JP2008101548A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of suppressing discharge of added fuel to the outside and efficiently utilizing added fuel, in an exhaust emission control device performing regeneration control including fuel addition on a further upstream side of an exhaust emission converting means. <P>SOLUTION: This exhaust emission control device for an internal combustion engine is provided with the exhaust emission converting means arranged in an exhaust passage, and a regeneration control executing means for executing the regeneration control for the exhaust emission converting means, including the fuel addition into exhaust gas on the further upstream side of the exhaust emission converting means. The regeneration control executing means does not add fuel (step 103) when, under a condition where fuel is not added, an air-fuel ratio of exhaust gas led to flow into the exhaust emission converting means is lower than a previously set reference exhaust air-fuel ratio and it is determined that a difference therebetween exceeds a range where a previously set fuel addition is possible. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  Generally, in-cylinder injection type internal combustion engines mounted on automobiles, for example, diesel engines, are required to remove nitrogen oxides (NOx) contained in exhaust gas. In response to such a demand, an exhaust purification device in which a NOx storage reduction catalyst is provided in an exhaust passage of an internal combustion engine is known. Such a NOx occlusion reduction catalyst occludes NOx contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, the oxygen concentration in the inflowing exhaust gas is reduced, and hydrocarbons ( If a reducing agent such as HC) or carbon monoxide (CO) is present, it has the action of removing the stored NOx and reducing and purifying it.

  In the NOx occlusion reduction catalyst as described above, the purification performance deteriorates as the amount of occluded NOx increases. Conventionally, when such an NOx occlusion reduction catalyst is used, it has been used for a certain period of time. When the purification performance of the NOx storage reduction catalyst is reduced or before it is reduced, the NOx stored in the NOx storage reduction catalyst is released and reduced and purified by adding fuel as a reducing agent upstream of the NOx storage reduction catalyst. (Hereinafter referred to as “NOx reduction process”).

  It is also known that sulfur poisoning (SOx) in the exhaust gas is occluded in the NOx occlusion reduction catalyst as described above, which causes so-called sulfur poisoning that deteriorates purification performance. In order to solve this problem, fuel may be added on the upstream side of the NOx occlusion reduction catalyst as in the case of the NOx reduction process (hereinafter referred to as “sulfur poisoning recovery process”).

  Also known is an exhaust purification device in which a particulate filter (hereinafter referred to as “filter”) is provided in the exhaust passage of the internal combustion engine in order to collect exhaust particulates contained in the exhaust gas of the internal combustion engine. Yes. In such a filter, if the amount of collected exhaust particulates increases, the back pressure in the exhaust system increases due to clogging of the filter and the engine performance decreases, so the collected exhaust particulates are removed by oxidation. (Hereinafter referred to as “filter regeneration processing”). And in order to perform the said filter regeneration process, a fuel may be added in the upstream of a filter.

  In addition, as a method of adding fuel in the NOx reduction treatment, sulfur poisoning recovery treatment, and filter regeneration treatment (hereinafter referred to as “NOx reduction treatment”), the fuel is added more than the NOx occlusion reduction catalyst or filter in the exhaust passage. There are a method of adding a fuel addition valve on the upstream side and adding fuel from the addition valve, a method of injecting fuel into the cylinder during the exhaust stroke of each cylinder of the internal combustion engine (so-called post injection method), and the like.

  By the way, in the above NOx reduction treatment or the like, it is preferable that the added fuel is smoothly transported to the downstream side without adhering to the exhaust manifold wall surface or flowing backward. For this reason, for example, in Patent Document 1, fuel is supplied from the fuel addition valve only in a period in which the exhaust flow rate of exhaust from a predetermined cylinder is larger than the exhaust flow rate of exhaust from other cylinders. An exhaust purification system is disclosed in which the added fuel is smoothly conveyed downstream.

JP 2006-22788 A Japanese Patent Laid-Open No. 11-81994 JP 2001-41091 A JP-A-11-141370 Japanese Patent Laid-Open No. 2005-232991 JP 2005-180290 A

  On the other hand, for example, when the intake air amount is smaller than the target intake air amount due to a response delay of the intake air amount during acceleration, and the combustion air-fuel ratio that is the air-fuel ratio in the combustion chamber is richer than the target air-fuel ratio, etc. If the addition of fuel for the NOx reduction process or the like is performed when the air-fuel ratio of the exhaust gas is rich, an excessive amount of fuel that cannot be sufficiently oxidized is supplied to the exhaust gas as a result. There is a case. In such a case, the added fuel, hydrocarbon (HC), passes through the catalyst and is discharged to the outside, so that the added fuel cannot be used efficiently and white smoke. May occur.

  The present invention has been made in view of such a problem, and an object of the present invention is to release the added fuel to the outside in an exhaust gas purification apparatus to which fuel is added for the NOx reduction treatment or the like. It is an object of the present invention to provide an exhaust emission control device that can suppress and efficiently use added fuel.

  The present invention provides an exhaust emission control device for an internal combustion engine described in each claim of the claims as means for solving the above-mentioned problems.

  According to a first aspect of the present invention, there is provided an exhaust purification means disposed in an exhaust passage, and a regeneration control execution means for performing regeneration control of the exhaust purification means including adding fuel to exhaust gas upstream of the exhaust purification means. In the exhaust gas purification apparatus for an internal combustion engine, the regeneration control execution means is configured such that the air-fuel ratio of the exhaust gas flowing into the exhaust purification means in a state where the addition of the fuel is not performed is greater than a predetermined reference exhaust air-fuel ratio. An exhaust purification device for an internal combustion engine is provided in which the addition of the fuel is not performed when it is determined that the difference is beyond a range in which the predetermined fuel addition is possible.

  As described above, in the first invention, it is determined that the air-fuel ratio of the exhaust gas flowing into the exhaust purification means is smaller than a predetermined reference exhaust air-fuel ratio, and the difference exceeds a predetermined fuel addition range. Sometimes the fuel is not added. In this way, by appropriately setting the reference exhaust air-fuel ratio and the fuel addition possible range, it is possible to suppress excessive fuel from being supplied into the exhaust gas as the regeneration control is performed. As a result, release of the added fuel to the outside can be suppressed, and the added fuel can be used efficiently.

  The exhaust purification means is, for example, a NOx storage reduction catalyst or a particulate filter, and the regeneration control is, for example, the above-described NOx reduction processing, sulfur poisoning recovery processing, filter regeneration processing, or the like. In the present application, the air-fuel ratio or the exhaust air-fuel ratio of the exhaust gas is the ratio of air and fuel supplied to the exhaust passage, combustion chamber, intake passage, or the like upstream of the exhaust purification means.

  In the second invention, in the first invention, when the actual intake air amount is smaller than the target intake air amount and the difference is larger than the predetermined intake air amount difference, or the actual intake air amount relative to the target intake air amount is When the ratio is smaller than a predetermined intake air amount ratio, the regeneration control execution means does not add the fuel.

  That is, in the second invention, when the actual intake air amount is smaller than the target intake air amount and the difference is larger than the predetermined intake air amount difference, or the ratio of the actual intake air amount to the target intake air amount is When the intake air amount ratio is smaller than the predetermined intake air amount ratio, it is determined that the air-fuel ratio of the exhaust gas flowing into the exhaust purification means is smaller than the reference exhaust air-fuel ratio and the difference exceeds the fuel addition possible range, and the regeneration control execution means is It can be said that the fuel is not added.

  When the actual intake air amount is smaller than the target intake air amount, or when the ratio of the actual intake air amount to the target intake air amount becomes small, the air-fuel ratio of the exhaust gas flowing into the exhaust purification means becomes rich. Therefore, according to the second aspect of the present invention, by appropriately setting the predetermined intake air amount difference and the predetermined intake air amount ratio, the exhaust gas is discharged along with the regeneration control. It is possible to suppress supply of excess fuel into the gas, and as a result, it is possible to efficiently use the added fuel while suppressing the release of the added fuel to the outside.

  In the third invention, in the first or second invention, when the actual combustion air-fuel ratio is smaller than the target combustion air-fuel ratio and the difference is larger than a predetermined air-fuel ratio difference, or the actual combustion air-fuel ratio with respect to the target combustion air-fuel ratio. When the ratio of the fuel ratio is smaller than the predetermined air-fuel ratio, the regeneration control execution means does not add the fuel.

  That is, in the third invention, when the actual combustion air-fuel ratio is smaller than the target combustion air-fuel ratio and the difference is larger than the predetermined air-fuel ratio difference, or the ratio of the actual combustion air-fuel ratio to the target combustion air-fuel ratio is predetermined. When the air-fuel ratio is smaller than that, it is determined that the air-fuel ratio of the exhaust gas flowing into the exhaust purification means is smaller than the reference exhaust air-fuel ratio and the difference exceeds the fuel addition possible range, and the regeneration control execution means It can be said that the addition of is not carried out.

  When the actual combustion air-fuel ratio is smaller than the target combustion air-fuel ratio, or when the ratio of the actual combustion air-fuel ratio to the target combustion air-fuel ratio becomes small, the air-fuel ratio of the exhaust gas flowing into the exhaust purification means becomes rich. Therefore, according to the third aspect of the present invention, by appropriately setting the predetermined air-fuel ratio difference and the predetermined air-fuel ratio, the exhaust gas is contained in the exhaust gas as the regeneration control is performed. As a result, it is possible to suppress the release of the added fuel to the outside and to efficiently use the added fuel.

  In the fourth invention, in any one of the first to third inventions, the exhaust gas is recirculated, and the EGR rate that is the ratio of the exhaust gas amount to the total gas amount sucked into the cylinder is controlled. An exhaust gas purification apparatus for an internal combustion engine, wherein an actual EGR rate is larger than a target EGR rate, and the difference is larger than a predetermined EGR rate difference, or a ratio of an actual EGR rate to a target EGR rate is predetermined EGR When the ratio is larger than the ratio, the regeneration control execution means does not add the fuel.

  That is, in the fourth invention, when the actual EGR rate is larger than the target EGR rate and the difference is larger than the difference between the predetermined EGR rates, or the ratio of the actual EGR rate to the target EGR rate is the predetermined EGR rate. When the ratio is greater than the ratio, it is determined that the air-fuel ratio of the exhaust gas flowing into the exhaust purification unit is smaller than the reference exhaust air-fuel ratio and the difference exceeds the fuel addition possible range, and the regeneration control execution unit performs the fuel addition. It can be said that it is not implemented.

  When the actual EGR rate is larger than the target EGR rate, or when the ratio of the actual EGR rate to the target EGR rate becomes large, the air-fuel ratio of the exhaust gas flowing into the exhaust purification means tends to be rich. Therefore, according to the fourth aspect of the present invention, by appropriately setting the difference in the predetermined EGR rate and the ratio of the predetermined EGR rate, excess exhaust gas is contained in the exhaust gas as the regeneration control is performed. As a result, it is possible to suppress the release of the added fuel to the outside and to efficiently use the added fuel.

  In the fifth invention, in any one of the first to fourth inventions, when the accelerator opening increase amount per unit time is larger than the predetermined accelerator opening increase amount, the regeneration control execution means adds the fuel. It is not implemented.

  That is, in the fifth aspect, when the accelerator opening increase amount per unit time is larger than the predetermined accelerator opening increase amount, the air-fuel ratio of the exhaust gas flowing into the exhaust purification means is smaller than the reference exhaust air-fuel ratio. It is determined that the difference exceeds the fuel addition possible range, and it can be said that the regeneration control execution unit does not add the fuel.

  In general, when the accelerator opening increases sharply, the combustion air-fuel ratio tends to become rich due to a response delay of the intake air amount, and as a result, the air-fuel ratio of the exhaust gas flowing into the exhaust purification means is reduced. This is when it tends to be rich. Therefore, according to the fifth aspect, by appropriately setting the predetermined accelerator opening increase amount, it is possible to suppress excessive fuel from being supplied into the exhaust gas when the regeneration control is performed. As a result, it is possible to efficiently use the added fuel while suppressing the release of the added fuel to the outside.

  In the sixth aspect of the invention, in any one of the first to fifth aspects of the invention, when the increase amount of the target in-cylinder fuel injection amount per unit time is larger than the predetermined increase amount of the target in-cylinder fuel injection amount, the regeneration control is performed. The implementation means does not perform the addition of the fuel.

  That is, in the sixth aspect, when the increase amount of the target in-cylinder fuel injection amount per unit time is larger than the predetermined increase amount of the target in-cylinder fuel injection amount, the air-fuel ratio of the exhaust gas flowing into the exhaust purification means is It is determined that the difference is smaller than the reference exhaust air-fuel ratio and exceeds the fuel addition possible range, and it can be said that the regeneration control execution means does not add the fuel.

  Generally, when the target in-cylinder fuel injection amount suddenly increases, the combustion air-fuel ratio tends to become rich due to a response delay of the intake air amount, and as a result, the exhaust gas flowing into the exhaust purification means This is when the air-fuel ratio tends to be rich. Therefore, according to the sixth aspect, by appropriately setting the predetermined increase amount of the target in-cylinder fuel injection amount, excess fuel is supplied into the exhaust gas as the regeneration control is performed. As a result, it is possible to efficiently use the added fuel while suppressing the release of the added fuel to the outside.

  In the seventh invention, in any one of the first to sixth inventions, when the increase amount of the target intake air amount per unit time is larger than the predetermined increase amount of the target intake air amount, the regeneration control execution means is The fuel is not added.

  That is, according to the seventh aspect, when the increase amount of the target intake air amount per unit time is larger than the predetermined increase amount of the target intake air amount, the air-fuel ratio of the exhaust gas flowing into the exhaust purification means is the reference exhaust air amount. It is determined that the difference is smaller than the fuel ratio and exceeds the fuel addition possible range, and it can be said that the regeneration control execution unit does not add the fuel. In general, when the target intake air amount suddenly increases, the combustion air-fuel ratio tends to become rich due to a response delay of the actual intake air amount, and as a result, the exhaust gas flowing into the exhaust purification means This is when the air-fuel ratio tends to be rich. Therefore, according to the seventh aspect, by appropriately setting the predetermined increase amount of the target intake air amount, it is possible to suppress excessive fuel from being supplied into the exhaust gas when the regeneration control is performed. As a result, it is possible to efficiently use the added fuel while suppressing the release of the added fuel to the outside.

  The invention described in each claim suppresses the release of the added fuel to the outside and efficiently uses the added fuel in the exhaust gas purification apparatus to which fuel is added for the regeneration control. The common effect of providing an exhaust emission control device that can be used is provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a view for explaining a case where the present invention is applied to a compression ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively.

  The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 through the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 8. A throttle valve 9 driven by a step motor is 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. An air flow meter 21 for measuring the intake air amount is provided between the compressor 7a and the air cleaner 8.

  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 storage reduction catalyst 11. A temperature sensor 20 for detecting the temperature of the NOx storage reduction catalyst 11 is attached to the NOx storage reduction catalyst 11. A fuel addition valve 13 for adding fuel as a reducing agent to the exhaust gas flowing through the exhaust manifold 5 is disposed at the outlet of the collecting portion of the exhaust manifold 5.

  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 embodiment shown in FIG. 1, the engine cooling water is guided into the EGR cooler 16, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a fuel reservoir, so-called common rail 18 via a fuel supply pipe 17. Fuel is supplied into the common rail 18 from an electronically controlled fuel pump 19 with variable discharge amount, and the fuel supplied into the common rail 18 is supplied to the fuel injection valve 3 via each fuel supply pipe 17.

  The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an output port 36. It comprises. Output signals from the temperature sensor 20 and the air flow meter 21 are input to the input port 35 via the corresponding AD converters 37. A load sensor 41 that generates an output voltage proportional to the accelerator opening 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. 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 driving step motor, the fuel addition valve 13, the EGR control valve 15, and the fuel pump 19 through corresponding drive circuits 38.

  As described above, the electronic control unit 30 is connected to various sensors and operating devices provided for controlling the internal combustion engine, and performs various controls necessary for the operation of the internal combustion engine by exchanging signals with them. It is supposed to be.

  By the way, the NOx occlusion reduction catalyst 11 used in the present embodiment is a known one, and when the air-fuel ratio of the inflowing exhaust gas is lean, the NOx contained in the exhaust gas is occluded and in the inflowing exhaust gas. If the oxygen concentration in the exhaust gas is reduced and a reducing agent such as HC or CO is present in the exhaust gas, the stored NOx is released and reduced and purified. In such a NOx occlusion reduction catalyst, the purification performance deteriorates as the amount of occluded NOx increases. Conventionally, when such an NOx occlusion reduction catalyst is used, the NOx occlusion reduction catalyst is used for a certain period of time. When the purification performance of the NOx storage reduction catalyst decreases, fuel is added on the upstream side of the NOx storage reduction catalyst, for example, so that NOx stored in the NOx storage reduction catalyst is released to perform NOx reduction treatment for reduction purification. ing.

  In this embodiment, such a NOx reduction process is performed, but the above NOx reduction process is simply performed in response to a NOx reduction process request accompanying a decrease in the purification performance of the NOx storage reduction catalyst. May cause inconvenience. That is, for example, when the intake air amount is smaller than the target intake air amount due to a response delay of the intake air amount during acceleration, and the combustion air-fuel ratio that is the air-fuel ratio in the combustion chamber is richer than the target air-fuel ratio, etc. If fuel addition for the NOx reduction process is performed when the air-fuel ratio of the exhaust gas is rich, as a result, excessive fuel may be supplied as a reducing agent in the exhaust gas. In such a case, the added fuel, HC, is discharged outside through the NOx storage reduction catalyst, and the added fuel cannot be used efficiently and white smoke is generated. There is also a risk of it.

  Therefore, in the present embodiment, in consideration of such a situation, control as described below is performed to suppress excessive fuel from being supplied into the exhaust gas as the NOx reduction process is performed, Release of the added fuel to the outside is suppressed so that the added fuel can be used efficiently. In other words, this control means that the air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction catalyst 11 is smaller than a predetermined reference exhaust air-fuel ratio when fuel is not added from the fuel addition valve 13. When it is determined that the specified fuel addition exceeds the possible range, the fuel addition is not performed even if the NOx reduction treatment is requested.

  Here, the reference exhaust air-fuel ratio is the air-fuel ratio of the exhaust gas assumed when fuel is added, and the NOx reduction process is performed assuming that the air-fuel ratio of the exhaust gas is the reference exhaust air-fuel ratio. The amount of fuel added is determined. The range in which the fuel can be added is determined in advance in consideration of, for example, suppression of release of the added fuel to the outside and efficient use.

  According to the control as described above, by appropriately setting the reference exhaust air-fuel ratio and the fuel addition possible range, excess fuel is supplied to the exhaust gas as the NOx reduction process is performed. Can be suppressed. As a result, release of the added fuel to the outside can be suppressed, and the added fuel can be used efficiently.

  With regard to the control as described above, it is determined whether or not the air-fuel ratio of the exhaust gas actually flowing into the NOx storage reduction catalyst 11 is smaller than the reference exhaust air-fuel ratio and the difference exceeds the fuel addition range. Specifically, it is possible by various methods.

  Hereinafter, an example of a specific method for realizing the above control will be described with reference to FIG. FIG. 2 is a flowchart showing a control routine for carrying out the control as described above. This control routine is executed by the electronic control unit 30 by interruption every predetermined time. When this control routine starts, first, at step 101, it is determined whether or not there is a request for NOx reduction processing for the NOx storage reduction catalyst 11. If it is determined in step 101 that there is no request for NOx reduction processing, the present control routine ends. If it is determined that there is a request for NOx reduction processing, the routine proceeds to step 102.

  In step 102, it is determined whether or not the ratio (Qar / Qat) of the actual intake air amount Qar to the target intake air amount Qat is smaller than a predetermined intake air amount ratio Rca. In the present embodiment, the target intake air amount Qat is set according to a required engine operating state such as a required torque determined based on the accelerator opening and the engine speed, and the actual intake air amount Qar is an air flow. It is measured by the meter 21.

  The intake air amount ratio Rca is used as a reference for determining whether the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 11 is smaller than the reference exhaust air-fuel ratio and the difference exceeds the fuel addition range. This value is set in advance and is set in advance in consideration of the suppression of the release of added fuel to the outside and the utilization of efficiency, for example, 0.7 (ie, 70%).

  If it is determined in step 102 that the ratio of the actual intake air amount Qar to the target intake air amount Qat is smaller than the intake air amount ratio Rca, the process proceeds to step 103 where fuel addition from the fuel addition valve 13 is performed. This control routine is terminated with the prohibition. On the other hand, if it is determined in step 102 that the ratio of the actual intake air amount Qar to the target intake air amount Qat is greater than or equal to the intake air amount ratio Rca, the process proceeds to step 104.

  In step 104, it is determined whether or not fuel addition from the fuel addition valve 13 is prohibited during the previous execution of the control routine. If it is determined in step 104 that fuel addition from the fuel addition valve 13 is prohibited during the previous execution of the control routine, the process proceeds to step 105. When the routine proceeds to step 105, fuel addition from the fuel addition valve 13 is delayed by a predetermined time (for example, 500 ms), and this control routine ends.

  On the other hand, if it is determined in step 104 that fuel addition from the fuel addition valve 13 is not prohibited during the previous execution of the control routine, the routine proceeds to step 106. When the routine proceeds to step 106, the fuel addition from the fuel addition valve 13 is immediately performed, and this control routine ends.

  As described above, in the present embodiment, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 11 when the ratio of the actual intake air amount Qar to the target intake air amount Qat is smaller than the predetermined intake air amount ratio Rca. Is smaller than the reference exhaust air-fuel ratio, and the difference exceeds the fuel addition possible range, so that the fuel addition is not performed even when the NOx reduction treatment is required. When the ratio of the actual intake air amount Qar to the target intake air amount Qat is small, it can be said that the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst 11 tends to become rich. According to the above, by appropriately setting the intake air amount ratio Rca, it is possible to suppress excessive fuel from being supplied into the exhaust gas as the NOx reduction process is performed. The added fuel can be efficiently used while suppressing the release of the added fuel to the outside.

  Note that the determination in step 102 may be performed based on the difference between the actual intake air amount Qar and the target intake air amount Qat. That is, in this case, it is determined whether or not the actual intake air amount Qar is smaller than the target intake air amount and the difference is larger than a predetermined intake air amount difference ΔQca. That is, in this case, the intake air amount difference ΔQca is a value set as a determination criterion, similar to the above-described intake air amount ratio Rca, and taking into consideration the suppression of release of added fuel to the outside and efficient use. Predetermined. If it is determined that the actual intake air amount Qar is less than the target intake air amount Qat and the difference is greater than the predetermined intake air amount difference ΔQca, the process proceeds to step 103. Otherwise, the process proceeds to step 104. Like that.

  That is, in this case, when the actual intake air amount Qar is less than the target intake air amount Qat and the difference is larger than the predetermined intake air amount difference ΔQca, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 11 Is smaller than the reference exhaust air-fuel ratio, and the difference exceeds the fuel addition possible range, so that the fuel addition is not performed even if the NOx reduction treatment is required.

  Even when the actual intake air amount is smaller than the target intake air amount, it can be said that the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst 11 tends to become rich. As a result of the NOx reduction treatment, it is possible to suppress the supply of excess fuel into the exhaust gas, and as a result, the added fuel can be efficiently suppressed by suppressing the release of the added fuel to the outside. Can be used.

  Further, the determination in step 102 may be performed based on the difference between the actual combustion air-fuel ratio and the target combustion air-fuel ratio or the ratio of the actual combustion air-fuel ratio to the target combustion air-fuel ratio. That is, in this case, whether or not the actual combustion air-fuel ratio is smaller than the target combustion air-fuel ratio and the difference is larger than the predetermined air-fuel ratio difference ΔAFc, or the ratio of the actual combustion air-fuel ratio to the target combustion air-fuel ratio is It is determined whether or not the air-fuel ratio Rcaf is smaller than a predetermined value. Here, the target combustion air-fuel ratio is set according to the required engine operation state such as required torque, and the actual combustion air-fuel ratio is the fuel injection amount and the intake air amount measured by the air flow meter 21. And can be calculated based on the above.

  In this case, the air-fuel ratio difference ΔAFc and the air-fuel ratio Rcaf are values set as determination criteria, similar to the above-described intake air amount difference ΔQca and intake air amount ratio Rca. It is determined in advance in consideration of emission control and efficiency utilization. When it is determined that the actual combustion air-fuel ratio is smaller than the target combustion air-fuel ratio and the difference is greater than the predetermined air-fuel ratio difference ΔAFc, or the ratio of the actual combustion air-fuel ratio to the target combustion air-fuel ratio is predetermined. If it is determined that the ratio is smaller than the fuel ratio Rcaf, the process proceeds to step 103, and if not, the process proceeds to step 104.

  That is, in this case, when the actual combustion air-fuel ratio is smaller than the target combustion air-fuel ratio and the difference is larger than the predetermined air-fuel ratio difference ΔAFc, or the ratio of the actual combustion air-fuel ratio to the target combustion air-fuel ratio is predetermined. When the air-fuel ratio Rcaf is smaller, it is determined that the air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction catalyst 11 is smaller than the reference exhaust air-fuel ratio and the difference exceeds the fuel addition range, and the NOx reduction process is performed. Even if requested, the fuel is not added.

  When the actual combustion air-fuel ratio is smaller than the target combustion air-fuel ratio, or when the ratio of the actual combustion air-fuel ratio to the target combustion air-fuel ratio is small, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 11 is Since it can be said that it is a time when there is a tendency to become rich, even in this case, it is possible to suppress excessive fuel from being supplied into the exhaust gas with the execution of the NOx reduction treatment, and as a result, The added fuel can be efficiently used while suppressing the release of the added fuel to the outside.

  In the internal combustion engine of the above-described embodiment, the exhaust gas is recirculated, and the EGR rate (that is, the EGR rate) that is the ratio of the exhaust gas amount to the total gas amount sucked into the cylinder according to the engine operating state = Intake Exhaust Gas Amount / (Intake Exhaust Gas Amount + Intake Air Amount)) is controlled. In such a case, the determination in step 102 is made based on the actual EGR rate and the target EGR rate. And the ratio of the actual EGR rate to the target EGR rate may be used as a reference.

  That is, in this case, whether or not the actual EGR rate is larger than the target EGR rate and the difference is larger than a predetermined EGR rate difference ΔRceg, or the ratio of the actual EGR rate to the target EGR rate is predetermined EGR. It is determined whether the rate ratio Rcreg is greater. Here, the target EGR rate is set according to the required engine operating state such as required torque, and the actual EGR rate is obtained by, for example, obtaining the pressure and temperature of the gas in the intake manifold 4. Can be calculated on the basis of the intake manifold gas amount Qgin calculated based on the intake air amount Qar and the intake air amount Qar measured by the air flow meter 21 (that is, actual EGR rate = (Qgin−Qar) / Qgin).

  Further, in this case, the EGR rate difference ΔRceg and the EGR rate ratio Rcreg are values set as determination criteria and added as in the above-described intake air amount difference ΔQca and intake air amount ratio Rca. It is determined in advance in consideration of suppression of fuel release to the outside and efficient use. Then, when it is determined that the actual EGR rate is larger than the target EGR rate and the difference is larger than the predetermined EGR rate difference ΔRceg, or the ratio of the actual EGR rate to the target EGR rate is the ratio of the predetermined EGR rate If it is determined that the value is larger than Rcreg, the process proceeds to step 103, and if not, the process proceeds to step 104.

  That is, in this case, when the actual EGR rate is larger than the target EGR rate and the difference is larger than the predetermined EGR rate difference ΔRceg, or the ratio of the actual EGR rate to the target EGR rate is the predetermined EGR rate. When the ratio Rcreg is larger, it is determined that the air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction catalyst 11 is smaller than the reference exhaust air-fuel ratio and the difference exceeds the fuel addition possible range, and the request for the NOx reduction process is made. Even if it exists, it is made not to add the said fuel.

  When the actual EGR rate is larger than the target EGR rate, or when the ratio of the actual EGR rate to the target EGR rate increases, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 11 tends to be rich. In this way, it is possible to suppress excessive fuel from being supplied into the exhaust gas as a result of the NOx reduction treatment, and as a result, It is possible to efficiently use the added fuel while suppressing the release to the outside.

  Further, the determination in step 102 is made based on the accelerator opening increase amount per unit time, the target cylinder fuel injection amount increase amount per unit time, or the target intake air amount increase amount per unit time. You may do it. That is, in these cases, whether or not the accelerator opening increase amount per unit time is larger than the predetermined accelerator opening increase amount Vcax, and the target cylinder fuel injection amount increase amount per unit time is a predetermined target. It is determined whether or not the in-cylinder fuel injection amount increase amount Vcfi is larger, or whether or not the target intake air amount increase amount per unit time is larger than a predetermined target intake air amount increase amount Vca. The

  That is, in these cases, the accelerator opening increase amount Vcax, the target in-cylinder fuel injection amount increase amount Vcfi, or the target intake air amount increase amount Vca is equal to the intake air amount difference ΔQca or the intake air amount ratio Rca. Similarly to the above, it is a value set as a determination criterion, and is determined in advance in consideration of suppression of release of added fuel to the outside and utilization of efficiency. When it is determined that the accelerator opening increase amount per unit time is larger than the predetermined accelerator opening increase amount Vcax, the target in-cylinder fuel injection amount increase per unit time is determined in advance. If it is determined that the amount is larger than the increase amount Vcfi, or if it is determined that the increase amount of the target intake air amount per unit time is larger than the predetermined increase amount Vca of the target intake air amount, step 103 is performed. If not, go to Step 104.

  That is, in these cases, when the accelerator opening increase amount per unit time is larger than the predetermined accelerator opening increase amount Vcax, the increase amount of the target in-cylinder fuel injection amount per unit time is determined in advance. When the fuel injection amount increase amount Vcfi is larger, or when the target intake air amount increase amount per unit time is larger than the predetermined target intake air amount increase amount Vca, it flows into the NOx storage reduction catalyst 11. It is determined that the air-fuel ratio of the exhaust gas is smaller than the reference exhaust air-fuel ratio and the difference exceeds the fuel addition possible range, so that the fuel addition is not performed even if the NOx reduction treatment is required.

  In general, when the accelerator opening increases rapidly, when the target in-cylinder fuel injection amount increases rapidly, or when the target intake air amount increases rapidly, the required torque increases at the time of acceleration. This is a time when the combustion air-fuel ratio tends to become rich due to a response delay of the air amount, and as a result, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 11 tends to become rich. Accordingly, even if the above is performed, the NOx reduction process is performed by appropriately setting the accelerator opening increase amount Vcax, the target in-cylinder fuel injection amount increase amount Vcfi, or the target intake air amount increase amount Vca. As a result, it is possible to suppress excessive fuel from being supplied into the exhaust gas, and as a result, to efficiently use the added fuel while suppressing the release of the added fuel to the outside. Can do.

  As is clear from the description so far, in step 102, a determination result is made using some or all of the determination criteria described above as the determination criteria, and the process proceeds to step 103 based on at least one determination criterion. If YES in step 103, the flow may proceed to step 103 and fuel addition may be prohibited.

  In the above description, the NOx reduction process for the NOx storage reduction catalyst 11 has been described as an example. However, the present invention is not limited to this, and the upstream side of the exhaust purification unit disposed in the exhaust passage. The present invention can be applied to any case where regeneration control for recovering the purification performance of the exhaust gas purification means including adding fuel to the exhaust gas is performed. Therefore, the present invention can be applied to, for example, the above-described sulfur poisoning recovery processing of the NOx storage reduction catalyst and filter regeneration processing of the filter.

  Further, in the above description, as a method of adding fuel to the exhaust gas, a method of adding the fuel addition valve 13 to the exhaust passage and adding the fuel from the fuel addition valve 13 has been adopted, but the present invention is not limited to this. However, in another embodiment, for example, a method of injecting fuel into the cylinder during the exhaust stroke of each cylinder of the internal combustion engine (so-called post injection method) may be employed.

  In addition, if fuel addition is prohibited for a long time, the regeneration control cannot be performed, so that the purification performance of the exhaust purification means is greatly reduced, and exhaust gas with insufficient purification is discharged to the outside. There is a risk. In order to cope with such a problem, in another embodiment, a step of determining whether to prohibit the addition of fuel based on the purification performance of the exhaust gas purification means is provided between step 102 and step 103. You may do it.

  In other words, in this case, when it is determined that the purification performance of the exhaust gas purification means has decreased to a predetermined lower limit level, the process should proceed to step 103 in step 102 (that is, fuel addition should be prohibited). Even if the determination result is output, the regeneration control is performed by adding fuel. In this way, a significant reduction in purification performance can be prevented, so that exhaust gas with insufficient purification can be prevented from being released to the outside.

FIG. 1 is a diagram for explaining a case where the present invention is applied to a compression ignition type internal combustion engine. FIG. 2 is a flowchart showing a control routine of control that can be performed by the exhaust gas purification apparatus for an internal combustion engine according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Fuel injection valve 4 Intake manifold 5 Exhaust manifold 7 Exhaust turbocharger 11 NOx storage reduction catalyst 13 Fuel addition valve 21 Air flow meter

Claims (7)

An exhaust purification means disposed in the exhaust passage;
An exhaust purification device for an internal combustion engine, comprising: regeneration control execution means for performing regeneration control of the exhaust purification means including adding fuel to exhaust gas upstream of the exhaust purification means;
The regeneration control execution means has a range in which the air-fuel ratio of the exhaust gas flowing into the exhaust purification means is smaller than a predetermined reference exhaust air-fuel ratio in a state where the fuel addition is not performed, and the difference is within a predetermined fuel addition range. The exhaust gas purification apparatus for an internal combustion engine is characterized in that the addition of the fuel is not carried out when it is determined that the amount exceeds the above.   When the actual intake air amount is less than the target intake air amount and the difference is larger than the predetermined intake air amount difference, or when the ratio of the actual intake air amount to the target intake air amount is smaller than the predetermined intake air amount ratio 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the regeneration control execution means does not add the fuel.   When the actual combustion air-fuel ratio is smaller than the target combustion air-fuel ratio and the difference is larger than the predetermined air-fuel ratio difference, or when the ratio of the actual combustion air-fuel ratio to the target combustion air-fuel ratio is smaller than the predetermined air-fuel ratio, The exhaust emission control device for an internal combustion engine according to claim 1 or 2, wherein the regeneration control execution means does not perform the addition of the fuel. An exhaust gas purification apparatus for an internal combustion engine in which recirculation of exhaust gas is performed and an EGR rate that is a ratio of an exhaust gas amount to a total gas amount sucked into a cylinder is controlled,
When the actual EGR rate is greater than the target EGR rate and the difference is greater than the difference between the predetermined EGR rates, or when the ratio of the actual EGR rate to the target EGR rate is greater than the predetermined EGR rate ratio, the regeneration control is performed. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the execution means does not add the fuel.   5. The regeneration control execution unit does not add the fuel when the accelerator opening increase amount per unit time is larger than a predetermined accelerator opening increase amount. An exhaust gas purification device for an internal combustion engine according to item.   When the increase amount of the target in-cylinder fuel injection amount per unit time is larger than the predetermined increase amount of the target in-cylinder fuel injection amount, the regeneration control execution unit does not add the fuel. Item 6. An exhaust emission control device for an internal combustion engine according to any one of Items 1 to 5.   7. The regeneration control execution unit does not add the fuel when the increase amount of the target intake air amount per unit time is larger than a predetermined increase amount of the target intake air amount. The exhaust gas purification apparatus for an internal combustion engine according to any one of the above.

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