where the exhaust passages are integrated into
The present invention relates to an exhaust gas purification device for an internal combustion engine suitable for efficiently regenerating (activating) an Ox catalyst.

[0002]

2. Related Background Art In a so-called lean burn engine which is operated at a lean air-fuel ratio in order to improve fuel efficiency, one of harmful substances is used as compared with an engine which is operated at a normal stoichiometric air-fuel ratio. A large amount of nitrogen oxides (NOx) are emitted. In order to remove NOx in such exhaust gas, a storage NOx is inserted into an exhaust passage of an internal combustion engine (engine).
It has been proposed to provide a catalyst. In addition, the storage type N
The Ox catalyst adsorbs NOx in the exhaust gas when the exhaust air-fuel ratio is lean, and when the exhaust air-fuel ratio is enriched and the oxygen concentration in the exhaust gas decreases, the NOx already adsorbed.
It has the function of releasing x.

In order to remove sulfur components (SOx) in exhaust gas, it has been considered to provide an SOx catalyst in addition to the NOx catalyst. This SOx catalyst adsorbs SOx in the exhaust gas when the exhaust air-fuel ratio is lean,
When the exhaust air-fuel ratio becomes rich, the already adsorbed SO
It has the function of releasing x. Further, the NOx
In addition to the catalyst, it has been considered to provide a three-way catalyst which exhibits a reducing action of NOx using hydrocarbons (HC) and carbon monoxide (CO) existing in the vicinity of the catalyst.

Incidentally, the amount of NOx adsorbed by the NOx catalyst has a limit, and the amount of SOx adsorbed by the SOx catalyst also has a limit. For this reason, when the adsorption amount of NOx or SOx reaches the limit and the adsorption capacity decreases, the internal combustion engine is temporarily operated in a rich manner to enrich the exhaust air-fuel ratio, and NOx or SOx is released from each catalyst. Thus, regeneration (activation) of the NOx catalyst or SOx catalyst is performed.

The sulfur component (S) adsorbed on the NOx catalyst
Ox) is released at a higher catalyst temperature than at the time of NOx release, whereby the NOx catalyst is regenerated.

[0006]

In an internal combustion engine having a plurality of rows of cylinder groups, such as a V-type engine or a horizontally opposed engine, a plurality of exhaust passages respectively derived from each cylinder group (bank) are provided. For example, the exhaust system is configured so as to be brought together into a tail pipe under the floor of the vehicle body. At this time, the NOx catalyst is provided on the downstream side of the collecting portion where the plurality of exhaust passages are integrated into one,
For the SOx catalyst and the three-way catalyst, it is considered that it is desirable to interpose the NOx catalyst in each of the exhaust passages in order to prevent the NOx catalyst from being poisoned by sulfur components in the exhaust gas or to activate the NOx catalyst at a low temperature at an early stage.

However, when the above-described configuration is adopted, each exhaust passage has a different layout structure and a different pipe length depending on the arrangement of the internal combustion engine with respect to the vehicle, and furthermore, each exhaust passage has a different cooling condition. It is unavoidable that a temperature difference occurs between the catalysts provided in the passages. For this reason, when the cylinder groups of the internal combustion engine are operated in the same rich manner to enrich the exhaust air-fuel ratio and release the sulfur component (SOx) adsorbed on the SOx catalyst, for example, the ignition timing is adjusted to increase the catalyst temperature. Is performed to raise the exhaust gas temperature, the temperature of the SOx catalyst on the specific exhaust passage side becomes
There is a possibility that the temperature exceeds the heat resistant temperature.

In particular, when releasing the sulfur component adsorbed on the NOx catalyst, it is necessary to make the air-fuel ratio richer and increase the temperature of the NOx catalyst than when releasing NOx. Accordingly, the temperature of the three-way catalyst and the SOx catalyst interposed on the specific exhaust passage on the upstream side of the NOx catalyst is further increased, and the temperature may exceed the heat-resistant temperature.
Such an excessively high temperature of the three-way catalyst or the SOx catalyst on the upstream side significantly impairs the durability of the catalyst and needs to be prevented beforehand.

The present invention has been made in view of such circumstances, and has as its object to provide thermal damage to a SOx catalyst and a three-way catalyst interposed in a plurality of exhaust passages, respectively. To provide an exhaust gas purifying apparatus for an internal combustion engine capable of regenerating the NOx catalyst by efficiently releasing a sulfur component from a NOx catalyst provided on a downstream side of a collecting portion in which the exhaust passages are integrated. It is in.

[0010]

SUMMARY OF THE INVENTION To achieve the above object, an exhaust gas purifying apparatus for an internal combustion engine according to the present invention includes a plurality of exhaust passages provided for each of a plurality of cylinder groups in an internal combustion engine.
A catalyst for purifying exhaust gas, for example, a three-way catalyst or an SOx catalyst, is interposed therebetween, and a downstream portion of the collecting section in which the exhaust passages are integrated into one unit. A NOx catalyst that adsorbs NOx and releases the NOx that has already been adsorbed when the oxygen concentration in the exhaust gas is reduced, and in particular, the deterioration detection means causes the NOx catalyst to be caused by the sulfur component in the exhaust gas. When deterioration of the purification characteristics of the NOx catalyst is detected, the operation of each cylinder group of the internal combustion engine is individually controlled in accordance with the temperature state of the catalyst interposed in each of the exhaust passages and the NOx catalyst is controlled. A catalyst regenerating means for releasing the adsorbed sulfur component is provided.

Preferably, the catalyst regenerating means detects a temperature of a catalyst interposed in each of the exhaust passages, and detects the temperature of each of the cylinders of the internal combustion engine in accordance with the detected catalyst temperature. It is characterized in that the operation of the group is individually controlled to enrich the exhaust air-fuel ratio. In the catalyst regenerating means, the operation of each of the cylinder groups is performed based on a predetermined catalyst temperature for exhaust gas purification corresponding to an operation state of each of the cylinder groups of the internal combustion engine. Are individually controlled to enrich the exhaust air-fuel ratio.

That is, according to the present invention, when a sulfur component is released from a NOx catalyst, a cylinder group of an internal combustion engine in which each exhaust passage is connected in accordance with a temperature state of a catalyst interposed in each of a plurality of exhaust passages upstream of the NOx catalyst. Operating conditions, specifically the degree of enrichment of the air-fuel ratio and the ignition timing are individually adjusted to prevent excessive temperature rise of the catalyst provided in each exhaust passage, thereby releasing sulfur components from the NOx catalyst. Is performed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An exhaust gas purifying apparatus for an internal combustion engine according to an embodiment of the present invention will be described below with reference to the drawings, taking a so-called V-type engine in which a plurality of cylinders are arranged in a V-shape as an example. . FIG. 1 shows a schematic configuration of an exhaust gas purification apparatus according to an embodiment. Reference numeral 1 denotes a V-type engine in which a plurality of cylinders are alternately arranged in a V-shape. The V-type engine 1 is mounted horizontally on a front portion of the vehicle with, for example, left and right banks (cylinder groups) positioned in the front-rear direction of the vehicle. Thus, the exhaust passages 2L and 2R derived from each bank are grouped together, for example, under the floor of the vehicle, and are led to a tail pipe (not shown) from the gathering portion.

In such an exhaust system, NOx in the exhaust gas is adsorbed on the downstream side of the collecting portion when the exhaust air-fuel ratio is lean, and is adsorbed when the oxygen concentration in the exhaust gas decreases. The NOx catalyst 3 for releasing the NOx is provided. Further, upstream catalysts 4L and 4R made of a three-way catalyst and an SOx catalyst are provided in a plurality of exhaust passages 2L and 2R corresponding to the respective banks on the upstream side of the collecting section. It is of course possible to provide both the three-way catalyst and the SOx catalyst as the upstream catalysts 4L and 4R.

The N provided in the exhaust system as described above
The Ox catalyst 3 adsorbs a large amount of NOx discharged into the exhaust gas when the V-type engine 1 is operated in a lean operation, and purifies the NOx. Further, the sulfur component contained in the exhaust gas is adsorbed by the upstream catalysts 4L and 4R, particularly by the SOx catalyst, and is oxidized and reduced by the three-way catalyst to be purified.

The feature of this apparatus is that NO
a SOx adsorption amount estimating unit 5 for detecting the deterioration of the purifying ability caused by the adhesion of the sulfur component to the x catalyst 3; and controlling the combustion of the V-type engine 1 to release the sulfur component from the NOx catalyst 3, whereby NOx The point is that a combustion control unit 6 for regenerating the catalyst 3 is provided. That is, the SOx adsorption amount estimating unit 5 calculates the NOx catalyst 3 from the integrated value of the injection pulse of the fuel injection valve during the lean operation of the V-type engine 1, for example.
To estimate the adsorption amount of SOx at
According to the Ox adsorption amount, the sulfur component (SO
It plays the role of detecting the deterioration of the purification capacity caused by x) (deterioration detection means). Further, the combustion control unit 6 determines that the SO
NOx catalyst 3 caused by sulfur component in x adsorption amount estimation unit 5
Is detected, the combustion of the V-type engine 1 is controlled to enrich the exhaust air-fuel ratio, and at the same time, the ignition timing is retarded to increase the exhaust gas temperature and, consequently, the catalyst temperature. NOx is controlled by such combustion control.
It plays a role of promoting the reduction action of the catalyst 3 and releasing the sulfur component (SOx) from the NOx catalyst 3 to regenerate the NOx catalyst 3 (regeneration control means).

At this time, the combustion control unit 6 individually controls the combustion of the V-type engine 1 for each bank (cylinder group) according to the temperature condition of each of the upstream catalysts 4L and 4R. I have. Specifically, the combustion control unit 6 detects the temperature of each of the catalysts 3, 4L, 4R from the output of a temperature sensor (not shown) provided downstream of each of the catalysts 3, 4L, 4R, for example. (Catalyst temperature detecting means 7) individually controls the combustion of each bank according to the temperature detection result. Alternatively, the combustion control unit 6 individually controls the combustion in each bank in accordance with the relationship between the combustion state of each bank and the upstream catalysts 4L and 4R previously determined in the temperature map 8. And by individual combustion control of these banks,
The temperatures of the upstream catalysts 4L, 4R provided in the respective exhaust passages 2L, 2R are made equal to each other.

More specifically, as shown in FIG. 2, for example, the procedure of the combustion control is shown in FIG.
The amount of SOx adsorbed on the NOx catalyst 3 is estimated from the integrated value of the injection pulse of the fuel injection valve during the lean operation of the engine 1 and it is determined whether the estimated amount of SOx adsorbed exceeds a predetermined value [Step] S1]. When the SOx adsorption amount exceeds a predetermined value, NO
It is determined that the purification ability of the x catalyst 3 has deteriorated, and that the NOx catalyst 3 needs to be regenerated by releasing the sulfur component. If the SOx adsorption amount is less than the above-described predetermined value, it is determined that the purification ability of the NOx catalyst 3 has not deteriorated, and the process returns without executing the NOx catalyst 3 regeneration process described below.

When the deterioration of the NOx catalyst 3 is determined (detected) as described above, it is necessary to regenerate the NOx catalyst 3 according to the operating state at that time by referring to the temperature map 8 described above, for example. The combustion conditions are determined for each bank so that the combustion conditions of the V-type engine 1 are such that the temperatures of the upstream catalysts 4L and 4R provided in the exhaust passages 2L and 2R are equal to each other [Step S2]. ]. Incidentally, such combustion conditions are obtained by testing in advance operating conditions (air-fuel ratio, ignition timing, etc.) when the temperatures of the upstream catalysts 4L, 4R become equal to each other in various operating conditions, and this is determined by a temperature map. 8 is given.

When the combustion conditions (operating conditions) for each bank are obtained from the temperature map 8 in this way, the combustion of each bank of the V-type engine 1 is individually controlled according to the control information [Step S3]. . Each of the banks is operated in a rich manner, and the ignition timing is retarded (retarded) to adjust the exhaust gas temperature individually, so that each upstream side is controlled independently of the layout structure of the exhaust passages 2L and 2R. The temperatures of the catalysts 4L and 4R are made equal to each other. Such a temperature adjustment by the combustion control of each bank is performed so that the temperature of the NOx catalyst 3 becomes equal to or higher than a temperature required for releasing the SOx within a range where the upstream catalysts 4L and 4R are not excessively heated. The control is performed.

The combustion control for regenerating the NOx catalyst 3 is repeatedly executed until the control time reaches a preset time limit, for example [Step S4].
The time limit is set as a time period during which SOx can be almost completely released from the NOx catalyst 3 at a predetermined exhaust air-fuel ratio and a predetermined catalyst temperature. By monitoring such a combustion control time, the exhaust air-fuel ratio is controlled so that the enrichment of the exhaust air-fuel ratio is unintentionally continued for a long time, and the fuel consumption is not deteriorated by this.

Thus, according to the above-described combustion control for the V-type engine 1, since the combustion conditions of each bank are individually controlled, the combustion conditions are provided for each bank irrespective of the layout structure of the exhaust passages 2L and 2R. Upstream catalyst 4L, 4R
The temperature of the NOx catalyst 3 can be increased to a temperature required for releasing SOx while the temperatures of the NOx catalysts are made equal to each other. As a result, without excessively heating the upstream side catalysts 4L and 4R, NO
x The sulfur component (SOx) is efficiently released from the catalyst 3,
The NOx catalyst 3 can be regenerated.

By the way, in the above-described control mode, the relationship between the temperatures of the upstream-side catalysts 4L and 4R and the operating conditions of each bank, which are obtained in advance by a test, is searched from the temperature map 8.
This is a simple control method for individually controlling the operating conditions of each bank according to the search information. However, as described above, the combustion of the V-type engine 1 is controlled for each bank while detecting the temperature of each of the catalysts 3, 4L, 4R, whereby NO
It is also possible to regenerate x catalyst 3.

FIG. 3 shows a processing procedure of such a combustion control. Also in this case, N
The process is started by estimating the SOx adsorption amount in the Ox catalyst 3 and determining whether or not the NOx catalyst 3 needs to be regenerated (step S11). If the deterioration of the NOx catalyst 3 is detected, the rich operation of the engine body 1 is started under the combustion control unit 6 and the exhaust passages 2L,
In order to individually control the temperatures of the upstream catalysts 4L and 4R in 2R, retard (retard) control of the ignition timing in each bank is started [Step S12].

The adjustment of the ignition timing in each bank, which is executed together with the enrichment of the exhaust air-fuel ratio, is performed by adjusting each of the catalysts 3,
It is executed while detecting the temperatures of 4L and 4R. Specifically, the temperature T _NOX of the NOx catalyst 3 is an operating temperature required for releasing the sulfur component from the NOx catalyst 3, for example, 600
It is determined whether the temperature is equal to or higher than C (Step S13). When the temperature T _NOX of the NOx catalyst 3 is less than 600 ° C., the ignition timing in each bank is retarded (retarded) in order to raise the temperature of the exhaust gas and raise the temperature of the NOx catalyst 3 [Step S14].

After the ignition timing in each bank is retarded (retarded) in this way, or when the temperature T _NOX of the NOx catalyst 3 exceeds 600 ° C., the upstream side catalysts 4L, 4R the temperature difference, for example, <T _L -T _R
>, And determines whether the temperature difference is within a predetermined value, specifically, for example, within 30 ° C. [Step S15]. If the temperature difference exceeds 30 ° C., in order to increase the temperature of the low temperature side upstream catalysts 4L, 4R and reduce the temperature difference, the exhaust passages 2L, 2R on the side where the catalysts are provided. The ignition timing of the bank is further retarded [step S16]. That is, the ignition timing is retarded only for the bank having the lower catalyst temperature, the temperature of the exhaust gas discharged from the bank is increased, and the large temperature difference between the upstream catalysts 4L and 4R is corrected.
The catalyst temperatures are made substantially equal.

In addition to the above-described combustion control for each bank, the temperatures T _L , T _{R of the} upstream catalysts 4L, 4R are further increased.
It is determined whether the temperature is equal to or lower than the heat-resistant temperature, for example, 900 ° C. [Step S17].
In this case, the ignition timing of the bank exceeding the threshold is advanced and the temperature of the exhaust gas from that bank is reduced [Step S1]
8].

The ignition timing control of each bank based on the catalyst temperature is repeatedly executed while being sequentially fed back until the control time reaches a predetermined time limit [step S19]. As a result, the operating conditions of each bank are individually controlled in accordance with the temperature of each of the catalysts 3, 4L, 4R, so that the temperature T _NOX of the NOx catalyst 3 becomes 600 ° C. or more, and the temperature T _{L of} the upstream catalysts 4L, 4R, T _R is 900 ℃
In the following, the temperature difference is set so as to be within 30 ° C. (substantially equal).

Therefore, the layout structure of the exhaust passages 2L, 2R respectively derived from the respective banks of the V-type engine 1 is different, and as a result, the upstream catalysts 4L, 4R interposed in the exhaust passages 2L, 2R, respectively. Even when the temperature environment is different, the NOx catalyst 3 is controlled while controlling the upstream catalysts 4L and 4R to be substantially equal to or lower than the allowable temperature limit.
, The sulfur component (SOx) can be efficiently released from the NOx catalyst 3, and the NOx catalyst 3 can be regenerated.
In particular, it is possible to prevent a problem that only the upstream catalyst on one side is excessively heated and its durability is significantly deteriorated.

The present invention is not limited to the above embodiment. The operation control executed individually for each bank so as to equalize the temperature of the upstream catalyst provided in each exhaust passage is described in, for example, an engine of a type in which fuel is directly injected into a combustion chamber. In addition to adjusting the ignition timing, the fuel injection timing is adjusted, and furthermore, the fuel is injected in two stages, the intake stroke and the expansion stroke, to adjust the temperature of the combustion exhaust gas. It is also possible to adopt. Further, based on the relationship between the output of a temperature sensor provided downstream of the NOx catalyst 3 and the temperature difference between the NOx catalyst 3 and the upstream catalysts 4L and 4R obtained in advance through tests or the like, the temperature of the upstream catalysts 4L and 4R is determined. , The combustion control for each bank may be executed. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0031]

As described above, according to the present invention, a plurality of exhaust passages provided for each of a plurality of rows of cylinder groups of an internal combustion engine are combined with a NOx catalyst provided on the downstream side of an integrated portion. When the sulfur component is released to regenerate the NOx catalyst, the operation of each cylinder group of the internal combustion engine is individually controlled in accordance with the temperature state of the upstream catalyst provided in each of the exhaust passages. Thus, it is possible to make the temperatures of the upstream catalysts substantially equal and to sufficiently raise the temperature of the NOx catalyst while preventing the excessive temperature rise. As a result, it is possible to efficiently regenerate the NOx catalyst without impairing the durability of the catalyst.

In particular, in the second aspect, the NOx catalyst can be efficiently regenerated while accurately controlling the catalyst temperature. According to the third aspect, the effect that the NOx catalyst can be easily and effectively regenerated can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an exhaust gas purification device during an internal combustion period according to an embodiment of the present invention.

FIG. 2 is a diagram showing a control procedure of combustion control for each bank of the internal combustion engine executed based on a temperature map.

FIG. 3 is a diagram showing a control procedure of combustion control for each bank of the internal combustion engine that is executed based on the temperature of each catalyst detected by a temperature sensor.

[Explanation of symbols]

Reference Signs List 1 V-type engine 2L, 2R Exhaust passage 3 NOx catalyst 4L, 4R Upstream catalyst (three-way catalyst, SOx catalyst) 5 SOx adsorption amount estimation unit (deterioration detection unit) 6 Combustion control unit (regeneration control unit; rich air-fuel ratio) 7) Catalyst temperature detection means 8 Temperature map

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/24 ZAB F01N 3/24 ZABE F02D 41/34 ZAB F02D 41/34 ZABN F02P 5/15 ZAB F02P 5/15 ZABB

Claims (3)

[Claims] 1. A plurality of exhaust passages provided for each of a plurality of cylinder groups of an internal combustion engine; an exhaust gas purification catalyst interposed in each of the exhaust passages; and each of the exhaust passages is integrated. NO in the exhaust gas when the exhaust air-fuel ratio is lean.
a NOx catalyst that adsorbs x and releases the already adsorbed NOx when the oxygen concentration in the exhaust gas decreases, and a deterioration detecting unit that detects a deterioration state of the NOx catalyst caused by a sulfur component in the exhaust gas When deterioration of the NOx catalyst is detected by the deterioration detecting means, the operation of each cylinder group of the internal combustion engine is individually controlled in accordance with the temperature state of the catalyst provided in each of the exhaust passages. An exhaust gas purification device for an internal combustion engine, comprising: catalyst regeneration means for releasing the sulfur component adsorbed on the NOx catalyst. 2. The catalyst regeneration means detects a temperature of a catalyst interposed in each of the exhaust passages, and individually controls the operation of each cylinder group of the internal combustion engine according to the detected catalyst temperature. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust air-fuel ratio is enriched by the exhaust gas. 3. The catalyst regenerating means individually controls the operation of each of the cylinder groups based on a predetermined catalyst temperature for exhaust gas purification corresponding to the operation state of each of the cylinder groups of the internal combustion engine. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust air-fuel ratio is made rich.