JP4327584B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

As an exhaust purification device that purifies exhaust gas from an internal combustion engine, a particulate filter (hereinafter referred to as “filter”) carrying an NO _X storage agent is known. _The NO _X storage agent when the air-fuel ratio of the inflowing exhaust gas is lean occludes NO _X in the exhaust gas, absorbing and releasing action of the NO _X that the oxygen concentration of the inflowing exhaust gas to release NO _X that is occluded when lowered It was carried out, can be purified of the NO _X in the exhaust gas.

The NO _X storage agent stores not only NO _X in the exhaust gas but also sulfur content such as SO _X when the air-fuel ratio of the inflowing exhaust gas is lean. Since the sulfur content is often occluded in the NO _X absorbent is _the NO _X storage ability of the NO _X absorbent is lowered, it is necessary to release the sulfur that has been occluded in the NO _X absorbent from _the NO _X storage agent. However, since the sulfur content is stored in the NO _x storage agent in a relatively stable state, in order to release the sulfur content from the NO _x storage agent, the oxygen concentration of the inflowing exhaust gas is reduced and at the same time the NO _x storage agent. It is necessary to execute sulfur content release control for raising the temperature of the filter carrying the catalyst to a sulfur content release temperature (for example, 600 ° C. to 700 ° C.).

  On the other hand, the filter collects particulates such as particulate matter (Particulate Matter) in the inflowing exhaust gas. If the particulates collected and deposited by the filter are left as they are, the filter will be clogged, and it is necessary to remove the deposited particulates. The removal of the fine particles is performed by executing fine particle removal control in which the filter is heated to a fine particle combustion temperature (for example, 500 ° C.) with the air-fuel ratio of the inflowing exhaust gas made lean to burn the fine particles.

  Since the sulfur release temperature is higher than the particulate combustion temperature, the temperature of the filter is equal to or higher than the particulate combustion temperature when the sulfur release control is executed. If the air-fuel ratio is approximately the stoichiometric air-fuel ratio or rich (hereinafter referred to as “stoichiometric rich”) and lean, it is considered that fine particles can also be removed by sulfur content release control. However, if the sulfur content release control described above is executed in a state where a large amount of fine particles are deposited on the filter, the fuel (reducing agent) is also burned in addition to the fine particle combustion, so the temperature of the filter is the sulfur content release temperature. Gradually increases, and thermal deterioration of the filter increases. In order to prevent such a large thermal deterioration of the filter, it is necessary to control the temperature of the filter, but it is difficult to control the temperature of such a filter.

  In order to avoid such difficulty in controlling the temperature of the filter, the exhaust gas purification device disclosed in Patent Document 1 first performs particulate removal control to completely remove particulates accumulated on the filter. After that, the sulfur release control will be executed. By doing so, almost no particulates are deposited on the filter during the sulfur content release control, and the difficulty in controlling the temperature of the filter during the sulfur content release control is avoided.

Japanese Patent No. 2727906 JP 2002-038930 A Japanese Patent No. 2605586 JP 2000-274232 A JP 2003-166415 A

  By the way, when performing particulate removal control and sulfur content release control, it is necessary to raise the temperature of the filter and maintain it at a high temperature, or to make the air-fuel ratio of the inflowing exhaust gas stoichiometric rich. Consume fuel. Therefore, the longer the execution time of these controls, the worse the fuel consumption.

  As described above, in the exhaust gas purification device disclosed in Patent Document 1, since the particulate matter accumulated on the filter is completely removed by particulate removal control, the sulfur content release control is performed, so both these controls are performed. The total time is long, leading to a deterioration in fuel consumption. For this reason, it is desired to make the total execution time of the particulate removal control and the sulfur content release control as short as possible.

  Accordingly, an object of the present invention is an internal combustion engine that suppresses deterioration of fuel consumption by shortening the execution time of these controls while reducing thermal deterioration of exhaust purification means such as filters by particulate removal control and sulfur content release control. An object is to provide an exhaust emission control device.

In order to solve the above problems, the first aspect of the invention, the exhaust gas control means and a particulate filter and _the NO _X storage agent is placed on the engine exhaust passage to trap particulates in the exhaust gas, the _the NO _X storage agent the sulfur content stored in the NO _X absorbent when the temperature is sulfur release temperature or more of the NO _X absorbent air-fuel ratio is a substantially stoichiometric or rich exhaust gas flowing into the exhaust purification means In the exhaust gas purification apparatus for an internal combustion engine to be released, when the amount of particulates deposited on the particulate filter is larger than a predetermined limit accumulation amount or the sulfur content storage amount of the NO _X storage agent is a predetermined limit If the amount exceeds the occlusion amount, the temperature of the particulate filter is maintained above the particulate combustion temperature, and the air-fuel ratio of the exhaust gas flowing into the exhaust purification means is made lean. Te starts particle removal control for removing by combustion of particulates deposited on the particulate filter, maintaining the start of the fine particle removal control after a predetermined time has elapsed, the temperature of the _the NO _X storage agent or sulfur release temperature multiple alternating substantially stoichiometric or rich to _the NO _X storage agent occluded in which the sulfur release control and the particle removal control to release sulfur in the air-fuel ratio of the exhaust gas flowing into the exhaust purification means as well as The sulfur release / particulate removal control is repeated repeatedly , and the predetermined time is determined in advance so that the particulate deposition amount on the particulate filter is less than the limit deposition amount and near zero after the particulate removal control is started. This is the time taken to reach the deposited amount, and the remaining fine particles are removed during execution of the sulfur content release / fine particle removal control .
During sulfur release and particulate removal control, the temperature of the particulate filter changes according to the amount of particulate deposition, and the particulate filter temperature gradually rises when the particulate deposition amount is large. The temperature of the curate filter does not rise very much. According to the first aspect of the invention, the particulate filter is large even during the sulfur release / particulate removal control because the sulfur release control is performed after the particulate removal amount is reduced to a certain extent by executing the particulate removal control. The temperature does not rise to such an extent that thermal degradation occurs, and if the sulfur content release control is performed before the amount of particulates deposited becomes almost zero, the total execution time of the particulate removal control and the sulfur content release control is achieved. Shortened.
Note that the limit accumulation amount is, for example, so high that the deposited particulates burn at once even if the temperature of the particulate filter is raised to near the sulfur release temperature, and the temperature of the particulate filter causes melting damage. The maximum deposition amount in a range that does not become, or a deposition amount slightly less than that. The limit storage amount is, for example, the maximum sulfur storage amount within a range in which the NO _X storage capacity of the NO _X storage agent does not significantly decrease, or a sulfur storage amount slightly smaller than that.
Further, the predetermined accumulation amount (allowable accumulation amount) means that the temperature of the particulate filter is raised to the sulfur content release temperature, and then the air-fuel ratio of the exhaust gas flowing into the particulate filter is set at a constant cycle. When the lean and the stoichiometric air-fuel ratio or rich are repeated, the amount of deposition that can maintain the temperature of the particulate filter near the sulfur release temperature, or the temperature of the particulate filter is close to the sulfur release temperature Even if the temperature is raised to a low level, the amount of accumulated particulates can control the combustion of the deposited fine particles and maintain the temperature of the particulate filter in the vicinity of the sulfur content release temperature. It is the amount of deposition.

In order to solve the above problems, in the second invention, the exhaust gas control means and a particulate filter and _the NO _X storage agent is placed on the engine exhaust passage to trap particulates in the exhaust gas, the _the NO _X storage agent the sulfur content stored in the NO _X absorbent when the temperature is sulfur release temperature or more of the NO _X absorbent air-fuel ratio is a substantially stoichiometric or rich exhaust gas flowing into the exhaust purification means In the exhaust emission control device of the internal combustion engine to be released, when the amount of particulates deposited on the particulate filter is larger than a predetermined limit accumulation amount, or the sulfur storage amount in the NO _X storage agent is predetermined. if it becomes more than the limit adsorption amount is substantially the stoichiometric air-fuel ratio of the exhaust gas flowing into the exhaust purification means while maintaining the temperature of the NO _X absorbent than sulfur release temperature or Sulfur repeatedly repeats the rich sulfur release control and the particulate removal control to maintain the particulate filter temperature above the particulate combustion temperature and to make the air-fuel ratio of the exhaust gas flowing into the exhaust purification means lean. The minute release / particulate removal control is executed, and the cycle of repeating the sulfur release control and the particulate removal control in the sulfur release / particulate removal control is made shorter as the particulate deposition amount is smaller.
When performing sulfur content release and particulate removal control with a large amount of particulate accumulation, the cycle of repeating sulfur content release control and particulate removal control, especially each particulate removal control period, is lengthened to increase the particulate filter cooling period. Otherwise, the temperature of the particulate filter will gradually rise. On the other hand, when the amount of accumulated particulates decreases, the temperature of the particulate filter does not increase so much even if the cycle is shortened. According to the second aspect of the present invention, since the cycle is changed based on the amount of accumulated particulates during the sulfur content release / particle removal control, the temperature of the particulate filter is prevented from gradually rising from the vicinity of the sulfur content release temperature. Will be able to. In addition, both the removal of the fine particles and the release of the sulfur content are performed during the sulfur content release / fine particle removal control without performing the sulfur content release control and the fine particle removal control separately. The execution time of control for performing discharge can be shortened.

In the third invention, in the first or second invention, the temperature of the exhaust gas purification means is maintained in the vicinity of the sulfur content release temperature during the sulfur content release / fine particle removal control.

  According to the present invention, while the thermal deterioration of the exhaust gas purifying means such as a filter by the particulate removal control and the sulfur content release control is suppressed to be small, the execution time of both these controls can be shortened and deterioration of fuel consumption can be suppressed.

  Hereinafter, an exhaust emission control device for an internal combustion engine according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a diesel-type compression self-ignition internal combustion engine in which the exhaust purification system of the present invention is used. The present invention is also applicable to a spark ignition type internal combustion engine.

  Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 through the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 8. A throttle valve 9 driven by a step motor is disposed in the intake duct 6, and a cooling device 10 for cooling the intake air flowing in the intake duct 6 is disposed around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 10 and the intake air is cooled by the engine cooling water. On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to a casing 12 containing a particulate filter (hereinafter referred to as “filter”) 11. A reducing agent addition valve 13 for adding a reducing agent made of, for example, hydrocarbon (HC) or carbon monoxide (CO) to the exhaust gas flowing in the exhaust manifold 5 is disposed at the outlet of the collecting portion of the exhaust manifold 5. . In the present embodiment, the reducing agent addition valve 13 is hereinafter referred to as a fuel addition valve because fuel is added as a reducing agent to the exhaust gas.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 14, and an electronically controlled EGR control valve 15 is disposed in the EGR passage 14. An EGR cooling device 16 for cooling the EGR gas flowing in the EGR passage 14 is disposed around the EGR passage 14. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 16, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a fuel reservoir, so-called common rail 18 via a fuel supply pipe 17. Fuel is supplied into the common rail 18 from an electronically controlled fuel pump 19 with variable discharge amount, and the fuel supplied into the common rail 18 is supplied to the fuel injection valve 3 via each fuel supply pipe 17.

  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. A temperature sensor 20 for detecting the temperature of the filter 11 is attached to the filter 11, and a differential pressure sensor 21 for detecting a vertical differential pressure of the filter 11 is attached to an exhaust pipe upstream and downstream of the filter 11. . Output signals from the temperature sensor 20 and the differential pressure sensor 21 are input to the input port 35 via the corresponding AD converters 37. A load sensor 41 that generates an output voltage proportional to the amount of depression 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. The Further, a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 ° is connected to the input port 35. On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 9, the fuel addition valve 13, the EGR control valve 15, and the fuel pump 19 through corresponding drive circuits 38.

  The filter 11 described above has a honeycomb structure made of a porous material such as cordierite, and includes a plurality of exhaust gas flow passages extending in parallel to each other. These exhaust gas flow passages are composed of exhaust gas inflow passages whose downstream ends are closed by plugs, and exhaust gas outflow passages whose upstream ends are closed by plugs, and these exhaust gas flow passages are alternately arranged through thin partition walls. Placed in. Therefore, the exhaust gas flowing into the exhaust gas inflow passage flows out into the adjacent exhaust gas outflow passage through the surrounding partition wall.

A support layer made of alumina is formed on the peripheral wall surface of each exhaust gas flow passage, that is, on both side surfaces of each partition wall and on the inner wall surface of the pores in the partition wall. On this support, a NO _x storage agent and a catalyst are formed. Precious metal is supported. Examples of the NO _x storage agent include alkali metals such as potassium (K), sodium (Na), lithium (Li), and cesium (Cs), and alkaline earth metals such as barium (Ba) and calcium (Ca). At least one selected from rare earths such as lanthanum (La) and yttrium (Y) is used. Further, as the catalyst noble metal, for example, at least one selected from platinum (Pt), palladium (Pd), rhodium (Rh), and iridium (Ir) is used.

The NO _X storage agent is an air-fuel ratio of exhaust gas flowing into the filter 11 (hereinafter referred to as “inflow exhaust gas”) (air supplied to and added to the exhaust passage upstream of the filter 11, the combustion chamber 5 and the intake passage). When the fuel ratio is lean, the NO _x in the inflowing exhaust gas is occluded, and the air-fuel ratio of the inflowing exhaust gas to the filter 11, that is, the NO _x storage agent, is almost the stoichiometric air-fuel ratio or rich (hereinafter, “stoichiki · When it is called “rich”, it performs an absorption / release action of releasing the stored NO _x . NO _X occluding NO released from the dosage _X is reduced by reacting with the fuel in the exhaust gas (a reducing agent), it is purified.

The mechanism of the NO _x absorption and release action by the NO _x storage agent has not been fully clarified. Hereinafter, the mechanism currently considered will be described with reference to an example in which platinum and barium are supported on a carrier.

When the air-fuel ratio of the inflowing exhaust gas becomes considerably leaner than the stoichiometric air-fuel ratio, the oxygen concentration in the exhaust gas greatly increases, and oxygen adheres to the platinum surface in the form of O ₂ ⁻ or O ²⁻ . On the other hand, NO in the inflowing exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of platinum to become NO ₂ (2NO + O ₂ → 2NO ₂ ). Next, NO ₂ in the inflowing exhaust gas and a part of the generated NO ₂ are further oxidized on the platinum while being absorbed in the NO _x storage agent and combined with barium oxide (BaO), and nitrate ions (NO ₃ ⁻ shape in either occluded diffused in _the NO _X storage agent), or nitrite (NO ₂ ^- in the form of) occluded by diffusing into _the NO _X storage agent.

On the other hand, when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric rich, the oxygen concentration in the exhaust gas decreases, the amount of NO ₂ generated decreases, and the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ). . Thus _the NO _X storage agent in the nitrate ion (NO ₃ ^-) and the like are released from _the NO _X storage agent in the form of NO _2. The released NO _x reacts with the fuel (reducing agent) in the exhaust gas and is reduced. Thus NO ₂ NO ₂ no longer exists on the surface of the platinum when the _the NO _X storage agent one after another is released, the amount of the NO _X being occluded is made to decrease in _the NO _X storage agent .

In the above description, it has been described that NO _x is absorbed by the NO _x storage agent (that is, accumulates in the form of nitrate or the like). However, whether NO _x is actually absorbed or adsorbed (that is, It is not always clear whether NO _x is adsorbed in the form of NO ₂ or the like, and the term occlusion including both the concepts of absorption and adsorption is used. Further, the term “release” from the NO _X storage agent is used to include the meaning of “desorption” corresponding to “adsorption” in addition to “release” corresponding to “absorption”. If attention is focused on the active oxygen O ^* , the NO _X storage agent can be considered to be an active oxygen generator that generates the active oxygen O ^* as NO _X is stored and released.

In the present embodiment, NO _X release reduction control, particulate removal control, and SO _X release control (sulfur content release control) described below are executed. During normal control (normal operation) in which these controls are not executed, the opening of the throttle valve 9 is controlled according to, for example, the depression amount of the accelerator pedal 40, and the fresh air amount is in the engine operating state, for example, the fuel injection amount and the engine speed. The opening degree of the EGR control valve 15 is controlled so as to coincide with the target fresh air amount determined according to the above. Here, the fuel injection amount is determined according to, for example, the depression amount of the accelerator pedal 40 and the engine speed. Further, during normal control, only the main fuel injection FM is performed, for example, in the vicinity of the compression top dead center (TDC) as shown in FIG. 2 (A), or the main fuel injection is performed as shown in FIG. 2 (B). Pilot injection FP is performed together with FM. In order to stabilize combustion, the pilot injection FP is performed, for example, at a crank angle of about 10 to 40 degrees before compression top dead center before the main fuel injection FM is performed.

By the way, the compression self-ignition internal combustion engine is continuously combusted under a lean air-fuel ratio, and therefore the air-fuel ratio of the exhaust gas flowing into the filter 11 is basically kept lean. For this reason, NO _X in the exhaust gas is stored in the NO _X storage agent.

However, there is a limit to _the NO _X storage capacity due to _the NO _X storage agent, when _the NO _X storage amount of the NO _X absorbent increases, _the NO _X storage agent hardly occludes more NO _X. Therefore, in this embodiment, was reduced to release NO _X which is stored in _the NO _X storage agent, to reduce _the NO _X storage amount of the NO _X absorbent, the air-fuel ratio of the exhaust gas flowing into the filter 11 performing temporary NO _X emission reduction control to switch to the stoichiometric-rich the.

Specifically, in the present embodiment, fuel is temporarily supplied from the fuel addition valve 13 so that the air-fuel ratio of the exhaust gas flowing into the filter 11 becomes stoichiometric rich. In this case, the fuel is added from the fuel addition valve 13 by an amount necessary for the NO _X storage amount of the NO _X storage agent to become a lower limit amount, for example, approximately zero. Such NO _x release reduction control is repeatedly performed at predetermined time intervals. This set time interval is set according to the engine operating state, for example, the fuel injection amount and the engine speed. Incidentally, seeking _the NO _X storage amount of the NO _X absorbent can also be performed for NO _X emission reduction control when _the NO _X storage amount of the NO _X occluding agent exceeds the upper limit amount.

  In general, in the compression self-ignition internal combustion engine used in the present embodiment, the exhaust gas discharged from the combustion chamber 2 contains fine particles made of carbon such as particulate matter. When flowing into the filter, these fine particles are collected on the partition walls of the filter 11. Thereby, discharge | release to the atmosphere of microparticles | fine-particles is suppressed.

Further, as described above, the NO _X storage agent carried on the filter 11 generates active oxygen O ^{* when} performing NO _X absorption and release. This active oxygen O ^* has a higher activity than oxygen. Therefore, even if the temperature of the filter 11 is relatively low, fine particles collected on the filter 11 are oxidized and removed. That, NO _X absorbent in the filter 11 by being supported, regardless of the air-fuel ratio of exhaust gas flowing into the filter 11, particulates trapped on the filter 11 is continuously oxidized.

  However, when the amount of fine particles flowing into the filter 11 per unit time increases, the amount of fine particles collected by the filter 11 exceeds the amount of fine particles that can be continuously oxidized by the filter 11, and the fine particles deposited on the filter 11. The amount gradually increases, and the pressure loss due to the filter 11 increases accordingly.

  Therefore, in the present embodiment, when the amount of particulates deposited on the filter 11 increases, particulate removal control for removing particulates deposited on the filter 11 is executed. In the particulate removal control, the temperature of the filter 11 is raised to a particulate combustion temperature (for example, 500 ° C.) or higher while the supply of EGR gas is stopped and the air-fuel ratio of the exhaust gas flowing into the filter 11 is kept lean. After the temperature raising process is performed, a temperature maintaining process is performed in which the temperature of the filter 11 is maintained at a temperature equal to or higher than the particulate combustion temperature, and particulates deposited on the filter 11 are forcibly burned and removed.

  Specifically, in the temperature raising process, until the temperature of the filter 11 detected by the temperature sensor 20 reaches the particulate combustion temperature, first, as shown in FIG. 2C, the pilot fuel injection FM and the pilot fuel injection FP After injection FA is performed. The after injection FA is performed, for example, at a crank angle of about 20 to 30 degrees after the compression top dead center in order to increase the temperature of the exhaust gas discharged from the combustion chamber. At this time, the injection timings of the main fuel injection FM and the pilot injection FP are retarded as compared with the normal control time (see FIG. 2B).

  When the temperature of the filter 11 is raised to the particulate combustion temperature by the temperature raising process, the high temperature maintenance process is performed. In the high temperature maintenance process, as shown in FIG. 2D, the pilot injection FP and the after injection FA are performed together with the main fuel injection FM, and further, for example, the post injection FPO is performed about 90 to 120 degrees after the compression top dead center. Is called. In this case, the injection amount of the post injection FPO is controlled so that the temperature of the filter 11 is maintained near the particulate combustion temperature. The post-injection FPO is different from the after-injection FA in that it does not contribute to the engine output.

By the way, the exhaust gas contains sulfur in the form of SO _x , for example, and the NO _x storage agent stores not only NO _x but also SO _x . It is considered that the storage mechanism of SO _{X in} the NO _X storage agent is basically the same as the storage mechanism of NO _X. That is, the case where platinum (Pt) and barium (Ba) are supported on the carrier will be briefly described as an example. As described above, when the air-fuel ratio of the exhaust gas flowing into the filter 11, that is, the NO _x storage agent, is lean. O ₂ is attached to the surface of platinum in the form of O ₂ ⁻ or O ₂ ⁻ , and SO ₂ in the inflowing exhaust gas is attached to the surface of platinum and O ₂ ⁻ or O ₂ ⁻ on the surface of the platinum. To SO ₃ . Next, the generated SO ₃ is further oxidized on the platinum while being absorbed by the NO _x storage agent and combined with barium oxide (BaO), and diffuses into the NO _x storage agent in the form of sulfate ions (SO ₄ ⁻ ). . The sulfate ions are then combined with barium ions (Ba ⁺ ) to form sulfate (BaSO ₄ ).

This sulfate (BaSO ₄ ) is difficult to decompose, and even if the air-fuel ratio of the exhaust gas flowing into the filter 11 is simply rich, the amount of sulfate in the NO _x storage agent does not decrease. For this reason, as time passes, the amount of sulfate in the NO _x storage agent increases, and as a result, the amount of NO _x that can be stored by the NO _x storage agent decreases.

However, if the air-fuel ratio of the exhaust gas flowing into the filter 11 is made stoichiometric rich while maintaining the temperature of the NO _X storage agent at, for example, 600 ° C. or higher, the sulfate in the NO _X storage agent decomposes and forms SO ₃ . Is released from the NO _X storage agent. The released SO ₃ reacts with the fuel (reducing agent) in the exhaust gas and is reduced to SO ₂ . In this way, the amount of SO _X stored in the form of sulfate in the NO _X storage agent gradually decreases, and at this time, SO _X does not flow out from the NO _X storage agent in the form of SO ₃ .

In this embodiment, when the SO _X storage amount stored in the NO _X absorbent increases, SO _X release control for releasing SO _X, which is occluded in the NO _X absorbent is performed. In the SO _X release control, the air-fuel ratio of the exhaust gas flowing into the filter 11 is maintained while maintaining the temperature of the NO _X storage agent, that is, the temperature of the filter 11 at or above the SO _X release temperature (sulfur content release temperature, for example, 600 ° C.). Is stoichiometric and rich.

Specifically, in the SO _X release control, the combustion of the engine is so-called EGR combustion, and fuel is added to the exhaust gas flowing from the fuel addition valve 13 into the NO _X storage agent. The EGR combustion is combustion performed by causing EGR gas, which is part of exhaust gas discharged from the combustion chamber 2, to be again sucked into the combustion chamber, and its EGR rate (EGR gas amount / (EGR gas amount + intake). The amount of air)) is higher than normal combustion. Generally, in a compression self-ignition internal combustion engine, the air-fuel ratio of exhaust gas discharged from the combustion chamber 2 is almost lean, and the degree of leanness is high (hereinafter referred to as “strong lean”). On the other hand, when EGR combustion is being performed, the amount of intake air into the combustion chamber 2 is suppressed to a low level, so the air-fuel ratio of the exhaust gas discharged from the combustion chamber 2 is lean but its lean degree is low (for example, The air-fuel ratio of the exhaust gas is 18 to 25. Hereinafter, it is referred to as “weak lean”). Further, since a lot of exhaust gas is returned to the combustion chamber 5 again, there is little exhaust gas reaching the filter 11. For this reason, even if the amount of fuel added from the fuel addition device to the exhaust gas is small, the air-fuel ratio of the exhaust gas flowing into the filter 11 can be stoichiometric and rich.

Further, in EGR combustion, a large amount of EGR gas having a temperature higher than that of the intake air into the combustion chamber 5 is sucked, so that the temperature of the exhaust gas discharged from the combustion chamber 2 is higher than when EGR combustion is not performed. Further, since the fuel is added from the fuel addition valve 13 to the exhaust gas having such a high temperature, the added fuel burns in the filter 11 and before the exhaust gas flows into the filter 11, and the temperature of the exhaust gas. And the temperature of the filter 11 is raised. Therefore, by setting the combustion of the engine to EGR combustion and adding fuel from the fuel addition device 52, the temperature of the filter 11, that is, the temperature of the NO _X storage agent, can be maintained at the SO _X release temperature or higher.

  EGR combustion includes low temperature combustion and high EGR combustion. Here, the low temperature combustion and the high EGR combustion will be briefly described. In general, in a compression self-ignition internal combustion engine, when the ratio of EGR gas in the air-fuel mixture flowing into the combustion chamber 5 is increased with conditions such as the fuel injection timing being constant (hereinafter referred to as “EGR rate”), Although the amount of smoke generated increases, when the peak of a certain amount of smoke generated is exceeded, the amount of smoke generated decreases conversely.

  Low temperature combustion refers to combustion performed by inhaling EGR gas into the combustion chamber 5 at a high EGR rate that exceeds the peak of the amount of smoke generated, and high EGR combustion is a range that does not exceed the peak of the amount of smoke generated The combustion is performed by sucking EGR gas into the combustion chamber at a relatively high EGR rate. In this case, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber is set to, for example, about 18 to 20 in the low temperature combustion, and is set to about 22 to 25 in the high EGR combustion. Note that the air-fuel ratio during normal control is about 25 to 70. On the other hand, in the low temperature combustion, only the main fuel injection is performed at a crank angle of about 20 degrees before the compression top dead center, and in the high EGR combustion, only the main fuel injection is performed in the vicinity of the compression top dead center.

  In this specification, these low-temperature combustion and high EGR combustion are simply described as EGR combustion, but in this embodiment, these low-temperature combustion and high EGR combustion are selectively used depending on the situation during EGR combustion. Yes.

Further, EGR combustion including low temperature combustion and high EGR combustion becomes difficult to execute when the engine load is high, the fuel injection amount is large, or the required torque for the internal combustion engine is large. This is because the temperature of the fuel and surrounding gas during combustion increases. Therefore, in such a case, it is difficult to make the air-fuel ratio of the exhaust gas flowing into the filter 11 stoichiometric rich. Therefore, in the SO _X release control of the present embodiment, EGR combustion is not performed in such a case, combustion is performed with a considerably low or almost zero EGR rate as in the normal control, and fuel is added from the fuel addition valve 13. Thus, the temperature of the filter 11 is maintained at the SO _X release temperature or higher. In other words, in the SO _X release control, basically, the air-fuel ratio of the exhaust gas flowing into the filter 11 is stoichiometric and rich, and the temperature of the NO _X storage agent is raised to the SO _X release temperature and maintained. Although it is difficult to make the air-fuel ratio stoichiometric rich when the engine load is high, etc., only the temperature rise and temperature maintenance of the filter 11 are executed. However, in the following description, it is assumed that SO _X release control is performed even at the time described above.

In the above-described particulate removal control and SO _X release control, it is necessary to raise the temperature of the filter 11 in any of the controls, but for raising the temperature of the filter 11, as described above, pilot injection, after injection, and post It is necessary to perform injection and to add fuel from the fuel addition valve 13, which causes an increase in fuel consumption. Therefore, in the present embodiment, when the amount of particulates deposited on the filter 11 exceeds a predetermined limit accumulation amount, or when the SO _X storage amount of the NO _X storage agent exceeds a predetermined limit storage amount. In addition, from the viewpoint of suppressing deterioration in fuel consumption, the particulate removal control and the SO _X release control are continuously performed to reduce the number of times of temperature rise of the filter 11. Here, the limit accumulation amount is, for example, that even if the temperature of the filter 11 is raised to the vicinity of the SO _X release temperature, the fine particles accumulated on the filter 11 burn at once, and the temperature of the filter 11 is dissolved in the filter 11. It is below the maximum deposition amount within a range where the temperature does not become high enough to cause damage, and is the same amount as the threshold of the particulate deposition amount when executing particulate removal control in the conventional exhaust purification apparatus. In addition, the limit adsorption amount, for example, the largest SO _X storage amount, or slightly less SO _X storage amount than in free range to _the NO _X storage capacity decreases markedly in _the NO _X storage agent.

By the way, in the conventional exhaust purification apparatus, when the particulate removal control and the SO _X release control are continuously performed, the particulate removal control is executed prior to the SO _X release control, and the amount of particulate deposition on the filter 11 is substantially reduced. It was decided to perform SO _X release control after zeroing. That is, in the conventional SO _X release control, if the air-fuel ratio of the exhaust gas flowing into the filter 11 is actually maintained to be stoichiometric and rich, the fuel (reducing agent) adheres to the carrier surface of the filter 11 and therefore flows into the filter 11. Fuel is added so that the air-fuel ratio of the exhaust gas repeats lean, stoichiometric and rich at a constant cycle, and the fuel adhering to the carrier surface of the filter 11 is burned. However, when such conventional SO _X release control is executed in a state where a large amount of fine particles are deposited on the filter 11, the fine particles on the filter 11 are easily burned during execution of the SO _X release control. For this reason, the temperature of the filter 11 becomes considerably high during execution of the SO _X release control, and the thermal deterioration of the filter 11 becomes large. Further, in this case, since it is difficult to control the combustion of the fine particles, it is difficult to maintain the temperature of the filter 11 in the vicinity of the SO _X release temperature so that the temperature of the filter 11 does not become a considerably high temperature. Therefore, by executing the particulate removal control first to reduce the amount of particulate deposition to almost zero and then performing the SO _X release control, large thermal deterioration is prevented and the difficulty of maintaining the filter temperature is avoided.

However, the particulate removal control described above requires fuel to maintain the temperature of the filter 11 at or above the particulate combustion temperature, and the SO _X release control makes the air-fuel ratio of the exhaust gas flowing into the filter 11 stoichiometric rich. Need fuel. Therefore, the fuel consumption increases as the total execution time of both controls becomes longer. In the conventional exhaust purification device, the SO _X release control is performed after the fine particles on the filter 11 are completely removed by the fine particle removal control in order to avoid the difficulty of maintaining the temperature of the filter in a state where a large amount of fine particles are accumulated. However, from the viewpoint of reducing fuel consumption, it is preferable to shorten the total execution time of both controls as much as possible.

Therefore, in the present embodiment, when executing a particulate removal control and SO _X release control, the start of the earlier particulate removal control, the SO _X release control and particulate removal control from the start of the particle removal control after a predetermined time has elapsed The SO _X release / particle removal control (sulfur content release / particle removal control), which is alternately repeated a plurality of times, is executed.

In the present embodiment, during the SO _X release / particulate removal control, the temperature of the filter 11 is maintained at the SO _X release temperature or higher while the exhaust gas flowing into the filter 11 is maintained, as in the conventional SO _X release control. The air-fuel ratio is made to repeat lean and stoichiometric rich. Then, the air-fuel ratio of the inflowing exhaust gas particulates deposited on the filter 11 as a particulate removal control is removed when the lean, when the air-fuel ratio of the inflowing exhaust gas is stoichiometric-rich from _the NO _X storage agent as SO _X release control SO _X is released. Therefore, at the end of the SO _X release / fine particle removal control, the SO _X storage amount and the fine particle accumulation amount are substantially zero.

Further, if the SO _X release / particulate removal control is executed in a state where the amount of particulates deposited on the filter 11 is large, the combustion speed of the particulates, that is, the speed at which the particulates spread is fast, and the temperature of the filter 11 is maintained near the SO _X release temperature. Although it is difficult, when the deposited amount of the particulate matter onto the filter 11 is small slow burn rate of fine particles, readily sO _X release temperature near the temperature of the filter 11 is also running a sO _X release-particle removal control for Can be maintained. In the present embodiment, by performing the previously particulate removal control predetermined time, since the SO _X release-particle removal control after reducing the particulate deposition amount is performed, even SO _X release-particle removal control in the filter The temperature of 11 can be easily maintained in the vicinity of the SO _x release temperature.

Furthermore, if the SO _X release / particulate removal control is started before the particulate accumulation amount becomes zero, the total execution time of both controls can be shortened as compared with the conventional exhaust purification device. That is, in the SO _X release / particulate removal control of this embodiment, it is considered that the particulates are removed prior to SO _X in most cases. Therefore, the conventional SO _X release control and the SO _X release / particulate removal in this embodiment are considered. Although the control is performed only for the time required for the release of SO _x , and therefore substantially the same time, the execution time of the particulate removal control in this embodiment is shorter than that of the conventional exhaust purification device. For this reason, according to this embodiment, the total execution time of these controls can be shortened compared with the conventional exhaust purification apparatus, and the fuel consumption by these controls can be reduced. Therefore, according to the present embodiment, the total execution time of both controls can be shortened while maintaining the temperature of the filter 11 during the SO _X release / particulate removal control in the vicinity of the SO _X release temperature.

  Here, the predetermined time may be a fixed time regardless of the amount of particulate deposition, or may be a time varying according to the amount of particulate deposition on the filter 11. In the case where the predetermined time is set to a constant time regardless of the amount of fine particles deposited, for example, even if the fine particle removal control is executed, the fine particles that have basically accumulated to near the limit accumulation amount are completely removed. This is a constant time that is determined experimentally in advance.

  In the case where the predetermined time is a time that varies depending on the amount of particulate deposition, for example, the predetermined time is, for example, when the particulate deposition amount on the particulate filter is less than the limit deposition amount and zero after the particulate removal control is started. It is the time taken to reach a predetermined allowable deposition amount that is greater than the vicinity. The allowable deposition amount is, for example, a deposition amount that is 50% of the limit deposition amount.

This will be specifically described with reference to FIG. In the embodiment of the present invention, the particulate accumulation amount ΣPM on the filter 11 is calculated based on the differential pressure across the filter 11 detected by the differential pressure sensor 21 and the engine speed. This is because the up-and-down differential pressure of the filter 11 changes according to the amount of particulates deposited on the filter 11 when the engine speed is constant. On the other hand, the SO _X storage amount ΣSO _X is calculated by sequentially integrating the SO _X amount flowing into the NO _X storage agent per unit time. This inflow SO _X amount per unit time corresponds to the SO _X amount discharged from the combustion chamber 2 per unit time, and this exhaust SO _X amount depends on the engine operating state, for example, the fuel injection amount and the sulfur concentration in the fuel. Can be calculated.

When the calculated particulate accumulation amount ΣPM exceeds the limit accumulation amount ΣPMH, or when the SO _X storage amount ΣSOX exceeds the limit storage amount ΣSOXH, the above-described particulate removal control is first started (time in FIG. 3). t _0). When the particulate removal control is started, the temperature raising process is performed, and the temperature Tc of the filter 11 is raised (time t _{0 to} t ₁ ). When the temperature Tc of the filter 11 detected by the temperature sensor 20 reaches the particulate combustion temperature, the temperature is switched to the high temperature maintenance process (time t ₁ ), and the temperature Tc of the filter 11 is maintained near the particulate combustion temperature. During the high temperature maintenance process of the particulate removal control (time t _{1 to} t ₂ ), the particulate accumulation amount ΣPM on the filter 11 gradually decreases. When the predetermined time is set to be a constant time regardless of the amount of fine particles deposited, the fine particle removal control is stopped when the predetermined time has elapsed from the start of the fine particle removal control, and the SO _X release / fine particle removal control is started (time). t _2).
On the other hand, when the predetermined time is set as a time that changes according to the amount of deposited fine particles, for example, the amount of fine particles that decrease per unit time is calculated according to the temperature of the filter 11. Then, the amount of fine particles decreasing per unit time is successively subtracted from the fine particle accumulation amount at the start of fine particle removal control, and when the fine particle accumulation amount ΣPM reaches the allowable accumulation amount ΣPML, the fine particle removal control is stopped, and SO _X release / fine particle Removal control is started (time t ₂ ).

When the SO _X release / particulate removal control is started, fuel is added from the fuel addition valve 13 so that the air-fuel ratio A / F of the inflowing exhaust gas repeats stoichiometric rich and lean, and the air-fuel ratio A of the inflowing exhaust gas. When / F changes from stoichiometric rich to lean, the fuel (reducing agent) and fine particles adhering to the surface of the filter 11 burn, so the temperature of the filter 11 rises. Even after the combustion of the fuel is finished, the combustion of the fine particles continues, but since the amount of the fine particles deposited on the filter 11 is small, the combustion speed is slow, and the temperature Tc of the filter 11 decreases. In addition, the particulate accumulation amount ΣPM on the filter 11 decreases with the combustion of the particulates, and finally becomes almost zero. Further, during the SO _X release / fine particle removal control, the SO _X storage amount ΣSOX of the NO _X storage agent gradually decreases mainly when the air-fuel ratio A / F of the inflowing exhaust gas is stoichiometric and rich. The amount of SO _X that decreases per unit time can be calculated according to the temperature of the filter 11, for example. In this embodiment, the SO _X amount which decreases per unit time sequentially subtracted from the SO _X storage amount, SO _X storage amount lower limit, SO _X release control is completed when the example becomes zero (time t _3). That is, the normal control is restored.

  FIGS. 4 and 5 show an exhaust purification routine in the present embodiment in which the predetermined time is set to a fixed time regardless of the amount of deposited particulates. This routine is executed by interruption every predetermined time.

Referring to FIGS. 4 and 5, first, at step 100, the SO _X storage amount ΣSOX of the NO _X storage agent and the particulate accumulation amount ΣPM on the filter 11 are calculated. These are calculated not only during normal control but also during particulate removal control and SO _x release / particle removal control. Next, at step 101, it is judged if the SO _X release / particulate removal flag XSPM is set. The SO _X release / particulate removal flag XSPM is set when the SO _X release / particulate removal control is to be executed (XSPM = 1), and is not set otherwise (XSPM = 0). When the SO _X release / particulate removal flag XSPM is not set, the routine proceeds to step 102, where it is judged if the particulate removal flag XPM is set. The particulate removal flag XPM is set when the particulate removal control is to be executed (XPM = 1), and is not set otherwise (XPM = 0).

When the particulate removal flag XPM is not set, the routine proceeds to step 103, where it is judged if the particulate accumulation amount ΣPM on the filter 11 exceeds the limit accumulation amount ΣPMH. When ΣPM ≦ ΣPMH, the routine proceeds to step 104, where it is determined whether or not the SO _X storage amount ΣSOX of the NO _X storage agent exceeds the limit storage amount ΣSOXH. When ΣSOX ≦ ΣSOXH, the routine proceeds to step 105 where it is determined whether or not an execution condition for NO _X release reduction control is satisfied. In the present embodiment, the execution condition of the NO _X release reduction control is satisfied when the set time interval described above has elapsed from the previous NO _X release reduction control and the temperature of the NO _X storage agent is higher than a set temperature, for example, 190 ° C. Otherwise, it is determined that the conditions for executing the NO _x release reduction control are not satisfied. When it is determined that the execution condition for the NO _x release reduction control is not satisfied, the routine proceeds to step 106 where normal control is performed. On the other hand, when it is determined that the execution condition for the NO _x release reduction control is satisfied, the routine proceeds to step 107 where the NO _x release reduction control is performed.

  On the other hand, when ΣPM> ΣPMH at step 103 or ΣSOX> ΣSOXH at step 104, the routine proceeds to step 108 where the particulate removal flag XPM is set.

When the particulate removal flag XPM is set, the routine proceeds from step 102 to step 109, where it is determined whether or not a predetermined time has elapsed since the particulate removal flag XPM was set. When the predetermined time has not elapsed, the routine proceeds to step 110 where particulate removal control is executed. On the other hand, when the predetermined time has elapsed, the particulate removal flag XPM is reset in step 111 (XPM = 0), and the particulate removal control is ended. In the following step 112, the SO _X release / particulate removal flag XSPM is set (XSPM = 1).

When the SO _X release / particulate removal flag XSPM is set, the routine proceeds from step 101 to step 113, where it is determined whether or not the SO _X storage amount ΣSOX of the NO _X storage agent is substantially zero. When the SO _X storage amount is not zero, the routine proceeds to step 114 where SO _X release / fine particle removal control is executed. On the other hand, when the SO _X storage amount is substantially zero, the routine proceeds to step 115 where the SO _X release / particle removal flag XSPM is reset (XSPM = 0). That is, the SO _X release control ends.

  In the case where the predetermined time is a time that varies depending on the amount of particulate deposition, for example, it is determined in step 109 whether the particulate deposition amount ΣPM on the filter 11 is equal to or less than the allowable deposition amount ΣPML. . When ΣPM> ΣPML, the routine proceeds to step 110 where particulate removal control is executed. On the other hand, when ΣPM ≦ ΣPML, the particulate removal flag XPM is reset at step 111 (XPM = 0), and the particulate removal control is terminated.

By the way, it has been explained that if SO _X release control is executed in a state where a large amount of fine particles are accumulated on the filter 11, it is difficult to control the combustion of the fine particles and maintain the temperature of the filter 11 near the SO _X release temperature. The reason for this will be described in detail below.

In general, in the SO _X release control, as described above, fuel is added so that the air-fuel ratio of the exhaust gas flowing into the filter 11 repeats lean, stoichiometric and rich at a constant cycle, and adheres to the carrier surface of the filter 11. The burned fuel is burned. In this case, during the SO _X release control, the temperature of the filter 11 rises due to fuel combustion when the air-fuel ratio of the inflowing exhaust gas is switched from stoichiometric rich to lean. However, the temperature rise of the filter 11 is temporary, and when the combustion of the fuel is finished, the temperature of the filter 11 is lowered by being cooled by the exhaust gas, and fine particles are not deposited on the filter 11. The temperature of the filter 11 is maintained at a substantially constant temperature while repeating some fluctuations.

  However, when a large amount of fine particles are accumulated on the filter 11, since the fine particles are burned during the period when the temperature of the filter 11 is lowered, the rate of temperature decrease is very slow. For this reason, the temperature of the filter 11 is not sufficiently lowered between the time when the air-fuel ratio of the inflowing exhaust gas is once switched from stoichiometric rich to lean and the next time when the same switching is performed again. Therefore, if the repetition between lean and stoichiometric rich of the air-fuel ratio of the inflowing exhaust gas at a constant cycle is continued, the temperature of the filter 11 gradually rises to an extremely high temperature, and the thermal deterioration of the filter 11 is reduced. It gets bigger.

  On the other hand, the repetition period of one cycle for repeating the lean and stoichiometric richness of the air-fuel ratio of the exhaust gas flowing into the filter 11 is lengthened. (Hereinafter referred to as “lean period”) is lengthened and the air-fuel ratio of the inflowing exhaust gas is once switched from stoichiometric rich to lean even when a large amount of fine particles are accumulated on the filter 11 It is also conceivable that the temperature of the filter 11 is sufficiently lowered before the same switching is performed again.

  Here, the burning rate of the fine particles deposited on the filter 11, that is, the speed at which the fine particles burn and spread varies depending on the amount of fine particles deposited on the filter 11. In a state where a large amount of fine particles are accumulated, the interval between the deposited fine particles is short, and when a certain fine particle is burned, the combustion heat is easily transmitted to the fine particles deposited nearby. For this reason, the burning speed of the fine particles is fast, and the temperature of the filter 11 is unlikely to decrease. On the other hand, in a state where the amount of particulates deposited is small, the distance between the particulates that are deposited close to each other is long, so that the combustion rate of the particulates is slow and the temperature of the filter 11 tends to decrease.

Therefore, if the repetitive cycle of the air-fuel ratio of the inflowing exhaust gas, particularly the lean period, is determined in accordance with the case where a large amount of fine particles are accumulated on the filter 11, the filter 11 is reduced when the amount of fine particles deposited on the filter 11 decreases. Thus, the temperature is lowered more than necessary, and the temperature becomes lower than the SO _X release temperature. For this reason, the execution time of the SO _X release control becomes unnecessarily long, and in order to continue the SO _X release control, the temperature increase control is required, which leads to deterioration of fuel consumption.

Therefore, in the second embodiment of the present invention, when a large amount of fine particles are accumulated on the filter 11 or when a large amount of SO _x is occluded in the NO _x storage agent, it is accumulated on the filter 11. The SO _X release / particulate removal control is executed by alternately repeating the particulate removal control for removing the particulates and the SO _X release control for releasing the SO _X stored in the NO _X storage agent. In the SO _X release / particulate removal control, the cycle of repeating the SO _X release control and the particulate removal control is sequentially changed according to the amount of particulate deposition. In particular, the period is shortened as the particulate deposition amount decreases.

For example, during the SO _X release / particulate removal control, the air-fuel ratio of the exhaust gas flowing into the filter 11 repeats lean and stoichiometric rich while maintaining the temperature of the filter 11 at or above the SO _X release temperature. The cycle in which the air-fuel ratio of the inflowing exhaust gas repeats lean, stoichiometric, and rich is made shorter as the amount of accumulated particulate matter decreases.

  Referring to FIG. 6, in more detail, in the present embodiment, the air-fuel ratio of the inflowing exhaust gas is kept constant while the stoichiometric rich period b is constant in the repetition period a of the air-fuel ratio A / F of the inflowing exhaust gas. The A / F repetition period a is changed in accordance with the amount of particulate deposition. The repetition period a is increased when the amount of particulate deposition is large, and the repetition period a is shortened when the amount of particulate deposition decreases. Yes. Alternatively, in the present embodiment, the lean period c excluding the stoichiometric / rich period b in the repetitive period a may be changed according to the amount of particulate deposition. In the present embodiment, the stoichiometric rich period is constant, but it is not necessarily constant. In that case, the ratio of the length of the repetition period a or the length of the lean period c to the stoichiometric rich period b is changed. You may make it do.

Thereby, when a large amount of fine particles are accumulated on the filter 11, a sufficient time for lowering the temperature of the filter 11 is ensured, and when the amount of fine particle accumulation on the filter 11 has decreased, The temperature of the filter 11 can be maintained without being excessively lowered. That is, the temperature of the filter 11 can be maintained in the vicinity of the SO _X release temperature.

Here, it is considered that the temperature of the filter 11 fluctuates as shown in FIG. 6 during the SO _X release / fine particle removal control. That is, when the air-fuel ratio A / F of the inflowing exhaust gas is switched from stoichiometric rich to lean, a large amount of oxygen flows into the filter 11, so that the fine particles deposited on the filter 11 are burned and on the carrier surface. The fuel (reducing agent) adhering to the fuel burns, and the temperature Tc of the filter 11 temporarily rises. When the combustion of fuel is completed, the temperature Tc of the filter 11 decreases. That is, even if the combustion of the fuel is completed, the fine particles continue to burn, but when the temperature Tc of the filter 11 is in the vicinity of the SO _x release temperature, the thermal energy due to the combustion of the fine particles is not so large that the temperature of the filter 11 is increased. It is considered a thing. When the air-fuel ratio A / F of the inflowing exhaust gas is switched again from lean to stoichiometric rich, the oxygen concentration in the inflowing exhaust gas decreases, so that the combustion of particulates is suppressed and the temperature Tc of the filter 11 becomes faster. It goes down.

  Considering the above inference, regarding the temperature decrease of the filter 11, the length of the period excluding the temperature increase period d during which the temperature Tc of the filter 11 increases due to the combustion of the fuel adhering to the carrier during the lean period is affected. It is considered a thing. Therefore, as a method for changing the switching timing of the inflowing exhaust gas, the following method may be adopted in addition to the change of the repetition cycle and the change of the lean period.

  That is, the temperature decrease period e excluding the temperature increase period d in the lean period is changed according to the amount of particulate deposition, or the period f obtained by adding the temperature decrease period e and the stoichiometric rich period b is the particulate deposition amount. Change according to. Regardless of which method is employed, the periods e and f are lengthened when the amount of particulate deposition is large, and the periods e and f are shortened when the amount of particulate deposition decreases.

The second embodiment will be specifically described with reference to FIG. In the second embodiment, when the particulate accumulation amount ΣPM calculated based on various sensors or the like exceeds the limit accumulation amount ΣPMH, or when the SO _X storage amount ΣSOX exceeds the limit storage amount ΣSOXH, the SO _X release / Fine particle removal control is executed (time t _{4 in} FIG. 7). When the SO _X release / fine particle removal control is started, the temperature raising process is first performed, and the temperature of the filter 11 is raised (time t _{4 to} t ₅ ). When the temperature Tc of the filter 11 detected by the temperature sensor 20 reaches the SO _X release temperature, the temperature raising process is stopped, and the repetition between lean and stoichiometric rich of the air-fuel ratio A / F of the inflowing exhaust gas is started. The At this time, the length of each stoichiometric rich period is substantially constant, but the length of each lean period t _l is a value obtained by adding a correction coefficient Δt to the basic lean time t _lb (t _l = t _lb + Δt). Here, the basic lean time is a value calculated based on the engine speed and the fuel injection amount using a map obtained in advance through experiments or the like, and is a value determined independently of the amount of particulate accumulation. The correction coefficient Δt is calculated based on the particulate accumulation amount ΣPM using a map obtained in advance through experiments or the like, and is a value that varies according to the particulate accumulation amount ΣPM, for example, as shown in FIG. During the SO _X release / particulate removal control, the particulate accumulation amount ΣPM on the filter 11 and the SO _X storage amount ΣSOX of the NO _X storage agent gradually decrease, and the particulate deposition amount ΣPM and the SO _X storage amount ΣSOX become almost zero. Control is terminated (time t ₆ ).

  8 and 9 show an exhaust purification routine in the second embodiment. This routine is executed by interruption every predetermined time. Steps 150 to 157 in FIGS. 8 and 9 are basically the same as steps 100, 101, and 103 to 108 in FIGS.

When the SO _X release / particulate removal flag is set at step 157 (XSPM = 1), the routine proceeds from step 151 to steps 158 and 159 when the next routine is executed, and the SO _X storage amount ΣSOX of the NO _X storage agent is substantially zero. And whether or not the particulate accumulation amount ΣPM on the filter 11 is substantially zero. When at least one of the SO _X storage amount ΣSOX and the particulate accumulation amount ΣPM is not zero, the routine proceeds to step 160. In step 160, the basic lean time t _lb is calculated based on the engine speed and the fuel injection amount, and the correction coefficient Δt is calculated based on the particulate accumulation amount ΣPM calculated in step 150. Next, at step 161, the lean time t _l is calculated by adding the correction coefficient Δt to the basic lean time t _lb calculated at step 160. In step 162, the SO _X release / particulate removal control is executed at the lean time t ₁ calculated in step 161 (t ₁ = t _lb + Δt). On the other hand, when the SO _X storage amount ΣSOX and the particulate matter deposition amount ΣPM by SO _X release-particle removal control becomes both substantially zero, the process proceeds from step 158 and 159 to step 163, SO _X release-particulate removal flag XSPM Is reset (XSPM = 0). That is, the SO _X release / fine particle removal control ends.

It is also possible to combine the exhaust purification device of the first embodiment and the exhaust purification device of the second embodiment. Therefore, for example, the fine particle removal control is executed until the fine particle accumulation amount becomes a constant accumulation amount, and then the SO _X release / fine particle removal control is executed to adjust the lean period as shown in the second embodiment. SO _X may be released from the NO _X storage agent.

In all the embodiments described above, the case where the filter 11 carrying the NO _x storage agent and the catalyst noble metal is used as the exhaust purification means. However, the exhaust purification means is not limited to this, and for example, NO _x The present invention can also be applied to an exhaust purification means having a monolith type NO _x storage reduction catalyst carrying a storage agent and a catalyst noble metal and a particulate filter. In this case, the NO _x storage reduction catalyst and the particulate filter may be built in the same casing or may be built in separate casings.

It is a figure which shows the whole internal combustion engine which has an exhaust gas purification apparatus of this invention. It is a figure for demonstrating the form and timing of fuel injection. It is a time chart for demonstrating 1st embodiment of this invention. It is a part of flowchart of the exhaust gas purification routine in 1st embodiment. It is a part of flowchart of the exhaust gas purification routine in 1st embodiment. It is a figure for demonstrating the switching timing in 2nd embodiment. It is a time chart for demonstrating 2nd embodiment of this invention. It is a part of flowchart of the exhaust gas purification routine in 2nd embodiment. It is a part of flowchart of the exhaust gas purification routine in 2nd embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Engine main body 2 ... Combustion chamber 3 ... Fuel injection valve 11 ... Filter 13 ... Fuel addition valve 14 ... EGR passage 20 ... Temperature sensor 21 ... Differential pressure sensor 30 ... ECU

Claims (3)

An exhaust purification means having a particulate filter for collecting particulates in the exhaust gas and an NO _X storage agent is disposed on the engine exhaust passage, and the NO _X storage agent has an air-fuel ratio of the exhaust gas flowing into the exhaust purification means. In an exhaust gas purification apparatus for an internal combustion engine that releases a sulfur content stored in the NO _X storage agent when it is substantially the stoichiometric air-fuel ratio or rich and the temperature of the NO _X storage agent is equal to or higher than the sulfur content release temperature,
When the particulate accumulation amount on the particulate filter is larger than a predetermined limit accumulation amount or when the sulfur storage amount of the NO _X storage agent is larger than a predetermined limit storage amount Particulate removal control is started to maintain the temperature of the particulate filter above the particulate combustion temperature and to make the air-fuel ratio of the exhaust gas flowing into the exhaust purification means lean and to burn and remove particulates deposited on the particulate filter. After a predetermined time has elapsed from the start of the particulate removal control, the temperature of the NO _X storage agent is maintained at the sulfur content release temperature or higher, and the air-fuel ratio of the exhaust gas flowing into the exhaust gas purification means is substantially stoichiometric or rich. sulfur is repeated a plurality of times _the NO _X storage agent occluded in which the sulfur release control and the particle removal control to release sulfur into alternating Running release-particle removal control,
The predetermined time is the time taken from the start of the particulate removal control until the particulate deposition amount on the particulate filter becomes a predetermined deposition amount that is less than the limit deposition amount and greater than near zero, An exhaust gas purification apparatus for an internal combustion engine in which the remaining fine particles are removed during execution of the sulfur content release / fine particle removal control . An exhaust purification means having a particulate filter for collecting particulates in the exhaust gas and an NO _X storage agent is disposed on the engine exhaust passage, and the NO _X storage agent has an air-fuel ratio of the exhaust gas flowing into the exhaust purification means. In an exhaust gas purification apparatus for an internal combustion engine that releases a sulfur content stored in the NO _X storage agent when it is substantially the stoichiometric air-fuel ratio or rich and the temperature of the NO _X storage agent is equal to or higher than the sulfur content release temperature,
When the deposition amount of the particulate said particulate filter becomes more than the limit storage amount sulfur storage amount reaches a predetermined to advance Where the stated becomes greater than the limit deposition amount or the NO _X absorbent Maintains the temperature of the NO _X storage agent at the sulfur content release temperature or higher and controls the sulfur content release control so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification means is substantially the stoichiometric air-fuel ratio or rich, and the temperature of the particulate filter. Sulfur content release / particulate removal control is executed repeatedly maintaining a particulate combustion temperature at a temperature higher than the particulate combustion temperature and the particulate removal control to make the air-fuel ratio of the exhaust gas flowing into the exhaust purification means lean multiple times. Exhaust gas purification device for an internal combustion engine in which the cycle of repeating sulfur content release control and particulate removal control in the removal control is made shorter as the amount of particulate accumulation is smaller The exhaust purification device according to claim 1 or 2 , wherein the temperature of the exhaust gas purification means is maintained in the vicinity of the sulfur content discharge temperature during the sulfur content release / fine particle removal control.

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