JP3882401B2 - 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 a diesel engine but also in a spark ignition type internal combustion engine, how to reduce the amount of unburned HC generated during engine low load operation, particularly during engine warm-up operation, is a big 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 the exhaust control valve is placed in the engine exhaust passage that is considerably spaced from the outlet of the engine exhaust port. When the exhaust control valve is substantially fully closed, the amount of unburned HC generated in the combustion chamber is reduced by the synergistic effect of the combustion of these auxiliary fuels and the exhaust throttling action of the exhaust control valve. It has been found that the amount of reduced fuel 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 the above-mentioned 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]
As described above, in order to greatly reduce the amount of unburned HC discharged into the atmosphere, it is necessary to keep the temperature of the exhaust gas discharged from the combustion chamber into the exhaust passage as high as possible. In this case, the exhaust gas temperature becomes higher as the injection amount of the auxiliary fuel is increased. Therefore, the injection amount of the auxiliary fuel may be increased in order to raise the exhaust gas temperature. However, if the injection amount of the auxiliary fuel is increased, the fuel consumption amount is increased. Accordingly, considering the fuel consumption, the exhaust gas temperature cannot be extremely increased, and therefore there is an optimum value for the exhaust gas temperature.
[0016]
An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can greatly reduce the amount of unburned HC discharged into the atmosphere while taking into account the fuel consumption.
[0017]
[Means for Solving the Problems]
  In order to achieve the above object, according to the present invention, an exhaust control valve is arranged in the exhaust passage connected to the outlet of the engine exhaust port at a predetermined distance from the outlet of the exhaust port, and unburned to the atmosphere. When it is determined that the amount of HC emissions should be reduced, 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. In addition, the auxiliary fuel is additionally injected into the combustion chamber at a predetermined time during the expansion stroke or the exhaust stroke in which the auxiliary fuel can burn, and the exhaust gas temperature in the exhaust passage upstream of the exhaust control valve is predetermined. When the amount of secondary fuel injection is controlled so that the target temperature is reached, and the exhaust control valve is almost fully closed, the torque generated by the engine when the exhaust control valve is fully opened under the same engine operating condition. The same institution to get closer So as to increase the injection quantity of the main fuel in comparison with the case where the original exhaust control valve of the rolling state was fully openedIn addition, there is a judgment means for judging whether or not sufficient oxygen for burning the auxiliary fuel remains in the combustion chamber, and presence of sufficient oxygen for burning the auxiliary fuel based on the judgment result by the judgment means. The injection amount of the auxiliary fuel is controlled so that the auxiliary fuel can be burned down, and the intake air amount is increased when it is determined that there is not enough oxygen remaining in the combustion chamber to burn the auxiliary fuel. I try to let them.
[0024]
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.
[0025]
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.
[0026]
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, in the embodiment shown in FIG. 1, the ignition order is 1-3-3-4-2, and as shown in FIG. The exhaust ports 11 of the remaining cylinders # 2 and # 3, which are connected to a common first exhaust manifold 19 and have an alternate ignition order, are connected to a common second exhaust manifold 20. The first exhaust manifold 19 and the second exhaust manifold 20 are connected to a common exhaust pipe 21, and the exhaust pipe 21 is further connected to another exhaust pipe 22. An exhaust control valve 24 driven by an actuator 23 comprising a negative pressure diaphragm device or an electric motor is disposed in the exhaust pipe 22.
[0027]
As shown in FIG. 1, the exhaust pipe 21 and the surge tank 13 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 25, and an electric control type EGR control valve 26 is disposed in the EGR passage 25. Is done. The fuel injection valve 6 is connected to a common fuel reservoir, so-called common rail 27. The fuel in the fuel tank 28 is supplied into the common rail 27 via an electrically controlled fuel pump 29 with variable discharge amount, and the fuel supplied in the common rail 27 is supplied to each fuel injection valve 6. A fuel pressure sensor 30 for detecting the fuel pressure in the common rail 27 is attached to the common rail 27, and a fuel pump 29 is used so that the fuel pressure in the common rail 27 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 30. The discharge amount is controlled.
[0028]
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 31 for detecting the engine cooling water temperature is attached to the engine body 1, and an output signal of the water temperature sensor 31 is input to the input port 45 via the corresponding AD converter 47.
[0029]
A temperature sensor 32 for detecting the exhaust gas temperature at the outlet of the exhaust port 11 is disposed at the branch pipe inlet of the first exhaust manifold 19, and an output signal of the temperature sensor 32 is passed through a corresponding AD converter 47. To the input port 45. Further, a sensor 33 for determining whether or not sufficient oxygen for burning the auxiliary fuel remains in the combustion chamber 5 is disposed at the collecting portion of the exhaust pipe 21. In the embodiment shown in FIG. 1, the sensor 33 comprises an air-fuel ratio sensor that generates a current I corresponding to the air-fuel ratio A / F as shown in FIG. The current I generated by the air-fuel ratio sensor 33 is converted into a voltage and input to the input port 45 via the corresponding AD converter 47. Further, the output signal of the fuel pressure sensor 30 is input to the input port 45 via the corresponding AD converter 47.
[0030]
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 23, EGR control valve 26, and fuel pump 29 via corresponding drive circuits 48. The
[0031]
FIG. 4 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. 4, 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. 4, 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 the period, 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 air-fuel ratio A / F becomes higher when the required load L becomes higher. The fuel ratio A / F is made rich. Note that only the required load L is the operation region in which the fuel injection Q2 is performed only at the end of the compression stroke, the operation region in which the fuel injections Q1 and Q2 are performed twice, and the operation 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.
[0032]
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. 4), 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.
[0033]
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.
[0034]
On the other hand, the required load L is L₂If it is larger, 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. 4, and this homogeneous mixture is ignited by the spark plug 7.
Next, an unburned HC reduction method according to the present invention will be described schematically with reference to FIG. In FIG. 5, the horizontal axis indicates the crank angle, and BTDC and ATDC indicate before the top dead center and after the top dead center, respectively.
[0035]
FIG. 5A shows a case where it is not particularly necessary to reduce unburned HC by the method according to the present invention, and the required load L is L.₁The fuel injection timing when it is smaller than is shown. As shown in FIG. 5A, 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. 5B, 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. FIG. 5A and FIG. 5B 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, FIG. The injection amount of the main fuel Qm in the case shown in FIG. 5 (B) is increased compared to the injection amount of the main fuel Qm in the case shown in FIG. 5 (A).
[0036]
FIG. 6 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. 6, the black triangle indicates unburned 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. 5A 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 an extremely high value of 6000 ppm or more.
[0037]
On the other hand, in the example shown in FIG. 6, 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. 5B. 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.
[0038]
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. 6, 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, by promoting the oxidation reaction of unburned HC in the exhaust passage, the amount of unburned HC discharged into the atmosphere 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.
[0039]
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.
[0040]
According to the present invention, when the amount of unburned HC discharged into the atmosphere is to be reduced, the exhaust control valve 24 is almost fully closed. Thus, when the exhaust control valve 24 is almost fully closed, the pressure in the exhaust port 11, the exhaust manifolds 19 and 20, the exhaust pipe 21, and the exhaust pipe 22 upstream of the exhaust control valve 24, that is, the back pressure is increased. It gets quite expensive.
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.
[0041]
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.
[0042]
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. If the exhaust control valve 24 is arranged at a distance necessary to sufficiently reduce unburned HC from the outlet of the exhaust port 11, the concentration of unburned HC is greatly reduced as shown by the solid line in FIG. 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.
[0043]
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.
[0044]
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.
[0045]
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 in the combustion chamber 5 becomes considerably high. In this way, 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.
[0046]
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 approximately 50 ° to approximately 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 engine output.
[0047]
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. 5B, the injection timing of the auxiliary fuel Qa is approximately 60 ° after compression top dead center (ATDC).
[0048]
The optimal injection timing of the auxiliary fuel Qa varies 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 does not easily 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.
[0049]
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 present invention, when the exhaust control valve 24 is almost fully closed as shown in FIG. 5B, the exhaust control valve 24 is operated under the same engine operating state as shown in FIG. 5A. 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 it 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.
[0050]
FIG. 7 shows a change in the main fuel Qm required to obtain the required generation torque of the engine with respect to the required load L. In FIG. 7, the solid line indicates the case where the exhaust control valve 24 is almost fully closed, and the broken line indicates the case where the exhaust control valve 24 is fully opened.
On the other hand, FIG. 8 shows the relationship between the main fuel Qm and the sub 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. Therefore, 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.
[0051]
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.
[0052]
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. Even when the burnt gas temperature in the combustion chamber 5 is raised mainly by the combustion heat of the auxiliary fuel Qa in this way, if the main fuel Qm increases, the combustion gas temperature rises, so the main fuel Qm increases. The secondary fuel Qa can be reduced as much as possible.
[0053]
Therefore, in the embodiment according to the present invention, the injection amount Qa of the auxiliary fuel is calculated based on the following equation.
Qa = K ・ Qm
Here, K represents a correction coefficient. As shown in FIG. 9, the correction coefficient K is smaller than 1.0, and the correction coefficient K decreases as the main fuel injection amount Qm increases. That is, as the main fuel injection amount Qm increases, the ratio of the sub fuel injection amount Qa to the main fuel injection amount Qm gradually decreases.
[0054]
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, the pressure in the exhaust passage upstream of the exhaust control valve 24 is used to reduce the concentration of unburned HC to about 150 ppm as shown in FIG. The gauge pressure must be approximately 80 KPa or higher. At this time, the closing ratio of the exhaust passage sectional area by the exhaust control valve 24 is approximately 95% or more.
[0055]
Therefore, in the embodiment shown in FIG. 1, when the discharge amount of unburned gas to the atmosphere should be greatly reduced, the exhaust control is performed so that the closing ratio of the exhaust passage cross-sectional area by the exhaust control valve 24 becomes approximately 95% or more. The valve 24 is almost fully closed. If it is sufficient to reduce the unburned HC from about 600 p.pm to about 800 p.pm in the exhaust passage from the exhaust port 11 to the exhaust control valve 24, the pressure in the exhaust passage upstream of the exhaust control valve 24 is gauged. A pressure of about 30 KPa is sufficient. At this time, the closing ratio of the exhaust passage sectional area by the exhaust control valve 24 is approximately 90%.
[0056]
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 started and warmed up, and the engine is under a low load. Therefore, a large amount of unburned HC is generated when the engine is started and warmed up and when the engine is under a low load. It will be. Thus, when the temperature in the combustion chamber 5 is low, even if a catalyst having an oxidizing function is arranged in the exhaust passage, the catalyst temperature is low and the catalyst is not activated, so a large amount of unburned HC generated at this time is generated. It is difficult to oxidize with a catalyst.
[0057]
Therefore, in the embodiment according to the present invention, the exhaust control valve 24 is almost fully closed at the time of engine start-up and warm-up operation, and at the time of engine low load, the main fuel Qm is increased and the sub fuel Qa is additionally injected, thereby The amount of unburned HC that is discharged is greatly reduced.
FIG. 10 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. 10, the solid line X indicates the optimal injection amount of the main fuel Qm when the exhaust control valve 24 is substantially fully closed, and the broken line Y indicates the optimal main fuel when the exhaust control valve 24 is fully open. The injection quantity of Qm is shown. As can be seen from FIG. 10, 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.
[0058]
FIG. 11 shows an example of changes in the main fuel Qm and the opening degree of the exhaust control valve 24 when the engine is under a low load. In FIG. 11, 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. 11, the optimum injection amount Y of the main fuel Qm when the exhaust control valve 24 is almost fully closed at the time of low engine load and the exhaust control valve 24 is fully opened under the same engine operating state. As a result, the injection amount X of the main fuel Qm is increased, and the auxiliary fuel Qa is additionally injected.
[0059]
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. In this case, in order to increase the exhaust gas temperature at the outlet of the exhaust port 11, the injection amount of the auxiliary fuel Qa may be increased. However, if the injection amount of the auxiliary fuel Qa is increased, the fuel consumption increases. Therefore, considering the fuel consumption, there is an optimum temperature for the exhaust gas temperature at the outlet of the exhaust port 11.
[0060]
Therefore, in the present invention, the injection amount of the auxiliary fuel Qa is controlled so that the exhaust gas temperature in the exhaust passage upstream of the exhaust control valve 24 becomes a predetermined target temperature. More specifically, in the embodiment according to the present invention, the exhaust gas temperature at the outlet of the exhaust port 11 is detected by the temperature sensor 32, and when the exhaust gas temperature becomes lower than a predetermined target temperature, for example, 800 ° C., the auxiliary fuel is detected. The injection amount of Qa is increased, and when the exhaust gas temperature becomes higher than a predetermined target temperature, the injection amount of the auxiliary fuel Qa is decreased.
[0061]
In addition, if the amount of oxygen in the combustion chamber 5 is insufficient when the injection amount of the auxiliary fuel Q2 is increased, a large amount of unburned HC is generated. Therefore, in the first embodiment according to the present invention, when the air-fuel ratio detected by the air-fuel ratio sensor 32 becomes smaller than the limit air-fuel ratio that is slightly lean with respect to the stoichiometric air-fuel ratio, for example, 15.0, the increase in the auxiliary fuel Qa is increased. The action is stopped.
[0062]
That is, as shown in FIG. 12, in the first embodiment, the air-fuel ratio A / F is the limit air-fuel ratio (A / F). If the exhaust gas temperature TE at the outlet of the exhaust port 11 is lower than the target temperature TEO, the injection amount Qa of the auxiliary fuel is gradually increased, and the exhaust gas temperature TE at the outlet of the exhaust port 11 is higher than the target temperature TEO. If it becomes higher, the injection amount Qa of the auxiliary fuel is gradually decreased. Thus, the exhaust gas temperature TE at the outlet of the exhaust port 11 is controlled to the target temperature TEO.
[0063]
On the other hand, the air-fuel ratio A / F becomes smaller and the limit air-fuel ratio (A / F)_oWhen the value reaches the value, the injection amount Qa of the auxiliary fuel is decreased by a certain amount, and as a result, the air-fuel ratio A / F is increased. Therefore, the air-fuel ratio A / F is the critical air-fuel ratio (A / F)_oSince it will not become smaller, there will be sufficient oxygen remaining in the combustion chamber 5 to burn the secondary fuel during combustion of the secondary fuel, thus preventing the generation of a large amount of unburned HC. can do. When the air-fuel ratio A / F is increased, the injection quantity Qa of the auxiliary fuel is increased again. Therefore, as shown in FIG. 12, while TE <TEO, the air-fuel ratio A / F becomes the limit air-fuel ratio (A / F)_oMaintained in the vicinity.
[0064]
FIG. 13 shows an operation control routine for executing the first embodiment.
Referring to FIG. 13, first, at step 100, it is judged if the engine is starting or warming up. When it is not during engine start-up and warm-up operation, the routine jumps to step 102 to determine whether or not the engine is under low load. When the engine load is not low, the routine proceeds to step 103 where the exhaust control valve 24 is fully opened, and then the routine proceeds to step 104 where injection control of the main fuel Qm is performed. At this time, the auxiliary fuel Qa is not injected.
[0065]
On the other hand, when it is determined at step 100 that the engine is being started and the engine is warming up, the routine proceeds to step 101 where it is determined whether or not a predetermined set period has elapsed after the engine is started. When the set period has not elapsed, the routine proceeds to step 105, and when the set period has elapsed, the routine proceeds to step 102. On the other hand, when it is determined in step 102 that the engine is under a low load, the routine also proceeds to step 105.
[0066]
In step 105, the exhaust control valve 24 is almost fully closed. Next, at step 106, the injection amount of the main fuel Qm is calculated. That is, the injection amount of the main fuel Qm is X shown in FIG. 10 when the engine is starting and warming up, and the injection amount of the main fuel Qm is X shown in FIG. The Next, at step 107, it is judged if the engine is in an operating state in which the average air-fuel ratio in the combustion chamber 5 is made rich as at the time of engine start. When the operation state is such that the average air-fuel ratio in the combustion chamber 5 is rich, the routine jumps to step 109, where the injection control of the main fuel Qm is performed. At this time, the auxiliary fuel Qa is not injected.
[0067]
In contrast, when the average air-fuel ratio in the combustion chamber 5 is not in an operating state in which the air-fuel ratio is rich, the routine proceeds to step 108 where the injection amount of the auxiliary fuel Qa is calculated. FIG. 14 shows a routine for calculating the injection amount of the auxiliary fuel Qa. Next, at step 109, injection control of the main fuel Qm and sub fuel Qa is performed.
Referring to FIG. 14, first, at step 110, the correction coefficient K is calculated from the relationship shown in FIG. Next, at step 111, the injection amount Qa (= K · Qm) of the auxiliary fuel is calculated by multiplying the injection amount Qm of the main fuel by the correction coefficient K. Next, at step 112, the air-fuel ratio A / F detected by the air-fuel ratio sensor 33 is the critical air-fuel ratio (A / F)._oOr less is determined. A / F ≧ (A / F)_oWhen the air-fuel ratio is lean, the routine proceeds to step 113.
[0068]
In step 113, it is determined whether or not the exhaust gas temperature TE at the outlet of the exhaust port 11 detected by the temperature sensor 32 is higher than the target temperature TEO. When TE> TEO, the routine proceeds to step 114, where the constant value α is subtracted from the correction value ΔQ for the auxiliary fuel Qa. Next, the routine proceeds to step 116. On the other hand, when TE ≦ TEO, the routine proceeds to step 115, where the constant value α is added to the correction value ΔQ, and then the routine proceeds to step 116. In step 116, the final auxiliary fuel injection amount Qa is calculated by adding the correction value ΔQ to the auxiliary fuel injection amount Qa calculated in step 111.
[0069]
In this way, when TE> TEO, the auxiliary fuel injection amount Qa is decreased, and when TE ≦ TEO, the auxiliary fuel injection amount Qa is increased, whereby the exhaust gas temperature TE is controlled to the target temperature TEO.
On the other hand, in step 112, A / F <(A / F)_oWhen it is determined that the constant value β is determined, the routine proceeds to step 117, where the constant value β (> α) is subtracted from the correction value ΔQ, and then the routine proceeds to step 116. Therefore, at this time, the injection amount Qa of the auxiliary fuel is decreased by a constant value β.
[0070]
FIG. 15 shows a case where an HC concentration sensor 33 that can detect the concentration of unburned HC in the exhaust gas is used instead of the air-fuel ratio sensor 33. If sufficient oxygen does not remain in the combustion chamber 5 when the auxiliary fuel Qa is injected, the amount of unburned HC in the exhaust gas greatly increases. Therefore, the amount of unburned HC in the exhaust gas. Therefore, it can be determined whether or not sufficient oxygen remains in the combustion chamber 5 to combust the auxiliary fuel Qa. Accordingly, in the second embodiment shown in FIG. 15, when the unburned HC concentration D in the exhaust gas reaches a predetermined limit concentration DO, the injection amount Qa of the auxiliary fuel is decreased by a certain amount. .
[0071]
Also in the second embodiment, the operation control routine shown in FIG. 13 is used. However, the sub fuel injection amount calculation routine shown in FIG. 16 is used only for step 108 in FIG. 13, and therefore only the routine shown in FIG. 16 will be described below.
Referring to FIG. 16, first, at step 150, the correction coefficient K is calculated from the relationship shown in FIG. Next, at step 151, the injection amount Qa (= K · Qm) of the auxiliary fuel is calculated by multiplying the injection amount Qm of the main fuel by the correction coefficient K. Next, at step 152, it is judged if the HC concentration D in the exhaust gas detected by the HC concentration sensor 33 is higher than the limit concentration DO. When D ≦ DO, the process proceeds to step 153.
[0072]
In step 153, it is determined whether or not the exhaust gas temperature TE at the outlet of the exhaust port 11 detected by the temperature sensor 32 is higher than the target temperature TEO. When TE> TEO, the routine proceeds to step 154, where the constant value α is subtracted from the correction value ΔQ for the auxiliary fuel Qa. Next, the routine proceeds to step 156. On the other hand, when TE ≦ TEO, the routine proceeds to step 155, where the constant value α is added to the correction value ΔQ, and then the routine proceeds to step 156. In step 156, the final sub fuel injection amount Qa is calculated by adding the correction value ΔQ to the sub fuel injection amount Qa calculated in step 151.
[0073]
In this way, when TE> TEO, the auxiliary fuel injection amount Qa is decreased, and when TE ≦ TEO, the auxiliary fuel injection amount Qa is increased, whereby the exhaust gas temperature TE is controlled to the target temperature TEO.
On the other hand, when it is determined at step 152 that D> DO, the routine proceeds to step 157 where the constant value β (> α) is subtracted from the correction value ΔQ, and then the routine proceeds to step 156. Therefore, at this time, the injection amount Qa of the auxiliary fuel is decreased by a constant value β.
[0074]
FIG. 17 shows a third embodiment. Also in the third embodiment, the air-fuel ratio A / F detected by the air-fuel ratio sensor 33 is the limit air-fuel ratio (A / F)._oIf the exhaust gas temperature TE at the outlet of the exhaust port 11 is higher than the target temperature TEO, the injection amount Qa of the auxiliary fuel is decreased, and the exhaust gas TE at the outlet of the exhaust port 11 can be lower than the target temperature TEO. In this case, the injection amount Qa of the auxiliary fuel is increased. As a result, the exhaust gas temperature TE at the outlet of the exhaust port 11 is controlled to the target temperature TEO.
[0075]
On the other hand, in this third embodiment, the air-fuel ratio A / F is the limit air-fuel ratio (A / F)._oWhen the angle becomes smaller, the opening degree TA of the throttle valve 18 is increased. When the opening degree TA of the throttle valve 18 is increased, the air-fuel ratio A / F is increased, and as a result, the injection amount Qa of the auxiliary fuel is increased. When the injection amount Qa of the auxiliary fuel is increased, the air-fuel ratio A / F becomes the limit air-fuel ratio (A / F)._oAs a result, the opening degree TA of the throttle valve 18 is increased. Therefore, actually, as shown in FIG. 17, the air-fuel ratio A / F is the limit air-fuel ratio (A / F)._o, The opening degree TA of the throttle valve 18 is increased and the injection amount Qa of the auxiliary fuel is increased. During this time, the air-fuel ratio A / F is the critical air-fuel ratio (A / F)._oMaintained in the vicinity.
[0076]
As described above, in the third embodiment, as long as the exhaust gas temperature TE at the outlet of the exhaust port 11 is lower than the target temperature TEO, the auxiliary fuel injection amount Qa continues to increase. Therefore, the third embodiment has an advantage that the exhaust gas temperature TE can be rapidly raised to the target temperature TEO.
In this third embodiment, the air-fuel ratio A / F is a predetermined lean air-fuel ratio (A / F) shown in FIG._rWhen it becomes larger, the opening degree TA of the throttle valve 18 is gradually decreased.
[0077]
FIG. 18 shows an operation control routine for executing the third embodiment.
Referring to FIG. 18, first, at step 200, it is judged if the engine is starting or warming up. When it is not during engine start-up and warm-up operation, the routine jumps to step 202, where it is judged if the engine is under low load. When the engine load is not low, the routine proceeds to step 203 where the exhaust control valve 24 is fully opened, then the routine proceeds to step 204 where injection control of the main fuel Qm is performed. At this time, the auxiliary fuel Qa is not injected. Next, at step 205, the throttle valve 18 is controlled to the target opening.
[0078]
On the other hand, when it is determined at step 200 that the engine is being started and the engine is warming up, the routine proceeds to step 201 where it is determined whether or not a predetermined set period has elapsed after the engine is started. When the set period has not elapsed, the routine proceeds to step 206, and when the set period has elapsed, the routine proceeds to step 202. On the other hand, when it is determined in step 202 that the engine is under low load, the routine also proceeds to step 206.
[0079]
In step 206, the exhaust control valve 24 is almost fully closed. Next, at step 207, the injection amount of the main fuel Qm is calculated. That is, the injection amount of the main fuel Qm is X shown in FIG. 10 when the engine is starting and warming up, and the injection amount of the main fuel Qm is X shown in FIG. The Next, at step 208, the target opening degree STO of the throttle valve 18 is calculated. Next, at step 209, it is determined whether or not the engine is in an operating state in which the average air-fuel ratio in the combustion chamber 5 is made rich as when the engine is started. When the operation state is such that the average air-fuel ratio in the combustion chamber 5 is rich, the routine jumps to step 211, where the injection control of the main fuel Qm is performed. At this time, the auxiliary fuel Qa is not injected.
[0080]
In contrast, when the average air-fuel ratio in the combustion chamber 5 is not in an operation state in which the average air-fuel ratio is rich, the routine proceeds to step 210, where the injection amount of the auxiliary fuel Qa is calculated. FIG. 19 shows a routine for calculating the injection amount of the auxiliary fuel Qa. Next, at step 211, injection control of the main fuel Qm and the auxiliary fuel Qa is performed. Next, at step 212, the opening degree TA of the throttle valve 18 is controlled to the target opening degree STO.
[0081]
Referring to FIG. 19, first, at step 213, the correction coefficient K is calculated from the relationship shown in FIG. Next, at step 214, the injection amount Qa (= K · Qm) of the auxiliary fuel is calculated by multiplying the injection amount Qm of the main fuel by the correction coefficient K.
Next, at step 215, the air-fuel ratio A / F detected by the air-fuel ratio sensor 33 is the critical air-fuel ratio (A / F)._oOr less is determined. A / F ≧ (A / F)_oWhen the air fuel ratio is lean, the routine proceeds to step 216. In step 216, the air-fuel ratio A / F detected by the air-fuel ratio sensor 33 is a predetermined lean air-fuel ratio (A / F)._rIt is determined whether or not it is larger than (FIG. 17). A / F ≦ (A / F)_rJumps to step 218.
[0082]
In step 218, it is determined whether or not the exhaust gas temperature TE at the outlet of the exhaust port 11 detected by the temperature sensor 32 is higher than the target temperature TEO. When TE> TEO, the routine proceeds to step 219, where the constant value α is subtracted from the correction value ΔQ for the auxiliary fuel Qa. Next, the routine proceeds to step 221. On the other hand, when TE ≦ TEO, the routine proceeds to step 220 where the constant value α is added to the correction value ΔQ, and then the routine proceeds to step 221.
[0083]
  On the other hand, in step 215, A / F <(A / F)_o When it is determined that, the routine proceeds to step 223, where the fixed value δ is added to the correction value ΔS for the opening degree TA of the throttle valve 18. Next, the routine proceeds to step 221. In step 216, A / F> (A / F)_r When it is determined that, the routine proceeds to step 217, where the constant value δ is subtracted from the correction value ΔS. However, ΔS is zero or a positive value. Then step 218Proceed to
[0084]
In step 221, the final sub fuel injection amount Qa is calculated by adding the correction value ΔQ to the sub fuel injection amount Qa calculated in step 214.
Next, at step 222, the final target opening STO of the throttle valve 18 is calculated by adding the correction value ΔS to the target opening STO of the throttle valve 18 calculated at step 208 (FIG. 18).
[0085]
As can be seen from the routine shown in FIG. 19, A / F ≧ (A / F)_oIn this case, when TE> TEO, the auxiliary fuel injection amount Qa is decreased, and when TE ≦ TEO, the auxiliary fuel injection amount Qa is increased. Thus, the exhaust gas temperature TE is controlled to the target temperature TEO.
On the other hand, A / F <(A / F)_oThen, the opening degree TA of the throttle valve 18 is increased by a constant value δ, and at this time, the injection amount Qa of the auxiliary fuel cannot be changed. However, if the opening degree TA of the throttle valve 18 increases, A / F ≧ (A / F)_oTherefore, at this time, if TE ≦ TEO, the injection amount Qa of the auxiliary fuel is increased. When the injection amount Qa of the auxiliary fuel is increased, A / F <(A / F)_oThus, the opening degree TA of the throttle valve 18 is increased by a constant value δ. That is, when TE ≦ TEO, the opening degree TA of the throttle valve 18 is gradually increased and the injection amount Qa of the auxiliary fuel is gradually increased.
[0086]
  FIG. 20 shows a case where an HC concentration sensor 33 capable of detecting the concentration of unburned HC in the exhaust gas is used instead of the air-fuel ratio sensor 33 in the third embodiment. Figure20In the fourth embodiment shown in FIG. 4, when the unburned HC concentration D in the exhaust gas rises to a predetermined limit concentration DO, the opening degree TA of the throttle valve 18 is increased and the injection amount Qa of the auxiliary fuel is increased. It is done.
[0087]
Also in the fourth embodiment, the operation control routine shown in FIG. 18 is used. However, the sub-fuel injection amount calculation routine shown in FIG. 21 is used only for step 210 in FIG. 18, and therefore only the routine shown in FIG. 21 will be described below.
Referring to FIG. 21, first, at step 250, the correction coefficient K is calculated from the relationship shown in FIG. Next, at step 251, the injection amount Qa (= K · Qm) of the auxiliary fuel is calculated by multiplying the injection amount Qm of the main fuel by the correction coefficient K. Next, at step 252, it is judged if the HC concentration D in the exhaust gas detected by the HC concentration sensor 33 is higher than the limit concentration DO. When D ≦ DO, the process proceeds to step 253. In step 253, the HC concentration D detected by the HC concentration sensor 33 is set to a predetermined HC concentration DO.₁It is determined whether or not it is lower than (FIG. 20). D ≧ DO₁Jumps to step 255.
[0088]
In step 255, it is determined whether or not the exhaust gas temperature TE at the outlet of the exhaust port 11 detected by the temperature sensor 32 is higher than the target temperature TEO. When TE> TEO, the routine proceeds to step 256, where the constant value α is subtracted from the correction value ΔQ for the auxiliary fuel Qa. Next, the routine proceeds to step 258. On the other hand, when TE ≦ TEO, the routine proceeds to step 257 where the constant value α is added to the correction value ΔQ, and then the routine proceeds to step 258.
[0089]
On the other hand, when it is determined in step 252 that D> DO, the routine proceeds to step 260, where a fixed value δ is added to the correction value ΔS for the opening degree TA of the throttle valve 18. Next, the routine proceeds to step 258. In step 253, D <DO₁When it is determined that the value is, the routine proceeds to step 254, where the constant value δ is subtracted from the correction value ΔS. However, ΔS is zero or a positive value. Next, the routine proceeds to step 255.
[0090]
In step 258, the final auxiliary fuel injection amount Qa is calculated by adding the correction value ΔQ to the auxiliary fuel injection amount Qa calculated in step 251. Next, at step 259, the final target opening STO of the throttle valve 18 is calculated by adding the correction value ΔS to the target opening STO of the throttle valve 18 calculated at step 208 (FIG. 18).
[0091]
As can be seen from the routine shown in FIG. 21, when D ≦ DO, the injection amount Qa of the auxiliary fuel is decreased when TE> TEO, and the injection amount Qa of the auxiliary fuel is increased when TE ≦ TEO. Thus, the exhaust gas temperature TE is controlled to the target temperature TEO.
On the other hand, when D> DO, the opening degree TA of the throttle valve 18 is increased by a constant value δ, and at this time, the injection amount Qa of the auxiliary fuel is not changed. However, if the opening degree TA of the throttle valve 18 is increased, D ≦ DO is satisfied. At this time, if TE ≦ TEO, the auxiliary fuel injection amount Qa is increased. When the injection amount Qa of the auxiliary fuel is increased, D> DO, and the opening degree TA of the throttle valve 18 is increased by a constant value δ. That is, when TE ≦ TEO, the opening degree TA of the throttle valve 18 is gradually increased and the injection amount Qa of the auxiliary fuel is gradually increased.
[0092]
FIG. 22 shows another embodiment. In this embodiment, a catalyst 60 is disposed in the exhaust pipe 22 upstream of the exhaust control valve 24. Thus, when the catalyst 60 is arranged in the exhaust pipe 22 upstream of the exhaust control valve 24, the auxiliary fuel Qa is additionally injected, and when the exhaust control valve 24 is almost fully closed, the catalyst 60 is at a high temperature. It is heated strongly by the exhaust gas. Therefore, the catalyst 60 can be activated early during engine start-up and warm-up operation.
[0093]
Examples of the catalyst 60 disposed in the exhaust pipe 22 include an oxidation catalyst, a three-way catalyst, and NO._xAn absorbent or an HC adsorption catalyst can be 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.
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.
[0094]
On the other hand, for HC adsorption catalyst, for example, zeolite, alumina Al₂O_Three, Silica alumina SiO₂・ Al₂O_Three, Activated carbon, titania TiO₂A noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir, or a transition metal such as copper Cu, iron Fe, cobalt Co, and nickel Ni is supported on the porous carrier.
[0095]
In such an HC adsorption catalyst, unburned HC in the exhaust gas is physically adsorbed in the catalyst, and the amount of unburned HC adsorbed increases as the temperature of the catalyst decreases, and increases as the pressure of the exhaust gas flowing through the catalyst increases. To do. Therefore, in the embodiment shown in FIG. 22, the exhaust gas is low when the temperature of the catalyst 60 is low and the back pressure is increased by the exhaust throttle action of the exhaust control valve 24, that is, during engine start-up and warm-up operation, and during low engine load. Unburned HC contained therein is adsorbed by the HC adsorption catalyst. Therefore, the amount of unburned HC released into the atmosphere can be further reduced. The unburned HC adsorbed on the HC adsorption catalyst is released from the HC adsorption catalyst when the back pressure becomes low or when the temperature of the HC adsorption catalyst becomes high.
[0096]
FIG. 23 shows still another embodiment.
In this embodiment, NO in the exhaust pipe 22 upstream of the exhaust control valve 24._xA catalyst 60 made of an absorbent or an HC adsorption catalyst is disposed, and an oxidation function such as an oxidation catalyst or a three-way catalyst is provided between the first exhaust manifold 19 and the exhaust pipe 21 and between the second exhaust manifold 20 and the exhaust pipe 21. Catalysts 61 and 62 having the following are arranged.
[0097]
【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 a change in current generated by an air-fuel ratio sensor.
FIG. 4 is a diagram showing an injection amount, an injection timing, and an air-fuel ratio.
FIG. 5 is a diagram showing injection timing.
FIG. 6 is a diagram showing the concentration of unburned HC.
FIG. 7 is a diagram showing an injection amount of main fuel.
FIG. 8 is a diagram showing a relationship between an injection amount of main fuel and an injection amount of sub fuel.
9 is a diagram showing a correction coefficient K. FIG.
FIG. 10 is a diagram showing an injection amount of main fuel and an opening degree of an exhaust control valve.
FIG. 11 is a diagram showing an injection amount of main fuel and an opening degree of an exhaust control valve.
FIG. 12 is a time chart showing changes in the injection amount of auxiliary fuel and the like in the first embodiment.
FIG. 13 is a flowchart for performing operation control.
FIG. 14 is a flowchart for calculating an injection amount of sub fuel in the first embodiment.
FIG. 15 is a time chart showing changes in the injection amount of auxiliary fuel and the like in the second embodiment.
FIG. 16 is a flowchart for calculating an injection amount of auxiliary fuel in the second embodiment.
FIG. 17 is a time chart showing changes in the injection amount of auxiliary fuel and the like in the third embodiment.
FIG. 18 is a flowchart for performing operation control.
FIG. 19 is a flowchart for calculating an injection amount of auxiliary fuel in the third embodiment.
FIG. 20 is a time chart showing changes in the injection amount of auxiliary fuel and the like in the fourth embodiment.
FIG. 21 is a flowchart for calculating an injection amount of auxiliary fuel in the fourth embodiment.
FIG. 22 is an overall view showing another embodiment of the internal combustion engine.
FIG. 23 is an overall view showing still another embodiment of the internal combustion engine.
[Explanation of symbols]
6 ... Fuel injection valve
22 ... Exhaust pipe
24. Exhaust control valve
32 ... Temperature sensor

Claims (2)

An exhaust control valve should be placed in the exhaust passage connected to the outlet of the engine exhaust port at a predetermined distance from the outlet of the exhaust port to reduce the amount of unburned HC discharged into the atmosphere. When judged, the exhaust control valve is almost fully closed, and in addition to burning the main fuel injected into the combustion chamber under excess air to generate engine output, the auxiliary fuel burns the auxiliary fuel. The amount of auxiliary fuel injected so that additional injection is performed into the combustion chamber at a predetermined time during the expansion stroke or exhaust stroke, and the exhaust gas temperature in the exhaust passage upstream of the exhaust control valve becomes a predetermined target temperature. When the exhaust control valve is almost fully closed, the same engine operating condition is set so that the engine generated torque is approached when the exhaust control valve is fully opened under the same engine operating condition. To fully open the exhaust control valve. So as to increase the injection quantity of the main fuel in comparison with the case where was, though allowed to further burn the auxiliary fuel comprises a determining means for determining whether sufficient oxygen remains in the combustion chamber, said determining means Based on the result of the determination, the injection amount of the secondary fuel is controlled so that the secondary fuel can be burned in the presence of sufficient oxygen to burn the secondary fuel, and there is sufficient oxygen to burn the secondary fuel. An exhaust emission control device for an internal combustion engine, which increases an intake air amount when it is determined that the air does not remain in the combustion chamber . 2. The internal combustion engine according to claim 1 , wherein when it is determined that sufficient oxygen for burning the auxiliary fuel does not remain in the combustion chamber, the intake air amount is increased and the injection amount of the auxiliary fuel is increased . Exhaust purification device.

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