JP3551789B2 - 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]
However, NO_xWhen new combustion is not being performed when the fuel is to be released and reduced, that is, when conventional combustion is being performed, the air-fuel ratio must be made rich under conventional combustion. As described above, under the conventional combustion, combustion is performed under excess air, that is, under excess oxygen. Therefore NO_xNO to release and reduce NO_xTo maintain the exhaust gas flowing into the absorbent in a reducing atmosphere, NO_xIn addition to the fuel required for the emission reduction of fuel, the amount of fuel required to consume the oxygen in the incoming exhaust gas must be increased. That is, fuel efficiency is deteriorated.
[0013]
An object of the present invention is to reduce NO without deteriorating fuel economy._xNO from the absorbent_xIt is an object of the present invention to provide an internal combustion engine capable of releasing and reducing fuel.
[0014]
[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_xAnd the NO absorbed when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich._xReleases NO_xThe first combustion in which the absorbent is disposed in the engine exhaust passage, 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 becomes a 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 NO_xNO from absorbent_xWhen the NO should be released_xThe oxygen in the exhaust gas flowing into the absorbent is consumed and the NO_xNO from absorbent_xOxygen consuming means is provided to reduce the amount of reducing agent consumed during discharge.
[0015]
That is, NO_xNO_xOxygen in exhaust gas is consumed when it should be released from the absorbent, and NO_xThe amount of oxygen in the exhaust gas flowing into the absorbent is reduced. In other words, NO_xExhaust gas flowing into the absorbent is reduced to a reducing atmosphere.
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.
[0016]
According to a third aspect, in the second aspect, the exhaust gas recirculation rate is approximately 55% or more.
According to a fourth aspect, in the first aspect, the oxygen consuming means is an oxidation catalyst, a three-way catalyst, or NO._xConsists of at least one of an absorbent.
According to a fifth aspect, in the first aspect, the operating range of the engine is divided into a first operating range on the low load side and a second operating range on the high load side, and the first operating range is divided into the first operating range on the high load side. Combustion is performed, and second combustion is performed in the second operation region.
[0017]
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.
[0018]
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.
[0019]
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.
[0020]
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.
[0021]
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.
[0022]
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.
[0023]
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.
[0024]
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.
[0025]
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. .
[0026]
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.
[0027]
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.
[0028]
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 a catalyst having an oxidation function as described above, it is determined whether the hydrocarbon is discharged from the combustion chamber 5 in the state of the precursor of soot or before it, or is discharged from the combustion chamber 5 in the form of soot. 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 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.
[0029]
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.
[0030]
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, almost no heat absorbing action of the combustion heat of the fuel of the air separated from the fuel is performed. In this case, since the combustion temperature becomes extremely high locally, the unburned hydrocarbons that have received the heat of combustion will generate soot.
[0031]
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.
[0032]
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.
[0033]
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.
[0034]
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.
[0035]
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.
[0036]
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.
[0037]
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.
[0038]
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.
[0039]
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.₀In the larger range, the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio unless the EGR gas ratio is reduced as the required load increases. In other words, when supercharging is not performed, the required load is L₀If the air-fuel ratio is to be maintained at the stoichiometric air-fuel ratio in a region larger than the required load, the EGR rate decreases as the required load increases.₀In the larger region, the temperature of the fuel and its surrounding gas cannot be maintained below the temperature at which soot is produced.
[0040]
However, as shown in FIG. 1, when the EGR gas is recirculated through the EGR passage 29 to the inlet side of the supercharger, that is, into the air suction pipe 17 of the exhaust turbocharger 15, the required load becomes L.₀In the larger region, the EGR rate 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. Request load is L₀When the EGR rate is set to 55% or more in a larger region, the EGR control valve 31 is fully opened and the throttle valve 20 is slightly closed.
[0041]
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.
[0042]
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.
[0043]
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.
[0044]
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
[0045]
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).
[0046]
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.
[0047]
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.
[0048]
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, 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.
[0049]
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.
[0050]
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.
[0051]
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.
[0052]
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.
[0053]
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.
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.
[0054]
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. .
[0055]
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.
[0056]
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.
[0057]
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, the exhaust pipe 24 is provided with a particulate filter 53 for collecting fine particles (diesel particulates) such as soot, unburned hydrocarbons, and soluble organic components (SOF) contained in the exhaust gas.
[0058]
The particulate filter 53 is usually formed of a filter material having heat resistance such as ceramics, and filters and collects particulates in exhaust gas. Therefore, the collected particulates accumulate in the filter 53 with time, so that it is necessary to periodically regenerate and remove the collected particulates. Usually, regeneration of this filter is performed by heating the particulates collected by the filter to an ignition temperature (about 600 ° C.) or higher and burning it. As described above, the particulates are composed of soot, unburned hydrocarbons, SOF, and the like, so that depending on the conditions, reducing gases such as CO are generated by combustion. In this embodiment, NO_xNO from absorbent_xDuring the discharging operation, as will be described in detail later, the exhaust gas temperature is raised to the particulate ignition temperature or higher, and the particulates collected by the filter 53 are burned. As a result, the oxygen in the exhaust gas is consumed in the particulate combustion, the exhaust oxygen concentration decreases, and CO, CO is reduced by the particulate combustion.₂And reducing gas such as NO_xSupplied to the absorbent.
[0059]
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.
[0060]
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.
[0061]
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 absorbed in the absorbent while being oxidized on the platinum Pt and combined with barium oxide BaO, as shown in FIG.₃ ⁻Diffuses into the absorbent in the form of 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.
[0062]
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 the nitrate ions NO in the absorbent₃ ⁻Is NO₂Released from the absorbent in the form of 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 Pt₂When no longer exists, NO is changed from one absorbent to the next₂Is 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.
[0063]
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.
[0064]
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.
[0065]
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 amount ΣNOX is estimated.
[0066]
As will be described in detail later, in the embodiment according to the present invention, this NO_xNO when the absorption amount ΣNOX exceeds a predetermined allowable maximum value MAX._xNO from absorbent 25_xIs to be released. That is, when low-temperature combustion is being performed, NO_xWhen the absorption amount ΣNOX exceeds the allowable maximum value MAX, the fuel injection amount is increased by a predetermined increment Qa, and the air-fuel ratio in the combustion chamber 5 is temporarily made rich, whereby the NO_xNO from absorbent 25_xIs released. The predetermined increment Qa is calculated based on the required load L and the engine speed N, and 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. I have. As described above, even when the air-fuel ratio is made rich during low-temperature combustion, almost no soot is generated.
[0067]
On the other hand, when the second combustion is being performed, NO_xWhen the absorption amount ΣNOX exceeds the allowable maximum value MAX, the amount of this increment Qb becomes NO_xThe air-fuel ratio of the exhaust gas flowing into the absorbent 25 is determined to be rich, so that when the fuel increased by the increment Qb is injected, NO_xNO from absorbent 25_xWill be released. The predetermined increment Qb is calculated based on the required load L and the engine speed N, and 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. .
[0068]
FIG. 18 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.
Referring to FIG. 18, first, at step 100, it is determined whether or not a graph I indicating that the operating region of the engine is the first operating 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 exceeds the allowable maximum value MAX.と If NOX> MAX, proceed to step 104 and NO for a predetermined time._xA process for setting a release flag is performed, and then in step 105, ΣNOX is made zero.
[0069]
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. NO_xThe absorption amount B is calculated. Next, at step 107, NO_xB is added to the absorption amount ΣNOX. Next, at step 108, NO_xIt is determined whether or not the absorption amount ＸNOX exceeds the allowable maximum value MAX.と If NOX> MAX, the process proceeds to step 109 and NO for a predetermined time._xA process for setting the release flag is performed, and then in step 110, ΣNOX is made zero.
[0070]
Then NO_xNO of absorbent 25_xThe discharge reduction operation will be schematically described. First, the above-mentioned NO_xNO when the release flag is set and the operating region of the engine is in the first operating region 1, that is, when low-temperature combustion is being performed._xNO of absorbent 25_xIt is determined whether or not a condition for performing the discharge reduction operation (hereinafter, a first execution condition) is satisfied. The first execution condition is that the engine exhaust temperature is equal to or higher than a predetermined value. The engine exhaust temperature is detected by an exhaust temperature sensor 56 attached to the exhaust pipe 24. The output signal of the exhaust gas temperature sensor 56 is input to the input port 45 via the corresponding AD converter 47. The predetermined value of the engine exhaust temperature is NO_xThe temperature of the absorbent 25 is NO_xThe temperature is set to be higher than the activation temperature for release and reduction.
[0071]
When the first execution condition is satisfied, the regeneration of the particulate filter 53 is executed. That is, in low-temperature combustion, the fuel injection amount is increased by a predetermined increment Qa read from the map in FIG. 19 so that the air-fuel ratio in the combustion chamber 5 becomes richer than the stoichiometric air-fuel ratio, and the engine exhaust temperature is particulate-ignited. The temperature is raised to a temperature (about 600 ° C.) or higher. As a result, the particulate filter 53 starts burning the collected exhaust particulates. If the air-fuel ratio in the combustion chamber 5 is made richer than the stoichiometric air-fuel ratio, components such as unburned HC and CO in the exhaust gas increase. In addition, since exhaust particulates such as soot trapped in the particulate filter 53 start burning, oxygen in the exhaust gas is consumed by this combustion, and the oxygen concentration in the exhaust gas further decreases, and CO2 is reduced by the combustion of the soot and the like. And the like, the reducing components such as unburned HC and CO in the exhaust gas further increase, and NO_xNO in absorbent 25_xAre released and reduced.
[0072]
Also NO_xAbsorbent 25 absorbs NO as temperature increases_xAt the ignition temperature of the particulate filter 53 of 600 ° C. or higher._xThe release rate becomes extremely high. Therefore, as in the present embodiment, the NO_xNO from absorbent 25_xNO in a short time by performing release reduction_xNO from absorbent 25_xRelease and reduction can be completed.
[0073]
If the first execution condition is not satisfied or if NO_xIf the first execution condition is not satisfied during the execution of the discharge reduction operation, the engine operation returns to the stoichiometric air-fuel ratio or low-temperature combustion slightly leaner than the stoichiometric air-fuel ratio.
As described above, in the present embodiment, when the operating region of the engine is in the first operating region I, NO is determined by the regeneration operation of the particulate filter 53._xNO in absorbent 25_xBy starting release and reduction, (1) NO_xReduction of oxygen concentration in exhaust gas flowing into the absorbent, (2) increase of reducing components such as CO and HC in exhaust gas, and (3) NO due to increase of exhaust temperature_xAt the same time, the emission reduction time is shortened.
[0074]
On the other hand, the above NO_xNO when the release flag is set and the operating region of the engine is in the second operating region II_xNO of absorbent 25_xIt is determined whether or not a condition for performing the discharge reduction operation (hereinafter, a second execution condition) is satisfied. The second execution condition is (1) that the engine exhaust temperature is equal to or higher than a predetermined value, and (2) that the vehicle is performing a deceleration operation. The condition (1) is the same as the first execution condition. The determination (2) that the vehicle is decelerating is made based on the fact that the engine speed is equal to or higher than the predetermined value and the accelerator opening is fully closed. NO_xThe reason why the discharge reduction operation is performed only during the vehicle deceleration operation is to prevent the occurrence of torque shock because it is necessary to close the throttle valve 20 and reduce the engine intake during the discharge reduction as described later.
[0075]
When the second execution condition is satisfied, the regeneration of the particulate filter 53 is executed. That is, the throttle valve 20 is closed to reduce the amount of intake air into the combustion chamber 5, and the fuel injection amount is increased by a predetermined increment Qb read from the map of FIG. Raise the temperature to the ignition temperature (about 600 ° C) or higher. As a result, the particulate filter 53 starts burning the collected exhaust particulates. When the operating range of the engine is in the second operating range II, that is, when the conventional combustion is performed, the exhaust air-fuel ratio is significantly lean, but the intake air amount decreases due to the throttle valve closing and the fuel injection amount decreases. As a result, the exhaust air-fuel ratio shifts to the rich side, and components such as unburned HC and CO in the exhaust gas greatly increase. In addition, since the exhaust particulates such as soot collected by the particulate filter 53 start burning as described above, the oxygen in the exhaust gas is consumed by this combustion, and the oxygen concentration in the exhaust gas further decreases, and the combustion of the soot and the like also occurs. Generates CO and the like, so that the reducing components such as unburned HC and CO in the exhaust gas further increase, and NO_xNO in absorbent 25_xRelease and reduction conditions are established.
[0076]
If the second execution condition is not satisfied or NO_xIf the second execution condition is not satisfied during execution of the discharge reduction operation, the throttle valve 80 is opened and the fuel injection increase is stopped, and the operation region of the engine returns to the normal second operation region II. I do. As described above, in the present embodiment, even when the operating region of the engine is in the second operating region II, NO is determined by the regeneration operation of the particulate filter 53._xNO in absorbent 25_xBy starting release and reduction, (1) NO_xReduction of oxygen concentration in exhaust gas flowing into the absorbent, (2) increase of reducing components such as CO and HC in exhaust gas, and (3) NO due to increase of exhaust temperature_xAt the same time, the emission reduction time is shortened.
[0077]
In the above-described embodiment, the particulate ignition is performed only by the exhaust gas temperature rise due to the closing of the throttle valve 20 and the increase in the fuel injection amount. However, the particulate filter 53 is provided with an electric heater for ignition, and the exhaust gas temperature is increased. The ignition may be promoted in combination.
Next, the operation control will be described with reference to FIG.
[0078]
Referring to FIG. 21, 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.
[0079]
That is, in step 203, 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 204, 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 to the target opening SE. Next, at step 205, NO_xIt is determined whether the release flag is set. NO_xWhen the release flag is not set, the routine proceeds to step 206, where the fuel injection of the amount Q calculated from the map of FIG. 12 is performed so as to obtain the air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed under a lean air-fuel ratio.
[0080]
On the other hand, NO_xWhen it is determined that the release flag is set, the routine proceeds to step 207, where it is determined whether the first execution condition is satisfied. When the first execution condition is not satisfied, the routine proceeds to step 206, where the above-described fuel injection is performed. On the other hand, when the first execution condition is satisfied in step 207, the process proceeds to step 208, and the fuel injection of the amount obtained by adding the increment Qa calculated from the map of FIG. 19 to the amount Q calculated from the map of FIG. Thus, injection control for enriching the average air-fuel ratio in the combustion chamber 5 is performed. NO at this time_xNO from absorbent 25_xIs released.
[0081]
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. Then, the routine proceeds to step 211, where the second combustion is performed.
That is, in step 211, 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 211, 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 as the target opening SE. Next, at step 213, NO_xIt is determined whether the release flag is set. NO_xWhen the release flag is not set, the routine proceeds to step 214, where the fuel injection of the amount Q calculated from the map of FIG. 15 is performed so as to obtain the air-fuel ratio shown in FIG. At this time, the second combustion is performed under the lean air-fuel ratio.
[0082]
On the other hand, in step 213, NO_xWhen it is determined that the release flag is set, the routine proceeds to step 215, where it is determined whether the second execution condition is satisfied. When the second execution condition is not satisfied, the routine proceeds to step 214, where the above-described fuel injection is performed. On the other hand, when the second execution condition is satisfied at step 215, the routine proceeds to step 216, where the throttle valve 20 is closed, and the increment Qb calculated from the map of FIG. The added amount of fuel is injected and NO_xThe injection control is performed so that the air-fuel ratio of the exhaust gas flowing into the absorbent 25 becomes rich._xNO from absorbent 25_xIs released.
[0083]
When the flag I is reset, in the next processing cycle, the process proceeds from step 200 to step 209 to determine whether the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), the routine proceeds to step 211, where the second combustion is performed under a lean air-fuel ratio.
On the other hand, when it is determined in step 209 that L <Y (N), the routine proceeds to step 210, where the flag I is set. Next, the routine proceeds to step 203, where low-temperature combustion is performed.
[0084]
Note that when the second combustion is being performed in the first embodiment, NO_xWhen the absorption amount ΣNOX exceeds the permissible maximum value MAX, the amount of fuel Qb to be increased separately from the engine driving injection is injected into the expansion stroke or the exhaust stroke of the engine without increasing the fuel injection amount. Is also good. Therefore, when additional fuel Qb is injected, NO_xNO from absorbent 19_xWill be released.
[0085]
Next, FIG. 22 shows a second embodiment of the present invention. 22, the same reference numerals as those in FIG. 1 indicate the same elements. This embodiment differs from the embodiment of FIG. 1 in that a burner 55 using fuel oil is provided at the entrance of the particulate filter 53. That is, in the present embodiment, when the operating region of the engine is in the second operating region II, when the particulate filter 53 is regenerated, the throttle valve 20 is closed and the burner 55 burns the fuel oil to increase the exhaust gas. The temperature is increased, and the fuel injection amount to the engine is not increased. According to the present embodiment, even when the trapped amount of exhaust particulates in the particulate filter 53 is small and the exhaust gas temperature rise in the particulate filter 53 is not sufficient, the exhaust gas temperature rise is increased by increasing the fuel supply amount to the burner 55. And oxygen consumption can be achieved,_xNO in absorbent 25_xThere is an advantage that the timing of performing the discharge reduction operation is not affected by the amount of trapped exhaust particulates of the particulate filter 53. In this embodiment, the unburned HC and CO generated from the burner 55 are NO._xIs the same as the embodiment of FIG. The burner 55 is connected to the output port 46 via the corresponding drive circuit 48.
[0086]
FIG. 23 shows a third embodiment of the present invention. In this embodiment, the particulate filter of the embodiment shown in FIGS. 1 and 22 is not provided, a burner 55 using fuel oil and a glow heater 56 for ignition are arranged in the exhaust pipe 24, and the operating range of the engine is the second. NO in combustion in burner 55 when in operating region II_xNO in absorbent 25_xRelease and reduce. That is, in this embodiment, when the operation region of the engine is in the second operation region II, all the effects of the oxygen consumption and the reduction component generation by the combustion in the particulate filter and the exhaust gas heating in the first embodiment are throttled. This is performed only by closing the valve 20 and burning the burner 54. This makes NO_xNO in absorbent 25_xThere is an advantage that the timing of the discharge reduction operation can be freely set. The glow heater 56 is connected to the output port 46 via a corresponding drive circuit 48.
[0087]
Next, FIG. 24 shows a fourth embodiment of the present invention. In this embodiment, NO_xA small-volume oxidation catalyst 57 is disposed on the exhaust pipe 24 upstream of the absorbent 25, preferably immediately downstream of the exhaust manifold. As the catalyst 57, a metal carrier having a small heat capacity is used. In this embodiment, the oxygen consumption and the exhaust gas temperature are increased by the oxidation catalyst 57. That is, when the operating range of the engine is in the first operating range I, the air-fuel ratio in the combustion chamber 5 is made richer than the stoichiometric air-fuel ratio when the first execution condition is satisfied, and when the engine is in the second operating range II. When the second execution condition is satisfied, the throttle valve 20 of the intake pipe 2 is closed, the amount of fuel injected into the combustion chamber 5 is increased, and the air-fuel ratio is largely shifted to the rich side. As a result, components such as unburned HC and CO in the exhaust gas increase, an oxidation reaction occurs in the catalyst 57, oxygen in the exhaust gas is consumed, and the exhaust temperature rises due to reaction heat. Further, since the catalyst 57 has a small capacity, only a part of the unburned HC and CO in the exhaust gas generated by the increase in the fuel injection amount can be consumed. NO after passing_xNO that reaches the absorbent 25 and is released_xUsed as a reducing agent.
[0088]
By the way, the temperature of the exhaust gas drops significantly when passing through the exhaust turbine 23. At this time, if the exhaust gas temperature is lower than the activation temperature required for the oxidation catalyst 57 to burn unburned HC or the like, oxygen cannot be consumed in the oxidation catalyst 57 as intended. Therefore, in the present embodiment, a small-sized oxidation catalyst 58 is disposed in the exhaust manifold 22 adjacent to the exhaust turbine 23. Since high-temperature exhaust gas before the temperature is reduced in the exhaust turbine 23 flows into the oxidation catalyst 58, unburned HC and the like in the exhaust gas easily burn in the oxidation catalyst 58. That is, the temperature of the exhaust gas flowing into the oxidation catalyst 58 is increased. Therefore, the temperature of the exhaust gas flowing into the oxidation catalyst 57 disposed downstream of the exhaust turbine 23 is maintained at or above its activation temperature.
[0089]
In this embodiment, an oxidation catalyst is used as the catalyst 57._xSince the absorbent has a function as an oxidation catalyst, a small amount of NO_xIt is also possible to use absorbents. Thus, a small amount of NO is used instead of the catalyst 57._xIf the absorbent is to be disposed, NO disposed downstream_xNO as a whole together with the absorbent_xProcessing capacity can be increased.
[0090]
In any of the above-described embodiments, when the operating region of the engine is in the second operating region II,_xThe throttle valve 20 of the air suction pipe 17 is closed at the time of release reduction to reduce the amount of intake air. For example, in these cases, the combined use of exhaust gas recirculation (EGR) is more effective in reducing the amount of oxygen in exhaust gas. There is. Although the above embodiment has been described only with respect to a diesel engine, the present invention is also applicable to a gasoline engine (lean burn engine) that performs lean combustion.
[0091]
【The invention's effect】
NO_xSince the exhaust gas flowing into the absorbent is reduced to a reducing atmosphere, NO_xNO with a small amount of reducing agent in the absorbent_xCan be released and reduced.
[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.
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 flowchart for processing a release flag.
FIG. 19 is a diagram showing increments in a first operation region I.
FIG. 20 is a diagram showing an increment in a second operation region II.
FIG. 21 is a flowchart for controlling operation of the engine.
FIG. 22 is an overall view showing a second embodiment of the compression ignition type internal combustion engine.
FIG. 23 is an overall view showing a third embodiment of the compression ignition type internal combustion engine.
FIG. 24 is an overall view showing a fourth embodiment of the compression ignition type internal combustion engine.
[Explanation of symbols]
6 ... Fuel injection valve
15 Exhaust turbocharger
20 ... Throttle valve
29… EGR passage
31 ... EGR control valve

Claims (5)

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 Comprising a switching means for switching the baked selectively, by consuming oxygen in the exhaust gas flowing into the _the NO _x absorbent to when releasing the NO _x from the NO _x absorbent from the _the NO _x absorbent internal combustion engine, characterized in that a oxygen consumption means for reducing the reducing agent consumption during _the NO _x releasing. 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 internal combustion engine of claim 1 wherein the oxygen consumption means comprising at least one oxidation catalyst, three-way catalyst or _the NO _x absorbent. 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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