JP2003293750A - Exhaust emission control device for multicylinder internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for a multicylinder internal combustion engine, capable of sufficiently utilizing catalyst performance while improving the output of the internal combustion engine. <P>SOLUTION: An upstream side catalyst converter 24 having a three-way catalyst function is arranged only in an upstream side exhaust passage 22a, one of a plurality of upstream side exhaust passages 22 provided for every cylinder group in the multicylinder internal combustion engine 1. A downstream side catalyst converter 30 having catalyst functions 32, 34 is provided in a downstream side exhaust passage 28. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification apparatus for a multi-cylinder internal combustion engine, and more particularly, it has a front-stage catalytic converter (FCC or MCC) on the upstream side of an exhaust passage and an underfloor catalytic converter (UCC) on the downstream side. ) Related to the exhaust gas purification device.

[0002]

Related Background Art Generally, an exhaust system of an internal combustion engine (engine) for an automobile is provided with an underfloor catalytic converter (underfloor catalyzer converter, hereinafter abbreviated as UCC), which is located under the floor of the vehicle, for example. In this underfloor catalytic converter, HC (hydrocarbon), C in the exhaust gas is mainly contained in the three-way catalyst built in the catalytic converter.
Purifies and reduces O (carbon monoxide) and NOx (nitrogen oxides). In recent years, an underfloor catalytic converter, together with a three-way catalyst, absorbs NOx in an oxidizing atmosphere and releases the absorbed NOx in a reducing atmosphere to reduce the NOx.
A vehicle equipped with an Ox catalyst (NOx trap catalyst) has also been put into practical use.

Further, recently, in addition to the underfloor catalytic converter, a separate pre-stage catalytic converter (manifold catalyzer converter or front) is provided in the exhaust manifold or immediately after the exhaust manifold where the high-temperature combustion gas from the engine is apt to be activated for the purpose of early activation of the catalyst. An exhaust gas purification device has been developed and put into practical use, in which a catalyzer converter (hereinafter, abbreviated as MCC and FCC, respectively) is interposed, and high exhaust gas purification performance can be exhibited even immediately after a cold start of the engine.

Further, as an exhaust system, for example, two exhaust passages (dual) are provided between cylinders whose ignition order is not continuous.
In general, a dual type exhaust manifold system that uses exhaust inertia or exhaust pulsation to improve full-open performance and obtains high output is widely adopted.In the dual type exhaust manifold system, A pre-stage catalytic converter is provided in each of the above.

[0005]

By the way, when only an underfloor catalytic converter is provided, the exhaust pipe cools when a small vehicle with a small displacement or a low load operation, especially at the cold start. There is a problem that the temperature of the exhaust gas flowing into the underfloor catalytic converter becomes too low to activate the underfloor catalytic converter sufficiently, while it flows into the underfloor catalytic converter during heavy-duty vehicles with large displacement or medium-high load operation. Since the temperature of the exhaust gas is high, the reaction of unburned components such as HC and CO in the exhaust gas is promoted in the exhaust passage, and the temperature of the exhaust gas further rises. Performance range (eg 3
There is a problem that the temperature exceeds 50 to 450 ° C. Even if the NOx storage catalyst is in the high performance range, the higher the temperature of the exhaust gas is, the higher the temperature of the exhaust gas is, so that the release rate of NOx is increased in the reducing atmosphere. There is also the problem of being released.

When the upstream catalytic converter is arranged on the upstream side of the underfloor catalytic converter, most of the heat of exhaust gas is used for raising the temperature of the upstream catalytic converter. However, there is a problem in that it is difficult to activate the underfloor catalytic converter, and even if a reducing atmosphere is used, H
Since the reducing agent (HC etc.) such as C is consumed, the released NOx cannot be reduced sufficiently, and if the reducing atmosphere is strengthened, the fuel consumption increases and the fuel consumption deteriorates or the reducing agent (H
There is a problem that (C etc.) becomes a surplus and is released into the atmosphere.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a multi-cylinder internal combustion engine capable of sufficiently utilizing the catalytic performance while improving the output of the internal combustion engine. To provide an exhaust emission control device.

[0008]

In order to achieve the above object, in the invention of claim 1, a plurality of upstream side exhaust passages provided for each of a plurality of cylinder groups of a multi-cylinder internal combustion engine and the plurality of upstream side exhaust passages are provided. A downstream exhaust passage that extends by gathering the upstream exhaust passages,
An upstream side catalytic converter that is provided only in one of the plurality of upstream side exhaust passages and has a three-way catalytic function, and a downstream side that is provided in the downstream side exhaust passage and has a catalytic function. It is characterized by including a catalytic converter.

That is, one of the plurality of upstream exhaust passages is provided with an upstream catalytic converter having a three-way catalytic function, while the other upstream exhaust passage is provided with a catalytic converter. Regarding the exhaust gas flowing through one upstream exhaust passage, HC, CO, etc. flowing into the downstream catalytic converter are reduced as a whole because the upstream catalytic converter purifies HC, CO, etc.
On the other hand, regarding the exhaust gas flowing through the other upstream exhaust passage,
It flows into the downstream catalytic converter while containing HC, CO, etc. and without being deprived of heat by the catalytic converter.

As a result, the underfloor catalytic converter is well activated by the heat of the exhaust gas from the other upstream side exhaust passage even during low load operation, and HC, CO, etc. as a whole during medium and high load operation. Since it is reduced, the promotion of the reaction of HC, CO, etc. in the exhaust passage is moderated, the temperature rise of the underfloor catalytic converter is suppressed, and, for example, the occlusion type NOx catalyst is prevented from exceeding the high performance range. . Further, for example, when releasing NOx from the occlusion type NOx catalyst, HC and CO in exhaust gas from other upstream exhaust passages are not increased without increasing the reducing agent (HC etc.) to strengthen the reducing atmosphere.
As a result, a reducing atmosphere is satisfactorily formed, NOx is reduced and removed, and deterioration of fuel consumption and release of HC and NOx to the atmosphere are prevented. That is, the catalyst performance is fully utilized regardless of the operating state of the internal combustion engine.

Further, the invention of claim 2 is characterized in that an exhaust throttle means is provided in an upstream exhaust passage other than the one upstream exhaust passage among the plurality of upstream exhaust passages. Therefore, the exhaust resistance is large in one upstream exhaust passage due to the upstream catalytic converter, and the exhaust resistance is small in the other upstream exhaust passage due to the absence of a catalytic converter. Although it occurs, by providing the exhaust throttle means in the other upstream side exhaust passage, the exhaust resistance becomes uniform and the fluctuation of the engine output is prevented.

Further, according to the invention of claim 3, the exhaust throttle means is a carrier portion of the catalytic converter. Therefore, by adopting the carrier portion of the catalytic converter as the exhaust throttle means, even in the other upstream side exhaust passages, the exhaust resistance that is substantially equal to the exhaust resistance of the one upstream side exhaust passage in which the upstream side catalytic converter is arranged is provided. As a result, fluctuations in engine output can be effectively prevented.

Further, in the invention of claim 4, the plurality of upstream side exhaust passages are provided for each cylinder group of a plurality of cylinders of which combustion does not continue among the cylinders of the multi-cylinder internal combustion engine. I am trying. That is, by adopting a so-called dual type exhaust manifold system in which a plurality of upstream exhaust passages are provided for each cylinder group consisting of a plurality of cylinders that do not continuously burn, the effect of exhaust inertia or exhaust pulsation can be obtained.

As a result, the full-open performance of the internal combustion engine is improved, the high output is ensured, the underfloor catalytic converter is activated early, fuel consumption is deteriorated and HC and NOx are prevented from being released into the atmosphere. The catalyst performance is fully utilized. Further, the invention of claim 5 is characterized by further comprising operating parameter changing means for changing the operating parameter for each of a plurality of cylinder groups of the multi-cylinder internal combustion engine.

Therefore, even if there is a difference in engine torque due to exhaust resistance or exhaust pulsation between one upstream exhaust passage and another upstream exhaust passage, operating parameters such as ignition timing and fuel injection timing are set. The engine torque difference is favorably prevented by optimally changing the cylinder group. Further, for example, by setting the combustion air-fuel ratio so that the exhaust air-fuel ratio in one upstream exhaust passage is leaner than the exhaust air-fuel ratio in the other upstream exhaust passage, in the upstream catalytic converter It becomes possible to purify HC, CO, etc. more efficiently, and during low load operation, the underfloor catalytic converter is better activated by the heat of oxidation reaction in the upstream side catalytic converter. HC, CO, etc. are further reduced, and the excessive temperature rise of the underfloor catalytic converter is reliably suppressed.

Further, for example, at the time of low load operation, the ignition timing is retarded for each of the other cylinder groups on the upstream exhaust passage side, or when the cylinder injection type internal combustion engine is used, the secondary injection is performed after the expansion stroke. By carrying out (two-stage combustion),
The temperature rise of the exhaust gas is promoted, and the underfloor catalytic converter is activated even better.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust purification system for a multi-cylinder internal combustion engine according to the present invention, and the configuration of the exhaust purification system will be described below. As shown in the figure, the engine main body (hereinafter, simply referred to as an engine) 1 which is a multi-cylinder internal combustion engine is, for example, a fuel injection in an intake stroke (intake stroke injection) and a compression stroke by switching a fuel injection mode. In-cylinder spark ignition type 4-cycle 4 capable of performing fuel injection (compression stroke injection)
A cylinder gasoline engine is adopted. This in-cylinder injection type engine 1 can realize operation at a stoichiometric air-fuel ratio, operation at a rich air-fuel ratio (rich air-fuel ratio operation) and operation at a lean air-fuel ratio (lean air-fuel ratio operation). Is.

As shown in the figure, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, whereby the fuel is directly injected into the combustion chamber. It is possible. An ignition coil 8 that outputs a high voltage is connected to the spark plug 4. A fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe 7. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, which supplies the fuel in the fuel tank to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. Can be injected from the fuel injection valve 6 toward the combustion chamber at a desired fuel pressure.

An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected so as to communicate with each intake port. The intake manifold 10 is provided with an electromagnetic throttle valve 14 that adjusts the intake air amount. Further, the cylinder head 2 is formed with an exhaust port in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 20 is connected so as to communicate with each exhaust port. As the exhaust manifold 20, a dual type exhaust manifold system as shown in FIG. 2 is adopted here.

In the exhaust manifold 20 comprising the dual type exhaust manifold system, the exhaust passage 20a from the # 1 cylinder, the exhaust passage 20d from the # 4 cylinder, the exhaust passage 20b from the # 2 cylinder and the exhaust passage 20c from the # 3 cylinder. Are merged (when the combustion order is # 1 → # 3 → # 4 → # 2). In other words, the # 1 cylinder and # 4 cylinder, which do not burn continuously, form one cylinder group (#
No. 1 and # 4 cylinder groups), and again, the # 2 cylinder and # 3 cylinder, which do not continue to burn, are other cylinder groups (# 2 and # 3 cylinder groups).
I am trying to put together. As a result, in the exhaust manifold 20, as described above, exhaust interference is reduced, and a large effect of exhaust inertia or exhaust pulsation is obtained.

An exhaust pipe 28 is connected to the other end of the exhaust manifold 20 via a collecting pipe 22.
Is a collecting pipe 22a through which exhaust gas from the exhaust passage 20a and the exhaust passage 20d flows, the exhaust passage 20b, and the exhaust passage 2
It is composed of two conduits (dual conduit) of the collecting pipe 22b through which the exhaust gas from 0c flows. That is, in the collecting pipe 22, exhaust gas from one cylinder group including the # 1 cylinder and # 4 cylinder flows through the collecting pipe 22a, and exhaust gas from another cylinder group including the # 2 cylinder and the # 3 cylinder collects into the collecting pipe 22b. Is configured to flow through.

A three-way catalyst (upstream side catalytic converter, hereinafter referred to as M
CC) 24 is interposed. In addition, the transition from the collecting pipe 22 to the exhaust pipe 28, that is, the collecting pipe 22a and the collecting pipe 22.
A linear air-fuel ratio sensor (λ sensor, hereinafter abbreviated as LAFS) 29 is provided as an exhaust gas sensor in the collecting portion 27 with b.

An underfloor catalytic converter (downstream catalytic converter, UCC) 30 is further provided in the exhaust pipe 28. As shown in the figure, the UCC 30 has a three-way catalyst 32 arranged on the upstream side and a storage type NOx catalyst 34 arranged on the downstream side. Storage type NOx catalyst 3
No. 4 is configured to store NOx when the exhaust air-fuel ratio is a lean air-fuel ratio (oxidizing atmosphere), while releasing the stored NOx when the exhaust air-fuel ratio is a rich air-fuel ratio (reducing atmosphere). It is a catalyst.

An EGR passage 40 for recirculating a part of the exhaust gas (EGR gas) to the intake system extends from the collecting pipe 22a, and the tip of the EGR passage 40 is connected to the intake manifold 10. Then, the EGR passage 4
At 0, an EGR valve 42 for adjusting the recirculation amount of exhaust gas is installed. Electronic control unit (ECU) 60
Includes an input / output device, a storage device (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like, and the ECU 60 allows the exhaust purification device including the engine 1 to be comprehensively integrated. Control is performed.

On the input side of the ECU 60, the above-mentioned LAF is provided.
Various sensors such as S29 are connected, and the detection information from these sensors is input. On the other hand, various output devices such as the fuel injection valve 6, the ignition coil 8, the throttle valve 14, the EGR valve 42, etc. are connected to the output side of the ECU 60, and these various output devices are detected by various sensors. The commands such as the fuel injection amount, the fuel injection timing, the ignition timing, the EGR amount, etc., which are calculated based on the information, are respectively output, whereby the fuel injection valve 6 injects an appropriate amount of fuel at an appropriate timing, and the spark plug 4 As a result, spark ignition is performed at an appropriate timing, and appropriate EGR control is performed.

In the engine 1, the LAFS2
Based on the exhaust air-fuel ratio information from 9, the feedback control (air-fuel ratio F / B control) of the combustion air-fuel ratio is performed so that the exhaust air-fuel ratio becomes the predetermined air-fuel ratio. The operation of the exhaust gas purifying apparatus for a multi-cylinder internal combustion engine according to the present invention, which is configured as described above, will be described below in different operating states.

"Cold start (during low load operation)" When the engine 1 is cold started, the MCC 24 is located close to the engine 1. Therefore, in the collecting pipe 22a, the MCC 24 is activated early by the heat of the exhaust gas. HC and C in the exhaust
O and the like are satisfactorily purified. On the other hand, in the collecting pipe 22b, the exhaust gas passes through the exhaust pipe 28 and the UCC 30 as it is without purification of HC, CO, etc., so that the exhaust gas temperature is slightly lowered by the air cooling of the exhaust pipe 28.
CC30, that is, three-way catalyst 32 and occlusion type NOx catalyst 34
As for the above, the early activation can be achieved by the heat of the exhaust gas.

That is, if the MCC is provided not only in the collecting pipe 22a but also in the collecting pipe 22b as in the conventional case, most of the heat of the exhaust gas flowing out from the engine 1 is used for activating the temperature rise of the MCC and the UCC is sufficient. However, by not providing the MCC in the collecting pipe 22b, the UCC 30 can be activated early.

By the way, the MCC 24 is provided only in the collecting pipe 22a.
Is provided, the collecting pipe 22 provided with the MCC 24
On the a side, the exhaust resistance increases while the collecting pipe 22
On the b side, since the exhaust resistance becomes small, the output torque of the engine 1 may fluctuate between the # 1 and # 4 cylinder groups and the # 2 and # 3 cylinder groups due to the variation of the exhaust pulsation. There is.

Therefore, here, according to a command from the ECU 60, the ignition timing, the fuel injection timing and the like (operating parameters) of the engine 1 are set for each cylinder group, that is, # 1 and # 4 cylinder groups.
Different settings are made for the 2nd and 3rd cylinder groups to suppress output torque fluctuations of the engine 1 (operating parameter changing means). Further, here, the combustion air-fuel ratio (operating parameter) of the # 1 and # 4 cylinder groups is set to be leaner than the combustion air-fuel ratio of the # 2 and # 3 cylinder groups (operating parameter changing means). ). By doing so, the exhaust air-fuel ratio in the collecting pipe 22a becomes a lean air-fuel ratio, and HC in the MCC 24 exists in the presence of sufficient oxygen.
Oxidation reaction of CO and the like progresses rapidly, and more reaction heat is generated. As a result, the temperature of the exhaust gas that reaches the UCC 30 via the exhaust pipe 28 becomes even higher, and the UCC 30
Is well activated.

In this case, for the # 2 and # 3 cylinder groups, the combustion air-fuel ratio is set to the rich air-fuel ratio, the ignition timing is retarded, and the secondary injection of fuel is performed after the expansion stroke (two-stage combustion). It is often done, and if this is done, the collecting pipe 22
b, the reaction in the exhaust pipe 28 is promoted, the exhaust gas temperature rises, and the UCC 30 is more favorably activated (operation parameter changing means).

The ignition timing, fuel injection timing, sub-injection timing, combustion air-fuel ratio, etc. (operating parameters) may be instantaneous values or average values. “In normal operation (during medium and high load operation)” When the engine 1 shifts from the cold state to the warm state and the MCC 24 is in the active state, the collecting pipe 22
HC, CO, etc. in the exhaust gas flowing through a are satisfactorily purified by the MCC 24. That is, the exhaust gas flowing through the exhaust pipe 28 via the collecting pipe 22b is supplied to the UCC 30 while containing HC, CO, etc., while the exhaust gas flowing through the exhaust pipe 28 via the collecting pipe 22a contains almost no HC, CO, etc. It is supplied to the UCC 30 without being included. That is, when the MCC 24 is provided in the collecting pipe 22a, the MCC2
HC, CO reaching UCC30 compared to the case without 4
As a whole, the amount of etc. is reduced to about half.

HC, C reaching the UCC 30 in this way
When the amount of O or the like is substantially halved as a whole, the oxidation reaction of HC, CO and the like in the three-way catalyst 32 of the UCC 30 is suppressed, the generation of reaction heat is reduced, and the excessive temperature rise of the UCC 30 is prevented. As a result, the storage type NOx catalyst 34 located downstream of the three-way catalyst 32 has an optimum temperature range for purifying NOx, that is, a high performance range (for example, 350 to 450 ° C.). The temperature of the storage type NOx catalyst 34 is preferably prevented from exceeding the high performance range. In addition, the three-way catalyst 32 and the occlusion type NOx catalyst 3
Melting loss of No. 4 is also effectively prevented.

Also in this case, the ignition timing, the fuel injection timing, etc. (operating parameters) of the engine 1 for each cylinder group, that is, the cylinder groups # 1, # 4 and # 2, # 3, are commanded by the ECU 60. The setting is different for each cylinder group so that the output torque fluctuation of the engine 1 is suppressed. Further, the combustion air-fuel ratio of the # 1 and # 4 cylinder groups is set to be leaner than the combustion air-fuel ratio of the # 2 and # 3 cylinder groups. In this way, in the presence of sufficient oxygen, M
In CC24, HC, CO, etc. are sufficiently purified and reliably reduced, and the temperature of the occlusion-type NOx catalyst 34 is prevented from exceeding the high performance range. In addition, the three-way catalyst 32 and the occlusion type NOx catalyst 3
Melting loss of No. 4 is prevented even better.

"During NOx purge operation" Storage type NOx catalyst 3
It is necessary to periodically release the NOx stored in No. 4 and reduce it (NOx purge), but when the NOx storage amount reaches a predetermined amount, the combustion air-fuel ratio of the # 1 and # 4 cylinder groups remains unchanged. # 2, # 3 Cylinder group combustion air-fuel ratio is set to rich air-fuel ratio and reducing agent (HC, CO, etc.) is stored NO
x is supplied to the catalyst 34. In this way, the collecting pipe 22
Since b has no catalytic converter that causes any obstacle, the exhaust air-fuel ratio of the exhaust gas supplied from the collecting pipe 22b to the occlusion-type NOx catalyst 34 through the exhaust pipe 28 can be efficiently made into the rich air-fuel ratio (reducing atmosphere), and the occlusion can be performed. The NOx purge of the type NOx catalyst 34 can be carried out satisfactorily.

That is, together with the collecting pipe 22a, the collecting pipe 22a
When MCC is also provided in b, even if the combustion air-fuel ratio is set to the rich air-fuel ratio and the exhaust air-fuel ratio is set to the rich air-fuel ratio (reducing atmosphere), HC, CO, etc. are used for the oxidation reaction in the MCC and consumed. NOx is stored and HC, CO, etc. are occluded
The catalyst 34 is not satisfactorily supplied. Therefore, it is necessary to enhance the rich degree of the combustion air-fuel ratio and strengthen the reducing atmosphere by increasing the fuel injection amount, but in the present invention, the combustion air-fuel ratio is It is not necessary to increase the rich degree of the
It is possible to prevent the release of NOx into the atmosphere that cannot be reduced due to a shortage of CO and the like, and the release of excessively supplied HC, CO and the like into the atmosphere.

Further, as described above, the UCC 30 and thus the occlusion type NOx catalyst 34 are prevented from excessively rising in temperature. Therefore, the higher the catalyst temperature, the higher the NOx release rate during NOx purging and the shortage of HC, CO, etc. By NOx
May not be reduced, but such N
The situation where Ox is not reduced is avoided, and NOx is also prevented from being released into the atmosphere.

As described above, according to the exhaust gas purifying apparatus of the present invention, the MCC 24 is provided only in the collecting pipe 22a and the catalytic converter is not provided in the collecting pipe 22b.
Operating state of engine 1 (low load operation, medium and high load operation, N
UCC together with MCC24 regardless of Ox purge operation)
It is possible to fully utilize the catalytic performance of 30. In particular, by adopting a dual-type exhaust manifold system for the exhaust manifold 20 so as to obtain the effect of exhaust inertia or exhaust pulsation, the full-open performance of the engine 1 is improved, and a high output is ensured, while the UCC 30 is provided together with the MCC 24. The catalytic performance of can be fully utilized.

The upstream end of the EGR passage 40 is connected to the collecting pipe 2
Since it is connected to the downstream part of MCC24 of 2a,
The MCC 24 functions as a filter, and the deposit component in the EGR gas can be reduced. By the way, referring to FIG. 3, there is shown a modified example of the above-described embodiment. As shown in the figure, the collecting pipe 22b is composed only of a carrier of a catalytic converter, that is, a carrier portion having a lattice-like cross section without a catalyst layer. Catalyst carrier (exhaust restrictor, cordierite, etc.)
26 may be interposed.

In this way, the catalyst carrier 26 is attached to the collecting pipe 22b.
When the catalyst carrier 26 is not provided, the exhaust resistance on the side of the collecting pipe 22a provided with the MCC 24 is large, while the exhaust resistance on the side of the collecting pipe 22b is small.
Although variations in the output of the engine 1 occur between the 4-cylinder group and the # 2, # 3 cylinder groups, the exhaust resistance on the collecting pipe 22b side becomes substantially equal to the exhaust resistance on the collecting pipe 22a side, and The output fluctuation is favorably prevented, and the output of the engine 1 is improved. In particular, the exhaust manifold 20
The dual exhaust manifold system is also used to obtain the effect of exhaust inertia or exhaust pulsation to further improve the full-open performance of the engine 1 and secure the high output, while at the same time improving the catalytic performance of the UCC30 with the MCC24. It can be fully utilized.

Further, in order to increase the exhaust resistance on the side of the collecting pipe 22b, the flow passage cross-sectional area of the collecting pipe 22b may be narrowed. As shown in another modified example in FIG.
Alternatively, the throttle valve 26 'may be interposed. In this case, the opening of the throttle valve 26 'may be appropriately adjusted so that the exhaust resistance on the collecting pipe 22b side is substantially equal to the exhaust resistance on the collecting pipe 22a side. The opening may be fixed to be approximately equal to the exhaust resistance on the collecting pipe 22a side.

Although the description of the embodiment has been completed, the present invention is not limited to the above embodiment. For example, in the above embodiment, the MCC 24 is arranged only in the collecting pipe 22a, but the MCC 2 is arranged only in the other collecting pipe 22b.
4 may be provided. In the above embodiment, the engine 1 has four cylinders, and the collecting pipe 22 is the collecting pipe 2.
The case where the engine 1 has a plurality of cylinders, and the collecting pipe 22 may have three or more pipes, In this case, it is preferable that only one of the collecting pipes is not provided with the catalytic converter.

In the above embodiment, the case where the UCC 30 is provided with the storage type NOx catalyst 34 has been described.
The UCC 30 may be composed of only the three-way catalyst 32, and even in this case, a sufficient effect regarding early activation and the like can be obtained. Further, the UCC 30 may be composed only of the storage type NOx catalyst 34, and the storage type NOx catalyst 3
The three-way catalyst may be provided upstream and downstream of 4, and the three-way catalyst may be provided downstream of the occlusion type NOx catalyst 34.

In the above embodiment, one of the collecting pipes 2 is
Although the MCC 24 is arranged only in 2a and the other collecting pipe 22b is not provided with a catalytic converter,
The other collecting pipe 22b may be provided with an MCC having a smaller amount of precious metal carried than the MCC 24, that is, having a lower catalytic performance. Further, in the above embodiment, the cylinder injection type spark ignition type 4-cycle 4-cylinder gasoline engine is used as the engine 1. However, even if it is an intake pipe injection type gasoline engine, 2-cycle gasoline engine, diesel engine, etc. The invention is well applicable.

[0045]

As described in detail above, according to the exhaust purification system for a multi-cylinder internal combustion engine of claim 1 of the present invention, one of the plurality of upstream exhaust passages has three upstream exhaust passages. Since the upstream side catalytic converter having the original catalytic function is provided, while the other upstream side exhaust passages are not provided with the catalytic converters, the exhaust gas flowing through one upstream side exhaust passage is converted into HC and CO by the upstream side catalytic converter. Etc. can be purified to reduce HC, CO, etc. flowing into the downstream side catalytic converter as a whole, while the exhaust gas flowing through the other upstream side exhaust passage can contain HC, CO, etc. The heat can be allowed to flow into the downstream catalytic converter without being deprived of heat.

As a result, the underfloor catalytic converter can be satisfactorily activated by the heat of the exhaust gas from the other upstream side exhaust passage even during low load operation, and HC, CO, etc. as a whole during medium and high load operation. For example, the storage type NOx catalyst can be prevented from exceeding the high performance range by reducing the temperature rise of the underfloor catalytic converter and further, for example, the storage type NOx.
When releasing NOx from the catalyst, HC, CO, etc. in the exhaust gas from the other upstream exhaust passage form a favorable reducing atmosphere to reduce and remove NOx, thereby reducing fuel consumption and reducing HC and N
Ox can be prevented from being released into the atmosphere, and the catalyst performance can be fully utilized regardless of the operating state of the internal combustion engine.

According to the exhaust gas purifying apparatus for a multi-cylinder internal combustion engine of claim 2, the exhaust resistance is large because there is an upstream side catalytic converter in one upstream side exhaust passage, and the catalytic converter is in another upstream side exhaust passage. Although the exhaust resistance is small due to the absence of exhaust gas, the exhaust resistance can be made uniform by providing the exhaust throttle means in the other upstream exhaust passage, and the fluctuation of the engine output can be prevented.

Further, according to the exhaust gas purifying apparatus for a multi-cylinder internal combustion engine of claim 3, since the carrier portion of the catalytic converter is adopted as the exhaust throttle means, the upstream catalytic converter is arranged also in the other upstream exhaust passages. It is possible to obtain an exhaust resistance that is substantially equivalent to the exhaust resistance of the one upstream exhaust passage that has been set, and it is possible to favorably prevent fluctuations in engine output. Further, according to the exhaust purification system of a multi-cylinder internal combustion engine of claim 4, a so-called dual type exhaust manifold system in which a plurality of upstream side exhaust passages are provided for each cylinder group composed of a plurality of cylinders which do not continuously burn is adopted. Since this is done, the effect of exhaust inertia or exhaust pulsation can be obtained. As a result, the full-open performance of the internal combustion engine can be improved, high output can be secured, the underfloor catalytic converter can be activated quickly, and fuel consumption can be prevented from deteriorating and HC and NOx can be prevented from being released into the atmosphere. Can be used for.

According to the exhaust purification system of a multi-cylinder internal combustion engine of claim 5, when there is a difference in engine torque due to exhaust resistance or exhaust pulsation between one upstream exhaust passage and another upstream exhaust passage. However, the engine torque difference can be satisfactorily prevented by optimally changing the operating parameters such as the ignition timing and the fuel injection timing for each cylinder group. By setting the combustion air-fuel ratio such that the fuel ratio is leaner than the exhaust air-fuel ratio in the other upstream side exhaust passage, HC, C in the upstream side catalytic converter are increased.
O and the like can be purified more efficiently, the underfloor catalytic converter can be activated more favorably by the oxidation reaction heat in the upstream side catalytic converter during low load operation, and HC during medium and high load operation, CO and the like can be further reduced to reliably suppress excessive temperature rise of the underfloor catalytic converter, and, for example, at the time of low load operation, the ignition timing can be retarded for each cylinder group on the upstream exhaust passage side, In the case of an in-cylinder internal combustion engine, by performing sub-injection (two-stage combustion) after the expansion stroke, it is possible to accelerate the exhaust gas temperature rise and activate the underfloor catalytic converter even better. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an exhaust gas purification device for a multi-cylinder internal combustion engine according to the present invention.

FIG. 2 is a diagram showing a dual type exhaust manifold system according to the present invention.

FIG. 3 is a diagram showing a dual type exhaust manifold system according to a modification of the present invention.

FIG. 4 is a diagram showing a dual type exhaust manifold system according to another modification of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 engine 6 fuel injection valve 20 exhaust manifolds 22a, 22b collecting pipe (upstream exhaust passage) 24 three-way catalyst (upstream catalytic converter, MCC) 26 catalyst carrier (exhaust throttle means) 28 exhaust pipe (downstream exhaust passage) 30 Underfloor catalytic converter (downstream catalytic converter, U
CC) 32 three-way catalyst 34 occlusion type NOx catalyst 60 electronic control unit (ECU)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/28 301 F02D 9/04 E F02D 9/04 41/02 301H 41/02 301 F02P 5/15 N F02P 5/15 B01D 53/36 103B F term (reference) 3G022 AA06 AA09 AA10 3G065 AA04 AA09 CA00 CA12 CA13 EA02 3G091 AA02 AA11 AA12 AA15 AA17 AA18 AA24 A01 AA24 A01 A01 AA24 A01 AB12 AB03 DA02 DB10 DC01 EA30 EA34 FA02 FA04 FA11 FB02 FB03 FB10 FB11 FB12 FC04 FC07 FC08 GB01X GB10X GB17X HA03 HA10 HA12 HA36 HA37 HA47 HB02 HB03 HB05 3G301 HA08 HA13 HA15 HA18 JA01 LA18 MA01 MA18 CC07 A48 A4 4A0A12 DA02 DA20 EA04

Claims (5)

[Claims] 1. A plurality of upstream side exhaust passages provided for each of a plurality of cylinder groups of a multi-cylinder internal combustion engine, a downstream side exhaust passage extending together with the plurality of upstream side exhaust passages, and a plurality of upstream sides. An upstream side catalytic converter provided only in one of the exhaust passages and having a three-way catalytic function, and a downstream catalytic converter provided in the downstream side exhaust passage and having a catalytic function. An exhaust gas purification device for a multi-cylinder internal combustion engine, comprising: 2. The multi-cylinder according to claim 1, further comprising exhaust throttle means in an upstream exhaust passage other than the one upstream exhaust passage among the plurality of upstream exhaust passages. Exhaust gas purification device for internal combustion engine. 3. The exhaust purification system for a multi-cylinder internal combustion engine according to claim 2, wherein the exhaust throttle means is a carrier portion of a catalytic converter. 4. The plurality of upstream exhaust passages are provided for each cylinder group of a plurality of cylinders of a multi-cylinder internal combustion engine in which combustion does not continue. 4. An exhaust gas purification device for a multi-cylinder internal combustion engine according to any one of 3 above. 5. The multi-cylinder internal combustion engine according to claim 1, further comprising operation parameter changing means for changing an operation parameter for each of a plurality of cylinder groups of the multi-cylinder internal combustion engine. Exhaust purification device.