JP2000130218A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out the stable combustion without the generation of a smoke and an accidental fire at the warming up time of an engine. SOLUTION: A first combustion in which EGR gas amount in a combustion chamber 5 is much more than EGR gas amount in which the generation amount of a soot becomes peek and the soot is scarcely generated and a second combustion in which EGR gas amount in the combustion chamber 5 is less than EGR gas amount in which the generation amount of the soot becomes peek are carried out selectively. At the warming up time of an engine, the fuel injection timing is quickened, the fuel injection pressure is increased, the re-circulation exhaust gas ratio is dropped or the air fuel ratio is enlarged in comparison with after finishing the engine warming up.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an internal combustion engine.

[0002]

Conventionally than internal combustion engines, for example exhaust gas recirculation and engine exhaust passage and the engine intake passage in order to suppress the generation of the NO _x in the diesel engine (hereinafter, referred to as EGR) connected by passages, the Exhaust gas, that is, EGR gas, is recirculated through the EGR passage into the engine intake passage. In this case, the EGR gas has a relatively high specific heat, and therefore can absorb a large amount of heat.
The combustion temperature in the combustion chamber decreases as the GR gas amount increases, that is, as the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) increases. When the combustion temperature is lowered to decrease the generated amount of NO _x, thus the generation amount of the more NO _x to be increased EGR rate is lowered.

[0003] It has been found that can reduce the generation amount of the NO _x Thus conventionally increasing the EGR rate. However, when the EGR rate is increased, the soot generation amount, that is, smoke, starts to increase rapidly when the EGR rate exceeds a certain limit. In this regard, it has conventionally been considered that if the EGR rate is further increased, the smoke will increase indefinitely. Therefore, the smoke starts to increase rapidly.
The GR rate is considered to be the maximum allowable limit of the EGR rate.

Therefore, conventionally, the EGR rate is set within a range not exceeding the maximum allowable limit. The maximum allowable EGR rate varies considerably depending on the type of engine and fuel, but is approximately 30 to 50%.
Therefore, in a conventional diesel engine, the EGR rate is at most 3
It is reduced from 0% to about 50%.

As described above, conventionally, it has been considered that the maximum allowable limit exists for the EGR rate.
If the R rate is within the range not exceeding this maximum allowable limit, NO
_It was set so that the amount of _x and smoke generated was as small as possible. However, in this way EGR
Rate that there is a limit to the reduction of the NO _x and the amount of generated NO _x and the amount of smoke produced also defined to be as small as possible of smoke, in fact still a significant amount of N
At present, O _x and smoke are generated.

However, if the EGR rate is made larger than the maximum allowable limit in the course of research on the combustion of a diesel engine, the smoke rapidly increases as described above. However, the amount of generated smoke has a peak, and the peak exceeds this peak. EGR
When the rate is further increased, the smoke starts to decrease rapidly, 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. It was found that it was almost zero, that is, almost no soot was generated. In this case, N
Generation amount of O _x is also found that a very small amount.
After that, the reason why no soot was generated was examined based on this finding, and as a result, unprecedented soot and NO
_This has led to the construction of a new combustion system capable of simultaneously reducing _x . 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 stage until the hydrocarbons grow into soot.

That is, as a result of repeated experimental studies, it has been found that when the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is lower than a certain temperature, the growth of hydrocarbons is stopped at a halfway stage before reaching soot. However, when the temperature of the fuel and the gas around it rises above a certain temperature, the hydrocarbons grow into 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.

Accordingly, if the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, soot will not be generated, and the fuel during combustion in the combustion chamber and its surroundings will not be generated. Can be suppressed to a temperature 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 this new combustion system has already been filed by the present applicant (Japanese Patent Application No. 9-305850).

[0009]

However, in order to perform this new combustion, it is necessary to maintain the temperature of the fuel and the surrounding gas at the time of combustion at a low temperature below a certain temperature as described above. If it is too high, smoke is generated, and if it is too low, poor combustion occurs. That is, in order to perform this new combustion, it is necessary to maintain the temperature of the fuel and the surrounding gas during the combustion within the optimum temperature range. For this purpose, there are optimum values for the injection timing, the EGR rate, the air-fuel ratio, and the like. I do. Therefore, when performing new combustion, it is necessary to control the injection timing, the EGR rate, the air-fuel ratio, and the like to these optimum values.

However, the optimum values such as the injection timing, the EGR rate, and the air-fuel ratio necessary for maintaining the temperature of the fuel and the surrounding gas during combustion within the optimum temperature range are greatly affected by the engine temperature. The value differs during the warm-up operation and after the warm-up is completed. Therefore, when performing new combustion, it is necessary to control the injection timing, the EGR rate, the air-fuel ratio, etc. in consideration of this.

[0011]

Therefore, in the first invention,
As the amount of recirculated exhaust gas supplied to the combustion chamber increases, the amount of soot generation gradually increases and reaches a peak in an internal combustion engine. Increasing the amount of recirculated exhaust gas supplied to the engine, comprising means for judging whether or not the engine is warming up. Alternatively, the fuel injection pressure is increased, the recirculated exhaust gas rate is reduced, or the air-fuel ratio is increased.

In the second invention, in the first invention,
A catalyst having an oxidation function is placed in the engine exhaust passage.
You. In a third aspect, in the second aspect, the catalyst is an acid.
Catalyst, three-way catalyst or NO _xFrom at least one of the absorbents
Become. In the fourth invention, the exhaust gas is provided in the first invention.
The recirculation rate is approximately 55% or more.

In a fifth aspect, in the first aspect,
First combustion in which 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 soot is peaked and little soot is generated, and the recirculated gas at which the amount of soot is peaked There is provided switching means for selectively switching between the second combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is smaller than the amount in the second combustion.

In the sixth invention, in the fifth invention,
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. Combustion is performed.

[0015]

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 pipe 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.

On the other hand, the exhaust port 10 is connected to the exhaust manifold 2.
1 and the exhaust turbocharger 15 via the exhaust pipe 22
The exhaust gas turbine 23 is connected to a catalytic converter 26 having a built-in catalyst 25 having an oxidizing function via an exhaust pipe 24. An air-fuel ratio sensor 27 is arranged in the exhaust manifold 21.

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 EGR passage 29. The EGR passage 29 is driven by a step motor 30. EGR
A control valve 31 is arranged. 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, engine cooling water is guided into the intercooler 32,
The EGR gas is cooled by the engine cooling water.

On the other hand, the fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 34, via a fuel supply pipe 33. 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.

The electronic control unit 40 is composed of a digital computer, and a ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45, An output port 46 is provided. The output signal of the air-fuel ratio sensor 27 is input to the input port 45 via the corresponding AD converter 47, and the output signal of the fuel pressure sensor 36 is also input to the input port 45 via the corresponding AD converter 47. A temperature sensor 37 for detecting an engine cooling water temperature is attached to the engine main body 1, and an output signal of the temperature sensor 37 is input to an input port 45 via a corresponding AD converter 47. Accelerator pedal 5
To 0, a load sensor 51 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 50 is connected, 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 throttle valve control step motor 19, the EG via a corresponding drive circuit 48.
Step motor 30 for controlling R control valve and fuel pump 3
5 is connected.

FIG. 2 shows the throttle valve 2 when the engine is under low load operation.
Change in the output torque when changing the air-fuel ratio A / F (abscissa in FIG. 2) by changing the opening and the EGR rate of 0, and smoke, HC, CO, a change in emission of the NO _x It shows the experimental example 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.

As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the smoke is reduced when the EGR rate becomes close to 40% and the air-fuel ratio A / F becomes about 30. The generation starts to increase. 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 is around 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 N
The generation amount of O _x is considerably reduced. On the other hand, at this time, HC,
The amount of generated CO starts to increase.

FIG. 3A shows a change in the combustion pressure in the combustion chamber 5 when the amount of generated smoke is the largest when the air-fuel ratio A / F is around 21, and FIG. 3B shows the air-fuel ratio A / F. The graph shows the change in the combustion pressure in the combustion chamber 5 when the smoke generation amount is substantially zero when F is around 18. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), in the case of FIG. 3 (B) where the amount of smoke generation is almost zero, FIG.
It can be seen that the combustion pressure is lower than in the case shown in (A).

The following can be said from the experimental results shown in FIGS. That is, first, the air-fuel ratio A / F is 1
FIG. 2 when the smoke generation amount is almost zero at 5.0 or less.
As shown in ₍₁₎ , the generation amount of NOx is considerably reduced. N
That the generation amount of O _x produced falls means that the combustion temperature in the combustion chamber 5 is reduced, thus the combustion temperature in the combustion chamber 5 becomes low when the soot is hardly generated I can say. The same can be said from FIG. That is, in the state shown in FIG. 3B where almost no soot is generated, the combustion pressure is low.
The combustion temperature inside is low.

Second, when the amount of generated smoke, that is, the amount of generated soot becomes almost zero, as shown in FIG.
Emissions increase. This means that hydrocarbons are emitted without growing to soot. That is, the linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 4 are thermally decomposed when the temperature is increased in a state of lack of oxygen, soot precursors are formed, and then mainly, Soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot production 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 amount of generated soot becomes substantially zero, the emission amounts of HC and CO increase as shown in FIG. 2, but HC at this time is a precursor of soot or a hydrocarbon in a state before it. .

The above considerations based on the experimental results shown in FIGS. 2 and 3 can be summarized as follows. When the combustion temperature in the combustion chamber 5 is low, the amount of soot generation becomes almost zero. Is discharged from the combustion chamber 5. As a result of further detailed experimental study on this, if 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.

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, depends on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. Although the change can not be said that how many times since this certain temperature has a generation amount and the closely related of the nO _x, therefore this certain temperature is defined to a certain degree from the generation amount of the nO _x be able to. That is, the fuel and the gas temperature surrounding it at the time of combustion and the greater the EGR rate, decreases, the amount of the NO _x is reduced. Generation amount at this time NO _x is soot is hardly generated when it is around or less 10 ppm. Therefore, the above certain temperature is NO
It almost coincides with the temperature when the amount of generated _x is about 10 p.pm or less.

Once soot has been 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 a catalyst having an oxidation function as described above, it is extremely difficult to discharge hydrocarbons from the combustion chamber 5 in the state of a precursor of soot or in the state before the soot or in the form of soot from the combustion chamber 5. There is a big difference. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a 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.

Now, in order to stop the growth of hydrocarbons before the soot is generated, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 is set to a temperature lower than the temperature at which the soot is generated. It needs to be suppressed. 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.

That is, if there is only air around the fuel, the evaporated fuel immediately reacts with oxygen in the air and burns. In this case, the temperature of the air separated from the fuel does not rise so much, and only the temperature around the fuel becomes extremely high locally. That is, at this time, the air separated from the fuel hardly absorbs the heat of combustion heat of the fuel. In this case, since the combustion temperature becomes extremely high locally, the unburned hydrocarbons that have received the heat of combustion will generate soot.

On the other hand, the situation is slightly different when fuel is present in a mixed gas of a large amount of inert gas and a small amount of air.
In this case, the fuel vapor diffuses to the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, the combustion temperature is not increased so much because the combustion heat is absorbed by the surrounding inert gas. 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.

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 formed, an amount of the inert gas that can absorb a sufficient amount of heat to do so is required. . Therefore, if the fuel amount increases, the required amount of inert gas increases accordingly. In this case, the endothermic effect becomes stronger as the specific heat of the inert gas increases, and therefore, the inert gas preferably has a higher specific heat. In this regard, it can be said that it is preferable to use EGR gas as the inert gas since CO ₂ and EGR gas have relatively large specific heats.

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, a curve A indicates that the EGR gas temperature is substantially 9
Curve B shows the case where the EGR gas is cooled by a small cooling device, and curve C shows the case where the temperature is maintained at 0 ° C.
Indicates a case where the EGR gas is not forcibly cooled.

As shown by the curve A in FIG. 5, when the EGR gas is cooled strongly, the soot generation peaks at a point where the EGR rate is slightly lower than 50%. Above a percentage, little soot is generated. On the other hand, as shown by the curve B in FIG. 5, when the EGR gas is slightly cooled, the soot generation amount reaches a peak at a point where the EGR rate is slightly higher than 50%. In this case, the EGR rate is increased to about 65% or more. If so, almost no soot is generated.

As shown by the curve C in FIG.
When the R gas is not forcibly cooled, the EGR rate becomes 5
The soot generation amount peaks near 5%, and in this case, if the EGR rate is set to approximately 70% or more, 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 soot is hardly generated is reduced. 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.

FIG. 6 shows the mixing of EGR gas and air necessary to make the temperature of fuel during combustion and the surrounding gas temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas. It shows the gas amount, the ratio of air in the mixed gas amount, and the ratio of EGR gas in the mixed gas. In FIG. 6, the vertical axis indicates the total intake gas amount sucked into the combustion chamber 5, and the dashed line Y indicates the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis indicates the required load.

Referring to FIG. 6, the proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air necessary 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 soot is formed. The required minimum EGR gas amount is shown. This EGR gas amount is approximately 55% or more in terms of the EGR rate. In the embodiment shown in FIG.
0% or more. 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 of the air amount to the EGR gas amount in the total intake gas amount X is shown in FIG.
When the ratio is as shown in the following, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is generated, and thus no soot is generated. Further, the NO _x generation amount at this time is around 10 p.pm or less.
The amount of O _x generated is extremely small.

If the fuel injection amount 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 the soot is generated, the heat generated by the EGR gas is required. Must be increased. Therefore, 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.

By the way, when supercharging is not performed,
The upper limit of the total intake gas amount X sucked into the firing chamber 5 is Y.
Therefore, in FIG.₀Territory larger than
In the region, the EGR gas ratio increases as the required load increases.
The air-fuel ratio can be maintained at the stoichiometric air-fuel ratio unless reduced.
Can not. In other words, it is necessary when there is no supercharging.
Load demand is L₀Air-fuel ratio in the larger area than theoretical
When trying to maintain the fuel ratio, the required load increases.
As a result, the EGR rate decreases, and thus the required load becomes L ₀Than
In areas where the fuel and the surrounding gas temperature are
It will not be possible to maintain a temperature lower than the temperature produced.

[0039] However recirculating the required load is larger than L ₀ of the EGR gas into the air intake pipe 17 on the inlet side i.e. the exhaust turbocharger 15 via the EGR passage 29 supercharger as shown in FIG. 1 EGR rate of 5 in the region
It can be maintained at 5% or more, for example 70%, so that the temperature of the fuel and its surrounding gas can be kept 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.

[0040] In this case, the required load is EGR control valve 31 is fully opened is when the EGR rate more than 55 percent in the region larger than L _0, the throttle valve 20
Is slightly closed. 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. 10p.pm the generation amount of the NO _x while preventing the occurrence of longitudinal or can below, also be more than the amount of air shown the amount of air in FIG. 6, that is, the average of the air-fuel ratio Even when leaning from 17 to 18, the amount of generated NO _x can be reduced to around 10 ppm or less while preventing the generation of soot.

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 into soot, and soot is generated. There is no. Further, at this time NO _x even only an extremely small amount of generated. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature 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 _x
Only very small amounts are generated.

As described above, when low-temperature combustion is performed, soot is 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. Sarezu, the amount of the NO _x becomes extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time.

By the way, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, only when the engine is operating at low load and the calorific value due to combustion is relatively small. Can be 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 is usually 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 soot generation amount is at a peak, as is clear from the description so far. The second combustion, that is, the combustion that has been performed normally in the past, 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 is peaked. Say that.

FIG. 7 shows a first operation region I in which the first combustion, that is, low-temperature combustion is performed, and a second operation region II in which the second combustion, that is, combustion by the conventional combustion method, is performed. I have. In FIG. 7, the vertical axis TQ indicates the required torque, and the horizontal axis N indicates the engine speed. In FIG. 7, X (N) represents a first operation region I and a second operation region II.
, And Y (N) indicates a second boundary between the first operation region I and the second operation region II.
The determination of the change of the operating region from the first operating region I to the second operating region II is made based on the first boundary X (N),
Of the operating range from the operating range II to the first operating range I is determined based on the second boundary Y (N).

That is, when the operating state of the engine is in the first operating region I
The required torque TQ when low-temperature combustion is being performed
Exceeds the first boundary X (N) which is a function of the engine speed N, it is determined that the operating region has shifted to the second operating region II,
Combustion is performed by a conventional combustion method. Next, a second boundary Y (N) in which the required torque TQ is a function of the engine speed N
If it becomes lower than this, it is determined that the operation region has shifted to the first operation region I, and low-temperature combustion is performed again.

The two boundaries of the first boundary X (N) and the second boundary Y (N) having a lower torque side than the first boundary X (N) are provided as follows. For three reasons. The first reason is that the combustion temperature is relatively high on the high torque side of the second operating region II, and at this time, the required torque TQ
This is because even if the temperature becomes lower than (N), low-temperature combustion cannot be performed immediately. That is, the low-temperature combustion does not immediately start unless the required torque TQ becomes considerably low, that is, when the required torque TQ becomes lower than the second boundary Y (N). The second reason is that the first operating region I and the second operating region II
This is because hysteresis is provided for a change in the operating region during the period.

By the way, 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 the unburned hydrocarbon is replaced by the precursor of soot or the state before the soot. It is discharged from the combustion chamber 5 in the form. At this time, the unburned hydrocarbon discharged from the combustion chamber 5 is oxidized well by the catalyst 25 having an oxidizing function. Catalyst 2
As 5, an oxidation catalyst, a three-way catalyst, or a NO _x absorbent can be used. _The NO _x absorbent absorbs NO _x when the mean air-fuel ratio in the combustion chamber 5 of the lean, the combustion chamber 5
The average air-fuel ratio in the internal has a function of releasing NO _x becomes rich.

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

Not only the oxidation catalyst but also the three-way catalyst and the NO
_{The x} absorbent also has an oxidizing function, so that a three-way catalyst and a NO _x absorbent can be used as the catalyst 25 as described above. 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.

Next, 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 torque TQ. As shown in FIG. 9, in the first operating region I where the required torque TQ 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 degree of opening of the EGR control valve 31 is gradually increased from almost fully closed to fully open as the required torque TQ 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.

In other words, in the first operating region I, the EGR
The opening of the throttle valve 20 and the opening of the EGR control valve 31 are controlled such that the rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. At this time, the air-fuel ratio is controlled to the target lean air-fuel ratio by correcting the opening of the EGR control valve 31 based on the output signal of the air-fuel ratio sensor 27. 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 torque TQ is increased, and the injection completion timing θE is also changed to the injection start timing θS
Slows down as it slows down.

During 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. Throttle valve 2
If the valve is closed close to 0, 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.

On the other hand, the operating range of the engine is the first operating range I.
From the second operating region II 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, the EGR rate at which the EGR rate generates a large amount of smoke
The engine operating range is the first because it jumps over the rate range (Fig. 5).
A large amount of smoke does not occur when changing from the operating region I to the second operating region II.

In the second operation region II, the second combustion, that is, the conventional combustion is performed. In this combustion method generates little soot and NO _x, but the heat efficiency is higher than the low temperature combustion, thus as the operating region of the engine is shown in Figure 9 from the first operation area I changes to the second operating region II Thus, the injection amount is reduced stepwise. In the second operation region II, the throttle valve 20 is held in a fully open state except for a part, and the opening of the EGR control valve 31 is gradually reduced as the required torque TQ increases. In addition, this operation area II
In this case, the EGR rate decreases as the required torque TQ increases, and the air-fuel ratio decreases as the required torque TQ increases. However, the air-fuel ratio is a lean air-fuel ratio even when the required torque TQ increases. In the second operation region II, the injection start timing θS is set near the compression top dead center TDC. FIG.
(A) shows the relationship between the required torque TQ, the depression amount L of the accelerator pedal 50, and the engine speed N. In addition,
In FIG. 10A, each curve represents an equal torque curve, a curve indicated by TQ = 0 indicates that the torque is zero, and the remaining curves are TQ = a, TQ = b, and TQ =
The required torque gradually increases in the order of c and TQ = d. FIG.
The required torque TQ shown at 0 (A) is stored in the ROM 42 in advance in the form of a map as a function of the depression amount L of the accelerator pedal 50 and the engine speed N as shown in FIG. According to the present invention, the depression amount L of the accelerator pedal 50 and the engine speed N are obtained from the map shown in FIG.
Is calculated first, and the fuel injection amount and the like are calculated based on the required torque TQ.

FIG. 11 shows the air-fuel ratio A / F in the first operating region I after the completion of warm-up. In FIG. 11, A /
F = 15.5, A / F = 16, A / F = 17, A / F =
Each curve shown by 18 has an air-fuel ratio of 15.5, 16,
17 and 18, and the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 11, the air-fuel ratio is lean in the first operating region I, and the air-fuel ratio A / F is leaner in the first operating region I as the required torque TQ decreases.

That is, the lower the required torque TQ, the smaller the amount of heat generated by combustion. Therefore, as the required torque TQ decreases, low-temperature combustion can be performed even if the EGR rate is reduced. As the EGR rate decreases, the air-fuel ratio increases,
Therefore, as shown in FIG. 11, as the required torque TQ decreases, the air-fuel ratio A / F increases. Air / fuel ratio A / F
As the fuel torque increases, the air-fuel ratio A / F increases as the required torque TQ decreases in order to make the air-fuel ratio as lean as possible.

FIG. 12A shows the injection amount Q in the first operation region I, and FIG. 12B shows the injection start timing θS in the first operation region I after the completion of the warm-up. . As shown in FIG. 12A, the injection amount Q in the first operating region I is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N, and FIG. As shown in FIG.
Is also stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N.

The target opening ST of the throttle valve 20 required for setting the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 3 (A), EGR is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N, and is necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. FIG. 13 shows the target opening SE of the control valve 31.
As shown in (B), it is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N.

Further, in the embodiment according to the present invention, the fuel injection pressure in the first operating region I after the completion of the warm-up, that is, the target fuel pressure P in the common rail 34, as shown in FIG. It is stored in the ROM 42 in advance in the form of a map as a function of the engine speed N. FIG. 14 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 14, A / F = 24, A / F = 35, A / F = 45, A
/ F = 60 indicate target air-fuel ratios of 24 and 3 respectively.
5, 45, and 60 are shown.

FIG. 15A shows the injection amount Q in the second operation region II, and FIG. 15B shows the second operation region.
The injection start timing θS in II is shown. FIG.
As shown in FIG. 1A, the injection amount Q in the second operating region II is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N.
As shown in FIG. 5 (B), the injection start timing θS in the second operation region II is also stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N.

The target opening degree ST of the throttle valve 20 required for setting the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 6 (A), the EGR necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. 14 is stored in the ROM 42 in advance as a function of the required torque TQ and the engine speed N. FIG. 16 shows the target opening SE of the control valve 31.
As shown in (B), it is stored in the ROM 42 in advance in the form of a map as a function of the required torque TQ and the engine speed N.

Further, in the embodiment according to the present invention, the fuel injection pressure in the second operating region II, that is, the target fuel pressure P in the common rail 34 is changed to the required torque TQ and the engine speed N as shown in FIG. The function is stored in the ROM 42 in advance in the form of a map. FIG. 17 shows the relationship between the injection advance angle and the EGR rate at which good low-temperature combustion can be performed. That is, in FIG. 17, the area below the curve X1 indicates a misfire area in which misfire occurs after the completion of warm-up, and the area above the curve X2 indicates a smoke area in which smoke occurs after the completion of warm-up. , Curve X1 and curve X
The area surrounded by 2 indicates an appropriate area where good low-temperature combustion can be performed after the completion of warm-up.

In FIG. 17, the area below the curve Y1 indicates a misfire area where misfire occurs before the completion of warm-up, and the area above the curve Y2 indicates a smoke area where smoke occurs before the completion of warm-up. And the curve Y
The area surrounded by 1 and the curve Y2 indicates an appropriate area where good low-temperature combustion can be performed before the completion of warm-up. Before the completion of the warm-up, the engine temperature is lower than after the completion of the warm-up, and therefore, the temperature of the compressed air compressed in the combustion chamber 5 becomes lower, so that combustion becomes difficult. At this time, good combustion can be obtained by reducing the EGR rate and increasing the amount of air around the fuel.
Therefore, as can be seen from FIG. 17, the adaptation region Y before the completion of warm-up is lower than the adaptation region X after the completion of warm-up.
Become the rate side.

If the temperature of the compressed air is lower, the evaporation of the injected fuel will not be sufficiently promoted unless the fuel is injected earlier. Therefore, as can be seen from FIG. It is on the more advanced side of the injection timing than X. Therefore, in the present invention, the injection timing is advanced as the engine cooling water temperature TW is lower, as shown in FIG. 18A, or the engine cooling water temperature T, as shown in FIG.
The lower the W, the lower the EGR rate, or the lower the engine coolant temperature TW, the earlier the injection timing and the EGR
The rate is reduced. Incidentally, T ₀ represents the engine cooling water temperature is judged that warm-up of the engine has been completed in FIG. 18.

More specifically, the optimum value of the injection start timing θS at several engine cooling water temperatures TW lower than T ₀ is determined as a function of the required torque TQ and the engine speed N in FIG.
Before the warm-up is completed, the optimum value of the injection start timing θS is calculated from the plurality of maps by interpolation calculation based on the engine cooling water temperature TW before the warm-up is completed. Is done.

Similarly, at some engine cooling water temperatures TW lower than T ₀ , the target opening ST of the throttle valve 20 and the EGR control valve 3 required to make the EGR rate the optimum value are obtained.
1 target opening degree SE is required torque TQ and engine speed N
Is stored in the ROM 42 in advance in the form of a map as shown in FIGS.
Before the completion of the warming-up, the target opening of the throttle valve 20 and the EGR control valve 31 that provide the optimum EGR rate is calculated from the plurality of maps by interpolation based on the engine cooling water temperature TW.

When the fuel pressure in the common rail 34, that is, the fuel injection pressure is increased, the injection period is shortened, so that the same effect as when the injection timing is advanced is produced. Therefore, the target fuel pressure in the common rail 34 can be increased as the engine cooling water temperature TW decreases, as shown in FIG. In this case, the common rail 3 at some engine cooling water temperatures TW lower than T ₀
4 is stored in the ROM 42 in advance in the form of a map as shown in FIG. 13C as a function of the required torque TQ and the engine speed N. Based on the TW, a target fuel pressure in the common rail 34 is calculated from the plurality of maps by interpolation calculation.

When the air-fuel ratio is increased, the amount of air around the fuel increases, so that the fuel is easily burned. Therefore, FIG.
As shown in (D), the lower the engine cooling water temperature TW, the larger the air-fuel ratio A / F can be. In this case,
The target opening ST of the throttle valve 20 and the target opening SE of the EGR control valve 31 necessary for setting the air-fuel ratio to the optimum value at several engine cooling water temperatures TW lower than T ₀ are equal to the required torque TQ and the engine speed. FIG. 13 as a function of N
(A) and a map as shown in FIG. 13 (B) are stored in the ROM 42 in advance. Before the completion of the warm-up, the optimum empty space is calculated by interpolation from the plurality of maps based on the engine cooling water temperature TW. Throttle valve 20 and E to be fuel ratio
The target opening of the GR control valve 31 is calculated.

Next, the operation control will be described with reference to FIG. Referring to FIG. 19, first, step 1
At 00, 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, step 10
The program proceeds to 1 to determine whether the required torque TQ has become larger than the first boundary X1 (N). TQ ≦ X1 (N)
In the case of, the routine proceeds to step 103, where low-temperature combustion is performed.

That is, in step 103, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 104, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. Next, at step 105, the injection amount Q is calculated from the map shown in FIG. Next, at step 106, the injection start timing θS is calculated from the map shown in FIG. Next, at step 107, the target fuel pressure in the common rail 34, that is, the injection pressure P is calculated from the map shown in FIG.

Next, at step 108, the temperature sensor 37
The detected engine coolant temperature TW is whether lower than T ₀ is determined by. When TW> T ₀ , the processing cycle is completed. On the other hand, when TW ≦ T ₀ , the routine proceeds to step 109, in which the injection start timing is advanced based on the engine cooling water temperature TW, the fuel injection pressure is increased, or the EGR rate is reduced by the method described above. Or the air-fuel ratio is increased.

On the other hand, in step 101, TQ> X
When it is determined that (N) has been reached, the routine proceeds to step 102, where the flag I is reset.
And the second combustion is performed. That is, step 112
Then, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 113, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. Next, at step 114, FIG.
The injection amount Q is calculated from the map shown in FIG. Next, at step 115, the injection start timing θS is calculated from the map shown in FIG. Next, at step 116, the target fuel pressure in the common rail 34, that is, the injection pressure P is calculated from the map shown in FIG.

When the flag I is reset, in the next processing cycle, the routine proceeds from step 100 to step 110, where it is determined whether or not the required torque TQ has become lower than the second boundary Y (N). Step 1 when L ≧ Y (N)
Proceeding to 12, the second combustion is performed under the lean air-fuel ratio. On the other hand, if it is determined in step 110 that TQ <Y (N), the routine proceeds to step 111, where the flag I is set, and then proceeds to step 103 to perform low-temperature combustion.

[0074]

As described above, good low-temperature combustion can be obtained even during warm-up operation.

[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 NO _x 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 a required torque.

FIG. 11 is a diagram showing an air-fuel ratio in a first operation region I.

FIG. 12 is a diagram showing a map of an injection amount and the like.

FIG. 13 is a diagram showing a map of a target opening of the throttle valve and the like.

FIG. 14 is a view showing an air-fuel ratio in a second combustion.

FIG. 15 is a diagram showing a map of an injection amount and the like.

FIG. 16 is a view showing a map of a target opening of a throttle valve and the like.

FIG. 17 is a diagram showing an adaptation region in which good low-temperature combustion can be performed.

FIG. 18 is a diagram showing an injection advance angle and the like.

FIG. 19 is a flowchart for controlling operation of the engine.

[Explanation of symbols]

 6 Fuel injection valve 20 Throttle valve 29 EGR passage

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/24 F01N 3/24 R S Z F02D 21/08 301 F02D 21/08 301D 311 311B 41/02 380 41/02 380E 43/00 301 43/00 301J 301G 301N F02M 25/07 550 F02M 25/07 550H (72) Inventor Takekazu Ito 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Invention Person Yoshi ▲ Saki ▼ Koji 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Hiroki Murata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F term (reference) 3G062 AA01 AA05 BA02 BA05 BA06 CA02 CA06 EB05 ED08 FA09 FA10 GA04 GA05 GA06 GA08 GA15 GA21 3G084 AA01 BA09 BA14 BA15 BA20 CA02 DA10 DA28 EB08 EC03 FA10 FA38 3G091 AA10 AA11 AA18 AA28 AB02 AB03 AB06 BA15 BA17 BA19 CB00 CB02 CB03 CB07 CB08 DA02 DA05 DB10 EA00 EA02 EA07 EA16 EA30 EA31 EA34 FA02 GB04 GB03W12 GB04 GB03W12 GB AA17 AA18 BB06 BB08 DC09 EA03 EA07 EA11 EA21 FA17 FA18 GA02 GA05 GA06 HA11Z HB03X HB03Z HC03X HC03Z HD05Z HD07X HD07Z HE03Z HE08Z HF08Z 3G301 NE02 JA11 JA25 JA26 KA08 KA09 KA08 KA09 KA08 KA09 KA09 KA09 KA08 KA09 PA11A PA17Z PD03A PD15A PE01Z PE03Z PE04Z PF03Z

Claims (6)

[Claims] 1. An internal combustion engine in which the amount of soot generated gradually increases as the amount of recirculated exhaust gas supplied into a combustion chamber increases and reaches a peak, the amount of recirculated exhaust gas having a peak soot generation. Means for increasing the amount of recirculated exhaust gas supplied into the combustion chamber than the amount of fuel and for determining whether or not the engine is warming up. An internal combustion engine that has advanced timing, increased fuel injection pressure, reduced recirculated exhaust gas rate, or increased air-fuel ratio. 2. The internal combustion engine according to claim 1, wherein a catalyst having an oxidation function is disposed in the engine exhaust passage. 3. The catalyst according to claim 1, wherein said catalyst is an oxidation catalyst, a three-way catalyst or NO _x.
3. The internal combustion engine according to claim 2, wherein the internal combustion engine comprises at least one absorbent. 4. The internal combustion engine according to claim 11, wherein the exhaust gas recirculation rate is approximately 55% or more. 5. The first 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 amount of generated soot is at a peak and little soot is generated, and the amount of generated soot is at a peak. 2. The internal combustion engine according to claim 1, further comprising a switching unit that selectively switches between a second combustion in which an amount of recirculated exhaust gas supplied to the combustion chamber is smaller than an amount of recirculated gas that becomes the second combustion. 6. The engine operating region is divided into a first operating region on a low load side and a second operating region on a high load side, and a first combustion is performed in the first operating region. The internal combustion engine according to claim 5, wherein the second combustion is performed in the region.