JP4357917B2 - 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.

  In general, in-cylinder injection internal combustion engines such as diesel engines mounted on automobiles and the like are required to remove nitrogen oxides (NOx) contained in exhaust gas. In response to such a demand, an exhaust purification device of a system in which a NOx storage agent is arranged in an exhaust passage of an internal combustion engine has been proposed.

  The NOx storage agent used in such an exhaust purification device stores NOx when the air-fuel ratio of the exhaust gas is lean, the air-fuel ratio in the exhaust gas becomes small, and a reducing agent such as HC or CO in the exhaust gas. If NO exists, it has the action of removing and reducing the stored NOx (NOx storage and release and reduction and purification action). And using this action, when the air-fuel ratio of the exhaust gas is lean, the NOx in the exhaust gas is stored in the NOx storage agent, and when the storage efficiency of the NOx storage agent decreases after a certain period of use or before it decreases A reduction agent (fuel) is added on the upstream side of the NOx storage agent, for example, to reduce and purify NOx stored in the NOx storage agent.

In this specification, the term “occlusion” is used to include both “absorption” and “adsorption”. Therefore, the “NOx storage agent” includes both “NOx absorbent” and “NOx adsorbent”. The former accumulates NOx in the form of nitrate or the like, and the latter adsorbs in the form of NO ₂ or the like. The term “desorption” from the NOx storage agent is also used to include the meaning of “desorption” corresponding to “adsorption” in addition to “release” corresponding to “absorption”.

  By the way, the fuel of the internal combustion engine may contain a sulfur (S) component, and in this case, the exhaust gas contains sulfur oxide (SOx). When SOx is present in the exhaust gas, the NOx occlusion agent occludes SOx in the exhaust gas by exactly the same mechanism as the NOx occlusion action.

  However, SOx occluded in the NOx occlusion agent is relatively stable and generally tends to accumulate in the NOx occlusion agent. When the amount of SOx stored in the NOx storage agent increases, the NOx storage capacity of the NOx storage agent decreases and the NOx in the exhaust gas cannot be sufficiently removed, so that the NOx purification efficiency decreases, so-called sulfur poisoning Problem arises. In particular, the problem of sulfur poisoning is likely to occur in diesel engines that use light oil containing a relatively large amount of sulfur as a fuel.

  On the other hand, it is known that SOx stored in the NOx storage agent can be separated by the same mechanism as NOx. However, since SOx is occluded in the NOx occlusion agent in a relatively stable form, the SOx occluded in the NOx occlusion agent is released at a temperature at which normal NOx reduction and purification control is performed (for example, about 250 ° C. or higher). It is difficult. For this reason, in order to eliminate sulfur poisoning, the NOx storage agent is heated to a temperature higher than that during normal NOx reduction purification control, that is, the sulfur release temperature (for example, 600 ° C. or higher), and the exhaust gas flowing in It is necessary to periodically perform sulfur poisoning regeneration control that makes the air-fuel ratio substantially the stoichiometric air-fuel ratio or rich (hereinafter simply referred to as rich).

  As a specific method for such sulfur poisoning regeneration control, for example, a method of intermittently adding fuel (reducing agent) to the engine exhaust system is known (see, for example, Patent Document 1). ) According to this method, it is possible to efficiently regenerate sulfur poisoning while preventing the NOx storage agent from being overheated and thermally deteriorating.

JP 2003-166415 A Japanese Patent No. 2727906 JP 2001-173498 A

  However, when sulfur poisoning regeneration control is performed by the above method, that is, for example, a method of adding fuel (reducing agent) into the exhaust passage, there may be a problem that white smoke is discharged after the regeneration control. is there. That is, if fuel (reducing agent) is added during sulfur poisoning regeneration control, part of the added fuel (reducing agent) adheres to the inner surface of the exhaust passage (for example, the inner surface of the exhaust pipe). When the sulfur poisoning regeneration control ends and returns to the normal state (normal control), the temperature of the exhaust gas that circulates decreases. Therefore, when the sulfur poisoning regeneration control ends, the exhaust gas adheres to the inner surface of the exhaust passage. The fuel (reducing agent) may remain as it is after that. Such residual fuel (residual reducing agent) is desorbed and purified by some factor after the sulfur poisoning regeneration control (for example, the temperature of exhaust gas flowing through the exhaust passage temporarily increases due to an increase in engine load). If it is released into the atmosphere without being discharged, white smoke will be emitted.

  Here, since the NOx storage agent as described above generally has an oxidation function in the activated state, if the temperature is sufficiently high, the desorbed and flowing fuel (reducing agent) can be purified. Is possible. Therefore, the problem of white smoke generation as described above is more specifically, the temperature of the NOx storage agent (or an oxidation catalyst disposed downstream thereof, etc.) has decreased after the sulfur poisoning regeneration control. It is thought that it sometimes occurs when the residual fuel (residual reducing agent) is desorbed.

  The present invention has been made in view of the problem of white smoke generation after sulfur poisoning regeneration control as described above, and its purpose is to add fuel (reducing agent) into the exhaust passage in sulfur poisoning regeneration control. In the exhaust gas purification apparatus for an internal combustion engine in which is performed, the exhaust gas purification apparatus is configured to suppress the generation of white smoke after the sulfur poisoning regeneration control.

  According to a first aspect of the present invention, when an exhaust purification means including at least a NOx storage agent is disposed in the exhaust passage, and when the sulfur content should be released from the NOx storage agent, the exhaust purification means is disposed upstream of the exhaust purification means in the exhaust passage. In the exhaust gas purification apparatus for an internal combustion engine in which sulfur poisoning regeneration control including adding fuel or a reducing agent to the exhaust gas is performed to release sulfur from the NOx storage agent, when the sulfur poisoning regeneration control is completed or When the fuel or reducing agent addition is stopped when the fuel or reducing agent is stopped before completion, a portion of the exhaust passage from the vicinity of the fuel or reducing agent addition position to the exhaust purification means is reached. After sulfur poisoning regeneration temperature control that increases or maintains the temperature or suppresses the temperature drop of the part is performed for a predetermined time, then return to normal control. To provide an exhaust purifying apparatus that.

  When the fuel or reducing agent is added into the exhaust passage in the sulfur poisoning regeneration control, the added fuel or reducing agent is added to the exhaust passage inner surface (for example, the exhaust pipe inner surface) or the upstream end of the exhaust purification means. In some cases, it adheres to the part and remains after the sulfur poisoning regeneration control. In particular, a large amount of fuel or reducing agent may adhere and remain on the inner surface of the exhaust passage in the vicinity of the fuel or reducing agent addition position. Such residual fuel or reducing agent is desorbed due to some factors after the sulfur poisoning regeneration control and released into the atmosphere without being purified, causing white smoke emission.

  According to the first invention, when the sulfur poisoning regeneration control in which the fuel or reducing agent is added to the exhaust passage is completed or stopped before completion, the fuel or reducing agent remains. Increase or maintain the temperature of the highly probable portion, that is, the portion of the exhaust passage from the vicinity of the fuel or reducing agent addition position to the exhaust purification means, or suppress the decrease in the temperature of the portion. The temperature control after the sulfur poisoning regeneration is performed for a predetermined time. As a result, the remaining fuel or the reducing agent is reduced by, for example, promoting the evaporation of the fuel or the reducing agent adhering to the portion. Here, the portion of the exhaust passage from the vicinity of the fuel or reducing agent addition position to the exhaust purification means is, for example, from the vicinity of the fuel or reducing agent addition position to the exhaust purification means. It is the exhaust pipe part up to.

  The temperature control after the sulfur poisoning regeneration is continuously performed immediately after the sulfur poisoning regeneration control. Therefore, when the temperature control after the sulfur poisoning regeneration is performed, the temperature of the exhaust purification means is not Relatively high. Therefore, the fuel or reducing agent evaporated as described above flows into the exhaust purification means and can be purified by the oxidation function of the NOx storage agent.

  As described above, according to the first aspect, the residual fuel or the reducing agent can be reduced by performing the temperature control after the sulfur poisoning regeneration. And since it returns to normal control after implementation of the temperature control after sulfur poisoning regeneration, generation of white smoke after sulfur poisoning regeneration control can be suppressed. In particular, in the first invention, the temperature of the exhaust passage near the fuel or reducing agent addition position where a large amount of fuel or reducing agent may remain attached can be increased, maintained, or suppressed. Thus, it is possible to effectively reduce the residual fuel or reducing agent and suppress the generation of white smoke. Further, by appropriately setting the predetermined time, it is possible to efficiently and sufficiently reduce the remaining fuel or the reducing agent. Here, the normal control is, for example, the above-mentioned sulfur poisoning regeneration control, NOx reduction purification control for releasing / reducing NOx stored in the NOx storage agent, and exhaust particulate removal for removing accumulated exhaust particulates. It means the control of the exhaust gas purification device that is normally performed when no special control such as control is performed.

  In the second invention, in the first invention, in the temperature control after regeneration by sulfur poisoning, the temperature of the exhaust gas purification means is further maintained, or a decrease in the temperature of the exhaust gas purification means is suppressed.

  According to the second aspect of the invention, in the temperature control after the sulfur poisoning regeneration, the temperature of the exhaust gas purification means is maintained, or a decrease in the temperature of the exhaust gas purification means is suppressed. The fuel or the reducing agent flowing into the exhaust purification means during the post-temperature control can be reliably purified by the oxidation function of the NOx storage agent. In particular, when the temperature of the exhaust gas purification means is maintained, the fuel or the reducing agent that flows in can be more reliably purified while preventing thermal deterioration of the exhaust gas purification means. Further, when a decrease in the temperature of the exhaust gas purification means is suppressed, the temperature change of the exhaust gas purification means becomes gentle, so that, for example, the occurrence of cracks is reduced.

  In the third invention, in the first or second invention, the fuel injection in the temperature control after the sulfur poisoning regeneration control is delayed from the compression top dead center, and the pilot injection performed immediately before the main injection And after-injection performed after the main injection and in the early stage of the expansion stroke.

  By performing such fuel injection control, it is possible to increase the temperature of the exhaust gas at the time when it is discharged from the combustion chamber. As a result, the temperature of the portion of the exhaust passage from the vicinity of the fuel or reducing agent addition position to the exhaust purification means can be increased or maintained, and the temperature of the portion can be reduced. It can also be suppressed. At the same time, it is possible to maintain the temperature of the exhaust gas purification means, or to suppress a decrease in the temperature of the exhaust gas purification means. Thus, according to the third invention, the temperature control after the sulfur poisoning regeneration control can be performed by simple fuel injection control, and the same operation and effect as those of the first or second invention can be obtained. Can do. Here, the initial stage of the expansion stroke specifically means a range in which the crank angle after compression top dead center is up to 40 °.

  The invention described in each claim has a common effect of suppressing the generation of white smoke after the sulfur poisoning regeneration control.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, although this invention can be implemented even if it uses any of NOx absorbent and NOx adsorbent which are NOx occlusion agents, the case where NOx absorbent is used is demonstrated below.
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.

  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. An air flow meter 43 for detecting the intake air amount is provided between the air cleaner 8 and the compressor 7a. A throttle valve 9 driven by a step motor is arranged in the intake duct 6, and a cooling device (intercooler) 10 for cooling intake air flowing in the intake duct 6 is arranged around the intake duct 6. . In the embodiment shown in FIG. 1, the engine cooling water is guided into the intercooler 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 the casing 12 containing the NOx absorption catalyst 11. Between the outlet of the exhaust turbine 7 b and the casing 12, a reducing agent addition valve 13 for adding a reducing agent made of, for example, hydrocarbons into the exhaust passage is disposed upstream of the NOx absorption catalyst 11. In this embodiment, the fuel for the internal combustion engine is used as the reducing agent. An air-fuel ratio sensor 44 for detecting the air-fuel ratio of the exhaust gas is disposed downstream of the casing 12, that is, downstream of the NOx absorption catalyst 11.

  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. A cooling device (EGR cooler) 16 for cooling the EGR gas flowing in the EGR passage 14 is disposed around the EGR passage 14. In the present embodiment, the engine cooling water is guided into the EGR cooler 16 and the EGR gas is cooled by the engine cooling water. Furthermore, in the present embodiment, an oxidation catalyst 20 is provided upstream of the EGR cooler 16 in the EGR passage 14, and hydrocarbons and the like contained in the EGR gas are treated to a certain extent before flowing into the EGR cooler 16, so that the EGR cooler 16 is prevented and the EGR control valve 15 is stuck.

  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. Output signals from the air flow meter 43 and the air-fuel ratio sensor 44 described above are input to the input port 35 via the corresponding AD converter 37. 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, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. On the other hand, the output port 36 is connected to the fuel injection valve 3, the throttle valve 9 drive step motor, the reducing agent addition valve 13, the EGR control valve 15, the fuel pump 19, and the like via corresponding drive circuits 38.

FIG. 2A shows the relationship between the required torque TQ, the depression amount L of the accelerator pedal 40, and the engine speed N. In FIG. 2A, each curve represents an equal torque curve, a curve indicated by TQ = 0 indicates that the torque is zero, and the remaining curves are TQ = a, TQ = b, The required torque gradually increases in the order of TQ = c and TQ = d. The required torque TQ shown in FIG. 2 (A) is stored in advance in the ROM 32 in the form of a map as a function of the depression amount L of the accelerator pedal 40 and the engine speed N as shown in FIG. 2 (B). In the embodiment according to the present invention, the required torque TQ corresponding to the depression amount L of the accelerator pedal 40 and the engine speed N is first calculated from the map shown in FIG. 2B, and the fuel injection amount is based on the required torque TQ. Etc. are calculated.
The ECU 30 exchanges signals with each component of the internal combustion engine in this way to perform basic control of the engine such as fuel injection amount control, as well as sulfur poisoning regeneration control of a NOx absorbent (NOx absorption catalyst 11), which will be described later. Various controls are performed.

  The NOx absorption catalyst 11 shown in FIG. 1 is a honeycomb-shaped monolith carrier carrying a NOx absorbent, and constitutes an exhaust purification means in this embodiment. This NOx absorbent is at least selected from alkali metals such as potassium K, sodium Na, lithium Li and cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y. One and a noble metal such as platinum Pt. The NOx absorbent absorbs NOx when the air-fuel ratio of the flowing exhaust gas is lean, reduces the air-fuel ratio of the flowing exhaust gas, and if the reducing agent is present, releases the absorbed NOx to reduce and purify. It has an action (NOx absorption / release and reduction / purification action).

  In the compression ignition type internal combustion engine as shown in FIG. 1, the exhaust gas air-fuel ratio during normal operation is lean, and the NOx absorbent absorbs NOx in the exhaust gas. Further, when the air-fuel ratio of the exhaust gas flowing through the addition of the reducing agent is reduced and the reducing agent is present, the NOx absorbent releases the absorbed NOx and reduces and purifies the released NOx.

  In the present embodiment, by utilizing such NOx absorption / release and reduction and purification action of the NOx absorbent, NOx in the exhaust gas is converted into NOx absorbent (NOx absorbent catalyst 11) when the air-fuel ratio of the exhaust gas is lean. When it is determined that it is necessary to release and reduce the absorbed NOx, such as when the NOx purification rate decreases after a certain period of use, the reducing agent is added from the reducing agent addition valve 13 to the NOx absorbent. NOx reduction and purification control is performed to release the absorbed NOx and reduce and purify it.

Next, with reference to FIG. 3, the mechanism of the absorption and release and reduction and purification action will be briefly described by taking as an example the case of carrying platinum Pt and barium Ba. That is, when the air-fuel ratio of the exhaust gas flowing becomes considerably lean, the oxygen concentration in the exhaust gas increases greatly, and these oxygen O ₂ forms O ₂ ⁻ or O ²⁻ as shown in FIG. It adheres to the surface of platinum Pt. On the other hand, NO in the exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of platinum Pt to become NO ₂ . Then part of the produced NO ₂ while bonding with the barium oxide BaO is absorbed while being further oxidized on the platinum Pt in the NOx absorbent, FIG nitrate as shown in (A) ions NO ₃ ^- in Diffuses in the form of NOx absorbent. In this way, NOx is absorbed into the NOx absorbent.

On the other hand, when the oxygen concentration in the exhaust gas decreases and the amount of NO ₂ produced decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), so that the nitrate ions NO ₃ ⁻ in the NOx absorbent are NO. Released from the NOx absorbent in the form of ₂ . That is, when the oxygen concentration in the exhaust gas decreases, NOx is released from the NOx absorbent. If the degree of exhaust gas lean decreases, the oxygen concentration in the exhaust gas decreases. Therefore, if the degree of exhaust gas lean decreases, NOx is released from the NOx absorbent.

Further, if the air-fuel ratio of the exhaust gas is reduced, the oxygen concentration in the exhaust gas is extremely reduced, so that NO ₂ is released from the NOx absorbent. In this case, the released NO ₂ is shown in FIG. As shown in B), it is reduced and purified by reacting with unburned HC and CO. When NO ₂ no longer exists on the surface of platinum Pt in this way, NO ₂ is released from the NOx absorbent to the next. Accordingly, when the air-fuel ratio of the exhaust gas flowing through the NOx absorbent is reduced and the reducing agent is present, NOx is released from the NOx absorbent and reduced and purified in a short time.
The air-fuel ratio of the exhaust gas here refers to the ratio of the air and fuel supplied to the exhaust passage upstream of the NOx absorbent (NOx absorption catalyst 11) and the combustion chamber 2 or the intake passage.

Next, the mechanism of sulfur poisoning of the NOx absorbent will be described. When the SOx component is contained in the exhaust gas, the NOx absorbent absorbs SOx in the exhaust gas by the same mechanism as the above NOx absorption. That is, when the air-fuel ratio of the exhaust gas is lean, SOx (for example, SO ₂ ) in the exhaust gas is oxidized on platinum Pt to become SO ₃ ⁻ , SO ₄ ⁻ and combines with barium oxide BaO to form BaSO ₄ . To do. BaSO ₄ is relatively stable, and since crystals are likely to be coarse, once they are produced, they are not easily decomposed and released. For this reason, when the amount of BaSO ₄ produced in the NOx absorbent increases, the amount of BaO that can participate in NOx absorption decreases, and the NOx absorption capacity decreases.

In order to eliminate this sulfur poisoning, BaSO ₄ generated in the NOx absorbent is decomposed at a high temperature, and SO ₃ ⁻ and SO ₄ ⁻ sulfate ions generated thereby are almost theoretically including light lean. It is necessary to perform reduction under an air-fuel ratio or a rich atmosphere (hereinafter simply referred to as “rich atmosphere”), convert it into gaseous SO ₂ , and release it from the NOx absorbent. That is, in order to perform sulfur poisoning regeneration, it is necessary to carry out sulfur poisoning regeneration control that brings the NOx absorbent into a high temperature and rich atmosphere.

  As a specific method for such sulfur poisoning regeneration control, a rich atmosphere is created by adding a reducing agent (fuel) upstream of the NOx absorbent (NOx purification catalyst 11). Various methods are known, but according to such a method, white smoke may be emitted after the sulfur poisoning regeneration control.

  That is, when the reducing agent (fuel) is added during the sulfur poisoning regeneration control, a part of the added reducing agent (fuel) adheres to the inner surface of the exhaust passage (for example, the inner surface of the exhaust pipe). These attached reducing agents (attached fuel) are gradually vaporized because the temperature of the exhaust gas that circulates is relatively high during the sulfur poisoning regeneration control, but the sulfur poisoning regeneration control ends. When the normal state (normal control) is restored, the temperature of the exhaust gas that circulates decreases. Therefore, when the sulfur poisoning regeneration control ends, the reducing agent (fuel) adhering to the inner surface of the exhaust passage remains unchanged. May remain in the state. Such residual reducing agent (residual fuel) is desorbed and purified by some factor after the sulfur poisoning regeneration control (for example, the temperature of exhaust gas flowing through the exhaust passage temporarily increases due to an increase in engine load). If it is released into the atmosphere without being discharged, white smoke will be emitted.

  Here, since the NOx absorbent as described above generally has an oxidizing function in an activated state, it is necessary to purify the reducing agent (fuel) that is desorbed and flows in if the temperature is sufficiently high. Is possible. Therefore, more specifically, the problem of the generation of white smoke as described above is that the residual reducing agent (residual fuel) is desorbed when the temperature of the NOx absorbent decreases after the execution of sulfur poisoning regeneration control. This is considered to occur if

  The present embodiment is intended to suppress the generation of such white smoke. Next, a specific method implemented by the configuration shown in FIG. 1 for realizing this will be described. FIG. 4 is a flowchart showing a control routine for carrying out this method. This control routine is executed by the ECU 30 by interruption every predetermined time.

  When this control routine is started, first, at step 101, it is determined whether or not the execution condition for the sulfur poisoning regeneration control of the NOx absorbent (NOx absorbent catalyst 11) is satisfied. The sulfur poisoning regeneration control execution condition includes an execution requirement condition and an executable condition in detail. When both conditions are satisfied, it is determined that the sulfur poisoning regeneration control execution condition is satisfied. The implementation requirement is, for example, that the amount of SOx absorbed in the NOx absorbent, that is, the amount of absorbed SOx becomes a certain amount or more. However, in this case, it is difficult to directly determine the amount of absorbed SOx. The amount of absorbed SOx is estimated based on the amount of SOx discharged from the engine, that is, for example, the integrated value (fuel consumption) of the fuel injection amount. That is, when the integrated value of the fuel injection amount from the time when the previous sulfur poisoning regeneration control was performed becomes larger than a predetermined set value, it is determined that the above-described implementation requirement is satisfied. Alternatively, based on the same idea, the determination may be made based on the vehicle travel distance instead of the integrated value of the fuel injection amount.

  On the other hand, it is determined whether or not the above feasible condition is satisfied based on the operating state of the engine at that time, that is, the load state of the engine. This is because, as will be described later, in this embodiment, the sulfur poisoning regeneration control cannot be performed unless the operating state of the engine is within a certain range (that is, within a relatively low range of the engine load). For this reason, for example, a map as shown in FIG. 5 showing the feasible region and infeasible region of the sulfur poisoning regeneration control based on the required torque TQ and the engine speed N is created in advance, and the required torque TQ at that time On the basis of the engine speed N, it is determined whether or not the engine operating state at that time is within the sulfur poisoning regeneration control feasible region, thereby judging whether or not the feasible condition is satisfied. In FIG. 5, the region below the boundary line L1, that is, the region X and the region Y represent the feasible region for sulfur poisoning regeneration control (the difference between the region X and the region Y will be described later). The area above the boundary line L1, that is, the area Z represents an inoperable area. Therefore, if the point on the map of FIG. 5 represented by the required torque TQ and the engine speed N at that time is within the region X or the region Y, it is determined that the enablement condition is satisfied, If it is within the region Z, it is determined that the enablement condition is not satisfied.

  If it is determined in step 101 that the sulfur poisoning regeneration control execution condition is not satisfied, the present control routine is ended. If it is determined that the sulfur poisoning regeneration control execution condition is satisfied, step 103 is performed. Proceed to In step 103, sulfur poisoning regeneration control is performed.

  In the present embodiment, the sulfur poisoning regeneration control is a temperature rise control for raising the temperature of the NOx absorbent (NOx absorption catalyst 11) to a temperature at which the sulfur content can be released (a sulfur content release temperature (for example, 600 ° C. or higher)). And a sulfur content release control for releasing the sulfur content in a rich atmosphere state while maintaining the temperature of the NOx absorbent (NOx absorption catalyst 11).

When the sulfur poisoning regeneration control is started in step 103, first, the temperature rise control is performed. In the present embodiment, this temperature increase control is performed by controlling the fuel injection pattern as described below.
That is, FIG. 6 is a schematic diagram showing four examples of fuel injection patterns that can be implemented in the internal combustion engine shown in FIG. 1, but during normal control of the exhaust emission control device of this embodiment (that is, normal engine operation). During operation, the injection pattern shown in (I) or (II) of FIG. 6 is set according to the operating state of the engine. That is, in the injection pattern shown in FIG. 6 (I), only the main fuel injection (main injection) Qm is performed near the compression top dead center, and in the injection pattern shown in (II), the main fuel near the compression top dead center. In addition to the injection Qm, the pilot injection Qp is performed immediately before that. On the other hand, when the sulfur poisoning regeneration control is started in step 103 and it is necessary to raise the temperature of the NOx absorbent, the fuel injection pattern as shown in FIG. Is done. That is, the injection timing of the main injection Qm is retarded until after the compression top dead center, and accordingly, the injection timing of the pilot injection Qp is also retarded, and further, the after injection Qa is made early in the expansion stroke after the main injection Qm. To do. Here, the injection timing of the after injection Qa is generally in a range where the crank angle after compression top dead center is up to 40 °, and more preferably, the crank angle after compression top dead center is in the range of 20 ° to 30 °. .

With such a fuel injection pattern, the temperature of the exhaust gas can be raised by increasing the post-burn period, increasing the total amount of fuel injected, or the like. In particular, in this case, since the injection timing of after injection is early, most of the injected fuel burns in the combustion chamber, so that the temperature of the exhaust gas at the time of being discharged from the combustion chamber can be raised. And by raising the exhaust gas temperature in this way, the temperature of the NOx absorbent can be raised.
In this embodiment, the EGR control valve 15 is controlled and exhaust gas recirculation (EGR) is performed during normal control (that is, during normal operation of the engine). However, during the temperature increase control, the EGR control valve 15 is controlled. Is closed and exhaust gas recirculation is not performed. This is for increasing the amount of air and promoting the temperature rise of the exhaust gas.

  If it is determined that the temperature of the NOx absorbent has risen and the temperature has risen sufficiently to release the sulfur content, then the sulfur content release control is performed. Note that whether or not the temperature rise of the NOx absorbent is sufficient is determined based on, for example, the duration of the temperature rise control. That is, it is determined that the temperature of the NOx absorbent has been sufficiently raised when the execution duration time of the temperature increase control is equal to or longer than a predetermined time. Alternatively, a temperature sensor for detecting the temperature of the NOx absorbent (NOx absorption catalyst 11) may be provided, and the determination may be made based on the detected temperature.

  In the present embodiment, the sulfur content release control is performed by setting the combustion of the engine to so-called low temperature combustion or high EGR combustion and adding a reducing agent into the exhaust passage by the reducing agent addition valve 13. Note that whether low-temperature combustion or high-EGR combustion is used is determined based on the engine operating state at that time, as will be described later.

  Here, the low temperature combustion and the high EGR combustion will be briefly described. In the compression ignition type internal combustion engine as shown in FIG. 1, when the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) is increased with the fuel injection timing fixed, the amount of smoke generated gradually increases. If it increases and reaches a peak and the EGR rate is further increased, the amount of smoke generated decreases rapidly. This is because when the EGR rate is high, the temperature of the fuel and the surrounding gas during combustion is not so high due to the endothermic action of the EGR gas, and as a result, hydrocarbons do not grow to soot. Low-temperature combustion utilizes such a phenomenon, and is combustion with a small amount of smoke generated by making the EGR rate larger than a value at which the amount of smoke generated reaches a peak. On the other hand, high EGR combustion is combustion performed by setting the EGR rate relatively high in a range smaller than the value at which the amount of smoke generated reaches a peak. Since all of these combustions have a high EGR rate, the exhaust gas temperature tends to be higher than that of normal combustion (that is, combustion performed during normal operation of the engine), and the temperature of the NOx absorbent is kept high. Preferred above. Further, since the EGR rate is high, the air-fuel ratio can be lowered as compared with the normal combustion. Specifically, for example, the air-fuel ratio at low temperature combustion can be 18 to 20, and the air-fuel ratio at high EGR combustion can be 22 to 25. And since an air fuel ratio can be made low in this way, in order to create a rich atmosphere, the quantity of the reducing agent added from the reducing agent addition valve 13 can be reduced.

  On the other hand, when the required torque TQ increases, that is, when the fuel injection amount increases, the low temperature combustion becomes difficult to implement because the temperature of the fuel and the surrounding gas during combustion increase. That is, low-temperature combustion can be performed only when the amount of heat generated by combustion is small and the engine load is low. Further, since it is necessary to lower the EGR rate during high load operation, high EGR combustion can be performed only when the engine load is relatively low. For this reason, as described above, in this embodiment, the sulfur poisoning regeneration control cannot be performed unless the operating state of the engine is within a certain range (that is, within a relatively low range of the engine load).

  As described above, FIG. 5 is a map showing the feasible region (X, Y) and the impracticable region (Z) of the sulfur poisoning regeneration control based on the required torque TQ and the engine speed N. In the sulfur content release control, a region (X) where low temperature combustion is performed and a region (Y) where high EGR combustion is performed are shown. That is, in FIG. 5, the boundary line L1 represents the boundary between the feasible region and the impracticable region, and the boundary line L2 represents the region (X) where low temperature combustion is performed and the region (Y) where high EGR combustion is performed in the sulfur content release control. ). Here, it can be considered that the boundary line L1 represents the feasible limit of high EGR combustion, and the boundary line L2 represents the feasible limit of low temperature combustion. In the present embodiment, whether to perform low temperature combustion or high EGR combustion in the sulfur content release control is determined based on the map of FIG. That is, when performing sulfur content release control, if the point on the map of FIG. 5 represented by the required torque TQ and the engine speed N at that time is within the region X, low temperature combustion is performed, and the region If it is within Y, high EGR combustion is performed.

  In addition, you may make it provide a hysteresis with respect to the change of the driving | running | working area | region between the area | region X and the area | region Y. FIG. That is, a boundary line when the engine operating state moves from the region X to the region Y and a boundary line when the engine operation state moves from the region Y to the region X are provided separately so that the former boundary line is on the high load side. . If it does in this way, when operation is performed in the boundary part of two fields, it can control that combustion changes frequently. Similarly, hysteresis may be provided for changes in the operation region between the region Y and the region Z.

  Further, when low-temperature combustion is performed in the present embodiment, the fuel injection pattern is controlled to be as shown in (IV) of FIG. That is, the main injection Qm is advanced. On the other hand, when high EGR combustion is performed, the fuel injection pattern is controlled to be as shown in FIG.

The addition of the reducing agent into the exhaust passage by the reducing agent addition valve 13 is performed so that the air-fuel ratio of the exhaust gas flowing into the NOx absorption catalyst 11 becomes intermittently or continuously rich. At this time, the reducing agent addition valve 13 and the throttle valve 9 are feedback controlled based on the output from the air-fuel ratio sensor 44. This control is the same when low temperature combustion is performed and when high EGR combustion is performed.
Then, the NOx absorbent is brought to a high temperature and rich atmosphere by the control as described above, and the sulfur content is released from the NOx absorbent.

  When the sulfur content release control is started in step 103, the routine proceeds to step 105, where it is determined whether or not the sulfur poisoning regeneration control end condition is satisfied. More specifically, the sulfur poisoning regeneration control termination condition includes a completion condition when the sulfur poisoning regeneration is completed and a termination condition when the sulfur poisoning regeneration is terminated before the sulfur poisoning regeneration is completed. And are included. If any one of the conditions is satisfied, it is determined that the sulfur poisoning regeneration control end condition is satisfied.

  The completion condition is, for example, that the amount of SOx remaining in the NOx absorbent becomes zero. However, since it is difficult to directly determine the amount of residual SOx, for example, in the sulfur content release control, a rich atmosphere is obtained. The remaining SOx amount is estimated based on the accumulated value of the remaining time. Then, when the remaining SOx amount becomes zero, it is determined that the completion condition is satisfied. The amount of residual SOx is determined in advance from the relationship between the temperature of the NOx absorbent (NOx absorbent catalyst 11) and the SOx release rate, and the rich atmosphere at each temperature and temperature of the NOx absorbent (NOx absorbent catalyst 11). It may be estimated based on the time when In this case, the temperature of the NOx absorbent (NOx absorbent catalyst 11) is obtained by providing a temperature sensor in the vicinity of the NOx absorbent catalyst 11 or the like.

  On the other hand, examples of the stop condition include a case where the engine operating state deviates from the above-described sulfur poisoning regeneration control executable region. In this case, it may be determined that the cancellation condition is satisfied when the engine operation state deviates from the sulfur poisoning regeneration control executable region and a predetermined time has passed. That is, for example, when the engine operating state deviates from the sulfur poisoning regeneration control feasible region, the NOx is controlled by controlling fuel injection, reducing agent addition, etc. as a part of the sulfur poisoning regeneration control for a predetermined time thereafter. Control is performed to maintain the temperature of the absorption catalyst 11 at or above the sulfur content release temperature. If this is done, the sulfur content is not released during the temperature maintenance control because the rich atmosphere is not created. However, when the engine operation state again enters the sulfur poisoning regeneration control executable region, the sulfur content is immediately released. The minute release can be resumed.

  If it is determined in step 105 that the sulfur poisoning regeneration control termination condition is not satisfied, the process returns to step 103 and the sulfur content release control is continued. On the other hand, when it is determined that the sulfur poisoning regeneration control termination condition is satisfied, the routine proceeds to step 107 where the sulfur content release control is terminated (that is, the reducing agent into the exhaust passage by the reducing agent addition valve 13). And the like proceeds to step 109.

  In step 109, the temperature of the portion of the exhaust passage from the vicinity of the reducing agent addition valve 13 to the NOx absorption catalyst 11 is increased or maintained, or the decrease in the temperature of the portion is suppressed. Temperature control is performed after sulfur poisoning regeneration. This control is performed in order to evaporate and purify the reducing agent that remains on the exhaust passage inner surface (for example, the exhaust pipe inner surface) and the like when the sulfur content release control is performed in Step 103. .

  In the present embodiment, the temperature control after the sulfur poisoning regeneration is performed by controlling the fuel injection pattern as shown in (III) of FIG. That is, as described in relation to the temperature rise control in step 103, the injection timing of the main injection Qm is retarded until after the compression top dead center, and accordingly, the injection timing of the pilot injection Qp is also retarded. After injection Qa is performed at the beginning of the expansion stroke after the main injection Qm. Here, the injection timing of the after injection Qa is generally in a range where the crank angle after compression top dead center is up to 40 °, and more preferably, the crank angle after compression top dead center is in the range of 20 ° to 30 °. .

  As described above, with such a fuel injection pattern, the temperature of the exhaust gas at the time of being discharged from the combustion chamber can be increased as compared with that during normal control (that is, during normal operation of the engine). As a result, the temperature of the portion of the exhaust passage from the vicinity of the reducing agent addition valve 13 to the NOx absorption catalyst 11 can be increased or maintained, or the decrease in the temperature of the portion can be suppressed. be able to. Note that the temperature rise, maintenance, and reduction suppression can be controlled by adjusting the retard amount of the main injection Qm, the injection timing and the injection amount of the after injection Qa, and the like. Further, the amount of the reducing agent attached may be estimated from the duration of the sulfur content release control or the like, and it may be determined whether to increase, maintain, or suppress the decrease depending on the amount attached. Further, a temperature sensor may be provided in the exhaust passage portion, and the retard amount of the main injection Qm, the injection timing and the injection amount of the after injection Qa, etc. may be adjusted based on the detected temperature.

  As described above, the temperature of the portion of the exhaust passage from the vicinity of the reducing agent addition valve 13 to the NOx absorption catalyst 11 is increased or maintained, or the decrease in the temperature of the portion is suppressed. Thus, evaporation of the reducing agent adhering to the part is promoted, and the remaining reducing agent can be reduced. Further, since the temperature control after the sulfur poisoning regeneration is continuously performed immediately after the sulfur poisoning regeneration control, the NOx absorbent (NOx absorption catalyst) is used when the temperature control after the sulfur poisoning regeneration is performed. The temperature of 11) is still relatively high, so that the reducing agent evaporated as described above flows into the NOx absorption catalyst 11 and can be purified by the oxidation function of the NOx absorbent.

  Further, as described above, by controlling the fuel injection pattern to raise the temperature of the exhaust gas, the portion from the vicinity of the reducing agent addition valve 13 to the NOx absorption catalyst 11 in the exhaust passage is described above. In addition to performing such temperature control, it is also possible to maintain the temperature of the NOx absorbent (NOx absorption catalyst 11) or to suppress the temperature drop. The maintenance and suppression of the temperature can also be controlled by adjusting the retard amount of the main injection Qm, the injection timing and the injection amount of the after injection Qa, and the like. Further, a temperature sensor may be provided at or near the NOx absorption catalyst 11, and the retard amount of the main injection Qm, the injection timing and the injection amount of the after injection Qa, etc. may be adjusted based on the detected temperature.

By maintaining or suppressing the temperature of the NOx absorbent (NOx absorbent catalyst 11), the reducing agent flowing into the NOx absorbent catalyst 11 during the temperature control after the sulfur poisoning regeneration is reduced. It can be reliably purified by the oxidation function. In particular, when the temperature of the NOx absorption catalyst 11 is maintained, the reducing agent flowing in can be more reliably purified while preventing thermal degradation of the NOx absorbent. Further, when a decrease in the temperature of the NOx absorption catalyst 11 is suppressed, the temperature change of the NOx absorption catalyst 11 becomes gentle, so that, for example, the occurrence of cracks is reduced. Note that, by maintaining or suppressing the temperature of the NOx absorbent (NOx absorbent catalyst 11), the reducing agent remaining on the NOx absorbent catalyst 11 can be removed.
In the present embodiment, the EGR control valve 15 is closed and the exhaust gas recirculation is not performed during the temperature control after the sulfur poisoning regeneration. Naturally, the addition of the reducing agent into the exhaust passage by the reducing agent addition valve 13 is stopped during the temperature control after the sulfur poisoning regeneration.

  When the temperature control after sulfur poisoning regeneration is started in step 109, the routine proceeds to step 111, where it is determined whether or not the temperature control end condition after sulfur poisoning regeneration is satisfied. The temperature control end condition after the sulfur poisoning regeneration is, for example, that the execution time of the control reaches a predetermined time. The time used as the determination criterion is determined by previously obtaining a sufficient time for removing the remaining fuel by experiments or the like, and may be, for example, 3 minutes. Or you may make it determine according to the implementation time (continuation time) of sulfur content discharge | release control before performing temperature control after the sulfur poisoning reproduction | regeneration, and sulfur poisoning reproduction | regeneration control completion conditions. By appropriately setting the time for performing the temperature control after the sulfur poisoning regeneration, the remaining reducing agent can be efficiently and sufficiently removed.

  When it is determined in step 111 that the temperature control end condition after sulfur poisoning regeneration is not satisfied, the process returns to step 109 and the temperature control after sulfur poisoning regeneration is continued. On the other hand, if it is determined that the temperature control termination condition after sulfur poisoning regeneration is satisfied, the routine proceeds to step 113 where the temperature control after sulfur poisoning regeneration is terminated, and then the normal control is returned to at step 115. The control routine ends.

  As described above, in this embodiment, when the sulfur poisoning regeneration control is completed or stopped before completion, the temperature control after sulfur poisoning regeneration as described above is performed. Thereby, since the reducing agent remaining in the exhaust passage is removed, the generation of white smoke after the sulfur poisoning regeneration control can be suppressed as a result.

  FIG. 7 schematically shows changes over time in the temperature Tc, the exhaust gas temperature Te, the remaining or attached reducing agent amount RQ of the NOx absorption catalyst 11 for an example when the control routine shown in the flowchart of FIG. 4 is executed. It is. In the figure, Ts represents a sulfur content release temperature, and Tv represents a temperature (activation temperature) at which the NOx absorbent can sufficiently exhibit an oxidation function.

  In this example, normal control is performed at time t0, and sulfur poisoning regeneration control is started at time t1. During the period from the time t1 to the time t2, the temperature increase control in the sulfur poisoning regeneration control is performed. As a result, the exhaust gas temperature Te rises, and the temperature Tc of the NOx absorption catalyst 11 is also raised above the sulfur content release temperature Ts. On the other hand, the remaining or adhesion reducing agent amount RQ remains substantially zero until time t2. At time t2, sulfur content release control in the sulfur poisoning regeneration control is started.

When the sulfur content release control is started, the exhaust gas temperature Te slightly decreases, but the temperature Tc of the NOx absorption catalyst 11 is maintained at the sulfur content release temperature Ts or higher. On the other hand, the remaining or attached reducing agent amount RQ gradually increases when the sulfur content release control is started.
At time t3, sulfur poisoning regeneration control is terminated, and temperature control after sulfur poisoning regeneration is started. The temperature control after sulfur poisoning regeneration is carried out until time t4, and then returns to the normal control. Note that, after time t3, the dotted lines indicate the temperature Tc of the NOx absorption catalyst 11 and the exhaust gas temperature Te when normal control is started immediately without performing temperature control after sulfur poisoning regeneration at time t3. This is a change with time in the amount RQ of the remaining or attached reducing agent.

  In this example, when the temperature control after sulfur poisoning regeneration is started, the exhaust gas temperature Te slightly increases. Therefore, in this example, it is considered that the temperature of the portion from the vicinity of the reducing agent addition valve 13 to the NOx absorption catalyst 11 in the exhaust passage is slightly increased by the temperature control after sulfur poisoning regeneration. On the other hand, the temperature Tc of the NOx absorption catalyst 11 is gradually lowered when the temperature control after the sulfur poisoning regeneration is started. That is, as apparent from the comparison with the case where the temperature control after the sulfur poisoning regeneration is not performed, which is indicated by the dotted line, in this example, the temperature control after the sulfur poisoning regeneration is suppressed from decreasing the temperature Tc of the NOx absorption catalyst 11. Has been. As a result, the time during which the temperature Tc of the NOx absorption catalyst 11 is equal to or higher than the activation temperature Tv is extended, so that the reducing agent flowing into the NOx absorption catalyst 11 is reliably purified during the temperature control after sulfur poisoning regeneration. It has become.

  The remaining or attached reducing agent amount RQ starts to decrease with the start of the temperature control after sulfur poisoning regeneration at time t3, and is substantially zero at the time t4 when the temperature control after sulfur poisoning regeneration ends. On the other hand, when the temperature control is not performed after the sulfur poisoning regeneration, the residual or attached reducing agent amount RQ is only slightly decreased when returning to the normal control at the time t3, and a large amount of reducing agent remains thereafter. It remains. If such residual reducing agent is desorbed for some reason during normal control (that is, during normal operation of the engine) where the temperature Tc of the NOx absorption catalyst 11 is lower than the activation temperature Tv, it is released into the atmosphere without being purified. As a result, white smoke is formed. That is, by removing the remaining reducing agent by the temperature control after sulfur poisoning regeneration, it is possible to suppress the generation of white smoke after the sulfur poisoning regeneration control as a result.

  Next, another embodiment of the present invention will be described with reference to FIG. The configuration shown in FIG. 8 is basically the same as the configuration shown in FIG. 1, and the description of the parts common to the configuration shown in FIG. 1 is omitted. In FIG. 8, the same reference numerals are assigned to the same or similar components as those in FIG.

  Referring to FIG. 8, in the present embodiment, an intake air temperature sensor 45 and an intake pressure sensor 46 for detecting the temperature and pressure of intake air flowing in the intake duct 6 are provided on the downstream side of the intercooler 10. An air-fuel ratio sensor 47 for detecting the air-fuel ratio of the exhaust gas flowing in the exhaust passage is provided between the outlet of the exhaust turbine 7 b and the reducing agent addition valve 13. Further, in the present embodiment, a NOx absorption catalyst 11, a NOx absorbent-carrying filter (hereinafter referred to as “NOx absorption filter”) 52, and an oxidation catalyst 53 are built in the casing 12 from the upstream side, and these serve as exhaust purification means. It is composed. Between the NOx absorption catalyst 11 and the NOx absorption filter 52 in the casing 12, a temperature sensor 49 is further provided for detecting the temperature of the exhaust gas purification means.

  An exhaust throttle valve 48 that can be used for an exhaust brake or the like is further provided between the outlet of the exhaust turbine 7 b and the casing 12. In the configuration shown in FIG. 8, the exhaust throttle valve 48 is disposed on the downstream side of the reducing agent addition valve 13. However, the exhaust throttle valve 48 is disposed anywhere between the outlet of the exhaust turbine 7 b and the casing 12. May be.

Further, a differential pressure sensor 51 for detecting a differential pressure upstream and downstream of the casing 12, that is, upstream and downstream of the exhaust gas purification means is also provided. This differential pressure sensor 51 can detect a pressure loss in the exhaust purification means. Further, a temperature sensor 50 for detecting the temperature of the exhaust gas flowing out from the exhaust purification means is provided downstream of the casing 12.
The output signal of each sensor is input to the input port 35 via the corresponding AD converter 37. The exhaust throttle valve 48 is connected to the output port 36 via a corresponding drive circuit 38.

  FIGS. 9A and 9B show the structure of the NOx absorption filter 52. 9A shows a front view of the NOx absorption filter 52, and FIG. 9B shows a side sectional view of the NOx absorption filter 52. As shown in FIGS. 9A and 9B, the NOx absorption filter 52 has a honeycomb structure and includes a plurality of exhaust flow passages 60 and 61 extending in parallel with each other. These exhaust flow passages include an exhaust gas inflow passage 60 whose downstream end is closed by a plug 62 and an exhaust gas outflow passage 61 whose upstream end is closed by a plug 63. In addition, the hatched part in FIG. Therefore, the exhaust gas inflow passages 60 and the exhaust gas outflow passages 61 are alternately arranged via the thin partition walls 64. In other words, in the exhaust gas inflow passage 60 and the exhaust gas outflow passage 61, each exhaust gas inflow passage 60 is surrounded by four exhaust gas outflow passages 61, and each exhaust gas outflow passage 61 is surrounded by four exhaust gas inflow passages 60. Are arranged as follows.

  The NOx absorption filter 52 is made of, for example, a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 60 is contained in the surrounding partition wall 64 as indicated by an arrow in FIG. 9B. Through the exhaust gas outflow passage 61 adjacent thereto. At this time, the exhaust particulates contained in the exhaust gas are collected by the porous material and removed from the exhaust gas, thereby preventing the exhaust particulates from being released into the atmosphere. In addition, a NOx absorbent is carried on the surface of the partition wall 64 and in the internal pores, and the NOx absorption / release and reduction / purification actions as described above are also exhibited.

  As is apparent from the above description and FIG. 8, the NOx absorbent is included in the exhaust purification unit also in this embodiment. As described above, since the NOx absorbent receives sulfur poisoning, it is necessary to perform sulfur poisoning regeneration control. Therefore, in this embodiment as well, the sulfur poisoning regeneration control is performed by a method involving the addition of a reducing agent in the exhaust passage and the subsequent generation of white smoke is performed in substantially the same manner as described with reference to FIG. It is suppressed.

  In the present embodiment, the exhaust purification unit includes a filter. The exhaust particulates collected by the NOx absorption filter 52 are normally burned and removed continuously. However, when the amount of exhaust particulates is extremely large, the exhaust particulates are not completely removed and accumulate in layers on the filter. May end up. In such a case, it is necessary to perform exhaust particulate removal control (hereinafter referred to as “PM removal control”) in which the exhaust particulate deposited by raising the temperature of the NOx absorption filter 52 is forcibly burned and removed.

Based on the above, control executed in the configuration shown in FIG. 8 will be described next. Note that this control includes portions common to the control described with reference to FIG. 4, and description of these portions will be omitted in principle.
FIG. 10 is a flowchart showing a control routine of this control. This control routine is executed by the ECU 30 by interruption every predetermined time.

  When this control routine starts, it is first determined in step 201 whether or not the PM removal control execution condition is satisfied. The PM removal control execution condition is, for example, that the exhaust particulate accumulation amount of the NOx absorption filter 52 becomes a certain amount or more, but in this case, it is difficult to directly obtain the exhaust particulate accumulation amount. Based on the pressure loss in the exhaust gas purification means detected by 51, the exhaust particulate accumulation amount is estimated. That is, it is determined that the PM removal control execution condition is satisfied when the pressure loss in the exhaust gas purification unit detected by the differential pressure sensor 51 becomes larger than a predetermined set value.

  If it is determined in step 201 that the PM removal control execution condition is satisfied, the process proceeds to step 203, where PM removal control is performed. When PM removal control is started in the present embodiment, the fuel injection pattern is first set to a fuel injection pattern as shown in FIG. That is, the injection timing of the main injection Qm is retarded until after the compression top dead center, and accordingly, the injection timing of the pilot injection Qp is also retarded, and further, the after injection Qa is made early in the expansion stroke after the main injection Qm. To do. By adopting such a fuel injection pattern, the exhaust gas temperature is raised, and thereby the exhaust purification means is heated.

  If it is determined that the exhaust purification means has risen sufficiently to burn and remove the accumulated exhaust particulates, then the fuel injection pattern is the after injection Qa in the fuel injection pattern shown in FIG. 6 (III). After that, a fuel injection pattern (not shown) is obtained by further adding auxiliary fuel injection (post injection). The post-injection injection timing and injection amount are feedback-controlled based on the temperature detected by the temperature sensor 49 so that the exhaust purification means does not overheat. By performing such control, the temperature of the exhaust gas purification means is maintained, and the exhausted exhaust particulates are removed by combustion.

  When the temperature maintenance of the exhaust gas purification means and the combustion removal of the exhaust particulates are started in step 203 as described above, the routine proceeds to step 205, where it is determined whether the PM removal control end condition is satisfied. The PM removal control end condition is, for example, that the amount of exhaust particulate accumulated in the NOx absorption filter 52 becomes zero, but it is difficult to directly determine the amount of particulate exhaust accumulated as described above. As in the case of the PM removal control execution condition, the exhaust particulate accumulation amount is estimated based on the pressure loss in the exhaust purification means detected by the differential pressure sensor 51. That is, it is determined that the PM removal control end condition is satisfied when the pressure loss in the exhaust gas purification unit detected by the differential pressure sensor 51 becomes smaller than a predetermined set value.

  If it is determined in step 205 that the PM removal control end condition is not satisfied, the process returns to step 203, and the temperature maintenance of the exhaust purification means and the combustion removal of the exhaust particulates are continued. On the other hand, if it is determined that the PM removal control termination condition is satisfied, the routine proceeds to step 207 where PM removal control is terminated, and the routine proceeds to the subsequent step 209.

  In this embodiment, the EGR control valve 15 is controlled and exhaust gas recirculation is performed during normal control (that is, during normal operation of the engine), but the EGR control valve 15 is closed during the PM removal control. There is no exhaust gas recirculation. In addition, when the PM removal control is performed when the engine is in an idling state, the exhaust throttle valve 48 is controlled to the closed side to increase the engine load and promote the increase in the exhaust gas temperature. It may be.

  On the other hand, if it is determined in step 201 that the PM removal control execution condition is not satisfied, the process proceeds to step 211. In step 211, it is determined whether or not the necessary conditions for performing sulfur poisoning regeneration control are satisfied. This implementation requirement is the same as the implementation requirement described in connection with step 101 in FIG. 4. For example, it is estimated that the amount of absorbed SOx is equal to or greater than a predetermined amount.

  If it is determined in step 211 that the required execution condition is not satisfied, the present control routine ends. If it is determined that the required execution condition is satisfied, the process proceeds to step 213 and PM removal control is performed. Is implemented. Here, the control in step 213 and subsequent steps 215 and 217 is the same as the control in steps 203, 205, and 207 described above and will not be described. However, as is clear from the above description, in this embodiment, Even if it is determined in step 201 that the PM removal control execution condition is not satisfied, the PM removal control is executed when it is necessary to perform the sulfur poisoning regeneration control. After step 217, the process proceeds to step 219.

  On the other hand, when the PM removal control is terminated in step 207 and the process proceeds to step 209, it is determined whether or not the necessary conditions for implementing the sulfur poisoning regeneration control are satisfied. The implementation requirement here is, for example, that the absorbed SOx amount is estimated to be greater than or equal to a predetermined amount, as in the case of step 211 described above. It is preferable to keep it less than the case. This is a case where the exhaust gas purification means has already been heated by PM removal control when proceeding to step 209, and in order to effectively utilize this opportunity, sulfur poisoning regeneration can be performed even if the amount of absorbed SOx is small to some extent. It is because it is preferable to carry out.

If it is determined in step 209 that the necessary execution conditions are not satisfied, the present control routine is terminated. If it is determined that the required execution conditions are satisfied, the process proceeds to step 219.
In step 219, it is determined whether or not the conditions for enabling sulfur poisoning regeneration control are satisfied. This feasible condition is the same as the feasible condition described in relation to step 101 in FIG. 4. For example, it is determined whether or not the condition is satisfied based on the operating state of the engine at that time, that is, the load state of the engine. .

  If it is determined in step 219 that the enablement condition is not satisfied, the control routine ends. If it is determined that the enablement condition is satisfied, the process proceeds to step 221 and sulfur poisoning is performed. Playback control is performed. In the sulfur poisoning regeneration control in step 221, only the sulfur content release control described in relation to step 103 in FIG. 4 is performed. This is because when the process proceeds to step 221, PM removal control has been performed first, and the exhaust purification means has already been heated, so it is necessary to perform the temperature increase control in the sulfur poisoning regeneration control in step 221. Because there is no.

  Since the control after step 221, that is, the control from step 221 to step 233 is almost the same as the control from step 103 to step 115 in FIG. 4, detailed description is omitted, but in this embodiment various controls (exhaust gas) The control of the gas air-fuel ratio, the temperature control of the exhaust purification means, etc.) can be performed based on the detection values from various sensors. Further, the control in step 227 is a control for removing the reducing agent remaining in the exhaust passage as in the control in step 109 of FIG. 4, but in this embodiment, the control flowed into the exhaust purification means at this time. The reducing agent can be purified by the oxidation catalyst 53 in addition to the NOx absorbent 11 of the NOx absorbent catalyst 11 and the NOx absorbent filter 52.

  As described above, in the present embodiment as well, the control (step 227) for removing the reducing agent remaining in the exhaust passage is performed in the same manner as the control in step 109 of FIG. The reducing agent remaining in the exhaust passage by the regeneration control is removed, and as a result, the generation of white smoke after the sulfur poisoning regeneration control is suppressed.

FIG. 1 is a diagram showing an example of a configuration when the present invention is applied to a compression ignition type internal combustion engine. FIG. 2 is a diagram showing the required torque of the engine. FIG. 3 is a diagram for explaining the NOx absorption / release and reduction and purification action. FIG. 4 is a flowchart showing a control routine of control that can be implemented by the configuration shown in FIG. FIG. 5 is a diagram showing a feasible region and a non-feasible region of sulfur poisoning regeneration control. FIG. 6 is a diagram for explaining the fuel injection control. FIG. 7 is a diagram schematically showing a change with time of the temperature Tc of the NOx absorption catalyst, the exhaust gas temperature Te, the remaining or attached reducing agent amount RQ, for an example when the control routine shown in the flowchart of FIG. 4 is executed. is there. FIG. 8 is a diagram showing another example of the configuration when the present invention is applied to a compression ignition type internal combustion engine. FIG. 9 is a view showing a NOx absorbent-carrying filter. FIG. 10 is a flowchart showing a control routine of control that can be implemented by the configuration shown in FIG.

Explanation of symbols

3 ... Fuel injection valve 4 ... Intake manifold 5 ... Exhaust manifold 7 ... Exhaust turbocharger 11 ... NOx absorption catalyst 13 ... Reductant addition valve

Claims (3)

When the exhaust purification means including at least the NOx storage agent is disposed in the exhaust passage and the sulfur content should be released from the NOx storage agent, the fuel or the reducing agent is introduced into the exhaust passage upstream of the exhaust purification means. In an exhaust gas purification apparatus for an internal combustion engine in which sulfur poisoning regeneration control including addition is performed and sulfur content is released from the NOx storage agent,
When the sulfur poisoning regeneration control is completed or stopped before completion, the addition of the fuel or reducing agent is stopped and the fuel or reducing agent is added from the vicinity of the fuel or reducing agent addition position in the exhaust passage. After the sulfur poisoning regeneration temperature control for increasing or maintaining the temperature until reaching the exhaust purification means, or suppressing the decrease in the temperature of the portion after a predetermined time, the normal control is performed. Exhaust gas purification device that comes back.   The exhaust emission control device according to claim 1, wherein the temperature control of the exhaust gas purification unit is further maintained in the temperature control after the sulfur poisoning regeneration, or a decrease in the temperature of the exhaust gas purification unit is suppressed.   The fuel injection in the temperature control after the sulfur poisoning regeneration control is delayed from the compression top dead center, the pilot injection performed immediately before the main injection, and the initial stage of the expansion stroke after the main injection. The exhaust emission control device for an internal combustion engine according to claim 1 or 2, comprising after-injection performed in step (1).

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