JP2001059446A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To significantly reduce unburned HC discharged into the atmosphere during engine start and warm-up operation. SOLUTION: Branch pipes 19a of an exhaust manifold 19 are connected to each other by a communication pipe 20. An exhaust control valve 24 is arranged in the exhaust pipe 23. When the engine is started and the engine is warmed up, the exhaust control valve 24 is almost completely closed, and additional fuel is injected during the expansion stroke.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

2. Description of the Related Art In a diesel engine, the temperature in a combustion chamber becomes low during low-speed low-load operation of the engine, particularly during warm-up operation of the engine, and as a result, a large amount of unburned HC is generated. Therefore, an exhaust control valve is arranged in the engine exhaust passage, the exhaust control valve is closed during low-speed engine low-load operation, and the fuel injection amount is increased to increase the temperature of the combustion chamber to increase the temperature of the combustion chamber and thereby inject the injected fuel into the combustion chamber. There is known a diesel engine in which combustion is completely performed by the above-described method to thereby suppress the amount of unburned HC generated (see Japanese Patent Application Laid-Open No. 49-80414).

In addition, when an exhaust gas purifying catalyst is disposed in an engine exhaust passage, a satisfactory exhaust gas purifying action cannot be performed by the catalyst unless the catalyst temperature becomes sufficiently high. Therefore, in addition to the injection of the main fuel for generating the engine output, the auxiliary fuel is injected during the expansion stroke, and the auxiliary fuel is burned to raise the exhaust gas temperature, thereby raising the temperature of the catalyst. BACKGROUND ART Internal combustion engines are known (Japanese Patent Laid-Open No. 8-303).
290 and JP-A-10-212995).

[0004] Further, a catalyst capable of adsorbing unburned HC has been conventionally known. This catalyst has a property that the adsorbed amount of unburned HC increases as the surrounding pressure increases, and releases the adsorbed unburned HC as the surrounding pressure decreases. Therefore, in order to reduce NO _x by unburned HC released from the catalyst by utilizing this property, this catalyst is arranged in the engine exhaust passage and an exhaust control valve is arranged in the engine exhaust passage downstream of the catalyst, During low-speed engine low-load operation with a small amount of NO _x generated, a small amount of auxiliary fuel is injected during the expansion stroke or the exhaust stroke in addition to the main fuel for generating the engine output, thereby generating a large amount of unburned H.
C is discharged from the combustion chamber, and at this time, the pressure in the exhaust passage is increased by closing the exhaust control valve to a relatively small opening so that the engine output falls within an allowable range. a large amount of unburned HC discharged is adsorbed on the catalyst, is in the event a large amount of engine high speed or high load operation of the NO _x reducing the pressure in the exhaust passage in the fully opened exhaust valve, released from the catalyst at this time NO by unburned HC
An internal combustion engine configured to reduce _x is known (see Japanese Patent Application Laid-Open No. H10-238336).

[0005]

Now, how to reduce the amount of unburned HC generated in a low-load engine operation, particularly in a warm-up operation of the engine, not only in a diesel engine but also in a spark ignition type internal combustion engine at present. Is a major problem.
Therefore, the present inventor conducted experimental research to solve this problem. As a result, in order to significantly reduce the amount of unburned HC discharged into the atmosphere during a warm-up operation of the engine or the like, unburned HC in the combustion chamber was required. It has been found that the amount of combustion HC must be reduced and the amount of reduction of unburned HC in the exhaust passage must be increased at the same time.

More specifically, during the expansion stroke or the exhaust stroke, additional fuel is injected into the combustion chamber to burn the fuel, and the exhaust gas is discharged into the engine exhaust passage at a distance from the outlet of the engine exhaust port. When a control valve is provided and the exhaust control valve is almost fully closed, the unburned H2 in the combustion chamber is generated due to the synergistic effect of combustion of these auxiliary fuels and the exhaust throttle action of the exhaust control valve.
The amount of C generated is reduced and unburned H in the exhaust passage is reduced.
It has been found that the amount of reduction of C is increased, and thus the amount of unburned HC discharged into the atmosphere can be significantly reduced.

More specifically, when the auxiliary fuel is injected, not only the auxiliary fuel itself is burned, but also unburned HC, which is the unburned main fuel, is burned in the combustion chamber. Therefore, not only is the amount of unburned HC generated in the combustion chamber significantly reduced, but also the unburned HC remaining as unburned main fuel is reduced.
In addition, the burned gas temperature becomes considerably high because the auxiliary fuel is burned.

On the other hand, when the exhaust control valve is almost fully closed, the pressure in the exhaust passage from the exhaust port of the engine to the exhaust control valve, that is, the back pressure, becomes considerably high. The high back pressure means that the temperature of the exhaust gas discharged from the combustion chamber does not drop so much, and the temperature of the exhaust gas in the exhaust port is considerably high. On the other hand, a high back pressure means that the flow rate of the exhaust gas discharged into the exhaust port is low, and therefore, the exhaust gas is kept at a high temperature in the exhaust passage upstream of the exhaust control valve for a long time. Will stay. During this time, the unburned HC contained in the exhaust gas is oxidized, and the amount of unburned HC discharged into the atmosphere is greatly reduced.

In this case, if the auxiliary fuel is not injected, a large amount of unburned HC is generated in the combustion chamber since unburned HC remaining unburned in the main fuel remains as it is. If the auxiliary fuel is not injected, the temperature of the burned gas in the combustion chamber does not increase so much. Therefore, even if the exhaust control valve is almost fully closed at this time, the unburned HC in the exhaust passage upstream of the exhaust control valve is not used. Cannot be expected to have a sufficient oxidizing effect. Therefore, at this time, a large amount of unburned HC is discharged into the atmosphere.

On the other hand, even when the exhaust control valve does not perform the exhaust throttling function, if the auxiliary fuel is injected, the amount of unburned HC generated in the combustion chamber is reduced, and the temperature of the burned gas in the combustion chamber is increased. However, if the exhaust control valve does not perform the exhaust throttling action, the exhaust gas pressure immediately drops as soon as the exhaust gas is exhausted from the combustion chamber, and thus the exhaust gas temperature immediately drops. Therefore, in this case, almost no oxidizing action of the unburned HC in the exhaust passage can be expected, and thus also at this time, a large amount of unburned HC is discharged into the atmosphere.

That is, in order to significantly reduce the amount of unburned HC discharged into the atmosphere, it is necessary to inject the auxiliary fuel and at the same time to close the exhaust control valve almost completely. In the diesel engine described in JP-A-49-80414, the auxiliary fuel is not injected, and the injection amount of the main fuel is greatly increased. Are generated in the combustion chamber. When an extremely large amount of unburned HC is generated in the combustion chamber in this way, even if the unburned HC is oxidized in the exhaust passage, only a part of the unburned HC is oxidized, so that a large amount of unburned HC is discharged to the atmosphere. Will be discharged.

On the other hand, in the internal combustion engine described in the above-mentioned Japanese Patent Application Laid-Open No. Hei 8-303290 or Japanese Patent Application Laid-Open No. Hei 10-212995, since the exhaust throttle function is not performed by the exhaust control valve, the unburned HC in the exhaust passage is reduced. Oxidation can hardly be expected. Therefore, even in this internal combustion engine, a large amount of unburned HC is discharged into the atmosphere. Further, in the internal combustion engine described in the above-mentioned Japanese Patent Application Laid-Open No. 10-238336, the exhaust control valve is closed to a relatively small opening so that the output reduction of the engine falls within an allowable range. However, the back pressure is not so high with the closing amount of the exhaust control valve such that the output of the engine falls within an allowable range.

Further, in this internal combustion engine, a small amount of auxiliary fuel is injected during an expansion stroke or an exhaust stroke in order to generate unburned HC to be adsorbed by a catalyst. In this case, if the auxiliary fuel is satisfactorily burned, unburned HC will not be generated. Therefore, it is considered that the injection control of the auxiliary fuel is performed in this internal combustion engine so that the auxiliary fuel is not satisfactorily burned. Therefore, in this internal combustion engine, it is considered that a small amount of auxiliary fuel does not significantly contribute to the increase in the temperature of the burned gas.

Thus, in this internal combustion engine, a large amount of unburned H
Since C is generated in the combustion chamber and the back pressure is not so high and the temperature of the burned gas does not increase so much, it is considered that unburned HC is not oxidized so much in the exhaust passage. The purpose of this internal combustion engine is to adsorb as much unburned HC as possible to the catalyst, and thus it can be said that it is reasonable to think in this way.

An object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine capable of greatly reducing the amount of unburned HC discharged into the atmosphere while ensuring stable operation of the engine.

[0016]

According to a first aspect of the present invention, each branch pipe of an exhaust manifold is connected to an outlet of a corresponding engine exhaust port, and an exhaust pipe connected to an outlet of the exhaust manifold is provided. Place an exhaust control valve in the passage,
When it is determined that the emission of unburned HC into the atmosphere should be reduced, the exhaust control valve is almost fully closed, and the main fuel injected into the combustion chamber to generate engine output is over-aired. The auxiliary fuel is additionally injected into the combustion chamber at a predetermined time during an expansion stroke or an exhaust stroke in which the auxiliary fuel can burn, and the engine exhaust gas is supplied to an engine exhaust port or an exhaust manifold branch pipe. Exhaust pulsation reducing means for reducing exhaust pulsation generated in the port and the exhaust manifold is provided.

In the second invention, in the first invention,
The exhaust pulsation reducing means includes a communication pipe that communicates each branch pipe of the exhaust manifold with each other. According to a third aspect, in the second aspect, an on-off valve which opens when the exhaust control valve is substantially fully closed and closes when the exhaust control valve is fully opened is provided in each communication pipe.

In the fourth invention, in the first invention,
When the exhaust control valve is almost fully closed, the exhaust control valve is operated under the same engine operating condition so as to approach the generated torque of the engine when the exhaust control valve is fully opened under the same engine operating condition. , The main fuel injection amount is increased as compared with the case where the valve is fully opened. In a fifth aspect based on the first aspect, a catalyst is disposed in each branch pipe of the exhaust manifold.

In the sixth invention, in the first invention,
A catalyst is located in an exhaust passage connected to the outlet of the exhaust manifold.

[0020]

1 and 2 show a case where the present invention is applied to a stratified combustion internal combustion engine. However, the present invention is also applicable to spark-ignition internal combustion engines that burn under a uniform lean air-fuel ratio and diesel engines that burn under excess air.

Referring to FIG. 1, reference numeral 1 denotes an engine body;
Engine body 1 is # 1 cylinder # 1, # 2 cylinder # 2, # 3 cylinder #
It has four cylinders consisting of the third and fourth cylinders # 4. FIG. 2 is a side sectional view of each of the cylinders # 1, # 2, # 3, and # 4. Referring to FIG. 2, 2 is a cylinder block, 3
Is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is a fuel injection valve arranged at a peripheral portion of an inner wall surface of the cylinder head 3, 7 is an ignition plug arranged at a central portion of the inner wall surface of the cylinder head 3, and 8 is An intake valve, 9 is an intake port, 10 is an exhaust valve,
Reference numeral 11 denotes an exhaust port.

Referring to FIGS. 1 and 2, the intake port 9 is connected to a surge tank 13 via a corresponding intake branch pipe 12, and the surge tank 13 is connected to an air cleaner 16 via an intake duct 14 and an air flow meter 15. Is done. A throttle valve 18 driven by a step motor 17 is arranged in the intake duct 14. On the other hand, the exhaust ports 11 of the cylinders # 1, # 2, # 3, and # 4 are connected to the branch pipes 19a of the corresponding exhaust manifolds 19, respectively. They are in communication with each other. These communication pipes 20 form exhaust pulsation reduction means. On the other hand, the exhaust manifold 19
Is connected via an exhaust pipe 21 to a catalytic converter 22a containing a catalyst 22, and an exhaust pipe 23 is connected to the catalytic converter 22a. The actuator 2 is provided in the exhaust pipe 23.
An exhaust control valve 24 controlled by 5 is arranged.

As shown in FIG. 1, the exhaust manifold 19
And the surge tank 13 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 26, and the EGR passage 2
An electric control type EGR control valve 27 is arranged in 6. The fuel injectors 6 are connected to a common fuel reservoir, a so-called common rail 28. The fuel in the fuel tank 29 is supplied into the common rail 28 via an electric control type variable discharge fuel pump 30, and the fuel supplied in the common rail 28 is supplied to each fuel injection valve 6. A fuel pressure sensor 31 for detecting the fuel pressure in the common rail 28 is attached to the common rail 28. The fuel pump 30 is controlled so that the fuel pressure in the common rail 28 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 31. Is controlled.

The electronic control unit 40 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45, An output port 46 is provided. The air flow meter 15 generates an output voltage proportional to the amount of intake air.
7 is input to the input port 45. A water temperature sensor 32 for detecting the temperature of the engine cooling water is attached to the engine body 1, and an output signal of the water temperature sensor 32 is output from a corresponding AD.
The data is input to the input port 45 via the converter 47. Further, the output signal of the fuel pressure sensor 31 is input to the input port 45 via the corresponding AD converter 47.

The exhaust pipe 21 has an exhaust manifold 1 therein.
9 and an output sensor 33 for detecting the pressure of the exhaust gas in the exhaust pipe 21, that is, the back pressure, and an output signal of the pressure sensor 33 is input to an input port 45 via a corresponding AD converter 47. You. A temperature sensor 34 for detecting the temperature of the catalyst 22 is attached to the catalytic converter 22a, and the output signal of the temperature sensor 34
The data is input to the input port 45 via the converter 47.

A load sensor 51 for generating an output voltage proportional to the amount of depression L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is supplied to an input port via a corresponding AD converter 47. 45 is input. The input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. On the other hand, the output port 46 is connected to the fuel injection valve 6, the ignition plug 7, the step motor 17 for controlling the throttle valve, the actuator 25 for controlling the exhaust control valve, the EGR control valve 27, and the fuel pump 30 via the corresponding drive circuit 48. You.

FIG. 3 shows the fuel injection amounts Q1, Q2, Q (= Q _1).
+ Q ₂ ), the injection start timing θS1, θS2, the injection completion timing θE1, θE2, and the average air-fuel ratio A in the combustion chamber 5.
/ F. In FIG. 3, the horizontal axis L indicates the amount of depression of the accelerator pedal 50, that is, the required load.
When 3 required load L as can be seen from is lower than L ₁ is the fuel injection Q2 is performed between θE2 from θS2 of the end of the compression stroke. At this time, the average air-fuel ratio A / F is considerably lean. Required load L first fuel injection Q1 is performed between θE1 from the beginning of the intake stroke of θS1 when between L ₁ and L _2, then the second fuel in between θS2 of θE2 of the end of the compression stroke Injection Q2 is performed. At this time, the air-fuel ratio A / F is lean. When the required load L is greater than L ₂ the fuel injection Q1 is performed between θE1 from the beginning of the intake stroke of the? S1. At this time, in the region where the required load L is low, the average air-fuel ratio A / F is lean, and the required load L
Becomes higher, the average air-fuel ratio A / F becomes the stoichiometric air-fuel ratio, and if the required load L further increases, the average air-fuel ratio A / F becomes rich. The operation region where the fuel injection Q2 is performed only at the end of the compression stroke, the operation region where the fuel injections Q1 and Q2 are performed twice, and the fuel injection Q only at the beginning of the intake stroke.
The operation range in which 1 is performed is not determined only by the required load L, but is actually determined by the required load L and the engine speed.

FIG. 2 shows that the fuel injection Q2 is performed only when the required load L is smaller than L ₁ (FIG. 3), that is, only at the end of the compression stroke.
Is performed. Cavity 4a is to the top surface of the piston 4 as shown in FIG. 2 are formed, required load L fuel injection valve when less than L ₁ 6
Is injected toward the bottom wall of the cavity 4a at the end of the compression stroke. This fuel is guided by the peripheral wall surface of the cavity 4a toward the spark plug 7, whereby an air-fuel mixture G is formed around the spark plug 7. Then this mixture G
Is ignited by the spark plug 7.

On the other hand, the fuel injection is performed in two batches when the required load L as described above is between L ₁ and L _2. In this case, a lean mixture is formed in the combustion chamber 5 by the first fuel injection Q1 performed at the beginning of the intake stroke. Next, an air-fuel mixture having an optimum concentration is formed around the ignition plug 7 by the second fuel injection Q2 performed at the end of the compression stroke. This mixture is ignited by the spark plug 7,
This ignition flame causes the lean mixture to burn.

On the other hand, the required load L is homogeneous mixture of lean or stoichiometric or rich air-fuel ratio is formed in the combustion chamber 5 as is shown in Figure 3 when greater than L _2, the homogeneous mixture is It is ignited by the spark plug 7. Next, a method for reducing unburned HC according to the present invention will be schematically described first with reference to FIG. In FIG. 4, the horizontal axis indicates the crank angle, and BTDC and ATD
C indicates before the top dead center and after the top dead center, respectively.

[0031] FIG. 4 (A) shows the fuel injection timing when the required load L even if no particular need to reduce the unburned HC by the method according to the present invention is smaller than L _1. As shown in FIG. 4A, at this time, only the main fuel Qm is injected at the end of the compression stroke, and at this time, the exhaust control valve 24 is maintained in a fully open state. On the other hand, when it is necessary to reduce the unburned HC by the method according to the present invention, the exhaust control valve 24 is almost completely closed.
As shown in FIG. 4B, in addition to the injection of the main fuel Qm for generating the engine output, during the expansion stroke, in the example shown in FIG. The auxiliary fuel Qa is additionally injected. In this case, after the main fuel Qm has been burned, the main fuel Qm is burned with excess air so that sufficient oxygen remains in the combustion chamber 5 to completely burn the sub fuel Qa. FIG. 4 (A)
FIG. 4B and FIG. 4B show the fuel injection period when the engine load and the engine speed are the same. Therefore, when the engine load and the engine speed are the same, the fuel injection period is shown in FIG. The injection amount of the main fuel Qm in the case is increased compared to the injection amount of the main fuel Qm in the case shown in FIG.

FIG. 5 shows an example of the concentration (ppm) of unburned HC in the exhaust gas at each position in the engine exhaust passage.
In the example shown in FIG. 5, the black triangle indicates unburned fuel in the exhaust gas at the outlet of the exhaust port 11 when the main fuel Qm is injected at the end of the compression stroke as shown in FIG. 4A with the exhaust control valve 24 fully opened. The HC concentration (ppm) is shown.
In this case, the concentration of unburned HC in the exhaust gas at the outlet of the exhaust port 11 is an extremely high value of 6000 ppm or more.

On the other hand, in the example shown in FIG. 5, a black circle and a solid line indicate that the exhaust control valve 24 is almost fully closed, and the main fuel Qm and the sub fuel Qa are injected as shown in FIG. Indicates the concentration (ppm) of unburned HC.
In this case, the concentration of unburned HC in the exhaust gas at the outlet of the exhaust port 11 becomes 2000 ppm or less, and the concentration of unburned HC in the exhaust gas near the exhaust control valve 24 becomes 1 ppm.
It decreases to about 50 ppm. Therefore, in this case, it can be seen that the amount of unburned HC discharged into the atmosphere is greatly reduced.

The reason why the unburned HC is reduced in the exhaust passage upstream of the exhaust control valve 24 is that the oxidation reaction of the unburned HC is promoted. However, as shown by a black triangle in FIG.
When the amount of C is large, that is, when the amount of unburned HC generated in the combustion chamber 5 is large, even if the oxidation reaction of unburned HC in the exhaust passage is promoted, the unburned HC discharged into the atmosphere is increased. Does not decrease much. That is, the unburned H in the exhaust passage
The fact that the amount of unburned HC discharged into the atmosphere can be significantly reduced by promoting the oxidation reaction of C is because the concentration of unburned HC at the outlet of the exhaust port 11 is low as shown by the black circle in FIG. That is, when the amount of unburned HC generated in the combustion chamber 5 is small.

As described above, in order to reduce the amount of unburned HC discharged into the atmosphere, the amount of unburned HC generated in the combustion chamber 5 is reduced and the oxidation reaction of unburned HC in the exhaust passage is reduced. It is necessary to fulfill both demands for promotion at the same time. Therefore, the second requirement, that is, the promotion of the oxidation reaction of unburned HC in the exhaust passage will be described first.

According to the present invention, unburned H discharged into the atmosphere
When the amount of C is to be reduced, the exhaust control valve 24 is almost fully closed. When the exhaust control valve 24 is almost fully closed in this way, the pressure in the exhaust port 11, the exhaust manifold 19, and the exhaust pipe 21 upstream of the exhaust control valve 24, that is, the back pressure, becomes considerably high. The increase in the back pressure means that the pressure of the exhaust gas does not decrease so much when the exhaust gas is discharged from the combustion chamber 5 into the exhaust port 11, and therefore the temperature of the exhaust gas discharged from the combustion chamber 5 also decreases significantly. Means not. Therefore, the temperature of the exhaust gas discharged into the exhaust port 11 is maintained at a considerably high temperature. On the other hand, a high back pressure means that the density of the exhaust gas is high, and a high density of the exhaust gas means that the flow rate of the exhaust gas in the exhaust passage from the exhaust port 11 to the exhaust control valve 24 is high. It means late. Therefore, the exhaust gas discharged into the exhaust port 11 stays in the exhaust passage upstream of the exhaust control valve 24 for a long time at a high temperature.

As described above, when the exhaust gas is kept in the exhaust passage upstream of the exhaust control valve 24 for a long time at a high temperature, the oxidation reaction of the unburned HC is accelerated. In this case, according to an experiment by the inventor, in order to promote the oxidation reaction of the unburned HC in the exhaust passage, the exhaust port 11 is required.
It has been found that the exhaust gas temperature at the outlet needs to be approximately 750 ° C. or higher, preferably 800 ° C. or higher.

The longer the high-temperature exhaust gas remains in the exhaust passage upstream of the exhaust control valve 24, the greater the amount of unburned HC reduction. This residence time becomes longer as the position of the exhaust control valve 24 is further away from the outlet of the exhaust port 11, so that the exhaust control valve 24 is
It is necessary to arrange a distance necessary for sufficiently reducing unburned HC from one outlet. According to experiments by the present inventors, it has been found that it is preferable that the distance from the outlet of the exhaust port 11 to the exhaust control valve 24 be 1 meter or more in order to sufficiently reduce unburned HC.

By the way, the oxidizing action of unburned HC is accelerated as the exhaust gas temperature is higher. Therefore, it is preferable that the exhaust gas is kept in a region where the exhaust gas temperature is higher as much as possible. Therefore, in the present invention, the exhaust manifold branch pipes 19a are connected to each other by the communication pipe 20. That is,
In a normal internal combustion engine, when the exhaust valve 10 is opened, exhaust pulsation is used to discharge burned gas in the combustion chamber 5 from the combustion chamber 5 as soon as possible. That is, in the internal combustion engine, when the exhaust valve 10 is opened, a large positive pressure is temporarily generated in the exhaust port 11, and this positive pressure is reflected at the gathering portion of the exhaust manifold 19, and this time, in the form of a negative pressure, Come back inside 11. When the pressure in the exhaust port 11 becomes negative, the combustion chamber 5
Burned gas is rapidly discharged from inside. Therefore, in a normal internal combustion engine, the size of the exhaust manifold branch pipe 19a is set so that a negative pressure is generated in the exhaust port 11 at an optimum time. In this case, if the communication pipe 20 as shown in FIG. 1 is provided, the negative pressure generated in the exhaust port 11 is reduced, that is, the exhaust pulsation is reduced, and thus the burned gas is rapidly discharged from the combustion chamber 5. It cannot be discharged. Therefore, such a communication pipe 20 is not usually provided in an internal combustion engine.

However, in the present invention, the purpose of the present invention is to promote the oxidation reaction of unburned HC. Therefore, the exhaust gas discharged from the combustion chamber 5 is kept in the exhaust port 11 and the exhaust manifold 19 where the exhaust gas temperature is kept high. It is preferable to stay for as long a time as possible. For this purpose, in the embodiment according to the present invention, the respective exhaust manifolds 19a are connected to each other by the communication pipe 19a. That is, when the exhaust manifolds 19a communicate with each other through the communication pipes 19a, the exhaust gas flows in the exhaust port 11 and the exhaust manifold 19 relatively slowly at a high temperature.
As a result, the exhaust gas is maintained at a high temperature for a long time, and thus the oxidation reaction of the unburned HC is promoted.

On the other hand, as described above, in order to promote the oxidation reaction of unburned HC in the exhaust passage, the exhaust port 11
The exhaust gas temperature at the outlet needs to be approximately 750 ° C. or higher, preferably 800 ° C. or higher. Further, in order to reduce the amount of unburned HC discharged into the atmosphere, the first requirement described above must be satisfied. That is, it is necessary to reduce the amount of unburned HC generated in the combustion chamber 5. Therefore, in the present invention, in addition to the main fuel Qm for generating the engine output, the auxiliary fuel Qa is additionally injected after the injection of the main fuel Qm so that the auxiliary fuel Qa is burned in the combustion chamber 5.

That is, when the auxiliary fuel Qa is burned in the combustion chamber 5, a large amount of unburned HC which is the unburned main fuel Qm is burned when the auxiliary fuel Qa is burned. Further, since the auxiliary fuel Qa is injected into the high-temperature gas, the auxiliary fuel Qa is satisfactorily burned, so that unburned HC, which is the remaining unburned auxiliary fuel Qa, is not generated much. Thus, the amount of unburned HC finally generated in the combustion chamber 5 is considerably reduced.

When the auxiliary fuel Qa is burned in the combustion chamber 5, the heat generated by the combustion of the main fuel Qm itself and the auxiliary fuel Qa itself, and the combustion heat of the unburned HC remaining as unburned main fuel Qm are added. Therefore, the temperature of the burned gas in the combustion chamber 5 becomes considerably high. As described above, the auxiliary fuel Qa is additionally injected in addition to the main fuel Qm to burn the auxiliary fuel Qa, thereby reducing the amount of unburned HC generated in the combustion chamber 5 and reducing the exhaust gas temperature at the outlet of the exhaust port 11 to 750. C. or higher, preferably 800 C. or higher.

As described above, in the present invention, it is necessary to burn the auxiliary fuel Qa in the combustion chamber 5, and for this purpose,
It is necessary that sufficient oxygen remains in the combustion chamber 5 at the time of combustion of a, and that the auxiliary fuel Qa must be injected at a time when the injected auxiliary fuel Qa can be satisfactorily burned in the combustion chamber 5. There is. Therefore, in the present invention, the main fuel Q is controlled so that sufficient oxygen can remain in the combustion chamber 5 during combustion of the auxiliary fuel Qa.
m is burned under excess air. Further, the injection timing at which the auxiliary fuel Qa injected in the stratified combustion internal combustion engine shown in FIG. 2 is favorably burned in the combustion chamber 5 is after the compression top dead center (AT
DC) The expansion stroke is approximately 50 ° to approximately 90 °, and therefore, in the stratified combustion internal combustion engine shown in FIG. 2, the auxiliary fuel Qa has an expansion stroke approximately 50 ° to approximately 90 ° after compression top dead center (ATDC). Is injected. The auxiliary fuel Qa injected during the expansion stroke from approximately 50 ° to approximately 90 ° after the compression top dead center (ATDC) does not contribute to the generation of engine output.

According to experiments conducted by the present inventors, FIG.
In the stratified combustion internal combustion engine shown in FIG. 1, when the auxiliary fuel Qa is injected at around 60 ° after the compression top dead center (ATDC), the amount of unburned HC discharged into the atmosphere is the smallest.
Therefore, in the embodiment according to the present invention, as shown in FIG. 4B, the injection timing of the auxiliary fuel Qa is almost after the compression top dead center (ATD
C) It is around 60 °.

The optimum injection timing of the auxiliary fuel Qa differs depending on the model of the engine.
Is during the expansion stroke or the exhaust stroke. Therefore, in the present invention, the fuel injection of the auxiliary fuel Qa is performed during the expansion stroke or the exhaust stroke. On the other hand, the temperature of the burned gas in the combustion chamber 5 is affected by both the combustion heat of the main fuel Qm and the combustion heat of the auxiliary fuel Qa. That is, the burned gas temperature in the combustion chamber 5 increases as the injection amount of the main fuel Qm increases, and the sub-fuel Qa
Increases as the injection amount of the fuel increases. Further, the temperature of the burned gas in the combustion chamber 5 is affected by the back pressure. That is, as the back pressure becomes higher, the burned gas is less likely to flow out of the combustion chamber 5, so that the burned gas amount remaining in the combustion chamber 5 increases. Thus, when the exhaust control valve 24 is almost completely closed. The temperature of the burned gas in the combustion chamber 5 is increased.

By the way, the exhaust control valve 24 is almost closed, and when the back pressure increases, the generated torque of the engine decreases from the optimum required generated torque. Therefore, in the embodiment according to the present invention, when the exhaust control valve 24 is almost completely closed as shown in FIG. 4B, the exhaust control is performed under the same engine operating state as shown in FIG. The exhaust control valve 2 is operated under the same engine operating condition so as to approach the required torque of the engine when the valve 24 is fully opened.
The injection amount of the main fuel Qm is increased as compared with the case where 4 is fully opened. In the embodiment according to the present invention, when the exhaust control valve 24 is almost completely closed, the generated torque of the engine at that time is the same as that of the engine when the exhaust control valve 24 is fully opened under the same engine operating state. The main fuel Qm is increased so as to match the required generated torque.

FIG. 6 shows a change in the main fuel Qm required to obtain the required generated torque of the engine with respect to the required load L. In FIG. 6, the solid line shows the case where the exhaust control valve 24 is almost completely closed, and the broken line shows the exhaust control valve 2.
4 shows a case in which it is fully opened. On the other hand, FIG. 7 shows the relationship between the main fuel Qm and the auxiliary fuel Qa required to bring the exhaust gas temperature at the outlet of the exhaust port 11 from approximately 750 ° C. to approximately 800 ° C. when the exhaust control valve 24 is almost fully closed. ing. As described above, even if the main fuel Qm is increased, the burned gas temperature in the combustion chamber 5 increases, and even if the auxiliary fuel Qa is increased, the burned gas temperature in the combustion chamber 5 increases. Therefore, the temperature of the exhaust gas at the outlet of the exhaust port 11 is almost 750 ° C.
As shown in FIG. 7, the relationship between the main fuel Qm and the auxiliary fuel Qa required to make the temperature approximately 800 ° C. is as follows. As shown in FIG. 7, when the main fuel Qm is increased, the auxiliary fuel Qa is decreased. The fuel Qa has an increasing relationship.

However, when the main fuel Qm and the sub fuel Qa are increased by the same amount, the temperature increase in the combustion chamber 5 is much larger when the sub fuel Qa is increased than when the main fuel Qm is increased. Become larger. Therefore, from the viewpoint of reducing the fuel consumption, it can be said that it is preferable to increase the temperature of the burned gas in the combustion chamber 5 by increasing the auxiliary fuel Qa.

Therefore, in the embodiment according to the present invention, when the exhaust control valve 24 is almost fully closed, the main fuel Qm is increased by an amount necessary to increase the generated torque of the engine to the required generated torque.
And the temperature of the burned gas in the combustion chamber 5 is increased mainly by the combustion heat of the auxiliary fuel Qa. In this way, the exhaust control valve 24 is almost completely closed, and the exhaust port 11
When the auxiliary fuel Qa is injected in an amount necessary to make the exhaust gas at the outlet approximately 750 ° C. or higher, preferably approximately 800 ° C. or higher, the concentration of unburned HC in the exhaust passage from the exhaust port 11 to the exhaust control valve 24 is reduced. Can be greatly reduced. At this time, in the exhaust passage from the exhaust port 11 to the exhaust control valve 24, as shown in FIG.
In order to reduce the concentration to about 150 p.pm, the pressure in the exhaust passage upstream of the exhaust control valve 24 must be increased to about 80 KPa or more by a gauge pressure. At this time, the closing ratio of the exhaust passage cross-sectional area by the exhaust control valve 24 is approximately 95% or more. Therefore, in the embodiment shown in FIG. 1, when the amount of unburned gas discharged into the atmosphere is to be greatly reduced, the exhaust control valve 24 is almost completely closed so that the back pressure becomes approximately 80 KPa.

A large amount of unburned HC is generated in the internal combustion engine when the temperature in the combustion chamber 5 is low. When the temperature in the combustion chamber 5 is low, the engine is being started and the engine is warming up.
C will occur. When the temperature in the combustion chamber 5 is low as described above, even if the catalyst 22 having an oxidizing function is arranged in the exhaust passage, the catalyst temperature is low and the catalyst 22 is not activated. Fuel HC
Is difficult to oxidize with the catalyst 22.

Therefore, in the embodiment according to the present invention, when the engine is started and the engine is warmed up, the exhaust control valve 24 is almost completely closed until the catalyst 22 is activated, the main fuel Qm is increased, and the auxiliary fuel Qa is additionally injected. Thereby, the amount of unburned HC discharged into the atmosphere is greatly reduced. FIG. 8 shows the main fuel Q during engine start and warm-up operation.
7 shows an example of the change of m and the opening degree of the exhaust control valve 24. In FIG. 8, a solid line X indicates an optimum injection amount of the main fuel Qm when the exhaust control valve 24 is almost fully closed, and a broken line Y indicates an optimum main fuel Q when the exhaust control valve 24 is fully opened. The injection amount of Qm is shown. As can be seen from FIG. 8, when the engine is started and the engine is warmed up, the exhaust control valve 24 is almost fully closed, and when the exhaust control valve 24 is fully opened under the same engine operating state, the optimum main fuel Qm is determined. The injection amount X of the main fuel Qm is increased more than the injection amount Y,
Further, the auxiliary fuel Qa is additionally injected.

FIG. 9 shows an operation control routine. Referring to FIG. 9, first, at step 100, it is determined whether or not a warm-up completion flag indicating that the catalyst 22 has been activated is set. When the warm-up completion flag is not set, that is, when the catalyst 22 is not activated, the routine proceeds to step 101, where the exhaust control valve 24 is almost completely closed. At this time, the opening degree of the exhaust control valve 24 is feedback-controlled based on the output signal of the pressure sensor 33 so that the back pressure becomes 80 KPa. Then step 10
At 2, control is performed such that the injection amount of the main fuel Qm becomes X shown in FIG. Next, at step 103, the auxiliary fuel Qa
Is performed. Next, at step 104, it is determined whether or not the temperature Tc of the catalyst 22 has exceeded the activation temperature To, for example, 250 ° C., based on the output signal of the temperature sensor 34. If Tc> To, the routine proceeds to step 105, where the warm-up is performed. The completion flag is set.

When the warm-up completion flag is set, that is, when the catalyst 22 is activated, Steps 100 to 10 are executed.
The program proceeds to 6 where the exhaust control valve 24 is fully opened, and then the program proceeds to step 107 where injection control of the main fuel Qm is performed. At this time, the injection of the auxiliary fuel Qa is not performed. FIG. 10 shows another embodiment.

In this embodiment, an on-off valve 60 controlled by an actuator 61 is arranged in each communication pipe 20. The on-off valve 60 is fully opened when the exhaust control valve 24 is almost fully closed, and is fully closed when the exhaust control valve 24 is fully opened. Therefore, when the exhaust control valve 24 is almost completely closed, the exhaust pulsation is weakened, so that the oxidizing action of the unburned HC is promoted. When the exhaust control valve 24 is fully opened, the burned combustion in the combustion chamber 5 is caused by the exhaust pulsation. Gases are exhausted rapidly.

Next, a case where another catalyst 62 is arranged upstream of the catalyst 22 will be described. That is, in the example shown in FIG. 11, the catalyst 62 is disposed in each exhaust manifold branch pipe 19a. On the other hand, in the example shown in FIG. 12A, the ignition order is set to 1-3-4-2, and as shown in FIG. 12A, the ignition order of every other cylinder # 1 and # 4 is changed. The exhaust ports 11 are connected to a common first exhaust manifold 63, and the exhaust ports 11 of the remaining cylinders # 2, # 3 in alternate firing order are connected to a common second exhaust manifold 64. The collecting part of the first exhaust manifold 63 is connected to a first catalytic converter 65 containing the catalyst 62, and the collecting part of the second exhaust manifold 64 is connected to the second catalytic converter 65 containing the catalyst 62.
Is connected to the catalytic converter 66. The first catalytic converter 65 and the second catalytic converter 66 are connected to the exhaust pipe 21 via a common exhaust pipe 67.

In the example shown in FIG. 12B, all cylinders #
Exhaust manifold 19 common to 1, # 2, # 3 and # 4
A catalyst converter 68 containing a catalyst 62 is connected to an outlet of the exhaust pipe 21. In these examples, an oxidation catalyst or a three-way catalyst is used as the catalyst 62, and an oxidation catalyst, a three-way catalyst or a NO _x absorbent is used as the catalyst 22. _The NO _x absorbent when the mean air-fuel ratio in the combustion chamber 5 of the lean NO _x
And releases NO _x when the average air-fuel ratio in the combustion chamber 5 becomes rich.

This NO _x absorbent uses, for example, alumina as a carrier and, for example, potassium K, sodium N
a, at least one selected from alkali metals such as lithium Li and cesium Cs, alkaline earths such as barium Ba and calcium Ca, rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. It is carried.

By arranging the catalyst 62 upstream of the catalyst 22, the oxidation reaction of unburned HC is prevented until the catalyst 22 is activated, that is, while the exhaust control valve 24 is almost fully closed. When the catalyst 22 is activated and the exhaust control valve 24 is fully opened, most of the unburned HC is sent to the catalyst 22 without being oxidized by the catalyst 62, and the unburned HC
The catalyst 22 can be maintained in an activated state by the oxidizing action of. Next, this will be described with reference to FIGS.

FIG. 13 shows FIGS. 11 and 12 (A),
3B shows a catalytic reaction activated state of the catalyst 22 shown in FIG. In FIG. 13, the vertical axis Tc indicates the temperature of the catalyst 22, and the horizontal axis SV indicates the space velocity (= volume flow rate of exhaust gas per unit time / volume of catalyst). To indicates the activation temperature of the catalyst 22, and the curve K
Indicates a catalytic reaction activation limit at which the catalytic reaction of the catalyst 22 is activated. That is, a region I above the catalytic reaction activation limit K indicates a catalytic reaction activation region where the catalytic reaction is activated, and a region II below the catalytic reaction activation limit K.
Indicates a catalytic reaction inactive region where no catalytic reaction is performed. Further, R30, R50 and R90 have the purifying rates of the reducing components in the exhaust gas by the catalyst 22 of 30%, 50% and 9%, respectively.
The case where it is 0% is shown.

The increase in the space velocity SV means that the flow rate of the exhaust gas flowing through the catalyst 22 increases, and therefore, the higher the space velocity SV, the more the catalyst 2
2, the contact time of the exhaust gas with the exhaust gas becomes shorter. On the other hand, the catalyst 22 is activated when it reaches the activation temperature To regardless of the space velocity SV. However, even when the catalyst 22 reaches the activation temperature To, if the space velocity SV increases, the contact time of the exhaust gas with the catalyst 22 becomes short, so that the catalytic reaction is not performed. In this case, if the temperature Tc of the catalyst 22 increases, a catalytic reaction is performed. Therefore, the catalytic reaction activation limit K is as shown in FIG.

On the other hand, as the temperature Tc of the catalyst 22 becomes higher than the catalytic reaction activation temperature limit K, the catalytic reaction becomes more active. Therefore, as the temperature Tc of the catalyst 22 becomes higher, the purification of reduced components in the exhaust gas becomes more efficient. Rate is higher. Therefore, each purification rate R30, R50, R9 of the reducing component in the exhaust gas
0 is as shown in FIG. By the way, as can be seen from FIG. 13, even when the exhaust gas temperature is low, that is, even when the temperature Tc of the catalyst 22 is low, in order to keep the catalyst 22 in the catalytic reaction activation region I, the catalyst 2
The space velocity SV of the exhaust gas flowing through the inside 2 must be reduced, and for that purpose the catalyst 22 must be increased. However, when the size of the catalyst 22 is increased, it is difficult to dispose the catalyst 22 in the engine room, so that the catalyst 22 has to be disposed under the floor of the vehicle body away from the engine. However, when the catalyst 22 is disposed at a position distant from the engine, the temperature of the exhaust gas flowing through the catalyst 22 decreases, and as a result, the catalyst 22 is moved to the catalytic reaction activation region I.
It is difficult to maintain within.

In this case, in order to maintain the catalyst 22 in the catalytic reaction activation region I, it is necessary to raise the temperature Tc of the catalyst 22, and the most appropriate method for this is to reduce the reducing component in the exhaust gas to the catalyst 22. In this method, the catalyst 22 is kept at a high temperature by the oxidation reaction heat generated at that time. On the other hand, for a while after the start of the engine, the temperature Tc of the catalyst 22 is considerably low, and at this time, the oxidizing action of the reducing component in the exhaust gas by the catalyst 22 cannot be expected. Therefore, in this embodiment, the catalyst 62 is disposed near the engine as shown in FIGS. 11 and 12A and 12B, and the unburned HC, C
The reducing components in the exhaust gas such as O are oxidized.

However, during the operation of the engine, if the reducing component in the exhaust gas is continuously oxidized in the catalyst 62, the catalyst 22
It is difficult to maintain the catalyst 22 in the catalytic reaction activation region I because the amount of the reducing component in the exhaust gas flowing into the catalyst decreases, and as a result, sufficient heat of oxidation reaction is not generated in the catalyst 22. Becomes That is, when the catalyst 22 requires a large amount of reducing components, it is necessary to suppress the oxidizing action of the reducing components in the catalyst 62.

As described above, the catalyst 22 is NO.
When using _x absorbent is air-fuel ratio is made rich in the combustion chamber 5 when releasing the NO _x from the NO _x absorbent, a large amount of unburned HC, CO, i.e. a large amount of reducing components combustion chamber Exhausted from 5 In this case, if the large amount of the reducing component is oxidized by the catalyst 62, the NO _x absorbent cannot release NO _x . That is, also in this case, the catalyst 2
When 2 requires a large amount of reducing components, it is necessary to suppress the oxidizing action of the reducing components in the catalyst 62.

Therefore, in this embodiment, when the reduction component in the exhaust gas is to be mainly oxidized by the catalyst 62, the catalyst 62
The oxidation rate of the reducing components in the exhaust gas at
When the reduction component in the exhaust gas is to be mainly oxidized by the catalyst 22, the oxidation rate of the reduction component in the exhaust gas in the catalyst 62 is reduced. That is, in FIG. 14, (1) shows a change in the flow velocity of the exhaust gas near the outlet of the exhaust port 11 during the low engine load operation, and (2)
Indicates a change in the flow rate of the exhaust gas near the outlet of the exhaust port 11 during the engine high load operation. In FIG. 14, (3) shows the change in the flow rate of the exhaust gas in the catalyst 22 during the low-load operation of the engine, and (4) shows the flow rate of the exhaust gas in the catalyst 22 during the high-load operation of the engine. Shows the change.

When the exhaust valve 10 is opened, exhaust gas is blown out of the combustion chamber 5 into the exhaust port 11 at a stretch.
4 (1) and (2), the flow rate of the exhaust gas near the outlet of the exhaust port 11 temporarily increases each time the exhaust valve 10 is opened. In this case, as the engine load increases, the pressure of the burned gas in the combustion chamber 5 increases, so that the flow rate of the exhaust gas near the outlet of the exhaust port 11 is as shown in FIG.
14 (1) is much faster than during the low-load operation shown in FIG. On the other hand, the peak value of the exhaust gas gradually decreases while flowing in the exhaust passage,
Further, the exhaust gas flowing out from each exhaust port 11 merges with each other and flows into the catalyst 22, so that the flow velocity of the exhaust gas in the catalyst 22 becomes as shown in FIGS.

On the other hand, in FIGS. 14 (3) and (4), K indicates the catalytic reaction activation limit shown in FIG. When the flow rate of the exhaust gas becomes higher than the catalytic reaction activation limit K, a catalytic reaction inactive region II shown in FIG. 13 is obtained, and therefore, the oxidizing action of the reducing component in the exhaust gas in the catalyst 22 is interrupted. In FIGS. 14 (3) and (4), the flow rate of the exhaust gas is always lower than the catalytic reaction activation limit K, and therefore, the oxidizing action of the reducing component in the exhaust gas is always performed. In the embodiment according to the present invention, when the warm-up is completed, the catalytic reaction activation limit K is usually at the position shown in FIGS. 14 (3) and (4).

On the other hand, a catalyst having exactly the same size and structure as the catalyst 22 was used as the catalyst 62, and this catalyst 62 was used in FIG.
Each branch pipe 1 of the exhaust manifold 19 is similar to the example shown in FIG.
Assuming that the catalysts are arranged within 9a, the catalytic reaction activation limit K for each catalyst 62 is as shown in FIGS. 14 (1) and 14 (2). That is, in this case, since the temperature of the catalyst 62 is much higher than that of the catalyst 22, the catalyst reaction activation limit K is smaller than that in the case shown in FIG.
The case shown in (1) is higher, and the case shown in FIG. 14 (2) is higher than the case shown in FIG. 14 (4).

In the embodiment according to the present invention, the volume of the catalyst 62 is made considerably smaller than the volume of the catalyst 22 as shown in FIG. 11 to thereby activate the catalytic reaction as shown in FIGS. The limit K is greatly reduced by ΔK and ΔK ′. That is, when the volume of the catalyst 62 is reduced, the contact time of the exhaust gas with the catalyst 62 is shortened. If the contact time of the exhaust gas with the catalyst 62 becomes short, the catalytic reaction in the catalyst 62 does not take place unless the flow rate of the exhaust gas becomes slow. Thus, when the volume of the catalyst 62 is reduced, the results are shown in FIGS. As shown, the catalytic reaction activation limit K decreases.

The solid lines shown in FIGS. 15A and 15B show enlarged views of FIGS. 14A and 14B when the volume of the catalyst 62 is considerably smaller than the volume of the catalyst 22, respectively. In this case, the catalytic reaction activation limit K decreases as described above. FIGS. 15A and 15B also show lines where the purification rate of the reducing components in the exhaust gas is 50%.

In FIGS. 15 (1) and (2), when the flow rate of the exhaust gas exceeds the catalytic reaction activation limit K, the oxidizing action of the reducing component in the exhaust gas is not performed. Passes through the catalyst 62. On the other hand, when the flow rate of the exhaust gas is lower than the catalytic reaction activation limit K, the reducing component in the exhaust gas is oxidized. However, in this case, as the flow rate of the exhaust gas decreases, the oxidizing action of the reducing component in the exhaust gas is promoted. Therefore, as the flow rate of the exhaust gas decreases, the purification rate of the reducing component in the exhaust gas increases.

When the catalyst 62 having a considerably smaller volume than the catalyst 22 is arranged in each branch pipe 19a of the exhaust manifold 19 as shown in FIG. 11, a considerable amount of the reducing component in the exhaust gas is reduced. Therefore, a considerable amount of the reducing components in the exhaust gas is sent into the catalyst 22. As can be seen by comparing FIGS. 15 (1) and (2), the catalyst 62 during the high-load operation of the engine shown in FIG. 15 (2) is better than that during the low-load operation of the engine shown in FIG. 15 (1). The amount of the reducing component that passes through is increased.

On the other hand, in the embodiment according to the present invention, when the purification rate of the reducing components in the exhaust gas by the catalyst 62 is to be increased, the exhaust control valve 24 is almost completely closed and the on-off valve 60 is fully opened. More specifically, in the embodiment according to the present invention, at this time, about 95% of the flow path area of the exhaust pipe 23 is closed by the exhaust control valve 24, and at this time, the pressure in the exhaust manifold 19 and the exhaust pipe 21, ie, the back pressure, Is almost 80
KPa. That is, at this time, the back pressure becomes almost twice the atmospheric pressure.

As described above, when the back pressure becomes almost twice the atmospheric pressure, the outflow speed of the exhaust gas from the combustion chamber 5 to the exhaust port 11 decreases. Further, when the back pressure becomes almost twice the atmospheric pressure, the density of the exhaust gas increases, and accordingly, the flow velocity of the exhaust gas flowing in the exhaust passage also decreases. Further, at this time, since the on-off valve 60 is fully opened, the exhaust pulsation is weakened, and the exhaust port 11
And the flow velocity of the exhaust gas flowing in the exhaust manifold branch pipe 19a is reduced. Therefore, at this time, the catalyst 62
Is always lower than the catalytic reaction activation limit K as shown by the broken line in FIG. As a result, at this time, most of the reducing components in the exhaust gas are oxidized in the catalyst 62, and a small amount of the reducing components flow into the catalyst 22 through the catalyst 62.

When the exhaust control valve 24 is fully opened and the on-off valve 60 is fully closed in this way, the flow rate of the exhaust gas increases as shown by the solid line in FIG. When the amount of the reducing component passes through the catalyst 62 and is sent into the catalyst 22, the exhaust control valve 24 is almost completely closed, and the on-off valve 60 is fully opened, and as shown by a broken line in FIG. Most of the reducing components contained in the catalyst are oxidized in the catalyst 62.

By the way, during a period of time after the operation of the engine is started, a low load operation is usually performed.
The temperature of 2 is low. Therefore, at this time, catalyst 2
2, the oxidizing action of the reduced components in the exhaust gas, ie, unburned H
Almost no purifying action of C and CO can be expected. Therefore, in the embodiment according to the present invention, when the low-load operation is performed between the start of the operation of the engine and the activation of the catalyst 22, the exhaust control valve 24 is almost completely closed and the on-off valve 60 is fully opened. Can be At this time, the flow rate of the exhaust gas flowing in the catalyst 62 becomes slow as shown by the broken line in FIG. 15A, and thus a considerable amount of unburned HC and CO contained in the exhaust gas is purified by the catalyst 62. I'm sick

Next, when the catalyst 22 is activated, the exhaust control valve 24 is fully closed, and the on-off valve 60 is fully closed. At this time, as can be seen from the solid lines in FIGS. 15A and 15B, a considerable amount of unburned HC contained in the exhaust gas,
CO flows through the catalyst 62 into the catalyst 22. As a result, a large amount of unburned HC and CO is oxidized in the catalyst 22, so that a large amount of heat of oxidation reaction is generated in the catalyst 22, and the catalyst 22 is maintained in a catalytic reaction activated state. In FIG. 13, a region M surrounded by a chain line is
In the embodiment according to the present invention, the range which the catalyst 22 can normally take, that is, the usage region of the catalyst 22 is shown.

[0079]

According to the present invention, the amount of unburned HC discharged into the atmosphere can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a side sectional view of a combustion chamber.

FIG. 3 is a diagram showing an injection amount, an injection timing, and an air-fuel ratio.

FIG. 4 is a view showing an injection timing.

FIG. 5 is a diagram showing the concentration of unburned HC.

FIG. 6 is a diagram showing an injection amount of a main fuel.

FIG. 7 is a diagram showing a relationship between an injection amount of a main fuel and an injection amount of a sub fuel.

FIG. 8 is a diagram showing an injection amount of a main fuel and an opening degree of an exhaust control valve.

FIG. 9 is a flowchart for performing operation control.

FIG. 10 is an overall view showing another embodiment of the internal combustion engine.

FIG. 11 is an overall view of an internal combustion engine showing an example of an arrangement of a catalyst.

FIG. 12 is an overall view of an internal combustion engine showing another example of the arrangement of the catalyst.

FIG. 13 is a diagram showing a catalytic reaction activation region.

FIG. 14 is a diagram showing a change in the flow velocity of exhaust gas.

FIG. 15 is a diagram showing a change in the flow rate of exhaust gas.

[Explanation of symbols]

 19 ... Exhaust manifold 20 ... Communication pipe 22 ... Catalyst 24 ... Exhaust control valve

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shunsuke Toshioka 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3G091 AA02 AA11 AA12 AA13 AA17 AA18 AA24 AB03 AB05 AB06 AB09 BA15 CA18 CB00 CB02 CB03 DA02 DB10 EA00 EA01 EA02 EA05 EA07 EA16 EA18 EA32 FA04 FB10 FB12 GB02W GB03W GB04W GB05W HA01 HA03 HA08 HA11 HA12 HA18 HB01 HB03 3G301 HA00 HA01 HA02 HA04 HA13 HA16 NE25 JA26 KA01 KA05 LA01 MA01 NB05 MA00 NE15 PA01Z PA17Z PB08A PB08Z PD00Z PD12Z PD14Z PE01Z PE04Z PE08Z PF03Z

Claims (6)

[Claims] An exhaust manifold is connected to an outlet of a corresponding engine exhaust port, an exhaust control valve is disposed in an exhaust passage connected to an outlet of the exhaust manifold, and unburned HC into the atmosphere is provided. When it is determined that the emission of fuel should be reduced, the exhaust control valve should be almost fully closed and the main fuel injected into the combustion chamber to generate engine output should be burned with excess air. In addition to the above, auxiliary fuel is additionally injected into the combustion chamber at a predetermined time during an expansion stroke or an exhaust stroke in which the auxiliary fuel can combust, and is generated in an engine exhaust port or an exhaust manifold branch pipe in the engine exhaust port and the exhaust manifold. An exhaust gas purifying apparatus for an internal combustion engine provided with exhaust pulsation reducing means for reducing exhaust pulsation caused by the exhaust pulsation. 2. The exhaust pulsation reducing means comprises a communication pipe which communicates each branch pipe of the exhaust manifold with each other.
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 3. The internal combustion engine according to claim 2, wherein an on-off valve that opens when the exhaust control valve is substantially fully closed and closes when the exhaust control valve is fully opened is disposed in each communication pipe. Engine exhaust purification device. 4. When the exhaust control valve is almost fully closed, the same engine operating state is set so as to approach the generated torque of the engine when the exhaust control valve is fully opened under the same engine operating state. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the main fuel injection amount is increased as compared with the case where the exhaust control valve is fully opened. 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a catalyst is disposed in each branch pipe of the exhaust manifold. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a catalyst is disposed in an exhaust passage connected to an outlet of the exhaust manifold.