JP2000179329A - Exhaust purifying apparatus of multi-cylinder internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust purifying apparatus of a multi-cylinder internal combustion engine which has a catalyst in a main exhaust passage where a plurality of exhaust passages gather which are connected independently per cylinder group, wherein the apparatus is capable of improving a characteristic of an exhaust gas by efficiently increasing a temperature of the catalyst at an early stage while preventing the increase in rotational fluctuation due to a pumping loss. SOLUTION: A catalyst 30 is provided in a main exhaust passage 26. A reflux passage 14 is provided so as to connect a second exhaust passage 19 with an air-intake passage 10 located downstream of an air-quantity adjusting means 11. On a specific operating condition, a partial cylinder operating means discontinues combustion of a second cylinder-group 1b, and a valve means 16 simultaneously opens the reflux passage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for a multi-cylinder internal combustion engine, and more particularly, to exhaust gas flowing through independently connected exhaust passages for a plurality of cylinder groups and then collecting the exhaust gas at a main exhaust passage. The present invention relates to a catalyst temperature rising technique for an exhaust system configured to cause the temperature rise.

[0002]

[Related Background Art] A front catalyst (front-stage catalyst) is arranged near an exhaust manifold upstream of an underfloor catalyst (catalyst) provided in an exhaust passage of a multi-cylinder internal combustion engine to heat up the front catalyst quickly. Exhaust gas purification devices that improve exhaust gas characteristics have been put to practical use. In particular, in a multi-cylinder internal combustion engine such as a V-type multi-cylinder engine in which exhaust manifolds extend independently from a plurality of cylinder groups on the front bank side and the rear bank side, other parts in the engine room are arranged. An exhaust gas purifying apparatus is known in which a front catalyst is provided only on one bank side (for example, on the front bank side) so as not to deteriorate performance and increase costs.

[0003] In such a multi-cylinder internal combustion engine having a front catalyst only on one bank side, the rich air-fuel ratio operation is performed on the one bank side under specific operating conditions, while the fuel on the other bank side is operated. Injection is stopped, partial cylinder operation is performed, and exhaust gas containing unburned fuel (HC, etc.) from one bank through the pre-catalyst (front catalyst) and fresh air not containing fuel from the other bank are used. Japanese Patent Application Laid-Open No. Hei 7-133716 discloses an exhaust gas purifying apparatus having a structure in which the temperature of exhaust gas is raised by reacting the same in an exhaust pipe, thereby raising the temperature of a main catalyst (underfloor catalyst) early.

[0004]

However, in the exhaust gas purifying apparatus disclosed in the above publication, when the temperature of the main catalyst is to be raised to the activation temperature, the rich air-fuel ratio operation is performed on one bank side. No matter how much high-temperature exhaust gas containing unburned fuel discharged from one bank through the pre-catalyst flows into the main catalyst, it is always discharged from the other bank to burn the unburned fuel. Even if the cooled fresh air (for example, at normal temperature) is throttle-controlled by the throttle valve, a large amount flows into the main catalyst to cool the main catalyst, thereby causing a problem that the temperature of the main catalyst is not sufficiently increased. .

In order to prevent cold fresh air from flowing into the main catalyst, even if the throttle valve provided in the intake passage connected to the other bank is closed precisely,
There is also a problem that the inside of the cylinder becomes a vacuum, the pumping loss increases, and the rotation fluctuation of the internal combustion engine increases. The present invention has been made to solve such a problem, and an object of the present invention is to provide a multiple exhaust passage having a catalyst in a main exhaust passage in which a plurality of exhaust passages independently connected to each cylinder group are gathered. To provide an exhaust purification device for a multi-cylinder internal combustion engine capable of efficiently raising the temperature of a catalyst early and improving exhaust gas characteristics while preventing an increase in rotation fluctuation due to pumping loss. It is in.

[0006]

To achieve the above object, according to the first aspect of the present invention, a first exhaust passage and a second exhaust passage are independently connected to a first cylinder group and a second cylinder group, respectively. In an exhaust system in which the first exhaust passage and the second exhaust passage collectively extend as a main exhaust passage, a catalyst is provided in the main exhaust passage, and the catalyst is provided downstream of the second exhaust passage and the air amount adjusting means. A recirculation passage is provided to connect to the intake passage. When the specific operating condition is reached, the combustion in the second cylinder group is interrupted by the partial cylinder operating means, and at the same time, the recirculation passage is opened by the valve means.

Therefore, for example, under specific operating conditions that require the temperature of the catalyst to be raised, such as at the time of a cold start, combustion is stopped by stopping fuel injection by the injection valve or stopping ignition by the spark plug on the second cylinder group side. That is, only the first cylinder group burns the fuel injected from the injection valve and the high temperature exhaust gas discharged from the cylinder reaches the catalyst, while the fresh air sucked into the combustion chamber from the second cylinder group does not burn. The discharged fresh air is returned to the intake passage through the return passage almost without reaching the catalyst.

As a result, only the high-temperature exhaust gas from the first cylinder group flows into the catalyst, and the inflow of cold (for example, normal temperature) fresh air from the second cylinder group is suppressed. Can be efficiently heated without carelessly cooling, and the exhaust gas characteristics can be improved early. At this time, the amount of fuel supplied to the first cylinder group increases due to the necessity of obtaining a desired engine output by combustion of only the first cylinder group, and the temperature of exhaust gas discharged from the first cylinder group necessarily becomes extremely high. Become higher. Therefore, the temperature of the catalyst can be raised early.

In particular, when the cylinder head and the cylinder block are independent of each other in the first cylinder group and the second cylinder group, such as the front bank and the rear bank of a V-type multi-cylinder engine, the first bank is used. Since the heat of combustion in the cylinder group (for example, the front bank) is not easily taken by the second cylinder group (for example, the rear bank), the exhaust gas sufficiently rises due to the combustion heat, and the catalyst also quickly rises in temperature. It is possible.

Preferably, an on-off valve is provided at a position downstream of the branch of the recirculation passage in the second exhaust passage, and the valve is closed during partial cylinder operation to prevent exhaust gas (here, fresh air) from flowing to the catalyst side. Therefore, all the fresh air discharged from the second cylinder group is returned to the intake passage via the recirculation passage without reaching the catalyst, so that the temperature of the catalyst can be raised more efficiently.

In the first cylinder group, it is preferable to perform an exhaust gas heating operation in order to positively increase the exhaust gas temperature. That is, it is preferable that the ignition timing is retarded so that the unburned fuel reacts in the expansion stroke or the first exhaust passage. Further, when the multi-cylinder internal combustion engine is a direct injection type spark ignition type internal combustion engine, In other words, it is preferable to perform a two-stage injection in which a sub-injection is performed in the expansion stroke in addition to the main injection to cause the unburned fuel to react in the expansion stroke or the first exhaust passage.

Further, by disposing the pre-stage catalyst only in the first exhaust passage, the temperature of the pre-stage catalyst can be quickly raised, and the exhaust gas characteristics can be further improved.

[0013]

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 device for a multi-cylinder internal combustion engine according to the present invention mounted on a vehicle. The configuration of the device will be described.

Engine body (hereinafter simply referred to as engine) 1
For example, in-cylinder injection spark ignition capable of performing fuel injection in an intake stroke (intake stroke injection mode) or fuel injection in a compression stroke (compression stroke injection mode) by switching a fuel injection mode (operation mode), for example. It is a V-type 6-cylinder gasoline engine. The in-cylinder injection type engine 1 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric ratio), at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio.

As shown in FIG. 1, a front bank portion (first cylinder group, hereinafter abbreviated as F bank) 1a and a rear bank portion (a second cylinder group, hereinafter referred to as R bank) of the engine 1. In each cylinder head 2 of 1b,
An electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder
Is attached, so that fuel can be directly injected into the combustion chamber 8. The ignition plug 4 is connected to an ignition coil 5.

A fuel supply device (both not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, whereby the fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. From the fuel injection valve 6 into the combustion chamber at a desired fuel pressure. At this time, the fuel injection amount is determined from the fuel discharge pressure of the high-pressure fuel pump and the valve opening time of the fuel injection valve 6, that is, the fuel injection time.

In each cylinder head 2, an intake port is formed in a substantially upright direction for each cylinder, and one end of an intake manifold (intake passage) 10 is connected to communicate with each intake port. I have. The other end of the intake manifold 10 is connected to an electromagnetic type, that is, a drive-by-wire type throttle valve (air amount adjusting means) 11 which is opened and closed by a solenoid unit 13. The throttle valve 11 has a throttle opening θth. Is provided with a throttle position sensor (TPS) 12 for detecting the throttle position. Specifically, the throttle opening θth is detected based on the TPS output (voltage value) from the TPS 12.

An exhaust port is formed in each cylinder head 2 in a substantially horizontal direction for each cylinder, and a front exhaust manifold (first exhaust passage) 18 and a rear exhaust passage 18 communicate with each exhaust port. Manifold (2nd
One end of each of the exhaust passages 19 is connected. In the figure, reference numeral 20 denotes a crank angle sensor for detecting a crank angle.
Is detectable. Reference numeral 22 denotes a water temperature sensor that detects a cooling water temperature WT of the engine 1. The water temperature sensor 22 can determine whether the engine 1 is in a cold state or a warm-up state.

The in-cylinder injection type engine 1 is already known, and the detailed description of its configuration is omitted here. As shown in the figure, a small close three-way catalyst (front-stage catalyst) 24 is provided in the front exhaust manifold 18.
The exhaust pipe (main exhaust passage) 26 is connected via the.
On the other hand, the exhaust pipe 26 is directly connected to the rear exhaust manifold 19.
Is connected. That is, the proximity three-way catalyst 24 is provided only on the F bank 1a side. A muffler (not shown) is connected to the exhaust pipe 26 via an exhaust purification catalyst device (catalyst) 30.

The exhaust purification catalyst device 30 includes a NOx catalyst 30
a and a three-way catalyst 30b, and the three-way catalyst 30b is disposed downstream of the NOx catalyst 30a. Here, as the NOx catalyst 30a, a storage-type NOx catalyst is employed. Storage NOx
The catalyst uses N2 in the exhaust gas in an oxidizing atmosphere in an oxygen-excess state.
It is a known catalyst having the function of storing Ox. The three-way catalyst 30b is a commonly used three-way catalyst.

The proximity three-way catalyst 24 is provided close to the front exhaust manifold 18 so as to be quickly activated even when the engine 1 is in a cold state. Immediately after starting the system, HC (hydrocarbon) and CO (carbon monoxide) can be satisfactorily purified. Further, the proximity three-way catalyst 24 also has an effect of raising the temperature of the downstream exhaust purification catalyst device 30 early by reaction heat generated by the catalytic reaction.

The exhaust pipe 26 is provided with an O ₂ sensor 27 for detecting the oxygen concentration in the exhaust gas, and a high temperature sensor 32 for detecting the exhaust gas temperature is provided immediately upstream of the exhaust purification catalyst device 30 of the exhaust pipe 26. Have been. Rear exhaust manifold 1
From 9, a recirculation pipe (recirculation passage) 14 extends so as to open into the intake manifold 10 downstream of the throttle valve 11, and the exhaust gas from the rear exhaust manifold 19 can be recirculated into the intake manifold 10. I have. The return pipe 14 is provided with an electromagnetic return valve (valve means) 16 which is opened and closed by a solenoid 17 to open and close the flow in the return pipe 14.

A butterfly type electromagnetic valve, which is opened / closed by a solenoid portion 29 to shut off or cut off the flow in the rear exhaust manifold 19 or to adjust the flow rate, downstream of the branch position of the recirculation pipe 14 of the rear exhaust manifold 19. A shut-off valve 28 of the type is provided. Further, an ECU including an input / output device, a storage device (ROM, RAM, nonvolatile RAM, and the like), a central processing unit (CPU), a timer counter, and the like.
(Electronic control unit) 40 is installed,
The ECU 40 performs comprehensive control of the exhaust purification device of the multi-cylinder internal combustion engine including the engine 1 according to the present invention. On the input side of the ECU 40, the above-described TPS12,
Crank angle sensor 20, water temperature sensor 22, O ₂ sensor 2
7. Various sensors such as a high temperature sensor 32 are connected, and detection information from these sensors is input.

On the other hand, the output side of the ECU 40 is connected to the ignition coil 5, the fuel injection valve 6, the solenoid 13 of the throttle valve 11, the solenoid 17 of the recirculation valve 16, the solenoid 29 of the shutoff valve 28, and the like. The information calculated based on the detection information from the various sensors is output. For example, optimal values such as a fuel injection amount and an ignition timing calculated based on detection information from various sensors are output to the ignition coil 5, the fuel injection valve 6, and the like.
As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and ignition is performed by the spark plug 4 at an appropriate timing.

The ECU 40 calculates a target in-cylinder pressure corresponding to the engine load, that is, a target average effective pressure Pe based on the throttle opening information θth from the TPS 12 and the engine rotation speed information Ne from the crank angle sensor 20. And the target average effective pressure P
The fuel injection mode is set from a fuel injection mode setting map (not shown) according to e and the engine speed information Ne. For example, when the target average effective pressure Pe and the engine rotation speed Ne are both low, the fuel injection mode is the compression stroke injection mode, and the fuel is injected in the compression stroke, while the target average effective pressure Pe increases or the engine rotation speed increases. When the speed Ne increases, the fuel injection mode is set to the intake stroke injection mode, and fuel is injected during the intake stroke. The intake stroke injection mode includes an intake lean mode having a lean air-fuel ratio, a stoichiometric feedback mode (stoichiometric F / B mode) in which feedback control is performed to a stoichiometric air-fuel ratio based on oxygen concentration information from the O ₂ sensor 27,
And an open loop mode (O
/ L mode).

From the target average effective pressure Pe and the engine speed Ne, a target air-fuel ratio (target A / A
F) is set, and the appropriate amount of fuel injection is set to the target A /
It is determined based on F. Further, from the exhaust gas temperature information detected by the high temperature sensor 32,
The temperature of 0 (mainly the NOx catalyst 30a), that is, the catalyst temperature Tcat is estimated. Specifically, the high temperature sensor 32 is set to NOx
A temperature difference map (not shown) is set in advance by an experiment or the like according to the target average effective pressure Pe and the engine rotation speed information Ne in order to correct an error generated due to the inability to directly install the catalyst 30a. And the catalyst temperature Tcat
Is uniquely estimated when the target average effective pressure Pe and the engine speed information Ne are determined.

Hereinafter, the operation of the exhaust gas purifying apparatus for a multi-cylinder internal combustion engine according to the present invention, that is, a method of increasing the temperature of the exhaust gas purifying catalyst device 30 when the engine 1 is cold started will be described. Referring to FIG. 2, a flowchart of the catalyst temperature increase control executed by the ECU 40 is shown, and the description will be made with reference to the flowchart.

First, in step S10, it is determined whether or not the temperature of the exhaust purification catalyst device 30, that is, the catalyst temperature Tcat is lower than a predetermined activation temperature Tcat1. The determination result is true (Yes), and the catalyst temperature Tcat is equal to the predetermined activation temperature Tcat1.
If it is smaller, the process proceeds to step S12. In step S12, the temperature raising operation is performed on the F bank 1a side. Here, as the heating operation, two-stage injection is performed.
Specifically, fuel injection as main injection is performed in an intake stroke or a compression stroke, fuel injection as sub-injection is performed in an expansion stroke, and fuel by the sub-injection is burned during the expansion stroke or in the front exhaust manifold 18. Raise the exhaust gas temperature. As a result, the temperature of the proximity three-way catalyst 24 is rapidly raised, and the temperature of the exhaust purification catalyst device 30 is raised. Further, when the temperature of the proximity three-way catalyst 24 rises to some extent, the fuel due to the sub-injection also burns in the proximity three-way catalyst 24, which also causes the exhaust purification catalyst device 30.
Is satisfactorily heated.

At this time, for example, the air-fuel ratio of the main injection and the sub-injection, that is, the overall air-fuel ratio (overall A / F) is preferably a lean air-fuel ratio. (Compression stroke injection mode or intake lean mode). Thus, the amount of sub-injection can be increased as much as possible with respect to the main injection, and sufficient oxygen can be obtained to reliably burn fuel by sub-injection.

Further, the ignition timing may be retarded as a temperature raising operation. In this case, too, the exhaust gas is sufficiently heated by slow combustion. In step S14, the fuel injection on the R bank 1b side is stopped (partial cylinder operating means). That is, when the exhaust gas purification catalyst device 30 is not sufficiently activated, the fresh air sucked into the combustion chamber 8 is kept as it is on the side of the R bank 1b having no close three-way catalyst by stopping the fuel injection. The cylinder is closed so that it is discharged, and no exhaust gas containing harmful substances (HC, CO, NOx, etc.) is generated. This suitably prevents the harmful substances in the exhaust gas from passing through the inactive exhaust gas purifying catalyst device 30 without being purified.

Then, in step S16, the recirculation valve 16 is fully opened, and the shutoff valve 28 is fully closed (the state shown by the broken line in FIG. 1). That is, fresh air discharged from the R bank 1b is returned to the intake manifold 10 again through the return pipe 14 without reaching the exhaust purification catalyst device 30. As described above, when the discharged fresh air is caused to recirculate into the intake manifold 10 and is prevented from flowing to the exhaust purification catalyst device 30, the exhaust gas that has become hot due to the temperature raising operation on the side of the F bank 1a causes The exhaust purification catalyst device 30 that rises in temperature is never inadvertently cooled by fresh air at a relatively low temperature and room temperature. As a result, the exhaust purification catalyst device 30 efficiently and early activates the activation temperature T.
As the temperature rises to cat1, the exhaust gas characteristics are brought into a favorable state early.

When the fuel injection on the R bank 1b is stopped and the combustion on the R bank 1b is interrupted, it is necessary to obtain a desired engine output by the combustion on the F bank 1a only. That is, the amount of fuel supplied to the F bank 1a increases. Accordingly, the temperature of the exhaust gas discharged from the F bank 1a naturally becomes extremely high, and the temperature of the exhaust gas purifying catalyst device 30 rises at an early stage.

In the V-type engine 1, since the cylinder head 2 and the cylinder portion of the cylinder block are independent of each other in the F bank 1a and the R bank 1b, the combustion heat on the F bank 1a side is reduced by the R bank 1b. Hard to be robbed. Therefore, the temperature of the exhaust gas sufficiently rises due to the combustion heat, and the temperature of the exhaust purification catalyst device 30 also rises early from this.

When the engine 1 is started in a cold state, not only the amount of fuel is increased but also the amount of fuel injection is generally increased. Therefore, if the entire A / F on the F bank 1a side is set to the lean air-fuel ratio as described above, a large amount of air is required on the F bank 1a side, and the throttle valve 11 is fully opened. Therefore, the pumping loss on the side of the R bank 1b is very small and convenient.

The temperature of the exhaust purification catalyst device 30 rises, and the result of the determination in step S10 is false (No), that is, the catalyst temperature Tcat.
Is determined to be equal to or higher than the predetermined activation temperature Tcat1, the process proceeds to step S18. In step S18, the suspension of the fuel injection on the R bank 1b side is released and the recirculation valve 1
6, the shut-off valve 28 is switched from the fully-closed state to the fully-opened state (the state indicated by the solid line in FIG. 1), and both the F bank 1a and the R bank 1b normally operate according to the fuel injection mode setting map. Try to drive. This allows
The catalyst temperature raising control ends.

Next, another embodiment will be described. Referring to FIG. 3, there is shown a schematic configuration diagram of an exhaust emission control device for a multi-cylinder internal combustion engine according to another embodiment of the present invention, and the configuration, operation, and effects of the other embodiment will be described based on the diagram. explain. Here, only the parts different from the above embodiment will be described.

As shown in FIG. 3, a communication pipe 50 extends from the rear exhaust manifold 19 so as to open into the front exhaust manifold 18. And
The connecting pipe 50 is provided with a one-way valve 52 that allows only gas flow from the rear exhaust manifold 19 to the front exhaust manifold 18. When the communication pipe 50 is provided in this manner, the two-stage injection is performed on the F bank 1a side and the fuel injection is stopped on the R bank 1b side by the catalyst temperature increase control, as described above, so that the R bank 1
When the combustion on the b side is interrupted and the recirculation valve 16 is controlled to the valve closing side and the shutoff valve 28 is controlled to the valve closing side (the state shown by the broken line in FIG. 3), the inside of the front exhaust manifold 18 and the rear exhaust Due to the differential pressure in the manifold 19,
Part of the fresh air discharged to the rear exhaust manifold 19 is satisfactorily transmitted through the connecting pipe 50 to the front exhaust manifold 18.
Supplied within. As a result, the rear exhaust manifold 1
The fresh air or a thin air-fuel mixture discharged into the fuel cell 9 acts as secondary air, and unburned fuel components (such as HC) discharged by the two-stage injection are mixed with the fresh air on the F bank 1a side. The combustion is further improved, and the temperature rise of the exhaust purification catalyst device 30 is promoted together with the proximity three-way catalyst 24.

That is, by configuring the exhaust gas purifying apparatus as in the other embodiment, when performing the catalyst temperature increase control, a secondary air pump is not separately provided, cost is not increased, and a simple configuration is achieved. The secondary air can be supplied to the F bank 1a side, and the temperature of the exhaust purification catalyst device 30 can be raised more efficiently and earlier. In each of the above-described embodiments, the small-sized three-way catalyst 24 is provided in the front exhaust manifold 18. However, in the embodiment of the present invention, the small-sized three-way catalyst 24 is not particularly provided. Is also good. In this case, the reaction heat generated in the close three-way catalyst 24 is lost.
It is preferable to increase the injection amount of the sub-injection by the stage injection and increase the amount of heat generated on the F bank 1a side to increase the temperature of the exhaust purification catalyst device 30. Thereby, it is possible to realize an exhaust gas purification device that is lower in cost than the above embodiments.

Further, in each of the above embodiments, the shutoff valve 28 is an electromagnetic valve. However, as shown in FIG.
A mechanical shutoff valve 28 'configured to open and close the valve body 28'a against the urging force of the spring 28'b in response to the exhaust pressure may be used. In this case, the strength of the spring 28'b may be set so that the valve body 28'a does not open to the extent that only fresh air is discharged without expansion due to combustion. With this configuration, when the fuel injection to the R bank 1b is stopped, fresh air is surely flown to the recirculation pipe 14 or the communication pipe 50, and the exhaust purification catalyst device 30 has a simple and inexpensive configuration.
Can be prevented from flowing.

In practicing the present invention, the shut-off valve 28 and the shut-off valve 28 'need not always be provided.
If the cross-sectional area of the tube flow tube 14 is large to some extent, the discharged fresh air is favorably sucked by the negative pressure in the intake manifold 10, and substantially the entire amount thereof is returned to the intake manifold 10. Therefore, the shutoff valve 28 or the shutoff valve 28 '
, The discharged fresh air is satisfactorily recirculated without flowing to the exhaust purification catalyst device 30.

Although the catalyst temperature raising control is performed based on the catalyst temperature Tcat detected by the high temperature sensor 32, the cooling water detected by the water temperature sensor 22 is replaced with the catalyst temperature Tcat. The catalyst temperature increase control may be performed based on the temperature WT. That is, the determination in step S10 of the flowchart in FIG. 2 may be replaced with a determination as to whether the coolant temperature WT is lower than a predetermined warm-up temperature, and the present invention can also be suitably implemented.

In practice, it is preferable that the recirculation pipe 14 and the recirculation valve 16 are configured as an EGR system, and the present invention is implemented by using the EGR system. As a result, the present invention can be realized without increasing the cost without newly providing a dedicated passage for the EGR system. In each of the above embodiments, the shut-off valve 28 is returned from the fully closed state to the fully open state only when the catalyst temperature Tcat is determined to be equal to or higher than the predetermined activation temperature Tcat1.
When cat has risen to a certain degree, the shutoff valve 28 may be gradually opened. In this case, the shut-off valve 28
A small amount of fresh air flows through the exhaust purification catalyst device 30 through the exhaust gas, and the fresh air also acts as secondary air, whereby the temperature rise of the exhaust purification catalyst device 30 is further promoted. If the shut-off valves 28 and 28 'are not provided, the recirculation valve 16 is gradually closed to allow fresh air to naturally flow through the exhaust purification catalyst device 30.
, Thereby obtaining a similar temperature increasing effect. In this case, it is preferable to correct the opening of the throttle valve 11, that is, the throttle opening θth, in accordance with the opening of the recirculation valve 16, that is, the amount of recirculated fresh air.

In each of the above embodiments, the F bank 1a
Although the heating operation is performed on the side, the fuel injection amount is generally increased and the calorific value is increased at the time of the cold start as described above, so that such a heating operation is not necessarily performed. Even in this case, unless a large amount of cooled fresh air flows from the R bank 1b side, the temperature of the exhaust purification catalyst device 30 rises relatively early.

In the partial cylinder operating means of this embodiment, the fuel injection on the R bank 1b side is stopped and the combustion on the R bank 1b side is interrupted. It is sufficient that the combustion in the cylinder group (one bank in the embodiment) is interrupted. For example, the combustion is interrupted by stopping the ignition with the spark plug, or the fuel injection amount does not contribute to the combustion. The combustion in one of the cylinder groups may be interrupted by decreasing the fuel injection amount to the maximum.

In each of the above embodiments, the catalyst temperature increase control is described by taking the cold start of the engine 1 as an example. However, even during normal operation, for example, the engine speed Ne is low and the lean air-fuel ratio is low. During operation (compression stroke injection mode or intake lean mode), the catalyst temperature Tca
Since t may be lower than the predetermined activation temperature Tcat1, the present invention can be applied.

Further, in each of the above embodiments, the engine 1 is a V-type six-cylinder gasoline engine having the F bank 1a and the R bank 1b. The engine 1 may have any configuration as long as the front stage catalyst is disposed only in a part (for example, one) of the two (2) exhaust passages. The present invention can be favorably applied to a type engine.

In each of the above embodiments, the engine 1 is an in-cylinder injection type engine. However, the invention is not limited to this. The engine 1 may be a diesel engine or a general intake pipe injection type engine. . In the case of an intake pipe injection engine, when performing a temperature raising operation on a cylinder group on the first exhaust passage side in which a pre-stage catalyst is disposed, ignition timing retard may be performed.

[0048]

As described above in detail, according to the exhaust gas purifying apparatus for a multi-cylinder internal combustion engine of the first aspect of the present invention, the first
By burning fuel only in the cylinder group and supplying high-temperature exhaust gas to the catalyst, cooled (for example, normal temperature) fresh air discharged from the second cylinder group is returned to the intake passage again by the recirculation passage, whereby the catalyst is cooled. Can be efficiently and quickly raised without inadvertent cooling, and the exhaust gas characteristics can be improved at an early stage.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing a catalyst temperature increasing control procedure of the exhaust gas purifying apparatus for a multi-cylinder internal combustion engine according to the present invention.

FIG. 3 is a schematic configuration diagram of an exhaust emission control device for a multi-cylinder internal combustion engine according to another embodiment of the present invention.

FIG. 4 is a sectional view showing a mechanical shut-off valve provided in a rear exhaust manifold.

[Description of Signs] 1 Engine (multi-cylinder internal combustion engine) 1a Front bank (first cylinder group) 1b Rear bank (second cylinder group) 6 Fuel injection valve 10 Intake manifold (intake passage) 11 Throttle valve (air amount adjusting means) 14 recirculation pipe (recirculation passage) 16 recirculation valve (valve means) 18 front exhaust manifold (first exhaust passage) 19 rear exhaust manifold (second exhaust passage) 24 proximity three-way catalyst (pre-stage catalyst) 26 exhaust pipe (main exhaust passage) ) 28 Shutoff valve 30 Exhaust purification catalyst device (catalyst) 32 High temperature sensor 40 Electronic control unit (ECU)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 25/07 570 F02M 25/07 570N F-term (Reference) 3G062 AA03 CA01 EA12 EB15 ED04 ED14 GA08 GA09 GA15 3G091 AA11 AA17 AA24 AA29 AB03 AB06 BA27 BA28 CA13 CB02 CB05 CB06 DA02 DA08 DA10 EA17 EA18 FA01 FB02 FB10 FC07 GA06 HA03 HA08 HA12 HA36 HA42 HA47 HB03 HB05 3G092 AA01 AA06 AA14 AB02 BB01 DC08 DE03S EA02 EA02 HE08Z

Claims (1)

[Claims] An intake passage for supplying air to each cylinder; an air amount adjusting means provided in the intake passage for adjusting an amount of air supplied to each cylinder; a first cylinder group and a second cylinder group A first exhaust passage and a second exhaust passage independently connected to each other; a main exhaust passage in which the first exhaust passage and the second exhaust passage collectively extend as a single passage; A catalyst for purifying harmful substances in exhaust gas; a partial cylinder operating means for interrupting combustion of the second cylinder group under specific operating conditions; one end connected to the second exhaust passage; A recirculation passage connected to an intake passage downstream of the air amount adjusting means; and a recirculation passage provided in the recirculation passage, wherein the recirculation passage is opened when combustion of the second cylinder group is interrupted by the partial cylinder operating means. And a valve means, and Exhaust emission control device for a multi-cylinder internal combustion engine that.