JP2001073812A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remarkably reduce combustible HC exhausted to atmosphere and actuate an exhaust turbocharger during acceleration at once. SOLUTION: An exhaust turbine 23 of an exhaust turbocharger 15 and an exhaust control valve 28 are arranged inside an exhaust passage. The exhaust control valve 28 is substantially fully closed during warming up the engine and under low load operation after it. An injection amount of main fuel is increased compared to an optimum injection amount at the time of full closing of the exhaust control valve. Sub-fuel is additionally injected during an expansion process. The exhaust control valve 28 is then fully opened when acceleration is carried out under substantially full closing of the exhaust control valve 28.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

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

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

[0005]

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

More specifically, during the expansion stroke or the exhaust stroke, an auxiliary fuel is additionally injected into the combustion chamber to burn the auxiliary fuel, and the fuel is injected into the engine exhaust passage at a considerable distance from the outlet of the engine exhaust port. When the exhaust control valve is provided and the exhaust control valve is almost 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 throttle action of the exhaust control valve, and the exhaust passage is reduced. It has been found that the amount of reduction of unburned HC in the inside increases, and thus the amount of unburned HC discharged into the atmosphere can be significantly reduced.

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

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

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

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

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

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

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

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

As described above, in order to greatly reduce the amount of unburned HC discharged into the atmosphere, it is necessary to inject the auxiliary fuel and at the same time substantially close the exhaust control valve. However, when the auxiliary fuel is injected and the exhaust control valve is almost fully closed, the exhaust gas discharged from the exhaust port is maintained at a high temperature and a high pressure as described above. That is, when the auxiliary fuel is injected and the exhaust control valve is almost fully closed, high-temperature and high-pressure exhaust gas is formed in the exhaust passage upstream of the exhaust control valve, so that the high-temperature and high-pressure exhaust gas is used as effectively as possible. It is desired.

An object of the present invention is to provide unburned H discharged into the atmosphere.
An object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine that effectively utilizes the energy of high-temperature and high-pressure exhaust gas formed when the amount of C is to be greatly reduced.

[0017]

According to a first aspect of the present invention, an exhaust turbine of an exhaust turbocharger and an exhaust control valve are disposed in an exhaust passage connected to an outlet of an engine exhaust port. When it is determined that the amount of unburned HC to be discharged into the engine 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 supplied with excess air. In addition to burning in the original, additional fuel is additionally injected into the combustion chamber at a predetermined time during an expansion stroke or an exhaust stroke in which the auxiliary fuel can burn,
When the acceleration operation is performed while the exhaust control valve is almost fully closed, the opening degree of the exhaust control valve is increased.

In the second invention, in the first invention,
An exhaust control valve is arranged in an exhaust passage downstream of the exhaust turbine. According to a third aspect of the present invention, in the first aspect, when the exhaust control valve is almost fully closed, the same torque is obtained so as to approach the generated torque of the engine when the exhaust control valve is fully opened under the same engine operating condition. The main fuel injection amount is increased as compared with the case where the exhaust control valve is fully opened under the engine operation state.

In the fourth invention, in the first invention,
When the engine is being warmed up, it is determined that the emission of unburned HC into the atmosphere should be reduced. In a fifth aspect based on the first aspect, it is determined that the emission of unburned HC into the atmosphere should be reduced when the engine is under low load operation.

[0020]

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

Referring to FIG. 2, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston,
Reference numeral 5 denotes a combustion chamber, 6 denotes a fuel injection valve disposed at a peripheral portion of an inner wall surface of the cylinder head 3, 7 denotes a spark plug disposed at a central portion of the inner wall surface of the cylinder head 3, 8 denotes an intake valve, 9 denotes an intake port, Reference numeral 10 denotes an exhaust valve, and reference numeral 11 denotes an exhaust port. FIG.
Referring to FIG. 2 and FIG. 2, the intake port 9 is connected to the surge tank 13 through the corresponding intake branch pipe 12, and the surge tank 13 is connected to the intake duct 14, the exhaust turbocharger 1 and the like.
5 is connected to an air cleaner 19 via a compressor 16, an intake duct 17 and an air flow meter 18.
A throttle valve 21 driven by a step motor 20 is arranged in the intake duct 17. On the other hand, the exhaust manifold 22 is an exhaust turbine 2 of the exhaust turbocharger 15.
3 and an exhaust pipe 24 connected to a catalytic converter 26 containing a catalyst 25. An exhaust pipe 24 has an actuator 27 comprising a negative pressure diaphragm device or an electric motor.
Is disposed.

As shown in FIG. 1, the exhaust manifold 22
And the surge tank 13 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 29, and the EGR passage 2
An electric control type EGR control valve 30 is arranged in 9. The fuel injectors 6 are connected to a common fuel reservoir, a so-called common rail 31. The fuel in the fuel tank 32 is supplied to the common rail 31 via a fuel pump 33 of an electrically controlled variable discharge amount, and the fuel supplied to the common rail 31 is supplied to each fuel injection valve 6. A fuel pressure sensor 34 for detecting the fuel pressure in the common rail 31 is attached to the common rail 31. Based on an output signal of the fuel pressure sensor 34, a fuel pump 33 is provided so that the fuel pressure in the common rail 31 becomes a target fuel pressure. Is controlled.

The electronic control unit 40 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45, An output port 46 is provided. The air flow meter 18 generates an output voltage proportional to the amount of intake air, and this output voltage is applied to the corresponding AD converter 4.
7 is input to the input port 45. Further, an input port 45 receives an AD signal corresponding to the output signal of the fuel pressure sensor 34.
It is input via the converter 47.

A load sensor 51 for generating 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 supplied to an input port via a corresponding AD converter 47. 45 is input. The input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. On the other hand, the output port 46 is connected to the fuel injection valve 6, the ignition plug 7, the step motor 20 for controlling the throttle valve, the actuator 27 for controlling the exhaust control valve, the EGR control valve 30, and the fuel pump 33 via the corresponding drive circuit 48. You.

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

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

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

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

[0029] FIG. 4 (A) shows the fuel injection timing when the required load L even if no particular need to reduce the unburned HC by the method according to the present invention is smaller than L _1. As shown in FIG. 4A, at this time, only the main fuel Qm is injected at the end of the compression stroke, and at this time, the exhaust control valve 28 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 28 is almost completely closed.
As shown in FIG. 4B, in addition to the injection of the main fuel Qm for generating the engine output, during the expansion stroke, in the example shown in FIG. The auxiliary fuel Qa is additionally injected. In this case, after the main fuel Qm has been burned, the main fuel Qm is burned with excess air so that sufficient oxygen remains in the combustion chamber 5 to completely burn the sub fuel Qa. FIG. 4 (A)
FIG. 4B and FIG. 4B show the fuel injection period when the engine load and the engine speed are the same. Therefore, when the engine load and the engine speed are the same, the fuel injection period is shown in FIG. The injection amount of the main fuel Qm in the case is increased compared to the injection amount of the main fuel Qm in the case shown in FIG.

FIG. 5 shows an example of the concentration (ppm) of unburned HC in the exhaust gas at each position in the engine exhaust passage. In the example shown in FIG. 5, the black triangle indicates unburned fuel in the exhaust gas at the outlet of the exhaust port 11 when the main fuel Qm is injected at the end of the compression stroke as shown in FIG. 4A with the exhaust control valve 28 fully opened. Shows the concentration (ppm) of HC. In this case, the concentration of unburned HC in the exhaust gas at the outlet of the exhaust port 11 is an extremely high value of 6000 ppm or more.

On the other hand, in the example shown in FIG. 5, a black circle and a solid line indicate that the exhaust control valve 28 is almost fully closed, and the main fuel Qm and the sub fuel Qa are injected as shown in FIG. Indicates the concentration (ppm) of the unburned HC in FIG. In this case, the concentration of unburned HC in the exhaust gas at the outlet of the exhaust port 11 becomes 2000 ppm or less, and the exhaust control valve 2
8, the concentration of unburned HC in the exhaust gas is 15
It decreases to about 0 ppm. Therefore, in this case, it can be seen that the amount of unburned HC discharged into the atmosphere is greatly reduced.

The reason why the unburned HC is reduced in the exhaust passage upstream of the exhaust control valve 28 is that the oxidation reaction of the unburned HC is promoted. However, as shown by a black triangle in FIG.
When the amount of C is large, that is, when the amount of unburned HC generated in the combustion chamber 5 is large, even if the oxidation reaction of unburned HC in the exhaust passage is promoted, the unburned HC discharged into the atmosphere is increased. Does not decrease much. That is, the unburned H in the exhaust passage
The fact that the amount of unburned HC discharged into the atmosphere can be significantly reduced by promoting the oxidation reaction of C is because the concentration of unburned HC at the outlet of the exhaust port 11 is low as shown by the black circle in FIG. That is, when the amount of unburned HC generated in the combustion chamber 5 is small.

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

According to the present invention, unburned H discharged into the atmosphere
When the amount of C should be reduced, the exhaust control valve 28 is almost fully closed. When the exhaust control valve 28 is almost fully closed in this way, the pressure in the exhaust port 11 and the exhaust manifold 22, that is, the back pressure, becomes considerably high. The increase in the back pressure means that the pressure of the exhaust gas does not decrease so much when the exhaust gas is discharged from the combustion chamber 5 into the exhaust port 11, and therefore the temperature of the exhaust gas discharged from the combustion chamber 5 also decreases significantly. Means not. Therefore, the temperature of the exhaust gas discharged into the exhaust port 11 is maintained at a considerably high temperature. On the other hand, a high back pressure means that the density of the exhaust gas is high, and a high density of the exhaust gas means that the flow rate of the exhaust gas in the exhaust passage from the exhaust port 11 to the exhaust control valve 28 is high. It means late. Therefore, the exhaust gas discharged into the exhaust port 11 stays in the exhaust passage upstream of the exhaust control valve 28 for a long time at a high temperature.

As described above, when the exhaust gas is kept in the exhaust passage upstream of the exhaust control valve 28 at a high temperature for a long time, the oxidation reaction of the unburned HC is accelerated. In this case, according to an experiment by the inventor, in order to promote the oxidation reaction of the unburned HC in the exhaust passage, the exhaust port 11 is required.
It has been found that the exhaust gas temperature at the outlet needs to be approximately 750 ° C. or higher, preferably 800 ° C. or higher.

The longer the high-temperature exhaust gas stays in the exhaust passage upstream of the exhaust control valve 28, the greater the amount of unburned HC reduction. This residence time becomes longer as the position of the exhaust control valve 28 is further away from the outlet of the exhaust port 11, so that the exhaust control valve 28
It is necessary to arrange a distance necessary for sufficiently reducing unburned HC from one outlet. When the exhaust control valve 28 is arranged at a distance required to sufficiently reduce the unburned HC from the outlet of the exhaust port 11, the concentration of the unburned HC is greatly reduced as shown by the solid line in FIG.

As described above, in order to promote the oxidation reaction of unburned HC in the exhaust passage, the exhaust port 1
The exhaust gas temperature at one outlet needs to be approximately 750 ° C. or higher, preferably 800 ° C. or higher. Further, in order to reduce the amount of unburned HC discharged into the atmosphere, the first requirement described above must be satisfied. That is, it is necessary to reduce the amount of unburned HC generated in the combustion chamber 5. Therefore, in the present invention, in addition to the main fuel Qm for generating the engine output, the auxiliary fuel Qa is additionally injected after the injection of the main fuel Qm so that the auxiliary fuel Qa is burned in the combustion chamber 5.

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

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

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

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

The optimum injection timing of the auxiliary fuel Qa differs depending on the model of the engine.
Is during the expansion stroke or the exhaust stroke. Therefore, in the present invention, the fuel injection of the auxiliary fuel Qa is performed during the expansion stroke or the exhaust stroke. On the other hand, the temperature of the burned gas in the combustion chamber 5 is affected by both the combustion heat of the main fuel Qm and the combustion heat of the auxiliary fuel Qa. That is, the burned gas temperature in the combustion chamber 5 increases as the injection amount of the main fuel Qm increases, and the sub-fuel Qa
Increases as the injection amount of the fuel increases. Further, the temperature of the burned gas in the combustion chamber 5 is affected by the back pressure. That is, as the back pressure increases, the burned gas is less likely to flow out of the combustion chamber 5, so that the amount of burned gas remaining in the combustion chamber 5 increases. Thus, when the exhaust control valve 28 is almost completely closed. The temperature of the burned gas in the combustion chamber 5 is increased.

By the way, when the exhaust pressure control valve 28 is almost closed, thereby increasing the back pressure, the generated torque of the engine decreases from the optimum required generated torque. Therefore, in the present invention, when the exhaust control valve 28 is almost fully closed as shown in FIG. 4B, the exhaust control valve 28 is operated under the same engine operating state as shown in FIG. The injection amount of the main fuel Qm is increased as compared with the case where the exhaust control valve 28 is fully opened under the same engine operation state so as to approach the required generated torque of the engine when fully opened. In the embodiment according to the present invention, the exhaust control valve 28
Is almost completely closed, the main fuel Qm is adjusted so that the generated torque of the engine at that time matches the required generated torque of the engine when the exhaust control valve 28 is fully opened under the same engine operating state. Will be increased.

FIG. 6 shows a change in the main fuel Qm required to obtain the required torque of the engine with respect to the required load L. In FIG. 6, the solid line shows the case where the exhaust control valve 28 is almost completely closed, and the broken line shows the case where the exhaust control valve 2 is closed.
8 shows the case where it is fully opened. On the other hand, FIG. 7 shows the relationship between the main fuel Qm and the auxiliary fuel Qa required to bring the exhaust gas temperature at the outlet of the exhaust port 11 from approximately 750 ° C. to approximately 800 ° C. when the exhaust control valve 28 is almost fully closed. ing. As described above, even if the main fuel Qm is increased, the burned gas temperature in the combustion chamber 5 increases, and even if the auxiliary fuel Qa is increased, the burned gas temperature in the combustion chamber 5 increases. Therefore, the temperature of the exhaust gas at the outlet of the exhaust port 11 is almost 750 ° C.
As shown in FIG. 7, the relationship between the main fuel Qm and the auxiliary fuel Qa required to make the temperature approximately 800 ° C. is as follows. As shown in FIG. 7, when the main fuel Qm is increased, the auxiliary fuel Qa is decreased. The fuel Qa has an increasing relationship.

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

Therefore, in the embodiment according to the present invention, when the exhaust control valve 28 is almost fully closed, the main fuel Qm is increased by an amount necessary to increase the engine generated torque to the required generated torque.
And the temperature of the burned gas in the combustion chamber 5 is increased mainly by the combustion heat of the auxiliary fuel Qa. In this way, the exhaust control valve 28 is almost completely closed, and the exhaust port 11 is closed.
When the auxiliary fuel Qa is injected in an amount required to make the exhaust gas at the outlet approximately 750 ° C. or more, preferably approximately 800 ° C. or more, the concentration of unburned HC in the exhaust passage from the exhaust port 11 to the exhaust control valve 28 is reduced. Can be greatly reduced. At this time, in the exhaust passage from the exhaust port 11 to the exhaust control valve 28, as shown in FIG.
In order to reduce the concentration to about 150 ppm, it is necessary to make the pressure in the exhaust passage upstream of the exhaust control valve 28 about 80 KPa by gauge pressure. At this time, the closing ratio of the exhaust passage cross-sectional area by the exhaust control valve 28 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 is performed such that the closing ratio of the cross-sectional area of the exhaust passage by the exhaust control valve 28 becomes approximately 95% or more. The valve 28 is almost completely closed.

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 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 low load. Will be. As described above, when the temperature in the combustion chamber 5 is low, even if a catalyst having an oxidizing function is disposed in the exhaust passage, a large amount of unburned HC generated at this time is not activated because the catalyst having a low catalyst temperature is not activated. Is difficult to oxidize with a catalyst.

Therefore, in the embodiment according to the present invention, the exhaust control valve 28 is almost completely closed at the time of starting and warming-up of the engine and at the time of low engine load, so that the main fuel Qm is increased and the auxiliary fuel Qa is additionally injected. Thus, the amount of unburned HC discharged into the atmosphere is greatly reduced.
FIG. 8 shows an example of the change of the main fuel Qm and the opening of the exhaust control valve 24 at the time of engine start and warm-up operation.
In FIG. 8, a solid line X indicates an optimal injection amount of the main fuel Qm when the exhaust control valve 28 is almost fully closed.
A broken line Y indicates an optimal injection amount of the main fuel Qm when the exhaust control valve 28 is fully opened. As can be seen from FIG. 8, when the engine is started and the engine is warmed up, the exhaust control valve 28 is almost completely closed, and the exhaust control valve 2 is operated under the same engine operating condition.
The injection amount X of the main fuel Qm is increased more than the optimum injection amount Y of the main fuel Qm when the valve 8 is fully opened, and the auxiliary fuel Qa is additionally injected.

FIG. 9 shows an example of the change of the main fuel Qm and the opening of the exhaust control valve 28 when the engine is under a low load.
In FIG. 9, a solid line X indicates an optimal injection amount of the main fuel Qm when the exhaust control valve 28 is almost fully closed.
A broken line Y indicates an optimal injection amount of the main fuel Qm when the exhaust control valve 28 is fully opened. As can be seen from FIG. 9, when the engine is under a low load, the exhaust control valve 28 is almost completely closed,
The injection amount X of the main fuel Qm is increased more than the optimum injection amount Y of the main fuel Qm when the exhaust control valve 28 is fully opened under the same engine operating state, and the auxiliary fuel Qa is additionally injected. Is done.

In the embodiment according to the present invention, during the warm-up operation, the exhaust control valve 28 is almost completely closed as described above. On the other hand, the warm-up operation is usually performed under a low load, and thus the amount of exhaust gas is small. Therefore, at this time, the exhaust turbocharger 15 is not performing the supercharging operation.
On the other hand, when the vehicle is driven during such a warm-up operation and the accelerator pedal 50 is depressed to accelerate, the supercharging action of the exhaust turbocharger 15 is started immediately even during the warm-up operation, and the engine is started. It is preferable to increase the output of the device rapidly.

In this regard, the exhaust control valve 2 is provided in the exhaust passage downstream of the exhaust turbine 23 as in the embodiment of the present invention.
When the opening of the exhaust control valve 28 is increased when the acceleration operation is performed during the warm-up operation, the exhaust control valve 28 is changed from the almost fully closed state to the fully open state in the embodiment according to the present invention. The supercharging operation by the exhaust turbocharger 15 can be started immediately.

That is, when the exhaust control valve 28 is almost fully closed to reduce unburned HC during the warming-up operation, the exhaust gas in the exhaust passage upstream of the exhaust control valve 28 has a high temperature and a high pressure as described above. Has been maintained. At this time, the supercharging action by the exhaust turbocharger 15 is not performed, so that the pressure on the inlet side of the exhaust turbine 23 is substantially equal to the pressure on the outlet side of the exhaust turbine 23. In such a state, when the exhaust control valve 28 is fully opened, the pressure on the outlet side of the exhaust turbine 23 drops sharply, and thus the pressure on the inlet side of the exhaust turbine 23 and the pressure on the outlet side of the exhaust turbine 23 The pressure difference instantaneously increases. As a result, the rotation speed of the exhaust turbine 23 rapidly increases to a high rotation, and thus the supercharging action by the exhaust turbine 23 is started immediately. As a result, a favorable acceleration operation can be ensured because the engine output increases rapidly. Therefore, in the embodiment according to the present invention, when the acceleration operation is performed during the warm-up operation, the exhaust control valve 28 is fully opened from the almost fully closed state.

In the embodiment according to the present invention, as shown in FIG. 9, when the load increases during the low-load operation of the engine, the exhaust control valve 28 is fully opened from the almost fully closed state. That is,
When acceleration operation is performed during low engine load operation, the exhaust control valve 2
8 is fully opened from the almost fully closed state. Therefore, also at this time, when the acceleration operation is started, the rotation speed of the exhaust turbine 23 rapidly increases to a high rotation speed, and thus a favorable acceleration operation can be secured.

As described above, in the present invention, the supercharging action of the exhaust turbocharger 23 is started quickly by utilizing the high pressure generated upstream of the exhaust control valve 28 when the exhaust control valve 28 is almost fully closed. ing. Although the exhaust control valve 28 is provided downstream of the exhaust turbine 23 in the embodiment shown in FIG. 1, the exhaust control valve 28 may be arranged upstream of the exhaust turbine 23.

FIG. 10 shows an operation control routine.
Referring to FIG. 10, first, at step 100, it is determined whether or not the engine is being started and the engine is being warmed up.
Step 10 when the engine is being started and the engine is warming up.
Proceeding to 1, it is determined whether or not the vehicle is accelerating. When the acceleration operation is not being performed, the routine proceeds to step 102, where the exhaust control valve 28 is almost completely closed. Then, at step 103, the injection control of the main fuel Qm is performed. That is, the main fuel Qm
Is assumed to be X shown in FIG. Next, at step 104, injection control of the auxiliary fuel Qa is performed.

On the other hand, when it is determined in step 101 that the vehicle is in the acceleration operation, the routine proceeds to step 106, where the exhaust control valve 28 is fully opened, and then proceeds to step 107 to perform the injection control of the main fuel Qm. At this time, the injection of the auxiliary fuel Qa is not performed. Step 1
When it is determined at 00 that the engine is not being started or warmed up, the routine proceeds to step 105, where it is determined whether or not the engine is under a low load. When the engine is not in the low load state, the routine proceeds to step 106, where the exhaust control valve 28 is fully opened, and then proceeds to step 107, where injection control of the main fuel Qm is performed. At this time, the injection of the auxiliary fuel Qa is not performed.

On the other hand, when it is determined in step 105 that the engine is under low load, the routine proceeds to step 102, where the exhaust control valve 28 is almost completely closed. Then, in step 103, the injection control of the main fuel Qm is performed. Will be
That is, the injection amount of the main fuel Qm is set to X shown in FIG. Next, at step 104, injection control of the auxiliary fuel Qa is performed.

[0058]

According to the present invention, the supercharging action of the exhaust turbocharger can be immediately started during the acceleration operation while significantly reducing the amount of unburned HC discharged into the atmosphere.

[Brief description of the drawings]

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

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

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

FIG. 4 is a view showing an injection timing.

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

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

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

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

FIG. 9 is a diagram showing an injection amount of a main fuel and an opening degree of an exhaust control valve.

FIG. 10 is a flowchart for performing operation control.

[Explanation of symbols]

 6 fuel injection valve 15 exhaust turbocharger 23 exhaust turbine 28 exhaust control valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 375 F02D 41/04 375 41/06 330 41/06 330B 380 380B 41/34 41/34 H 41/38 41/38 B 43/00 301 43/00 301H 301J 301Z 45/00 310 45/00 310B 310E 310J F term (reference) 3G065 AA03 AA04 AA09 AA10 CA12 DA02 DA05 DA06 EA02 EA04 EA09 GA00 GA05 GA10 GA46 JA04 JA09 JA11 KA02 3G084 AA03 BA05 BA13 BA14 BA15 BA19 BA20 CA02 CA03 CA04 DA10 EA11 EC01 EC03 FA07 FA10 FA33 3G091 AA02 AA11 AA17 AA18 AA24 AA28 BA15 CB02 CB03 CB07 DB11 EA01 EA05 EA07 FA04 HA13 HA05 HA05 HA05 HA05 HA05 KA08 KA12 LA03 LB04 LB06 LC03 LC04 LC07 MA12 MA19 NA08 NC02 PA01Z PB08Z PE01Z PE03Z PF03Z

Claims (5)

[Claims] 1. An exhaust turbine of an exhaust turbocharger and an exhaust control valve are disposed in an exhaust passage connected to an outlet of an engine exhaust port, and it is determined that the emission of unburned HC into the atmosphere should be reduced. In this case, the exhaust control valve is almost fully closed, the main fuel injected into the combustion chamber for generating the engine output is burned under excess air, and the auxiliary fuel is burned. Additional injection is performed into the combustion chamber at a predetermined time during the expansion stroke or the exhaust stroke, and the opening degree of the exhaust control valve is increased when the acceleration operation is performed when the exhaust control valve is almost fully closed. Exhaust gas purifying apparatus for an internal combustion engine. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein an exhaust control valve is disposed in an exhaust passage downstream of the exhaust turbine. 3. When the exhaust control valve is almost fully closed, the same engine operating state is set so as to approach the generated torque of the engine when the exhaust control valve is fully opened under the same engine operating state. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the main fuel injection amount is increased as compared with the case where the exhaust control valve is fully opened. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein it is determined that the amount of unburned HC discharged into the atmosphere should be reduced when the engine is being warmed up. 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein it is determined that the amount of unburned HC discharged into the atmosphere should be reduced when the engine is under low load operation.