JP3539238B2 - Internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an internal combustion engine, for example, a diesel engine, an engine exhaust passage and an engine intake passage are connected by an exhaust gas recirculation (hereinafter, referred to as EGR) passage in order to suppress generation of NOx, and exhaust gas is passed through the EGR passage. Gas, that is, EGR gas is recirculated into the engine intake passage. In this case, the EGR gas has a relatively high specific heat and can absorb a large amount of heat. Therefore, as the EGR gas amount increases, the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) Increases, the combustion temperature in the combustion chamber decreases. When the combustion temperature decreases, the amount of generated NOx decreases. Therefore, the higher the EGR rate, the lower the amount of generated NOx.
[0003]
As described above, it is known that the amount of generated NOx can be reduced by increasing the EGR rate as compared with the related art. 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 so that the generation amount of NOx and smoke is minimized within a range not exceeding the maximum allowable limit. I was However, even if the EGR rate is determined so that the amount of NOx and smoke generated is as small as possible, the reduction of the amount of generated NOx and smoke is limited, and in fact, a considerable amount of NOx and smoke is still generated. The current situation is to do it.
[0006]
However, if the EGR rate is made larger than the maximum permissible limit in the course of research on the combustion of a diesel engine, the smoke rapidly increases as described above. However, a peak exists in the amount of generated smoke. When the EGR rate is further increased, the smoke starts to decrease sharply, and when the EGR rate is increased to 70% or more during idling operation, and when the EGR gas is strongly cooled, the smoke is reduced to about 55% or more. Becomes zero. That is, it was found that soot was hardly generated. At this time, it has also been found that the amount of generated NOx is extremely small. After that, the reason why soot was not generated was studied based on this finding, and as a result, a new combustion system capable of simultaneously reducing soot and NOx, which has never been seen before, was constructed. This new combustion system will be described in detail later, but in short, it is basically based on stopping the growth of hydrocarbons in the middle of the process until the hydrocarbons grow into soot.
[0007]
That is, as a result of repeated experimental research, it has been found that when the temperature of the fuel during combustion in the combustion chamber and the gas temperature around it are below a certain temperature, the growth of hydrocarbons stops at a stage before reaching soot, and the fuel When the temperature of the gas surrounding the gas exceeds a certain temperature, hydrocarbons grow to soot at a stretch. In this case, the temperature of the fuel and the surrounding gas is greatly affected by the heat absorbing action of the gas around the fuel when the fuel is burned, and the amount of heat absorbed by the gas around the fuel is adjusted according to the calorific value at the time of burning the fuel. As a result, the temperature of the fuel and the surrounding gas can be controlled.
[0008]
Therefore, if the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is suppressed to a temperature at which the growth of hydrocarbons stops halfway, soot will not be generated, and the temperature of the fuel and the surrounding gas during combustion in the combustion chamber will be reduced. Can be suppressed below the temperature at which the growth of hydrocarbons stops halfway, by adjusting the amount of heat absorbed by the gas around the fuel. On the other hand, hydrocarbons whose growth has stopped halfway before reaching soot can be easily purified by post-treatment using an oxidation catalyst or the like. This is the basic idea of a new combustion system.
[0009]
[Problems to be solved by the invention]
However, a new combustion system as described above has not been disclosed yet. Therefore, the conventional combustion system already disclosed cannot provide a new effect based on the new combustion system described above.
[0010]
Accordingly, the present invention provides a method for recirculating exhaust gas while simultaneously preventing the emission of soot and NOx from an internal combustion engine, and even when the capacity of a water-cooled cooling device cannot be increased significantly. It is an object of the present invention to provide an internal combustion engine capable of cooling a gas to a desired temperature and supplying recirculated exhaust gas at a stable temperature into a combustion chamber.
[0011]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided an exhaust gas recirculation device for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage, and the amount of recirculated exhaust gas supplied into the combustion chamber. As the amount of soot is gradually increased, the amount of soot gradually increases and reaches a peak, and when the amount of recirculated exhaust gas supplied into the combustion chamber is further increased, fuel during combustion in the combustion chamber and its surroundings An internal combustion engine in which the gas temperature of the engine is lower than the soot generation temperature and soot is hardly generated, and an air-cooled cooling device and a water-cooling device are provided in an exhaust gas recirculation passage connecting an engine exhaust passage and the engine intake passage. With cooling system When the amount of recirculated exhaust gas supplied into the combustion chamber is larger than the amount of recirculated exhaust gas at which the amount of generated soot becomes a peak, and combustion is performed in which almost no soot is generated. An internal combustion engine is provided in which recirculated exhaust gas flowing in the exhaust gas recirculation exhaust passage is first cooled by the air-cooled cooling device, and then cooled by the water-cooled cooling device.
[0012]
In the internal combustion engine according to the first aspect, it is possible to perform low-temperature combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is larger than the amount of recirculated exhaust gas at which the generation amount of soot is at a peak and soot is hardly generated. Therefore, the emission of soot and NOx can be simultaneously prevented. Furthermore, since the air-cooled cooling device as well as the water-cooled cooling device is arranged in the exhaust gas recirculation passage, even if the capacity of the water-cooled cooling device cannot be increased so much, the recirculated exhaust gas is cooled to a desired temperature. Therefore, the engine operating range in which low-temperature combustion can be performed can be expanded. In addition, the recirculated exhaust gas is first cooled by an air-cooled cooling device, and then cooled by a water-cooled cooling device whose cooling water temperature is relatively stable regardless of fluctuations in the outside air temperature. Gas can be supplied into the combustion chamber.
[0013]
According to the invention as set forth in claim 2, a compressor including an exhaust turbine supercharger, wherein a portion of the engine intake passage upstream of the compressor of the exhaust turbine supercharger and the water-cooled cooling device are connected. An upstream passage, and a compressor downstream passage connecting a portion of the engine intake passage downstream of the compressor of the exhaust turbine supercharger and the water-cooled cooling device, wherein the engine intake passage and the water cooling The internal combustion engine according to claim 1, wherein a passage communicating with the cooling device is switched to the compressor upstream passage or the compressor downstream passage in accordance with a required amount of recirculated exhaust gas.
[0014]
According to the third aspect of the present invention, when the required amount of recirculated exhaust gas is large, the engine intake passage and the water-cooled cooling device are communicated via the compressor upstream passage. Is provided.
[0015]
In the internal combustion engine according to claims 2 and 3, when the required amount of recirculated exhaust gas is large, the upstream of the compressor of the exhaust turbine supercharger in the engine intake passage and the water-cooled cooling device are connected. Since the engine intake passage communicates with the water-cooled cooling device via the side passage, the recirculated exhaust gas introduced into the engine intake passage is pressurized by the compressor. Therefore, a larger amount of recirculated exhaust gas can be supplied to the combustion chamber than when the compressor is not pressurized.
[0016]
According to the invention as set forth in claim 4, an exhaust turbine supercharger and a turbine downstream of the exhaust turbine supercharger in the engine exhaust passage for oxidizing unburned hydrocarbons discharged from the combustion chamber. A catalyst having an oxidation function disposed on the side, a turbine upstream passage connecting the air-cooling type cooling device and a portion of the engine exhaust passage upstream of the turbine of the exhaust turbine supercharger, A catalyst downstream passage connecting the air-cooled cooling device to the downstream portion of the catalyst in the engine exhaust passage, wherein a passage for communicating the engine exhaust passage with the air-cooled cooling device is required. 2. The internal combustion engine according to claim 1, wherein the internal combustion engine is switched to the turbine upstream passage or the catalyst downstream passage according to the amount of recirculated exhaust gas.
[0017]
According to the invention described in claim 5, when the required amount of recirculated exhaust gas is large, the engine exhaust passage and the air-cooled cooling device are communicated via the catalyst downstream passage. Is provided.
[0018]
In the internal combustion engine according to claims 4 and 5, when the required amount of recirculated exhaust gas is large, the engine is provided via a catalyst downstream passage connecting a portion downstream of the catalyst in the engine exhaust passage and an air-cooled cooling device. The exhaust passage communicates with the air-cooled cooling device, that is, the recirculated exhaust gas purified by the catalyst passes through the exhaust gas recirculation passage. As a result, it is possible to prevent a large amount of deposit from adhering in the exhaust gas recirculation passage. Furthermore, in the internal combustion engine according to the fourth and fifth aspects, when the required amount of recirculated exhaust gas is small, that is, when there is no fear that a large amount of deposits will adhere to the exhaust gas recirculation passage, the exhaust gas in the engine exhaust passage is reduced. The engine exhaust passage and the air-cooled cooling device are arranged upstream of the turbine of the turbine supercharger, i.e., through a turbine upstream passage connecting the portion closer to the engine than the downstream portion and the air-cooled cooling device. Communicated. As a result, the exhaust pressure of the engine can be used when supplying the recirculated exhaust gas into the combustion chamber.
[0019]
According to the invention described in claim 6, a recirculation exhaust gas control valve for reducing the amount of recirculation exhaust gas supplied into the combustion chamber is provided, and the water-cooled cooling device is connected to the engine intake passage. A passage with a recirculation exhaust gas control valve, and a passage with a recirculation exhaust gas control valve to have no recirculation exhaust gas control valve for reducing the amount of recirculation exhaust gas supplied into the combustion chamber. Also, the pressure loss of the recirculated exhaust gas is small and the water-cooled cooling device is provided with a passage without a recirculated exhaust gas control valve connecting the engine intake passage, and the engine intake passage and the water-cooled cooling device are provided. 2. The internal combustion engine according to claim 1, wherein the communication passage is switched to the passage with the recirculation exhaust gas control valve or the passage without the recirculation exhaust gas control valve in accordance with a required amount of the recirculation exhaust gas. You.
[0020]
According to the invention described in claim 7, when the required amount of recirculated exhaust gas is large, the engine intake passage and the water-cooled cooling device are communicated via the passage without the recirculated exhaust gas control valve. An internal combustion engine according to claim 6 is provided.
[0021]
In the internal combustion engine according to the sixth and seventh aspects, when the required recirculation exhaust gas amount is large, the engine intake passage and the water-cooled cooling device are communicated via the passage without the recirculation exhaust gas control valve. The pressure loss of the recirculated exhaust gas is smaller than in the case where the recirculated exhaust gas is supplied into the combustion chamber through the passage with the exhaust gas control valve. As a result, a large amount of recirculated exhaust gas can be easily supplied.
[0022]
According to the invention of claim 8, there is provided the internal combustion engine of claim 1, wherein a catalyst having an oxidation function is disposed in an engine exhaust passage for oxidizing unburned hydrocarbons discharged from the combustion chamber. Is done.
[0023]
According to the ninth aspect of the present invention, there is provided the internal combustion engine according to the eighth aspect, wherein the catalyst comprises at least one of an oxidation catalyst, a three-way catalyst, and a NOx absorbent.
[0024]
In the internal combustion engine according to claims 8 and 9, since unburned hydrocarbons discharged from the combustion chamber are oxidized in the engine exhaust passage, the unburned hydrocarbons are prevented from being discharged from the internal combustion engine. Can be.
[0025]
According to the tenth aspect of the present invention, the first combustion in which the soot is hardly generated and the refueling supplied to the combustion chamber are smaller than the amount of the recirculated exhaust gas in which the amount of soot is peaked. Switching means for selectively switching between the second combustion having a small amount of circulating exhaust gas and the second combustion; and the second combustion being switched to the first combustion from the first combustion. An internal combustion engine according to claim 1, wherein the exhaust gas recirculation rate is sometimes changed stepwise.
[0026]
In the internal combustion engine according to the present invention, when the first combustion is switched from the first combustion to the second combustion, or when the second combustion is switched to the first combustion, the exhaust gas recirculation rate is changed in a stepwise manner, so that the exhaust gas is changed. It is possible to prevent the gas recirculation rate from being set to the exhaust gas recirculation rate at which the generation amount of soot becomes a peak.
[0027]
According to the eleventh aspect, the exhaust gas recirculation rate during the first combustion is approximately 55% or more, and the exhaust gas when the second combustion is performed. An internal combustion engine according to claim 10, wherein the recirculation rate is less than or equal to about 50 percent.
[0028]
12. The internal combustion engine according to claim 11, wherein the exhaust gas recirculation rate during the first combustion is substantially equal to or more than 55%, and the exhaust gas recirculation rate during the second combustion is performed. Is set to approximately 50% or less, it is possible to prevent the exhaust gas recirculation rate from being set to the exhaust gas recirculation rate at which the generation amount of soot reaches a peak.
[0029]
According to the twelfth aspect of the present invention, the operating range of the engine is divided into the first operating range on the low load side and the second operating range on the high load side, and the first operating range in the first operating range. 11. The internal combustion engine according to claim 10, wherein the second combustion is performed in the second operation range.
[0030]
In the internal combustion engine according to the twelfth aspect, when the first combustion can be performed, that is, when the temperature of the fuel and the surrounding gas during the combustion in the combustion chamber can be maintained lower than the soot generation temperature, The first combustion is performed in the first operation region on the low load side and the second combustion is performed in the second operation region on the high load side because the heat generation amount is limited to the engine low load operation in which the heat generation is relatively small. I do. Therefore, appropriate combustion can be performed according to the operation range.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0032]
FIG. 1 shows an embodiment in which 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.
[0033]
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.
[0034]
The engine exhaust passage and the engine intake passage are connected to each other via an exhaust gas recirculation (hereinafter, referred to as EGR) passage 29, and a water-cooled EGR cooler 32 and an air-cooled EGR cooler 1032 are arranged in the EGR passage 29. You. EGR gas flowing through the EGR passage 29 from the engine exhaust passage toward the engine intake passage is first cooled to a certain temperature by an air-cooled EGR cooler 1032, and then cooled to a target temperature by a water-cooled EGR cooler 32. You.
[0035]
Specifically, the air suction pipe 17 on the upstream side of the compressor 16 and the water-cooled EGR cooler 32 are connected via a first passage 1029, and a portion of the engine intake passage downstream of the compressor 16 is connected to a water-cooled EGR cooler. 32 is connected via a second passage 2029. An EGR control valve 31 driven by a step motor 30 is disposed in the second passage 2029. Further, a portion of the engine exhaust passage upstream of the turbine 23 and the air-cooled EGR cooler 1032 are connected via a third passage 3029, and the exhaust pipe 28 downstream of the catalyst 25 and the air-cooled EGR cooler 1032 are connected to each other. They are connected via a fourth passage 4029. The switching of the communication between the first passage 1029, the second passage 2029, the third passage 3029, and the fourth passage 4029 is performed by the switching valve 60. Since the EGR control valve for reducing the amount of the EGR gas is not arranged in the first passage 1029, the pressure loss of the EGR gas flowing in the first passage 1029 is reduced by the EGR gas flowing in the second passage 2029 when the EGR control valve 31 is fully opened. Pressure loss. In the embodiment shown in FIG. 1, the engine cooling water is guided into the EGR cooler 32, and the engine cooling water cools the EGR gas.
[0036]
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.
[0037]
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 combustion 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 °. The engine speed is determined by the crank angle sensor 52. output It is calculated based on the value. On the other hand, the output port 46 is connected to the fuel injection valve 6, the throttle valve control step motor 19, the EGR control valve control step motor 30, the fuel pump 35, and the switching valve 60 via the corresponding drive circuit 48.
[0038]
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, An experimental example showing a change in CO and NOx emissions is shown. 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.
[0039]
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 the generation amount of NOx becomes considerably low. On the other hand, at this time, the generation amounts of HC and CO begin to increase.
[0040]
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.
[0041]
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, the amount of generated NOx is considerably reduced as shown in FIG. The decrease in the amount of generated NOx 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 has decreased 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.
[0042]
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. .
[0043]
Summarizing these considerations based on the experimental results shown in FIGS. 2 and 3, when the combustion temperature in the combustion chamber 5 is low, the amount of generated soot becomes almost zero. The hydrocarbon will be discharged from the combustion chamber 5. As a result of further detailed experimental research on this, when the temperature of the fuel and the surrounding gas in the combustion chamber 5 is lower than a certain temperature, the growth process of the soot is stopped halfway, that is, the soot is It was found that no soot was generated, and soot was generated when the temperature of the fuel and its surroundings in the combustion chamber 5 exceeded a certain temperature.
[0044]
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 depending on various factors such as the type of fuel and the compression ratio of the air-fuel ratio. Although it cannot be said how many times, this certain temperature is closely related to the amount of NOx generated, so that this certain temperature can be defined to some extent from the amount of NOx generated. That is, as the EGR rate increases, the temperature of the fuel during combustion and the gas temperature around it decrease, and the amount of generated NOx decreases. At this time, when the generation amount of NOx becomes about 10 p.pm or less, soot is hardly generated. Therefore, the above-mentioned certain temperature substantially coincides with the temperature when the amount of generated NOx is around 10 ppm or less.
[0045]
Once soot is produced, it cannot be purified by post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in a state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Considering the post-treatment with the catalyst having the oxidation function, it is extremely difficult to discharge the hydrocarbon from the combustion chamber 5 in the state of the precursor of soot or in the state before the soot, or to discharge the hydrocarbon from the combustion chamber 5 in the form of soot. 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 soot precursor or previous state without producing soot in the combustion chamber 5 and removes the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.
[0046]
Now, in order to stop the growth of hydrocarbons before soot is generated, it is necessary to suppress the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 to a temperature lower than the temperature at which soot is generated. There is. In this case, it has been found that the endothermic effect of the gas around the fuel when the fuel is burned has an extremely large effect on suppressing the temperature of the fuel and the gas around the fuel.
[0047]
That is, if there is only air around the fuel, the evaporated fuel immediately reacts with the oxygen in the air and burns. In this case, the temperature of the air separated from the fuel does not rise so much, and only the temperature around the fuel becomes extremely high locally. That is, 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 locally becomes extremely high, the unburned hydrocarbons that have received the combustion heat will generate soot.
[0048]
On the other hand, when fuel is present in a mixed gas of a large amount of inert gas and a small amount of air, the situation is slightly different. In this case, the fuel vapor diffuses to the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, since the combustion heat is absorbed by the surrounding inert gas, the combustion temperature does not rise so much. That is, the combustion temperature can be kept low. That is, the presence of the inert gas plays an important role in suppressing the combustion temperature, and the combustion temperature can be suppressed low by the endothermic effect of the inert gas.
[0049]
In this case, in order to suppress the temperature of the fuel and the surrounding gas to a temperature lower than the temperature at which the soot is generated, an amount of the inert gas is required to be able to absorb enough heat to do so. Therefore, if the fuel amount increases, the required amount of inert gas increases accordingly. In this case, the larger the specific heat of the inert gas, the stronger the endothermic action, and therefore, the inert gas is preferably a gas having a large specific heat. In this regard, CO _Two Since EGR gas has a relatively large specific heat, it can be said that it is preferable to use EGR gas as the inert gas.
[0050]
FIG. 5 shows the relationship between the EGR rate and the smoke when the EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 5, the curve A shows a case where the EGR gas is cooled strongly and the EGR gas temperature is maintained at approximately 90 ° C., and the curve B shows a case where the EGR gas is cooled by a small cooling device. , Curve C shows the case where the EGR gas is not forcibly cooled.
[0051]
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.
[0052]
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.
[0053]
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.
[0054]
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.
[0055]
FIG. 6 shows a mixed gas amount of the EGR gas and the air necessary for setting the fuel temperature during combustion and the surrounding gas temperature to a temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas; Further, the ratio of air in the mixed gas amount and the ratio of EGR gas in the mixed gas are shown. In FIG. 6, the vertical axis indicates the total intake gas amount drawn into the combustion chamber 5, and the dashed line Y indicates the total intake gas amount that can be drawn into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis indicates the required load.
[0056]
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. Further, the amount of NOx generated at this time is about 10 p.pm or less, and therefore, the amount of generated NOx is extremely small.
[0057]
As the amount of fuel injection increases, the amount of heat generated when the fuel burns increases. Therefore, in order to maintain the temperature of the fuel and the surrounding gas at a temperature lower than the temperature at which soot is generated, the amount of heat absorbed by the EGR gas Must be increased. Accordingly, as shown in FIG. 6, the EGR gas amount must be increased as the injected fuel amount increases. That is, the EGR gas amount needs to increase as the required load increases.
[0058]
When the supercharging is not performed, the upper limit of the total intake gas amount X sucked into the combustion chamber 5 is Y. 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 supercharging 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.
[0059]
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.
[0060]
As described above, FIG. 6 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, even if the air amount is smaller than the air amount shown in FIG. The generation amount of NOx can be reduced to about 10 p.pm or less while the generation of NOx is prevented. Even if the air amount is larger than the air amount shown in FIG. Even with a lean of 18 to 18, the generation amount of NOx can be reduced to around 10 ppm or less while preventing the generation of soot.
[0061]
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, only a very small amount of NOx 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 if the combustion temperature is high. Not generated at all. Further, only a very small amount of NOx is generated.
[0062]
In this way, when low-temperature combustion is being performed, soot is not generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean, The generation amount of NOx becomes extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time.
[0063]
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, during the low load operation in the engine, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas around it at a temperature below the temperature at which the growth of hydrocarbons stops halfway. In addition, the second combustion, that is, the combustion that is usually performed conventionally, is performed during the high load operation of the engine. Here, the first combustion, that is, the low-temperature combustion, as is clear from the above description, the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of soot is peaked, and soot is almost generated. The second combustion, that is, the combustion that has been performed conventionally, is a combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of soot generation peaks. Say that.
[0064]
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 the first boundary between the first operating region I and the second operating region II, and Y (N) indicates the first operating region I and the second operating 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 performed 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).
[0065]
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 determined to have shifted to the second operation region II, and combustion is performed by a 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.
[0066]
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 operating region II, and even if the required load L becomes lower than the first boundary X (N), low-temperature combustion cannot be performed immediately. Because. That is, the low-temperature combustion does not immediately start unless the required load L becomes considerably low, that is, when the required load L becomes lower than the second boundary Y (N). The second reason is to provide a hysteresis for a change in the operation region between the first operation region I and the second operation region II.
[0067]
By the way, when the operation region of the engine is in the first operation region I and low-temperature combustion is being performed, soot is hardly generated, and instead, unburned hydrocarbons are in the form of a precursor of soot or a state before it. It is discharged from the combustion chamber 5. At this time, the unburned hydrocarbon discharged from the combustion chamber 5 is oxidized well by the catalyst 25 having an oxidizing function.
[0068]
As the catalyst 25, an oxidation catalyst, a three-way catalyst, or a NOx absorbent can be used. The NOx absorbent has a function of absorbing NOx when the average air-fuel ratio in the combustion chamber 5 is lean, and releasing NOx when the average air-fuel ratio in the combustion chamber 5 becomes rich.
[0069]
The NOx absorbent uses, for example, alumina as a carrier, and on the carrier, for example, alkali metals such as potassium K, sodium Na, lithium Li, cesium Cs, alkaline earths such as barium Ba, calcium Ca, lanthanum La, yttrium Y And at least one noble metal such as platinum Pt.
[0070]
Not only the oxidation catalyst but also the three-way catalyst and the NOx absorbent have an oxidation function. Therefore, the three-way catalyst and the NOx absorbent can be used as the catalyst 25 as described above.
[0071]
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.
[0072]
Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG.
[0073]
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.
[0074]
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.
[0075]
At the time of the idling operation, the throttle valve 20 is closed until the valve is almost fully closed. At this time, the EGR control valve 31 is also closed almost completely. 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.
[0076]
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.
[0077]
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 opened state except for a part, and the opening 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.
[0078]
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.
[0079]
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, the embodiment according to the present invention increases the target air-fuel ratio A / F as the required load L decreases. .
[0080]
The target air-fuel ratio A / F shown in FIG. 10A is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 10B. . In addition, as shown in FIG. 11A, the target opening ST of the throttle valve 20 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening degree SE of the EGR control valve 31 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 10A is stored in advance in the ROM 42 in the form of a map as a function of N. As shown in FIG. 11 (B), it is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N.
[0081]
FIG. 12A shows the target air-fuel ratio A / F when the second combustion, that is, the normal combustion according to the conventional combustion method is performed. In FIG. 12A, 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. 12A 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. In addition, as shown in FIG. 13A, the target opening ST of the throttle valve 20 necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening 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. 12A is stored in advance in the ROM 42 in the form of a map as a function of N. As shown in FIG. 13 (B), a map is stored in advance in the ROM 42 as a function of the required load L and the engine speed N.
[0082]
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.
[0083]
Next, the operation control will be described with reference to FIG. Referring to FIG. 15, first, in step 100, 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 101, 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 105, where low-temperature combustion is performed.
[0084]
When it is determined in step 101 that L> X (N), the routine proceeds to step 102 where the flag I is reset, and then proceeds to step 119 to perform the second combustion.
[0085]
If the flag I indicating that the operating state of the engine is in the first operating region I is not set in step 100, that is, if it is determined that the operating state of the engine is in the second operating region II, step 103 is performed. It is determined whether the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), the routine proceeds to step 119, where the second combustion is performed under a lean air-fuel ratio.
[0086]
On the other hand, when it is determined in step 103 that L <Y (N), the routine proceeds to step 104, where the flag I is set, and then proceeds to step 105 to perform low-temperature combustion.
[0087]
In step 105, 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 106, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG. Next, at step 107, it is determined whether or not the target opening SE is the full opening SEmax. In the case of YES, it is determined that the required EGR amount is large, and in order to easily supply a large amount of EGR gas, the first passage 1029 having a small pressure loss of the EGR gas is communicated in step 108, and the pressure of the EGR gas is reduced in step 109. The high-loss second passage 2029 is blocked. Next, in order to prevent a large amount of deposit from adhering in the EGR passage 29, the third passage 3029 is shut off in step 110, and the fourth passage 4029 is communicated in step 111.
[0088]
On the other hand, when NO is determined in step 107, it is determined that the required EGR amount is small and the EGR amount needs to be finely adjusted, and the EGR control valve is determined in step 112 in order to easily supply an accurate amount of EGR gas. The first passage 1029 having no EGR valve is shut off, and the second passage 2029 having the EGR control valve 31 is communicated. Next, in order to supply the EGR gas using the exhaust pressure of the engine, the third passage 3029 is communicated in step 114, and the fourth passage 4029 is shut off in step 115.
[0089]
Next, at step 116, the mass flow rate (hereinafter simply referred to as "intake air amount") Ga of the intake air detected by the mass flow rate detector 21 is taken in. Next, at step 117, the target air-fuel ratio is obtained from the map shown in FIG. A / F is calculated. Next, at step 118, based on the intake air amount Ga and the target air-fuel ratio A / F, a fuel injection amount Q necessary for setting the air-fuel ratio to the target air-fuel ratio A / F is calculated.
[0090]
When the required load L or the engine speed N changes during such low-temperature combustion, the opening of the throttle valve 20 and the opening of the EGR control valve 31 are immediately changed to the target according to the required load L and the engine speed N. The opening degrees ST and SE are made to match. Therefore, for example, when the required load L is increased, the amount of air in the combustion chamber 5 is increased immediately, and the generated torque of the engine is immediately increased.
[0091]
On the other hand, when the opening degree of the throttle valve 20 or the opening degree of the EGR control valve 31 changes to change the intake air amount, the change in the intake air amount Ga is detected by the mass flow rate detector 21, and the detected intake air amount The fuel injection amount Q is controlled based on Ga. That is, the fuel injection amount Q is changed after the intake air amount Ga is actually changed.
[0092]
In step 119, the target fuel injection amount Q is calculated from the map shown in FIG. 14, and the fuel injection amount is set as the target fuel injection amount Q. Next, at step 120, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 121, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 13B, and the opening of the EGR control valve 31 is set as the target opening SE.
[0093]
Next, at step 122, the intake air amount Ga detected by the mass flow detector 21 is taken. Next, at step 123, the actual air-fuel ratio (A / F) is obtained from the fuel injection amount Q and the intake air amount Ga. _R Is calculated. Next, at step 124, the target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 125, the actual air-fuel ratio (A / F) _R Is larger than the target air-fuel ratio A / F. (A / F) _R If> A / F, the routine proceeds to step 126, where the correction value ΔST of the throttle opening is decreased by a constant value α, and then the routine proceeds to step 128. (A / F) _R If .ltoreq.A / F, the routine proceeds to step 127, where the correction value .DELTA.ST is increased by a constant value .alpha. In step 128, the final target opening ST is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20, and the opening of the throttle valve 20 is set as the final target opening ST. That is, the actual air-fuel ratio (A / F) _R Of the throttle valve 20 is controlled so that the target air-fuel ratio A / F is obtained.
[0094]
As described above, when the required load L or the engine speed N changes during the second combustion, the fuel injection amount is immediately matched with the target fuel injection amount Q corresponding to the required load L and the engine speed N. For example, when the required load L is increased, the fuel injection amount is immediately increased, and thus the torque generated by the engine is immediately increased.
[0095]
On the other hand, when the fuel injection amount Q is increased and the air-fuel ratio deviates from the target air-fuel ratio A / F, the opening of the throttle valve 20 is controlled so that the air-fuel ratio becomes the target air-fuel ratio A / F. That is, the air-fuel ratio is changed after the fuel injection amount Q changes.
[0096]
In the embodiments described so far, the fuel injection amount Q is subjected to open-loop control during low-temperature combustion, and the air-fuel ratio changes the opening of the throttle valve 20 during second combustion. Is controlled by However, the fuel injection amount Q can be feedback-controlled based on the output signal of the air-fuel ratio sensor 27 when the low-temperature combustion is being performed, and the air-fuel ratio can be controlled by the EGR control when the second combustion is being performed. The control can also be performed by changing the opening of the valve 31.
[0097]
As described above, according to the present embodiment, in steps 105 to 118, the amount of EGR gas supplied into the combustion chamber 5 is larger than the amount of EGR gas at which soot generation peaks, and the low temperature at which soot is hardly generated. Since combustion is performed, soot and NOx emissions can be simultaneously prevented. Furthermore, since the air-cooled EGR cooler 1032 as well as the water-cooled EGR cooler 32 is disposed in the EGR passage 29, the EGR gas is cooled to a desired temperature even when the capacity of the water-cooled EGR cooler 32 cannot be increased so much. Therefore, the engine operating range in which low-temperature combustion can be performed can be expanded. In addition, since the EGR gas is first cooled by the air-cooled EGR cooler 1032 and then cooled by the water-cooled EGR cooler 32 whose cooling water temperature is relatively stable irrespective of the fluctuation of the outside air temperature, the EGR gas having a stable temperature is cooled. It can be supplied into the combustion chamber 5.
[0098]
Further, according to the present embodiment, when it is determined in step 107 that the required EGR gas amount is large, the first passage 1029 connecting the air suction pipe 17 on the upstream side of the compressor 16 and the water-cooled EGR cooler 32 is determined in step 108. Since the engine intake passage and the water-cooled EGR cooler 32 are communicated with each other, the EGR gas introduced into the engine intake passage is pressurized by the compressor 16. Therefore, a larger amount of EGR gas can be supplied into the combustion chamber 5 than when it is not pressurized by the compressor.
[0099]
Further, according to this embodiment, when it is determined in step 107 that the required EGR gas amount is large, in step 111, the fourth passage 4029 connecting the exhaust pipe 28 downstream of the catalyst 25 and the air-cooled EGR cooler 1032 is connected. Thus, the engine exhaust passage communicates with the air-cooled EGR cooler 1032, that is, the EGR gas purified by the catalyst 25 flows through the EGR passage 29. As a result, it is possible to prevent a large amount of deposit from adhering in the EGR passage 29. Further, when it is determined in step 107 that the required EGR gas amount is small, and there is no concern that a large amount of deposits will adhere in the EGR passage 29, in step 114, a portion on the upstream side of the turbine 23, that is, downstream of the catalyst 25, The engine exhaust passage and the air-cooled EGR cooler 1032 are communicated via a third passage 3029 that connects a portion closer to the engine body 1 than the side portion and the air-cooled EGR cooler 1032. As a result, the exhaust pressure of the engine can be used when supplying the EGR gas into the combustion chamber 5.
[0100]
Further, according to the present embodiment, when it is determined in step 107 that the required EGR gas amount is large, in step 108, the engine intake passage and the water-cooled EGR cooler 32 are communicated via the first passage 1029 having no EGR control valve. Therefore, the pressure loss of the EGR gas is smaller than when the EGR gas is supplied into the combustion chamber 5 through the second passage 2029 having the EGR control valve 31. As a result, a large amount of EGR gas can be easily supplied.
[0101]
【The invention's effect】
According to the first aspect of the invention, the capacity of the water-cooled cooling device cannot be increased so much while simultaneously preventing soot (smoke) and NOx from being discharged from the internal combustion engine. Also, the recirculated exhaust gas can be cooled to a desired temperature, and the recirculated exhaust gas having a stable temperature can be supplied into the combustion chamber.
[0102]
According to the second and third aspects of the present invention, by compressing the recirculated exhaust gas introduced into the engine intake passage by the compressor, a larger amount of the recirculated exhaust gas is burned than when the compressor is not pressurized. Can be supplied indoors.
[0103]
According to the fourth and fifth aspects of the present invention, it is possible to prevent a large amount of deposit from adhering in the exhaust gas recirculation passage, and to reduce the exhaust pressure of the engine when supplying the recirculated exhaust gas into the combustion chamber. Can be used.
[0104]
According to the sixth and seventh aspects of the present invention, a large amount of recirculated exhaust gas can be easily supplied by reducing the pressure loss of the recirculated exhaust gas.
[0105]
According to the eighth and ninth aspects of the invention, it is possible to prevent unburned hydrocarbons from being discharged from the internal combustion engine.
[0106]
According to the tenth and eleventh aspects of the present invention, it is possible to prevent the exhaust gas recirculation rate from being set to the exhaust gas recirculation rate at which the generation amount of soot reaches a peak.
[0107]
According to the twelfth aspect, appropriate combustion can be performed according to the operation range.
[Brief description of the drawings]
FIG. 1 is an overall view of a compression ignition type internal combustion engine.
FIG. 2 is a diagram showing amounts of smoke and NOx generated, and the like.
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 an air-fuel ratio and the like in a second combustion.
FIG. 13 is a diagram showing a map of a target opening degree of a throttle valve and the like.
FIG. 14 is a diagram showing a map of a fuel injection amount.
FIG. 15 is a flowchart for controlling operation of the engine.
FIG. 16 is a flowchart for controlling operation of the engine.
[Explanation of symbols]
5. Combustion chamber
15 Exhaust turbocharger
29… EGR passage
31 ... EGR control valve
32 ... water-cooled EGR cooler
60 ... switching valve
1032 ... Air-cooled EGR cooler

Claims (12)

An exhaust gas recirculation device that recirculates exhaust gas discharged from the combustion chamber into the engine intake passage is provided, and when the amount of recirculated exhaust gas supplied into the combustion chamber is increased, the amount of soot generated is reduced. When the amount of recirculated exhaust gas supplied into the combustion chamber increases further and reaches a peak, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the soot generation temperature. An internal combustion engine that generates almost no soot, wherein an air-cooled cooling device and a water-cooled cooling device are disposed in an exhaust gas recirculation passage connecting an engine exhaust passage and the engine intake passage, thereby generating soot. The amount of the recirculated exhaust gas supplied into the combustion chamber is larger than the amount of the recirculated exhaust gas having a peak amount, and the amount of the recirculated exhaust gas flows through the exhaust gas recirculation exhaust passage when combustion in which little soot is generated is performed. Recirculation exhaust gas The first cooled by the air-cooling type cooling device, then an internal combustion engine which is adapted to cooled by the water-cooling unit. An exhaust turbine supercharger, a compressor upstream passage connecting the water-cooled cooling device and an upstream portion of the exhaust turbine supercharger in the engine intake passage with respect to the compressor, and an engine intake passage in the engine intake passage. The exhaust turbine turbocharger further includes a compressor downstream passage that connects a portion downstream of the compressor and the water-cooled cooling device, and a passage that communicates the engine intake passage with the water-cooled cooling device is required. 2. The internal combustion engine according to claim 1, wherein the internal combustion engine is switched to the compressor upstream passage or the compressor downstream passage in accordance with an amount of the recirculated exhaust gas. 3. The internal combustion engine according to claim 2, wherein when a required amount of recirculated exhaust gas is large, the engine intake passage and the water-cooled cooling device are communicated via the compressor upstream passage. An exhaust turbine supercharger, and a catalyst having an oxidation function disposed in the engine exhaust passage downstream of a turbine of the exhaust turbine supercharger to oxidize unburned hydrocarbons discharged from the combustion chamber. A turbine upstream passage connecting the air-cooling type cooling device with a portion of the exhaust turbine turbocharger upstream of the turbine in the engine exhaust passage, and downstream of the catalyst in the engine exhaust passage. A catalyst downstream side passage connecting the side portion and the air-cooled cooling device, wherein a passage communicating the engine exhaust passage and the air-cooled cooling device is provided in accordance with an amount of recirculated exhaust gas required. The internal combustion engine according to claim 1, wherein the internal combustion engine is switched to the turbine upstream passage or the catalyst downstream passage. The internal combustion engine according to claim 4, wherein when a required amount of recirculated exhaust gas is large, the engine exhaust passage and the air-cooled cooling device are communicated via the catalyst downstream passage. A passage with a recirculation exhaust gas control valve comprising a recirculation exhaust gas control valve for reducing the amount of recirculation exhaust gas supplied to the combustion chamber and connecting the water-cooled cooling device and the engine intake passage; Since there is no recirculation exhaust gas control valve for reducing the amount of recirculation exhaust gas supplied to the combustion chamber, the pressure loss of the recirculation exhaust gas is smaller than that of the passage with the recirculation exhaust gas control valve, and A recirculation exhaust gas control valve-free passage connecting the water-cooled cooling device and the engine intake passage, wherein a passage for communicating the engine intake passage with the water-cooled cooling device is provided with a required recirculated exhaust gas; 2. The internal combustion engine according to claim 1, wherein the passage is switched to the passage with the recirculation exhaust gas control valve or the passage without the recirculation exhaust gas control valve according to the amount of gas. 7. The internal combustion engine according to claim 6, wherein when a required amount of the recirculated exhaust gas is large, the engine intake passage and the water-cooled cooling device are communicated via the passage without the recirculated exhaust gas control valve. The internal combustion engine according to claim 1, wherein a catalyst having an oxidizing function is disposed in an engine exhaust passage for oxidizing unburned hydrocarbons discharged from the combustion chamber. 9. The internal combustion engine according to claim 8, wherein the catalyst comprises at least one of an oxidation catalyst, a three-way catalyst, and a NOx absorbent. A first combustion in which the soot is hardly generated, and a second combustion in which the amount of the recirculated exhaust gas supplied to the combustion chamber is smaller than the amount of the recirculated exhaust gas in which the amount of generated soot becomes a peak. Switching means for selectively switching between the first combustion and the second combustion or the second combustion to the first combustion when the exhaust gas recirculation rate is changed stepwise. 2. The internal combustion engine according to claim 1, wherein said internal combustion engine is varied. The exhaust gas recirculation rate when the first combustion is performed is approximately 55% or more, and the exhaust gas recirculation rate when the second combustion is performed is approximately 50% or less. Item 11. The internal combustion engine according to Item 10. 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 combustion is performed in the first operating range, and the second operating range is performed. The internal combustion engine according to claim 10, wherein the second combustion is performed.

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