JP4701566B2 - Exhaust gas purification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification device.
[0002]
[Prior art]
Conventionally, in a diesel engine, in order to remove particulates contained in the exhaust gas, a particulate filter is disposed in the engine exhaust passage, and particulates in the exhaust gas are once collected by this particulate filter, and the particulate filter The particulate filter is regenerated by igniting and burning the fine particles collected above. In this case, it takes a considerably high temperature and a considerable time to ignite and burn the collected fine particles.
[0003]
On the other hand, when the air-fuel ratio is lean, NO _X Is absorbed and the air-fuel ratio is made rich, the absorbed NO _X NO to release and reduce _X An internal combustion engine in which an absorbent is carried on a particulate filter is known (see Japanese Patent Application Laid-Open No. 6-1559037). In this internal combustion engine, the engine is normally operated under a lean air-fuel ratio, and NO _X NO absorbed by the absorbent _X NO when quantity exceeds tolerance _X NO from absorbent _X The air-fuel ratio is temporarily enriched to release the.
[0004]
NO _X NO from absorbent _X NO is released and reduced _X The temperature of the particulate filter rises due to the heat generated during the reduction. Therefore, in this example of the internal combustion engine, NO _X When the release of the air is completed, the air-fuel ratio is returned to lean again, and the particulates deposited on the particulate filter are burned by utilizing the fact that the temperature of the particulate filter is rising at this time. In another example, NO _X NO from absorbent _X When the exhaust pressure upstream of the particulate filter does not exceed a certain pressure when the exhaust gas is to be released, the air-fuel ratio is simply made rich, and when the exhaust pressure upstream of the particulate filter exceeds the certain pressure, the air-fuel ratio is made rich and NO. _X NO from absorbent _X After the air is released, the air-fuel ratio is made lean so that the fine particles deposited on the particulate filter are burned.
[0005]
[Problems to be solved by the invention]
Incidentally, as described above, it takes a considerably high temperature and a considerable time to ignite and burn the particulates collected on the particulate filter. In this case, in order to raise the temperature of the particulate filter to a temperature at which the deposited particulates ignite and burn, energy must be supplied from the outside. For this reason, an additional fuel is usually supplied or a particulate matter is used using an electric heater. The temperature of the curate filter is raised. Of course, it is preferable that the energy supplied from the outside be as small as possible.
[0006]
As a result of studying the properties of the deposited fine particles from such a point of view, the properties of the deposited fine particles have gradually become clear. Although the details will be described later, simply speaking, it has been found that as the deposition time of the fine particles on the particulate filter becomes longer, the deposited fine particles become difficult to oxidize, that is, the oxidizability of the fine particles gradually changes. .
[0007]
When the fine particles have a relatively high oxidizability, less energy is required to ignite and burn the fine particles. However, when the fine particles have a relatively low oxidizability, the fine particles cannot be ignited and burned without much energy. For this reason, if the temperature of the particulate filter is merely increased, the energy from the outside becomes excessive when the particulate oxidizability is high, and the particulate cannot be reliably ignited and combusted when the particulate oxidizability is low. There is a fear.
[0008]
On the other hand, for example, when the internal combustion engine is stopped while the fine particles deposited on the particulate filter are burning, the combustion of the fine particles is interrupted. During the combustion of the fine particles, the fine particles deposited on the particulate filter are exposed to high-temperature exhaust gas for a long time with a lean air-fuel ratio. However, as will be described later in detail, it has been found that if the fine particles are exposed to a high-temperature exhaust gas with a lean air-fuel ratio for a long time, the oxidizability of the fine particles is greatly reduced. Therefore, when the particulate combustion is interrupted, the particulates remaining on the particulate filter have a considerably low oxidizability. In order to reignite and burn these particulates having a very low oxidizability, considerable external energy is required. There is a problem that is necessary.
[0009]
SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust gas purifying apparatus capable of effectively using energy supplied from the outside in order to oxidize and remove fine particles deposited on a particulate filter.
[0010]
[Means for Solving the Problems]
In order to solve the above-described problem, according to the first invention, a particulate filter for collecting and removing particulates in the exhaust gas is disposed in the engine exhaust passage, and continuously under a lean air-fuel ratio. In an internal combustion engine where combustion takes place, the oxidation of fine particles deposited on the particulate filter calculate Oxidizing Calculation Means for determining whether or not the amount of particulates deposited on the particulate filter exceeds a predetermined amount, and determining that the amount of particulates deposited on the particulate filter exceeds a predetermined amount In order to oxidize and remove particulates deposited on the particulate filter, the temperature of the particulate filter is raised under a lean air-fuel ratio based on temperature control conditions determined according to the oxidizability of the particulates deposited on the particulate filter. Temperature control means.
[0011]
According to a second invention, in the first invention, the temperature control means raises the temperature of the particulate filter to a set temperature determined by the temperature control condition and maintains the set temperature, and the set temperature is the particulate filter. When the oxidizability of the fine particles deposited thereon is low, it is set higher than when it is high.
[0012]
According to a third aspect, in the first aspect, the temperature control means raises the temperature of the particulate filter over a set time determined by the temperature control condition, and the set time is used to oxidize particulates deposited on the particulate filter. When the property is low, it is set longer than when it is high.
[0013]
According to a fourth aspect of the present invention for solving the above-described problem, a particulate filter for collecting and removing particulates in the exhaust gas is disposed in the engine exhaust passage, and is continued under a lean air-fuel ratio. Temperature control means capable of raising the temperature of the particulate filter under a lean air-fuel ratio in order to oxidize and remove particulates deposited on the particulate filter in an internal combustion engine in which combustion is performed, and the particulate First determination means for determining whether or not the amount of particulates deposited on the filter exceeds a predetermined first amount, and temperature when the amount of particulates deposited on the particulate filter exceeds the first amount. A first temperature control executing means for executing temperature control by the control means; and a particulate filter when temperature control by the temperature control means is interrupted. A second determination means for determining whether or not a deposition amount of the fine particles remaining on the filter is larger than a predetermined second amount; and a deposition amount of the fine particles remaining on the particulate filter is When the amount is larger than the second amount, the air-fuel ratio of the exhaust gas flowing into the particulate filter is temporarily switched from lean to rich in order to change the property of the fine particles remaining on the particulate filter to the property of being easily oxidized. Then, second temperature control execution means for executing temperature control by the temperature control means is provided.
[0014]
If the properties of the fine particles can be changed to a property that is easy to oxidize when the deposited fine particles are difficult to oxidize, the external energy required for the combustion of the fine particles can be reduced, and therefore can be used effectively. As a result of further research on this point, it has been found that if the air-fuel ratio is temporarily made rich, the properties of the deposited fine particles can be changed to properties that are easily oxidized.
[0015]
Therefore, in the fourth aspect of the invention, the air-fuel ratio of the exhaust gas flowing into the particulate filter is temporarily switched from lean to rich in order to change the properties of the fine particles remaining on the particulate filter into properties that are easily oxidized. Next, in order to oxidize and remove the fine particles remaining on the particulate filter, the temperature of the particulate filter is increased under a lean air-fuel ratio.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a spark ignition type internal combustion engine.
[0017]
Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Is an exhaust valve, and 10 is an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a compressor 15 of an exhaust turbocharger 14 via an intake duct 13. A throttle valve 17 driven by a step motor 16 is disposed in the intake duct 13, and a cooling device 18 for cooling intake air flowing through the intake duct 13 is disposed around the intake duct 13. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 18 and the intake air is cooled by the engine cooling water. On the other hand, the exhaust port 10 is connected to an exhaust turbine 21 of an exhaust turbocharger 14 via an exhaust manifold 19 and an exhaust pipe 20, and an outlet of the exhaust turbine 21 is connected to a casing 23 containing a particulate filter 22.
[0018]
The exhaust manifold 19 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 24, and an electrically controlled EGR control valve 25 is disposed in the EGR passage 24. A cooling device 26 for cooling the EGR gas flowing in the EGR passage 24 is disposed around the EGR passage 24. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 26, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 6 is connected to a fuel reservoir, so-called common rail 27, through a fuel supply pipe 6a. Fuel is supplied into the common rail 27 from an electrically controlled fuel pump 28 with variable discharge amount, and the fuel supplied into the common rail 27 is supplied to the fuel injection valve 6 via each fuel supply pipe 6a. A fuel pressure sensor 29 for detecting the fuel pressure in the common rail 27 is attached to the common rail 27, and a fuel pump 28 is set so that the fuel pressure in the common rail 27 becomes a target fuel pressure based on an output signal of the fuel pressure sensor 29. The discharge amount is controlled.
[0019]
The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, an input port 35 and an output port 36. It comprises. The output signal of the fuel pressure sensor 29 is input to the input port 35 via the corresponding AD converter 37. A temperature sensor 39 for detecting the temperature of the particulate filter 22 is attached to the particulate filter 22, and an output signal of the temperature sensor 39 is input to the input port 35 via the corresponding AD converter 37. . The particulate filter 22 includes a pressure sensor (differential pressure sensor) 43 for detecting a pressure difference between the upstream exhaust gas pressure and the downstream exhaust gas pressure of the particulate filter 22, that is, a pressure loss in the particulate filter 22. The output signal of this pressure sensor 43 is input to the input port 35 via the corresponding AD converter 37.
[0020]
On the other hand, a load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Is done. Further, a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 30 ° is connected to the input port 35. On the other hand, the output port 36 is connected to the fuel injection valve 6, the throttle valve driving step motor 16, the EGR control valve 25, and the fuel pump 28 via corresponding drive circuits 38.
[0021]
FIG. 2 shows the structure of the particulate filter 22. 2A shows a front view of the particulate filter 22, and FIG. 2B shows a side sectional view of the particulate filter 22. FIG. As shown in FIGS. 2A and 2B, the particulate filter 22 has a honeycomb structure and includes a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. These exhaust flow passages include an exhaust gas inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust gas outflow passage 51 whose upstream end is closed by a plug 53. In FIG. 2A, hatched portions indicate plugs 53. Therefore, the exhaust gas inflow passages 50 and the exhaust gas outflow passages 51 are alternately arranged via the thin partition walls 54. In other words, in the exhaust gas inflow passage 50 and the exhaust gas outflow passage 51, each exhaust gas inflow passage 50 is surrounded by four exhaust gas outflow passages 51, and each exhaust gas outflow passage 51 is surrounded by four exhaust gas inflow passages 50. Are arranged as follows.
[0022]
The particulate filter 22 is made of, for example, a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 50 is contained in the surrounding partition wall 54 as indicated by an arrow in FIG. Through the exhaust gas outflow passage 51 adjacent thereto.
[0023]
In the embodiment according to the present invention, a carrier layer made of alumina, for example, is formed on the peripheral wall surfaces of the exhaust gas inflow passages 50 and the exhaust gas outflow passages 51, that is, on both side surfaces of the partition walls 54 and on the pore inner wall surfaces of the partition walls 54. A noble metal catalyst such as platinum Pt or a rare earth catalyst such as cerium Ce is supported on this support. Note that the lean air-fuel ratio is NO. _X Absorbs NO with rich air-fuel ratio _X NO release _X It is also possible to carry the absorbent on the particulate filter 22.
[0024]
Fine particles mainly composed of carbon solid contained in the exhaust gas are collected and deposited on the particulate filter 22. The particulates deposited on the particulate filter 22 are sequentially oxidized within about 30 seconds to 1 hour, and therefore particulates are constantly deposited on the particulate filter 22. When the temperature of the particulate filter 22 is maintained at a temperature at which particulates can be oxidized, for example, 250 ° C. or higher, the particulates are someday oxidized when the amount of particulates fed into the particulate filter 22 is not so large. Therefore, in this case, all the fine particles are continuously oxidized.
[0025]
On the other hand, when the amount of particulates fed into the particulate filter 22 increases per unit time or when the temperature of the particulate filter 22 decreases, the amount of particulates that are not sufficiently oxidized increases, so that the amount of particulates deposited on the particulate filter 22 increases. Increase. In an actual operation state, the amount of particulates sent to the particulate filter 22 per unit time may increase, or the temperature of the particulate filter 22 may decrease, so that the amount of particulates deposited on the particulate filter 22 gradually increases. To do.
[0026]
Therefore, in the embodiment according to the present invention, it is determined whether or not the deposition amount of the particulates on the particulate filter 22 exceeds a predetermined first upper limit amount, and the particulate deposition amount on the particulate filter 22 is the first. When the upper limit is exceeded, the temperature of the particulate filter 22 is raised under a lean air-fuel ratio in order to oxidize and remove the particulates deposited on the particulate filter 22. That is, as shown in FIG. 3, when the amount of accumulated particulate matter on the particulate filter 22 exceeds the first upper limit UL1, the temperature TF of the particulate filter 22 is raised over the set time SP, and the temperature of the particulate filter 22 is increased. Temperature increase control is performed to raise TF to the set temperature ST and maintain the set temperature ST. When the set temperature SP has elapsed since the start of the temperature increase control, the temperature increase control is stopped, and at this time, the amount of particulates deposited is smaller than the lower limit amount LL. In this way, the particulate filter 22 is regenerated.
[0027]
Next, with reference to FIG. 4, the degree of oxidization of the fine particles deposited on the particulate filter 22, that is, the fine particle oxidation property will be described. In FIG. 4, A / F indicates the air-fuel ratio of the exhaust gas flowing into the particulate filter 22. In the present application, the ratio of the air and the fuel supplied into the exhaust passage upstream of the intake passage, the combustion chamber 5 and the particulate filter 22 is referred to as the air-fuel ratio of the exhaust gas.
[0028]
In FIG. 4, a solid line X ₁ Indicates when the temperature of the particulate filter 22 is relatively low, and the broken line X ₂ Indicates when the temperature of the particulate filter 22 is high. When fine particles are deposited on the particulate filter 22, a large number of pores or voids are formed in the accumulated fine particle lump, and accordingly, the surface area S in the fine particle lump and the volume V of the fine particle lump. The ratio, that is, the surface area volume ratio S / V is a considerably large value. A large surface area volume ratio S / V means that the contact area between the fine particles and oxygen is large, and therefore the fine particles have good oxidizability.
[0029]
On the other hand, if the air-fuel ratio A / F continues to be lean after the fine particles are collected, the fine particles are aggregated to gradually increase the size of the fine particles. As a result, the pores or voids in the fine particle lump. Gradually decreases. Accordingly, the surface area volume ratio S / V of the mass of fine particles gradually decreases, and thus X in FIG. ₁ , X ₂ As shown in the graph, the oxidizability of the fine particles gradually decreases. The agglomeration effect between the fine particles becomes more severe as the temperature rises, and therefore, as shown in FIG. ₂ The solid line X is at the high temperature indicated by ₁ The oxidizability of the fine particles is lowered earlier than in the case of the low temperature indicated by
[0030]
When the particulates are relatively highly oxidizable, the particulates deposited on the particulate filter 22 can be satisfactorily oxidized and removed even if the temperature of the particulate filter 22 is low or the temperature raising control time is short. On the other hand, when the particulate oxidizability is relatively low, it is necessary to increase the temperature of the particulate filter 22 or to control the temperature rise for a long time in order to surely oxidize and remove the particulate.
[0031]
Therefore, in the embodiment according to the present invention, when the fine particles deposited on the particulate filter 22 are to be oxidized and removed, the oxidizability of the fine particles deposited on the particulate filter 22 is obtained, and the temperature rises according to the oxidizability of the fine particles. The condition is obtained, and the temperature rise control of the particulate filter 22 is executed based on the temperature rise condition.
[0032]
FIG. 5 shows the basic concept of the temperature rise control according to the embodiment of the present invention. In FIG. 5, TF indicates the temperature of the particulate filter 22.
[0033]
In the example shown in FIG. 5A, the set time SP is maintained at a constant PC, and the set temperature ST is changed according to the particulate oxidation property. That is, the solid line W in FIG. ₁ When the particulate oxidation property indicated by (2) is relatively high, the temperature TF of the particulate filter 22 is raised to a relatively low temperature TL, and the broken line W in FIG. ₂ When the particulate oxidization property indicated by (2) is relatively low, the temperature TF of the particulate filter 22 is raised to a relatively high temperature TH. In other words, the set temperature ST is set to TL when the particulate oxidation property is relatively high, and the set temperature ST is set to TH when the particulate oxidation property is relatively low.
[0034]
The set temperature ST in this case is used to reduce the amount of particulates deposited on the particulate filter 22 from the first upper limit value UL1 to the lower limit amount LL when the temperature TF of the particulate filter 22 is raised over a certain PC. This is the required time and is obtained in advance through experiments. As shown in FIG. 6A, the set temperature ST becomes lower as the fine particle oxidation becomes higher. The set temperature ST is stored in advance in the ROM 32 in the form of a map shown in FIG.
[0035]
On the other hand, in the example shown in FIG. 5B, the set temperature ST is maintained at a constant PT, and the set time SP is changed according to the particulate oxidation property. That is, the solid line Z in FIG. ₁ 5 is relatively high, the temperature TF of the particulate filter 22 is raised over a relatively short time PS, and the broken line Z in FIG. ₂ When the particulate oxidation property indicated by (2) is relatively low, the temperature TF of the particulate filter 22 is raised over a relatively long time PL. In other words, the set time SP is set to PS when the particulate oxidation property is relatively high, and the set time SP is set to PL when the particulate oxidation property is relatively low.
[0036]
In this case, the set time SP is such that when the temperature TF of the particulate filter 22 is raised to a constant TC and maintained, the amount of particulates deposited on the particulate filter 22 is reduced from the first upper limit value UL1 to the lower limit amount LL. It is a time required for this, and is obtained by experiments in advance. As shown in FIG. 6B, the set time SP becomes shorter as the fine particle oxidation becomes higher. The set time SP is stored in advance in the ROM 32 in the form of a map shown in FIG.
[0037]
There are various methods for raising the temperature of the particulate filter 22. For example, an electric heater is arranged at the upstream end of the particulate filter 22 and the exhaust gas flowing into the particulate filter 22 or the particulate filter 22 is heated by the electric heater, or fuel is introduced into the exhaust passage upstream of the particulate filter 22. There are a method of heating the particulate filter 22 by injecting and burning this fuel, and a method of raising the temperature of the particulate filter 22 by raising the exhaust gas temperature.
[0038]
Here, the last method, that is, a method of raising the exhaust gas temperature will be briefly described with reference to FIG.
[0039]
One effective method for raising the exhaust gas temperature is to retard the fuel injection timing until after compression top dead center. That is, the normal main fuel Qm is injected near the compression top dead center as shown in FIG. In this case, as shown in FIG. 7 (II), when the injection timing of the main fuel Qm is retarded, the afterburning period becomes longer, and thus the exhaust gas temperature rises. As the exhaust gas temperature increases, the temperature TF of the particulate filter 22 increases accordingly.
[0040]
Further, in order to raise the exhaust gas temperature, auxiliary fuel Qv can be injected in the vicinity of the intake top dead center in addition to the main fuel Qm as shown in FIG. 7 (III). When the auxiliary fuel Qv is additionally injected in this manner, the amount of fuel combusted by the amount of the auxiliary fuel Qv increases, so that the exhaust gas temperature rises and thus the temperature TF of the particulate filter 22 rises.
[0041]
On the other hand, when the auxiliary fuel Qv is injected in the vicinity of the intake top dead center in this way, intermediate products such as aldehyde, ketone, peroxide, carbon monoxide and the like are generated from the auxiliary fuel Qv by the compression heat during the compression stroke. The product accelerates the reaction of the main fuel Qm. Therefore, in this case, as shown in (III) of FIG. 7, even if the injection timing of the main fuel Qm is greatly delayed, good combustion can be obtained without causing misfire. That is, since the injection timing of the main fuel Qm can be greatly delayed in this way, the exhaust gas temperature becomes considerably high, and thus the temperature TF of the particulate filter 22 can be quickly raised.
[0042]
Further, as shown in FIG. 7 (IV), in addition to the main fuel Qm, the auxiliary fuel Qp can be injected during the expansion stroke or the exhaust stroke. That is, in this case, most of the auxiliary fuel Qp is discharged into the exhaust passage in the form of unburned HC without burning. The unburned HC is oxidized on the particulate filter 22 by excess oxygen, and the temperature TF of the particulate filter 22 is raised by the oxidation reaction heat generated at this time.
[0043]
Here, in the example shown in FIG. 7 (II), the main fuel injection timing is changed, and in the example shown in FIG. 7 (III), the main fuel injection timing or the amount of the auxiliary fuel Qv is changed. In the example shown in FIG. 7 (IV), the temperature of the exhaust gas can be changed by changing the amount of the auxiliary fuel Qp. Therefore, the temperature TF of the particulate filter 22 is matched with various set temperatures ST. be able to.
[0044]
As described above with reference to FIG. 3, when the particulate accumulation amount exceeds the first upper limit value UL1, the temperature increase control of the particulate filter 22 is started, and when the set time SP has elapsed, the temperature increase control is stopped, that is, completed. Is done.
[0045]
However, for example, if the internal combustion engine is stopped during the temperature rise control, or if the auxiliary fuel Qv in the example shown in FIG. 7 (IV) cannot be injected, the temperature rise control cannot be continued. In other words, the temperature rise control is interrupted when such a temperature rise control interruption event occurs. At this time, fine particles remain on the particulate filter 22.
[0046]
Therefore, in the embodiment according to the present invention, it is determined whether or not the accumulation amount of the fine particles remaining on the particulate filter 22 when the temperature raising control is interrupted is larger than a predetermined second upper limit amount. When the accumulation amount of the fine particles remaining on the particulate filter 22 is larger than the second upper limit amount, the particulates remaining on the particulate filter 22 are oxidized under the lean air-fuel ratio in order to oxidize and remove the fine particles. The temperature of the curate filter 22 is raised.
[0047]
However, as described above with reference to FIG. 4, when the air-fuel ratio A / F is maintained lean, the oxidization property of the fine particles decreases. At this time, the higher the temperature TF of the particulate filter 22, the lower the oxidization property of the fine particles. To do. During the temperature rise control, the air-fuel ratio A / F is maintained lean with the temperature TF of the particulate filter 22 being high, and accordingly, the particulates remaining on the particulate filter 22 when the temperature rise control is interrupted. Oxidizing properties are considerably low. Thus, a large external energy is required to oxidize and remove fine particles having a considerably low oxidizability.
[0048]
However, it has been found that when the air-fuel ratio A / F is made rich as shown in FIG. Although the reason for this is not clear, it is considered that making the air-fuel ratio A / F rich is similar to the activation action during coke generation. That is, when the air-fuel ratio A / F is made rich, the amount of oxygen is extremely small, so that the CO in the exhaust gas ₂ And H ₂ It is thought that O breaks the carbon bond, and as a result, a large number of pores or voids are generated again. In fact, when the surface area volume ratio S / V of the lump of fine particles after the air-fuel ratio A / F is made rich is measured, the surface area volume ratio S / V increases considerably. In FIG. 8A, a solid line X ₁ Indicates the case where the temperature TF of the particulate filter 22 is low, and the broken line X ₂ Indicates a case where the temperature TF of the particulate filter 22 is high.
[0049]
In this case, the higher the temperature TF of the particulate filter 22 is, the more CO 2 ₂ And H ₂ The attack by O becomes intense, and therefore the broken line Y in FIG. ₂ When the temperature TF of the particulate filter 22 shown in FIG. ₁ Compared with the case where the temperature TF of the particulate filter 22 shown in FIG.
[0050]
Therefore, in the embodiment according to the present invention, when the amount of the fine particles remaining on the particulate filter 22 is larger than the second upper limit amount, the properties of the fine particles remaining on the particulate filter 22 are easily oxidized. The air-fuel ratio of the exhaust gas flowing into the particulate filter 22 is temporarily switched from lean to rich so that the particulates remaining on the particulate filter 22 are oxidized and removed. Thus, the temperature of the particulate filter 22 is raised.
[0051]
There are various methods for temporarily switching the air-fuel ratio A / F from lean to rich. For example, a method of enriching the average air-fuel ratio in the combustion chamber 5, a method of injecting additional fuel into the combustion chamber 5 during the latter half of the expansion stroke or during the exhaust stroke, and an additional passage in the exhaust passage upstream of the particulate filter 22 There is a method of injecting fuel.
[0052]
FIG. 9 shows the basic concept of temperature rise control and operation control according to an embodiment of the present invention.
[0053]
When the amount of accumulated particulate matter exceeds the first upper limit value UL1, the temperature of the particulate filter 22 is raised to the set temperature ST and maintained at ST. If a temperature rise control interruption event occurs during this temperature rise control, the temperature rise control is interrupted. Next, when the reason for the interruption is eliminated, it is determined whether or not the amount of particulates remaining on the particulate filter 22 at this time is larger than the second upper limit value UL2, and the amount of particulates accumulated is the second upper limit value UL2. When the ratio is larger, the air-fuel ratio of the exhaust gas flowing into the particulate filter 22 is temporarily switched from lean to rich in order to change the property of the fine particles remaining on the particulate filter 22 to the property of being easily oxidized. Next, in order to oxidize and remove the fine particles remaining on the particulate filter 22, the temperature rise control is performed such that the temperature of the particulate filter 22 is raised to the set temperature ST over the set time SP under the lean air-fuel ratio and maintained at ST. Is done.
[0054]
In FIG. 9, the method (IV) in FIG. 7 is used to raise the temperature of the particulate filter 22 in order to burn the deposited fine particles. Therefore, as shown in FIG. 9, when the temperature of the particulate filter 22 is to be increased, the air-fuel ratio A / F is slightly reduced.
[0055]
FIG. 10 shows a flowchart for executing the temperature raising control and the operation control according to the embodiment of the present invention.
[0056]
Referring to FIG. 10, first, at step 70, it is determined whether or not a cause for interrupting the temperature raising control has occurred. When the interruption reason has not occurred, the routine proceeds to step 71 where it is determined whether or not the temperature raising control is being interrupted. When the temperature raising control is not interrupted, the routine proceeds to step 72, where whether or not the amount of particulates deposited on the particulate filter 22 exceeds the first upper limit amount, that is, the pressure loss in the particulate filter 22 detected by the pressure sensor 43. It is determined whether or not the PD has exceeded an allowable limit PDX1 corresponding to UL1 in FIGS. When PD ≦ PDX1, the routine jumps to step 78. When PD> PDX1, the routine proceeds to step 73 where the particulate oxidation property calculated in another routine is read. In the following step 74, the temperature increase condition of the temperature increase control, that is, the set temperature ST or the set time SP is calculated using the map shown in FIG. 6A or 6B. In the subsequent step 75, temperature increase control is performed under the lean air-fuel ratio based on the calculated temperature increase condition, whereby fine particles deposited on the particulate filter 22 are combusted.
[0057]
In the following step 76, it is determined whether or not the temperature raising control is completed. When the temperature raising control has not been completed, the routine proceeds to step 77 where it is determined whether or not a reason for interruption of the temperature raising control has occurred. When the interruption reason has not occurred, the process returns to step 75 and the temperature increase control is continued. On the other hand, when an interruption event occurs, the routine proceeds to step 78 where normal operation is performed. That is, the temperature rise control is interrupted.
[0058]
The process proceeds from step 70 to step 78 until there is no reason for interruption of the temperature increase control, and therefore the temperature increase control is not performed. Next, when there is no reason for interruption, the routine proceeds from step 70 to step 71 and then to step 79, where the temperature T at which the particulate filter 22 can oxidize particulates T _o For example, the pressure loss PD in the particulate filter 22 detected by the pressure sensor 43 as to whether or not the accumulated amount of fine particles on the particulate filter 22 is higher than 250 ° C. and exceeds the second upper limit amount is shown in FIGS. It is determined whether or not the allowable limit PDX2 is larger than the allowable limit PD2. TF ≦ T _o Alternatively, when PD ≦ PDX2, the routine proceeds to step 78 where normal operation is performed.
[0059]
TF> T _o When PD> PDX2, the routine then proceeds to step 80, where rich processing for temporarily enriching the air-fuel ratio A / F is performed, whereby the oxidizability of the fine particles is recovered. When this rich process is completed, the routine proceeds to step 73, where fine particle oxidization is read, and at step 74, the temperature raising condition is calculated. In this case, the temperature increase condition described above with reference to FIG. 6 is corrected according to the amount of fine particles remaining on the particulate filter 22. Next, the routine proceeds to step 75 where temperature increase control is performed under a lean air-fuel ratio based on the calculated temperature increase condition. When it is determined in step 76 that the temperature raising control has been completed, the routine proceeds to step 78 where normal operation is resumed, that is, the temperature raising control is stopped.
[0060]
Next, with reference to FIGS. 11 to 24, first to fifth embodiments for obtaining fine particle oxidation will be described.
[0061]
In the first embodiment shown in FIG. 11 and FIG. 12, the amount of decrease or increase in oxidation per unit time of fine particles deposited on the particulate filter 22 is calculated, and based on the amount of decrease or increase in oxidation. Therefore, it seeks to oxidize fine particles.
[0062]
That is, as described with reference to FIGS. 4 and 8, when the air-fuel ratio A / F is maintained lean, the higher the temperature TF of the particulate filter 22, the lower the oxidizability of the particulates. When F is rich, the higher the temperature TF of the particulate filter 22, the greater the oxidizability of the fine particles. Accordingly, roughly speaking, the oxidation reduction amount ΔDEO per unit time of the fine particles can be expressed as shown in FIG. That is, when the air-fuel ratio A / F is lean, as shown by a solid line L, the amount of decrease in oxidation of particulates ΔDEO increases as the temperature TF of the particulate filter 22 increases. On the other hand, when the air-fuel ratio A / F is rich, as shown by the solid line R, the amount of decrease ΔDEO in the particulate oxidation becomes negative, and the absolute value of the amount of decrease ΔDEO, that is, the amount of increase in particulate oxidation per unit time is The temperature increases as the temperature TF of the curate filter 22 increases.
[0063]
Accordingly, the amount of decrease in oxidation of the fine particles can be determined by calculating the amount of decrease ΔDEO in the fine particles shown in FIG. 11 per unit time and integrating the calculated amount of decrease ΔDEO. In the first embodiment, it is determined that the particulate oxidation is lower when the amount of reduction in the oxidation of the particulate is large than when it is small.
[0064]
FIG. 12 shows a flowchart for executing the first embodiment.
[0065]
Referring to FIG. 12, first, at step 100, it is determined whether or not the temperature raising control of the particulate filter 22 has been completed, or whether or not the rich process has been performed to enhance the particulate oxidation property. When the temperature raising process has not been completed and the rich process has not been performed, the routine proceeds to step 101, where the oxidation reduction amount ΔDEO of the fine particles is calculated based on FIG. In the subsequent step 102, the oxidation reduction amount ΔDEO of the fine particles is added to DEO. In this way, DEO representing fine particle oxidation is calculated.
[0066]
On the other hand, when the temperature raising control is completed or the rich process is performed, the process proceeds from step 100 to step 103, and the particulate oxidation reduction amount DEO is cleared.
[0067]
A second embodiment is shown in FIGS. In this second embodiment, among the fine particles deposited on the particulate filter 22, the amount of fine particles having the lowest oxidizability is calculated using a model, and the fine particle oxidizability is obtained based on the amount of fine particles having the lowest oxidizability. I am doing so.
[0068]
First, referring to FIG. 13, the solid line Z in FIG. 13 indicates the oxidation rate of fine particles on the particulate filter 22, that is, for example, the amount G (g / min) of fine particles that can be oxidized and removed per minute and the particulate filter 22. The relationship with temperature TF is shown. That is, the curve Z in FIG. 13 shows a balance point where the amount of fine particles flowing into the particulate filter 22 coincides with the fine particle amount G that can be removed by oxidation. At this time, since the amount of inflowing particulates is equal to the amount of particulates removed by oxidation, the amount of particulates deposited on the particulate filter 22 is kept constant. On the other hand, in region I in FIG. 13, the amount of inflowing particulates is less than the amount of particulates that can be removed by oxidation, so the amount of deposited particulates decreases. In region II in FIG. The amount of deposited fine particles increases.
[0069]
FIG. 14 schematically shows a model of the state of the deposited fine particles when the inflow fine particle amount coincides with the fine particle amount G that can be removed by oxidation. In FIG. 14, the numbers 1 to 5 arranged along the horizontal axis indicate the oxidizing properties of the deposited fine particles, and the oxidizing properties deteriorate toward the numbers 1 to 5. In FIG. 14, W1, W2, W3, W4, and W5 indicate the amounts of fine particles deposited at a certain time and have oxidation properties of 1, 2, 3, 4, and 5, respectively. , WO4, WO5 indicate the amount of fine particles that have been oxidized and removed after a certain time, and WR1, WR2, WR3, WR4, WR5 indicate the amount of residual fine particles still deposited at this time.
[0070]
In this model, the fine particles W1 flowing into the particulate filter 22 are oxidized and removed only by WO1 for a certain period, so that the fine particles remain only by WR1, and the fine particles WR1 are reduced in oxidizing property from 1 to 2 and then remain. Since the fine particles W2 are oxidized and removed only by WO2 during a certain period, the fine particles remain only by WR2, and the fine particles WR2 are considered to be reduced in oxidation property from 2 to 3. Therefore, as can be seen from FIG. 14, in this model, W2 matches WR1, W3 matches WR2, W4 matches WR3, and W5 matches WR4.
[0071]
Further, in this model, the proportion of each of the deposited fine particle amounts W1, W2, W3, W4, W5 that are oxidized and removed during a certain period of time WO1, WO2, WO3, WO4, WO5. W2, WO3 / W3, WO4 / W4, and WO5 / W5 are fixed. In this case, it is considered that these ratios become smaller as the oxidizability of the fine particles decreases. Therefore, in this model, WO1 / W1 is 60%, WO2 / W2 is 57%, WO3 / W3 is 54%, and WO4 / W4 is 52%. , WO5 / W5 is 50%.
[0072]
Further, since WO5 / W5 is 50%, WR5 / W5 is also 50%, and the remaining fine particles WR5 are oxidized and removed during the subsequent fixed time. In this way, the model shown in FIG. 14 is created.
[0073]
On the other hand, when the inflowing particulate amount is larger than the particulate amount G that can be removed by oxidation, as shown in FIG. 15A, the ratio of WO1 to W1, the ratio of WO2 to W2, the ratio of WO3 to W3, and the ratio of WO4 to W4. , The ratio of WO5 to W5 is smaller than that shown in FIG. As a result, the residual fine particle amounts WR1, WR2, WR3, WR4, and WR5 increase compared to the case shown in FIG. If such a state continues, as shown in FIG. 15B, the amount W5 of fine particles having an oxidizing property of 5 increases greatly.
[0074]
In other words, considering such a model, it is possible to determine the finest particle amount W5 having the worst oxidation property.
[0075]
Next, a method for calculating the most oxidizable fine particle amount W5 will be schematically described.
[0076]
FIGS. 16A and 16B show a case where the balance points between the amount of inflowing fine particles and the amount G of fine particles that can be oxidized and removed are the points A and B in FIG. 13, respectively. FIGS. 16A and 16B show the state of fine particles as in FIG. 14, but in FIGS. 16A and 16B, the horizontal axis represents time. That is, in FIG. 16 (A), the horizontal axis shows 5 minutes, 10 minutes, 15 minutes, 20 minutes, and 25 minutes after the inflow of fine particles, respectively, and in FIG. 16 (B), the horizontal axis Indicates 2 minutes, 4 minutes, 6 minutes, 8 minutes and 10 minutes after the inflow of fine particles.
[0077]
In FIG. 13B, the amount of fine particles G that can be oxidized and removed, that is, the amount of inflowing fine particles is larger than the point A, so the amount of fine particles W1 in FIG. 16B is larger than the amount of fine particles W1 in FIG. Become. On the other hand, since the temperature TF of the particulate filter 22 is higher at the point B in FIG. Nevertheless, the fact that the fine particles are removed by oxidation before the oxidizability becomes 5 means that the fine particles have been removed by oxidation early as shown in FIG.
[0078]
The time Δt required for 60% of the fine particles W1 to be removed by oxidation or the time Δt required for 57% of the fine particles W2 to be removed by oxidation is 5 minutes in FIG. In B) it is 2 minutes. Thus, the time Δt becomes shorter as the temperature TF of the particulate filter 22 becomes higher as shown in FIG.
[0079]
In the second embodiment, the residual fine particle amounts WR1, WR2, WR3, WR4, and WR5 are calculated every time the time Δt elapses, and it is determined that the fine particle oxidation is lower when the residual fine particle amount WR5 is large than when it is small. I am doing so.
[0080]
In order to calculate the amount of residual fine particles, the amount of inflowing fine particles, that is, the amount of fine particles discharged from the engine must be obtained. The amount of discharged fine particles varies depending on the engine model, but when the engine model is determined, it becomes a function of the required torque TQ and the engine speed N. FIG. 18A shows the amount M of discharged fine particles of the internal combustion engine shown in FIG. ₁ , M ₂ , M _Three , M _Four , M _Five Is the amount of fine particles discharged (M ₁ <M ₂ <M _Three <M _Four <M _Five ). In the example shown in FIG. 18A, the amount M of discharged particulate increases as the required torque TQ increases. The discharged particulate amount M shown in FIG. 18A is stored in advance in the ROM 32 in the form of a map shown in FIG. 18B as a function of the required torque TQ and the engine speed N.
[0081]
FIG. 19 shows a flowchart for executing the second embodiment.
[0082]
Referring to FIGS. 15 and 16, first, in step 200, it is determined whether or not the temperature increase control of the particulate filter 22 has been completed or the rich process has been performed in order to enhance the particulate oxidation property. When the temperature raising process has not been completed and the rich process has not been performed, the routine proceeds to step 201, where the time Δt is calculated from the relationship shown in FIG. Next, at step 202, the integrated amount ΣM of the discharged particulate amount M shown in FIG. Next, at step 203, the integrated amount ΣG of the oxidizable and removable fine particle amount G shown in FIG. Next, at step 204, it is judged if Δt time has elapsed. When Δt time has not elapsed, the processing cycle is terminated, and when Δt time has elapsed, the routine proceeds to step 205.
[0083]
In step 205, the amount of fine particles to be oxidized and removed WO1 (= ΣG × 0.6), WO2 (= WR1 × 0.57), WO3 (= WR2 × 0.54), WO4 (= WR3 × 0.52), WO5 (= WR4 × 0.5) is calculated. Next, at step 206, the respective residual fine particle amounts WR5, WR4, WR3, WR2, WR1 are calculated based on the following equation.
[0084]
WR5 ← WR4-WO5
WR4 ← WR3-WO4
WR3 ← WR2-WO3
WR2 ← WR1-WO2
WR1 ← ΣM-WO1
The meaning of these equations is considered to be clear from FIG. In this way, the residual fine particle amount WR5 representing the fine particle oxidation property is calculated.
[0085]
On the other hand, when the temperature raising control is completed or the rich process is performed, the process proceeds from step 200 to step 207, where initialization is performed.
[0086]
20 and 21 show a third embodiment. In this embodiment, the pressure loss in the particulate filter 22 is estimated on the one hand, and the actual pressure loss in the particulate filter 22 is detected on the other hand, and the particulate oxidation property is obtained based on the pressure loss difference between the estimated pressure loss and the actual pressure loss. I am doing so. That is, when the oxidizability of the fine particles decreases, the fine particles are deposited without being sufficiently oxidized, so that the pressure loss in the particulate filter 22 increases. Therefore, it can be determined from this how much the oxidizability of the fine particles has been reduced.
[0087]
First, a method for estimating the pressure loss in the particulate filter 22 will be described. In this embodiment, the accumulation amount ΣWR of the fine particles is calculated from the discharged fine particle amount M and the oxidizable and removable fine particle amount G. FIG. 20A shows the relationship between the particulate deposition amount ΣWR and the pressure loss ΔPD in the reference state. Therefore, when the particulate deposition amount ΣWR is obtained, the pressure loss ΔPD in the reference state is obtained from the relationship shown in FIG. .
[0088]
On the other hand, even if the particulate accumulation amount ΣWR is the same, the pressure loss changes as the temperature TF of the particulate filter 22 and the exhaust gas amount GE change. In the embodiment according to the present invention, the correction coefficient K for the pressure loss ΔPD in the reference state is stored in advance in the ROM 32 in the form of a map as shown in FIG. 20B, and the pressure loss ΔPD is multiplied by the correction coefficient K. As a result, the pressure loss PDD corresponding to the temperature TF of the particulate filter 22 and the exhaust gas amount GE is calculated.
[0089]
When the oxidizability of the fine particles decreases, the actual pressure loss PD detected by the pressure sensor 43 becomes higher than the pressure loss PDD calculated as shown in FIG. In the third embodiment, when the pressure loss difference DIF (= PD−PDD) is large, it is judged that the fine particle oxidation property is lower than when the pressure loss difference DIF is small.
[0090]
FIG. 21 shows a flowchart for executing the third embodiment.
[0091]
Referring to FIG. 21, first, at step 300, it is judged if the temperature raising control of the particulate filter 22 has been completed or the rich process has been performed to enhance the particulate oxidation property. When the temperature raising process has not been completed and the rich process has not been performed, the routine proceeds to step 301 where the discharged particulate amount M is calculated from the map shown in FIG. 18B, and can be removed by oxidation from the relationship shown in FIG. The amount G of fine particles is calculated. Next, at step 302, the current amount of deposited fine particles ΣWR (= (M + WR)) is obtained by subtracting the amount of fine particles G that can be removed by oxidation from the sum (M + WR) of the amount of fine particles WR and the amount of discharged fine particles M accumulated during the previous processing cycle. -G) is calculated. Next, at step 303, ΣWR is set to WR.
[0092]
Next, at step 304, it is judged if a certain time has passed. When the predetermined time has not elapsed, the processing cycle is ended, and when the predetermined time has elapsed, the process proceeds to Step 305. In step 305, the pressure loss ΔPD is calculated from the relationship shown in FIG. 20A based on the amount of deposited fine particles ΣWR, and the estimated value PDD of the pressure loss is calculated from the pressure loss ΔPD and the correction coefficient K shown in FIG. Next, at step 306, a pressure loss difference DIF (= PD−PDD) between the actual pressure loss PD detected by the pressure sensor 43 and the estimated pressure loss value PDD is calculated. In this way, the pressure loss difference DIF representing the particulate oxidation property is calculated.
[0093]
On the other hand, when the temperature raising control is completed or the rich process is performed, the process proceeds from step 300 to step 307, and the pressure loss difference DIF is cleared.
[0094]
22 and 23 show a fourth embodiment. In this embodiment, the temperature TF of the particulate filter 22 is temporarily raised to about 450 ° C. to oxidize some of the deposited fine particles, and the fine particle oxidizability is obtained based on the magnitude of the subsequent pressure loss. .
[0095]
That is, when the temperature TF of the particulate filter 22 is raised, a large amount of deposited fine particles are oxidized when the fine particles have high oxidizability, but the deposited fine particles are hardly oxidized when the fine particles have low oxidizability. Therefore, the pressure loss after raising the temperature TF of the particulate filter 22 is low when the fine particle has high oxidation property, as shown by the solid line PDD in FIG. 22A, and the fine particle has low oxidation property. As shown by a broken line PD in FIG. Therefore, when the difference DIF (= PD−PDD) between these pressure losses PD and PDD is large, it can be determined that the fine particle oxidation is lower than when the difference DIF is small.
[0096]
Specifically, in this embodiment, the temperature rise control of the particulate filter 22 is performed when the actual pressure loss PD detected by the pressure sensor 43 reaches a predetermined target value PDT. The target value PDT is stored in advance in the ROM 32 as a function of the required torque TQ and the engine speed N as shown in FIG. Next, after completion of the temperature rise control, when the determination time TK shown in FIG. 22A is reached, the actual pressure loss PD is compared with the pressure loss PDD when the fine particles are highly oxidizable. The pressure loss PDD is obtained in advance by experiments or the like, and the pressure loss PDD is stored in advance in the ROM 32 as a function of the required torque TQ and the engine speed N as shown in FIG. In this embodiment, when the pressure loss difference DIF (= PD−PDD) is large, it is judged that the fine particle oxidation is lower than when the pressure loss difference DIF (= PD−PDD) is small.
[0097]
FIG. 23 shows a flowchart for executing the fourth embodiment.
[0098]
Referring to FIG. 23, first, at step 400, it is judged if the temperature raising control of the particulate filter 22 has been completed or the rich process has been performed to enhance the particulate oxidation property. When the temperature raising process has not been completed and the rich process has not been performed, the routine proceeds to step 401, where the actual pressure loss PD detected by the pressure sensor 43 has reached the target value PDT shown in FIG. It is determined whether or not. When PD is not PDT, the processing cycle is terminated, and when PD is PDT, the process proceeds to step 402. In step 402, temperature increase control for temporarily increasing the temperature TF of the particulate filter 22 is performed. When the temperature raising control is completed, the routine proceeds to step 403, where it is judged if the judgment time TK shown in FIG. When the determination time TK is reached, the routine proceeds to step 404 where the pressure loss difference DIF (= PD−PDD) between the actual pressure PD detected by the pressure sensor 43 and the pressure loss PDD obtained from the map shown in FIG. Is done. In this way, the pressure loss difference DIF representing the particulate oxidation property is calculated.
[0099]
On the other hand, when the temperature raising control is completed or the rich process is performed, the process proceeds from step 300 to step 405, and the pressure loss difference DIF is cleared.
[0100]
Next, a fifth embodiment will be described. It is considered that the particulate oxidation property gradually decreases as the elapsed time from the completion of the temperature rise control of the particulate filter 22 or the rich processing for increasing the oxidation property of the particulates deposited on the particulate filter 22 becomes longer. Therefore, for example, when the engine operating time after completion of the temperature rise control or the rich process, the cumulative value of the engine speed, or the vehicle travel distance is large, it can be determined that the particulate oxidation is lower than when it is small. Become.
[0101]
Therefore, in this embodiment, when the accumulated value of the engine speed after completion of the temperature rise control or the rich process is large, it is determined that the particulate oxidation is lower than when it is small.
[0102]
FIG. 24 shows a flowchart for executing the fifth embodiment.
[0103]
Referring to FIG. 24, first, at step 500, it is judged if the temperature raising control of the particulate filter 22 has been completed or the rich process has been performed to enhance the particulate oxidation property. When the temperature raising process has not been completed and the rich process has not been performed, the routine proceeds to step 501 where the current engine speed N is added to the cumulative value ΣN. In this way, ΣN representing fine particle oxidation is calculated.
[0104]
On the other hand, when the temperature raising control is completed or the rich process is performed, the process proceeds from step 500 to step 502, and the cumulative value ΣN is cleared.
[0105]
Next, a low-temperature combustion method suitable for carrying out the present invention will be briefly described with reference to FIGS.
[0106]
In the internal combustion engine shown in FIG. 1, as the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) increases, the amount of smoke generated gradually increases and reaches a peak, and the EGR rate is further increased. This time, the amount of smoke generated decreases rapidly. This will be described with reference to FIG. 25 showing the relationship between the EGR rate and smoke when the degree of cooling of the EGR gas is changed. In FIG. 25, curve A shows the case where EGR gas is strongly cooled and the EGR gas temperature is maintained at about 90 ° C., and curve B shows the case where EGR gas is cooled by a small cooling device. Curve C shows the case where the EGR gas is not forcibly cooled.
[0107]
As shown by the curve A in FIG. 25, when the EGR gas is strongly cooled, the amount of smoke generated peaks when the EGR rate is slightly lower than 50%. In this case, the EGR rate is increased to about 55% or more. If this is done, smoke will hardly occur. On the other hand, as shown by curve B in FIG. 25, when the EGR gas is slightly cooled, the amount of smoke generated reaches a peak when the EGR rate is slightly higher than 50%. In this case, the EGR rate is approximately 65% or more. If it is made, smoke will hardly occur. In addition, as shown by the curve C in FIG. 25, when the EGR gas is not forcibly cooled, the amount of smoke generated reaches a peak when the EGR rate is around 55%. In this case, the EGR rate is approximately 70%. If it is more than a percentage, smoke is hardly generated.
[0108]
As described above, when the EGR gas ratio is 55% or more, smoke is not generated because the endothermic action of the EGR gas does not cause the temperature of the fuel and the surrounding gas to be so high, that is, low-temperature combustion is performed. This is because hydrocarbons do not grow to soot.
[0109]
This low-temperature combustion suppresses the generation of smoke regardless of the air-fuel ratio, while NO. _X It has the characteristic that the generation amount of can be reduced. That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but the combustion temperature is suppressed to a low temperature, so that the excessive fuel does not grow to the soot, and thus smoke does not occur. At this time, NO _X However, only a very small amount is generated. On the other hand, even 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 produced if the combustion temperature is high, but the combustion temperature is suppressed to a low temperature under low-temperature combustion. NO smoke at all, NO _X However, only a very small amount is generated.
[0110]
By the way, when the required torque TQ of the engine is increased, that is, when the fuel injection amount is increased, the temperature of the fuel and the surrounding gas at the time of combustion is increased, so that it is difficult to perform low temperature combustion. That is, low-temperature combustion can be performed only when the engine is in a low load operation where the amount of heat generated by combustion is relatively small. In FIG. 26A, a region I is an operation region in which the first combustion in which the amount of inert gas in the combustion chamber 5 is larger than the amount of inert gas in which the amount of soot generation reaches a peak, that is, low-temperature combustion can be performed. Region II shows a second combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas in which the amount of soot generation reaches a peak, that is, an operating region in which only normal combustion can be performed. Yes.
[0111]
FIG. 26B shows the target air-fuel ratio A / F when low-temperature combustion is performed in the operation region I, and FIG. 27 shows the throttle valve 17 corresponding to the required torque TQ when low-temperature combustion is performed in the operation region I. The opening degree, the opening degree of the EGR control valve 25, the EGR rate, the air-fuel ratio, the injection start timing θS, the injection completion timing θE, and the injection amount are shown. FIG. 27 also shows the opening of the throttle valve 17 during normal combustion performed in the operation region II.
[0112]
26B and 27, when the low temperature combustion is performed in the operation region I, the EGR rate is 55% or more, and the air-fuel ratio A / F is a lean air-fuel ratio of about 15.5 to 18. I understand. As described above, when low-temperature combustion is performed, there is an advantage that smoke, that is, fine particles are hardly discharged, so that a large amount of fine particles can be prevented from being deposited on the particulate filter 22.
[0113]
Further, when low temperature combustion is used, the air-fuel ratio in the combustion chamber 5 can be made rich without generating a large amount of soot, that is, a large amount of fine particles. Therefore, when it is determined that the air-fuel ratio A / F should be temporarily made rich to increase the oxidizability of the fine particles when the operating state of the engine is in the second operating region II shown in FIG. It is preferable not to make the air-fuel ratio A / F rich until the operating state shifts to the first operating region I, and to make the air-fuel ratio A / F rich after the operating state of the engine shifts to the first operating region II. .
[0114]
【The invention's effect】
The energy supplied from the outside can be used effectively in order to oxidize and remove the fine particles deposited on the particulate filter.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
FIG. 2 is a diagram showing a particulate filter.
FIG. 3 is a diagram illustrating an example of temperature rise control.
FIG. 4 is a diagram showing changes in the oxidizability of fine particles.
FIG. 5 is a diagram illustrating an example of temperature rise control.
FIG. 6 is a diagram showing an example of temperature raising conditions.
FIG. 7 is a view for explaining injection control.
FIG. 8 is a diagram showing a change in oxidizing property of fine particles.
FIG. 9 is a diagram illustrating an example of temperature rise control and engine operation control.
FIG. 10 is a flowchart for executing temperature rise control and engine operation control.
FIG. 11 is a diagram showing a decrease amount of fine particle oxidation.
FIG. 12 is a flowchart for calculating fine particle oxidation.
FIG. 13 is a graph showing the relationship between the amount of fine particles that can be removed by oxidation and the temperature of the particulate filter.
FIG. 14 is a diagram for explaining the state of deposited fine particles.
FIG. 15 is a diagram for explaining the state of deposited fine particles.
FIG. 16 is a diagram for explaining the state of deposited fine particles.
FIG. 17 is a diagram illustrating time Δt.
FIG. 18 is a diagram showing the amount of discharged fine particles.
FIG. 19 is a flowchart for calculating fine particle oxidation.
FIG. 20 is a diagram for explaining a change in pressure loss.
FIG. 21 is a flowchart for calculating fine particle oxidation.
FIG. 22 is a diagram for explaining a change in pressure loss.
FIG. 23 is a flowchart for calculating fine particle oxidation.
FIG. 24 is a flowchart for calculating fine particle oxidation.
FIG. 25 is a diagram showing the amount of smoke generated.
FIG. 26 is a diagram showing an engine operating region and the like.
FIG. 27 is a diagram showing changes in throttle valve opening and the like.
[Explanation of symbols]
5 ... Combustion chamber
6 ... Fuel injection valve
22 ... Particulate filter

Claims (4)

A particulate filter for collecting and removing particulates in the exhaust gas is disposed in the engine exhaust passage, and deposited on the particulate filter in an internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio. An oxidizing property calculating means for calculating the oxidizing property of the fine particles, a determining means for determining whether or not the amount of the fine particles deposited on the particulate filter exceeds a predetermined amount, and the amount of the fine particles deposited on the particulate filter are When it is determined that the predetermined amount has been exceeded, the lean air-fuel ratio is determined based on the temperature control condition determined according to the oxidizability of the fine particles deposited on the particulate filter in order to oxidize and remove the fine particles accumulated on the particulate filter. Exhaust gas purification provided with temperature control means for raising the temperature of the particulate filter Apparatus.   The temperature control means raises the temperature of the particulate filter to a set temperature determined by the temperature control condition and maintains the set temperature, and the set temperature is high when the oxidizability of the fine particles deposited on the particulate filter is low. The exhaust gas purification device according to claim 1, wherein the exhaust gas purification device is set to be higher than that of the exhaust gas purification device.   The temperature control means increases the temperature of the particulate filter over a set time determined by the temperature control condition, and the set time is set longer than when the particulates deposited on the particulate filter are low in oxidizability. The exhaust gas purification device according to claim 1.   A particulate filter for collecting and removing particulates in the exhaust gas is disposed in the engine exhaust passage, and deposited on the particulate filter in an internal combustion engine in which combustion is continuously performed under a lean air-fuel ratio. A temperature control means capable of raising the temperature of the particulate filter under a lean air-fuel ratio in order to oxidize and remove the particulates; and a first amount in which the amount of particulates deposited on the particulate filter is predetermined. A first determination means for determining whether or not the amount has exceeded, a first temperature control execution means for executing temperature control by the temperature control means when the amount of particulates deposited on the particulate filter exceeds the first amount, The amount of particulates remaining on the particulate filter when the temperature control by the temperature control means is interrupted is predetermined. Second determination means for determining whether or not the amount is larger than 2, and when the amount of particulates remaining on the particulate filter is larger than the second amount, it remains on the particulate filter. Second temperature control execution in which the air-fuel ratio of the exhaust gas flowing into the particulate filter is temporarily switched from lean to rich in order to change the properties of the particulates to easily oxidize, and then the temperature control by the temperature control means is executed. And an exhaust gas purifying device.

Images