JP2005113703A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal combustion engine capable of preventing purifying of exhaust gas from becoming insufficient due to lowering of temperature of an exhaust emission control device including a catalyst after the engine is restarted, in the case of the engine being temporarily stopped by economic running control or hybrid control. <P>SOLUTION: In this internal combustion engine, when the amount of inactive gas inside a combustion chamber is increased, the generated amount of soot increases and reaches its peak. The exhaust emission control device including the catalyst having an oxidation function is positioned in the engine exhaust passage. Before the engine is temporarily stopped, an operating mode is performed wherein the generated amount of substances, which causes an exothermic reaction in the exhaust emission control device, increases. The substances generating exothermic reaction are unburned HC and CO. In the operating mode, control is performed so that the amount of inert gas inside the combustion chamber is more than the amount of inert gas wherein the generation amount of soot is at its peak. Before the engine is temporarily stopped, the operating mode is performed at least during a set time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an internal combustion engine, and particularly when the engine is temporarily stopped by eco-run control, hybrid control, or the like, the temperature of an exhaust purification device including a catalyst is lowered, and exhaust purification after engine restart is insufficient. It is related with the internal combustion engine which can prevent becoming.

In a vehicle such as an automobile, a catalyst or as a three-way catalyst for purifying NO _X is a harmful components contained in engine exhaust, HC, to prevent their release into the atmosphere of CO them simultaneously, in the exhaust A particulate filter (such as DPF) that physically collects particulates is used. Exhaust purification devices such as catalysts and particulate filters do not operate effectively unless they are heated by engine exhaust and warmed (heated) above a certain activation temperature.

JP 2002-285878 A JP 2000-145512 A Japanese Patent No. 3230438 JP 2000-97078 A

  However, recently, while driving the vehicle, an eco-run vehicle that temporarily stops the engine when the vehicle is temporarily stopped due to traffic lights or traffic congestion, or a hybrid vehicle that properly uses the two driving sources of the engine and electric motor according to the driving state of the vehicle In these eco-run vehicles and hybrid vehicles, when the engine is temporarily stopped by eco-run control or hybrid control, high-temperature exhaust gas does not flow from the engine to the exhaust purification device, and the heat source flows for a long time. Will be lost. Therefore, there is a possibility that the temperature of the exhaust purification device may be lowered, and if the temperature is not within the temperature activation window of the exhaust purification device, exhaust emission after the engine is restarted is deteriorated.

  In Patent Document 1 (Japanese Patent Laid-Open No. 2002-285878), in an eco-run vehicle or a hybrid vehicle, the engine is temporarily stopped, and the temperature of the engine exhaust purification catalyst is a predetermined lower limit required for maintaining the purification function. There is disclosed a method for restarting the engine when a predetermined vehicle operation condition (engine temporary stop condition) is satisfied when the threshold value is lowered to the threshold value. However, according to this method, even when the vehicle is driven only by the motor, the engine is restarted in order to increase the catalyst temperature.

The object of the present invention is to prevent the exhaust gas purification device including the catalyst from dropping in temperature when the engine is temporarily stopped by eco-run control, hybrid control, etc., and exhaust gas purification after engine restart is insufficient. It is to provide an internal combustion engine that can.
Another object of the present invention is that when the engine is temporarily stopped by eco-run control, hybrid control, etc., the temperature of the exhaust purification device including the catalyst is lowered, and exhaust purification after the engine restart becomes insufficient. And an internal combustion engine capable of suppressing vibration when the internal combustion engine is stopped.

The internal combustion engine of the present invention is an internal combustion engine in which an exhaust purification device including a catalyst having an oxidizing function is disposed in an engine exhaust passage, and causes an exothermic reaction in the exhaust purification device before the engine is temporarily stopped. It is characterized in that an operation mode in which the amount of substances generated increases is executed.

  The internal combustion engine of the present invention is an internal combustion engine in which the generation amount of soot gradually increases and reaches a peak as the amount of inert gas in the combustion chamber increases, and includes a catalyst having an oxidation function in the engine exhaust passage Before the engine is temporarily stopped after the exhaust purification device is arranged, an operation mode in which the amount of substances that cause an exothermic reaction increases in the exhaust purification device is executed. In the operation mode, the amount of soot generated reaches a peak. The amount of inert gas in the combustion chamber is controlled to be larger than the amount of inert gas. The execution time of the operation mode is preferably immediately before the engine is temporarily stopped. When the operation mode is executed, the operation mode is switched from another operation mode. Substances that cause an exothermic reaction in the exhaust purification device include unburned HC and CO.

  In the internal combustion engine of the present invention, the operation mode is executed at least for a set time before the engine is temporarily stopped.

  The internal combustion engine of the present invention is characterized in that the execution time of the operation mode before the engine is temporarily stopped is changed according to the temperature of the exhaust purification device.

  The internal combustion engine of the present invention is characterized in that the operation mode before the engine is temporarily stopped is executed until the temperature of the exhaust purification device reaches a set temperature.

  In the internal combustion engine of the present invention, the air-fuel ratio is made rich in the operation mode before the engine is temporarily stopped.

  The internal combustion engine of the present invention is characterized in that in the operation mode before the engine is temporarily stopped, an operation in which the exhaust gas temperature is further increased is performed.

  According to the present invention, when the engine is temporarily stopped by eco-run control, hybrid control, or the like, the temperature of the exhaust purification device including the catalyst is prevented from being lowered and exhaust purification after the engine is restarted is prevented. can do.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 shows a case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. In FIG. 1, reference numeral 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, and 9 is Exhaust valves 10 indicate exhaust ports, respectively. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11. The surge tank 12 is connected to an outlet portion of a compressor 16 of a supercharger, for example, an exhaust turbocharger 15 via an intake duct 13 and an intercooler 14. An inlet portion of the compressor 16 is connected to an air cleaner 18 via an air suction pipe 17. A throttle valve 20 driven by a step motor 19 is disposed in the air suction pipe 17.

The exhaust port 10 is connected to an inlet portion of an exhaust turbine 23 of the exhaust turbocharger 15 via an exhaust manifold 21 and an exhaust pipe 22. An outlet portion of the exhaust turbine 23 is connected via an exhaust pipe 24 to a catalytic converter 26 having a built-in catalyst 25a having an oxidizing function and a particulate filter 25b for collecting particulates. The catalytic converter 26 is provided with a temperature sensor 27 for detecting the temperature of the catalyst 25a. Here, the temperature sensor 27 may be a sensor that detects the temperature of the particulate filter 25b instead of the temperature of the catalyst 25a.

  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. An EGR control valve 31 driven by a step motor 30 is disposed in the EGR passage 29. An intercooler 32 for cooling the EGR gas flowing through the EGR passage 29 is disposed in the EGR passage 29. The engine cooling water is guided into the intercooler 32, and the EGR gas is cooled by the engine cooling water.

  The fuel injection valve 6 is connected to a fuel reservoir, so-called common lane 34, through a fuel supply pipe 33. Fuel is supplied into the common lane 34 from an electrically controlled fuel pump 35 with variable discharge amount. The fuel supplied into the common lane 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 lane 34 is attached to the common lane 34. Based on the output signal of the fuel pressure sensor 36, the discharge amount of the fuel pump 35 is controlled so that the fuel pressure in the common lane 34 becomes the target fuel pressure.

  The crankshaft 37 is connected to the automatic transmission 38. The electronic control unit 40 comprises a digital computer and is connected to each other by a bidirectional bus 41. 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. The output signal of the temperature sensor 27 is input to the input port 45 via the corresponding AD converter 47. The output signal of the fuel pressure sensor 36 is also input to the input port 45 via the corresponding AD converter 47. In the surge tank 12, a pressure sensor 39 for detecting the absolute pressure in the surge tank 12 is disposed. A mass flow meter 49 for detecting the mass flow rate of the intake air is disposed in the air suction pipe 17 upstream of the throttle valve 20. The output signals of the pressure sensor 39 and the mass flow meter 49 are input to the input port 45 via the corresponding AD converter 47.

  Connected to the accelerator pedal 50 is a load sensor 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50. 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, 30 °. Further, an output pulse representing the vehicle speed of the vehicle speed sensor 53 is input to the input port 45. Further, the output signal of the neutral sensor 54 for detecting whether or not the automatic transmission 38 is in the neutral position is input to the input port 45. 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, and the fuel pump 35 via corresponding drive circuits 48.

In the present embodiment, before the engine is temporarily stopped by eco-run control or hybrid control, the present applicant discloses in Japanese Patent No. 3116876, Japanese Patent Laid-Open No. 2000-97078, Japanese Patent Laid-Open No. 2000-145512, and the like. The so-called low temperature combustion is performed. Here, as described in the above publication, low-temperature combustion is an internal combustion engine in which the generation amount of soot gradually increases and reaches a peak as the amount of inert gas in the combustion chamber increases. By controlling the amount of inert gas in the combustion chamber to be larger than the amount of inert gas that produces a peak, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is suppressed to a temperature lower than the temperature at which soot is generated. Thus, it is combustion that suppresses the generation of soot in the combustion chamber (almost no soot is generated).
Hereinafter, the low temperature combustion will be described in detail.

FIG. 2 shows changes in output torque when the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening degree and EGR rate of the throttle valve 20 during engine low load operation, and smoke, HC , CO, represents an experimental example illustrating changes in emissions of NO _x. As can be seen from FIG. 2, in this experimental example, the EGR rate increases as the air-fuel ratio A / F decreases, and the EGR rate is 65% or more when the air-fuel ratio is less than or equal to the theoretical air-fuel ratio (≈14.6).

As shown in FIG. 2, when the air-fuel ratio A / F is decreased by increasing the EGR rate, smoke is generated when the EGR rate becomes around 40% and the air-fuel ratio A / F becomes about 30. The amount starts to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is decreased, the amount of smoke generated increases rapidly and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke suddenly decreases, the EGR rate is increased to 65% or more, and when the air-fuel ratio A / F is near 15.0, the smoke becomes almost zero. . That is, almost no wrinkles occur. At this time, the output torque of the engine is slightly reduced and the generation amount of the NO _x becomes considerably lower. On the other hand, the generation amount of HC and CO starts to increase at this time. In addition, the experimental result of FIG. 2 was performed with the fuel injection timing fixed.

  FIG. 3A shows the combustion pressure change in the combustion chamber 5 when the air-fuel ratio A / F is near 21 and the amount of smoke generated is the largest. FIG. 3-2 shows the change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 18 and the amount of smoke generated is almost zero. As can be seen from a comparison between FIGS. 3-1 and 3-2, the case shown in FIG. 3-2 where the amount of smoke generated is almost zero is the case shown in FIG. 3-1, where the amount of smoke generated is large. It can be seen that the combustion pressure is low.

The following can be said from the experimental results shown in FIG. 2, FIG. 3-1, and FIG. That is, first, when the air-fuel ratio A / F is 15.0 or less and the amount of smoke generated is almost zero, the amount of NO _x generated decreases considerably as shown in FIG. That the generation amount of the NO _x is decreased, means that the combustion temperature in the combustion chamber 5 is lowered, when the soot is hardly generated, therefore, the combustion temperature in the combustion chamber 5 becomes lower I can say that. The same can be said from FIG. That is, in the state shown in FIG. 3-2 in which almost no soot is generated, the combustion pressure is low, and thus the combustion temperature in the combustion chamber 5 is low at this time.

  Second, when the amount of smoke generated, that is, the amount of soot is substantially zero, the HC and CO emissions increase as shown in FIG. This means that the hydrocarbons are discharged without growing up to the soot. That is, linear hydrocarbons and aromatic hydrocarbons as shown in FIG. 4 contained in the fuel are thermally decomposed to form soot precursors when the temperature is raised in an oxygen-deficient state. A soot made of a solid in which carbon atoms are gathered is generated. In this case, the actual soot formation process is complicated, and it is not clear what form the soot precursor will take, but in any case, the hydrocarbon as shown in FIG. It will grow up to heels through the body. Therefore, as described above, when the generation amount of soot becomes almost zero, the emission amount of HC and CO increases as shown in FIG. 2. At this time, HC is carbonized in the precursor of soot or in the previous state. Hydrogen (hereinafter referred to as unburned HC).

Summarizing these considerations based on the experimental results shown in FIG. 2, FIG. 3-1, and FIG. 3-2, when the combustion temperature in the combustion chamber 5 is low, the amount of soot generated becomes almost zero. The precursor or the hydrocarbon in the previous state is discharged from the combustion chamber 5. As a result of further detailed experimental research on this, if the temperature of the fuel in the combustion chamber 5 and the gas surrounding it are below a certain temperature, the soot growth process stops midway, that is, the soot It has been found that soot is not generated at all, and soot is generated when the temperature of the fuel in the combustion chamber 5 and the surrounding temperature rise above a certain temperature.

By the way, when the hydrocarbon production process stops in the state of soot precursor, the temperature of the fuel and its surroundings, that is, the certain temperature described above, varies depending on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. Although not say 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 to some extent from the generation amount of the nO _x Can be prescribed. That is, as the EGR rate increases, the temperature of the fuel and the surrounding gas during combustion decreases, and the amount of NO _x generated decreases. At this time, almost no soot is generated when the amount of NO _x generated is around 10 p.pm or less. Therefore, the above-mentioned certain temperature substantially coincides with the temperature when the amount of NO _x generated is around 10 p.pm or less.

  Once soot is produced, it cannot be purified by post-treatment using a catalyst having an oxidizing function. On the other hand, the precursor of soot or the hydrocarbon in the previous state can be easily purified by post-treatment using a catalyst having an oxidation function. Considering the post-treatment with a catalyst having an oxidizing function in this way, whether hydrocarbons are discharged from the combustion chamber 5 in the soot precursor or in the previous state or from the combustion chamber 5 in the form of soot. There is a huge difference. The combustion system employed in the present embodiment allows hydrocarbons to be discharged from the combustion chamber 5 in the form of the soot precursor or its previous state without generating soot in the combustion chamber 5. The core is to oxidize hydrogen with a catalyst having an oxidizing function.

  In order to stop the growth of hydrocarbons before the soot is generated, the temperature of the fuel and the surrounding gas in the combustion chamber 5 is suppressed to a temperature lower than the temperature at which the soot is generated. There is a need to. In this case, in order to suppress the temperature of the fuel and the surrounding gas, it has been found that the endothermic action of the gas around the fuel when the fuel burns has a great influence.

  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 away from the fuel does not increase so much, and only the temperature around the fuel becomes extremely high locally. That is, at this time, the air away from the fuel hardly performs the endothermic action of the combustion heat of the fuel. In this case, since the combustion temperature becomes extremely high locally, the unburned hydrocarbons that have received this heat of combustion produce soot.

  On the other hand, when fuel is present in a mixed gas of a large amount of inert gas and a small amount of air, the situation is slightly different. In this case, the evaporated fuel reacts with the oxygen diffused around and 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, in order to suppress the combustion temperature, the presence of the inert gas plays an important role, and the combustion temperature can be kept low by the endothermic action 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 soot is generated, an amount of inert gas that can absorb a sufficient amount of heat is required. Therefore, as the amount of fuel increases, the amount of inert gas required increases accordingly. In this case, the greater the specific heat of the inert gas, the stronger the endothermic action. Therefore, the inert gas is preferably a gas having a large specific heat. In this regard, it can be said that it is preferable to use EGR gas as an inert gas because CO ₂ and EGR gas have a relatively large specific heat.

FIG. 5 shows the relationship between the EGR rate and smoke when EGR gas is used as the inert gas and the cooling degree of the EGR gas is changed. That is, in FIG. 5, curve A shows a case where the EGR gas is strongly cooled and the EGR gas temperature is maintained at approximately 90 ° C. A curve B shows a case where the EGR gas is cooled by a small cooling device. A curve C shows a case where the EGR gas is not forcibly cooled.

  As shown by the curve A in FIG. 5, when the EGR gas is strongly cooled, the amount of soot generated peaks when the EGR rate is slightly lower than 50%. In this case, the EGR rate is approximately 55%. If the percentage is exceeded, almost no wrinkles occur. On the other hand, as shown by the curve B in FIG. 5, when the EGR gas is slightly cooled, the amount of soot generated peaks when the EGR rate is slightly higher than 50%. In this case, the EGR rate is approximately 65%. If the percentage is exceeded, almost no wrinkles occur.

  Further, as shown by the curve C in FIG. 5, when the EGR gas is not forcibly cooled, the amount of soot generated peaks when the EGR rate is around 55%. In this case, the EGR rate If almost 70% is set, almost no wrinkle is generated. FIG. 5 shows the amount of smoke generated when the engine load is relatively high. When the engine load is reduced, the EGR rate at which the amount of soot reaches a peak slightly decreases and soot hardly occurs. The lower limit of the EGR rate also decreases slightly. Thus, the lower limit of the EGR rate at which soot hardly occurs varies depending on the degree of cooling of the EGR gas and the engine load.

  FIG. 6 shows a mixed gas of EGR gas and air necessary for making the temperature of the fuel and the surrounding gas lower than the temperature at which soot is generated when EGR gas is used as the inert gas. And the ratio of air in the gas mixture and the ratio of EGR gas in the gas mixture. In FIG. 6, the vertical axis indicates the total intake gas amount sucked into the combustion chamber 5. A chain line Y indicates the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. The horizontal axis indicates the required load.

Referring to FIG. 6, the ratio of air, that is, the amount of air in the mixed gas indicates the amount of air necessary for completely burning 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 EGR gas, that is, the amount of EGR gas in the mixed gas, makes the temperature of the fuel and the surrounding gas lower than the temperature at which soot is formed when the injected fuel is burned. This shows the minimum amount of EGR gas required for this. This EGR gas amount is approximately 55% or more when expressed in terms of EGR rate, and in the embodiment shown in FIG. 6, it is 70% or more. That is, if the total intake gas amount sucked into the combustion chamber 5 is a solid line X in FIG. 6, and the ratio of the air amount and the EGR gas amount in the total intake gas amount X is a ratio as shown in FIG. The temperature of the fuel and the surrounding gas is lower than the temperature at which soot is produced, and so no soot is generated. Further, NO _x generation amount at this time, before and after 10 ppm, or at less, thus the generation amount of the NO _x becomes extremely small.

  If the amount of fuel injection increases, the amount of heat generated when the fuel burns increases, so 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 heat generated by the EGR gas The amount of absorption must be increased. Therefore, as shown in FIG. 6, the amount of EGR gas must be increased as the amount of injected fuel increases. That is, the amount of EGR gas 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 combustion chamber 5 is Y. Therefore, in the region where the required load is larger than L ₀ in FIG. The air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio unless the EGR gas ratio is decreased as the load increases. In other words, when supercharging is not performed and the air-fuel ratio is maintained at the stoichiometric air-fuel ratio in a region where the required load is greater than L ₀ , the EGR rate decreases as the required load increases. Thus, in a region where the required load is larger than L ₀ , the temperature of the fuel and the surrounding gas cannot be maintained at a temperature lower than the temperature at which soot is generated.

However, as shown in FIG. 1, the recirculated into the air intake pipe 17 on the inlet side i.e. the exhaust turbocharger 15 of turbocharger via the EGR passage 29 EGR gas, the required load is larger than L ₀ region The EGR rate can be maintained at 55 percent or higher, for example 70 percent, so that the fuel and surrounding gas temperatures can be maintained at a temperature lower than 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 intake gas boosted by the compressor 16 of the exhaust turbocharger 15 also becomes 70%. Thus, the temperature of the fuel and the surrounding gas can be maintained at a temperature lower than the temperature at which the soot is generated up to a limit that can be increased by the compressor 16. Therefore, the operating range of the engine that can cause low temperature combustion can be expanded.

In this case, when the EGR rate is set to 55% or more in a region where the required load is larger than L ₀ , the EGR control valve 31 is fully opened and 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 made smaller than that shown in FIG. 6, that is, the air-fuel ratio is made rich. However, the generation amount of NO _x can be reduced to around 10 p.pm or less while preventing the generation of soot, and even if the air amount is made larger than the air amount shown in FIG. Even if the average value is 17 to 18, the generation amount of NO _x can be reduced to around 10 p.pm 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 excessive fuel does not grow to soot, and so no soot is generated. . At this time, only a very small amount of NO _x 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 becomes high, but in this embodiment, the combustion temperature is suppressed to a low temperature. , No traps are generated. Furthermore, only a very small amount of NO _x is generated.

Thus, when low-temperature combustion is performed, soot is not generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean, NO is generated. The amount of _x generated is 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 during combustion in the combustion chamber and the gas temperature around it can be suppressed to a temperature below the temperature at which hydrocarbon growth stops halfway, only during low load operation in the engine where the amount of heat generated by combustion is relatively small. It is done. Therefore, in the present embodiment, at the time of engine low load operation, the temperature of the fuel during combustion and the surrounding gas is suppressed to a temperature below the temperature at which the growth of hydrocarbons stops midway, and the first combustion, that is, low temperature combustion is performed. Thus, during the engine high load operation, the second combustion, that is, the combustion normally performed conventionally is performed.
Here, the first combustion, that is, low-temperature combustion, is clear from the description so far, and as described above, the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of soot generation peaks. This refers to combustion in which almost no soot is generated, and the second combustion, that is, combustion that is normally performed in the past, is the amount of inert gas in the combustion chamber rather than the amount of inert gas in which the amount of soot peaks. Refers to low combustion.

FIG. 7 shows a first operation region I in which the first combustion, that is, low-temperature combustion is performed, and a second combustion region II in which the second combustion, that is, combustion by the conventional combustion method is performed.
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) indicates the first boundary between the first operation region I and the second operation region II, and Y (N) indicates the first operation region I and the first operation region I. The 2nd boundary with the driving | operation area | region II of 2 is shown. The change determination 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 from the second operation region II to the first operation region I. The operation region change determination is performed based on the second boundary Y (N).

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

  The two reasons for providing the first boundary X (N) and the second boundary Y (N) on the lower torque side than the first boundary X (N) are as follows. by. The first reason is that the combustion temperature is relatively high on the high torque side of the second operation region II, and even if the required torque TQ becomes lower than the first boundary X (N) at this time, the low temperature combustion can be performed immediately. Because there is no. That is, the low-temperature combustion is not started immediately unless the required torque TQ is considerably low, that is, when the required torque TQ is not lower than the second boundary Y (N). The second reason is to provide hysteresis with respect to a change in the operation region between the first operation region I and the second operation region II.

  By the way, when the engine operating state is in the first operating region I and low-temperature combustion is being performed, soot is hardly generated, and instead, unburned hydrocarbons are in the form of soot precursor or the state before that. Thus, it is discharged from the combustion chamber 5. At this time, if the catalyst 25a and the particulate filter 25b are activated, the unburned hydrocarbons discharged from the combustion chamber 5 are satisfactorily oxidized by the catalyst 25a and the particulate filter 25b having an oxidizing function. In the present embodiment, this action is actively used to suppress the temperature drop of the catalyst 25a and the particulate filter 25b when the engine is temporarily stopped by the eco-run control or the hybrid control, and the exhaust emission immediately after the engine is restarted. To reduce the deterioration. That is, when the engine is temporarily stopped by eco-run control or hybrid control in a state where the catalyst 25a and the particulate filter 25b are in the temperature activation window (above the catalyst activation temperature), low-temperature combustion is performed before the suspension. Then, hydrocarbons and carbon monoxide generated by low temperature combustion are supplied to the catalyst 25a and the particulate filter 25b to cause an exothermic reaction in the catalyst 25a and the particulate filter 25b, and then temporarily stop the engine. . Thereby, the temperature drop of the catalyst 25a and the particulate filter 25b when the engine is stopped is suppressed.

As the catalyst 25a can be used an oxidation catalyst, a three way catalyst or _the NO _x absorbent. The NO _x absorbent has a function of absorbing NO _x when the average air-fuel ratio in the combustion chamber 5 is lean, and releasing NO _x when the average air-fuel ratio in the combustion chamber 5 becomes rich. This NO _x absorbent is, for example, alumina as a carrier, and on this carrier, for example, alkaline metal such as potassium K, sodium Na, lithium Li, cesium Cs, alkaline earth such as barium Ba, calcium Ca, lanthanum La, yttrium. At least one selected from rare earths such as Y and a noble metal such as platinum Pt are supported.

In addition to the oxidation catalyst, the three-way catalyst and the NO _x absorbent also have an oxidizing function, and therefore the three-way catalyst and the NO _x absorbent can be used as the catalyst 25a as described above.

  The particulate filter 25b will be described with reference to FIGS. 12-1 and 12-2. Fig. 12-1 is a front view of the particulate filter 25b, and Fig. 12-2 is a side sectional view of the particulate filter 25b.

As shown in FIGS. 12A and 12B, the particulate filter 25b has a honeycomb structure and includes a plurality of exhaust flow passages 60 and 61 extending in parallel with each other. These exhaust flow passages are constituted by an exhaust gas inflow passage 60 whose downstream end is closed by a plug 62 and an exhaust gas outflow passage 61 whose upstream end is closed by a plug 63. In addition, in FIG. 12A, the hatched part shows the stopper 63. The exhaust gas inflow passages 60 and the exhaust gas outflow passages 61 are alternately arranged via thin partition walls 64. In other words, in the exhaust gas inflow passage 60 and the exhaust gas outflow passage 61, each exhaust gas inflow passage 60 is surrounded by four exhaust gas outflow passages 61, and each exhaust gas outflow passage 61 is constituted by four exhaust gas inflow passages 60. Arranged to be surrounded.

  The particulate filter 25b is made of a porous material such as cordierite, for example. Therefore, the exhaust gas that has flowed into the exhaust gas inflow passage 60 flows out into the adjacent exhaust gas outflow passage 61 through the surrounding partition wall 64 as indicated by an arrow in FIG. In the present embodiment, a carrier made of alumina, for example, is provided on the peripheral wall surfaces of the exhaust gas inflow passages 60 and the exhaust gas outflow passages 61, that is, on both side surfaces of the partition walls 64 and on the pore inner wall surfaces in the partition walls 64. A noble metal catalyst such as platinum Pt is supported on this support.

  In the combustion chamber 5, fine particles (particulates) mainly made of carbon C are generated, and therefore, these fine particles are contained in the exhaust gas. These fine particles contained in the exhaust gas become particulate when the exhaust gas flows in the exhaust gas inflow passage 60 of the particulate filter 25b or when going from the exhaust gas inflow passage 60 to the exhaust gas outflow passage 61. It is collected on the curate filter 25b.

  When the temperature of the particulate filter 25b is high and the amount of particulates in the exhaust gas is not so large, the particulates collected on the particulate filter 25b are oxidized without emitting a luminous flame in about several minutes to several tens of minutes. It can be removed.

  Next, operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG. FIG. 8 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. 8, in the first operation region I where the required torque TQ is low, the opening of the throttle valve 20 gradually increases from near full close to about 2/3 as the required load L increases. As the required load L increases, the opening degree of the EGR control valve 31 is gradually increased from near full close to full open. In the example shown in FIG. 8, in the first operating 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 opening degree of the throttle valve 20 and the opening degree of the EGR control valve 31 are controlled so that the EGR rate becomes approximately 70% and the air / fuel ratio becomes a slightly lean air / fuel ratio. Is done. In the first operating region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS becomes later as the required load L becomes higher. Further, the injection completion timing θE is delayed as the injection start timing θS is delayed.

  During the idling operation, the throttle valve 20 is closed to near full close, and at this time, the EGR control valve 31 is also closed to close to full close. When the throttle valve 20 is closed close to being fully closed, the pressure in the combustion chamber 5 at the start of compression becomes low, so the compression pressure becomes small. When the compression pressure is reduced, the compression work by the piston 4 is reduced, so that the vibration of the engine body 1 is reduced. That is, at the time of idling operation, the throttle valve 20 is closed to almost fully closed in order to suppress vibration of the engine body 1.

On the other hand, when the engine operating range is changed from the first operating range I to the second operating range II, the opening degree of the throttle valve 20 is increased stepwise from about 2/3 opening degree to the full opening direction. At this time, in the example shown in FIG. 8, the EGR rate is decreased in a step-like manner from approximately 70% to 40% or less, and the air-fuel ratio is increased in a step-like manner. That is, since the EGR rate exceeds the EGR rate range (FIG. 5) that generates a large amount of smoke, 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 nothing to do.

In the second operation region II, the second combustion, that is, the conventional combustion is performed. In this combustion method, soot and NO _x are generated slightly, but the thermal efficiency is higher than that of the low temperature combustion. Therefore, when the engine operating region is changed from the first operating region I to the second operating region II, it is shown in FIG. As a result, 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 thereof, and the opening degree of the EGR control valve 31 is gradually decreased as the required torque TQ increases. In this operation region II, 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 made a lean air-fuel ratio even when the required torque TQ increases. Further, in the second operation region II, the injection start timing θS is set near the compression top dead center TDC.

  FIG. 9 shows the relationship among the required torque TQ, the depression amount L of the accelerator pedal 50, and the engine speed N. In FIG. 9, each curve represents an equal torque curve, the curve indicated by TQ = 0 indicates that the torque is zero, and the remaining curves are TQ = a, TQ = b, TQ = The required torque gradually increases in the order of c and TQ = d. The required torque TQ shown in FIG. 9 is stored in advance in the ROM 42 in the form of a map as a function of the depression amount L of the accelerator pedal 50 and the engine speed N. In the present embodiment, the required torque TQ corresponding to the depression amount L of the accelerator pedal 50 and the engine speed N is first calculated, and the fuel injection amount and the like are calculated based on the required torque TQ.

  FIG. 10 shows the air-fuel ratio A / F in the first operating region I. In FIG. 10, the curves indicated by A / F = 15.5, A / F = 16, A / F = 17, and A / F = 18 have air-fuel ratios of 15.5, 16, 17, and 18, respectively. A certain time is shown, and the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 10, in the first operating region I, the air-fuel ratio is lean, and in the first operating region I, the air-fuel ratio A / F is made lean as the required torque TQ decreases. The

  That is, the lower the required torque TQ, the smaller the amount of heat generated by combustion. Therefore, the lower the required torque TQ, the lower the temperature combustion can be performed even if the EGR rate is lowered. When the EGR rate is lowered, the air-fuel ratio increases, so as shown in FIG. 10, the air-fuel ratio A / F increases as the required torque TQ decreases. As the air-fuel ratio A / F increases, the fuel consumption rate improves. Therefore, in order to make the air-fuel ratio as lean as possible, in this embodiment, the air-fuel ratio A / F is increased as the required torque TQ is decreased. .

  The injection amount Q in the first operation region I is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N. The injection start timing θS in the first operating region I is also stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N.

  Further, the target opening ST of the throttle valve 20 necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. 10 is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N. ing. The target opening degree SE of the EGR control valve 31 necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. 10 is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N. .

  Further, in the present embodiment, the fuel injection pressure in the first operation region I, that is, the target fuel pressure P in the common rail 34 is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N. Yes. FIG. 11 shows the target air-fuel ratio when the second combustion, that is, normal combustion by the conventional combustion method is performed. In FIG. 11, the curves indicated by A / F = 24, A / F = 35, A / F = 45, and A / F = 60 indicate the target air-fuel ratios 24, 35, 45, and 60, respectively. Yes.

  The injection amount Q in the second operation region II is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N. The injection start timing θS in the second operation region II is also stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N.

  Further, the target opening ST of the throttle valve 20 necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. 11 is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N. ing. The target opening degree SE of the EGR control valve 31 necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. 11 is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N. Yes.

  Further, in the present embodiment, the fuel injection pressure in the second operation region II, that is, the target fuel pressure P in the common rail 34 is stored in advance in the ROM 42 in the form of a map as a function of the required torque TQ and the engine speed N. Yes.

  By the way, the catalyst 25a and the particulate filter 25b do not exhibit a good oxidation / purification function unless the activation temperature corresponding to the type of the catalyst or the like, for example, 250 ° C. is raised, and therefore, the unburned gas contained in the exhaust gas. In order to oxidize and purify hydrocarbons and the like satisfactorily, it is necessary to keep the temperature of the catalyst 25a and the particulate filter 25b at an activation temperature or higher, for example, 350 ° C. or higher.

  However, in an eco-run vehicle or a hybrid vehicle, when the engine is temporarily stopped by eco-run control or hybrid control, high-temperature exhaust gas does not flow from the engine to the catalyst 25a or the particulate filter 25b, and the inflow of the heat source is interrupted for a long time. become. Therefore, there is a possibility that the temperature of the catalyst 25a and the particulate filter 25b may be lowered. If the temperature falls outside the temperature activation window of the catalyst 25a and the particulate filter 25b, the exhaust emission after the engine is restarted may be deteriorated. Become.

Therefore, in the present embodiment, immediately after normal combustion (second operation in the second operation region II), when the engine is temporarily stopped by eco-run control, hybrid control, or the like, the engine is immediately stopped as it is. The engine is temporarily stopped after the low temperature combustion (first operation in the first operation region I) is performed.
Immediately after the engine is restarted, an unheated HC or CO generated by low temperature combustion causes an exothermic reaction in the catalyst 25a or the particulate filter 25b to suppress the temperature drop of the catalyst 25a or the particulate filter 25b when the engine is stopped. To reduce the deterioration of exhaust emissions.

  Next, the operation of the present embodiment will be described with reference to FIG. The control shown in the flowchart described below is incorporated as a part of the operation program in the ROM 42 of the electronic control unit 40 of the eco-run vehicle or the hybrid vehicle according to this embodiment, and is started at the same time as the vehicle operation is started.

As shown in FIG. 13, first, it is determined whether or not low-temperature combustion is being performed (step 90).
). The low-temperature combustion here is the low-temperature combustion already described above, and starts because the required torque TQ is lower than the second boundary Y (N) that is a function of the engine speed N as shown in FIG. The low-temperature combustion that has been performed continuously since the required torque TQ does not exceed the first boundary X (N) that is a function of the engine speed N is included. Further, the low-temperature combustion in step 90 includes low-temperature combustion performed at the time of deceleration even when the above conditions shown in FIG. 7 are not satisfied. This low-temperature combustion at the time of deceleration is also performed in a range where the required torque does not increase at the time of deceleration.

  If it is determined as a result of step 90 that the low-temperature combustion is being performed, a counter for counting the execution time of the low-temperature combustion is incremented (step 91). On the other hand, if it is determined that the low temperature combustion is not being performed, the counter is reset (step 92). After step 91 or 92, proceed to step 100.

  In step 100, it is determined whether or not an engine pause command is output. Here, the engine temporary stop command is a command for temporarily stopping the engine by eco-run control, hybrid control, or the like. Since the present embodiment is a hybrid vehicle and includes a transmission that can relatively freely select a load applied to the engine, the timing at which the engine is temporarily stopped is selected in consideration of the fuel consumption and the temperature of the catalyst 25a and the like. Depending on the vehicle speed, etc., the vehicle may be driven at a high load with being high geared. For example, in the diesel engine according to the present embodiment, when the engine is rotated at a low load, the exhaust gas temperature is low and the catalyst 25a and the like are cooled. Therefore, the engine is temporarily stopped at a low load to maintain the temperature of the catalyst 25a. Is done.

  When the engine temporary stop command is output (S100-YES), the routine proceeds to step 101. When the engine temporary stop command is not output (S100-NO), the process returns to the first step 90 in FIG. 13 without performing the following steps 101 to 230 (return).

  In step 101, it is determined whether or not the engine is disconnected from the drive system. Here, because the engine temporary stop command is output (S100-YES), it is not necessary to transmit the engine output to the drive system. Here, since the engine is not yet disconnected from the drive system (S101-NO), the process proceeds to step 102. In step 102, an operation of disconnecting the engine from the drive system is performed. After step 102, the process proceeds to step 105. On the other hand, if the engine is disconnected from the drive system as a result of step 101 (S101-YES), step 102 is not executed and the routine proceeds to step 105.

  In step 105, it is determined whether or not low-temperature combustion is being performed. The low-temperature combustion in step 105 includes both low-temperature combustion performed in accordance with the above-described conditions in FIG. If it is determined as a result of step 105 that low temperature combustion is not being performed, the routine proceeds to step 200.

  In step 200, low temperature combustion is performed. In order to perform the low-temperature combustion, parameters such as the engine speed N, the opening ST of the throttle valve 20, the air-fuel ratio A / F, the fuel injection amount Q, the opening SE of the EGR control valve 31, and the like are predetermined values for low-temperature combustion. Controlled. As an example of control in this case, each parameter can be controlled so that the idling operation is performed under low temperature combustion. However, the low temperature combustion performed in step 200 is not limited to the idling operation, and various operation states can be considered in consideration of the amount of unburned HC and CO to be generated by the low temperature combustion. Hereinafter, as an example of step 200, control for performing an idling operation under low temperature combustion will be described.

  During the idling operation, as described above, the throttle valve 20 and the EGR control valve 31 are closed to near full close. During the idling operation, the engine idling speed N is controlled so as to become the target idling speed tN. The idling speed is controlled by controlling the opening degree of the throttle valve 20, that is, the intake air amount. Done by controlling.

  On the other hand, an actual intake air mass flow rate Ga (hereinafter simply referred to as intake air amount Ga) sucked into the combustion chamber 5 is detected by a mass flow meter 49. During the idling operation, the fuel injection amount Q required to make the air-fuel ratio the target air-fuel ratio A / F is calculated from the actual intake air amount Ga and the target air-fuel ratio A / F during idling. Therefore, during idling operation, if the intake air amount is increased to increase the engine speed, the fuel injection amount Q is increased, and if the intake air amount is decreased to decrease the engine speed, the fuel injection amount Q is It can be reduced.

  Further, during the idling operation, the EGR rate is controlled based on the pressure PM in the intake passage downstream of the throttle valve 20 so as to become the target EGR rate during the idling operation. That is, when the intake air amount Ga and the EGR gas amount are determined, the pressure PM in the intake passage downstream of the throttle valve 20 is determined. During the idling operation, the intake air amount Ga is substantially constant. Therefore, if the EGR gas amount is the target amount at this time, that is, if the EGR rate is the target EGR rate, the intake passage downstream of the throttle valve 20 The internal pressure PM becomes a certain constant pressure. Therefore, conversely, if the EGR amount is controlled so that the pressure PM in the intake passage downstream of the throttle valve 20 becomes this certain constant pressure, the EGR rate becomes the target EGR rate.

  Therefore, a certain constant pressure in the intake passage is stored in advance as the target pressure PM0, and the opening degree of the EGR control valve 31 is set so that the pressure PM in the intake passage downstream of the throttle valve 20 becomes the target pressure PM0. Is controlled so that the EGR rate becomes the target EGR rate. As a result, idling operation is performed under low temperature combustion. After step 200, the process proceeds to step 210.

  If it is determined in step 105 that the low-temperature combustion is being performed, the process proceeds to step 210 without executing step 200. This is because if low temperature combustion is currently being performed, control for performing low temperature combustion again in step 200 is not necessary.

  Although not shown, if it is determined in step 105 that the low-temperature combustion is being performed (S105-YES), the operation state of the low-temperature combustion similar to that in step 200 (above described) is determined before proceeding to step 210. In the example, each of the above parameters can be controlled to a predetermined value so that the idling operation is performed, and then the process can proceed to step 210.

  In step 210, it is determined whether or not the count value of the counter is equal to or greater than a predetermined threshold value. The count value of the counter indicates the time during which low-temperature combustion is continuously performed as shown in steps 91 and 92 above. The threshold value is set to a time necessary for obtaining a desired amount of unburned HC and CO generated by low-temperature combustion, that is, unburned HC and CO supplied to the catalyst 25a and the particulate filter 25b. Is done. In other words, the amount of unburned HC and CO generated corresponds to the amount of heat and the heat generation time in the catalyst 25a and the particulate filter 25b, and accordingly the temperature of the catalyst 25a and the particulate filter 25b decreases when the engine is stopped. The threshold value is set so that the suppression effect can be obtained to a desired level.

If the result of step 210 is that the count value of the counter is greater than or equal to the threshold value (S210-YES), permission to pause the engine is output (step 220). As a result, the engine is temporarily stopped based on the engine temporary stop command in step 100. Thereafter, the process proceeds to step 230, and the disconnection from the engine drive system performed in step 102 is released. Thereafter, the process returns to the top step 90 in FIG. 13 and the above-described flow is repeatedly executed (return).

  On the other hand, if the result of step 210 is that the count value of the counter is not equal to or greater than the threshold value (S210-NO), steps 220 and 230 are not executed, and the process returns to the top step 90 in FIG. The above flow is repeatedly executed (return).

  That is, if the count value is not greater than or equal to the threshold value as a result of step 210, it is determined that the time for continuously performing low-temperature combustion is insufficient and the amount of unburned HC and CO generated is insufficient. Thus, the temporary stop of the engine is not permitted and the disconnection from the engine drive system is not released, and the process returns to step 90 again. In this case, in step 90, since it is determined that low temperature combustion is being performed, the count value of the counter is incremented (S90-YES, S91). In the next step 100, the previous engine pause command is output without being executed (the previous step 210 is NO, so step 220 is not executed), so the engine pause command is being output. (S100-YES), the process proceeds to step 101.

  In step 101, since the state where the engine was previously disconnected from the drive system continues (S101-YES), the process proceeds to step 105 without executing step 102. In step 105, since it is determined that low temperature combustion is being performed (S105-YES), the process proceeds to step 210 without executing step 200. In step 210, it is determined again whether or not the counter value is equal to or greater than the threshold value.

  If it is determined in step 210 that the threshold is not equal to or greater than the above threshold (S210-NO), the engine temporary stop permission is not output and the disconnection from the engine drive system is not released. Then, the process returns to step 90 again. Thereafter, the above flow is repeated until the counter value becomes equal to or greater than the threshold value in step 210, and when the counter value becomes equal to or greater than the threshold value in step 210, permission to pause the engine is output. (S220), the state where the engine is disconnected from the drive system is released (S230).

Next, the effect of this embodiment will be described with reference to FIG.
Conventionally, as shown by the broken line in FIG. 14, since the engine temporary stop permission is issued immediately after the engine temporary stop command is output at the time of symbol a and the engine is stopped, the engine is stopped. From the point of time, the temperature of the catalyst 25a and the particulate filter 25b began to drop, and at the point of time d when the engine was restarted, the temperature of the catalyst 25a and the particulate filter 25b was lower than the lowest activation temperature Tcco. Therefore, the exhaust emission after the engine was restarted was getting worse. That is, after the engine is restarted, the exhaust gas discharged from the engine is heated by the catalyst 25a and the particulate filter 25b and the exhaust gas is not sufficiently purified until the activation minimum temperature Tcco is exceeded.

On the other hand, in the present embodiment, as indicated by the solid line in FIG. 14, low-temperature combustion for a predetermined time is always performed from when the engine temporary stop command is output until the engine temporary stop permission is issued. When low-temperature combustion is performed at the point of symbol a, a relatively large amount of a substance that reacts with a catalyst such as unburned HC or CO is generated, and the relatively large amount of unburned HC or CO is converted into a catalyst 25a or a particulate filter 25b. As a result, an exothermic reaction with a relatively large calorific value occurs in the catalyst 25a and the particulate filter 25b. Therefore, the temperature of the catalyst 25a and the particulate filter 25b rises. The temperature of the catalyst 25a and the particulate filter 25b starts to rise immediately after the low temperature combustion is started at the time point a, and a predetermined low temperature combustion time (step 210) indicated by the symbol b elapses. For a while after the engine is stopped and the engine is stopped, the temperature rises due to the oxidation reaction heat of unburned HC and CO supplied to the catalyst 25a and the particulate filter 25b within the period of symbol b. to continue. After the engine has stopped, the temperature gradually decreases from where it has risen, but in almost all normal cases, at a time point d before falling below the minimum activation temperature Tcco of the catalyst 25a and the particulate filter 25b. Since the engine is restarted, deterioration of exhaust emission after restart is reduced.

  As a means for raising the temperature of the catalyst instead of performing low temperature combustion, there is a method of raising the exhaust gas temperature by delaying the injection timing or the like. However, as in this embodiment, a long time after the engine is stopped. It is not necessarily suitable as a method for maintaining the temperature of the catalyst at a high temperature. This is because the method of discharging the exhaust gas temperature at a high temperature is effective only until the engine is stopped (while exhaust gas is discharged). On the other hand, in low-temperature combustion, unburned HC and CO contained in the exhaust gas discharged before the engine is stopped are supplied to the catalyst, and heat is generated in the catalyst even after the engine is stopped. Later, the temperature of the catalyst continues to rise, and the time during which the temperature is kept high becomes longer.

  Further, in the present embodiment, the following effects can be obtained by performing the low temperature combustion control immediately before the engine is stopped. During low-temperature combustion, since the negative pressure in the intake manifold is reduced by reducing the valve opening of the throttle valve 20, combustion noise is reduced, and vibration during stop of the engine itself can be suppressed. When low-temperature combustion is performed in the idling operation state, when the valve opening of the throttle valve 20 is closed to close to the fully closed state, the pressure in the combustion chamber 5 at the start of compression decreases, so the compression pressure decreases. When the compression pressure is reduced, the compression work by the piston 4 is reduced, so that the vibration of the engine body 1 is reduced.

  When low-temperature combustion is performed, the temperature of the fuel and the surrounding gas decreases, but the exhaust gas temperature increases. This contributes to an increase in the temperature of the catalyst 25a and the particulate filter 25b before the engine is stopped. An increase in exhaust gas temperature during low-temperature combustion will be described with reference to FIGS. 15-1 and 15-2.

  The solid line in FIG. 15A shows the relationship between the average gas temperature Tg in the combustion chamber 5 and the crank angle when low-temperature combustion is performed. The broken line in FIG. 15A shows the relationship between the average gas temperature Tg in the combustion chamber 5 and the crank angle when normal combustion is performed. The solid line in FIG. 15-2 shows the relationship between the crank angle and the fuel and its surrounding gas temperature Tf when low temperature combustion is performed. The broken line in FIG. 15-2 shows the relationship between the fuel and the surrounding gas temperature Tf and the crank angle when normal combustion is performed.

  When low-temperature combustion is performed, the amount of EGR gas is larger than when normal combustion is performed. Therefore, as shown in FIG. 15-1, before compression top dead center, that is, during the compression process. The average gas temperature Tg during low-temperature combustion indicated by the solid line is higher than the average gas temperature Tg during normal combustion indicated by the broken line. At this time, as shown in FIG. 15B, the fuel and the surrounding gas temperature Tf are substantially equal to the average gas temperature Tg.

Next, combustion is started near the compression top dead center. In this case, when low-temperature combustion is being performed, as shown by the solid line in FIG. The gas temperature Tf is not so high. On the other hand, when normal combustion is performed, since a large amount of oxygen exists around the fuel, as shown by the broken line in FIG. Extremely high. Thus, when normal combustion is performed, the temperature of the fuel and the surrounding gas temperature Tf are considerably higher than when low-temperature combustion is performed, but the temperatures of the other gases that occupy most of the fuel. Is lower in the case where the normal combustion is performed than in the case where the low temperature combustion is performed. Therefore, as shown in FIG. The average gas temperature Tg in 5 is higher when low-temperature combustion is performed than when normal combustion is performed. As a result, as shown in FIG. 15A, the burnt gas temperature in the combustion chamber 5 after the combustion is completed is higher when the low temperature combustion is performed than when the normal combustion is performed. Therefore, when the low temperature combustion is performed, the exhaust gas temperature becomes high.

Next, a second embodiment will be described with reference to FIG.
In the second embodiment, only part of the operation flow is different from that in the first embodiment, and the rest is common. Common points will be denoted by the same reference numerals, detailed description thereof will be omitted, and differences will be mainly described.

  As shown in FIG. 16, first, it is determined whether or not low-temperature combustion is being performed (step 90). If the low temperature combustion is being performed, a counter for counting the execution time of the low temperature combustion is incremented (step 91). On the other hand, if the low temperature combustion is not being performed, the counter is reset (step 92). After step 91 or 92, proceed to step 100. In step 100, it is determined whether or not an engine pause command is output. When the engine temporary stop command is output (S100-YES), the routine proceeds to step 101. When the engine temporary stop command is not output (S100-NO), the process returns to the first step 90 in FIG. 16 without performing the following steps 101 to 230 (return).

  In step 101, it is determined whether or not the engine is disconnected from the drive system. Here, since the engine is not yet disconnected from the drive system (S101-NO), the process proceeds to step 102. In step 102, an operation of disconnecting the engine from the drive system is performed. After step 102, the process proceeds to step 301. On the other hand, if the engine is disconnected from the drive system as a result of step 101 (S101-YES), step 102 is not executed and the routine proceeds to step 301.

  In step 301, it is determined whether or not the temperature Tc of the catalyst 25a or the particulate filter 25b is lower than a preset temperature Tset1. Here, the temperature Tset1 is a temperature higher than the lowest activation temperature Tcco. As a result of step 301, when the temperature Tc of the catalyst 25a or the particulate filter 25b is lower than the preset temperature Tset1, the flag 1 is set (step 302), and then the process proceeds to step 105. As a result of step 301, when the temperature Tc is not lower than the temperature Tset1, the process proceeds to step 105 as it is.

  In step 105, it is determined whether or not low-temperature combustion is being performed. If the result of step 105 is that low temperature combustion is not being performed, the routine proceeds to step 200.

  In step 200, low temperature combustion is performed. In order to perform the low-temperature combustion, parameters such as the engine speed N, the opening ST of the throttle valve 20, the air-fuel ratio A / F, the fuel injection amount Q, the opening SE of the EGR control valve 31, and the like are predetermined values for low-temperature combustion. To be controlled. After step 200, the process proceeds to step 303. If it is determined in step 105 that low temperature combustion is being performed, the process proceeds to step 303 without executing step 200.

Although not shown, if it is determined in step 105 that the low-temperature combustion is being performed (S105-YES), the operation state of the low-temperature combustion is the same as that in step 200 before proceeding to step 303. As described above, the above parameters can be controlled to predetermined values, and thereafter, the process can proceed to step 303.

  In step 303, it is determined whether or not flag 1 is set. If flag 1 is set, the process proceeds to step 304; otherwise, the process proceeds to step 305.

  In step 304, it is determined whether or not the count value of the counter is equal to or greater than a first set value. In step 305, it is determined whether or not the count value of the counter is greater than or equal to a second set value. Here, the first set value is larger than the second set value. As a result of step 304, if it is determined that the counter value is equal to or greater than the first set value, permission to pause the engine is output (step 220). Similarly, if it is determined in step 305 that the counter value is greater than or equal to the second set value, permission to temporarily stop the engine is output (step 220). After step 220, the process proceeds to step 230, and the disconnection from the engine drive system performed in step 102 is released. After step 230, the process proceeds to step 306, where the flag 1 is reset. Thereafter, the process returns to the top step 90 in FIG. 16, and the above-described flow is repeatedly executed (return).

  In the second embodiment, when the temperature Tc of the catalyst 25a or the particulate filter 25b is not equal to or higher than the set temperature Tset1 in step 301, the time is longer than when the temperature Tc is equal to or higher than the set temperature Tset1. (First setting value) If the low-temperature combustion is not continuously performed, the engine is not allowed to be temporarily stopped. As a result, when the engine temporary stop command is issued, the catalyst 25a and the particulate filter 25b having a relatively low temperature are subjected to low temperature combustion for a relatively long period of time, and a relatively large amount of unburned HC. When CO and CO are supplied to the catalyst 25a and the particulate filter 25b, the heat generation amount and the heat generation time in the catalyst 25a and the particulate filter 25b can be relatively increased, and the catalyst 25a and the particulate filter 25b A relatively large temperature rise can be secured. Therefore, it is possible to sufficiently prepare for the temperature drop of the catalyst 25a or the particulate filter 25b after the subsequent temporary stop of the engine.

Next, a third embodiment will be described.
In the third embodiment, only a part of the operation flow is different from that in the first embodiment, and the rest is common. For common points, detailed description thereof is omitted, and differences will be mainly described.

  In the third embodiment, when it is determined in step 210 of the first embodiment shown in FIG. 13 that the counter value is equal to or greater than a predetermined value, the temperature Tc of the catalyst 25a or the particulate filter 25b is preset. It is determined whether or not the temperature is equal to or higher than Tset2. As a result of the determination, the low temperature combustion is continued without proceeding to step 220 in FIG. 13 until the temperature Tc becomes equal to or higher than the preset temperature Tset2. As a result of the determination, when the temperature Tc becomes equal to or higher than the preset temperature Tset2, a permission to stop the engine is output (S220).

  In the first embodiment, when it is determined in step 210 that the counter value is equal to or greater than the predetermined value, the engine temporary stop permission is output immediately (S220). In the third embodiment, In step 210, even if the counter value is equal to or greater than a predetermined value, the low-temperature combustion is not stopped unless the temperature Tc of the catalyst 25a or the particulate filter 25b has risen to a preset temperature Tset2 or higher (engine temporary combustion). Do not allow suspension). This further reliably reduces the deterioration of exhaust emission when the engine is restarted after being temporarily stopped.

Next, a fourth embodiment will be described.
The fourth embodiment is the same as the first embodiment except for a part of the operation flow and the rest. For common points, detailed description thereof is omitted, and differences will be mainly described.

  In the fourth embodiment, in step 200 of the first embodiment, the air-fuel ratio when the low temperature combustion is performed is further made rich. During low temperature combustion before the permission to pause the engine is output, by making the air-fuel ratio rich, a larger amount of unburned HC and CO can be discharged from the engine, and the oxidation reaction heat causes a catalyst. The temperature of 25a or the particulate filter 25b can be raised. This will be described in detail below.

First operation region I performed according to the conditions of FIG. 7, that is, as shown in FIG. 7, is started because the required torque TQ is lower than the second boundary Y (N) that is a function of the engine speed N. In the low-temperature combustion that is continuously performed because the required torque TQ does not exceed the first boundary X (N) that is a function of the engine speed N, the lean air Low temperature combustion is performed under the fuel ratio. Accordingly, excess oxygen is contained in the exhaust gas, and this excess oxygen is adsorbed in the catalyst 25a or the particulate filter 25b (O ₂ storage effect). Even when the second operation region II (normal combustion) is performed according to the conditions of FIG. 7 instead of the first operation region I, the normal combustion is normally performed at a lean air-fuel ratio. Therefore, the exhaust gas contains excess oxygen, and the excess oxygen is adsorbed in the catalyst 25a or the particulate filter 25b (O ₂ storage effect). Therefore, even when either low-temperature combustion or normal combustion is performed, the O ₂ storage effect is sufficiently achieved. When the fuel HC and CO are discharged, the unburned HC and CO are oxidized by a large amount of oxygen adsorbed on the catalyst 25a or the particulate filter 25b, and the catalyst 25a or the particulates are generated by the oxidation reaction heat at this time. The temperature of the curate filter 25b is raised.

  Therefore, in the fourth embodiment, as shown in step 200a, the air-fuel ratio is made rich in the low-temperature combustion performed immediately before the temporary stop of the engine. When the air-fuel ratio is made rich, a large amount of unburned HC and CO is discharged from the engine, and thus the temperature Tc of the catalyst 25a or the particulate filter 25b rises due to the heat of oxidation reaction. As a result, it is possible to effectively prepare for a decrease in the temperature of the catalyst 25a or the particulate filter 25b after the subsequent temporary stop of the engine. Further, in the low temperature combustion performed immediately before the engine is temporarily stopped, the temperature of the catalyst 25a and the like can be increased by making the air-fuel ratio rich even if the execution time of the low temperature combustion performed immediately before the engine is temporarily stopped is short. Can do.

Next, a fifth embodiment will be described.
In the fifth embodiment, only part of the operation flow is different from that of the second embodiment, and the rest is common. For common points, detailed description thereof is omitted, and differences will be mainly described.

  Unlike the second embodiment, when the temperature Tc of the catalyst 25a or the particulate filter 25b is not equal to or higher than the set temperature Tset1 and the flag 1 is set (S303-YES), the air-fuel ratio at the time of low-temperature combustion is rich. If the temperature Tc is equal to or higher than the set temperature Tset1 (S303-NO), the air-fuel ratio at the time of low-temperature combustion is not made rich (usually made lean).

As a result, when the engine pause command is issued, the catalyst 25a and the particulate filter 25b having a relatively low temperature are made rich in the air-fuel ratio in the low temperature combustion performed immediately before the engine pause. Then, a large amount of unburned HC and CO are discharged from the engine, and the temperature Tc of the catalyst 25a or the particulate filter 25b is effectively raised by the heat of the oxidation reaction. As a result, it is possible to effectively prepare for a decrease in the temperature of the catalyst 25a or the particulate filter 25b after the subsequent temporary stop of the engine.

Next, a sixth embodiment will be described.
In the sixth embodiment, only a part of the operation flow is different from that of the fifth embodiment, and the rest is common. For common points, detailed description thereof is omitted, and differences will be mainly described.

  The sixth embodiment is different from the fifth embodiment only in the following points. That is, when the temperature Tc of the catalyst 25a or the particulate filter 25b is not equal to or higher than the set temperature Tset1 but the flag 1 is set (S303-YES), the temperature Tc is equal to or higher than the set temperature Tset1 (S303-NO). Unlike FIG. 17, as shown in FIG. 17, the injection start timing θS during low-temperature combustion is delayed by a predetermined value ΔθS. As a result, a portion where heat energy cannot be converted as torque remains as the injection start timing is delayed, and the portion is exhausted with heat, so that the exhaust gas temperature is raised, and thus the temperature of the catalyst 25 is increased. Tc is raised.

  Thus, at the time when the engine temporary stop command is issued, the injection start timing θS is determined in advance for the catalyst 25a and the particulate filter 25b having a relatively low temperature in the low temperature combustion performed immediately before the engine is temporarily stopped. As a result, the exhaust gas temperature is raised and the temperature Tc of the catalyst 25a or the particulate filter 25b is effectively raised. As a result, it is possible to effectively prepare for a decrease in the temperature of the catalyst 25a or the particulate filter 25b after the subsequent temporary stop of the engine.

Next, a seventh embodiment will be described.
In the seventh embodiment, only part of the operation flow is different from that in the fifth embodiment, and the rest is common. For common points, detailed description thereof is omitted, and differences will be mainly described.

The seventh embodiment is different from the fifth embodiment only in the following points. That is, when the temperature Tc of the catalyst 25a or the particulate filter 25b is not equal to or higher than the set temperature Tset1 but the flag 1 is set (S303-YES), the temperature Tc is equal to or higher than the set temperature Tset1 (S303-NO). ) and different, as shown in FIG. 18, the pilot injection Q _p is performed in the compression top dead center prior to the main injection Q _m. The injection amount of the pilot injection Q _p is small and constant. On the other hand, the main injection Q _m is performed after compression top dead center, and when the injection amount Q increases, the injection amount of the main injection Q _m is increased.

In this case, since the main injection Q injection timing of _m is slow, it decreases the output of the engine, thus to the engine speed N is lowered. When the engine speed N decreases, the intake air amount is increased to increase the engine speed N to the target speed N ₀ (for example, the target idling speed), and the fuel injection amount Q is increased accordingly. . When the fuel injection amount Q is increased, the exhaust gas temperature rises, and thus the temperature Tc of the catalyst 25 rises.

  As a result, at the time when the engine temporary stop command is issued, the relatively low temperature catalyst 25a and the particulate filter 25b are subjected to pilot injection and main injection in the low temperature combustion performed immediately before the temporary engine stop. By setting the injection timing after the compression top dead center, the exhaust gas temperature is raised, and the temperature Tc of the catalyst 25a or the particulate filter 25b is effectively raised. As a result, it is possible to effectively prepare for a decrease in the temperature of the catalyst 25a or the particulate filter 25b after the subsequent temporary stop of the engine.

Next, an eighth embodiment will be described.
In the eighth embodiment, only part of the operation flow is different from that in the fifth embodiment, and the rest is common. For common points, detailed description thereof is omitted, and differences will be mainly described.

  The eighth embodiment is different from the fifth embodiment only in the following points. That is, when the temperature Tc of the catalyst 25a or the particulate filter 25b is not equal to or higher than the set temperature Tset1 but the flag 1 is set (S303-YES), the temperature Tc is equal to or higher than the set temperature Tset1 (S303-NO). Unlike), the fuel injection pressure is reduced.

Specifically, the target fuel pressure P in the common rail 34 is lowered by a predetermined value ΔP. When the target fuel pressure in the common sole 34 is lowered, the fuel injection period becomes longer. When the fuel injection period becomes longer, the output of the engine decreases, and thus the engine speed N decreases. When the engine speed N decreases, the intake air amount is increased to increase the engine speed N to the target speed N ₀ (for example, the target idling speed), and the fuel injection amount Q is increased accordingly. When the fuel injection amount Q is increased, the exhaust gas temperature rises, and thus the temperature Tc of the catalyst 25 rises.

  As a result, when the engine pause command is issued, the catalyst 25a and the particulate filter 25b having a relatively low temperature are allowed to reduce the fuel injection pressure in the low-temperature combustion performed immediately before the engine is temporarily stopped. Then, the exhaust gas temperature is raised, and the temperature Tc of the catalyst 25a or the particulate filter 25b is effectively raised. As a result, it is possible to effectively prepare for a decrease in the temperature of the catalyst 25a or the particulate filter 25b after the subsequent temporary stop of the engine.

Next, a ninth embodiment will be described.
The ninth embodiment is the same as the fifth embodiment except for a part of the operation flow, and the rest is common. For common points, detailed description thereof is omitted, and differences will be mainly described.

  The ninth embodiment is different from the fifth embodiment only in the following points. That is, when the temperature Tc of the catalyst 25a or the particulate filter 25b is not equal to or higher than the set temperature Tset1 but the flag 1 is set (S303-YES), the temperature Tc is equal to or higher than the set temperature Tset1 (S303-NO). ), The target engine speed (for example, target idling speed) of the engine is increased.

  In the above, the target rotational speed (for example, the target idling rotational speed) tN is increased. If the target rotational speed tN is increased, the intake air amount is increased, and the fuel injection amount Q is increased accordingly. When the fuel injection amount Q is increased, the exhaust gas temperature rises, and thus the temperature Tc of the catalyst 25 rises.

  Thus, at the time when the engine temporary stop command is issued, the catalyst 25a and the particulate filter 25b having relatively low temperatures are subjected to the target engine speed (for example, low temperature combustion performed immediately before the engine temporary stop) (for example, By raising the target idling speed), the exhaust gas temperature is raised, and the temperature Tc of the catalyst 25a or the particulate filter 25b is effectively raised. As a result, it is possible to effectively prepare for a decrease in the temperature of the catalyst 25a or the particulate filter 25b after the subsequent temporary stop of the engine.

Next, a tenth embodiment will be described.
In the tenth embodiment, only a part of the operation flow is different from that in the first embodiment, and the rest is common. For common points, detailed description thereof is omitted, and differences will be mainly described.

  In the first embodiment, low-temperature combustion is performed immediately before the engine is temporarily stopped. In the tenth embodiment, so-called bigum (VIGOM) injection is performed instead of low-temperature combustion. Hereinafter, the rubber injection will be described.

As shown in FIG. 19, the first fuel injection Q _i is performed at the beginning of the intake stroke, and the second fuel injection, that is, the main injection Q _m is performed at the end of the compression stroke (bi-rubber injection). In the embodiment shown in FIG. 17, the injection amount of the first fuel injection Q _i is small and constant, and when the fuel injection amount Q increases, the injection amount of the main injection Q _m is increased.

On the other hand, in the tenth embodiment, as shown in FIG. 19, when the first fuel injection Q _i is performed during the intake stroke, this fuel forms a premixed gas spread throughout the combustion chamber 5. . This premixed gas is formed as, although the main injection Q ignition delay _{when m} is performed is short, a part of the premixed gas is discharged from the engine without being burned. That is, when such big rubber injection is performed, a large amount of unburned HC and CO are discharged from the engine. As a result, the temperature Tc of the catalyst 25a or the particulate filter 25b due to the oxidation reaction heat. Is raised.

  When the big rubber injection is performed, a relatively large amount of unburned HC and CO is generated, and the relatively large amount of unburned HC and CO is supplied to the catalyst 25a and the particulate filter 25b, thereby causing the catalyst 25a and the particulate filter 25b to enter. An exothermic reaction with a relatively large calorific value occurs in the curate filter 25b. Therefore, the temperature of the catalyst 25a and the particulate filter 25b rises. The transition of the temperature is the same as in FIG. That is, the temperature of the catalyst 25a and the particulate filter 25b starts to rise immediately after the big rubber injection is started, and when the predetermined big rubber injection time has elapsed, the engine is allowed to pause and the engine is stopped. After that, it continues to rise for a while. Although the temperature gradually decreases from where it has risen, in almost all normal cases, the engine restarts at a point before it falls below the minimum temperature Tcco for activation of the catalyst 25a and the particulate filter 25b. Deterioration of exhaust emission after restart is reduced.

Next, an eleventh embodiment will be described.
The eleventh embodiment is the same as the tenth embodiment except for a part of the operation flow, and the rest is common. For common points, detailed description thereof is omitted, and differences will be mainly described.

  The eleventh embodiment is different from the tenth embodiment only in the following points. When low-temperature combustion is not being performed, the air-fuel ratio is instantly made rich, and then the air-fuel ratio is made lean for a predetermined period. For example, the air-fuel ratio is greatly rich only during one fuel injection. That is, in this embodiment, a large amount of unburned HC and CO are sent to the catalyst 25a or the particulate filter 25b all at once, and the temperature of the catalyst 25a or the particulate filter 25b is rapidly increased by the oxidation reaction heat at this time. ing.

  In Step 400a, a relatively large amount of unburned HC or CO is generated, and the relatively large amount of unburned HC or CO is supplied to the catalyst 25a or the particulate filter 25b, whereby the inside of the catalyst 25a or the particulate filter 25b. An exothermic reaction with a relatively large calorific value occurs. Therefore, the temperature of the catalyst 25a and the particulate filter 25b rises. The transition of the temperature is the same as in FIG.

Next, a twelfth embodiment will be described.
The twelfth embodiment is the same as the tenth embodiment except for a part of the operation flow, and the rest is common. For common points, detailed description thereof is omitted, and differences will be mainly described.

The twelfth embodiment is different from the tenth embodiment only in the following points. If low temperature combustion is not being performed, additional fuel is added during the expansion stroke or exhaust process. For example, the additional fuel Q _add is injected during the second half of the expansion stroke or during the exhaust stroke only during one fuel injection. This additional fuel Q _add is discharged from the engine without burning. Therefore, also in this embodiment, a large amount of unburned HC and CO are sent to the catalyst 25a or the particulate filter 25b all at once, and the temperature of the catalyst 25a or the particulate filter 25b is rapidly increased by the oxidation reaction heat at this time. ing. The transition of the temperature is the same as in FIG.

  In each of the above embodiments, the catalyst 25a and the particulate filter 25b have been described as an example of the exhaust purification device. However, a known oxidation catalyst, diesel particulate filter, storage reduction type NOx catalyst, and storage reduction type NOx catalyst are supported. It may be a diesel particulate filter, a diesel particulate filter carrying an oxidation catalyst, or the like.

  In the sixth to ninth embodiments, the sixth to ninth embodiments are performed only when the temperature of the catalyst 25a or the particulate filter 25b is relatively low at the time when the engine temporary stop command is issued. An operation specific to the form is performed. Instead of these, a configuration that always carries out the operations specific to the sixth to ninth embodiments regardless of the temperature of the catalyst 25a or the particulate filter 25b at the time when the engine temporary stop command is issued. Can be.

  In the tenth to twelfth embodiments, the low temperature combustion is not performed immediately before the engine is temporarily stopped, and the operations specific to the tenth to twelfth embodiments are performed. The low-temperature combustion is performed immediately before the temporary stop, and when performing the low-temperature combustion, the operation specific to each of the tenth to twelfth embodiments can be performed.

  As described above, especially when the engine is temporarily stopped by eco-run control, hybrid control, etc., the temperature of the exhaust purification device including the catalyst is lowered, and the exhaust purification after the engine restart becomes insufficient. It is applicable to an internal combustion engine that can be prevented.

1 is an overall view of a compression ignition type internal combustion engine. It is a figure which shows the generation amount etc. of smoke and NOx. It is a figure which shows the combustion pressure change in a combustion chamber when the air fuel ratio is 21 vicinity and the amount of smoke generation is the largest. It is a figure which shows the combustion pressure change in a combustion chamber when the air fuel ratio is 18 vicinity and the generation amount of smoke is substantially zero. It is a figure which shows a fuel molecule | numerator. It is a figure which shows the relationship between the generation amount of smoke and an EGR rate. It is a figure which shows the relationship between the amount of injected fuel, and the amount of mixed gas. It is a figure which shows the 1st operation area | region I and the 2nd operation area | region II. It is a figure which shows the opening degree etc. of a throttle valve. It is a figure which shows the relationship between a request torque, the depression amount of an accelerator pedal, and an engine speed. FIG. 4 is a diagram showing an air-fuel ratio in a first operation region I. It is a figure which shows the air fuel ratio in the 2nd operation area | region II. It is a front view of a particulate filter. It is side surface sectional drawing of a particulate filter. It is a flowchart which shows operation | movement of 1st Embodiment. It is a figure which shows the catalyst temperature and time transition in 1st Embodiment. It is a figure which shows the relationship between the average gas temperature in a combustion chamber, and a crank angle when each of low temperature combustion and normal combustion is performed. It is a figure which shows the relationship between the temperature of fuel and its surrounding gas, and crank angle when each of low temperature combustion and normal combustion is performed. It is a flowchart which shows operation | movement of 2nd Embodiment. It is a figure which shows the injection timing in 6th Embodiment. It is a figure which shows the injection timing in 7th Embodiment. It is a figure which shows the injection timing in 10th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 5 Combustion chamber 6 Electric control type fuel injection valve 7 Intake valve 8 Intake port 9 Exhaust valve 10 Exhaust port 11 Intake branch pipe 12 Surge tank 17 Air suction pipe 19 Step motor for throttle valve control 20 Throttle valve 21 Exhaust manifold 22 Exhaust pipe 24 Exhaust pipe 25a catalyst 25b particulate filter 26 catalytic converter 27 temperature sensor 28 exhaust pipe 29 EGR passage 30 step motor for EGR control valve control 33 fuel supply pipe 34 common rail 35 fuel pump 36 fuel pressure sensor 39 pressure sensor 40 electronic control unit 42 ROM
43 RAM
44 CPU
45 Input port 46 Output port 49 Mass flow meter 50 Accelerator pedal 51 Load sensor 52 Crank angle sensor

Claims (7)

An internal combustion engine in which an exhaust purification device including a catalyst having an oxidation function is disposed in an engine exhaust passage,
An internal combustion engine in which an operation mode in which an amount of a substance that causes an exothermic reaction is increased in the exhaust purification device is executed before the engine is temporarily stopped. As the amount of inert gas in the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak,
An exhaust purification device including a catalyst having an oxidation function is disposed in the engine exhaust passage,
Before the engine is temporarily stopped, an operation mode is executed in which the amount of substances that cause an exothermic reaction is increased in the exhaust purification device,
In the operation mode, the internal combustion engine is controlled such that the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of soot generation reaches a peak. The internal combustion engine according to claim 1 or 2,
The internal combustion engine is characterized in that the operation mode is executed at least for a set time before the engine is temporarily stopped. The internal combustion engine according to any one of claims 1 to 3,
The internal combustion engine, wherein an execution time of the operation mode before the engine is temporarily stopped is changed according to a temperature of the exhaust gas purification device. The internal combustion engine according to any one of claims 1 to 4,
The internal combustion engine, wherein the operation mode before the engine is temporarily stopped is executed until the temperature of the exhaust purification device reaches a set temperature. The internal combustion engine according to any one of claims 1 to 5,
An internal combustion engine characterized in that the air-fuel ratio is made rich in the operation mode before the engine is temporarily stopped. The internal combustion engine according to any one of claims 1 to 5,
In the operation mode before the engine is temporarily stopped, an operation in which the exhaust gas temperature further increases is performed.

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