JP3536739B2 - Exhaust gas purification device for internal combustion engine - Google Patents

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. There is known a diesel engine in which complete combustion is performed by the above-described method, thereby suppressing the amount of unburned HC generated (see JP-A-49-80414).

[0003] When an exhaust gas purifying catalyst is arranged 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 output of the engine, 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. An internal combustion engine is 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 the adsorbed unburned HC is released as the surrounding pressure decreases. Therefore, in order to reduce NO _x by unburned HC emitted 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, large amount of unburned H with a small amount of auxiliary fuel in addition to the main fuel injection or during the exhaust stroke during the expansion stroke for of the NO _x generation amount less engine low speed low load operation of the engine output at the time of occurrence
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 JP-A-10-238336).

[0005]

Now, how to reduce the amount of unburned HC generated during low engine load operation, particularly during warm-up operation of an 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 inventors conducted experimental research to solve this problem, and as a result, in order to significantly reduce the amount of unburned HC discharged into the atmosphere during warm-up operation of the engine, etc. It has been found that it is necessary to reduce the amount of combustion HC generated and at the same time increase the amount of unburned HC reduction in the exhaust passage.

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 an 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 combustion of these auxiliary fuels and the exhaust throttling 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 the 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.
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 completely 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 drop so much, and therefore 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, unburned HC contained in the exhaust gas is oxidized, and thus 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 because 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. In this case, even if the exhaust control valve is almost fully closed, 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 throttle function, the amount of unburned HC generated in the combustion chamber is reduced by injecting the auxiliary fuel, and the temperature of the burned gas in the combustion chamber is increased. However, when the exhaust throttle function is not performed by the exhaust control valve, 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 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 completely close the exhaust control valve. 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 into the atmosphere. Will be discharged.

On the other hand, in the internal combustion engine described in the above-mentioned JP-A-8-303290 or JP-A-10-212995, the exhaust control valve does not perform the exhaust throttling operation, so that 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. H10-238336, the exhaust control valve is closed to a relatively small opening so that the engine output falls within an allowable range. The main fuel injection amount is maintained at the same injection amount when the control valve is fully opened and when the control valve is closed. 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.

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, no unburned HC is generated. Therefore, it is considered that the injection control of the auxiliary fuel is performed in this internal combustion engine so that the auxiliary fuel is not satisfactorily burned. Therefore, in this internal combustion engine, it is considered that a small amount of auxiliary fuel does not significantly contribute to the increase in the temperature of the burned gas.

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

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

[0016]

According to a first aspect of the present invention, an exhaust control system is provided in an exhaust passage connected to an outlet of an engine exhaust port at a predetermined distance from the outlet of the exhaust port. When it is determined that the amount of unburned HC discharged into the atmosphere should be reduced by disposing a valve, the exhaust control valve is almost fully closed and the fuel is injected into the combustion chamber to generate engine output. In addition to burning the main fuel under excess air, the auxiliary fuel is additionally injected into the combustion chamber at a predetermined time during the expansion stroke or the exhaust stroke where the auxiliary fuel can burn, and the exhaust control valve is almost completely exhausted. When the exhaust control valve is fully opened under the same engine operating condition so as to approach the generated torque of the engine when the exhaust control valve is fully opened under the same engine operating condition when closed Injection of main fuel compared to And so as to increase the amount.

In the second 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 third 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. According to a fourth aspect, in the first aspect, when it is determined that the amount of unburned HC discharged into the atmosphere should be reduced, the injection amount of the auxiliary fuel is decreased as the injection amount of the main fuel increases. .

According to a fifth aspect, in the first aspect,
In addition to the main fuel, the auxiliary fuel is burned under excess air. According to a sixth aspect, in the first aspect, an air-fuel mixture formed in a limited area in the combustion chamber by the main fuel is ignited by an ignition plug, and then an additional fuel is injected. In a seventh aspect based on the first aspect, a catalyst is disposed in the engine exhaust passage.

In the eighth invention, in the seventh invention,
Catalyst comprises an oxidation catalyst, three-way catalyst, NO _x absorbent or the HC adsorption catalyst. According to a ninth aspect, in the seventh aspect, there is provided a determination means for determining whether or not the catalyst is higher than the activation temperature, wherein the catalyst is lower than the activation temperature and the engine is warmed up. Sometimes it is determined that the amount of unburned HC emissions to the atmosphere should be reduced. According to a tenth aspect based on the seventh aspect, the method according to the seventh aspect, further comprising determining means for determining whether or not the catalyst is higher than the activation temperature, wherein the catalyst is lower than the activation temperature and the engine is under low load operation. It is determined that the emission of unburned HC into the atmosphere should be reduced.

In an eleventh aspect based on the seventh aspect, the catalyst is disposed in the engine exhaust passage upstream of the exhaust control valve. In a twelfth aspect based on the first aspect, when the amount of unburned HC discharged into the atmosphere is to be reduced, the pressure or temperature of the exhaust gas in the engine exhaust passage upstream of the exhaust control valve is set to a target value. The combustion in the combustion chamber is controlled. According to a thirteenth aspect, in the twelfth aspect, the main fuel injection amount or the auxiliary fuel injection amount,
Alternatively, the combustion in the combustion chamber is controlled by controlling at least one of the intake air amounts.

According to a fourteenth aspect, in the thirteenth aspect, when the pressure or the temperature of the exhaust gas in the engine exhaust passage upstream of the exhaust control valve is lower than a target value, the injection amount of the main fuel or the injection amount of the auxiliary fuel, Alternatively, at least one of the intake air amounts is increased. In a fifteenth aspect based on the first aspect, the exhaust control valve is switched from a fully open state to a substantially fully closed state when the engine is started. According to a sixteenth aspect based on the fifteenth aspect, the invention according to the fifteenth aspect further comprises a negative pressure tank for accumulating a negative pressure, and a negative pressure actuated actuator for driving an exhaust control valve, wherein the actuator has Activated by pressure.

[0022]

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

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

Referring to FIGS. 1 and 2, the intake port 9 is connected to a surge tank 13 via a corresponding intake branch pipe 12, and the surge tank 13 is connected to an air cleaner 16 via an intake duct 14 and an air flow meter 15. Is done. A throttle valve 18 driven by a step motor 17 is arranged in the intake duct 14. On the other hand, FIG.
In the embodiment shown in FIG. 1, the ignition order is set to 1-3-4-2, and as shown in FIG. 1, the exhaust ports 11 of the cylinders # 1 and # 4 whose ignition order is alternate are shared by the common first port. The exhaust ports 11 of the remaining cylinders # 2 and # 3, which are ignited every other 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 including a negative pressure diaphragm device or an electric motor is disposed in the exhaust pipe 22.

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 electrically controlled EGR control valve is provided in the EGR passage 25. 26 are arranged. The fuel injectors 6 are connected to a common fuel reservoir, a so-called common rail 27. Inside this common rail 27 is the fuel tank 2
The fuel in the fuel pump 8 is electrically controlled and has a variable discharge amount.
The fuel supplied through 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. The fuel pump 29 is controlled 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. Is controlled.

The electronic control unit 40 is composed of a digital computer, and is connected to a read only memory (ROM) 42, a random access memory (RAM) 43, a CPU (microprocessor) 44, an input port 45, An output port 46 is provided. The air flow meter 15 generates an output voltage proportional to the amount of intake air.
7 is input to the input port 45. A water temperature sensor 31 for detecting an engine cooling water temperature is attached to the engine main body 1, and an output signal of the water temperature sensor 31 is output from a corresponding AD converter.
The data is input to the input port 45 via the 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.

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 17 for controlling the throttle valve, the actuator 23 for controlling the exhaust control valve, the EGR control valve 26, and the fuel pump 29 via the corresponding drive circuit 48. You.

FIG. 4 shows the fuel injection amounts Q1, Q2, Q (= Q _1).
+ Q ₂ ), injection start timing θS1, θS2, injection completion timing θE1, θE2, and average air-fuel ratio A in the combustion chamber 5.
/ F. In FIG. 4, the horizontal axis L indicates the amount of depression of the accelerator pedal 50, that is, the required load.

[0029] Figure 4 required load L as can be seen from the when less than L ₁ 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. When the required load L is between L ₁ and L ₂ , θS 1 to θ
The first fuel injection Q1 is performed during E1, and then the second fuel injection Q1 is performed between θS2 and θE2 at the end of the compression stroke.
The second fuel 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, the required load L
Is low, the average air-fuel ratio A / F is lean. When the required load L increases, the average air-fuel ratio A / F becomes the stoichiometric air-fuel ratio. When the required load L further increases, the average air-fuel ratio A / F increases.
/ F is made rich. In the operation region where the fuel injection Q2 is performed only at the end of the compression stroke, the fuel injection Q2 is performed twice.
The operating region in which 1 and Q2 are performed and the operating region in which fuel injection Q1 is performed only at the beginning of the intake stroke are not determined only by the required load L, but are 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. 4), 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, when the required load L is between L ₁ and L ₂ as described above, 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 ignition plug 7 by the second fuel injection Q2 performed at the end of the compression stroke. This mixture is ignited by the spark plug 7,
This ignition flame causes the lean mixture to burn.

On the other hand, the required load L is homogeneous mixture of lean or stoichiometric or rich air-fuel ratio is formed in the combustion chamber 5 as is shown in Figure 4 when larger than L _2, the homogeneous mixture is It is ignited by the spark plug 7.

Next, the method for reducing unburned HC according to the present invention will be schematically described with reference to FIG. In FIG. 5, the horizontal axis indicates the crank angle, and BT
DC and ATDC indicate before and after top dead center, respectively.

[0034] FIG. 5 (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. 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 kept in a fully open state.

On the other hand, when it is necessary to reduce the unburned HC by the method according to the present invention, the exhaust control valve 24 is almost completely closed, and the engine output is generated as shown in FIG. In addition to the injection of the main fuel Qm
In the example shown in FIG. 5B, during the expansion stroke, the auxiliary fuel Qa is additionally injected at around 60 ° after the compression top dead center (ATDC). In this case, after the main fuel Qm is burned, the main fuel Qm is burned with an excess of air so that sufficient oxygen remains in the combustion chamber 5 to completely burn the sub fuel Qa. FIGS. 5A and 5B show the fuel injection period when the engine load and the engine speed are the same, and 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).

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 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. 5A with the exhaust control valve 24 fully opened. It 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. 6, a black circle and a solid line indicate that the exhaust control valve 24 is almost fully closed, and that 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
4, the concentration of unburned HC in the exhaust gas is 15
It decreases to about 0 ppm. Therefore, in this case, it is understood that the amount of unburned HC discharged into the atmosphere can be significantly reduced.

The reason why the unburned HC decreases 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 solid 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 promoted. Does not decrease so 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 the two demands for promotion at the same time. Therefore, the second requirement, that is, the promotion of the oxidation reaction of unburned HC in the exhaust passage will be described first.

According to the present invention, unburned H discharged into the atmosphere
When the amount of C is to be reduced, the exhaust control valve 24 is almost fully closed. When the exhaust control valve 24 is almost fully closed in this way, the inside of the exhaust port 11, the inside of the exhaust manifolds 19 and 20,
The exhaust pipe 22 inside the exhaust pipe 21 and upstream of the exhaust control valve 24
The internal pressure, the back pressure, is considerably higher. The increase in the back pressure means that the pressure of the exhaust gas does not decrease so much when the exhaust gas is exhausted from the combustion chamber 5 into the exhaust port 11, and therefore the temperature of the exhaust gas exhausted from the combustion chamber 5 also decreases significantly. Means not. Therefore, the exhaust port 11
The temperature of the exhaust gas discharged inside is maintained at a considerably high temperature. On the other hand, a high back pressure means that the density of the exhaust gas is high, and a high density of the exhaust gas means that the flow rate of the exhaust gas in the exhaust passage from the exhaust port 11 to the exhaust control valve 24 is high. It means late.
Therefore, the exhaust gas discharged into the exhaust port 11 stays in the exhaust passage upstream of the exhaust control valve 24 for a long time at a high temperature.

As described above, when the exhaust gas is kept at a high temperature in the exhaust passage upstream of the exhaust control valve 24 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 above approximately 750 ° C., preferably above 800 ° C.

The longer the high-temperature exhaust gas remains in the exhaust passage upstream of the exhaust control valve 24, the greater the amount of unburned HC reduction. This residence time becomes longer as the position of the exhaust control valve 24 is further away from the outlet of the exhaust port 11, so that the exhaust control valve 24 is
It is necessary to arrange a distance necessary for sufficiently reducing unburned HC from one outlet. When the exhaust control valve 24 is arranged at a distance required for sufficiently reducing 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. According to experiments conducted by the inventor, it has been found that the distance from the outlet of the exhaust port 11 to the exhaust control valve 24 is preferably 30 cm or more in order to sufficiently reduce unburned HC.

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 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. 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 C. or higher.

As described above, in the present invention, it is necessary to burn the auxiliary fuel Qa in the combustion chamber 5, and for this purpose,
It is necessary that sufficient oxygen remains in the combustion chamber 5 at the time of combustion of a, and that the auxiliary fuel Qa be injected at a time when the injected auxiliary fuel Qa is satisfactorily burned in the combustion chamber 5. There is.

Therefore, in the present invention, as described above, the auxiliary fuel Q
The main fuel Qm is burned under excess air so that sufficient oxygen can remain in the combustion chamber 5 during the combustion of a, and the auxiliary fuel Qa is also burned under excess air.
In this case, the average air-fuel ratio in the combustion chamber 5 during the combustion of the main fuel Qm is preferably about 30 or more, and the average air-fuel ratio in the combustion chamber 5 during the combustion of the auxiliary fuel Qa is about 1
It has been found that a value of 5.5 or more is preferable.

Further, the injection timing at which the auxiliary fuel Qa injected in the stratified charge combustion type internal combustion engine shown in FIG. 2 is satisfactorily burned in the combustion chamber 5 is determined after the compression top dead center (ATDC) indicated by the arrow Z in FIG. ) From approximately 50 ° to approximately 9
The expansion stroke is 0 °, and therefore, in the stratified combustion internal combustion engine shown in FIG.
DC) injected during an expansion stroke of approximately 50 ° to approximately 90 °. After compression top dead center (ATDC), approximately 50 °
Auxiliary fuel Q injected during an expansion stroke of approximately 90 ° from
a does not contribute significantly to the generation of engine output.

According to an experiment conducted by the inventor, FIG.
In the stratified combustion type internal combustion engine shown in FIG. 1, when the auxiliary fuel Qa is injected from around 60 ° to 70 ° 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. 5B, the injection timing of the auxiliary fuel Qa is set to approximately 60 ° after the top dead center of compression (ATDC).

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 the main fuel Q
m and the combustion heat of the auxiliary fuel Qa. That is, the temperature of the burned gas 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. 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 combustion chamber 5
The amount of burned gas remaining in the combustion chamber 5 increases because the burned gas does not easily flow out of the exhaust control valve 24.
Is substantially completely closed, the temperature of the burned gas in the combustion chamber 5 is increased.

By the way, the exhaust control valve 24 is almost closed, and when the back pressure increases, the generated torque of the engine is reduced from the optimum required generated torque even if the auxiliary fuel Qa is additionally injected. Therefore, in the present invention, FIG.
When the exhaust control valve 24 is almost completely closed as shown in FIG. 5B, the case where the exhaust control valve 24 is fully opened under the same engine operating condition as shown in FIG. 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 generated torque of the engine. In the embodiment according to the present invention, when the exhaust control valve 24 is almost completely closed, the generated torque of the engine at that time is the same as that of the engine when the exhaust control valve 24 is fully opened under the same engine operating state. The main fuel Qm is increased so as to match the required generated torque.

FIG. 7 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. 7, the solid line indicates the case where the exhaust control valve 24 is almost completely closed, and the broken line indicates the exhaust control valve 2.
4 shows a case where the shutter is completely closed.

On the other hand, FIG. 8 shows that the main fuel Qm and the auxiliary fuel Qa required to bring the exhaust gas temperature at the outlet of the exhaust port 11 from approximately 750 ° C. to approximately 800 ° C. when the exhaust control valve 24 is almost fully closed. Shows the relationship. 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. Accordingly, 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. is shown in FIG. Qa decreases,
When the main fuel Qm decreases, the auxiliary fuel Qa increases.

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 fuel consumption, it can be said that it is preferable to increase the temperature of the burned gas in the combustion chamber 5 by increasing the auxiliary fuel Qa.

Therefore, in the embodiment according to the present invention, when the exhaust control valve 24 is almost fully closed, the main fuel Qm is increased by an amount necessary to raise 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 heat of combustion of the auxiliary fuel Qa.

As described above, the exhaust control valve 24 is almost completely closed, and the exhaust gas at the outlet of the exhaust port 11 is reduced to approximately 750.
Injecting the amount of auxiliary fuel Qa required to make the temperature not less than 0 ° C., and preferably not less than approximately 800 ° C., can significantly reduce the concentration of unburned HC in the exhaust passage from the exhaust port 11 to the exhaust control valve 24. it can. At this time, in order to reduce the concentration of unburned HC to approximately 150 ppm in the exhaust passage from the exhaust port 11 to the exhaust control valve 24, as shown in FIG. Needs to be increased from approximately 60 KPa to 80 KPa by gauge pressure. At this time, the closing ratio of the exhaust passage cross-sectional area by the exhaust control valve 24 is about 95%.

Accordingly, in the embodiment shown in FIG. 1, when the amount of unburned gas discharged into the atmosphere is to be greatly reduced, the closing ratio of the cross section of the exhaust passage by the exhaust control valve 24 is about 95%. Then, the exhaust control valve 24 is almost completely closed. In this case, as shown in FIG. 3, a through hole 24a may be formed in the valve body of the exhaust control valve 24, and the exhaust control valve 24 may be completely closed.

On the other hand, the exhaust control valve 24
If it is sufficient to reduce the unburned HC from about 600 ppm to about 800 ppm in the exhaust passage leading to, it is sufficient if the pressure in the exhaust passage upstream of the exhaust control valve 24 is set to about 30 KPa by gauge pressure. In this case, the closing ratio of the exhaust passage cross-sectional area by the exhaust control valve 24 is approximately 90%.
It will be a percentage.

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 at the time of engine starting and warming up, and at the time of low engine 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 arranged in the exhaust passage, a large amount of gas generated at this time except when the catalyst is at or above the activation temperature is obtained. It is difficult to oxidize unburned HC with a catalyst.

Therefore, in the embodiment according to the present invention, the exhaust control valve 24 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. 9 shows an example of a change in the main fuel Qm and a change in the opening degree of the exhaust control valve 24 during the start of the engine and the warm-up operation. In FIG. 9, a solid line X indicates an optimal injection amount of the main fuel Qm when the exhaust control valve 24 is almost fully closed, and a broken line Y indicates an optimal main fuel Q when the exhaust control valve 24 is fully opened. The injection amount of Qm is shown. As can be seen from FIG. 9, when the engine is started, the exhaust control valve 24 is switched from the fully opened state to the almost fully closed state, and the optimum state is obtained 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 made larger than the injection amount Y of the main fuel Qm, and the auxiliary fuel Qa is additionally injected.

FIG. 10 shows the main fuel Qm at a low engine load.
And a change in the opening degree of the exhaust control valve 24. In FIG. 10, a solid line X indicates an optimal injection amount of the main fuel Qm when the exhaust control valve 24 is almost fully closed, and a broken line Y indicates an optimal main fuel Qm when the exhaust control valve 24 is fully opened. The injection amount of Qm is shown. As can be seen from FIG. 10, when the engine is under a low load, the exhaust control valve 24 is almost completely closed, and under the same engine operating state, the exhaust control valve 24 is closed.
Is the optimum injection amount Y of the main fuel Qm when the valve is fully opened.
Therefore, the injection amount X of the main fuel Qm is increased, and the auxiliary fuel Qa is additionally injected.

FIG. 11 shows an operation control routine.
Referring to FIG. 11, 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 not being started and the engine is not warming up
The routine jumps to 2 to determine whether or not the engine is under low load. When the engine is not in the low load state, the routine proceeds to step 103, where the exhaust control valve 24 is fully opened, and then proceeds to step 104 to perform the injection control of the main fuel Qm. At this time, the injection of the auxiliary fuel Qa is not performed.

On the other hand, if it is determined in step 100 that the engine is being started and the engine is being warmed up, step 1 is executed.
In step 01, after the start of the engine, it is determined whether a predetermined set period has elapsed. When the set period has not elapsed, the routine proceeds to step 105. On the other hand, when the set period has elapsed, the routine proceeds to step 102, and when it is determined in step 102 that the engine is under a low load, the routine also proceeds to step 105. In step 105, the exhaust control valve 24 is almost completely closed.
In, injection control of the main fuel Qm is performed. That is, the injection amount of the main fuel Qm is set to X shown in FIG. 9 when the engine is started and the engine is warmed up, and the injection amount of the main fuel Qm is set to X shown in FIG. You. Next, at step 107, injection control of the auxiliary fuel Qa is performed.

FIG. 12 shows a case where a negative pressure actuated actuator is used as the actuator 23. In addition,
In the example shown in FIG. 12, a negative pressure diaphragm device including a diaphragm 60 connected to the exhaust control valve 24, a diaphragm negative pressure chamber 61, and a diaphragm pressing compression spring 62 is used as a negative pressure operation type actuator.
Further, in the example shown in FIG. 12, a negative pressure tank 63 is provided, and the negative pressure tank 63 is connected to the surge tank 13 via a check valve 64 which can flow only toward the surge tank 13. On the other hand, it is connected to a diaphragm negative pressure chamber 61 via a switching valve 65 capable of communicating with the atmosphere.

The negative pressure in the surge tank 13 is
When the pressure becomes larger than the negative pressure in 3, the check valve 64 is opened, and thus the negative pressure tank 63 is maintained at the maximum negative pressure generated in the surge tank 13. When the switching operation of the switching valve 65 opens the diaphragm negative pressure chamber 61 to the atmosphere, the exhaust control valve 24 is fully opened, and the switching operation of the switching valve 65 connects the diaphragm negative pressure chamber 61 to the negative pressure tank 63. Then, the exhaust control valve 24 is almost completely closed.

When the engine is stopped, the exhaust control valve 24 is kept in a fully opened state so as not to be stuck in a closed state. Next, when the engine is started, the exhaust control valve 24 is switched from the fully open state to the almost fully closed state. In the example shown in FIG. 12, negative pressure is accumulated in the negative pressure tank 63 even when the engine is stopped,
Therefore, by connecting the diaphragm negative pressure chamber 61 to the negative pressure tank 63 when the engine is started, the exhaust control valve 24 can be reliably switched from the fully open state to the almost fully closed state.

FIG. 13 shows another embodiment. In this embodiment, a catalyst 70 is disposed in the exhaust pipe 22 upstream of the exhaust control valve 24. As described above, when the catalyst 70 is disposed 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 70 Strongly heated by hot exhaust gas. Therefore, the catalyst 70 can be activated early at the time of engine start and warm-up operation.

[0070] As the catalyst 70 disposed in the exhaust pipe 22 it can be an oxide catalyst, three-way catalyst, NO _x absorbent or the HC adsorption catalyst. _The NO _x absorbent absorbs NO _x when the mean air-fuel ratio is lean in the combustion chamber 5 has a function of releasing NO _x when the mean air-fuel ratio in the combustion chamber 5 becomes rich.

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

On the other hand, for the HC adsorption catalyst, for example, zeolite, alumina Al ₂ O ₃ , silica alumina SiO ₂ .A
Noble metals such as platinum Pt, palladium Pd, rhodium Rh, iridium Ir, or transitions such as copper Cu, iron Fe, cobalt Co, nickel Ni on a porous support such as l ₂ O ₃ , activated carbon, titania TiO ₂ Metal is carried.

In such an HC adsorption catalyst, the unburned HC in the exhaust gas is physically adsorbed in the catalyst, and the adsorbed amount of the unburned HC increases as the temperature of the catalyst decreases, and the pressure of the exhaust gas flowing through the catalyst decreases. It increases as it gets higher. Therefore, in the embodiment shown in FIG. 13, when the temperature of the catalyst 70 is low and the back pressure is increased by the exhaust throttle function of the exhaust control valve 24, that is, when the engine is started and warmed up, and when the engine is under a low load, the exhaust gas is not exhausted. 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 decreases or when the temperature of the HC adsorption catalyst increases.

FIG. 14 shows still another embodiment. In the example catalyst 70 consisting of _the NO _x absorbent or the HC adsorbing catalyst disposed in the exhaust control valve 24 upstream of the exhaust pipe 22, the first
Catalysts 71 and 72 having an oxidizing function such as an oxidation catalyst and a three-way catalyst are disposed between the exhaust manifold 19 and the exhaust pipe 21 and between the second exhaust manifold 20 and the exhaust pipe 21, respectively. The exhaust control valve 24 is almost completely closed and the auxiliary fuel Q
a is being injected, each exhaust manifold 19, 2
0, the exhaust gas temperature at the outlet of each exhaust manifold 19, 20 is thus significantly higher at the outlet of each exhaust manifold 19, 20.
When the catalysts 1 and 72 are arranged, the catalysts 71 and 72 are activated early after the engine is started. As a result, the catalysts 71, 72
Can further reduce the amount of unburned HC discharged into the atmosphere by the action of accelerating the oxidation reaction.

As shown in FIG. 14, when the catalysts 71 and 72 having an oxidizing function are arranged in the engine exhaust passage, even if the engine low load operation is not performed for a long time even if the engine low load operation is performed. The catalysts 71, 72 are maintained at or above the activation temperature. Further, when the engine is restarted within a short time after the engine is stopped, the catalysts 71 and 72 may be maintained at the activation temperature or higher even during the warm-up operation of the engine. If the catalysts 71 and 72 are activated, the unburned HC in the exhaust gas is purified by the catalysts 71 and 72, so that it is not necessary to inject the auxiliary fuel Qa which causes an increase in fuel consumption.

Therefore, in still another embodiment, as shown in FIG. 14, temperature sensors 73 and 74 for detecting the temperatures of the catalysts 71 and 72 are attached to the catalysts 71 and 72, respectively, and output signals of the temperature sensors 73 and 74 are provided. Any catalyst 7 based on
When the activation temperatures 1 and 72 also become equal to or higher than the activation temperature, the exhaust control valve 24 does not matter even during the warm-up operation or the engine low-load operation.
Are fully opened to stop the injection of the auxiliary fuel Qa.

FIG. 15 shows an operation control routine in such a case. Referring to FIG. 15, first, in step 200, it is determined whether or not the engine is being started and the engine is being warmed up. If the engine is not being started or the engine is being warmed up, the routine proceeds to step 201, where it is determined whether or not the engine is at a low load. When the engine is not under the low load condition, the routine proceeds to step 202, where the exhaust control valve 24 is fully opened, and then proceeds to step 203, where the 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, if it is determined in step 200 that the engine is being started and the engine is warming up,
If it is determined in step 01 that the engine is under low load, the routine proceeds to step 204, where the temperature T1 of the catalyst 71 detected by the temperature sensor 73 and the temperature T2 of the catalyst 72 detected by the temperature sensor 74 are both the activation temperature T _0. Is determined. T1 ≦ T ₀ or T2 ≦ T when ₀ is occupied Tozase all the exhaust control valve 24 substantially proceeds to step 205, then in step 206 the main fuel Qm
Is performed. That is, when the engine is started and the engine is warmed up, the injection amount of the main fuel Qm is set to X shown in FIG.
X shown in FIG. Next, at step 207, injection control of the auxiliary fuel Qa is performed.

On the other hand, at step 204, T1
> When it is determined that T is _0, and T2> T _0, i.e. the exhaust control valve 24 is fully opened the routine proceeds to step 202 when any catalyst 71 and 72 were also activated, then the main routine proceeds to step 203 The injection control of the fuel Qm is performed.

On the other hand, as described above, in order to greatly reduce the amount of unburned HC discharged into the atmosphere, the exhaust port 11
The exhaust gas temperature at the outlet needs to be about 75 ° C. or higher, and for that purpose, the back pressure needs to be maintained at about 60 to 80 KPa. However, for example, the exhaust pipe 22
There is a risk that the exhaust control valve 24 cannot be closed to the target opening degree due to the deposits therein, and as a result, the back pressure may not be sufficiently high. Even if the exhaust control valve 24 is closed to the target opening degree, The deposits reduce the flow area of the exhaust gas, and there is a risk that the back pressure becomes too high.

Therefore, in the embodiment described below, when the amount of unburned HC discharged into the atmosphere is to be reduced, the exhaust control valve 24
The combustion in the combustion chamber 5 is controlled so that the pressure or temperature of the exhaust gas in the upstream exhaust passage becomes a target value. Specifically, the main fuel Qm or the auxiliary fuel Q
If at least one of the injection amounts of a is increased, the combustion pressure and the combustion temperature in the combustion chamber 5 increase, and thus the back pressure and the exhaust gas temperature increase. Further, when the intake air amount is increased, the exhaust gas amount is increased, so that the back pressure and the exhaust gas temperature are increased.

Therefore, in the embodiment shown in FIG. 16, a pressure sensor 80 for detecting the back pressure is attached to the exhaust pipe 22, and when the back pressure is lower than the target value, the injection amount of the main fuel Qm or the auxiliary fuel Qa The amount of injection of the main fuel Qm, the amount of injection of the auxiliary fuel Qa, or the amount of intake air is reduced when the back pressure is higher than the target value.

In the embodiment shown in FIG. 17, a temperature sensor 81 for detecting the exhaust gas temperature at the outlet of the exhaust port 11 is attached to the plate pipe of the first exhaust manifold 19, and the exhaust gas temperature detected by the temperature sensor 81 is detected. Is lower than the target value, the injection amount of the main fuel Qm, the injection amount of the auxiliary fuel Qa, or the intake air amount is increased. When the exhaust gas temperature detected by the temperature sensor 81 is higher than the target value, the main fuel Qm is increased. , The injection amount of the auxiliary fuel Qa, or the intake air amount.

The exhaust control valve 24 can be arranged at the inlet of the exhaust pipe 22, as shown in FIG.
It can also be arranged at the outlet of the exhaust pipe 21.

FIG. 18 shows an operation control routine when the back pressure is controlled by controlling the main fuel Qm. Referring to FIG. 18, first, step 3
At 00, it is determined whether or not the engine is being started and the engine is being warmed up. If the engine is not being started and the engine is not warming up, the process jumps to step 302 to determine whether or not the engine is under low load. If the engine load is not low, step 303
Then, the exhaust control valve 24 is fully opened, and then the routine proceeds to step 304, where the 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 300 that the engine is being started and the engine is being warmed up, step 3 is executed.
In step 01, after the start of the engine, it is determined whether a predetermined set period has elapsed. If the set period has not elapsed, the process proceeds to step 305. On the other hand, when the set period has elapsed, the process proceeds to step 302, and step 302
Also, when it is determined that the engine is under low load, the process proceeds to step 305. In step 305, the exhaust control valve 24
Is almost completely closed.

Next, at step 306, the injection amount of the main fuel Qm predetermined according to the operating state of the engine (FIG. 9)
And X) in FIG. 10 are calculated. Then step 30
At 7, it is determined whether the back pressure P detected by the pressure sensor 80 is lower than a value (P ₀ −α) smaller than the target value P ₀ by a constant value α. When P <P ₀ -α, the routine proceeds to step 308, where a constant value km is added to the correction value ΔQm for the main fuel Qm. On the other hand, when P ≧ P ₀ −α, the routine proceeds to step 309, where the back pressure P becomes a constant value α from the target value P _0.
It is determined whether the value is higher than the value (P ₀ + α). When P> P ₀ + α, the routine proceeds to step 310, where a constant value km is subtracted from the correction value ΔQm.

Next, at step 311, the value obtained by adding ΔQm to Qm is set as the final main fuel injection amount Qmo.
That is, when P <P ₀ −α, the main fuel is increased, and when P> P ₀ + α, the main fuel is reduced,
Whereby the back pressure P is controlled to be _{P 0 -α <P <P 0} + α. Next, at step 312, the auxiliary fuel Qa
Is performed.

FIG. 19 shows an operation control routine when the back pressure is controlled by controlling the auxiliary fuel Qa. Referring to FIG. 19, first, step 4
At 00, it is determined whether or not the engine is being started and the engine is being warmed up. If the engine is not being started and the engine is not warming up, the routine jumps to step 402 to determine whether or not the engine is under a low load. Step 403 when the engine load is not low
Then, the exhaust control valve 24 is fully opened, and then the routine proceeds to step 404, where the 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, if it is determined in step 400 that the engine is being started and the engine is being warmed up, step 4 is executed.
In step 01, after the start of the engine, it is determined whether a predetermined set period has elapsed. If the set period has not elapsed, the process proceeds to step 405. On the other hand, when the set period has elapsed, the process proceeds to step 402, and step 402
Also, when it is determined that the engine is under low load, the process proceeds to step 405. In step 405, the exhaust control valve 24
Is almost completely closed, and then at step 406, injection control of the main fuel Qm is performed. That is, the injection amount of the main fuel Qm is set to X shown in FIG. 9 when the engine is started and the engine is warmed up, and the injection amount of the main fuel Qm is set to X shown in FIG. You.

Next, at step 407, the operating state of the engine
The injection amount of the auxiliary fuel Qa, which is predetermined according to the
Is done. Next, at step 408, the pressure sensor 80
The detected back pressure P is the target value P₀Smaller by a certain value α
Value (P₀−α) is determined. P <
P₀If -α, the routine proceeds to step 409, where the auxiliary fuel Qa
Constant value ka is added to correction value ΔQa for. one
, P ≧ P₀If -α, the process proceeds to step 410
Pressure P is the target value P₀A value larger by a constant value α (P ₀+
α) is determined. P> P₀+ Α
To the step 411, the correction value ΔQa
ka is subtracted.

Next, at step 412, the value obtained by adding ΔQa to Qa is used as the final auxiliary fuel injection amount Qao.
That is, when P <P ₀ −α, the auxiliary fuel is increased, and when P> P ₀ + α, the auxiliary fuel is reduced,
Whereby the back pressure P is controlled to be _{P 0 -α <P <P 0} + α.

FIG. 20 shows an operation control routine when the back pressure is controlled by controlling the intake air amount. Referring to FIG. 20, first, step 5
At 00, it is determined whether or not the engine is being started and the engine is being warmed up. If the engine is not being started and the engine is not warming up, the process jumps to step 502 to determine whether or not the engine is under a low load. Step 503 when the engine load is not low
Then, the exhaust control valve 24 is fully opened, and then the routine proceeds to step 504, where the 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, if it is determined in step 500 that the engine is being started and the engine is being warmed up, step 5 is executed.
In step 01, after the start of the engine, it is determined whether a predetermined set period has elapsed. If the set period has not elapsed, the process proceeds to step 505. On the other hand, when the set period has elapsed, the process proceeds to step 502, and step 502
Also, when it is determined that the engine is in the low load state, the process proceeds to step 505. In step 505, the exhaust control valve 24
Is almost completely closed.

Next, at step 506, a predetermined target opening θ of the throttle valve 18 is calculated according to the operating state of the engine. Next, at step 507, it is determined whether the back pressure P detected by the pressure sensor 80 is lower than a value (P ₀ −α) smaller than the target value P ₀ by a constant value α. When P <the P _0-.alpha. constant value k to the correction value Δθ with respect to the target opening degree θ of the throttle valve 18 proceeds to step 508 is added. On the other hand, when P ≧ P ₀ −α, the routine proceeds to step 509, where the back pressure P becomes a constant value α from the target value P _0.
It is determined whether the value is higher than the value (P ₀ + α). When P> P ₀ + α, the routine proceeds to step 510, where the fixed value k is subtracted from the correction value Δθ.

Next, at step 511, the value obtained by adding Δθ to θ is set as the final target opening θ ₀ of the throttle valve 18. That is, when P <P ₀ −α, the throttle valve 18
Is increased, the intake air amount is increased, and when P> P ₀ + α, the opening amount of the throttle valve 18 is decreased, so that the intake air amount is decreased, whereby the back pressure P is increased. Control is performed such that P ₀ −α <P <P ₀ + α. Next, at step 512, injection control of the main fuel Qm is performed. That is, when the engine is started and the engine is warmed up, the injection amount of the main fuel Qm is changed to X shown in FIG.
When the engine is under a low load, the injection amount of the main fuel Qm is set to X shown in FIG. Next, at step 513, injection control of the auxiliary fuel Qa is performed.

[0097]

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

[Brief description of the drawings]

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

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

FIG. 3 is a diagram showing one embodiment of an exhaust control valve.

FIG. 4 is a diagram showing an injection amount, an injection timing, and an air-fuel ratio.

FIG. 5 is a view showing an injection timing.

FIG. 6 is a diagram showing the concentration of unburned HC.

FIG. 7 is a diagram showing an injection amount of a main fuel.

FIG. 8 is a diagram showing a relationship between an injection amount of a main fuel and an injection amount of a sub fuel.

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

FIG. 10 is a diagram showing a main fuel injection amount and a change in an opening degree of an exhaust control valve.

FIG. 11 is a flowchart for performing operation control.

FIG. 12 is an overall view showing another embodiment of the internal combustion engine.

FIG. 13 is an overall view showing still another embodiment of the internal combustion engine.

FIG. 14 is an overall view showing still another embodiment of the internal combustion engine.

FIG. 15 is a flowchart for performing operation control.

FIG. 16 is an overall view showing still another embodiment of the internal combustion engine.

FIG. 17 is an overall view showing still another embodiment of the internal combustion engine.

FIG. 18 is a flowchart for performing operation control.

FIG. 19 is a flowchart for performing operation control.

FIG. 20 is a flowchart for performing operation control.

[Explanation of symbols]

6 ... Fuel injection valve 22 ... exhaust pipe 24 ... Exhaust control valve

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 41/06 335 F02D 41/06 335Z 43/00 301 43/00 301J 301Z (72) Inventor Toshiaki Tanaka Toyota-cho, Toyota-shi, Aichi Prefecture 1 Toyota Motor Corporation (56) References JP-A-10-238336 (JP, A) JP-A-7-63104 (JP, A) JP-A-10-212995 (JP, A) JP-A-10 JP-A-8-296485 (JP, A) JP-A-49-80414 (JP, A) JP-A-4-111540 (JP, U) JP-A-58-156132 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) F02D 41/00-41/40 F02D 9/00-11/10 F01N 1/00-9/00

Claims (16)

(57) [Claims] An exhaust control valve is disposed in an exhaust passage connected to an outlet of an 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 it is determined that the engine should be closed, the exhaust control valve is almost fully closed, the main fuel injected into the combustion chamber to generate the engine output is burned under excess air, and the auxiliary fuel is also discharged. Additional fuel is injected into the combustion chamber at a predetermined time during an expansion stroke or an exhaust stroke in which the auxiliary fuel can burn, and when the exhaust control valve is almost completely closed, the exhaust control valve is operated under the same engine operating condition. The internal combustion engine in which the injection amount of the main fuel is increased in comparison with the case where the exhaust control valve is fully opened under the same engine operating state so as to approach the generated torque of the engine when the engine is fully opened. Exhaust gas purification device. 2. 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. 3. 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. 4. The method according to claim 1, wherein when it is determined that the amount of unburned HC discharged into the atmosphere should be reduced, the injection amount of the auxiliary fuel is reduced as the injection amount of the main fuel is increased.
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the auxiliary fuel is burned under excess air in addition to the main fuel. 6. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein an air-fuel mixture formed in a limited area in the combustion chamber by the main fuel is ignited by an ignition plug, and then an auxiliary fuel is additionally injected. . 7. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a catalyst is arranged in the engine exhaust passage. 8. The catalyst oxidation catalyst, three-way catalyst, exhaust gas purification system of an internal combustion engine according to claim 7 consisting of _the NO _x absorbent or the HC adsorption catalyst. 9. A method for determining whether or not the temperature of the catalyst is higher than an activation temperature, the method comprising: determining whether the temperature of the catalyst is lower than the activation temperature and warming up the engine while the engine is being warmed up. The exhaust gas purifying apparatus for an internal combustion engine according to claim 7, wherein it is determined that the amount of unburned HC discharged to the engine should be reduced. 10. A device for determining whether or not the catalyst is higher than an activation temperature, wherein the catalyst is discharged to the atmosphere when the catalyst is lower than the activation temperature and the engine is under low load operation. The exhaust gas purifying apparatus for an internal combustion engine according to claim 7, wherein it is determined that the emission amount of unburned HC should be reduced. 11. An exhaust gas purifying apparatus for an internal combustion engine according to claim 7, wherein said catalyst is disposed in an engine exhaust passage upstream of said exhaust control valve. 12. When the amount of unburned HC discharged into the atmosphere is to be reduced, the combustion in the combustion chamber is controlled such that the pressure or temperature of the exhaust gas in the engine exhaust passage upstream of the exhaust control valve becomes a target value. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein 13. The combustion in the combustion chamber by controlling at least one of the main fuel injection amount, the auxiliary fuel injection amount, and the intake air amount.
3. The exhaust gas purification device for an internal combustion engine according to 2. 14. When the pressure or temperature of exhaust gas in the engine exhaust passage upstream of the exhaust control valve is lower than a target value, at least one of the main fuel injection amount, the auxiliary fuel injection amount, and the intake air amount. The exhaust gas purifying apparatus for an internal combustion engine according to claim 13, wherein? 15. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust control valve is switched from a fully open state to a substantially fully closed state when the engine is started. 16. A negative pressure tank for storing a negative pressure, and a negative pressure actuated actuator for driving an exhaust control valve, the actuator being operated by the negative pressure stored in the negative pressure tank. The exhaust gas purifying apparatus for an internal combustion engine according to claim 15, which is provided.