JP3551797B2 - Internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an internal combustion engine.
[0002]
[Prior art]
Conventionally engine, for example, exhaust gas recirculation and engine exhaust passage and the engine intake passage in order to suppress the generation of the NO _x in the diesel engine (hereinafter, referred to as EGR) connected by passage through the EGR passage Exhaust gas, that is, EGR gas, is recirculated into the engine intake passage. In this case, the EGR gas has a relatively high specific heat and can absorb a large amount of heat. Therefore, as the EGR gas amount increases, the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) Increases, the combustion temperature in the combustion chamber decreases. When the combustion temperature is lowered to decrease the generated amount of NO _x, thus the generation amount of the more NO _x to be increased EGR rate is lowered.
[0003]
Thus it may reduce the generation amount of the NO _x if increasing the EGR rate has conventionally been found. However, when the EGR rate is increased, when the EGR rate exceeds a certain limit, the amount of generated soot, that is, smoke starts to increase rapidly. In this regard, it has been conventionally considered that if the EGR rate is further increased, the smoke will increase infinitely. Therefore, the EGR rate at which the smoke starts to increase rapidly is considered to be the maximum allowable limit of the EGR rate. Has been.
[0004]
Therefore, conventionally, the EGR rate is set within a range not exceeding the maximum allowable limit. The maximum allowable EGR rate varies substantially depending on the type of engine and fuel, but is approximately 30 to 50%. Therefore, in the conventional diesel engine, the EGR rate is suppressed to about 30% to 50% at the maximum.
[0005]
Thus the maximum EGR rate than conventional since the allowable limit has been considered to exist determined as NO _x and the amount of smoke produced becomes as small as possible within a range not exceeding the maximum allowable limit with respect to the EGR rate in the conventional Had been. However, this way there is a limit to the EGR rate to decrease of the NO _x and NO _x and the amount of smoke produced be determined so that the amount generated is as small as possible of smoke, the actual NO _x and still a significant amount to At present, smoke is generated.
[0006]
However, if the EGR rate is made larger than the maximum permissible limit in the course of research on the combustion of a diesel engine, the smoke rapidly increases as described above. However, a peak exists in the amount of generated smoke. When the EGR rate is further increased, the smoke starts to decrease sharply, and when the EGR rate is increased to 70% or more during idling operation, and when the EGR gas is strongly cooled, the smoke is reduced to about 55% or more. Becomes zero. That is, it was found that soot was hardly generated. Further, it has been found that the generation amount of the NO _x becomes extremely small in this case. The reason why the soot is not generated based Thereafter this finding study is underway, the results so far no possibility to simultaneously reduce the soot and NO _x new combustion system is had come to be constructed. This new combustion system will be described in detail later, but in short, it is basically based on stopping the growth of hydrocarbons in the middle of the process until the hydrocarbons grow into soot.
[0007]
That is, as a result of repeated experimental research, it has been found that when the temperature of the fuel during combustion in the combustion chamber and the gas temperature around it are below a certain temperature, the growth of hydrocarbons stops at a stage before reaching soot, and the fuel When the temperature of the gas surrounding the gas exceeds a certain temperature, hydrocarbons grow to soot at a stretch. In this case, the temperature of the fuel and the surrounding gas is greatly affected by the heat absorbing action of the gas around the fuel when the fuel is burned, and the amount of heat absorbed by the gas around the fuel is adjusted according to the calorific value at the time of burning the fuel. As a result, the temperature of the fuel and the surrounding gas can be controlled.
[0008]
Therefore, if the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is suppressed to a temperature at which the growth of hydrocarbons stops halfway, soot will not be generated, and the temperature of the fuel and the surrounding gas during combustion in the combustion chamber will be reduced. Can be suppressed below the temperature at which the growth of hydrocarbons stops halfway, by adjusting the amount of heat absorbed by the gas around the fuel. On the other hand, hydrocarbons whose growth has stopped halfway before reaching soot can be easily purified by post-treatment using an oxidation catalyst or the like. This is the basic idea of a new combustion system. An internal combustion engine employing the new combustion system has already been filed by the present applicant (Japanese Patent Application No. 9-305850).
[0009]
[Problems to be solved by the invention]
By the way, in this new combustion system, as described above, hydrocarbons whose growth has stopped halfway before reaching soot are purified by post-treatment using an oxidation catalyst or the like. If the temperature is lower than the purifying temperature, that is, the activation temperature, the hydrocarbon cannot be purified. Therefore, there is a need for a system that can completely purify hydrocarbons.
[0010]
An object of the present invention is to construct a system capable of completely purifying hydrocarbons in a new combustion system.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, in the first invention, as the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and the amount of inert gas supplied into the combustion chamber increases. When the amount of active gas is further increased, the temperature of the fuel during combustion in the combustion chamber and the temperature of the surrounding gas become lower than the temperature at which soot is generated, so that HC in the exhaust gas is adsorbed in the internal combustion engine where almost no soot is generated. The HC adsorbent to be disposed is disposed in the engine exhaust passage.
[0012]
That is, hydrocarbons in the exhaust gas are adsorbed by the HC adsorbent.
According to a second aspect, in the first aspect, there is provided a recirculation device for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage, wherein the inert gas comprises recirculated exhaust gas.
According to a third aspect, in the second aspect, the exhaust gas recirculation rate is approximately 55% or more.
[0013]
In the first aspect according to the fourth aspect, when the air-fuel ratio of the exhaust gas flowing into the lean air-fuel ratio is stoichiometric or rich exhaust gas absorb and flowing the NO _x contained in the exhaust gas the _the NO _x absorbent to release the the absorbed NO _x arranged in the engine exhaust passage.
In the fifth invention to the fourth invention according, wherein _the NO _x absorbent has the function of oxidizing HC in exhaust gas at a predetermined temperature or higher, the temperature of the NO _x absorbent is defined the advance When the temperature is lower than the predetermined temperature, the timing of fuel injection into the combustion chamber is delayed.
[0014]
According to a sixth aspect, in the first aspect, the first combustion in which the amount of inert gas supplied into the combustion chamber is larger than the amount of inert gas at which the generation amount of soot is at a peak and soot is hardly generated, There is provided switching means for selectively switching between the second combustion in which the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas at which the generation amount of soot reaches a peak.
[0015]
According to a seventh aspect, in the sixth aspect, the operating region of the engine is divided into a first operating region on the low load side and a second operating region on the high load side, and the first operating region is divided into the first operating region on the high load side. Combustion is performed, and second combustion is performed in the second operation region.
According to an eighth aspect, in the sixth aspect, when the first adsorbent is to be removed while the first combustion is being performed, the first combustion is switched to the second combustion.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a case where the present invention is applied to a four-stroke compression ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch 11, and the surge tank 12 is connected to a supercharger, for example, an outlet of a compressor 16 of an exhaust turbocharger 15 via an intake duct 13 and an intercooler 14. Be linked. An inlet of the compressor 16 is connected to an air cleaner 18 via an air suction pipe 17, and a throttle valve 20 driven by a step motor 19 is arranged in the air suction pipe 17. A mass flow detector 21 for detecting the mass flow of the intake air is disposed in the air suction pipe 17 upstream of the throttle valve 20.
[0017]
On the other hand, the exhaust port 10 is connected to an inlet of an exhaust turbine 23 of an exhaust turbocharger 15 via an exhaust manifold 22, and an outlet of the exhaust turbine 23 is provided with a catalyst 25 having an oxidizing function via an exhaust pipe 24. Connected to converter 26. An air-fuel ratio sensor 27 is disposed in the exhaust manifold 22.
The exhaust pipe 28 connected to the outlet of the catalytic converter 26 and the air suction pipe 17 downstream of the throttle valve 20 are connected to each other via an exhaust gas recirculation (hereinafter, referred to as EGR) passage 29. An EGR control valve 31 driven by a step motor 30 is disposed. In the EGR passage 29, an intercooler 32 for cooling the EGR gas flowing in the EGR passage 29 is arranged. In the embodiment shown in FIG. 1, the engine cooling water is guided into the intercooler 32, and the engine cooling water cools the EGR gas.
[0018]
On the other hand, the fuel injection valve 6 is connected via a fuel supply pipe 33 to a fuel reservoir, a so-called common rail 34. Fuel is supplied into the common rail 34 from an electric control type variable discharge fuel pump 35, and the fuel supplied into the common rail 34 is supplied to the fuel injection valve 6 through each fuel supply pipe 33. A fuel pressure sensor 36 for detecting the fuel pressure in the common rail 34 is attached to the common rail 34, and the fuel pump 35 is controlled so that the fuel pressure in the common rail 34 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 36. Is controlled.
[0019]
The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41 such as a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45 and an output port 46. Is provided. The output signal of the mass flow detector 21 is input to the input port 45 via the corresponding AD converter 47, and the output signals of the air-fuel ratio sensor 27 and the fuel pressure sensor 36 are also input to the input port via the corresponding AD converter 47, respectively. 45 is input. A load sensor 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. . 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 step motor 19 for controlling the throttle valve, the step motor 30 for controlling the EGR control valve, and the fuel pump 35 via the corresponding drive circuit 48.
[0020]
FIG. 2 shows a change in the output torque when the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening degree and the EGR rate of the throttle valve 20 during the low load operation of the engine, and smoke, HC, CO, represents an experimental example illustrating changes in emissions of NO _x. As can be seen from FIG. 2, in this experimental example, the smaller the air-fuel ratio A / F, the higher the EGR rate. When the air-fuel ratio A / F is smaller than the stoichiometric air-fuel ratio (．14.6), the EGR rate is 65% or more.
[0021]
As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the amount of smoke generated when the EGR rate becomes about 40% and the air-fuel ratio A / F becomes about 30 is reduced. Start growing. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke is sharply reduced. When the EGR rate is increased to 65% or more, and the air-fuel ratio A / F becomes about 15.0, the smoke becomes almost zero. . That is, almost no soot is generated. At this time, the output torque of the engine is slightly reduced and the generation amount of the NO _x becomes considerably lower. On the other hand, at this time, the generation amounts of HC and CO begin to increase.
[0022]
FIG. 3A shows a change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of generated smoke is the largest, and FIG. The graph shows changes in the combustion pressure in the combustion chamber 5 when the amount of generated smoke is almost zero in the vicinity. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), FIG. 3 (B) in which the amount of smoke generation is almost zero is shown in FIG. 3 (A) where the amount of smoke generation is large. It can be seen that the combustion pressure is lower than in the case.
[0023]
The following can be said from the experimental results shown in FIGS. That is, the generation amount of the NO _x, as shown in FIG. 2 when the first air-fuel ratio A / F is approximately the amount of smoke produced at 15.0 below zero in the first drops significantly. That the generation amount of the NO _x produced falls means that the combustion temperature in the combustion chamber 5 is reduced, thus the combustion temperature in the combustion chamber 5 when the soot is hardly generated is lower I can say. The same can be said from FIG. That is, in the state shown in FIG. 3B where almost no soot is generated, the combustion pressure is low, and the combustion temperature in the combustion chamber 5 is low at this time.
[0024]
Second , when the amount of generated smoke, that is, the amount of generated soot becomes almost zero, the amount of HC and CO emissions increases as shown in FIG. This means that hydrocarbons are emitted without growing to soot. That is, the linear hydrocarbon and the aromatic hydrocarbon contained in the fuel as shown in FIG. 4 are thermally decomposed when the temperature is increased in a state of lack of oxygen, so that a precursor of soot is formed. A soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot generation process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. It will grow to soot. Therefore, as described above, when the generation amount of soot becomes almost zero, the emission amounts of HC and CO increase as shown in FIG. 2, but HC at this time is a soot precursor or a hydrocarbon in a state before it. .
[0025]
Summarizing these considerations based on the experimental results shown in FIGS. 2 and 3, when the combustion temperature in the combustion chamber 5 is low, the amount of generated soot becomes almost zero. The hydrocarbon will be discharged from the combustion chamber 5. As a result of further detailed experimental research on this, when the temperature of the fuel and the surrounding gas in the combustion chamber 5 is lower than a certain temperature, the growth process of the soot is stopped halfway, that is, the soot is It was found that no soot was generated, and soot was generated when the temperature of the fuel and its surroundings in the combustion chamber 5 exceeded a certain temperature.
[0026]
By the way, the temperature of the fuel and its surrounding when the process of producing hydrocarbons is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature varies depending on various factors such as the type of fuel, the air-fuel ratio , the compression ratio, and the like. Although not say that how many times has a generation amount and the deep relationship between the certain temperature is nO _x, therefore this certain temperature can be defined to a certain degree from the generation amount of the nO _x . That is, the fuel and the gas temperature surrounding it at the time of combustion and the greater the EGR rate, decreases, the amount of the NO _x is reduced. At this time, the generation amount of NOx is 10 _p . p. When it is less or equal to or less than m, almost no soot is generated. Therefore, at the above-mentioned certain temperature, the generation amount of NOx is 10 _p . p. m The temperature almost coincides with the temperature when the temperature becomes lower or higher.
[0027]
Once soot is produced, it cannot be purified by post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in a state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. This way the hydrocarbon consider post-treatment by the catalyst having an oxidation function is discharged from the combustion chamber 5 at the precursor or its previous state of the soot Luke, or in the form of soot or be discharged from the combustion chamber 5 There is a huge difference. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a soot precursor or previous state without producing soot in the combustion chamber 5 and removes the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function. The catalyst having an oxidation function oxidation catalyst, three-way catalyst, there is _the NO _x absorbent.
[0028]
Now, in order to stop the growth of hydrocarbons before soot is generated, it is necessary to suppress the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 to a temperature lower than the temperature at which soot is generated. There is. In this case, it has been found that the endothermic effect of the gas around the fuel when the fuel is burned has an extremely large effect on suppressing the temperature of the fuel and the gas around the fuel.
[0029]
That is, if there is only air around the fuel, the evaporated fuel immediately reacts with the oxygen in the air and burns. In this case, the temperature of the air separated from the fuel does not rise so much, and only the temperature around the fuel becomes extremely high locally. That is, the air away from the fuel in this case is not performed hardly absorb the heat of combustion of the fuel. In this case, since the combustion temperature locally becomes extremely high, the unburned hydrocarbons that have received the combustion heat will generate soot.
[0030]
On the other hand, when fuel is present in a mixed gas of a large amount of inert gas and a small amount of air, the situation is slightly different. In this case, the fuel vapor diffuses to the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, since the combustion heat is absorbed by the surrounding inert gas, the combustion temperature does not rise so much. That is, the combustion temperature can be kept low. That is, the presence of the inert gas plays an important role in suppressing the combustion temperature, and the combustion temperature can be suppressed low by the endothermic effect of the inert gas.
[0031]
In this case, in order to suppress the temperature of the fuel and the surrounding gas to a temperature lower than the temperature at which the soot is generated, an amount of the inert gas is required to be able to absorb enough heat to do so. Therefore, if the fuel amount increases, the required amount of inert gas increases accordingly. In this case, the larger the specific heat of the inert gas, the stronger the endothermic action, and therefore, the inert gas is preferably a gas having a large specific heat. In this regard, since CO ₂ and EGR gas have relatively large specific heats, it can be said that it is preferable to use EGR gas as the inert gas.
[0032]
FIG. 5 shows the relationship between the EGR rate and the smoke when the EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 5, the curve A shows a case where the EGR gas is cooled strongly and the EGR gas temperature is maintained at approximately 90 ° C., and the curve B shows a case where the EGR gas is cooled by a small cooling device. , Curve C shows the case where the EGR gas is not forcibly cooled.
[0033]
As shown by the curve A in FIG. 5, when the EGR gas is cooled strongly, the amount of soot generation peaks at a point where the EGR rate is slightly lower than 50%. In this case, the EGR rate is increased to approximately 55% or more. Then, almost no soot is generated. On the other hand, as shown by the curve B in FIG. 5, when the EGR gas is slightly cooled, the amount of soot generation peaks at a point where the EGR rate is slightly higher than 50%, and in this case, the EGR rate is increased to about 65% or more. So that almost no soot is generated.
[0034]
As shown by the curve C in FIG. 5, when the EGR gas is not forcibly cooled, the amount of soot generation reaches a peak when the EGR rate is around 55%. Above a percentage, soot is hardly generated. FIG. 5 shows the amount of smoke generated when the engine load is relatively high. When the engine load decreases, the EGR rate at which the amount of soot peaks slightly decreases, and the EGR rate at which almost no soot is generated Also lowers slightly. The lower limit of the EGR rate at which almost no soot is generated varies depending on the degree of cooling of the EGR gas and the engine load.
[0035]
FIG. 6 shows a mixed gas amount of the EGR gas and the air necessary for setting the fuel temperature during combustion and the surrounding gas temperature to a temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas; Further, the ratio of air in the mixed gas amount and the ratio of EGR gas in the mixed gas are shown. In FIG. 6, the vertical axis indicates the total intake gas amount drawn into the combustion chamber 5, and the dashed line Y indicates the total intake gas amount that can be drawn into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis indicates the required load.
[0036]
Referring to FIG. 6, the proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air required to completely burn the injected fuel. That is, in the case shown in FIG. 6, the ratio between the air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 6, the ratio of the EGR gas, that is, the amount of the EGR gas in the mixed gas, is set so that when the injected fuel is burned, the temperature of the fuel and the surrounding gas is lower than the temperature at which the soot is formed. The minimum required EGR gas amount is shown. This EGR gas amount is approximately 55% or more in terms of the EGR rate, and is 70% or more in the embodiment shown in FIG. That is, the total intake gas amount sucked into the combustion chamber 5 is indicated by a solid line X in FIG. 6, and the ratio between the air amount and the EGR gas amount in the total intake gas amount X is as shown in FIG. The temperature of the fuel and the gas around it will be lower than the temperature at which soot is produced, so that no soot is generated. In this case, the amount of generated NOx is 10 _p . p. m longitudinal, or at less, thus the generation amount of the NO _x becomes extremely small.
[0037]
As the amount of fuel injection increases, the amount of heat generated when the fuel burns increases. Therefore, in order to maintain the temperature of the fuel and the surrounding gas at a temperature lower than the temperature at which soot is generated, the amount of heat absorbed by the EGR gas Must be increased. Accordingly, as shown in FIG. 6, the EGR gas amount must be increased as the injected fuel amount increases. That is, the EGR gas amount needs to increase as the required load increases.
[0038]
However the upper limit of the total intake gas amount X sucked into the combustion chamber 5 when supercharging is not being performed is Y, thus the required load 6 is required load becomes large in a region larger than L ₀ Accordingly, the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio unless the EGR gas ratio is reduced. EGR rate decreases as say changing the required load when supercharging is not being performed is required load becomes high when an attempt is made to maintain the air-fuel ratio to the stoichiometric air-fuel ratio in the region greater than L _0, and thus Te required load is not E was maintained at a temperature lower than the temperature at which the fuel and the gas temperature around the soot is generated in a greater area than L _0.
[0039]
However EGR in the region recirculated to the required load EGR gas into the air intake pipe 17 on the inlet side i.e. the exhaust turbocharger 15 via the EGR passage 29 supercharger is larger than L ₀ as shown in FIG. 1 The rate can be maintained at or above 55 percent, such as 70 percent, so that the temperature of the fuel and its surrounding gas can be maintained below the temperature at which soot is produced. That is, if the EGR gas is recirculated so that the EGR rate in the air suction pipe 17 becomes, for example, 70%, the EGR rate of the suction gas boosted by the compressor 16 of the exhaust turbocharger 15 also becomes 70%. The temperature of the fuel and the surrounding gas can be maintained at a temperature lower than the temperature at which soot is generated, to the extent that the pressure can be increased by the compressor 16. Therefore, the operating range of the engine that can generate low-temperature combustion can be expanded. Required load EGR control valve 31 is fully opened is when the EGR rate more than 55 percent in the region larger than L _0, the throttle valve 20 is closed slightly.
[0040]
As described above, FIG. 6 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, even if the air amount is smaller than the air amount shown in FIG. The generation of NOx is reduced to 10 _p . p. m or less, and even if the air amount is larger than the air amount shown in FIG. 6, that is, the average value of the air-fuel ratio is 17 to 18 lean, soot generation is prevented. While the amount of generated NOx is 10 _p . p. m can be around or below.
[0041]
That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excess fuel does not grow to soot, and thus no soot is generated. Further, at this time NO _x even only an extremely small amount of generated. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature is high. Not generated at all. Further, NO _x is also only an extremely small amount of generated.
[0042]
In this way, when low-temperature combustion is being performed, soot is not generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean, generation amount of the NO _x becomes extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time.
[0043]
By the way, the temperature of the fuel and the surrounding gas at the time of combustion in the combustion chamber can be suppressed to a temperature at or below the temperature at which the growth of hydrocarbons stops halfway, only during low load operation in the engine, which generates a relatively small amount of heat by combustion. Therefore, in the embodiment according to the present invention, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas temperature around the same at or below the temperature at which the growth of hydrocarbons stops halfway during the low load operation in the engine. In addition, the second combustion, that is, the combustion that has been performed conventionally, is performed during the high load operation of the engine. Here, the first combustion, that is, the low-temperature combustion, has a larger amount of the inert gas in the combustion chamber than the amount of the inert gas at which the generation amount of soot is a peak, as is apparent from the description so far, and almost all the soot is generated. The second combustion, that is, the combustion that has been conventionally performed, is the combustion in which the amount of the inert gas in the combustion chamber is smaller than the amount of the inert gas at which the soot generation peaks. Say
[0044]
FIG. 7 shows a first operation region I in which first combustion, that is, low-temperature combustion is performed, and a second operation region II in which second combustion, that is, combustion by a conventional combustion method, is performed. In FIG. 7, the vertical axis L indicates the amount of depression of the accelerator pedal 50, that is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 7, X (N) indicates a first boundary between the first operation region I and the second operation region II, and Y (N) indicates the first operation region I and the second operation region. The second boundary with the area II is shown. The determination of the change of the operation region from the first operation region I to the second operation region II is made based on the first boundary X (N), and the change from the second operation region II to the first operation region I is performed. The determination of the change of the operating region is performed based on the second boundary Y (N).
[0045]
That is, if the required load L exceeds a first boundary X (N), which is a function of the engine speed N, when the operating state of the engine is in the first operating region I and low-temperature combustion is being performed, the operating region Is shifted to the second operation region II, and combustion is performed by the conventional combustion method. Next, when the required load L becomes lower than a second boundary Y (N) which is a function of the engine speed N, it is determined that the operation region has shifted to the first operation region I, and low-temperature combustion is performed again.
[0046]
The two boundaries of the first boundary X (N) and the second boundary Y (N) on the lower load side than the first boundary X (N) are provided for the following two reasons. . The first reason is that the combustion temperature is relatively high on the high load side of the second operation region II, and even if the required load L becomes lower than the first boundary X (N), low-temperature combustion cannot be performed immediately. Because. That is, the low-temperature combustion does not immediately start unless the required load L becomes considerably low, that is, when the required load L becomes lower than the second boundary Y (N). The second reason is that hysteresis is provided for a change in the operation range between the first operation range I and the second operation range II.
[0047]
By the way, when the operation region of the engine is in the first operation region I and low-temperature combustion is being performed, soot is hardly generated, and instead, unburned hydrocarbons are in the form of a precursor of soot or a state before it. It is discharged from the combustion chamber 5. At this time, unburned hydrocarbons discharged from the combustion chamber 5 are collected by a particulate filter 53 described later in detail.
FIG. 8 shows the output of the air-fuel ratio sensor 27. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 27 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 27.
[0048]
Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG.
FIG. 9 shows the opening degree of the throttle valve 20, the opening degree of the EGR control valve 31, the EGR rate, the air-fuel ratio, the injection timing, and the injection amount with respect to the required load L. As shown in FIG. 9, in the first operating region I where the required load L is low, the opening of the throttle valve 20 is gradually increased from almost fully closed to about 2/3 as the required load L increases. The opening degree of the EGR control valve 31 is gradually increased from near full closure to full opening as the required load L increases. In the example shown in FIG. 9, in the first operation region I, the EGR rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.
[0049]
In other words, in the first operating region I, the opening of the throttle valve 20 and the opening of the EGR control valve 31 are controlled such that the EGR rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS is delayed as the required load L is increased, and the injection completion timing θE is delayed as the injection start timing θS is delayed.
[0050]
At the time of idling operation, the throttle valve 20 is closed to almost fully closed, and at this time, the EGR control valve 31 is also closed to almost fully closed. When the throttle valve 20 is closed close to the fully closed state, the pressure in the combustion chamber 5 at the start of compression decreases, so that the compression pressure decreases. When the compression pressure decreases, the compression work by the piston 4 decreases, so that the vibration of the engine body 1 decreases. That is, at the time of idling operation, the throttle valve 20 is closed to almost fully closed in order to suppress the vibration of the engine body 1.
[0051]
On the other hand, when the operating region of the engine changes from the first operating region I to the second operating region II, the opening of the throttle valve 20 is increased stepwise from about 2/3 opening toward the full opening direction. At this time, in the example shown in FIG. 9, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. That is, since the EGR rate jumps over the EGR rate range (FIG. 5) in which a large amount of smoke is generated, a large amount of smoke is generated when the engine operating region changes from the first operating region I to the second operating region II. There is no.
[0052]
In the second operation region II, the conventional combustion is performed. In the second operation region II, the throttle valve 20 is held in a fully open state except for a part, and the opening degree of the EGR control valve 31 is gradually reduced as the required load L increases. In this operating region II, the EGR rate decreases as the required load L increases, and the air-fuel ratio decreases as the required load L increases. However, the air-fuel ratio is a lean air-fuel ratio even when the required load L increases. In the second operation region II, the injection start timing θS is set near the compression top dead center TDC.
[0053]
FIG. 10A shows the target air-fuel ratio A / F in the first operation region I. In FIG. 10 (A), curves indicated by A / F = 15.5, A / F = 16, A / F = 17, and A / F = 18 have target air-fuel ratios of 15.5, 16, and 17, respectively. , 18 and the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 10A, the air-fuel ratio is lean in the first operation region I, and the target air-fuel ratio A / F is made leaner as the required load L decreases in the first operation region I. You.
That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, as the required load L decreases, low-temperature combustion can be performed even if the EGR rate is reduced. When the EGR rate is decreased, the air-fuel ratio increases. Therefore, as shown in FIG. 10A, as the required load L decreases, the target air-fuel ratio A / F increases. As the target air-fuel ratio A / F increases, the fuel consumption rate increases. Therefore, in order to make the air-fuel ratio as lean as possible, in the embodiment according to the present invention, the target air-fuel ratio A / F increases as the required load L decreases. .
[0054]
The target air-fuel ratio A / F shown in FIG. 10A is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 10B. . In addition, as shown in FIG. 11A, the target opening ST of the throttle valve 20 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening degree SE of the EGR control valve 31 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 10A is stored in advance in the ROM 42 in the form of a map as a function of N. As shown in FIG. 11 (B), it is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N.
[0055]
Further, when the first combustion is being performed, the fuel injection amount Q is calculated based on the required load L and the engine speed N. The fuel injection amount Q is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.
FIG. 13A shows the target air-fuel ratio A / F when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 13A, curves A / F = 24, A / F = 35, A / F = 45, and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. ing. The target air-fuel ratio A / F shown in FIG. 13A is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 13B. Further, as shown in FIG. 14A, the target opening ST of the throttle valve 20 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening degree SE of the EGR control valve 31 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 13A is stored in the ROM 42 in advance in the form of a map as a function of N. As shown in FIG. 14 (B), a map is stored in the ROM 42 in advance as a function of the required load L and the engine speed N.
[0056]
Further, when the second combustion is being performed, the fuel injection amount Q is calculated based on the required load L and the engine speed N. The fuel injection amount Q is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.
Incidentally, an HC adsorbent 53 for adsorbing unburned hydrocarbons (HC) contained in the exhaust gas is disposed in the exhaust pipe 24. HC adsorbent 53 can absorb HC in _the NO _x absorbent is the temperature that can leave absorbing the NO _x, i.e. less than the activation temperature the temperature to be described later.
[0057]
On the other hand, NO _x absorbent 25 is disposed in the casing 26 in FIG. 1. _The NO _x absorbent 25, for example alumina as a carrier, the carrier on, for example potassium K, sodium Na, lithium Li, alkaline earth such as alkali metal, barium Ba, calcium Ca, such as cesium Cs, lanthanum La, yttrium At least one selected from rare earths such as Y and a noble metal such as platinum Pt are supported. Engine intake passage, NO of Toko called air-fuel ratio of exhaust gas flowing the ratio of the combustion chamber 5 and _the NO _x absorbent 25 upstream of the exhaust passage supplying air and fuel into the (hydrocarbon) to _the NO _x absorbent 25 _x absorbent 25 absorbs the NO _x when the air-fuel ratio of the inflowing exhaust gas is lean, perform absorption and release action of the NO _x that releases NO _x the air-fuel ratio is absorbed and becomes the stoichiometric air-fuel ratio or rich of the inflowing exhaust gas .
[0058]
_The NO _x absorbent 25 be disposed the _the NO _x absorbent 25 in the engine exhaust passage is performing absorption and release action of actually NO _x are also part not clear detailed mechanism of action out this absorbing and releasing. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.
[0059]
In the compression ignition type internal combustion engine shown in FIG. 1, combustion is performed in a state where the air-fuel ratio in the normal combustion chamber 5 is lean. Thus when the air-fuel ratio is performed is combusted in a lean state oxygen concentration in the exhaust gas is high, these oxygen O ₂ as is shown in FIG. 16 (A) at this time O ₂ ^- or O It adheres to the surface of platinum Pt in the form of ^2- . On the other hand, NO in the inflowing exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of the platinum Pt to become NO ₂ (2NO + O ₂ → 2NO ₂ ). Next, a part of the produced NO ₂ is absorbed in the absorbent while being oxidized on the platinum Pt, and is absorbed in the form of nitrate ion NO ₃ ⁻ as shown in FIG. 16A while being combined with barium oxide BaO. Diffuses into agent. In this way, NO _x is absorbed in the NO _x absorbent 25. As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and as long as the NO _x absorption capacity of the absorbent is not saturated, NO ₂ is absorbed in the absorbent and nitrate ions NO ₃ ⁻ are generated. You.
[0060]
On the other hand, the air-fuel ratio of the inflowing exhaust gas is lowered the oxygen concentration of the inflow exhaust gas is made rich, so that the amount of NO ₂ on the surface of the platinum Pt is lowered. When the production amount of NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ion NO ₃ ⁻ in the absorbent is released from the absorbent in the form of NO ₂ . In this case _the NO _x absorbent NO _x released from 25 large amount of unburned HC contained in the inflowing exhaust gas as shown in FIG. 16 (B), it is caused to reduction by reaction with CO. In this way, when NO ₂ is no longer present on the surface of the platinum Pt, NO ₂ is released from the absorbent one after another. Thus the air-fuel ratio of the inflowing exhaust gas is NO _x is released from _the NO _x absorbent 25 in a short time when it is rich, yet NO _x is discharged into the atmosphere to the released NO _x is reduced It will not be done.
[0061]
In this case, NO _x is released from the NO _x absorbent 25 even if the air-fuel ratio of the inflowing exhaust gas the stoichiometric air-fuel ratio. However to release all NO _x absorbed in _the NO _x absorbent 25 to NO _x from the NO _x absorbent 25 is not only released gradually when the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio It takes a little longer time.
[0062]
_The NO _x absorbent 25 as described above includes a noble metal such as platinum Pt, thus _the NO _x absorbent 25 has an oxidizing function. On the other hand, as described above, when the operating state of the engine is in the first operating region I and low-temperature combustion is being performed, soot is hardly generated, and instead, the unburned hydrocarbon is a precursor of soot or a former soot. It is discharged from the combustion chamber 5 in the form of a state. But as described above _the NO _x absorbent 25 is the temperature at which the temperature reaches a predetermined, that is, when it is the activation temperature or more has an oxidation function, the thus when the temperature of the NO _x absorbent 25 is higher than the activation temperature combustion unburned hydrocarbon discharged from the chamber 5 will be caused to favorably oxidized by _the NO _x absorbent 25. However small the required load such as during idling a time of engine startup, lower than its activity temperature the temperature of the NO _x absorbent 25 when this even when preferably the low temperature combustion is performed, unburnt hydrocarbons Cannot be purified. However HC adsorbent 53 disposed on the upstream side of the NO _x absorbent 25 can be the temperature of adsorbing unburned hydrocarbons even when the activation temperature below _the NO _x absorbent 25. That HC adsorbent 53 to a temperature of the NO _x absorbent 25 becomes equal to or higher than its activation temperature can be kept by adsorbing unburned hydrocarbons. Therefore the unburned hydrocarbons be performed low temperature combustion when the temperature of the NO _x absorbent 25 is lower than its activation temperature as the engine during startup according to the present invention flows out from the NO _x absorbent 25 to downstream Absent. The unburned hydrocarbons adsorbed on the HC adsorbent 53 are oxygen contained in a large amount in the exhaust gas when the first combustion, that is, the low-temperature combustion is switched to the second combustion, that is, the normal combustion. And is removed from the HC adsorbent 53.
[0063]
Meanwhile the absorption of NO _x capacity of the NO _x absorbent 25 is limited, absorption of NO _x capacity of the NO _x absorbent 25 needs to release the NO _x from the NO _x absorbent 25 before saturation. For this purpose it is necessary to estimate the amount of NO _x is absorbed in the NO _x absorbent 25. Therefore, in this embodiment of the present invention of a map as shown in FIG. 17 (A) as a function of the NO _x absorption amount A of the required load L and engine speed N per unit time when it is performed first combustion is previously obtained in the form of a map as shown in FIG. 17 (B) the absorption of NO _x amount B per unit time as a function of the required load L and engine speed N when the second combustion is being performed It is previously obtained in the form, per these unit time of absorption of NO _x amount a, so that to estimate the amount of NO _x ΣNOX being absorbed in the NO _x absorbent 25 by integrating the B.
[0064]
In the embodiment according to the present invention so that to release the NO _x from the NO _x absorbent 25 when exceeding the allowable maximum value that this absorption of NO _x amount ΣNOX has predetermined. Next, this will be described with reference to FIG.
Referring to FIG. 18, in the embodiment according to the present invention, two allowable maximum values, that is, an allowable maximum value MAX1 and an allowable maximum value MAX2 are set. Maximum allowable value MAX1 is the 30% of the maximum absorption of NO _x amount _the NO _x absorbent 25 can absorb, the allowable maximum value MAX2 is 80 percent of the maximum amount of absorption _the NO _x absorbent 25 can absorb Have been. The air-fuel ratio in order to release the NO _x from the NO _x absorbent 25 when the absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX1 When the first combustion is being performed is rich, the second combustion row air-fuel ratio is rich so as to release the NO _x from the NO _x absorbent 25 when it is switched to the first combustion from the second combustion when the absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX1 when that we is a, added late or during the exhaust stroke of the expansion stroke so as to release the NO _x from the NO _x absorbent 25 when the absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX2 when the second combustion is being performed Of fuel is injected.
[0065]
That is, in FIG. 18, the period X shows a case where the required load L is lower than the first boundary X (N) and the first combustion is performed, and at this time, the air-fuel ratio is slightly smaller than the stoichiometric air-fuel ratio. It has a lean air-fuel ratio. Very little occurrence amount of the NO _x when the first combustion is being performed, thus absorption of NO _x amount ΣNOX as is shown in Figure 18 at this time rises very slowly. Air-fuel ratio A / F when the absorption of NO _x amount ΣNOX exceeds the allowable maximum value MAX1 When the first combustion is being performed is temporarily rich, NO _x is released thereby from _the NO _x absorbent 25 You. The time of absorption of NO _x amount ΣNOX is set to zero.
[0066]
As described above, when the first combustion is performed, no soot is generated regardless of whether the air-fuel ratio is lean, the stoichiometric air-fuel ratio, or rich, and therefore, when the first combustion is performed. does not soot generated at this time also the air-fuel ratio a / F in order to release the nO _x from the nO _x absorbent 25 is made rich to.
Then the required load L at time t ₁ is switched from the first combustion exceeds the first boundary X (N) to the second combustion. As shown in FIG. 18, when the second combustion is being performed, the air-fuel ratio A / F becomes considerably lean. When the second combustion is being performed _the amount of NO _x ΣNOX when the generation amount of the NO _x as compared with the case where the first combustion is being performed is large and therefore the second combustion is being performed relatively quickly To rise.
[0067]
If the air-fuel ratio A / F is made rich while the second combustion is being performed, a large amount of soot is generated. Therefore, it is difficult to make the air-fuel ratio A / F rich when the second combustion is being performed. Can not. Thus the air-fuel ratio in order to release the NO _x from _the NO _x absorbent 25 as the second of the NO _x absorption amount ΣNOX when combustion is being performed has exceeded the allowable maximum value MAX1, as shown in FIG. 18 A / F is not made rich. The required load L as at time t ₂ in FIG. 18 when the _the NO _x absorbent when is switched from the second combustion is lower in the first combustion than the second boundary Y (N) 25 air-fuel ratio a / F in order to release the NO _x is rich temporarily from.
[0068]
Then from the first combustion is switched to the second combustion at the time t ₃ in FIG. 18, the second combustion during interim pleasure continues. The time of absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX1, then in the second half or the exhaust stroke of the expansion stroke so as to release the NO _x assuming that exceeds the allowable maximum value MAX2 at time _{t 4} at this time from _the NO _x absorbent 25 additional fuel is injected, the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent 25 is made rich.
[0069]
The additional fuel injected during the second half of the expansion stroke or during the exhaust stroke does not contribute to the generation of engine power, so it is preferable to inject additional fuel as little as possible. Thus when the absorption of NO _x amount ΣNOX when the second combustion is performed has exceeded the allowable maximum value MAX1 is temporarily rich air-fuel ratio A / F when it is switched to the first combustion from the second combustion to, so that to inject additional fuel only if special where absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX2.
[0070]
Figure 19 shows the processing routine for _the NO _x releasing flag which is set when releasing the NO _x from the NO _x absorbent 25, this routine is executed by interruption every predetermined time.
Referring to FIG. 19, first, at step 100, it is determined whether or not a flag I indicating that the operation region of the engine is the first operation region I is set. When the flag I is set, that the operating region of the engine absorption of NO _x amount A per unit time from the map shown in FIG. 17 (A) is calculated proceeds to step 101 when a first operating region I You. Then A is added to the absorption of NO _x amount ΣNOX step 102. Next, at step 103 NO _x absorption amount ΣNOX whether exceeds the allowable maximum value MAX1 is determined. Becomes the .SIGMA.NOX> MAX1 proceeds to step 104, NO _x releasing flag 1 indicating that it should release the NO _x is set when the first combustion is being performed.
[0071]
On the other hand, when it is determined in step 100 that the flag I has been reset, that is, when the operating region of the engine is in the second operating region II, the routine proceeds to step 106, and the unit time per unit time is obtained from the map shown in FIG. absorption B is calculated for NO _x. Then B is added to the absorption of NO _x amount ΣNOX step 107. Next, at step 108 NO _x absorption amount ΣNOX whether exceeds the allowable maximum value MAX1 is determined. .SIGMA.NOX> proceeds to become the step 109 to MAX1, NO _x releasing flag 1 indicating that it should release the NO _x is set when it is switched from the second combustion to the first combustion.
[0072]
In step 110, whether absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX2 is determined. .SIGMA.NOX> becomes the MAX2 proceeds to step 111, it is a set _the NO _x releasing flag 2 indicating that it should release the second half or NO _x in the exhaust stroke of the expansion stroke.
Further, the amount of HC that can be adsorbed by the HC adsorbent 53 is limited. Therefore, in the embodiment according to the present invention, the HC adsorption amount C per unit time when the first combustion is performed is a function of the required load L and the engine speed N in the form of a map as shown in FIG. The HC adsorption amount D per unit time during the second combustion is calculated as a function of the required load L and the engine speed N in the form of a map as shown in FIG. The amount of HC adsorbed on the HC adsorbent 53 is estimated by integrating the HC adsorbed amounts C and D per unit time in advance.
[0073]
In the embodiment of the present invention, when the amount of HC adsorbed by the HC adsorbent 53 exceeds the maximum value during the first combustion, the first combustion is performed to remove HC from the HC adsorbent 53 by the second combustion. Switch to combustion. In the second combustion, the exhaust gas having a considerably lean air-fuel ratio flows into the HC adsorbent 53. Therefore, the HC adsorbed on the HC adsorbent 53 reacts with the excess oxygen in the exhaust gas and is removed from the HC adsorbent 53.
[0074]
FIG. 21 shows a routine for processing an HC flag which is set when HC is to be removed from the HC adsorbent 53. This routine is executed by interruption every predetermined time.
Referring to FIG. 21, first, at step 200, it is determined whether or not a flag I indicating that the operation region of the engine is the first operation region I is set. When the flag I is set, that is, when the operation region of the engine is the first operation region I, the routine proceeds to step 201, where the HC adsorption amount C per unit time is calculated from the map shown in FIG. . Next, at step 202, C is added to the HC adsorption amount ΣHC. Next, at step 203, it is determined whether or not the HC adsorption amount ΣHC has exceeded the allowable maximum value MAX. If ΣHC> MAX, the routine proceeds to step 104, where processing for setting the HC flag is performed.
[0075]
On the other hand, when it is determined in step 200 that the flag I has been reset, that is, when the operating region of the engine is the second operating region II, the routine proceeds to step 206, where the map per unit time is obtained from the map shown in FIG. Is calculated. Next, at step 207, D is added to the HC adsorption amount ΣHC. Next, at step 208, it is determined whether or not the HC adsorption amount ΣHC has exceeded the allowable maximum value MAX. If ΣHC> MAX, the routine proceeds to step 209, where processing for setting the HC flag is performed.
[0076]
Meanwhile the temperature sensor 54 for detecting the temperature of the exhaust gas is attached to the exhaust passage 24 between the HC adsorbent 53 and _the NO _x absorbent 25. Estimating the temperature of the NO _x absorbent 25 from the temperature of the exhaust gas detected by the temperature sensor 54 in the present embodiment, the temperature at the be an exhaust gas temperature of the NO _x absorbent 25 is lower than its activation temperature is relatively low when the low temperature combustion is being performed, controls the operation of the engine so as to raise the temperature of the NO _x absorbent 25. That is, the timing of injecting fuel into the fuel chamber is delayed. Thus high temperature of the exhaust gas, the temperature of the NO _x absorbent 25 is raised.
[0077]
Next, the operation control will be described with reference to FIGS.
Referring to FIG. 22, first, in step 300, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 301, where it is determined whether or not the required load L has become larger than the first boundary X1 (N). Is done. When L ≦ X1 (N), the process proceeds to step 302a.
[0078]
Temperature at which the temperature T is a predetermined in step 302a _the NO _x absorbent 25, that _the NO _x absorbent 25 whether higher than the temperature _{T x} which can be performed absorbing and releasing of the NO _x is determined. When a T> _{T x} at step 302a the low temperature combustion is performed proceeds to step 303.
That is, in step 303, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 11A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 304, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 11B, and the opening of the EGR control valve 31 is set as the target opening SE. Next, at step 305 NO _x releasing flag 1 is whether it is set or not. Fuel injection quantity Q calculated from the map of FIG. 12 so that the air-fuel ratio shown in FIG. 10 proceeds to step 306 is performed when _the NO _x releasing flag 1 is not set. At this time, low-temperature combustion is performed under a lean air-fuel ratio.
[0079]
Meanwhile, the amount of addition of incremental Qa calculated from the map of FIG. 24 to the amount Q calculated from the map of FIG. 12 proceeds to step 307 when _the NO _x releasing flag 1 is judged as being set in step 305 Is performed, and injection control for enriching the average air-fuel ratio in the combustion chamber 5 is performed, and ΣNOX is made zero in step 307a. In this case NO _x is released from the NO _x absorbent 25.
[0080]
On the other hand, whether the HC flag is set is determined the routine proceeds to step 302b when a T ≦ T _X in step 302a. When it is determined in step 302b that the HC flag has been reset, the routine proceeds to step 302c, where low-temperature combustion is performed. That is, in step 302c, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 11A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 302d, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 11B, and the opening of the EGR control valve 31 is set as the target opening SE. Next, at step 302e, the valve opening timing SI of the fuel injection valve 6 is corrected and delayed. Next, at step 302f, the fuel injection of the amount Q calculated from the map of FIG. 12 is performed so that the air-fuel ratio shown in FIG. 10 is obtained.
[0081]
On the other hand, when it is determined that that L> X (N) in step 3 01 flag I is reset routine proceeds to step 3 02, then the second combustion is performed proceeds to step 310, HC flag in step 302b When it is determined that is set, the routine also proceeds to step 310, where the second combustion is performed. That is, in step 310, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 14A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 311, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 14B, and the opening of the EGR control valve 31 is set to the target opening SE. Then whether _the NO _x releasing flag 2 in step 312 is set or not. Fuel injection quantity Q calculated from the map of FIG. 15 so that the air-fuel ratio shown in FIG. 13 proceeds to step 313 is performed when _the NO _x releasing flag 2 has not been set. At this time, the second combustion is performed under the lean air-fuel ratio.
[0082]
On the other hand, when the _the NO _x releasing flag 2 in step 312 is determined to have been set is performed fuel injection quantity Q calculated from the map of FIG. 15 proceeds to step 314, the expansion stroke of the engine late or exhaust stroke injecting additional fuel into the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent 25 is injected controlled to be richer, thereby _the NO _x absorbent 25 from the NO _x is released. Next, at step 315, ΣNOX is made zero, and at step 316, ΣHC is made zero.
[0083]
When the flag I is reset, in the next processing cycle, the process proceeds from step 300 to step 308, where it is determined whether the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), the process proceeds to step 302a.
On the other hand, when it is determined in step 308 that L <Y (N), the routine proceeds to step 309, where the flag I is set. Next, the routine proceeds to step 302a.
[0084]
【The invention's effect】
According to the first to seventh aspects, HC released from the internal combustion engine is adsorbed by the HC adsorbent, so that HC is not released to the atmosphere.
Further fifth when below the temperature at which the temperature reaches a predetermined of the NO _x absorbent according to the invention HC is never HC to be adsorbed by the HC adsorbent flows out into the atmosphere, further injection timing of fuel at this time the early increase the temperature of the NO _x absorbent is delayed, the amount of HC temperature of the NO _x absorbent is adsorbed on the HC adsorbent if higher than the predetermined temperature even beyond its total capacity , HC is purified by _the NO _x absorbent. That HC discharged from the internal combustion engine when the temperature of the exhaust gas as immediately after engine startup is low is adsorbed by the HC adsorbent, the activation temperature the temperature of the NO _x absorbent is when gradually the temperature of the exhaust gas is increased since excess amount HC that if adsorbed on the HC adsorbent even exceeds the allowable amount, HC flowing out from the HC adsorbent is purified by _the NO _x absorbent. Therefore always regardless of the temperature of the HC adsorbent and _the NO _x absorbent can be prevented from flowing out to the atmosphere of the HC.
[Brief description of the drawings]
FIG. 1 is an overall view of a compression ignition type internal combustion engine.
2 is a diagram showing a generation amount of the smoke and NO _x.
FIG. 3 is a diagram showing a combustion pressure.
FIG. 4 is a diagram showing fuel molecules.
FIG. 5 is a diagram showing a relationship between a generation amount of smoke and an EGR rate.
FIG. 6 is a diagram showing a relationship between an injected fuel amount and a mixed gas amount.
FIG. 7 is a diagram showing a first operation region I and a second operation region II.
FIG. 8 is a diagram showing an output of an air-fuel ratio sensor.
FIG. 9 is a diagram showing an opening degree of a throttle valve and the like.
FIG. 10 is a diagram showing an air-fuel ratio and the like in a first operation region I.
FIG. 11 is a diagram showing a map of a target opening degree of a throttle valve and the like.
FIG. 12 is a diagram showing a map of a fuel injection amount.
FIG. 13 is a diagram showing an air-fuel ratio and the like in a second operation region.
FIG. 14 is a view showing a map of a target opening degree of a throttle valve and the like.
FIG. 15 is a diagram showing a map of a fuel injection amount.
16 is a diagram for explaining the absorbing and releasing action of NO _x.
17 is a diagram showing a map of the NO _x absorption amount per unit time.
18 is a diagram for explaining _the NO _x releasing control.
19 is a flowchart for processing _the NO _x releasing flag.
FIG. 20 is a diagram showing a map of the amount of HC adsorption per unit time.
FIG. 21 is a flowchart for processing an HC flag.
FIG. 22 is a part of a flowchart for controlling operation of the engine.
FIG. 23 is a part of a flowchart for controlling operation of the engine.
FIG. 24 is a view showing a map of an increment of an injected fuel amount in the first combustion.
[Explanation of symbols]
6 Fuel injection valve 15 Exhaust turbocharger 20 Throttle valve 29 EGR passage 31 EGR control valve

Claims (8)

As the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak. As the amount of inert gas supplied into the combustion chamber further increases, combustion in the combustion chamber increases. Internal combustion engine in which an HC adsorbent for adsorbing HC in exhaust gas is disposed in an engine exhaust passage in an internal combustion engine in which the temperature of the fuel at that time and the gas temperature around it become lower than the soot generation temperature and soot is hardly generated . 2. The internal combustion engine according to claim 1, further comprising a recirculation device for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage, wherein the inert gas comprises recirculated exhaust gas. 3. The internal combustion engine of claim 2, wherein the exhaust gas recirculation rate is greater than or equal to approximately 55 percent. The _the NO _x absorbent air-fuel ratio of the inflowing exhaust gas to release the NO _x when the air-fuel ratio of the exhaust gas absorb and flowing the NO _x contained in the exhaust gas is absorbed and becomes the stoichiometric air-fuel ratio or rich when the lean The internal combustion engine according to claim 1, wherein the internal combustion engine is disposed in the engine exhaust passage. Wherein _the NO _x absorbent has the function to oxidize HC in the exhaust gas at a predetermined temperature or higher, when the temperature of the NO _x absorbent is lower than the predetermined temperature is fuel injection timing into the combustion chamber The internal combustion engine according to claim 4, wherein the internal combustion engine is delayed. The first combustion in which the amount of inert gas supplied into the combustion chamber is larger than the amount of inert gas at which the generation amount of soot is peak and the soot is hardly generated, and the amount of inert gas at which the generation amount of soot peaks is 2. The internal combustion engine according to claim 1, further comprising a switching means for selectively switching between the second combustion and a small amount of inert gas supplied into the combustion chamber. The operating region of the engine is divided into a first operating region on the low load side and a second operating region on the high load side, and a first combustion is performed in the first operating region, and a second combustion is performed in the second operating region. 7. The internal combustion engine according to claim 6, wherein combustion is performed. 7. The internal combustion engine according to claim 6, wherein the first combustion is switched to the second combustion when the HC adsorbed on the HC adsorbent is to be removed during the first combustion.

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