JP2015052291A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine, including a filter provided in an exhaust passage for trapping PMs, for effectively reducing the pressure loss of the filter resulting from the accumulation of ashes while suppressing an increase of fuel consumption.SOLUTION: The exhaust emission control device for the internal combustion engine includes the filter for trapping the PMs, a first accumulation amount acquiring part for acquiring the accumulation amount of the PMs, a second accumulation amount acquiring part for acquiring the accumulation amount of the ashes, and a control part for executing regeneration processing to oxidize the accumulated PMs. When the accumulation amount of the ashes acquired by the second accumulation amount acquiring part is not smaller than a threshold amount, the control part executes the regeneration processing in the state that the accumulation amount of the acquired PMs reaches a predetermined amount allowing oxidation heat due to the regeneration processing to raise the temperature of the filter up to a predetermined temperature where the accumulated ashes are contracted.

Description

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

  Conventionally, a filter for collecting PM is provided in the exhaust passage in order to prevent particulate matter such as soot contained in the exhaust gas of the internal combustion engine (hereinafter referred to as “PM”) from being released to the atmosphere. ing. If the collected PM is excessively accumulated, there is a risk that the function of the filter will be reduced, such as an increase in pressure loss. Therefore, a regeneration process for removing the accumulated PM by oxidation is performed.

  By the way, the exhaust gas may contain incombustible substances (hereinafter referred to as “ash”) derived from components contained in the lubricating oil of the internal combustion engine. Since the ash is also collected by the filter, there is a possibility that the function of the filter is deteriorated when it is excessively accumulated. Here, since ash itself is nonflammable, it is difficult to remove it by oxidation like PM, but there is a problem that the oxidization rate of PM during regeneration treatment decreases due to ash accumulation. ing. In order to solve this problem, a technique has been proposed in which the target temperature of the filter during the regeneration process is corrected according to the amount and state of ash accumulated on the filter (see, for example, Patent Document 1). In this technique, the target temperature is corrected to be higher as the amount of accumulated ash increases, and the fuel injection amount and the injection timing are controlled so that the actual filter temperature reaches this target temperature. As a result, the filter temperature is raised to the target temperature set higher, so that the oxidation reaction of PM is further promoted. As a result, the PM oxidation rate lowered by the ash deposition is recovered.

JP 2011-69374 A

  By the way, as the function degradation of the filter induced by the accumulated ash, there is an increase in pressure loss due to a decrease in the filtration area of the filter caused by the ash deposition. The above-described conventional technique is a technique for further increasing the temperature of the filter in order to promote the oxidation reaction of PM, and thus is not a technique for actively solving the pressure loss of the filter due to ash deposition. Further, in the above-described conventional technology, the amount of unburned fuel contained in the exhaust gas is adjusted by controlling the fuel injection amount and the injection timing in order to raise the filter temperature to a higher corrected target temperature. Therefore, in this technique, there is a concern about an increase in fuel consumption.

  The present invention has been made in view of such a situation, and in an exhaust gas purification apparatus for an internal combustion engine provided with a filter for collecting PM in an exhaust passage, ash accumulation is achieved while suppressing an increase in fuel consumption. An object of the present invention is to effectively reduce the pressure loss of the filter caused by the above.

In order to solve the above-described problem, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes:
A filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
A first deposition amount acquisition unit for acquiring a deposition amount of particulate matter deposited on the filter;
A second accumulation amount acquisition unit for acquiring an accumulation amount of the non-combustible material accumulated on the filter;
A control unit that executes a regeneration process for oxidizing the particulate matter deposited on the filter, and when the accumulation amount of the incombustible substance acquired by the second accumulation amount acquisition unit is equal to or greater than a threshold amount, 1 The amount of particulate matter deposited acquired by the deposit amount acquisition unit has reached a predetermined amount that raises the temperature of the filter to a predetermined temperature at which the deposited incombustible material contracts by oxidation heat generated by the regeneration process. And a control unit for executing the reproduction process;
It was made to prepare.

  The particulate matter (hereinafter also referred to as “PM”) is a combustible solid material such as soot that is generated when fuel is burned in an internal combustion engine. When PM trapped in the filter is deposited, the pressure loss of the filter increases due to a decrease in the filtration area of the filter. Therefore, the first accumulation amount acquisition unit described above acquires the accumulation amount of PM accumulated on the filter based on, for example, the differential pressure across the filter, the operation history of the internal combustion engine, and the like. The PM deposited on the filter is oxidized when the temperature of the filter is sufficiently high (for example, about 400 ° C. or more) and sufficient oxygen is present in the filter. Therefore, the control unit of the exhaust gas purification apparatus according to the present invention executes a regeneration process for oxidizing the PM in order to remove the PM accumulated on the filter. Here, for example, in order to sufficiently suppress PM accumulation, the control unit executes the regeneration process at a stage where the amount of PM accumulation is relatively small. In this regeneration process, processes such as heating the filter and supplying oxygen to the filter are performed.

  On the other hand, the above-mentioned incombustible substances (hereinafter also referred to as “ash”) are incombustible solid substances derived from components such as additives contained in lubricating oil of internal combustion engines and sulfur contained in fuel. Since ash is collected and deposited in the filter in the same manner as PM, the pressure loss of the filter increases as the amount of ash deposited increases. Therefore, the second accumulation amount acquisition unit described above calculates the accumulation amount of ash accumulated on the filter by using the differential pressure across the filter (particularly immediately after the end of the regeneration process, where it is considered that only ash is substantially accumulated. It is acquired based on the differential pressure across the filter) and the operation history of the internal combustion engine. Since ash is nonflammable, it is difficult to remove by oxidation like PM, but shrinks when heated to a predetermined temperature (for example, about 750 ° C.) (the volume decreases and the density increases). )It is known. In particular, it is known that when heated to about 1050 ° C. or higher, the density shrinks to an extent that increases by about 50%. Therefore, if the filter temperature is increased to a predetermined temperature at which the unshrinked ash deposited on the filter contracts, the pressure loss of the filter can be reduced by increasing the filtration area of the filter. However, the predetermined temperature is higher than the temperature at which the filter temperature normally reaches during operation of the internal combustion engine or regeneration processing. Therefore, in order to raise the filter temperature to the predetermined temperature and contract the ash, it is necessary to additionally heat the filter. Here, for example, if the temperature of the exhaust gas flowing into the filter is raised, the filter can be additionally heated. However, this method is not preferable because fuel consumption increases.

  Therefore, the control unit of the exhaust emission control apparatus according to the present invention, when the ash accumulation amount acquired by the second accumulation amount acquisition unit is equal to or greater than the threshold amount, the PM accumulation acquired by the first accumulation amount acquisition unit. The regeneration process is executed in a state where the amount reaches a predetermined amount that raises the temperature of the filter to a predetermined temperature at which the deposited ash contracts by oxidation heat generated by the regeneration process. Here, the predetermined amount can be acquired based on, for example, the ash accumulation amount acquired by the second accumulation amount acquisition unit and the difference between the predetermined temperature and the actual temperature of the filter. The predetermined temperature may be a temperature at which the deposited ash sufficiently contracts and the filter does not reach an excessive temperature rise. For example, the ash contraction characteristics (for example, the ash density change rate with respect to the ash temperature) It can be set based on the heat resistance characteristics of the filter. Note that the above threshold amount related to the ash accumulation amount is an ash accumulation amount set to determine the necessity of ash shrinkage. For example, by reducing the ash shrinkage of the filter pressure loss is expected. What is necessary is just to set it as the accumulation amount of ash when possible, and should just set beforehand by experiment etc.

As described above, according to the present invention, the control unit executes a regeneration process for oxidizing and removing PM. When the ash accumulation amount is equal to or greater than the threshold amount, the PM accumulation amount is set to the predetermined amount. The reproduction process is not executed before the arrival. If the operation of the internal combustion engine is continued in a state where the regeneration process is not executed, the PM accumulation amount eventually reaches the predetermined amount. That is, when the ash accumulation amount is equal to or larger than the threshold amount, the control unit limits the execution of the regeneration process until the PM accumulation amount reaches the predetermined amount, and the PM accumulation amount is the predetermined amount. After reaching, playback processing is executed. As a result, according to the present invention, the regeneration process can be executed in a state where a predetermined amount of PM that generates oxidation heat necessary to raise the filter temperature to the predetermined temperature is accumulated. The ash can be shrunk without additional consumption. As a result, it is possible to effectively reduce the pressure loss of the filter while suppressing an increase in fuel consumption.

  Further, according to the present invention, the second accumulation amount acquisition unit accumulates an incombustible material accumulated on the filter based on a differential pressure across the filter immediately after the regeneration process is performed by the control unit. May be obtained. The differential pressure before and after the filter immediately after the regeneration process is executed is the differential pressure before and after the PM accumulated from the filter is removed, and thus the differential pressure before and after the influence of the accumulated PM is eliminated. Therefore, by using the differential pressure before and after, it is possible to acquire the ash accumulation amount with high accuracy.

  In addition, the exhaust gas purification apparatus for an internal combustion engine according to the present invention includes a deposit amount of the incombustible substance acquired by the second deposit amount acquisition unit, and a difference between the predetermined temperature and the actual temperature of the incombustible substance. A predetermined amount acquisition unit that acquires the predetermined amount may be further included. Here, the greater the amount of ash deposited, and the greater the difference between the predetermined temperature and the actual temperature of PM, the more oxidation heat is required to heat the ash, so more PM is required. become. Therefore, the predetermined amount acquisition unit acquires the predetermined amount based on these relationships. Thereby, the amount of PM necessary for raising the temperature of the filter to a temperature at which the deposited ash contracts can be obtained with high accuracy.

  According to the present invention, the internal combustion engine is a spark ignition type internal combustion engine capable of combustion at a stoichiometric air-fuel ratio, and the control unit supplies fuel to the internal combustion engine during decelerating operation. You may make it perform the said reproduction | regeneration process by performing a stop. Here, in the internal combustion engine, when fuel supply is stopped, high-concentration oxygen is supplied to the filter, so that PM deposited on the filter is suitably oxidized. Note that fuel supply is not normally required during deceleration operation of the internal combustion engine. Therefore, the control unit executes the regeneration process by stopping the fuel supply during the deceleration operation of the internal combustion engine. Note that, as described above, when the ash accumulation amount is equal to or greater than the threshold amount, the control unit does not perform the regeneration process until the PM accumulation amount reaches the predetermined amount. Therefore, in this case, the control unit does not stop the fuel supply even during the deceleration operation of the internal combustion engine. Then, the fuel supply is stopped after the PM accumulation amount reaches the predetermined amount. Thereby, according to this invention, when the accumulation amount of ash is more than the said threshold amount, a reproduction | regeneration process can be performed in the state which accumulated said predetermined amount PM. As a result, it is possible to effectively reduce the pressure loss of the filter while suppressing an increase in fuel consumption.

Further, according to the present invention, the control unit, when the accumulation amount of the incombustible substance is not less than the threshold amount, even if the accumulation amount of the particulate matter is less than the predetermined amount, the temperature of the filter When the temperature is lower than a second predetermined temperature at which the oxidation reaction due to the regeneration process does not occur, the fuel supply stop of the internal combustion engine may be executed during the deceleration operation of the internal combustion engine. Here, when the filter temperature is lower than the second predetermined temperature, even if the fuel supply is stopped and oxygen is supplied to the filter, the accumulated PM is not oxidized, so there is no need to limit the fuel supply stop. . Therefore, when the accumulation amount of ash is equal to or greater than the threshold amount, the control unit determines that the filter temperature is less than the second predetermined temperature even before the PM accumulation amount reaches the predetermined amount. , Stop fuel supply. As a result, the frequency of stopping the fuel supply increases, so that the fuel consumption of the internal combustion engine can be further reduced.

  According to the present invention, the internal combustion engine includes an oxidation catalyst provided upstream of the filter in the exhaust passage, and a fuel addition unit that adds fuel to the exhaust gas flowing into the oxidation catalyst. In the compression ignition type internal combustion engine, the control unit causes the fuel addition unit to generate fuel when the accumulation amount of the particulate matter deposited on the filter is equal to or greater than a second predetermined amount that is smaller than the predetermined amount. The control unit executes the regeneration process, and when the accumulation amount of the incombustible substance is equal to or greater than the threshold amount, the accumulation amount of the particulate matter is set to the second amount. The regeneration process may be executed by adding fuel by the fuel addition unit when the amount is equal to or greater than the predetermined amount instead of the predetermined amount. Here, when the fuel is added from the fuel addition section, the exhaust temperature rises due to the fuel being oxidized by the oxidation catalyst. Therefore, the temperature of the filter disposed downstream of the oxidation catalyst may be raised. it can. In the internal combustion engine, since the oxygen concentration in the exhaust gas is relatively high, PM accumulated in the filter can be oxidized by adding fuel from the fuel addition unit and raising the filter temperature to a temperature at which PM is oxidized. . The second predetermined amount is, for example, a PM accumulation amount set to determine the necessity of regeneration processing performed to sufficiently suppress PM accumulation and excessive temperature rise of the filter, The filter temperature during the regeneration process is an amount set to be smaller than the predetermined amount so as not to exceed the predetermined temperature at which the ash contracts.

  As described above, according to the present invention, the control unit causes the fuel addition unit to add fuel when the PM accumulation amount is equal to or greater than the second predetermined amount, but the ash accumulation amount is equal to or greater than the threshold amount. The fuel is added by the fuel addition unit when the PM accumulation amount is equal to or greater than the predetermined amount. In other words, when the ash accumulation amount is equal to or greater than the threshold amount, the control unit does not add fuel until the PM accumulation amount reaches the predetermined amount even if the PM accumulation amount exceeds the second predetermined amount. Thereby, according to this invention, when the accumulation amount of ash is more than the said threshold amount, a reproduction | regeneration process can be performed in the state which accumulated said predetermined amount PM. As a result, it is possible to effectively reduce the pressure loss of the filter while suppressing an increase in fuel consumption.

  According to the present invention, in an exhaust gas purification apparatus for an internal combustion engine provided with a filter for collecting PM in an exhaust passage, the pressure loss of the filter due to ash accumulation is effectively reduced while suppressing an increase in fuel consumption. It becomes possible to reduce.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an exhaust purification device according to Embodiment 1. FIG. It is a graph which shows the shrinkage | contraction characteristic of the ash deposited on the filter. 3 is a flowchart showing a fuel cut execution procedure according to the first embodiment. 6 is a flowchart illustrating a procedure of a fuel cut prohibition flag setting process according to the first embodiment. It is a graph which shows the relationship between the ash deposition amount with respect to the travel distance of a vehicle, and the pressure loss of a filter. It is a graph which shows the relationship between a target pressure loss and an ash shrinkage rate. It is a graph which shows the relationship between an ash shrinkage rate and target temperature. It is a graph which shows the relationship between the temperature rise range which is the difference of target temperature and the present temperature of a filter, and target PM deposition amount. It is a graph which shows the relationship between PM deposition amount and overheating temperature assumption temperature. It is a figure which shows schematic structure of the internal combustion engine and exhaust gas purification apparatus which concern on Example 2. FIG. 12 is a flowchart illustrating normal reproduction processing according to the second embodiment. 10 is a flowchart illustrating an ash contraction process according to the second embodiment.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

[Example 1]
FIG. 1 is a diagram showing a schematic configuration of an exhaust gas purification apparatus for an internal combustion engine according to the present embodiment. An internal combustion engine 10 that is a spark ignition type internal combustion engine mounted on a vehicle is a gasoline engine for a vehicle having a plurality of cylinders 11, and is a so-called direct injection gasoline engine in which fuel is directly injected into the cylinders 11. . The cylinder 11 is provided with a fuel injection valve 12 for injecting fuel into a combustion chamber provided in the upper part of the cylinder 11 and an ignition plug 13 for igniting an air-fuel mixture in the cylinder 11. The spark plug 13 ignites the air-fuel mixture by generating a spark between the electrodes provided at the tip.

  An intake passage 20 connected to the combustion chamber of the cylinder 11 via an intake port is provided with a throttle valve 21 for adjusting the flow rate of intake air taken into the cylinder 11 and an air flow meter 22 for detecting the flow rate. Yes. An exhaust passage 30 connected to the combustion chamber of the cylinder 11 via an exhaust port is provided with a catalyst 31 having an oxidation function and a filter 32 for collecting particulate matter (PM) in the exhaust. . The catalyst 31 is a catalyst that purifies the exhaust gas by oxidizing unburned fuel and carbon monoxide. The catalyst 31 may be, for example, a three-way catalyst, an oxidation catalyst, an occlusion reduction type NOx catalyst, or a selective reduction type NOx catalyst. The filter 32 is, for example, a wall flow type filter formed of a cordierite porous base material.

  An air-fuel ratio sensor 33 that detects the air-fuel ratio of the exhaust gas is provided in the exhaust passage 30 upstream of the catalyst 31. The air-fuel ratio sensor 33 may be an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas. A first temperature sensor 34 that detects the temperature of the exhaust gas is provided in the exhaust passage 30 downstream of the catalyst 31 and upstream of the filter 32. Based on the detection value of the first temperature sensor 34, the temperature of the catalyst 31 can be detected. A second temperature sensor 35 that detects the temperature of the exhaust is provided in the exhaust passage 30 downstream of the filter 32. Based on the detection value of the second temperature sensor 35, the temperature of the filter 32 can be detected. The exhaust passage 30 is provided with a differential pressure sensor 36 that detects a differential pressure across the filter 32 (a difference between an exhaust pressure upstream of the filter 32 and an exhaust pressure downstream).

  The internal combustion engine 10 is provided with an ECU 40 that is an electronic control unit for controlling the internal combustion engine 10. The ECU 40 is electrically connected to the fuel injection valve 12, the spark plug 13, and the throttle valve 21, and these are controlled by the ECU 40. The ECU 40 is electrically connected to the air flow meter 22, the air-fuel ratio sensor 33, the first temperature sensor 34, the second temperature sensor 35, and the differential pressure sensor 36 described above, and an output signal from these is sent to the ECU 40. Entered. Further, the ECU 40 includes an accelerator opening sensor 41 that detects the opening of an accelerator pedal (not shown) provided in the vehicle, and a crank position sensor 42 that detects the rotational position of the crankshaft 14 of the internal combustion engine 10 via electric wiring. The output signals from these are input to the ECU 40.

  Here, during normal operation of the internal combustion engine 10, the ECU 40 determines that the air-fuel ratio of the air-fuel mixture in the cylinder 11 is the stoichiometric air-fuel ratio or the vicinity thereof based on the detected values from the air flow meter 22, the air-fuel ratio sensor 33, and the like. The amount of fuel injection from the fuel injection valve 12 is controlled so that

The ECU 40 executes a regeneration process for oxidizing the PM accumulated on the filter 32 by executing a fuel cut for stopping the fuel supply to the internal combustion engine 10. Specifically, when the fuel cut is executed, the air taken into the cylinder 11 is discharged as it is, so that high concentration oxygen is supplied to the filter 32. Therefore, if the temperature of the filter 32 is within a predetermined temperature range where PM is oxidized, the PM deposited on the filter 32 is oxidized and removed by the supplied oxygen. In the present embodiment, the ECU 40 that executes the regeneration process in this way corresponds to the control unit in the present invention. Here, the regeneration processing in the present embodiment is normally performed within a predetermined temperature range sufficiently lower than the maximum temperature (for example, about 1400 ° C.) that the filter 32 can allow so that the filter 32 does not reach an excessive temperature rise. (For example, about 500 ° C. to about 650 ° C.) The filter temperature is changed. Hereinafter, such reproduction processing is referred to as “normal reproduction processing”.

  By the way, the exhaust gas discharged from the internal combustion engine 10 may contain ash which is a nonflammable solid substance derived from the components of the additive contained in the lubricating oil. The ash in the exhaust gas is also collected and deposited by the filter 32 in the same manner as PM. As the ash deposition proceeds, an increase in pressure loss due to a decrease in the filtration area of the filter 32 may be induced, but it is difficult to remove the deposited ash by oxidation like PM. Therefore, in the past, it was difficult to reduce the pressure loss increased due to the influence of ash.

  Here, recent studies have revealed that ash has the property of reducing its volume and increasing its density (shrinking) when heated to a temperature higher than the temperature range during normal regeneration processing. It was. Hereinafter, the shrinkage characteristics of the ash deposited on the filter will be described in detail with reference to FIG.

  FIG. 2 is a diagram showing the relationship between the ash temperature and the density change rate when the ash deposited on the filter 32 is heated. In FIG. 2, the horizontal axis indicates the ash temperature, and the vertical axis indicates the ash density change rate. As shown in FIG. 2, when the ash temperature is in a range corresponding to the above-described predetermined temperature range, the ash density change rate is approximately 0%. That is, the ash deposited on the filter 32 hardly shrinks during the normal regeneration process. However, the density change rate of the ash starts to rise when the ash temperature exceeds the temperature T1 (about 750 ° C.), and reaches about 50% when the ash temperature rises to the temperature T2 (about 1050 ° C.). In other words, the ash can be shrunk if the filter temperature is raised to at least the temperature T1, and if the temperature is raised to the temperature T2, the ash can be shrunk until the volume becomes about two thirds. However, if the filter temperature rises excessively, problems such as melting may occur.

  Based on the above, in this embodiment, the filter temperature is further raised by a regeneration process different from the normal regeneration process, and the ash deposited on the filter 32 is contracted. Specifically, in the case where the accumulated ash is contracted, the filter temperature is set to a predetermined contraction temperature (for example, the above-described temperature at which the ash sufficiently contracts, with the upper limit being a temperature at which the filter 32 does not reach an excessive temperature rise). The regeneration process for raising the temperature to T2) is executed. Hereinafter, such reproduction processing is referred to as “ash shrinkage processing”.

Here, as already described, since the normal regeneration process is executed so that the temperature of the filter 32 changes in a temperature range lower than the temperature T1, it is difficult to shrink the ash by the normal regeneration process. . Therefore, in order to raise the filter temperature to at least the temperature T1 or more, preferably near the low temperature side of the temperature T2, it is conceivable to raise the temperature of the exhaust gas discharged from the internal combustion engine 10. However, in the exhaust emission control device for the internal combustion engine 10 according to the present embodiment, the catalyst 31 is disposed upstream of the filter 32. However, since the upper limit temperature of the exhaust gas that can be allowed by the catalyst 31 is lower than the temperature T2, It is difficult to heat the filter 32 to the vicinity of the low temperature side of the temperature T2. Moreover, since it is necessary to consume additional fuel to raise the exhaust gas temperature, there is a concern that fuel consumption will deteriorate due to increased fuel consumption.

  Therefore, in the exhaust gas purification apparatus according to the present embodiment, when the ash needs to be contracted, the filter temperature is raised to a predetermined temperature at which the ash contracts using the oxidation heat generated from the PM deposited on the filter 32. I tried to make it. Specifically, the regeneration process is restricted until a predetermined amount of PM necessary for raising the filter temperature to the predetermined temperature is accumulated, and the regeneration process (that is, ashing is performed with the predetermined amount accumulated). (Shrinkage process) is executed.

  Next, the reproduction processing according to the present embodiment will be specifically described with reference to the drawings. First, the execution procedure of fuel cut will be described with reference to FIG. The flow shown in FIG. 3 is executed by executing a control program stored in the ECU 40 every predetermined time.

  In step S101, the ECU 40 determines whether or not the internal combustion engine 10 is in a decelerating operation. The ECU 40 makes the determination based on, for example, the detection value of the accelerator opening sensor 41 and the operating state of the internal combustion engine 10. If a negative determination is made in this step, this flow ends. On the other hand, if an affirmative determination is made in this flow, the ECU 40 proceeds to step S102.

  In step S102, the ECU 40 determines whether or not a fuel cut prohibition flag is ON. Here, the fuel cut prohibition flag is a flag set by a flow shown in FIG. 4 described later. In this embodiment, in step S102, a fuel cut prohibition flag set in advance by the flow shown in FIG. 4 is referred to. If an affirmative determination is made in this step, the ECU 40 proceeds to step S103, prohibits execution of fuel cut, and ends this flow. On the other hand, if a negative determination is made in this step, the ECU 40 proceeds to step S104, performs fuel cut by stopping fuel injection by the fuel injection valve 12, and then ends this flow.

  Next, the fuel cut prohibition flag setting process will be described with reference to FIG. FIG. 4 is a flowchart showing a procedure for setting a fuel cut prohibition flag. This flow is executed by executing a control program stored in the ECU 40 every predetermined time.

  In step S201, the ECU 40 acquires Mpm, which is the PM accumulation amount when executing this flow, and Mash, which is the ash accumulation amount. The ECU 40 acquires the PM accumulation amount Mpm based on the detection value from the differential pressure sensor 36, the operation history of the internal combustion engine 10, and the like. In addition to the detection value from the differential pressure sensor 36, the operation history of the internal combustion engine 10 and the like, the ECU 40 is based on the detection value detected by the differential pressure sensor 36 immediately after the normal regeneration process executed in the past. The ash accumulation amount Mash is acquired. Here, since the detected value is a value detected immediately after the PM is removed, it is a value from which the influence of the accumulated PM is eliminated. Therefore, by using the detected value (for example, by using the detected value and the detected value or the operation history after the detection of the detected value), the ash deposition amount Mash can be obtained with high accuracy. Become.

In step S202, the ECU 40 determines whether or not the ash accumulation amount Mash acquired in the previous step is equal to or larger than a predetermined threshold amount Ma in order to determine the necessity of contracting the ash. Here, referring to FIG. 5 showing the relationship between the ash accumulation amount Mash and the pressure loss ΔP of the filter 32 with respect to the travel distance of the vehicle, as shown in the graph L1, the ash accumulation amount Mash increases as the travel distance of the vehicle increases. Increase. Therefore, as shown in the graph L2, the pressure loss ΔP of the filter 32 also increases as the travel distance of the vehicle increases. Therefore, when the ash accumulation amount Mash exceeds the threshold amount Ma, the ECU 40 executes ash contraction processing to reduce the pressure loss ΔP to the target pressure loss Pt. The threshold amount Ma may be an ash accumulation amount when the pressure loss of the filter 32 can be expected to be reduced by contracting the ash, and may be obtained in advance by an experiment or the like. If an affirmative determination is made in this step, the ECU 40 proceeds to step S203. On the other hand, if a negative determination is made in this step, it means that the ash has not accumulated to the extent that ash shrinkage processing is necessary. In this case, since it is not necessary to limit the execution of the regeneration process, the fuel cut can be executed when the internal combustion engine 10 is decelerated. Therefore, the ECU 40 proceeds to step S213 to allow fuel cut, and ends this flow after setting the fuel cut prohibition flag to OFF. Thus, when the flow shown in FIG. 3 is executed after the end of this flow, the fuel cut is executed in step S104 if the internal combustion engine 10 is decelerating. If PM is deposited on the filter 32 and the filter temperature is sufficiently high, a normal regeneration process is performed in which the deposited PM is oxidized and removed.

  In step S203, the ECU 40 calculates a target pressure loss Pt that is a target value of the pressure loss. The ECU 40 calculates the target pressure loss Pt based on the ash accumulation amount Mash, the operation history of the internal combustion engine 10, the travel distance of the vehicle (or the travel distance since the previous ash contraction process was executed), the target fuel consumption, and the like. . For example, the target pressure loss Pt is calculated to be smaller when the ash accumulation amount Mash is large or when the deviation of the actual fuel consumption from the target fuel consumption is large.

  In step S204, the ECU 40 calculates an ash contraction rate α that can reduce the pressure loss ΔP to the target pressure loss Pt calculated in the previous step. The shrinkage rate is a numerical value represented by “(volume before shrinkage−volume after shrinkage) / volume before shrinkage”, and the larger the shrinkage rate, the smaller the volume after shrinkage. Here, the target pressure loss Pt of the filter 32 and the ash shrinkage rate α have a relationship as shown in FIG. 6 when the ash accumulation amount Mash is constant. That is, as the calculated target pressure loss Pt is smaller, it is necessary to increase the contraction rate α (that is, to further contract the ash). Although not shown, when the target pressure loss Pt is constant, it is necessary to increase the shrinkage rate α as the ash deposition amount Mash increases. The ECU 40 calculates a target contraction rate α in this flow based on these relationships.

  In step S205, the ECU 40 calculates the target temperature Tt of the filter 32 at which the ash contracts to the contraction rate α calculated in the previous step. Here, the target temperature Tt and the shrinkage rate α have a relationship as shown in FIG. That is, the target temperature Tt needs to be increased as the target contraction rate α is larger (that is, the ash needs to be contracted more). The ECU 40 calculates the target temperature Tt in this flow based on this relationship. The target temperature Tt is set with the above-mentioned temperature T2 as an upper limit. Note that the ECU 40 may acquire the target temperature Tt from the shrinkage characteristics of the ash shown in FIG.

In step S206, the ECU 40 calculates a target PM accumulation amount Mpmt, which is a PM accumulation amount necessary for raising the temperature of the filter 32 to the target temperature Tt by the oxidation heat of the accumulated PM. Here, the temperature rise width Tt−Tc, which is the difference between the target temperature Tt and the current temperature Tc (filter temperature at the time of execution of this flow), and the target PM accumulation amount Mpmt have a relationship as shown in FIG. . Here, the current temperature Tc can be regarded as corresponding to the ash temperature at the time of execution of this flow. In other words, the larger the temperature rise width Tt−Tc, the greater the amount of heat of oxidation required to heat the ash. Therefore, the target PM deposition amount Mpmt needs to be increased. Further, the larger the ash deposition amount Mash, the more the amount of heat of oxidation required for heating. EC
U40 calculates the target PM deposition amount Mpmt in this flow based on these relationships, the heat capacity of the filter 32, and the like. Note that the detected value from the second temperature sensor 35 may be used as the current temperature Tc.

  In step S207, the ECU 40 calculates an excessive temperature rise assumed temperature Tot that is a lower limit temperature of a predetermined filter temperature range. Here, the predetermined filter temperature range is a filter temperature range when the filter 32 is assumed to reach an excessive temperature rise if the PM deposited on the filter 32 is oxidized during the execution of this flow. Here, the PM deposition amount Mpm and the excessive temperature rise assumed temperature Tot have a relationship as shown in FIG. That is, as the PM deposition amount Mpm increases, the amount of heat of oxidation heat generated increases, and thus the overheated estimated temperature Tot decreases. Based on this relationship, the ECU 40 calculates the overheated estimated temperature Tot in this flow.

  In step S208, the ECU 40 determines whether or not the current temperature Tc of the filter 32 is lower than the overheated estimated temperature Tot calculated in the previous step. If a negative determination is made, it means that if the PM deposited on the filter 32 is oxidized, the filter 32 may be overheated. Therefore, the ECU 40 proceeds to step S209 to prohibit the fuel cut, sets the fuel cut prohibition flag to ON, and ends this flow.

  In contrast, if an affirmative determination is made in step S208, the ECU 40 proceeds to step S210 and determines whether or not the PM accumulation amount Mpm is equal to or greater than the target PM accumulation amount Mpmt. If a negative determination is made in this step, it means that the amount of PM necessary to raise the temperature of the filter 32 to the target temperature Tt is not accumulated in the filter 32 when this flow is executed. Therefore, the ECU 40 proceeds to step S211, and determines whether or not the current temperature Tc of the filter 32 is lower than the reproducible temperature Tlo, which is the lowest temperature of the filter when the oxidation reaction of PM occurs. If a negative determination is made, it means that if fuel cut is executed and oxygen is supplied to the filter 32, the accumulated PM is oxidized. Here, since the PM deposition amount Mpm is smaller than the target PM deposition amount Mpmt, if the oxidation of PM is started in this case, the temperature of the filter 32 does not rise to the target temperature Tt. Therefore, the ECU 40 proceeds to step S209, sets the fuel cut prohibition flag to ON, and ends this flow. Thus, when the flow shown in FIG. 3 is executed after the end of this flow, fuel cut is prohibited in step S103 even when the internal combustion engine 10 is decelerating. That is, when the amount of PM necessary for raising the temperature of the filter 32 to the target temperature Tt is not accumulated on the filter 32, the execution of the regeneration process is limited. As a result, it is avoided that PM is oxidized in a state where the filter temperature cannot be raised to the target temperature Tt. The reproducible temperature Tlo described above corresponds to the second predetermined temperature in the present invention.

  On the other hand, if an affirmative determination is made in step S211, even if fuel cut is performed and oxygen is supplied to the filter 32, the accumulated PM is not oxidized because the filter temperature is lower than the reproducible temperature Tlo. Means that. Therefore, in this case, since PM is not consumed by oxidation even if the fuel cut is executed, the fuel cut may be executed for the purpose of improving the fuel consumption. Therefore, the ECU 40 proceeds to step S213, sets the fuel cut prohibition flag to OFF, and ends this flow.

If an affirmative determination is made in step S210, the ECU 40 proceeds to step S212, and determines whether or not the current temperature Tc is equal to or higher than the reproducible temperature Tlo. If an affirmative determination is made in this step, the process proceeds to step S213, the fuel cut prohibition flag is set to OFF, and this flow ends. Accordingly, when the flow shown in FIG. 3 is executed after the end of this flow, if the internal combustion engine 10 is decelerating, the fuel cut is executed in step S104 and the PM deposited on the filter 32 is oxidized. Then, since the filter temperature rises to the target temperature Tt due to the oxidation heat generated from the oxidized PM, the ash deposited on the filter can be contracted to the contraction rate α. That is, the ash shrinkage process is executed in this way. As a result, the pressure loss of the filter 32 can be reduced to the target pressure loss Pt.

  If a negative determination is made in step S212, it means that the deposited PM is not oxidized even if the fuel cut is executed. Therefore, the ECU 40 proceeds to step S209, sets the fuel cut prohibition flag to ON, and ends this flow. Thus, when the flow shown in FIG. 3 is executed after the end of this flow, even if the internal combustion engine 10 decelerates, the fuel cut is not executed, so the exhaust temperature rises and the filter 32 is heated. As a result, the temperature of the filter 32 can be raised to the reproducible temperature Tlo or higher earlier. Note that if a negative determination is made in step S212, PM is not consumed by oxidation even if the fuel cut is executed, so the fuel cut may be executed for the purpose of improving fuel consumption or the like. That is, in this case, instead of proceeding to step S209, the ECU 40 may proceed to step S213 and set the fuel cut prohibition flag to OFF.

  As described above, according to the present embodiment, even when the ash accumulated on the filter 32 needs to be contracted, the fuel cut prohibition flag is set to ON when the target PM accumulation amount Mpmt is not accumulated. Is done. Thus, the fuel cut is prohibited until the PM accumulation amount reaches the target PM accumulation amount Mpmt. Therefore, even if the internal combustion engine 10 decelerates, the fuel cut is not executed. Thereafter, after PM has further accumulated and accumulated to the target PM accumulation amount Mpmt, the fuel cut is permitted by setting the fuel cut prohibition flag to OFF. Thereby, when the internal combustion engine 10 is decelerated, the fuel cut is executed and the accumulated PM is oxidized, so that the ash accumulated on the filter 32 is contracted by the oxidation heat. That is, according to the present embodiment, when it is necessary to shrink the ash, the fuel cut is limited until the PM of the target PM deposition amount Mpmt is deposited, and the PM of the target PM deposition amount Mpmt is deposited. Thus, the fuel cut is performed and the regeneration process is executed. As a result, it is possible to effectively reduce the pressure loss of the filter 32 while suppressing an increase in fuel consumption.

  Further, according to this embodiment, when the ash needs to be contracted, the fuel cut is performed when the filter temperature is lower than the reproducible temperature Tlo even before PM of the target PM deposition amount Mpmt is deposited. Is executed. Thereby, since the frequency of fuel cut execution increases, it becomes possible to further reduce the fuel consumption of the internal combustion engine 10.

  As described above, in this embodiment, the flow shown in FIG. 3 and the flow shown in FIG. 4 are executed independently of each other, and the fuel cut prohibition flag set in advance by the flow shown in FIG. Is referred to in step S102 of the flow shown in FIG. However, the execution mode of both flows is not limited to this. For example, the flow shown in FIG. 4 may be executed in step S102 of the flow shown in FIG. That is, when the internal combustion engine 10 is decelerated (step S101: Yes), the ECU 40 may determine whether or not to execute fuel cut by executing the flow shown in FIG. 4 in step S102.

[Example 2]
The first embodiment described above is an example when the exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to the internal combustion engine 10 which is a spark ignition type internal combustion engine, but the exhaust gas purification apparatus for an internal combustion engine according to the present invention. Can also be applied to an internal combustion engine (including an internal combustion engine other than a spark ignition type internal combustion engine) that includes a fuel addition unit that adds fuel to the exhaust gas flowing into the filter. Hereinafter, Embodiment 2 which is an example when the exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a compression ignition type internal combustion engine having a fuel addition portion will be described. In addition, about the structure similar to the structure of said Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  FIG. 10 is a diagram illustrating a schematic configuration of an exhaust gas purification apparatus for an internal combustion engine according to the present embodiment. An internal combustion engine 110 that is a compression ignition internal combustion engine mounted on a vehicle is a vehicle diesel engine having a plurality of cylinders 111. The cylinder 111 is provided with a fuel injection valve 112 that injects fuel into a combustion chamber provided in the upper part of the cylinder 111. Further, in the intake passage 120 and the exhaust passage 130 connected to the combustion chamber of the cylinder 111, those having the same functions as those of the sensor and device provided in the internal combustion engine 10 of the first embodiment are arranged. The exhaust passage 130 is provided with a filter 132 that collects PM in the exhaust, and a catalyst 131 having an oxidation function provided upstream of the filter 132. The catalyst 131 is a catalyst that purifies the exhaust gas by oxidizing unburned fuel and carbon monoxide. The filter 132 is a wall flow type filter formed of, for example, a porous substrate made of silicon carbide (SiC).

  A fuel addition valve 37 that adds fuel to the exhaust gas flowing into the catalyst 131 is provided in the exhaust passage 130 upstream of the catalyst 131. The internal combustion engine 110 is also provided with an ECU 140 for controlling the internal combustion engine 110. The ECU 140 controls each electrically connected device. Further, the above-described sensors and the like are electrically connected to ECU 140, and output signals from these are input to ECU 140.

  Also in the present embodiment, PM contained in the exhaust discharged from the internal combustion engine 110 accumulates on the filter 132. Generally, the exhaust temperature discharged from a diesel engine is lower than the exhaust temperature discharged from a gasoline engine. Therefore, in this embodiment, when the PM deposited on the filter 132 is oxidized, a regeneration process (forced regeneration process) is performed to forcibly raise the temperature of the filter 132 to a temperature at which PM is oxidized. In this forced regeneration process, the ECU 140 adds fuel to the exhaust gas flowing into the catalyst 131 through the fuel addition valve 37. The added fuel is oxidized in the catalyst 131 and generates heat, so that the temperature of the exhaust gas flowing out from the catalyst 131 rises. As a result, since the heated exhaust gas flows into the filter 132, the temperature of the filter 132 can be raised to a predetermined temperature range (for example, about 400 ° C. to about 500 ° C.) in which PM is oxidized. In the present embodiment, the ECU 140 that executes the regeneration process corresponds to the control unit in the present invention. Hereinafter, the regeneration process for raising the filter temperature to the predetermined temperature range is referred to as “normal regeneration process”.

  Here, the exhaust discharged from the internal combustion engine 110 may contain ash derived from components of additives contained in the lubricating oil, sulfur contained in the fuel, and the like, and thus ash accumulates on the filter 132. To do. Note that the contraction characteristic of ash discharged from the internal combustion engine 110 is the same as the contraction characteristic shown in FIG. Therefore, also in this embodiment, when it is necessary to shrink the ash, the “ash shrinking process” which is a reproduction process different from the normal reproduction process is executed. Specifically, the fuel is not added to the exhaust gas until the predetermined amount of PM necessary for raising the filter temperature to the predetermined temperature at which the ash contracts is accumulated, and the predetermined amount of PM is accumulated. Then, fuel addition was executed.

  Next, the reproduction processing according to the present embodiment will be specifically described with reference to the drawings. First, the flow of normal reproduction processing will be described with reference to FIG. The flow shown in FIG. 11 is executed by executing a control program stored in the ECU 140 every predetermined time.

In step S301, the ECU 140 determines that the PM accumulation amount PM during execution of this flow is equal to or greater than the threshold accumulation amount Mth that is the PM accumulation amount set to determine whether or not the normal regeneration process can be performed. It is determined whether or not. This threshold deposition amount Mth is a predetermined amount set sufficiently low to suppress excessive deposition of PM and excessive temperature rise during the regeneration process, and the temperature of the filter 132 reaches the target temperature Tt at which the ash contracts. This is an amount smaller than the target PM deposition amount Mpmt, which is the PM deposition amount necessary for the increase. In this embodiment, this threshold deposition amount Mth corresponds to the second predetermined amount in the present invention. If a negative determination is made in this step, it means that PM is not deposited on the filter 132 to the extent that it needs to be removed by the regeneration process, and thus this flow ends. On the other hand, when an affirmative determination is made in this flow, the ECU 140 proceeds to step S302 and executes fuel addition from the fuel addition valve 37. As a result, the temperature of the filter 132 rises to the predetermined temperature range described above, so that PM deposited on the filter 132 is removed by oxidation. The ECU 140 controls the amount of addition from the fuel addition valve 37 so that the filter temperature changes in the predetermined temperature range. Further, fuel may be supplied to the catalyst 131 by post injection by the fuel injection valve 112 instead of the fuel addition valve 37.

  Next, the flow of the ash contraction process will be described with reference to FIG. The flow shown in FIG. 12 is executed by executing a control program stored in ECU 140 every predetermined time. In this flow, processing similar to the processing from step S201 to S206 in the flow shown in FIG. 4 is performed. Therefore, these steps are denoted by the same step numbers and description thereof is omitted as appropriate.

  If an affirmative determination is made in step S202, ECU 140 determines that ash contraction processing is necessary, and executes steps S203 to S206 to calculate target PM accumulation amount Mpmt. When step S206 ends, the ECU 140 proceeds to step S401, and determines whether or not the PM accumulation amount Mpm at the time of execution of this flow is equal to or greater than the calculated target PM accumulation amount Mpmt. In the present embodiment, this target PM deposition amount Mpmt corresponds to a predetermined amount in the present invention. If a negative determination is made in this step, it means that the amount of PM necessary to raise the filter temperature to a predetermined temperature at which the ash contracts is not accumulated on the filter 132, and thus this flow is ended. Is done. On the other hand, if an affirmative determination is made in this flow, the ECU 140 proceeds to step S402 and executes fuel addition from the fuel addition valve 37. That is, in this embodiment, fuel addition from the fuel addition valve 37 is executed when the PM accumulation amount Mpm is equal to or more than the target PM accumulation amount Mpmt instead of the threshold accumulation amount Mth. As a result, the filter temperature rises to the target temperature Tt by the oxidation heat generated from the oxidized PM, so that the ash deposited on the filter can be contracted to the contraction rate α. As a result, the pressure loss of the filter 132 can be reduced to the target pressure loss Pt. If an affirmative determination is made in step S202, it is not necessary to execute the ash contraction process, so the process proceeds to step S403 and the above-described normal reproduction process is executed.

  As described above, according to the present embodiment, when the ash deposited on the filter 132 needs to be contracted, the PM deposition amount Mpm exceeds the threshold deposition amount Mth until the target PM deposition amount Mpmt is reached. Fuel addition to the catalyst 131 is limited. As a result, it is possible to effectively reduce the pressure loss of the filter 132 by contracting the accumulated ash while suppressing an increase in fuel consumption.

10, 110 Internal combustion engine 31, 131 Catalyst 32, 132 Filter 40, 140 ECU

Claims (6)

A filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
A first deposition amount acquisition unit for acquiring a deposition amount of particulate matter deposited on the filter;
A second accumulation amount acquisition unit for acquiring an accumulation amount of the non-combustible material accumulated on the filter;
A control unit that executes a regeneration process for oxidizing the particulate matter deposited on the filter, and when the accumulation amount of the incombustible substance acquired by the second accumulation amount acquisition unit is equal to or greater than a threshold amount, 1 The amount of particulate matter deposited acquired by the deposit amount acquisition unit has reached a predetermined amount that raises the temperature of the filter to a predetermined temperature at which the deposited incombustible material contracts by oxidation heat generated by the regeneration process. And a control unit for executing the reproduction process;
An exhaust purification device for an internal combustion engine, comprising:   The said 2nd accumulation amount acquisition part acquires the accumulation amount of the nonflammable substance accumulated on the said filter based on the differential pressure before and after the said filter immediately after the said regeneration process was performed by the said control part. An exhaust gas purification apparatus for an internal combustion engine as described.   A predetermined amount acquisition unit for acquiring the predetermined amount based on the accumulation amount of the non-combustible substance acquired by the second accumulation amount acquisition unit and a difference between the predetermined temperature and the actual temperature of the non-combustible substance; The exhaust emission control device for an internal combustion engine according to claim 1, further comprising: The internal combustion engine is a spark ignition type internal combustion engine capable of combustion at a stoichiometric air-fuel ratio, and the control unit executes the fuel supply stop of the internal combustion engine during deceleration operation of the internal combustion engine, thereby regenerating the regeneration Execute the process,
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3. When the accumulation amount of the incombustible substance is equal to or greater than the threshold amount, the control unit may cause an oxidation reaction due to the regeneration process even if the accumulation amount of the particulate matter is less than the predetermined amount. When the temperature is lower than the second predetermined temperature that does not occur, the fuel supply stop of the internal combustion engine is executed during the deceleration operation of the internal combustion engine.
The exhaust emission control device for an internal combustion engine according to claim 4. The internal combustion engine is a compression ignition type internal combustion engine having an oxidation catalyst provided upstream of the filter in the exhaust passage, and a fuel addition portion for adding fuel to the exhaust gas flowing into the oxidation catalyst. And
The control unit performs the regeneration process by adding fuel by the fuel addition unit when the amount of the particulate matter deposited on the filter is equal to or greater than a second predetermined amount that is less than the predetermined amount. To execute,
When the accumulation amount of the non-combustible substance is equal to or greater than the threshold amount, the control unit may change the fuel addition unit when the accumulation amount of the particulate matter is equal to or greater than the predetermined amount instead of the second predetermined amount. Performing the regeneration process by adding fuel by
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3.

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