JP3551790B2 - 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, in an internal combustion engine, for example, a diesel engine, NO_xThe engine exhaust passage and the engine intake passage are connected by an exhaust gas recirculation (hereinafter, referred to as EGR) passage in order to suppress the generation of the exhaust gas, that is, the exhaust gas, that is, the EGR gas is introduced into the engine intake passage through the EGR passage. I try to recirculate. 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. NO when combustion temperature drops_xThe more the EGR rate increases, the lower the NO_xWill decrease.
[0003]
If the EGR rate is increased as compared with the conventional case, NO_xIt has been known that the amount of generation of phenol can be reduced. 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]
As described above, conventionally, it has been considered that the maximum allowable limit exists for the EGR rate. Therefore, the EGR rate is conventionally set to a value within the range not exceeding the maximum allowable limit._xAnd the amount of smoke generated was determined to be as small as possible. However, in this way, the EGR rate is set to NO._xNO even if the amount of smoke generated is minimized_xAnd the reduction in the amount of smoke generated is limited, and in practice, a considerable amount of NO_xAt 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 increases sharply 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 cooled strongly, the smoke is reduced to about 55% or more. Becomes zero. That is, it was found that soot was hardly generated. In this case, NO_xIt has also been found that the amount of generation is extremely small. After that, based on this finding, the reason why soot was not generated was examined, and as a result, soot and NO_xThis has led to the construction of a new combustion system that can simultaneously reduce the combustion. 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, the EGR rate needs to be approximately 55% or more. However, the EGR rate can be increased to about 55% or more when the intake air amount is relatively small, that is, when the engine load is relatively low. If the intake air amount exceeds a certain limit, the intake air will be reduced unless the EGR rate is reduced. The amount of air cannot be increased. Therefore, when the amount of intake air exceeds a certain limit, it is necessary to switch to the conventional combustion.
[0010]
If the combustion is switched to the conventional combustion, the engine_xIs released to some extent. Further, under the conventional combustion, combustion is performed under excess air. Therefore, in the above internal combustion engine, when the air-fuel ratio of the inflowing exhaust gas is lean, NO contained in the exhaust gas_xAnd the NO absorbed when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich._xReleases NO_xThe absorbent is disposed in the engine exhaust passage, and NO_xIs prevented from being released to the atmosphere.
[0011]
NO in the above internal combustion engine_xIs to be released and reduced, the air-fuel ratio is made rich under fresh combustion, and NO_xWhen the air-fuel ratio of the exhaust gas flowing into the absorbent is made rich, NO_xIs released and reduced. Since the new combustion is performed at the stoichiometric air-fuel ratio or slightly lean, the amount of fuel to be increased in order to make the air-fuel ratio rich is very small.
[0012]
By the way, NO_xNO absorbed by the absorbent_xNO to estimate absorption_xAbsorbent NO_xNO indicating absorption amount_xAn absorption amount counter is provided, and when the engine is operated at a lean air-fuel ratio, the NO_xA predetermined addition amount determined according to the operating state of the engine is added to the absorption amount counter, and when the engine is operated at a rich or stoichiometric air-fuel ratio, the above NO is determined according to the operating time._xThere is known an internal combustion engine configured to decrease the value of an absorption counter.
[0013]
That is, during the operation of the engine, the amount of NO from the engine corresponding to the engine operating conditions such as the load and the number of revolutions is increased._xOccurs when the engine is operated at a lean air-fuel ratio (that is, NO_xWhen the air-fuel ratio of the exhaust gas flowing into the absorbent is lean), the generated NO_xA certain percentage of the amount is NO_xNO is absorbed by the absorbent_xNO absorbed in the absorbent_xIs the NO of the institution_xIt increases according to the amount of generation. When the engine is operated at a rich or stoichiometric air-fuel ratio, NO_xNO from absorbent_xIs released, so NO_xNO absorbed in the absorbent_xDecreases as the engine is operated at rich or stoichiometric. In this internal combustion engine, when the operating air-fuel ratio is a lean air-fuel ratio, a predetermined amount is added at regular intervals, and when the engine operating air-fuel ratio is a rich or stoichiometric air-fuel ratio, the predetermined amount is subtracted according to the operating time. NO_xNO by providing an absorption counter_xAbsorbent NO_xThe amount of absorption is estimated.
[0014]
[Problems to be solved by the invention]
However, when the engine is operated at a rich or stoichiometric air-fuel ratio as in the above-described apparatus, the NO_xIf the value of the absorption amount counter of the absorbent is decreased, NO_xNO absorbed by absorbent_xQuantity and NO_xThere is a problem that an error occurs between the value of the absorption counter and the value of the absorption counter.
[0015]
That is, NO per unit time_xNO released from absorbent_xAmount (NO_xRelease rate) is not always constant, and NO_xIt changes according to the temperature of the absorbent and the amount of components such as unburned HC and CO contained in the exhaust gas. Therefore, based on only the operation time of the rich or stoichiometric air-fuel ratio as in the above-described apparatus (that is, NO_xNO from absorbent_xNO (assuming constant release rate)_xIf the value of the absorption amount counter is decreased, the engine operation state or NO_xDepending on the temperature of the absorbent, the amount of decrease in the counter and the actual_xNO released from absorbent_xA large error may occur with the amount of
[0016]
In the above internal combustion engine, NO_xNO using the value of the absorption counter_xNO absorbed by the absorbent_xIs determined during lean air-fuel ratio operation._xWhen the amount of absorption increases and exceeds a predetermined value, the air-fuel ratio of the engine is forcibly switched to the rich air-fuel ratio, so that the NO_xNO from absorbent_xHas been released. Therefore, actually NO_xNO absorbed in the absorbent_xQuantity and NO_xIf there is an error with the value of the absorption counter, NO_xAbsorbent NO_xLow absorption, NO_xNO despite no need to release_xSince the value of the absorption amount counter has exceeded the predetermined value, switching to the rich air-fuel ratio operation is performed to deteriorate the fuel efficiency, or conversely, NO_xAbsorbent NO_xAbsorption increases and NO_xDespite the need to release NO_xNO because the value of the absorption counter does not exceed the predetermined value_xWithout releasing NO_xNO in the exhaust gas_xThis may cause problems such as the inability to absorb the water.
[0017]
The object of the present invention is NO_xNO absorbed in the absorbent_xIs to accurately estimate the amount of
[0018]
[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 soot that is supplied into the combustion chamber increases. When the amount of active gas is further increased, the temperature of fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the temperature at which soot is generated, and the air-fuel ratio of the inflowing exhaust gas is reduced in the internal combustion engine where almost no soot is generated. Is lean, NO contained in the exhaust gas_x  And the NO absorbed when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich._x  Releases NO_x  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 amount of generated soot is peak, and soot is hardly generated; 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 reaches a peak; and the internal combustion engine is operated at a lean air-fuel ratio. When the predetermined addition amount determined according to the engine operating state is_x  Absorbent NO_x  NO indicating absorption amount_x  When the internal combustion engine is operated at a rich or stoichiometric air-fuel ratio, a predetermined subtraction amount is added to the absorption amount counter at regular time intervals._x  By subtracting from the absorption amount counter, the NO_x  Absorbent NO_x  Estimate absorptionNO _x Absorption amount estimating means; and NO when the internal combustion engine is operated at a rich or stoichiometric air-fuel ratio._x  NO released from absorbent_x  NO to estimate the amount of_x  Means for estimating the amount of emission; and_x  NO based on release_x  A subtraction amount determining means for determining the subtraction amount of the absorption amount counter. That is, actually NO_x  NO released from absorbent_x  NO corresponding to the amount of_x  The absorption counter is decremented.
[0019]
According to the second invention, the NO in the first invention_xWhen the emission amount estimating means determines that the engine is operating at a rich or stoichiometric air-fuel ratio,_xNO based on the amount of fuel supplied to the absorbent_xEstimate the release.
According to a third aspect, in the first aspect, the NO_xNO_xNO based on the temperature of the absorbent_xEstimate the release.
[0020]
According to a fourth aspect, in the first aspect, the NO_xNO_xNO based on the degree of deterioration of the absorbent_xEstimate the release.
According to a fifth aspect, in the first aspect, the NO_xNO_xNO based on the amount of exhaust gas flowing into the absorbent_xEstimate the release.
According to a sixth 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.
[0021]
According to a seventh aspect, in the sixth aspect, the exhaust gas recirculation rate is approximately 55% or more.
According to an eighth aspect, in the first aspect, the operating region of the engine is divided into a first operating region on a low load side and a second operating region on a high load side. Combustion is performed, and second combustion is performed in the second operation region.
[0022]
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.
[0023]
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.
[0024]
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.
[0025]
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.
[0026]
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, NO_x4 shows an experimental example showing a change in the emission amount of the gas. 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.
[0027]
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 slightly decreases, and NO_xThe amount of generation is considerably low. On the other hand, at this time, the generation amounts of HC and CO begin to increase.
[0028]
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.
[0029]
The following can be said from the experimental results shown in FIGS. That is, first, when the air-fuel ratio A / F is 15.0 or less and the amount of generated smoke is almost zero, NO as shown in FIG._xThe amount of generation of methane is considerably reduced. NO_xThe decrease in the amount of the generated gas means that the combustion temperature in the combustion chamber 5 has decreased. Therefore, it can be said that the combustion temperature in the combustion chamber 5 is low when little soot is generated. 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.
[0030]
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. .
[0031]
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 fact, 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. 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.
[0032]
By the way, the temperature of the fuel and its surroundings when the process of producing hydrocarbons is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature varies with various factors such as the type of fuel and the compression ratio of the air-fuel ratio. I can not say how many times, but this certain temperature is NO_xIs closely related to the amount of NOx generated, so that this certain temperature is NO_xCan be defined to some extent from the amount of occurrence of. That is, as the EGR rate increases, the fuel temperature during combustion and the gas temperature around the fuel decrease, and the NO_xGeneration amount decreases. NO at this time_xIs 10 p. p. When it is less or equal to or less than m, almost no soot is generated. Therefore, the above certain temperature is NO_xIs 10 p. p. m The temperature almost coincides with the temperature when the temperature becomes lower or higher.
[0033]
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 the state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Considering the post-treatment with the catalyst having the oxidation function as described above, it is extremely difficult to discharge hydrocarbons from the combustion chamber 5 in the state of the precursor of soot or in the state before the soot or in the form of soot from the combustion chamber 5. There is a big difference. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a precursor or previous soot without producing soot in the combustion chamber 5 and removing the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.
[0034]
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 burns has an extremely large effect on suppressing the temperature of the fuel and the gas around the fuel.
[0035]
That is, if there is only air around the fuel, the evaporated fuel immediately reacts with 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, at this time, the air separated from the fuel hardly absorbs the heat of combustion heat of the fuel. In this case, since the combustion temperature becomes extremely high locally, the unburned hydrocarbons that have received the heat of combustion will generate soot.
[0036]
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 evaporated fuel 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 kept low by the endothermic effect of the inert gas.
[0037]
In this case, controlling the temperature of the fuel and its surrounding gas to a temperature lower than the temperature at which soot is generated requires an amount of an inert gas that can absorb a sufficient amount of heat to do so. Therefore, if the amount of fuel 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, CO₂Since EGR gas has a relatively large specific heat, it can be said that it is preferable to use EGR gas as the inert gas.
[0038]
FIG. 5 shows the relationship between the EGR rate and 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.
[0039]
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.
[0040]
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. As described above, 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.
[0041]
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; 2 shows the ratio of air in the mixed gas and the ratio of EGR gas in the mixed gas. 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 shows the required load.
[0042]
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, NO_xThe amount generated is 10 p. p. m around or below and therefore NO_xIs extremely small.
[0043]
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 its 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.
[0044]
By the way, when the supercharging is not performed, the upper limit of the total intake gas amount X sucked into the combustion chamber 5 is Y, and therefore, in FIG. 6, in the region where the required load is larger than Lo, as the required load increases, Unless the EGR gas ratio is reduced, the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio. In other words, when the supercharge is not performed, and when the required air-fuel ratio is maintained at the stoichiometric air-fuel ratio in a region where the required load is larger than Lo, the EGR rate decreases as the required load increases. In a region where the required load is larger than Lo, the temperature of the fuel and the surrounding gas cannot be maintained at a temperature lower than the temperature at which soot is generated.
[0045]
However, as shown in FIG. 1, when the EGR gas is recirculated through the EGR passage 29 into the inlet side of the supercharger, that is, into the air suction pipe 17 of the exhaust turbocharger 15, the EGR rate is increased in a region where the required load is larger than Lo. Can be maintained at or above 55 percent, for example, 70 percent, and thus 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. When the EGR rate is set to 55% or more in a region where the required load is larger than Lo, the EGR control valve 31 is fully opened and the throttle valve 20 is slightly closed.
[0046]
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. NO while preventing generation of_xIs 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. NO_xIs 10 p. p. m can be around or below.
[0047]
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. At this time, NO_xOnly a very small amount is 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 when the combustion temperature increases, but in the present invention, the soot is suppressed to a low temperature, so that the soot is reduced. Not generated at all. Furthermore, NO_xOnly a very small amount is generated.
[0048]
Thus, 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, NO_xIs 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.
[0049]
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
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).
[0050]
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.
[0051]
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 start immediately 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.
[0052]
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 hydrocarbon is in the form of a precursor of soot or a state before it. It is discharged from the combustion chamber 5. At this time, the unburned hydrocarbon discharged from the combustion chamber 5 is NO_xIt is oxidized well by the absorbent 25. 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.
[0053]
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.
[0054]
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.
[0055]
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.
[0056]
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.
[0057]
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.
[0058]
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.
[0059]
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. .
[0060]
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), a map is stored in advance in the ROM 42 as a function of the required load L and the engine speed N.
[0061]
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 advance in the ROM 42 as a function of the required load L and the engine speed N.
[0062]
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.
On the other hand, in FIG._xAn absorbent 25 is provided. NO_xThe absorbent 25 is made of, for example, alumina as a carrier. On this carrier, for example, potassium K, sodium Na, lithium Li, alkali metal such as cesium Cs, barium Ba, alkaline earth such as calcium Ca, lanthanum La, yttrium Y At least one selected from such rare earths and a noble metal such as platinum Pt are supported. Engine intake passage, combustion chamber 5 and NO_xThe ratio of air and fuel (hydrocarbon) supplied into the exhaust passage upstream of the absorbent 25 is set to NO._xWhen the air-fuel ratio of the exhaust gas flowing into the absorbent 25 is called this NO_xThe absorbent 25 is NO when the air-fuel ratio of the inflowing exhaust gas is lean._xNO when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich._xReleases NO_xPerforms the absorption and release action.
[0063]
This NO_xIf the absorbent 25 is arranged in the engine exhaust passage, NO_xAbsorbent 25 is actually NO_xHowever, there is a part where the detailed mechanism of the absorption / release action is not clear. 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 platinum Pt and barium Ba supported on a carrier as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.
[0064]
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. When the combustion is performed with the lean air-fuel ratio, the oxygen concentration in the exhaust gas is high. At this time, as shown in FIG.₂Is O₂ ⁻Or O^2-On the surface of platinum Pt. On the other hand, NO in the inflowing exhaust gas becomes O 2 on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂). NO generated next₂Is oxidized on platinum Pt while NO_xAs shown in FIG. 16 (A), nitrate ions NO are absorbed in the absorbent 25 and combined with barium oxide BaO.₃ ⁻NO in the form of_xIt diffuses into the absorbent 25. NO in this way_xIs NO_xIt is absorbed in the absorbent 25. NO on the surface of platinum Pt as long as the oxygen concentration in the inflowing exhaust gas is high₂Is generated, and the NO_xNO unless absorption capacity is saturated₂Is absorbed in the absorbent and nitrate ion NO₃ ⁻Is generated.
[0065]
On the other hand, when the air-fuel ratio of the inflowing exhaust gas is made rich, the oxygen concentration in the inflowing exhaust gas decreases, and as a result, NO on the surface of the platinum Pt is reduced.₂Is reduced. NO₂The reaction proceeds in the reverse direction (NO₃ ⁻→ NO₂) And thus NO_xNitrate ion NO in absorbent 25₃ ⁻Is NO₂NO in the form of_xIt is released from the absorbent 25. NO at this time_xNO released from absorbent 25_xIs reduced by reacting with a large amount of unburned HC and CO contained in the inflowing exhaust gas as shown in FIG. Thus, NO on the surface of platinum Pt₂NO when no longer exists_xNO from next to next from absorbent 25₂Is released. Therefore, if the air-fuel ratio of the inflowing exhaust gas is made rich, NO_xNO from absorbent 25_xIs released, and the released NO_xNO in the atmosphere to be reduced_xIs not emitted.
[0066]
In this case, even if the air-fuel ratio of the inflowing exhaust gas is set to the stoichiometric air-fuel ratio, NO_xNO from absorbent 25_xIs released. However, when the air-fuel ratio of the inflowing exhaust gas is set to the stoichiometric air-fuel ratio, NO_xNO from absorbent 25_xIs released only slowly_xTotal NO absorbed in absorbent 25_xIt takes a slightly longer time to release.
[0067]
NO as described above_xThe absorbent 25 contains a noble metal such as platinum Pt, and therefore NO_xThe 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. However, as described above, NO_xThe absorbent 25 has an oxidizing function, and the unburned hydrocarbon discharged from the combustion chamber 5 at this time is NO._xIt can be oxidized well by the absorbent 25.
[0068]
By the way, NO_xNO of absorbent 25_xAbsorption capacity is limited, NO_xNO of absorbent 25_xNO before absorption capacity is saturated_xNO from absorbent 25_xMust be released. NO for that_xNO absorbed by absorbent 25_xThe quantity needs to be estimated. Therefore, in the embodiment according to the present invention, NO per unit time when the first combustion is performed_xThe absorption amount A is determined in advance in the form of a map as shown in FIG. 17A as a function of the required load L and the engine speed N, and the NO per unit time during the second combustion is performed._xThe absorption amount B is previously obtained as a function of the required load L and the engine speed N in the form of a map as shown in FIG._xNO by integrating absorption amounts A and B_xNO absorbed by absorbent 25_xThe absorption amount ΣNOX is estimated.
[0069]
In the embodiment according to the present invention, this NO_xNO when the absorption amount ΣNOX exceeds a predetermined allowable maximum value._xNO from absorbent 25_xIs to be released. 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 NO_xMaximum NO that can be absorbed by the absorbent 25_xIt is about 30% of the absorption amount, and the allowable maximum value MAX2 is NO_xIt is about 80% of the maximum absorption amount that the absorbent 25 can absorb. NO when the first combustion is being performed_xNO when the absorption amount ΣNOX exceeds the allowable maximum value MAX1._xNO from absorbent 25_xWhen the air-fuel ratio is made rich and the second combustion is performed, NO_xWhen the absorption amount ΣNOX exceeds the permissible maximum value MAX1, when the second combustion is switched to the first combustion, NO_xNO from absorbent 25_xWhen the air-fuel ratio is made rich and the second combustion is performed, NO_xNO when the absorption amount ΣNOX exceeds the allowable maximum value MAX2._xNO from absorbent 25_xAdditional fuel is injected during the second half of the expansion stroke or during the exhaust stroke to release.
[0070]
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. NO when first combustion is being performed_xIs extremely small, and therefore, at this time, as shown in FIG._xThe absorption amount ΣNOX rises very slowly. NO when the first combustion is being performed_xWhen the absorption amount ΣNOX exceeds the allowable maximum value MAX1, the air-fuel ratio A / F is temporarily made rich, whereby the NO_xNO from absorbent 25_xIs released. NO at this time_xThe absorption amount ΣNOX is gradually reduced as described later in detail.
[0071]
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. NO_xNO from absorbent 25_xAt this time, no soot is generated even if the air-fuel ratio A / F is made rich in order to release the air.
Then at time t₁When the required load L exceeds the first boundary X (N), the first combustion is switched 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. NO is performed when the second combustion is performed, compared to when the first combustion is performed._xIs large when the second combustion is being performed._xThe amount ΣNOX rises relatively quickly.
[0072]
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. Therefore, when the second combustion is being performed as shown in FIG._xEven if the absorption amount ΣNOX exceeds the allowable maximum value MAX1, NO_xNO from absorbent 25_xThe air-fuel ratio A / F is not made rich in order to release the fuel. In this case, time t in FIG.₂When the required load L becomes lower than the second boundary Y (N) and the second combustion is switched to the first combustion as in_xNO from absorbent 25_xThe air-fuel ratio A / F is temporarily enriched to release_xNO from absorbent 25_xIs released. NO at this time_xThe absorption amount ΣNOX is gradually reduced as described later in detail.
[0073]
Next, at time t in FIG.₃Is switched from the first combustion to the second combustion, and the second combustion is continued for a while. NO at this time_xThe absorption amount ΣNOX exceeds the allowable maximum value MAX1.
Next, as the required load L increases, the air-fuel ratio A / F decreases, and the time t in FIG.₄At which the air-fuel ratio A / F becomes rich. NO at this time_xNO from absorbent 25_xIs released and NO_xThe absorption amount ΣNOX is gradually reduced as described later in detail.
[0074]
Next, at time t in FIG.₅, The air-fuel ratio A / F becomes lean, the second combustion continues for a while, and then at time t₆In this case, if the allowable maximum value MAX2 is exceeded, then NO_xNO from absorbent 25_xAdditional fuel is injected during the second half of the expansion stroke or during the exhaust stroke to release_xThe air-fuel ratio of the exhaust gas flowing into the absorbent 25 is made rich. NO at this time_xNO from absorbent 25_xIs released and NO_xThe absorption amount ΣNOX is gradually reduced as described later in detail.
[0075]
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 the additional fuel as little as possible. Therefore, when the second combustion is performed, NO_xWhen the absorption amount ΣNOX exceeds the allowable maximum value MAX1, the air-fuel ratio A / F is temporarily made rich when the second combustion is switched to the first combustion, and NO_xAdditional fuel is injected only in special cases where the absorption amount ΣNOX exceeds the allowable maximum value MAX2.
[0076]
By the way, when the air-fuel ratio A / F becomes rich and when the air-fuel ratio is made rich,_xThe amount of the HC and CO components flowing into the absorbent 25 is determined by subtracting the amount of fuel required to operate the engine at the stoichiometric air-fuel ratio from the amount of fuel supplied to the engine, that is, the amount of excess fuel. It increases in proportion to the amount. For this reason, NO_xNO released from absorbent 25_xAmount (NO_xThe discharge rate increases in accordance with the amount of excess fuel supplied to the engine in this unit time.
[0077]
Also, when additional fuel is injected during the latter half of the expansion stroke or during the exhaust stroke, NO_xThe amount of the HC component flowing into the absorbent 25 increases in proportion to the amount of supplied fuel, that is, the amount of excess fuel. Therefore NO_xThe release rate increases with this excess fuel amount.
Also NO_xNO is caused by the sulfur component contained in the exhaust gas adhering to the absorbent 25._xThe absorbent 25 deteriorates. Therefore NO_xNO that the absorbent 25 can release per unit time_xThe amount of is reduced. That is, NO_xThe release rate is this NO_xIt decreases according to the degree of deterioration of the absorbent 25.
[0078]
Further NO_xNO from absorbent_xRelease rate is NO_xAffected by the temperature of the absorbent, NO_xNO depending on absorbent temperature_xThe maximum value of the release rate is almost determined. That is, NO in the presence of sufficient excess fuel_xRelease rate is NO_xIt tends to increase as the temperature of the absorbent increases. In this way, NO increases with increasing temperature._xThe release rate increases with NO_xIt is considered that when the temperature of the absorbent is increased, nitrate ions bonded to BaO in the absorbent are easily separated. Therefore, even if the excess fuel amount is large, NO_xNO if the temperature of the absorbent is low_xThe release rate decreases.
[0079]
Further NO_xRelease rate is NO per unit time_xIt is affected by the amount of exhaust gas flowing into the absorbent (hereinafter referred to as the amount of exhaust gas flowing in). That is, NO_xThe discharge speed decreases as the inflow exhaust gas amount increases. This means that the larger the inflow exhaust gas amount, the more NO_xThe speed of the exhaust gas passing through the absorbent is high, and the fuel in the exhaust gas is NO_xThis is because sufficient time cannot be secured to contribute to the release action.
[0080]
Next, in this embodiment, NO_xNO from absorbent_xThe estimation of the release rate will be described in detail.
NO as described above_xNO from absorbent_xExact fuel and NO_xDeterioration degree of absorbent and NO_xIt is necessary to know the temperature of the absorbent and the amount of inflowing exhaust gas.
[0081]
FIG. 19 shows the excess fuel amount EF and NO_x5 shows an example of a relationship with the release speed V, and NO_xThe release speed V increases substantially in proportion to the increase in the excess fuel amount EF. FIG. 20 shows NO_xAbsorbent temperature T and NO_x5 shows an example of a relationship with the release speed V, and NO_xRelease speed V is NO_xIt increases as the absorbent temperature T increases. In this embodiment, the excess fuel amount EF and the NO_xBasic NO corresponding to absorbent temperature T_xAs shown in FIG. 21, when the release speed VB is higher than the excess fuel amount EF and NO._xIt is stored in the ROM 42 in advance in the form of a map as a function of the temperature of the absorbent T.
[0082]
Further, FIG._xDeterioration degree D and NO of absorbent_x5 shows an example of a relationship with the release speed V, and NO_xThe release speed V decreases as the degree of deterioration D increases. FIG. 23 shows the case where NO_xExhaust gas amount AE and NO flowing into the absorbent_x5 shows an example of a relationship with the release speed V, and NO_xThe discharge speed V decreases as the inflow exhaust gas amount AE increases. In this embodiment, NO corresponding to the degree of deterioration D and the inflow exhaust gas amount AE_xThe release speed correction coefficient K1 is stored in the ROM 42 in advance in the form of a map as a function of the deterioration degree D and the inflowing exhaust gas amount AE as shown in FIG.
[0083]
In this embodiment, NO_xNO from absorbent_xIs released when NO is released_xThe amount C to be reduced of the absorption amount ΣNOX is the basic NO calculated as described above._xRelease speed VB and NO_xIt is calculated according to the formula C = CB × VB × K1 using the release rate correction coefficient K1. Here, CB is a basic decrease amount.
In this embodiment, the excess fuel amount when the air-fuel ratio A / F is set to or becomes rich or stoichiometric is calculated from the air-fuel ratio and the intake air amount. Also, the amount of excess fuel when additional fuel is injected during the second half of the expansion stroke or during the exhaust stroke is equal to the amount of additional fuel injected into the combustion chamber per unit time. Also NO_xAbsorbent temperature is NO_xIt is calculated based on the temperature detected by the exhaust gas temperature sensor 53 provided in the exhaust passage downstream of the absorbent 25. The output signal of the exhaust temperature sensor 53 is input to the input port 45 via the corresponding AD converter 47.
[0084]
Also NO_xThe degree of deterioration of the absorbent is calculated based on the total operation time of the internal combustion engine, and the longer the total operation time, the greater the degree of deterioration. Further, the inflow exhaust gas amount is calculated based on the mass flow rate detected by the mass flow rate detector provided in the intake pipe.
FIG. 25 is NO_xNO from absorbent 25_xSet when to release_xThis shows a routine for processing the release flag, and this routine is executed by interruption every predetermined time.
[0085]
Referring to FIG. 25, 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 is, when the operation region of the engine is the first operation region I, the routine proceeds to step 101, where NO per unit time is obtained from the map shown in FIG._xThe absorption amount A is calculated. Next, at step 102, NO_xA is added to the absorption amount ΣNOX. Next, at step 103, NO_xIt is determined whether or not the absorption amount ＸNOX has exceeded the allowable maximum value MAX1. If ΣNOX> MAX1, the routine proceeds to step 104, where NO is set when the first combustion is being performed._xNO indicating that the gas should be released_xRelease flag 1 is set.
[0086]
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 the second operating region II, the routine proceeds to step 107, where the map per unit time is obtained from the map shown in FIG. NO_xThe absorption amount B is calculated. Next, at step 108, NO_xB is added to the absorption amount ΣNOX. Next, at step 103, NO_xIt is determined whether or not the absorption amount ＸNOX has exceeded the allowable maximum value MAX1. If ΣNOX> MAX1, the routine proceeds to step 104, where NO is set when the first combustion is being performed._xNO indicating that the gas should be released_xRelease flag 1 is set. That is, in this case, when the second combustion is switched to the first combustion, NO_xIs released.
[0087]
In step 105, NO_xIt is determined whether or not the absorption amount ＸNOX has exceeded the allowable maximum value MAX2. If ΣNOX> MAX2, the routine proceeds to step 106, where NO is set during the latter half of the expansion stroke or during the exhaust stroke._xNO indicating that the gas should be released_xRelease flag 2 is set.
Next, the operation control will be described with reference to FIGS. 26 and 27.
[0088]
Referring to FIG. 26, first, in step 200, 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 201, where it is determined whether the required load L has become larger than the first boundary X (N). Is done. When L ≦ X (N), the routine proceeds to step 203, where low-temperature combustion is performed.
[0089]
That is, in step 203, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 12A, and the opening of the throttle valve 20 is set to this target opening ST. Next, at step 204, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 12B, and the opening of the EGR control valve 31 is set as the target opening SE. Next, at step 205, NO_xIt is determined whether the release flag 1 is set. NO_xIf the release flag 1 has not been set, the routine proceeds to step 206, where fuel injection is performed so as to achieve the air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed under a lean air-fuel ratio.
[0090]
On the other hand, NO_xWhen it is determined that the release flag 1 is set, the routine proceeds to step 207, where the injection control I is performed. That is, the air-fuel ratio is set to a rich or stoichiometric air-fuel ratio.
On the other hand, when it is determined in step 201 that L> X (N), the routine proceeds to step 202, where the flag I is reset, and then proceeds to step 212 to perform the second combustion.
[0091]
That is, in step 212, 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 213, 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 this target opening SE. Next, at step 214, NO_xIt is determined whether the release flag 2 is set. NO_xIf the release flag 2 has not been set, the routine proceeds to step 215, where fuel injection is performed so as to achieve the air-fuel ratio shown in FIG. At this time, the second combustion is performed under the lean air-fuel ratio.
[0092]
On the other hand, in step 214, NO_xWhen it is determined that the release flag 2 is set, the routine proceeds to step 214, where the injection control II is performed. That is, additional fuel is injected during the latter half of the expansion stroke or during the exhaust stroke.
Next, at step 217 in FIG. 27, the subtraction amount C is calculated as described above. Note that the subtraction amount C is zero when the air-fuel ratio is lean. Next, at step 218, NO_xThe subtraction amount C is subtracted from the absorption amount ΣNOX. Next, at step 219, NO_xIt is determined whether the absorption amount ΣNOX is equal to or greater than zero. If ΣNOX ≧ 0, the process ends. On the other hand, if ΣNOX <0,_xThe absorption amount ΣNOX is set to zero, and the process ends.
[0093]
【The invention's effect】
According to the first to eighth inventions, NO_xNO released from absorbent_xNO by amount_xSince the absorption counter is decremented, NO_xNO absorbed in the absorbent_xIs accurately estimated.
[Brief description of the drawings]
FIG. 1 is an overall view of a compression ignition type internal combustion engine.
FIG. 2 Smoke and NO_xFIG.
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 II.
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.
FIG. 16 NO_xIt is a figure for explaining the absorption-release action of.
FIG. 17: NO per unit time_xIt is a figure showing a map of an amount of absorption.
FIG. 18 NO_xIt is a figure for explaining discharge control.
FIG. 19: Excess fuel amount and NO_xIt is a figure which shows the relationship with a release speed.
FIG. 20 NO_xAbsorbent temperature and NO_xIt is a figure which shows the relationship with a release speed.
FIG. 21: Basic NO_xIt is a figure showing a map of a release rate.
FIG. 22: Deterioration degree and NO_xIt is a figure which shows the relationship with a release speed.
FIG. 23: Inflow exhaust gas amount and NO_xIt is a figure which shows the relationship with a release speed.
FIG. 24 NO_xIt is a figure showing a map of a release rate correction coefficient.
FIG. 25_xIt is a flowchart for processing a release flag.
FIG. 26 is a flowchart for controlling operation of the engine.
FIG. 27 is a flowchart for controlling operation of the engine.
[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. in fuel and generates almost no longer becomes the internal combustion engine soot is lower than the formation temperature of the gas temperature is soot surrounding the case, when the air-fuel ratio of the exhaust gas flowing into the lean absorbing NO _x contained in the exhaust gas the _the NO _x absorbent when the air-fuel ratio of the exhaust gas flowing vital emits NO _x absorbed and becomes the stoichiometric air-fuel ratio or rich is arranged in the engine exhaust passage, from the inert gas where the amount of production of soot peaks Also, the first combustion in which the amount of inert gas supplied into the combustion chamber is large and soot is hardly generated, and the amount of inert gas supplied into the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot peaks. Second And switching means for switching the baked Optionally, said internal combustion engine when it is operated at a lean air-fuel ratio, the _the NO _x absorbent in a predetermined time interval a predetermined addition amount determined in accordance with the engine operating condition was added to the absorption of NO _x amount counter which represents the absorption of NO _x amount, the internal combustion engine when it is operating at a rich or stoichiometric air-fuel ratio is subtracted from the absorption of NO _x amount counter a predetermined subtraction amount for each predetermined time by, NO _x to estimate the absorption of NO _x of the _the NO _x absorbent Absorption amount estimation means, and _the NO _x releasing amount estimating means for estimating the amount of NO _x released from _the NO _x absorbent when said internal combustion engine is operated at a rich or stoichiometric air-fuel ratio, the internal combustion engine is rich or the internal combustion engine, characterized in that a subtraction amount determining means for determining the subtraction amount of the NO _x absorption amount counter based on the _the NO _x releasing amount when it is operated at the stoichiometric air-fuel ratio. Claims, characterized in that estimating the _the NO _x releasing amount based on the amount of fuel supplied to _the NO _x absorbent when the _the NO _x releasing amount estimating means the engine is operated at a rich or stoichiometric air-fuel ratio Item 2. The internal combustion engine according to Item 1. The internal combustion engine of claim 1, wherein the _the NO _x releasing amount estimating means estimates the _the NO _x releasing amount based on the temperature of the NO _x absorbent. Internal combustion engine according to claim 1, characterized in that estimating the _the NO _x releasing amount based the _the NO _x releasing amount estimating means the degree of deterioration of _the NO _x absorbent. Internal combustion engine according to claim 1, characterized in that estimating the _the NO _x releasing amount based on the amount of exhaust gas the _the NO _x releasing amount estimating means flows into _the NO _x absorbent. 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. The internal combustion engine of claim 6, wherein the exhaust gas recirculation rate is approximately 55 percent or greater. 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. The internal combustion engine according to claim 1, wherein combustion is performed.

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