JP3956107B2 - Exhaust purification device for multi-cylinder internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus for a multi-cylinder internal combustion engine, and more specifically, an exhaust gas purification apparatus having 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. About.
[0002]
[Related background]
In general, in an exhaust system of an automobile internal combustion engine (engine), for example, an underfloor catalytic converter (underfloor catalyzer converter, hereinafter abbreviated as UCC) is interposed under the floor of a vehicle. In this underfloor catalytic converter, HC (hydrocarbon), CO (carbon monoxide), and NOx (nitrogen oxide) in the exhaust gas are mainly purified and reduced by a three-way catalyst built in the catalytic converter. Further, in recent years, a vehicle including a three-way catalyst in an underfloor catalytic converter and a storage type NOx catalyst (NOx trap catalyst) that stores NOx in an oxidizing atmosphere and releases and reduces the stored NOx in a reducing atmosphere has been put into practical use. ing.
[0003]
Furthermore, recently, in addition to the underfloor catalytic converter, a separate pre-stage catalytic converter (manifold catalyzer converter or front catalyzer converter, in the exhaust manifold that is susceptible to high-temperature combustion gas from the engine or immediately after the exhaust manifold in order to activate the catalyst early. In the following, exhaust gas purifiers that are capable of exhibiting high exhaust gas purifying performance even immediately after the cold start of the engine have been developed and put into practical use.
[0004]
In addition, as an exhaust system, a dual type in which exhaust passages are combined into, for example, two (dual) between cylinders whose ignition order is not continuous, and exhaust performance or exhaust pulsation is used to improve full-open performance and obtain high output. Exhaust manifold systems are widely adopted, and in the dual type exhaust manifold system, a pre-stage catalytic converter is disposed in each collected exhaust passage.
[0005]
[Problems to be solved by the invention]
By the way, when only the underfloor catalytic converter is installed, the temperature of the exhaust gas flowing into the underfloor catalytic converter because it is cooled by the exhaust pipe, especially in the case of a light vehicle with a small displacement or low load operation, especially at the cold start. Has a problem that the underfloor catalytic converter cannot be sufficiently activated due to excessively low temperature. On the other hand, in heavy vehicles with a large displacement or during medium and high load operation, the exhaust passage flows into the underfloor catalytic converter because the temperature of the exhaust gas flowing into the underfloor catalytic converter is high. The reaction of unburned components such as HC and CO in the exhaust gas is promoted in the exhaust gas, and the exhaust gas temperature rises further. The underfloor catalytic converter overheats and the high performance range of the storage type NOx catalyst (for example, 350 to 450 ° C.) ) Is exceeded. Even if the storage type NOx catalyst is in the high performance range, the higher the exhaust gas temperature, the higher the NOx release rate in the reducing atmosphere. Therefore, a part of HC and NOx is not oxidized or reduced in the atmosphere. There is also the problem of being released.
[0006]
When the upstream catalytic converter is arranged upstream of the underfloor catalytic converter, most of the heat of the exhaust gas is used to raise the temperature of the upstream catalytic converter. There is a problem that it is difficult to activate the converter, and even if a reducing atmosphere is used, the reducing agent (HC, etc.) such as HC is consumed by the high-temperature pre-stage catalytic converter, so that the released NOx cannot be reduced sufficiently. However, if the reducing atmosphere is strengthened, there is a problem that fuel consumption increases and fuel consumption deteriorates, or reducing agent (HC or the like) becomes excessive and is released into the atmosphere.
[0007]
The present invention has been made to solve such problems, and an object of the present invention is to provide an exhaust emission control device for a multi-cylinder internal combustion engine that can fully utilize the catalyst performance while improving the output of the internal combustion engine. Is to provide.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a plurality of upstream exhaust passages provided for each of a plurality of cylinder groups of a multi-cylinder internal combustion engine and the plurality of upstream exhaust passages are collectively extended. A downstream exhaust passage and an upstream exhaust passage of only one of the plurality of upstream exhaust passages, an upstream catalytic converter having a three-way catalytic function, and a downstream exhaust passage; A downstream catalytic converter having a catalytic function; An exhaust throttle means provided in an upstream exhaust passage other than the one upstream exhaust passage among the plurality of upstream exhaust passages; It is characterized by having.
[0009]
That is, one upstream exhaust passage 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 not provided with a catalytic converter. As for the exhaust gas flowing through one upstream exhaust passage, HC, CO, etc. flowing into the downstream catalytic converter are reduced as a whole because HC, CO, etc. are purified by the upstream catalytic converter, while other The exhaust gas flowing through the upstream exhaust passage flows into the downstream catalytic converter while containing HC, CO, etc. and without taking heat away from the catalytic converter.
[0010]
As a result, even under low load operation, the underfloor catalytic converter is favorably activated by the heat of the exhaust gas from the other upstream exhaust passages, and HC, CO, etc. are reduced as a whole during medium and high load operation. Therefore, the acceleration of the reaction of HC, CO, etc. in the exhaust passage is mitigated and the temperature rise of the underfloor catalytic converter is suppressed, and for example, the storage NOx catalyst is prevented from exceeding the high performance range. For example, when NOx is released from the storage-type NOx catalyst, HC, CO, etc. in the exhaust gas from other upstream exhaust passages can be used without increasing the reducing agent (HC, etc.) and strengthening the reducing atmosphere. A good reducing atmosphere is formed and NOx is reduced and removed, thereby preventing deterioration of fuel consumption and release of HC and NOx into the atmosphere. That is, the catalyst performance is fully utilized regardless of the operating state of the internal combustion engine.
[0011]
In particular The exhaust throttle means is provided in an upstream exhaust passage other than the one upstream exhaust passage among the plurality of upstream exhaust passages. And In one upstream exhaust passage, there is an upstream catalytic converter, so the exhaust resistance is large, and in the other upstream exhaust passage, there is no catalytic converter, so the exhaust resistance is small, and the engine output of the internal combustion engine fluctuates due to variations. However, by providing the exhaust throttle means in the other upstream exhaust passage, the exhaust resistance becomes uniform and fluctuations in the engine output are prevented.
[0012]
Claims 2 In this invention, the exhaust throttle means is a carrier portion of a catalytic converter.
Therefore, by adopting the carrier portion of the catalytic converter as the exhaust throttle means, the exhaust resistance substantially equal to the exhaust resistance of one upstream exhaust passage in which the upstream catalytic converter is disposed also in other upstream exhaust passages. As a result, fluctuations in the engine output are satisfactorily prevented.
[0013]
Claims 3 This invention is characterized in that the plurality of upstream exhaust passages are provided for each cylinder group composed of a plurality of cylinders in which combustion does not continue among the cylinders of the multi-cylinder internal combustion engine.
In other words, 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 continue combustion, the effect of exhaust inertia or exhaust pulsation can be obtained.
[0014]
As a result, the fully open performance of the internal combustion engine is improved, the underfloor catalytic converter is activated early while ensuring high output, the deterioration of fuel consumption and the release of HC and NOx into the atmosphere are prevented, and the catalyst performance is improved. Fully utilized.
Claims 4 The invention further comprises an operation parameter changing means for changing the operation parameter for each of a plurality of cylinder groups of the multi-cylinder internal combustion engine.
[0015]
Therefore, even if there is a difference in engine torque due to exhaust resistance or exhaust pulsation between one upstream exhaust passage and the other upstream exhaust passage, operating parameters such as ignition timing and fuel injection timing are set for each cylinder group. The engine torque difference can be satisfactorily prevented by optimally changing the engine torque.
In addition, in the upstream catalytic converter, for example, by setting the combustion air-fuel ratio so that the exhaust air-fuel ratio in one upstream exhaust passage becomes a leaner air-fuel ratio than the exhaust air-fuel ratio in the other upstream exhaust passage. HC, CO, etc. can be purified more efficiently. During low-load operation, the underfloor catalytic converter is further activated by the oxidation reaction heat in the upstream catalytic converter, and during medium-high load operation. HC, CO, etc. are further reduced, and excessive temperature rise of the underfloor catalytic converter is reliably suppressed.
[0016]
Further, for example, during low load operation, the ignition timing is retarded for each cylinder group on the other upstream exhaust passage side, or sub-injection is performed after the expansion stroke in the case of a cylinder injection internal combustion engine (two (Stage combustion) or the like, the temperature rise of the exhaust gas is promoted, and the underfloor catalytic converter is activated even better.
[0017]
DETAILED DESCRIPTION OF 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 emission control device for a multi-cylinder internal combustion engine according to the present invention, and the configuration of the exhaust emission control device will be described below.
As shown in the figure, an engine main body (hereinafter simply referred to as an engine) 1 that is a multi-cylinder internal combustion engine, for example, in a compression stroke together with fuel injection in an intake stroke (intake stroke injection) by switching a fuel injection mode. An in-cylinder injection type spark ignition type 4-cycle 4-cylinder gasoline engine capable of performing the fuel injection (compression stroke injection) is employed. The in-cylinder injection type engine 1 can be operated at a rich air-fuel ratio (rich air-fuel ratio operation) or a lean air-fuel ratio operation (lean air-fuel ratio operation) in addition to the operation at the stoichiometric air-fuel ratio (stoichio). It is.
[0018]
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, so that fuel can be directly injected into the combustion chamber. .
An ignition coil 8 that outputs a high voltage is connected to the spark plug 4. Further, 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, whereby fuel in the fuel tank is supplied 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 into the combustion chamber at a desired fuel pressure.
[0019]
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 for adjusting the intake air amount.
Further, an exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of the exhaust manifold 20 is connected to communicate with each exhaust port. Here, as the exhaust manifold 20, a dual type exhaust manifold system as shown in FIG. 2 is employed.
[0020]
In the exhaust manifold 20 including 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 merge. (When the combustion order is # 1 → # 3 → # 4 → # 2). That is, the # 1 and # 4 cylinders that do not continue combustion are combined into one cylinder group (# 1, # 4 cylinder group), and the # 2 and # 3 cylinders that also do not continue combustion are combined with another cylinder group (# 2). , # 3 cylinder group). Thereby, in the exhaust manifold 20, as described above, the exhaust interference is reduced, and a large effect of exhaust inertia or exhaust pulsation can be obtained.
[0021]
An exhaust pipe 28 is connected to the other end of the exhaust manifold 20 via a collecting pipe 22, and the collecting pipe 22 is connected to the collecting pipe 22a and the exhaust passage 20b through which exhaust gas from the exhaust passage 20a and the exhaust passage 20d flows. It consists of two pipe lines (dual pipe lines) of the collecting pipe 22b through which the exhaust gas from the exhaust passage 20c flows. That is, in the collecting pipe 22, exhaust gas from one cylinder group consisting of # 1 cylinder and # 4 cylinder flows through the collecting pipe 22a, and exhaust gas from another cylinder group consisting of # 2 cylinder and # 3 cylinder is collected in the collecting pipe 22b. It is configured to flow through.
[0022]
A three-way catalyst (upstream catalytic converter, hereinafter referred to as MCC) 24 is interposed in the collecting pipe 22a as a pre-stage catalytic converter.
In addition, a linear air-fuel ratio sensor (λ sensor, hereinafter abbreviated as LAFS) 29 is provided as an exhaust sensor at a transition portion from the collecting pipe 22 to the exhaust pipe 28, that is, a collecting portion 27 of the collecting pipe 22a and the collecting pipe 22b. It has been.
[0023]
Further, an underfloor catalytic converter (downstream catalytic converter, hereinafter referred to as UCC) 30 is interposed in the exhaust pipe 28. As shown in the figure, the UCC 30 has a three-way catalyst 32 disposed on the upstream side and an occlusion-type NOx catalyst 34 disposed on the downstream side. The occlusion-type NOx catalyst 34 occludes NOx when the exhaust air-fuel ratio is a lean air-fuel ratio (oxidizing atmosphere), and releases the occluded NOx when the exhaust air-fuel ratio is made rich (reducing atmosphere). A catalyst configured to reduce.
[0024]
Further, an EGR passage 40 for returning 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. The EGR passage 40 is provided with an EGR valve 42 for adjusting the recirculation amount of the exhaust gas.
The 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. Overall control of the exhaust emission control device is performed.
[0025]
Various sensors such as the LAFS 29 described above are connected to the input side of the ECU 60, and 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, and the EGR valve 42 are connected to the output side of the ECU 60. These various output devices are detected by various sensors. Commands such as the fuel injection amount, the fuel injection timing, the ignition timing, and the EGR amount calculated based on the information are each output, whereby an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and the spark plug 4 Thus, spark ignition is performed at an appropriate timing, and appropriate EGR control is performed.
[0026]
In the engine 1, based on the exhaust air / fuel ratio information from the LAFS 29, the combustion air / fuel ratio is feedback-controlled (air / fuel ratio F / B control) so that the exhaust air / fuel ratio becomes a predetermined air / fuel ratio.
Hereinafter, the operation of the exhaust gas purification apparatus for a multi-cylinder internal combustion engine according to the present invention configured as described above will be described by dividing the operating state.
[0027]
“At cold start (low load operation)”
Since the MCC 24 is in a position close to the engine 1 when the engine 1 is cold started, the MCC 24 is activated early by the heat of the exhaust gas in the collecting pipe 22a, and HC, CO, etc. in the exhaust gas are purified well. .
On the other hand, in the collecting pipe 22b, the exhaust gas passes through the exhaust pipe 28 and the UCC 30 as they are without purification of HC, CO, etc., so although the exhaust gas temperature is slightly lowered by the air cooling of the exhaust pipe 28, the UCC 30, ie three The original catalyst 32 and the storage NOx catalyst 34 are also activated early by the heat of the exhaust gas.
[0028]
In other words, if the MCC is provided in the collecting pipe 22b as well as the collecting pipe 22a as in the prior art, most of the heat of the exhaust gas flowing out from the engine 1 is used to activate the temperature of the MCC and the UCC is sufficiently activated. Although it is not performed, early activation of the UCC 30 can be achieved by not providing the MCC for the collecting pipe 22b.
[0029]
By the way, if the MCC 24 is provided only in the collecting pipe 22a, the exhaust resistance increases on the collecting pipe 22a side where the MCC 24 is provided, whereas the exhaust resistance decreases on the collecting pipe 22b side. As a result, the output torque of the engine 1 may vary due to variations between the # 1, # 4 cylinder group and the # 2, # 3 cylinder group.
[0030]
Therefore, here, in accordance with a command from the ECU 60, the ignition timing, fuel injection timing, etc. (operating parameters) of the engine 1 are set for each cylinder group, that is, for the # 1, # 4 cylinder group and the # 2, # 3 cylinder group, respectively. Different settings are made to suppress output torque fluctuations of the engine 1 (operation parameter changing means).
Here, the combustion air-fuel ratio (operation parameter) of the # 1, # 4 cylinder group is set to a lean air-fuel ratio side with respect to the combustion air-fuel ratio of the # 2, # 3 cylinder group (operation parameter changing means). ). In this way, the exhaust air-fuel ratio in the collecting pipe 22a becomes a lean air-fuel ratio, and in the presence of sufficient oxygen, the oxidation reaction of HC, CO, etc. proceeds rapidly in the MCC 24, and more reaction heat is generated. . Thereby, the temperature of the exhaust gas that reaches the UCC 30 via the exhaust pipe 28 is further increased, and the UCC 30 is activated well.
[0031]
In this case, for the # 2 and # 3 cylinder groups, the combustion air-fuel ratio is made rich, the ignition timing is retarded, or the sub-injection of fuel is performed after the expansion stroke (two-stage combustion). In this way, the reaction in the collecting pipe 22b and the exhaust pipe 28 is promoted, the exhaust temperature rises, and the UCC 30 is activated even better (operation parameter changing means).
[0032]
Note that the ignition timing, fuel injection timing, sub-injection timing, combustion air-fuel ratio, etc. (operating parameters) may be instantaneous values or average values.
“During normal operation (medium / 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, HC, CO and the like in the exhaust gas flowing through the collecting pipe 22a are well 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 in a state containing HC, CO, etc., while the exhaust gas flowing through the exhaust pipe 28 via the collecting pipe 22a is almost free of HC, CO, etc. It is supplied to the UCC 30 in a state where it is not included. In other words, when the collecting pipe 22a is provided with the MCC 24, the amount of HC, CO, etc. reaching the UCC 30 is reduced to approximately half as a whole as compared with the case where the MCC 24 is not provided.
[0033]
Thus, when the amount of HC, CO, etc. reaching the UCC 30 is substantially halved as a whole, the oxidation reaction of HC, CO, etc. in the three-way catalyst 32 of the UCC 30 is suppressed, the generation of reaction heat is reduced, and the excess of the UCC 30 is exceeded. Temperature rise is prevented. Thereby, especially in the storage type NOx catalyst 34 positioned downstream of the three-way catalyst 32, there exists an optimum temperature range for purifying NOx, that is, a high performance range (for example, 350 to 450 ° C.). Thus, the temperature of the storage-type NOx catalyst 34 is well prevented from exceeding the high-performance range. Further, the three-way catalyst 32 and the occlusion-type NOx catalyst 34 can be prevented from being melted.
[0034]
Also in this case, the ignition timing and fuel injection timing (operation parameters) of the engine 1 are set for each cylinder group in accordance with a command from the ECU 60, that is, the # 1, # 4 cylinder group and the # 2, # 3 cylinder group. Therefore, the output torque fluctuation of the engine 1 is suppressed.
Further, the combustion air-fuel ratio of the # 1, # 4 cylinder group is set to the lean air-fuel ratio side with respect to the combustion air-fuel ratio of the # 2, # 3 cylinder group. In this way, in the presence of sufficient oxygen, HC, CO, etc. are sufficiently purified in the MCC 24 and reliably reduced, and the temperature of the storage type NOx catalyst 34 exceeds the high performance range. Is better prevented. Further, the three-way catalyst 32 and the occlusion-type NOx catalyst 34 are prevented from being melted more satisfactorily.
[0035]
"NOx purge operation"
The NOx stored in the storage type NOx catalyst 34 needs to be periodically released and reduced (NOx purge). When the stored amount of NOx reaches a predetermined amount, the combustion air-fuel ratios of the # 1, # 4 cylinder groups As is, the combustion air-fuel ratio of the # 2 and # 3 cylinder groups is set to the rich air-fuel ratio, and the reducing agent (HC, CO, etc.) is supplied to the storage-type NOx catalyst 34. In this way, since there is no catalytic converter in the collecting pipe 22b that obstructs anything, the exhaust air-fuel ratio of the exhaust gas supplied from the collecting pipe 22b through the exhaust pipe 28 to the occlusion-type NOx catalyst 34 is efficiently increased to a rich air-fuel ratio ( Reducing atmosphere), and the NOx purge of the storage-type NOx catalyst 34 can be carried out satisfactorily.
[0036]
That is, if MCC is provided in both the collecting pipe 22a and the collecting pipe 22b, even if the combustion air-fuel ratio is set to a rich air-fuel ratio and the exhaust air-fuel ratio is set to a rich air-fuel ratio (reducing atmosphere), HC, CO, etc. are MCC. HC, CO, etc. are not supplied well to the occlusion-type NOx catalyst 34, and therefore the richness of the combustion air-fuel ratio is increased by increasing the fuel injection amount, etc. However, in the present invention, it is not necessary to increase the richness of the combustion air-fuel ratio in this way, and the deterioration of fuel consumption is prevented, and the atmosphere of NOx that cannot be reduced due to lack of HC, CO, etc. Release into the atmosphere and release of excess HC, CO, etc. into the atmosphere are prevented.
[0037]
Further, as described above, the UCC 30 and hence the NOx storage catalyst 34 are prevented from excessively rising in temperature. Therefore, the higher the catalyst temperature, the higher the NOx release rate during the NOx purge. Although there is a possibility that it will not be reduced, such a situation where NOx is not reduced is avoided, and the release of NOx into the atmosphere is also prevented.
[0038]
As described above, according to the exhaust gas purification apparatus according to 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. It is possible to fully utilize the catalyst performance of the UCC 30 together with the MCC 24 regardless of the medium / high load operation and the NOx purge operation). 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 fully open performance of the engine 1 is improved and the UCC 30 together with the MCC 24 while ensuring high output. The catalyst performance of can be fully utilized.
[0039]
Since the upstream end of the EGR passage 40 is connected to the downstream portion of the MCC 24 in the collecting pipe 22a, the MCC 24 functions as a filter, and deposit components in the EGR gas can be reduced.
By the way, referring to FIG. 3, a modification of the above embodiment is shown. As shown in FIG. 3, the collecting pipe 22b is composed of only the carrier part of the catalytic converter, that is, the carrier part having a cross-sectional lattice shape without the catalyst layer. A catalyst carrier (exhaust throttle means, cordierite, etc.) 26 may be interposed.
[0040]
As described above, when the catalyst carrier 26 is interposed in the collecting pipe 22b, when the catalyst carrier 26 is not provided, the exhaust resistance on the collecting pipe 22a side provided with the MCC 24 is large, whereas the exhaust resistance on the collecting pipe 22b side is large. Although the output of the engine 1 varies between the # 1, # 4 cylinder group and the # 2, # 3 cylinder group due to variations, the exhaust resistance on the collecting pipe 22b side is substantially equal to the exhaust resistance on the collecting pipe 22a side. As a result, the output fluctuation of the engine 1 is prevented well, and the output of the engine 1 is improved. In particular, the dual exhaust manifold system is used in combination with the exhaust manifold 20 to obtain the effect of exhaust inertia or exhaust pulsation, thereby further improving the fully open performance of the engine 1 and ensuring high output while maintaining the high output. The catalytic performance of UCC30 can be fully utilized.
[0041]
Further, in order to increase the exhaust resistance on the collecting pipe 22b side, the flow passage cross-sectional area of the collecting pipe 22b may be throttled, and as shown in FIG. 4, another throttle valve 26 is provided in the collecting pipe 22b. You may be allowed to intervene. In this case, the opening of the throttle valve 26 ′ may be adjusted as appropriate 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.
[0042]
The description of the embodiment is finished as above, but the present invention is not limited to the above embodiment.
For example, in the above embodiment, the MCC 24 is disposed only on the collecting pipe 22a, but the MCC 24 may be disposed only on the other collecting pipe 22b.
In the above-described embodiment, the case where the engine 1 has four cylinders and the collecting pipe 22 includes two pipes (dual pipes) including the collecting pipe 22a and the collecting pipe 22b has been described. A plurality of cylinders may be used, and the number of collecting pipes 22 may be three or more. In this case, it is preferable that only one collecting pipe is not provided with a catalytic converter.
[0043]
Moreover, although the case where the storage type NOx catalyst 34 is provided in the UCC 30 has been described in the above embodiment, the UCC 30 may be configured by only the three-way catalyst 32, and even in this case, sufficient for early activation and the like is sufficient. An effect is obtained. Further, the UCC 30 may be configured only by the storage-type NOx catalyst 34, or may be configured by including a three-way catalyst upstream and downstream of the storage-type NOx catalyst 34, and downstream of the storage-type NOx catalyst 34. A three-way catalyst may be provided.
[0044]
In the above embodiment, the MCC 24 is disposed only in one collecting pipe 22a and the catalytic converter is not provided in the other collecting pipe 22b. However, the other collecting pipe 22b has a precious metal than the MCC 24. Alternatively, an MCC having a small amount of loading, that is, low catalytic performance may be provided.
In the above-described embodiment, a cylinder injection type spark ignition type four-cycle four-cylinder gasoline engine is used as the engine 1, but the present invention may be applied to an intake pipe injection type gasoline engine, a two-cycle gasoline engine, a diesel engine, or the like. The invention can be applied satisfactorily.
[0045]
【The invention's effect】
As described above in detail, according to the exhaust purification device for a multi-cylinder internal combustion engine of claim 1 of the present invention, one upstream exhaust passage of the plurality of upstream exhaust passages has a three-way catalyst function. Since the upstream catalytic converter is provided, while the other upstream exhaust passage is not provided with a catalytic converter, the exhaust gas flowing through one upstream exhaust passage is subjected to purification treatment of HC, CO, etc. by the upstream catalytic converter. HC, CO, etc. flowing into the downstream catalytic converter as a whole can be reduced as a whole, while the exhaust gas flowing through the other upstream exhaust passages still contains HC, CO, etc. and is deprived of heat by the catalytic converter. Without being introduced into the downstream catalytic converter.
[0046]
As a result, the underfloor catalytic converter can be satisfactorily activated by the heat of exhaust gas from other upstream exhaust passages even during low-load operation, and the HC, CO, etc. can be reduced as a whole during mid-high load operation. The temperature rise of the catalytic converter can be suppressed so that, for example, the storage-type NOx catalyst does not exceed the high-performance range, and further, for example, when NOx is released from the storage-type NOx catalyst, the exhaust gas from other upstream exhaust passages HC, CO, etc. in the interior form a reducing atmosphere and NOx can be reduced and removed to prevent fuel consumption deterioration and release of HC and NOx into the atmosphere. Can be fully utilized.
[0047]
And In one upstream exhaust passage, the exhaust resistance is large because of the upstream catalytic converter, and in the other upstream exhaust passage, the exhaust resistance is small because there is no catalytic converter. By providing the throttle means, exhaust resistance can be made uniform, and fluctuations in the engine output can be prevented.
[0048]
Claims 2 According to the exhaust purification device for a multi-cylinder internal combustion engine, since the carrier portion of the catalytic converter is employed as the exhaust throttle means, one upstream exhaust passage in which the upstream catalytic converter is disposed also in the other upstream exhaust passages Exhaust resistance substantially equal to the exhaust resistance can be obtained, and fluctuations in engine output can be satisfactorily prevented.
Claims 3 According to the multi-cylinder internal combustion engine exhaust gas purification apparatus, since 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 is employed. The effect of exhaust inertia or exhaust pulsation can be obtained. As a result, the fully open performance of the internal combustion engine can be improved, while ensuring high output, the underfloor catalytic converter can be activated early, the fuel consumption can be prevented, and the release of HC and NOx into the atmosphere can be prevented. It can be used for.
[0049]
Claims 4 According to this multi-cylinder internal combustion engine exhaust gas purification apparatus, even when there is an engine resistance difference due to exhaust resistance or exhaust pulsation between one upstream exhaust passage and another upstream exhaust passage, The engine torque difference can be satisfactorily prevented by optimally changing the operating parameters such as the fuel injection timing for each cylinder group. For example, the exhaust air-fuel ratio in one upstream exhaust passage is different from that in the other upstream exhaust passage. By setting the combustion air-fuel ratio so that it becomes leaner than the exhaust air-fuel ratio in the engine, it becomes possible to more efficiently purify HC, CO, etc. in the upstream catalytic converter, and during low-load operation Can activate the underfloor catalytic converter even better due to the oxidation reaction heat in the upstream catalytic converter, and further reduce the HC, CO, etc. during medium and high load operation to ensure overheating of the underfloor catalytic converter For example, during low load operation, the ignition timing is retarded for each cylinder group on the other upstream exhaust passage side, or sub-injection is performed after the expansion stroke in the case of a cylinder injection internal combustion engine. By implementing (two-stage combustion), it is possible to promote the temperature rise of the exhaust gas and to activate the underfloor catalytic converter even better.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an exhaust emission control 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 view showing a dual type exhaust manifold system according to a modification of the present invention.
FIG. 4 is a view showing a dual type exhaust manifold system according to another modification of the present invention.
[Explanation of symbols]
1 engine
6 Fuel injection valve
20 Exhaust manifold
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, UCC)
32 Three-way catalyst
34 NOx storage type catalyst
60 Electronic control unit (ECU)

Claims (4)

A plurality of upstream exhaust passages provided for a plurality of cylinder groups of the multi-cylinder internal combustion engine;
A downstream exhaust passage extending from the plurality of upstream exhaust passages;
An upstream catalytic converter disposed only in one upstream exhaust passage of the plurality of upstream exhaust passages and having a three-way catalytic function;
A downstream catalytic converter disposed in the downstream exhaust passage and having a catalytic function;
Exhaust throttle means provided in an upstream exhaust passage other than the one upstream exhaust passage among the plurality of upstream exhaust passages;
An exhaust emission control device for a multi-cylinder internal combustion engine. Wherein the exhaust throttle means is a carrier moiety of the catalytic converter, exhaust gas purification apparatus for a multi-cylinder internal combustion engine according to claim 1. 3. The multi-cylinder according to claim 1, wherein the plurality of upstream exhaust passages are provided for each cylinder group including a plurality of cylinders in which combustion does not continue among the cylinders of the multi-cylinder internal combustion engine. An exhaust purification device for an internal combustion engine. The exhaust purification device for a multi-cylinder internal combustion engine according to any one of claims 1 to 3 , 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.

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