JP3617382B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
In a diesel engine, the temperature in the combustion chamber becomes low during low-speed and low-load operation of the engine, particularly during warm-up 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, and the exhaust control valve is closed at the time of engine low speed and low load operation, and the fuel injection amount is greatly increased to increase the temperature in the combustion chamber, thereby injecting the injected fuel into the combustion chamber. There is known a diesel engine that is completely burned in order to suppress the amount of unburned HC generated (see Japanese Patent Laid-Open No. 49-80414).
[0003]
Further, when an exhaust purification catalyst is disposed in the engine exhaust passage, a good exhaust purification action by the catalyst is not performed unless the catalyst temperature is 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 combusted to raise the exhaust gas temperature, thereby raising the temperature of the catalyst. Internal combustion engines are known (see Japanese Patent Application Laid-Open Nos. 8-303290 and 10-212995).
[0004]
Conventionally, a catalyst capable of adsorbing unburned HC is known. This catalyst has the property of increasing the amount of unburned HC adsorbed as the ambient pressure increases, and releasing the adsorbed unburned HC as the ambient pressure decreases. Therefore, using this property, the unburned HC released from the catalyst causes NO._xIn order to reduce the NO, the catalyst is disposed in the engine exhaust passage and the exhaust control valve is disposed in the engine exhaust passage downstream of the catalyst._xDuring low-speed and low-load operation of the engine with a small amount of generation, in addition to the main fuel for generating engine output, a small amount of secondary fuel is injected during the expansion stroke or exhaust stroke to discharge a large amount of unburned HC from the combustion chamber, Further, at this time, a large amount of unburned HC discharged from the combustion chamber by increasing the pressure in the exhaust passage by closing the exhaust control valve to a relatively small opening degree so that the engine output drop falls within an allowable range. Is adsorbed in the catalyst and NO._xDuring high-speed or high-load operation with a large amount of generation, the exhaust control valve is fully opened to reduce the pressure in the exhaust passage. At this time, NO is released by unburned HC released from the catalyst._xAn internal combustion engine in which the above is reduced is known (see Japanese Patent Application Laid-Open No. 10-238336).
[0005]
[Problems to be solved by the invention]
Now, not only in diesel engines but also in spark ignition internal combustion engines, how to reduce the amount of unburned HC generated during engine low load operation, particularly during engine warm-up operation, has become a major problem. Therefore, the present inventor has conducted experimental research to solve this problem, and as a result, in order to greatly reduce the amount of unburned HC discharged into the atmosphere during engine warm-up operation, It has been found that it is necessary to reduce the amount of generated fuel HC and at the same time increase the amount of unburned HC in the exhaust passage.
[0006]
Specifically, during the expansion stroke or the exhaust stroke, additional fuel is injected into the combustion chamber to burn the secondary fuel, and an exhaust control valve is installed in the engine exhaust passage that is spaced from the outlet of the engine exhaust port. When this exhaust control valve is almost fully closed, the amount of unburned HC generated in the combustion chamber is reduced by the synergistic effect of combustion of these auxiliary fuels and exhaust throttling action of the exhaust control valve, and unburned in the exhaust passage. It has been found that the amount of reduction of HC increases, and thus the amount of unburned HC discharged into the atmosphere can be greatly reduced.
[0007]
More specifically, when the auxiliary fuel is injected, not only the auxiliary fuel is combusted but also unburned HC, which is the unburned main fuel, is combusted in the combustion chamber. Accordingly, not only the amount of unburned HC generated in the combustion chamber is greatly reduced, but also the unburned HC and auxiliary fuel, which are unburned main fuel, are burned, and the burnt gas temperature becomes considerably high.
[0008]
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. A high back pressure means that the temperature of the exhaust gas discharged from the combustion chamber does not decrease so much, and therefore the exhaust gas temperature 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 slow. Therefore, the exhaust gas is in a high temperature state for a long time in the exhaust passage upstream of the exhaust control valve. Will stay. During this time, unburned HC contained in the exhaust gas is oxidized, and thus the amount of unburned HC discharged into the atmosphere is greatly reduced.
[0009]
In this case, if the auxiliary fuel is not injected, the unburned unburned HC of the main fuel remains as it is, so that a large amount of unburned HC is generated in the combustion chamber. Further, when the auxiliary fuel is not injected, the burnt gas temperature in the combustion chamber does not increase so much, so even if the exhaust control valve is almost fully closed at this time, unburned HC in the exhaust passage upstream of the exhaust control valve. It is not possible to expect sufficient oxidizing action. Accordingly, at this time, a large amount of unburned HC is discharged into the atmosphere.
[0010]
On the other hand, even if the exhaust throttle action by the exhaust control valve is not performed, if the auxiliary fuel is injected, the amount of unburned HC generated in the combustion chamber is reduced, and the burnt gas temperature in the combustion chamber is increased. However, when the exhaust throttle action by the exhaust control valve is not performed, the exhaust gas pressure immediately decreases as soon as the exhaust gas is discharged from the combustion chamber, and thus the exhaust gas temperature also decreases immediately. Therefore, in this case, almost no oxidizing action of unburned HC in the exhaust passage can be expected, and thus a large amount of unburned HC is also discharged into the atmosphere at this time.
[0011]
That is, in order to greatly reduce the amount of unburned HC discharged into the atmosphere, it is necessary to inject auxiliary fuel and simultaneously close the exhaust control valve almost completely.
In the diesel engine described in Japanese Patent Laid-Open No. 49-80414, the auxiliary fuel is not injected and the injection amount of the main fuel is greatly increased, so that the exhaust gas temperature rises but an extremely large amount of unburned HC. Is generated in the combustion chamber. As described above, when an extremely large amount of unburned HC is generated in the combustion chamber, even if the unburned HC is oxidized in the exhaust passage, only a part of the unburned HC is oxidized. Will be discharged.
[0012]
On the other hand, in the internal combustion engine described in Japanese Patent Laid-Open No. 8-303290 or Japanese Patent Laid-Open No. 10-212995, the exhaust throttle action by the exhaust control valve is not performed, so the oxidation action of unburned HC in the exhaust passage is I can hardly expect it. Accordingly, even in this internal combustion engine, a large amount of unburned HC is discharged into the atmosphere.
Moreover, 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 engine output falls within an allowable range. However, the back pressure is not so high when the exhaust control valve is closed so that the engine output falls within the allowable range.
[0013]
In this internal combustion engine, a small amount of auxiliary fuel is injected during the expansion stroke or the exhaust stroke in order to generate unburned HC to be adsorbed by the catalyst. In this case, since the unburned HC is not generated if the auxiliary fuel is combusted satisfactorily, it is considered that the injection control of the auxiliary fuel is performed in this internal combustion engine so that the auxiliary fuel does not burn well. Therefore, in this internal combustion engine, it is considered that a small amount of auxiliary fuel does not contribute much to the temperature increase of the burnt gas temperature.
[0014]
In this way, in this internal combustion engine, a large amount of unburned HC is generated in the combustion chamber, and the back pressure is not so high and the burnt gas temperature does not rise so much. It is thought that it is not oxidized so much. The purpose of this internal combustion engine is to adsorb as much unburned HC as possible to the catalyst, so it can be said that it makes sense to think in this way.
[0015]
An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can greatly reduce the amount of unburned HC discharged into the atmosphere while ensuring stable operation of the engine.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, in the first invention, each branch pipe of the exhaust manifold is connected to the outlet of the corresponding engine exhaust port, and an exhaust control valve is disposed in the exhaust passage connected to the outlet of the exhaust manifold. When it is determined that the amount of unburned HC discharged 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 In addition to being burned under excess, the secondary fuel is additionally injected into the combustion chamber at a predetermined time during the expansion stroke or the exhaust stroke where the secondary fuel can burn, and is generated in the engine exhaust port and the exhaust manifold. To reduce exhaust pulsationThe adjacent branch pipes of the exhaust manifold are communicated with each other by a communication pipe, and are opened when the exhaust control valve is almost fully closed in each communication pipe, and are closed when the exhaust control valve is fully opened. An open / close valve is arranged.
[0018]
2In the second invention, in the first invention, when the exhaust control valve is almost fully closed, the same torque is generated so as to approach the generated torque of the engine when the exhaust control valve is fully opened under the same engine operating state. The injection amount of the main fuel is increased as compared with the case where the exhaust control valve is fully opened under the engine operation state.
3In the second invention, in the first invention, a catalyst is arranged in each branch pipe of the exhaust manifold.
[0019]
4In the second invention, in the first invention, the catalyst is arranged in the exhaust passage connected to the outlet of the exhaust manifold.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
1 and 2 show a case where the present invention is applied to a stratified combustion internal combustion engine. However, the present invention can also be applied to a spark ignition type internal combustion engine in which combustion is performed under a uniform lean air-fuel ratio and a diesel engine in which combustion is performed under excess air.
[0021]
Referring to FIG. 1, reference numeral 1 denotes an engine body, and the engine body 1 has four cylinders including a first cylinder # 1, a second cylinder # 2, a third cylinder # 3, and a fourth cylinder # 4. FIG. 2 shows a side sectional view of each cylinder # 1, # 2, # 3, # 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 disposed on the peripheral edge of the inner wall surface of the cylinder head 3, and 7 is an inside of the cylinder head 3. An ignition plug disposed at the center of the wall surface, 8 is an intake valve, 9 is an intake port, 10 is an exhaust valve, and 11 is an exhaust port.
[0022]
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. A throttle valve 18 driven by a step motor 17 is disposed 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 and are adjacent to each other.aAre connected to each other by a communication pipe 20. These communication pipes 20 form exhaust pulsation reducing means. On the other hand, the exhaust manifold 19 is connected to a catalytic converter 22a containing a catalyst 22 via an exhaust pipe 21, and an exhaust pipe 23 is connected to the catalytic converter 22a. An exhaust control valve 24 controlled by an actuator 25 is disposed in the exhaust pipe 23.
[0023]
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 an electrically controlled EGR control valve 27 is disposed in the EGR passage 26. Is done. The fuel injection valve 6 is connected to a common fuel reservoir, so-called common rail 28. The fuel in the fuel tank 29 is supplied into the common rail 28 via an electrically controlled fuel pump 30 with variable discharge amount, 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, and a fuel pump 30 is set so that the fuel pressure in the common rail 28 becomes a target fuel pressure based on an output signal of the fuel pressure sensor 31. The discharge amount is controlled.
[0024]
The electronic control unit 40 comprises a digital computer and is connected to each other by a bidirectional bus 41. A ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45 and an output port 46 are connected. It comprises. The air flow meter 15 generates an output voltage proportional to the amount of intake air, and this output voltage is input to the input port 45 via the corresponding AD converter 47. A water temperature sensor 32 for detecting the engine cooling water temperature is attached to the engine body 1, and the output signal of the water temperature sensor 32 is input to the input port 45 via the corresponding AD 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.
[0025]
Further, an exhaust manifold 19 and an output sensor 33 for detecting the pressure of exhaust gas in the exhaust pipe 21, that is, a back pressure, are arranged in the exhaust pipe 21, and an output signal of the pressure sensor 33 is a corresponding AD converter. It is input to the input port 45 via 47. A temperature sensor 34 for detecting the temperature of the catalyst 22 is attached to the catalytic converter 22a, and an output signal of the temperature sensor 34 is input to the input port 45 via the corresponding AD converter 47.
[0026]
A load sensor 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. Is done. The input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, 30 °. On the other hand, the output port 46 is connected to the fuel injection valve 6, spark plug 7, throttle valve control step motor 17, exhaust control valve control actuator 25, EGR control valve 27, and fuel pump 30 through corresponding drive circuits 48. The
[0027]
FIG. 3 shows fuel injection amounts Q1, Q2, Q (= Q₁+ Q₂), Injection start timings θS1 and θS2, injection completion timings θE1 and θE2, and an average air-fuel ratio A / F in the combustion chamber 5. In FIG. 3, the horizontal axis L indicates the amount of depression of the accelerator pedal 50, that is, the required load.
As can be seen from FIG. 3, the required load L is L.₁If it is lower, the fuel injection Q2 is performed between θS2 and θE2 at the end of the compression stroke. At this time, the average air-fuel ratio A / F is considerably lean. Required load L is L₁And L₂During this time, the first fuel injection Q1 is performed between θS1 and θE1 at the beginning of the intake stroke, and then the second fuel injection Q2 is performed between θS2 and θE2 at the end of the compression stroke. Also at this time, the air-fuel ratio A / F is lean. Required load L is L₂If it is larger than that, the fuel injection Q1 is performed between θS1 and θE1 in the initial stage of the intake stroke. At this time, the average air-fuel ratio A / F is lean in the region where the required load L is low, the average air-fuel ratio A / F is made the stoichiometric air-fuel ratio when the required load L increases, and the average The fuel ratio A / F is made rich. Note that only the required load L is the operating region in which the fuel injection Q2 is performed only at the end of the compression stroke, the operating region in which the fuel injections Q1 and Q2 are performed twice, and the operating region in which the fuel injection Q1 is performed only in the early stage of the intake stroke. Is actually determined by the required load L and the engine speed.
[0028]
FIG. 2 shows that the required load L is L₁It shows a case where the fuel injection Q2 is performed only when it is smaller than (FIG. 3), that is, at the end of the compression stroke. As shown in FIG. 2, a cavity 4a is formed on the top surface of the piston 4, and the required load L is L.₁When it is lower than that, fuel is injected from the fuel injection valve 6 toward the bottom wall surface of the cavity 4a at the end of the compression stroke. This fuel is guided by the peripheral wall surface of the cavity 4 a and travels toward the spark plug 7, whereby an air-fuel mixture G is formed around the spark plug 7. Next, the air-fuel mixture G is ignited by the spark plug 7.
[0029]
On the other hand, as described above, the required load L is L₁And L₂When it is between, fuel injection is performed twice. In this case, a lean air-fuel 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 spark plug 7 by the second fuel injection Q2 performed at the end of the compression stroke. The air-fuel mixture is ignited by the spark plug 7, and the lean air-fuel mixture is combusted by the ignition flame.
[0030]
On the other hand, the required load L is L₂If it is greater than that, a homogeneous mixture of lean, stoichiometric air-fuel ratio or rich air-fuel ratio is formed in the combustion chamber 5 as shown in FIG. 3, and this homogeneous mixture is ignited by the spark plug 7.
Next, a method for reducing unburned HC according to the present invention will be schematically described with reference to FIG. In FIG. 4, the horizontal axis indicates the crank angle, and BTDC and ATDC indicate before the top dead center and after the top dead center, respectively.
[0031]
FIG. 4A shows a case where it is not particularly necessary to reduce unburned HC by the method according to the present invention.₁The fuel injection timing when it is smaller than is shown. 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 held in a fully opened 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 fully closed, and further, as shown in FIG. In addition to the injection of the main fuel Qm, during the expansion stroke, in the example shown in FIG. 4B, the auxiliary fuel Qa is additionally injected in the vicinity of 60 ° after compression top dead center (ATDC). In this case, after combustion of the main fuel Qm, the main fuel Qm is burned under excess air so that sufficient oxygen remains in the combustion chamber 5 to completely burn the sub fuel Qa. 4 (A) and 4 (B) show the fuel injection period when the engine load and the engine speed are the same, and accordingly when the engine load and the engine speed are the same, FIG. The injection amount of the main fuel Qm in the case shown in FIG. 4 (B) is increased compared to the injection amount of the main fuel Qm in the case shown in FIG. 4 (A).
[0032]
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 triangles indicate unburned in 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 concentration of HC (ppm) is shown. In this case, the concentration of unburned HC in the exhaust gas at the outlet of the exhaust port 11 becomes a very high value of 6000 ppm or more.
[0033]
On the other hand, in the example shown in FIG. 5, the black circles and solid lines indicate that the exhaust control valve 24 is almost fully closed, and the unburned gas in the exhaust gas when the main fuel Qm and the sub fuel Qa are injected as shown in FIG. 4B. The concentration of HC (ppm) is shown. In this case, the concentration of unburned HC in the exhaust gas at the outlet of the exhaust port 11 is 2000 ppm or less, and in the vicinity of the exhaust control valve 24, the concentration of unburned HC in the exhaust gas is reduced to about 150 ppm. Therefore, in this case, it can be seen that the amount of unburned HC discharged into the atmosphere is greatly reduced.
[0034]
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 the black triangle in FIG. 5, when the amount of unburned HC at the outlet of the exhaust port 11 is large, that is, when the amount of unburned HC generated in the combustion chamber 5 is large, unburned in the exhaust passage. Even if the oxidation reaction of HC is promoted, the amount of unburned HC discharged into the atmosphere is not reduced so much. That is, the amount of unburned HC discharged into the atmosphere by promoting the oxidation reaction of unburned HC in the exhaust passage can be greatly reduced as shown by the black circle in FIG. This is when the concentration of unburned HC is low, that is, when the amount of unburned HC generated in the combustion chamber 5 is small.
[0035]
Thus, 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 promoted. It is necessary to satisfy two requirements at the same time. First, the second requirement, that is, promoting the oxidation reaction of unburned HC in the exhaust passage will be described.
[0036]
According to the present invention, the exhaust control valve 24 is almost fully closed when the amount of unburned HC discharged into the atmosphere is to be reduced. As described above, when the exhaust control valve 24 is almost fully closed, 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.
An increase in the back pressure means that when the exhaust gas is discharged from the combustion chamber 5 into the exhaust port 11, the pressure of the exhaust gas does not decrease so much, and therefore the temperature of the exhaust gas discharged from the combustion chamber 5 also decreases significantly. It means not to. 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. Means slow. 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.
[0037]
As described above, when the exhaust gas is retained in the exhaust passage upstream of the exhaust control valve 24 for a long time under a high temperature, the oxidation reaction of unburned HC is promoted during that time. In this case, according to experiments by the present inventor, in order to promote the oxidation reaction of unburned HC in the exhaust passage, the exhaust gas temperature at the outlet of the exhaust port 11 needs to be about 750 ° C. or higher, preferably 800 ° C. or higher. It has been found.
[0038]
Further, as the time during which the high-temperature exhaust gas stays in the exhaust passage upstream of the exhaust control valve 24 becomes longer, the reduction amount of unburned HC increases. 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 separated from the outlet of the exhaust port 11 by a distance necessary to sufficiently reduce unburned HC. Need to be placed. According to experiments by the present inventors, it has been found that the distance from the outlet of the exhaust port 11 to the exhaust control valve 24 is preferably 1 meter or more in order to sufficiently reduce unburned HC.
[0039]
By the way, the oxidation action of unburned HC is promoted as the exhaust gas temperature is high, and therefore, it is preferable to keep the exhaust gas as much as possible in the region where the exhaust gas temperature is high. Therefore, in the present invention, the exhaust manifold branch pipes 19 a are communicated with each other by the communication pipe 20.
That is, in an ordinary internal combustion engine, exhaust pulsation is used to exhaust burned gas in the combustion chamber 5 from the combustion chamber 5 as soon as possible when the exhaust valve 10 is opened. 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 by the collecting portion of the exhaust manifold 19, and this time, the exhaust port is in the form of a negative pressure. Come back in 11. When the exhaust port 11 has a negative pressure, the burned gas is rapidly discharged from the combustion chamber 5. Therefore, in a normal internal combustion engine, the dimensions of the exhaust manifold branch pipe 19a are set so that a negative pressure is generated in the exhaust port 11 at an optimal 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 becomes weak, that is, the exhaust pulsation is reduced, so that 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.
[0040]
However, the present invention aims to promote the oxidation reaction of unburned HC. Therefore, the exhaust gas discharged from the combustion chamber 5 can be as much as possible in the exhaust port 11 and the exhaust manifold 19 where the exhaust gas temperature is kept high. It is preferable to stay for a long time. Therefore, in the embodiment according to the present invention, the exhaust manifolds 19a are communicated with each other by the communication pipe 19a. That is, when the exhaust manifolds 19a communicate with each other through the communication pipe 19a, the exhaust gas flows relatively slowly through the exhaust port 11 and the exhaust manifold 19 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 unburned HC is promoted.
[0041]
On the other hand, as described above, in order to promote the oxidation reaction of unburned HC in the exhaust passage, the exhaust gas temperature at the outlet of the exhaust port 11 needs to be about 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, and the auxiliary fuel Qa is burned in the combustion chamber 5.
[0042]
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 burned well, so that unburned HC which is the unburned residue of the auxiliary fuel Qa is not generated so much. Thus, the amount of unburned HC finally generated in the combustion chamber 5 is considerably reduced.
[0043]
Further, when the auxiliary fuel Qa is burned in the combustion chamber 5, in addition to the heat generated by the combustion of the main fuel Qm and the auxiliary fuel Qa itself, the combustion heat of the unburned HC that is the unburned main fuel Qm is additionally generated. Therefore, the burnt gas temperature in the combustion chamber 5 becomes considerably high. In this manner, 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.degree. C. or higher.
[0044]
As described above, in the present invention, the auxiliary fuel Qa needs to be combusted in the combustion chamber 5, and for that purpose, it is necessary that sufficient oxygen remains in the combustion chamber 5 when the auxiliary fuel Qa is burned. It is necessary to inject the auxiliary fuel Qa at a time when the injected auxiliary fuel Qa is satisfactorily combusted in the combustion chamber 5.
Therefore, in the present invention, the main fuel Qm is burned under excess air so that sufficient oxygen can remain in the combustion chamber 5 during the combustion of the auxiliary fuel Qa. Further, the injection timing at which the auxiliary fuel Qa injected in the stratified combustion internal combustion engine shown in FIG. 2 is burned well in the combustion chamber 5 is approximately 50 after compression top dead center (ATDC) indicated by an arrow Z in FIG. Therefore, in the stratified combustion internal combustion engine shown in FIG. 2, the auxiliary fuel Qa is injected after the compression top dead center (ATDC) in the expansion stroke of about 50 ° to about 90 °. . The secondary fuel Qa injected in the expansion stroke from approximately 50 ° to approximately 90 ° after the compression top dead center (ATDC) does not contribute to the generation of the engine output.
[0045]
By the way, according to an experiment by the present inventor, in the stratified combustion internal combustion engine shown in FIG. 2, the unburned HC discharged into the atmosphere when the auxiliary fuel Qa is injected in the vicinity of 60 ° after compression top dead center (ATDC). The amount is the least. Therefore, in the embodiment according to the present invention, as shown in FIG. 4B, the injection timing of the auxiliary fuel Qa is approximately 60 ° after compression top dead center (ATDC).
[0046]
The optimal injection timing of the auxiliary fuel Qa differs depending on the engine type. For example, in a diesel engine, the optimal injection timing of the auxiliary fuel Qa is in the expansion stroke or in 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 burnt gas temperature 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 burnt gas temperature in the combustion chamber 5 increases as the injection amount of the main fuel Qm increases, and increases as the injection amount of the auxiliary fuel Qa increases. Furthermore, the burnt gas temperature in the combustion chamber 5 is affected by the back pressure. That is, as the back pressure increases, the amount of burned gas remaining in the combustion chamber 5 increases because the burned gas is less likely to flow out of the combustion chamber 5, and thus the exhaust control valve 24 is almost fully closed. The burnt gas temperature in the combustion chamber 5 is raised.
[0047]
By the way, when the exhaust control valve 24 is almost closed, and the back pressure becomes high, the generated torque of the engine decreases with respect to the optimum required generated torque. Therefore, in the embodiment according to the present invention, when the exhaust control valve 24 is almost fully closed as shown in FIG. 4 (B), the exhaust control is performed under the same engine operating state as shown in FIG. 4 (A). The injection amount of the main fuel Qm is increased as compared with the case where the exhaust control valve 24 is fully opened under the same engine operating state so as to approach the required generation torque of the engine when the valve 24 is fully opened. . In the embodiment according to the present invention, when the exhaust control valve 24 is almost fully closed, the engine generated when the exhaust control valve 24 is fully opened under the same engine operating state at that time. The main fuel Qm is increased so as to match the required generated torque.
[0048]
FIG. 6 shows a change in the main fuel Qm necessary for obtaining the required torque of the engine with respect to the required load L. In FIG. 6, a solid line indicates a case where the exhaust control valve 24 is almost fully closed, and a broken line indicates a case where the exhaust control valve 24 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 about 750 ° C. to about 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 burnt gas temperature in the combustion chamber 5 is increased, and even if the sub fuel Qa is increased, the burnt gas temperature in the combustion chamber 5 is increased. Accordingly, the relationship between the main fuel Qm and the sub fuel Qa required to change the exhaust gas temperature at the outlet of the exhaust port 11 from about 750 ° C. to about 800 ° C. is shown in FIG. Qa decreases, and if the main fuel Qm is decreased, the auxiliary fuel Qa increases.
[0049]
However, when the main fuel Qm and the auxiliary fuel Qa are increased by the same amount, the temperature increase in the combustion chamber 5 is much larger when the auxiliary fuel Qa is increased than when the main fuel Qm is increased. . Therefore, it can be said that it is preferable to raise the burnt gas temperature in the combustion chamber 5 by increasing the auxiliary fuel Qa from the viewpoint of reducing the fuel consumption.
[0050]
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 mainly the combustion heat of the auxiliary fuel Qa. Thus, the burnt gas temperature in the combustion chamber 5 is raised.
In this way, when the exhaust control valve 24 is almost fully closed and the amount of the auxiliary fuel Qa required to bring the exhaust gas at the outlet of the exhaust port 11 to about 750 ° C. or higher, preferably about 800 ° C. or higher, is injected from the exhaust port 11. In the exhaust passage leading to the exhaust control valve 24, the concentration of unburned HC 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. p. In order to reduce the pressure to about m 2, the pressure in the exhaust passage upstream of the exhaust control valve 24 needs to be about 80 KPa or more with gauge pressure. At this time, the closing ratio of the exhaust passage 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 fully closed so that the back pressure becomes approximately 80 KPa.
[0051]
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, it is during engine start-up and warm-up operation, and therefore a large amount of unburned HC is generated during engine start-up and warm-up operation. Thus, when the temperature in the combustion chamber 5 is low, 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. It is difficult to oxidize the fuel HC by the catalyst 22.
[0052]
Therefore, in the embodiment according to the present invention, when the engine is started and warmed up, the exhaust control valve 24 is almost fully closed until the catalyst 22 is activated, the main fuel Qm is increased, and the auxiliary fuel Qa is additionally injected, whereby the atmosphere The amount of unburned HC discharged inside is greatly reduced.
FIG. 8 shows an example of changes in the main fuel Qm and the opening degree of the exhaust control valve 24 at the time of engine start and warm-up operation. In FIG. 8, the solid line X indicates the optimum injection amount of the main fuel Qm when the exhaust control valve 24 is substantially fully closed, and the broken line Y indicates the optimum main fuel when the exhaust control valve 24 is fully opened. The injection quantity of Qm is shown. As can be seen from FIG. 8, when the engine is started and warmed up, the exhaust control valve 24 is almost fully closed, and the optimal main fuel Qm when the exhaust control valve 24 is fully opened under the same engine operating state. The injection amount X of the main fuel Qm is increased from the injection amount Y, and the auxiliary fuel Qa is additionally injected.
[0053]
FIG. 9 shows an operation control routine.
Referring to FIG. 9, first, at step 100, it is judged if 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 fully 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. Next, at step 102, the injection amount of the main fuel Qm is controlled to become X shown in FIG. Next, at step 103, injection control of the auxiliary fuel Qa is performed. Next, at step 104, it is determined based on the output signal of the temperature sensor 34 whether or not the temperature Tc of the catalyst 22 has exceeded the activation temperature To, for example, 250 ° C., and when Tc> To, the routine proceeds to step 105 where warming A completion flag is set.
[0054]
When the warm-up completion flag is set, that is, when the catalyst 22 is activated, the routine proceeds from step 100 to step 106 where the exhaust control valve 24 is fully opened, and then the routine proceeds to step 107 where injection control of the main fuel Qm is performed. At this time, the auxiliary fuel Qa is not injected.
FIG. 10 shows another embodiment.
[0055]
In this embodiment, an open / close valve 60 controlled by an actuator 61 is disposed 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 fully closed, the exhaust pulsation is weakened, so that the oxidation action of unburned HC is promoted. Gas is exhausted rapidly.
[0056]
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. 12 (A), the ignition order is 1-3-4-2, and as shown in FIG. 12 (A), every other cylinder # 1, # 4 has the ignition order. The exhaust ports 11 are connected to a common first exhaust manifold 63, and the exhaust ports 11 of the remaining cylinders # 2 and # 3 in which every other ignition order is connected are connected to a common second exhaust manifold 64. The collecting portion of the first exhaust manifold 63 is connected to the first catalytic converter 65 containing the catalyst 62, and the collecting portion of the second exhaust manifold 64 is connected to the second catalytic converter 66 containing the catalyst 62. . The first catalytic converter 65 and the second catalytic converter 66 are connected to the exhaust pipe 21 via a common exhaust pipe 67.
[0057]
In the example shown in FIG. 12B, a catalytic converter 68 containing a catalyst 62 is connected to the outlet of the common exhaust manifold 19 for all cylinders # 1, # 2, # 3, and # 4. Connected to 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 NO is used as the catalyst 22._xAbsorbent is used. NO_xThe absorbent is NO when the average air-fuel ratio in the combustion chamber 5 is lean._xWhen the average air-fuel ratio in the combustion chamber 5 becomes rich, NO is absorbed._xIt has a function of releasing.
[0058]
This NO_xThe absorbent is, for example, alumina as a carrier, and on this carrier, alkali metal such as potassium K, sodium Na, lithium Li, cesium Cs, alkaline earth such as barium Ba, calcium Ca, lanthanum La, yttrium Y, etc. At least one selected from rare earths and a noble metal such as platinum Pt are supported.
[0059]
When the catalyst 62 is arranged upstream of the catalyst 22 in this way, the oxidation reaction of unburned HC is further performed by the catalyst 62 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 is oxidized in the catalyst 22. The action enables the catalyst 22 to be maintained in an activated state. Next, this will be described with reference to FIGS.
[0060]
FIG. 13 shows the catalytic reaction activation state of the catalyst 22 shown in FIG. 11 and FIGS. 12 (A) and 12 (B). In FIG. 13, the vertical axis Tc indicates the temperature of the catalyst 22, and the horizontal axis SV indicates the space velocity (= the exhaust gas volume flow rate per unit time / the catalyst volume). Further, To represents the activation temperature of the catalyst 22, and the curve K represents the catalytic reaction activation limit at which the catalytic reaction of the catalyst 22 is activated. That is, the region I above the catalytic reaction activation limit K indicates the catalytic reaction activation region where the catalytic reaction is activated, and the region II below the catalytic reaction activation limit K does not perform the catalytic reaction. The catalytic reaction inactive region is shown. R30, R50, and R90 indicate cases where the purification rate of the reducing component in the exhaust gas by the catalyst 22 is 30%, 50%, and 90%, respectively.
[0061]
The increase in the space velocity SV means that the flow velocity of the exhaust gas flowing in the catalyst 22 is increased. Therefore, the contact time of the exhaust gas with respect to the catalyst 22 is shortened as the space velocity SV is increased. On the other hand, the catalyst 22 is activated when it reaches the activation temperature To regardless of the space velocity SV. However, even if the catalyst 22 reaches the activation temperature To, if the space velocity SV increases, the contact time of the exhaust gas with respect to the catalyst 22 becomes short, so that the catalytic reaction is not performed. In this case, when the temperature Tc of the catalyst 22 is increased, the catalytic reaction is performed. Therefore, the catalytic reaction activation limit K is as shown in FIG.
[0062]
On the other hand, the higher the temperature Tc of the catalyst 22 with respect to the catalyst reaction activation temperature limit K, the more active the catalytic reaction. Therefore, the higher the temperature Tc of the catalyst 22, the higher the purification rate of reducing components in the exhaust gas. Become. Accordingly, the purification rates R30, R50, R90 of the reducing components in the exhaust gas are as shown in FIG.
As can be seen from FIG. 13, in order to keep the catalyst 22 in the catalytic reaction activation region I even in the operating state where the exhaust gas temperature is low, that is, when the temperature Tc of the catalyst 22 is low. The space velocity SV of the exhaust gas flowing inside must be reduced, and for this purpose the catalyst 22 must be enlarged. However, if the catalyst 22 is enlarged, it becomes difficult to dispose the catalyst 22 in the engine room, and thus the catalyst 22 must be disposed under the floor of the vehicle main body away from the engine. However, if the catalyst 22 is arranged at a position away from the engine, the temperature of the exhaust gas flowing through the catalyst 22 is lowered, and as a result, it becomes difficult to maintain the catalyst 22 in the catalytic reaction activation region I.
[0063]
In this case, in order to maintain the catalyst 22 in the catalytic reaction activation region I, it is necessary to increase the temperature Tc of the catalyst 22, and the most appropriate method for that purpose is to oxidize the reducing component in the exhaust gas in the catalyst 22. In this method, the catalyst 22 is kept at a high temperature by the heat of oxidation reaction generated at that time.
On the other hand, for a while after the engine is started, the temperature Tc of the catalyst 22 is quite low, and at this time, the oxidizing action of the reducing component in the exhaust gas at the catalyst 22 cannot be expected. Therefore, in this embodiment, as shown in FIG. 11 and FIGS. 12A and 12B, a catalyst 62 is disposed near the engine, and for a while after the engine is started, the unburned HC and CO are kept in the catalyst 62 for a while. Such reducing components in the exhaust gas are oxidized.
[0064]
However, if the catalyst 62 continues to oxidize the reducing component in the exhaust gas during the operation of the engine, the amount of the reducing component in the exhaust gas flowing into the catalyst 22 decreases, and as a result, sufficient oxidation reaction heat is generated in the catalyst 22. Therefore, it is difficult to keep the catalyst 22 in the catalytic reaction activation region I. That is, when the catalyst 22 requires a large amount of reducing component, it is necessary to suppress the oxidizing action of the reducing component in the catalyst 62.
[0065]
Further, as described above, the catalyst 22 is NO._xNO when absorbent is used_xNO from absorbent_xWhen the air is to be released, the air-fuel ratio in the combustion chamber 5 is made rich, and a large amount of unburned HC and CO, that is, a large amount of reducing components are discharged from the combustion chamber 5. In this case, if this large amount of reducing component is oxidized by the catalyst 62, NO_xNO from absorbent_xCan no longer be released. That is, also in this case, when the catalyst 22 requires a large amount of reducing component, it is necessary to suppress the oxidizing action of the reducing component in the catalyst 62.
[0066]
Therefore, in this embodiment, when the reducing component in the exhaust gas should be mainly oxidized by the catalyst 62, the oxidation ratio of the reducing component in the exhaust gas in the catalyst 62 is increased, and the reducing component in the exhaust gas is mainly converted by the catalyst 22. When it should be oxidized, the oxidation ratio of the reducing component in the exhaust gas in the catalyst 62 is reduced.
That is, in FIG. 14, (1) shows the change in the exhaust gas flow velocity near the outlet of the exhaust port 11 during engine low load operation, and (2) shows the vicinity of the outlet of the exhaust port 11 during engine high load operation. The change in the flow rate of the exhaust gas is shown. In FIG. 14, (3) shows the change in the exhaust gas flow rate in the catalyst 22 during engine low load operation, and (4) the exhaust gas flow rate in the catalyst 22 during engine high load operation. Shows changes.
[0067]
When the exhaust valve 10 is opened, exhaust gas is expelled from the combustion chamber 5 into the exhaust port 11 at a stroke. Therefore, as shown in FIGS. 14 (1) and (2), the flow rate of the exhaust gas near the exhaust port 11 outlet is as follows. Each time the exhaust valve 10 is opened, it temporarily increases. In this case, since the pressure of the burned gas in the combustion chamber 5 increases as the engine load increases, the flow rate of the exhaust gas in the vicinity of the outlet of the exhaust port 11 is higher during the high load operation shown in FIG. It is much faster than during low-load operation shown in 1). On the other hand, the peak value of the exhaust gas gradually decreases while flowing in the exhaust passage, and the exhaust gases flowing out from the respective exhaust ports 11 merge with each other and flow into the catalyst 22, so that the flow velocity of the exhaust gas in the catalyst 22 is As shown in FIGS. 14 (3) and 14 (4).
[0068]
On the other hand, in FIGS. 14 (3) and 14 (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, the catalytic reaction inactive region II shown in FIG. 14 (3) and 14 (4), the flow rate of the exhaust gas is always lower than the catalytic reaction activation limit K. Therefore, the reducing component in the exhaust gas is always oxidized. In the embodiment according to the present invention, when the warm-up is completed, the catalytic reaction activation limit K is normally at the position shown in FIGS. 14 (3) and 14 (4).
[0069]
On the other hand, if a catalyst having exactly the same size and structure as the catalyst 22 is used as the catalyst 62 and this catalyst 62 is disposed in each branch pipe 19a of the exhaust manifold 19 in the same manner as the example shown in FIG. FIG. 14 (1) and FIG. 14 (2) show the catalyst reaction activation limit K for each catalyst 62. That is, in this case, the catalyst 62 has a much higher temperature than the catalyst 22, so that the catalytic reaction activation limit K is greater in the case shown in FIG. 14 (1) than in the case shown in FIG. 14 (3). 14 and higher in the case shown in FIG. 14 (2) than in the case shown in FIG. 14 (4).
[0070]
In the embodiment according to the present invention, the catalyst reaction activation limit K is set as shown in FIGS. 14 (1) and (2) by making the volume of the catalyst 62 considerably smaller than the volume of the catalyst 22 as shown in FIG. Only ΔK and ΔK ′ are lowered. That is, when the volume of the catalyst 62 is reduced, the contact time of the exhaust gas with the catalyst 62 is shortened. When the contact time of the exhaust gas with respect to 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. Therefore, when the volume of the catalyst 62 is made small, the results shown in FIGS. As shown, the catalytic reaction activation limit K decreases.
[0071]
The solid lines shown in FIGS. 15 (1) and 15 (2) show enlarged views of FIGS. 14 (1) and 14 (2) when the volume of the catalyst 62 is considerably smaller than the volume of the catalyst 22, respectively. In this case, as described above, the catalytic reaction activation limit K decreases. 15 (1) and (2) also show a line where the purification rate of the reducing component in the exhaust gas is 50%.
[0072]
In FIGS. 15 (1) and 15 (2), when the flow rate of the exhaust gas exceeds the catalytic reaction activation limit K, the reducing component in the exhaust gas is not oxidized. Go through. On the other hand, when the exhaust gas flow rate becomes lower than the catalytic reaction activation limit K, the reducing component in the exhaust gas is oxidized. However, in this case, the oxidizing action of the reducing component in the exhaust gas is promoted as the flow rate of the exhaust gas is lowered. Therefore, the purification rate of the reducing component in the exhaust gas is increased as the flow rate of the exhaust gas is lowered.
[0073]
Thus, 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 reducing components in the exhaust gas pass through the catalyst 62. Therefore, a considerable amount of the reducing component in the exhaust gas is sent into the catalyst 22. As can be seen by comparing FIGS. 15 (1) and 15 (2), the catalyst 62 in the engine high load operation shown in FIG. 15 (2) is compared to the engine 62 in the engine low load operation shown in FIG. 15 (1). The amount of the reducing component that passes through increases.
[0074]
On the other hand, in the embodiment according to the present invention, when the purification rate of the reducing component in the exhaust gas by the catalyst 62 should be increased, the exhaust control valve 24 is almost fully closed and the on-off valve 60 is fully opened. Specifically, in the embodiment according to the present invention, approximately 95% of the flow passage area of the exhaust pipe 23 is closed by the exhaust control valve 24 at this time. At this time, the pressure in the exhaust manifold 19 and the exhaust pipe 21, that is, the back pressure. Is approximately 80 KPa. That is, at this time, the back pressure is almost twice the atmospheric pressure.
[0075]
As described above, when the back pressure becomes almost twice the atmospheric pressure, the flow rate of the exhaust gas from the combustion chamber 5 into the exhaust port 11 decreases. Further, when the back pressure becomes almost twice the atmospheric pressure, the density of the exhaust gas increases, and therefore the flow rate of the exhaust gas flowing in the exhaust passage also decreases. Furthermore, since the on-off valve 60 is fully opened at this time, the exhaust pulsation is weakened, and the flow rate of the exhaust gas flowing through the exhaust port 11 and the exhaust manifold branch pipe 19a is reduced. Accordingly, at this time, the flow rate of the exhaust gas passing through 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 component in the exhaust gas is oxidized in the catalyst 62, and a small amount of the reducing component passes through the catalyst 62 and flows into the catalyst 22.
[0076]
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 is increased as shown by the solid line in FIG. 15A, and a considerable amount of reduction contained in the exhaust gas is obtained. When the components pass through the catalyst 62 and are fed into the catalyst 22, the exhaust control valve 24 is almost fully closed, and the on-off valve 60 is fully opened, it is contained in the exhaust gas as shown by the broken line in FIG. Most of the reducing component is oxidized in the catalyst 62.
[0077]
Incidentally, a low load operation is usually performed for a while after the engine is started, and at this time, the temperature of the catalyst 22 is low. Therefore, at this time, the oxidation action of the reducing component in the exhaust gas by the catalyst 22, that is, the purification action of unburned HC and CO can hardly be expected. Therefore, in the embodiment according to the present invention, when the low load operation is performed between the start of the engine operation and the activation of the catalyst 22, the exhaust control valve 24 is almost fully closed and the on-off valve 60 is fully opened. It is done. 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 in the catalyst 62. I'm damned.
[0078]
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. 15 (1) and (2), a considerable amount of unburned HC and CO contained in the exhaust gas passes through the catalyst 62 and flows into the catalyst 22. As a result, since a large amount of unburned HC and CO is oxidized in the catalyst 22, a large amount of heat of oxidation reaction is generated in the catalyst 22, and thus the catalyst 22 is maintained in the catalytic reaction activated state. A region M surrounded by a chain line in FIG. 13 indicates a range that the catalyst 22 can normally take in the embodiment according to the present invention, that is, a use region of the catalyst 22.
[0079]
【The invention's effect】
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 diagram showing injection timing.
FIG. 5 is a diagram showing the concentration of unburned HC.
FIG. 6 is a diagram showing an injection amount of main fuel.
FIG. 7 is a diagram showing a relationship between an injection amount of main fuel and an injection amount of sub fuel.
FIG. 8 is a diagram showing an injection amount of 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 the 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 graph showing changes in the flow rate of exhaust gas.
FIG. 15 is a graph showing changes in the flow rate of exhaust gas.
[Explanation of symbols]
19 ... Exhaust manifold
20 ... Communication pipe
22 ... Catalyst
24. Exhaust control valve

Claims (4)

Each branch pipe of the exhaust manifold is connected to the outlet of the corresponding engine exhaust port, and an exhaust control valve is placed in the exhaust passage connected to the outlet of the exhaust manifold, reducing the amount of unburned HC emissions into the atmosphere When it is determined that it should be, the exhaust control valve is almost fully closed, and the main fuel injected into the combustion chamber is burned under excess air to generate engine output, and the auxiliary fuel is added. In order to reduce exhaust pulsation generated in the engine exhaust port and the exhaust manifold at a predetermined time during an expansion stroke or an exhaust stroke in which the auxiliary fuel can be combusted, each adjacent to the exhaust manifold The branch pipes are communicated with each other through a communication pipe, and an open / close valve is provided in each communication pipe that opens when the exhaust control valve is almost fully closed and closes when the exhaust control valve is fully open. Exhaust purification system of an internal combustion engine. When the exhaust control valve is almost fully closed, the exhaust control valve is operated under the same engine operating condition so that it approaches the torque generated by the engine when the exhaust control valve is fully opened under the same engine operating condition. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the injection amount of the main fuel is increased as compared with a case where the fuel is fully opened . The exhaust emission control device for an internal combustion engine according to claim 1, wherein a catalyst is disposed in each branch pipe of the exhaust manifold . The exhaust gas purification 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 .

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