JP2017057830A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently reduce NOx in an exhaust emission control system including an NOx occlusion reduction type catalyst.SOLUTION: An exhaust emission control system includes: an NOx reduction type catalyst 32 for reducing NOx included in exhaust gas for purification; an NOx lambda sensor 45 provided on the exhaust downstream side of the catalyst 32; and an ECU 50 that performs NOx purge for recovering purification capacity of the NOx reduction type catalyst by switching an exhaust air-fuel ratio from a lean state to a rich state by using both of air system control and injection system control. The ECU 50 performs former stage rich control for injecting first injection amount of fuel obtained by adding injection amount corresponding to oxygen amount emitted from the catalyst 32 to injection amount necessary for reducing NOx emitted from the catalyst 32 and latter stage rich control for injecting second injection amount of fuel determined based on NOx amount occluded in the catalyst 32 and a catalyst temperature after performing the former stage rich control.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust purification system.

  Conventionally, a NOx occlusion reduction type catalyst is known as a catalyst for reducing and purifying nitrogen compounds (NOx) in exhaust gas discharged from an internal combustion engine. This NOx occlusion reduction type catalyst occludes NOx contained in the exhaust when the exhaust is in a lean atmosphere, and reduces and purifies NOx occluded by hydrocarbons contained in the exhaust when the exhaust is in a rich atmosphere. Detoxify and release. For this reason, when the NOx occlusion amount of the catalyst reaches a predetermined amount, so-called NOx purge that makes the exhaust rich by post injection or exhaust pipe injection needs to be performed periodically to restore the NOx occlusion capacity ( For example, see Patent Document 1).

  In addition, the amount of reducing agent required to reduce NOx released from the NOx storage reduction catalyst is added to the amount of reducing agent commensurate with the amount of oxygen released from the NOx storage reduction catalyst. By setting the total injection amount, NOx released from the NOx storage reduction catalyst can be reliably reduced (see, for example, Patent Document 2).

  In Patent Document 2, the target air-fuel ratio is made different between the first rich control until oxygen is released from the NOx storage reduction catalyst and the second rich control after oxygen is released. It is disclosed that the target air-fuel ratio is made larger than that in rich control.

JP 2008-202425 A JP 2006-70834 A

  By the way, the reduction efficiency of NOx occluded after oxygen is released varies depending on the influence of the catalyst temperature. For example, if the catalyst temperature is relatively low, the reduction efficiency is low, and if the catalyst temperature is relatively high, the reduction efficiency is high. For this reason, it is preferable to control the fuel injection amount in consideration of the catalyst temperature because NOx can be efficiently reduced.

  An object of the disclosed system is to efficiently reduce NOx in an exhaust purification system including a NOx storage reduction catalyst.

  The disclosed system is provided in an exhaust passage of an internal combustion engine to reduce and purify NOx in exhaust gas, and is provided on the downstream side of the exhaust passage with respect to the NOx reduction catalyst and flows through the exhaust passage. By switching the exhaust air / fuel ratio from the lean state to the rich state by using a sensor for detecting the excess air ratio of the exhaust, air system control for reducing the intake air amount, and injection system control for increasing the fuel injection amount, An exhaust purification system comprising a control unit that executes a regeneration process for recovering the purification ability of the NOx reduction catalyst, wherein the control unit is necessary for reducing NOx released from the NOx storage reduction catalyst A first rich control in which fuel is injected at a first injection amount obtained by adding an injection amount commensurate with the amount of oxygen released from the NOx occlusion reduction catalyst to an appropriate injection amount, and the first rich control. After implementation, performing a second rich control for injecting the fuel in the second injection quantity which is determined based on the temperature of the NOx amount occluded in the NOx occlusion reduction type catalyst and the NOx occlusion reduction type catalyst.

  According to the disclosed system, NOx can be efficiently reduced in an exhaust purification system including a NOx occlusion reduction catalyst.

1 is an overall configuration diagram showing an exhaust purification system according to an embodiment. It is a timing chart figure explaining NOx purge control concerning this embodiment. It is a block diagram which shows the setting process of the MAF target value at the time of NOx purge lean control which concerns on this embodiment. It is a block diagram which shows the setting process of the target injection quantity at the time of the first term NOx purge rich control which concerns on this embodiment. (A) is a block diagram showing a setting process of a target injection amount at the time of late NOx purge rich control according to the present embodiment, and (B) is a diagram schematically explaining a third target excess air ratio setting map. . It is a block diagram which shows the catalyst temperature estimation process which concerns on this embodiment. It is a block diagram which shows the occlusion amount estimation process which concerns on this embodiment. It is a block diagram which shows the process of the injection amount learning correction | amendment of the injector which concerns on this embodiment. It is a flowchart explaining the calculation process of the learning correction coefficient which concerns on this embodiment. It is a block diagram which shows the setting process of the MAF correction coefficient which concerns on this embodiment.

  Hereinafter, an exhaust purification system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1, each cylinder of a diesel engine (hereinafter simply referred to as “engine”) 10 is provided with an in-cylinder injector 11 that directly injects high-pressure fuel that is stored in a common rail (not shown) into each cylinder. Yes. The fuel injection amount and fuel injection timing of each in-cylinder injector 11 are controlled according to an instruction signal input from an electronic control unit (hereinafter referred to as ECU) 50.

  An intake passage 12 for introducing fresh air is connected to the intake manifold 10A of the engine 10, and an exhaust passage 13 for leading the exhaust to the outside is connected to the exhaust manifold 10B. In the intake passage 12, an air cleaner 14, an intake air amount sensor (hereinafter referred to as MAF sensor) 40, a compressor 20A of the variable displacement supercharger 20, an intercooler 15, an intake throttle valve 16 and the like are provided in order from the intake upstream side. ing. The exhaust passage 13 is provided with a turbine 20B of the variable displacement supercharger 20, an exhaust aftertreatment device 30 and the like in order from the exhaust upstream side. In FIG. 1, reference numeral 41 denotes an engine speed sensor, reference numeral 42 denotes an accelerator opening sensor, reference numeral 46 denotes a boost pressure sensor, reference numeral 47 denotes an outside air temperature sensor, and reference numeral 48 denotes an intake air temperature sensor.

  The EGR device 21 includes an EGR passage 22 that connects the exhaust manifold 10B and the intake manifold 10A, an EGR cooler 23 that cools EGR gas, and an EGR valve 24 that adjusts the EGR amount.

  The exhaust aftertreatment device 30 is configured by arranging an oxidation catalyst 31, a NOx occlusion reduction type catalyst 32, and a particulate filter (hereinafter simply referred to as a filter) 33 in order from the exhaust upstream side in a case 30A. The exhaust passage 13 upstream of the oxidation catalyst 31 is provided with an exhaust injector 34 that injects unburned fuel (mainly HC) into the exhaust passage 13 in accordance with an instruction signal input from the ECU 50. Yes.

  The oxidation catalyst 31 is formed, for example, by carrying an oxidation catalyst component on the surface of a ceramic carrier such as a honeycomb structure. When the unburned fuel is supplied by the exhaust pipe injection of the exhaust injector 34 or the post injection of the in-cylinder injector 11, the oxidation catalyst 31 oxidizes this and raises the exhaust temperature.

  The NOx storage reduction catalyst 32 is formed, for example, by supporting an alkali metal or the like on the surface of a ceramic carrier such as a honeycomb structure. The NOx occlusion reduction type catalyst 32 occludes NOx in the exhaust when the exhaust air-fuel ratio is in a lean state, and occludes with a reducing agent (HC or the like) contained in the exhaust when the exhaust air-fuel ratio is in a rich state. NOx is reduced and purified.

  The filter 33 is formed, for example, by arranging a large number of cells partitioned by porous partition walls along the flow direction of the exhaust gas and alternately plugging the upstream side and the downstream side of these cells. . The filter 33 collects PM in the exhaust gas in the pores and surfaces of the partition walls, and when the estimated amount of PM deposition reaches a predetermined amount, so-called filter forced regeneration is performed in which the PM is burned and removed. Filter forced regeneration is performed by supplying unburned fuel to the upstream side oxidation catalyst 31 by exhaust pipe injection or post injection, and raising the exhaust temperature flowing into the filter 33 to the PM combustion temperature.

  The first exhaust temperature sensor 43 is provided on the upstream side of the oxidation catalyst 31 and detects the exhaust temperature flowing into the oxidation catalyst 31. The second exhaust temperature sensor 44 is provided between the NOx storage reduction catalyst 32 and the filter 33 and detects the exhaust temperature flowing into the filter 33.

  The NOx / lambda sensor 45 is provided downstream of the filter 33 and detects the NOx value and lambda value (excess air ratio) of the exhaust gas that has passed through the NOx storage reduction catalyst 32. As the NOx / lambda sensor 45 of this embodiment, a binary type sensor whose output changes remarkably in the vicinity of the theoretical air-fuel ratio is used. Specifically, when the output conversion is set so that λ = 1.0 becomes the zero point, a type of sensor having a characteristic that reverses between plus and minus with λ = 1.0 as a boundary is used. ing. The NOx / lambda sensor 45 outputs a positive output (positive output) when the lambda value is 1.0 or more, and outputs a negative output (negative output) when the lambda value is less than 1.0. On the contrary, a negative output may be made when the lambda value is 1.0 or more, and a positive output may be made when the lambda value is less than 1.0.

  The ECU 50 performs various controls of the engine 10 and the like, and includes a known CPU, ROM, RAM, input port, output port, and the like. In order to perform these various controls, sensor values of the sensors 40 to 48 are input to the ECU 50. The ECU 50 also includes a filter regeneration control unit 51, a NOx purge control unit 60, a catalyst temperature estimation unit 70, an occlusion amount estimation unit 80, a MAF follow-up control unit 85, an injection amount learning correction unit 90, and an MAF correction. The coefficient calculation unit 95 is included as a part of functional elements. Each of these functional elements will be described as being included in the ECU 50 which is an integral hardware, but any one of these may be provided in separate hardware.

[Filter regeneration control]
The filter regeneration control unit 51 performs a filter regeneration process that burns and removes the PM deposited on the filter 33. The filter regeneration control unit 51 turns on the filter forced regeneration flag _FDPF when the estimated PM accumulation amount acquired from the PM accumulation amount estimation unit 52 exceeds a predetermined upper limit threshold. When the filter forced regeneration flag F _DPF is turned on, an instruction signal for performing exhaust pipe injection is transmitted to the exhaust injector 34, or an instruction signal for performing post injection to each in-cylinder injector 11 is transmitted. . As a result, the exhaust temperature is raised to the PM combustion temperature (for example, about 550 ° C.), and this temperature rise state is maintained. The filter forced regeneration flag F _DPF is turned off when the PM accumulation estimated amount falls to a predetermined lower threshold (determination threshold) indicating combustion removal. An injection amount instruction value (hereinafter referred to as a filter regeneration post injection amount instruction value Q _{DPF_Post_Trgt} ) when the filter forced regeneration is performed by post injection is also used for estimating the catalyst heat generation amount in the catalyst temperature estimation unit 70 described later in detail. Sent.

[NOx purge control]
The NOx purge control unit 60 restores the NOx occlusion ability of the NOx occlusion reduction catalyst 32 by making the exhaust rich and detoxifying and releasing NOx occluded in the NOx occlusion reduction catalyst 32 by reduction purification. A catalyst regeneration process (hereinafter, this control is referred to as NOx purge control) is executed.

The NOx purge flag F _NP for starting the NOx purge control is estimated when the NOx emission amount per unit time is estimated from the operating state of the engine 10 and the accumulated cumulative value ΣNOx obtained by accumulating the NOx purge flag exceeds a predetermined threshold (see FIG. 2). It is the time reference _{t 1).} Alternatively, the NOx purification rate by the NOx occlusion reduction type catalyst 32 is calculated from the NOx emission amount upstream of the catalyst estimated from the operating state of the engine 10 and the NOx amount downstream of the catalyst detected by the NOx / lambda sensor 45. When the NOx purification rate becomes lower than a predetermined determination threshold, the NOx purge flag F _NP is turned on.

  In the present embodiment, the enrichment by the NOx purge control is performed on the lean side of the excess air ratio from the stoichiometric air-fuel ratio equivalent value (about 1.0) from the time of steady operation (for example, about 1.5) by the air system control. NOx purge lean control for reducing to 1 target excess air ratio (for example, about 1.3) and injection system control to reduce the excess air ratio from the first target excess air ratio to the second target excess air ratio on the rich side (for example, about 0) .9) and NOx purge rich control for reducing the pressure to 9). The details of the NOx purge lean control and the NOx purge rich control will be described below.

[NOF purge lean control MAF target value setting]
FIG. 3 is a block diagram showing a process for setting the MAF target value MAF _{NPL_Trgt} during the NOx purge lean control. The first target excess air ratio setting map 61 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and during NOx purge lean control corresponding to the engine speed Ne and the accelerator opening Q. An excess air ratio target value λ _{NPL_Trgt} (first excess air ratio) is set in advance based on experiments or the like.

First, the excess air ratio target value λ _{NPL_Trgt} at the time of NOx purge lean control is read from the first target excess air ratio setting map 61 using the engine speed Ne and the accelerator opening Q as input signals, and is sent to the MAF target value calculation unit 62. Entered. Further, the MAF target value calculation unit 62 calculates the MAF target value MAF _{NPL_Trgt} at the time of NOx purge lean control based on the following formula (1).

数式（１）において、Ｑ_{ｆｎｌ＿ｃｏｒｒｄ}は後述する学習補正された燃料噴射量（ポスト噴射を除く）、Ｒｏ_Ｆｕｅｌは燃料比重、ＡＦＲ_ｓｔｏは理論空燃比、Ｍａｆ_{＿ｃｏｒｒ}は後述するＭＡＦ補正係数をそれぞれ示している。

In Equation (1), Q _{fnl_cord} represents a learning-corrected fuel injection amount (excluding post-injection) described later, Ro _Fuel represents fuel specific gravity, AFR _sto represents a theoretical air-fuel ratio, and _{Maf_corr} represents a MAF correction coefficient described later. Yes.

The MAF target value MAF _{NPL_Trgt} calculated by the MAF target value calculation unit 62 is input to the ramp processing unit 63 when the NOx purge flag F _NP is turned on (see time t _{1 in} FIG. 2). The ramp processing unit 63 reads the ramp coefficient from the respective ramp coefficient maps 63A and 63B using the engine speed Ne and the accelerator opening Q as input signals, and _{uses the} MAF target ramp value MAF _{NPL_Trgt_Ramp} to which the ramp coefficient is added as the valve control unit 64. To enter.

The valve control unit 64 throttles the intake throttle valve 16 to the _close side and opens the EGR valve 24 to the open side so that the actual MAF value MAF _Act input from the MAF sensor 40 becomes the MAF target ramp value MAF _{NPL_Trgt_Ramp.} Execute control.

Thus, in this embodiment, the MAF target value MAF _{NPL_Trgt} is set based on the excess air ratio target value λ _{NPL_Trgt} read from the first target excess air ratio setting map 61 and the fuel injection amount of each in-cylinder injector 11. The air system operation is feedback-controlled based on the MAF target value MAF _{NPL_Trgt} . Thus, without providing a lambda sensor upstream of the NOx storage reduction catalyst 32, or even when a lambda sensor is provided upstream of the NOx storage reduction catalyst 32, the sensor value of the lambda sensor is not used. It is possible to effectively reduce the exhaust gas to a desired excess air ratio required for NOx purge lean control.

_Further, by using the fuel injection amount Q _{fnl_corrd} after learning correction as the fuel injection amount of each in-cylinder injector 11, the MAF target value MAF _{NPL_Trgt} can be set by feedforward control. Effects such as deterioration and characteristic changes can be effectively eliminated.

Further, by adding a ramp coefficient that is set according to the operating state of the engine 10 to the MAF target value MAF _{NPL_Trgt} , it is possible to prevent misfire of the engine 10 due to a sudden change in the intake air amount, deterioration of drivability due to torque fluctuation, and the like. It can be effectively prevented.

[NOx purge rich control fuel injection amount setting]
FIG. 4 shows an exhaust pipe in NOx purge rich control, specifically, in the first rich control (an example of the first rich control of the present invention) in consideration of oxygen released from the NOx storage reduction catalyst 32 at the beginning of NOx purge. It is a block diagram which shows the setting process of the target injection quantity instruction _| indication value _{QNPR_Trgt_O2} (injection quantity per unit time) of injection or post injection.

The second target excess air ratio setting map 65A is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and during NOx purge rich control corresponding to the engine speed Ne and the accelerator opening Q. The air excess rate target value λ _{NPR_Trgt} (second target air excess rate) is preset based on experiments or the like. In the stored oxygen amount map 65B, the relationship between the amount of oxygen released from the NOx storage reduction catalyst 32 and the catalyst temperature is set in advance based on experiments and the like.

In the first half rich control, first, the excess air ratio target value λ _{NPR_Trgt} at the time of NOx purge rich control is read from the second target excess air ratio setting map 65A using the engine speed Ne and the accelerator opening Q as input signals, and the injection amount target. The value is input to the value calculation unit 66. Further, the injection amount target value calculation unit 66 calculates a target injection amount instruction value Q _{NPR_Trgt} at the time of NOx purge rich control based on the following formula (2).

数式（２）において、ＭＡＦ_{ＮＰＬ＿Ｔｒｇｔ}はＮＯｘパージリーンＭＡＦ目標値であって、前述のＭＡＦ目標値演算部６２から入力される。また、Ｑ_{ｆｎｌ＿ｃｏｒｒｄ}は後述する学習補正されたＭＡＦ追従制御適用前の燃料噴射量（ポスト噴射を除く）、Ｒｏ_Ｆｕｅｌは燃料比重、ＡＦＲ_ｓｔｏは理論空燃比、Ｍａｆ_{＿ｃｏｒｒ}は後述するＭＡＦ補正係数をそれぞれ示している。

In Expression (2), MAF _{NPL_Trgt} is a NOx purge lean MAF target value, and is input from the MAF target value calculation unit 62 described above. Q _{fnl_cord} is a fuel injection amount (excluding post-injection) before application of learning corrected MAF tracking control described later, Ro _Fuel is fuel specific gravity, AFR _sto is a theoretical air-fuel ratio, and _{Maf_corr} is a MAF correction coefficient described later. Show.

Next, from the stored oxygen amount map 65B, the amount of oxygen released at the start of the NOx purge control is read using the catalyst temperature from the catalyst temperature estimating unit 70, which will be described in detail later, as an input signal, and the injection amount target value calculating unit. 66. Further, the injection amount target value calculation unit 66 calculates a target injection amount instruction value Q _{O2_Trgt} corresponding to the oxygen amount by multiplying the oxygen amount acquired from the stored oxygen amount map 65B by a predetermined conversion coefficient C1. Note that the target injection amount instruction value Q _{O2_Trgt} may be read from the map by setting a MAP indicating the relationship with the oxygen amount in advance based on experiments or the like and using the oxygen amount as an input signal.

The injection amount target value calculation unit 66 adds the target injection amount instruction value Q _{O2_Trgt} to the target injection amount instruction value Q _{NPR_Trgt} calculated by the mathematical formula (2), so that the target injection amount instruction value Q _{NPR_Trgt_O2} considering the oxygen amount is _added. (An example of the first injection amount of the present invention) is acquired. The target injection amount instruction value _{Q NPR_Trgt_O2,} as shown at time _{t 1} in FIG. 2, when the NOx purge flag _{F NP} is on, is sent as the injection instruction signal to the exhaust injector 34 or each cylinder injector 11 (hereinafter, In particular, the injection amount instruction value of the post injection transmitted to the in-cylinder injector 11 is referred to as NOx purge rich / post injection amount instruction value Q _{NPR_Post_Trgt} ). The NOx purge rich / post-injection amount instruction value Q _{NPR_Post_Trgt} is also transmitted to the catalyst temperature estimation unit 70 in order to estimate the catalyst heat generation amount.

Thus, in this embodiment, the excess air ratio target value λ _{NPR_Trgt} and the target injection amount instruction value Q _{NPR_Trgt} set based on the fuel injection amount of each in-cylinder injector 11 are released from the storage reduction catalyst 32. that since the target injection amount instruction value _{Q O2_Trgt} commensurate to the amount of oxygen and using the target injection amount instruction value _{Q NPR_Trgt_O2} computed by adding the even fuel (reducing agent) is consumed by the released oxygen, NOx Can be sufficiently reduced and purified.

Further, the target injection amount instruction value Q _{NPR_Trgt} is set based on the excess air ratio target value λ _{NPR_Trgt} read from the second target excess air ratio setting map 65 and the fuel injection amount of each in-cylinder injector 11. Yes. Thus, without providing a lambda sensor upstream of the NOx storage reduction catalyst 32, or even when a lambda sensor is provided upstream of the NOx storage reduction catalyst 32, the sensor value of the lambda sensor is not used. It is possible to effectively reduce the exhaust gas to a desired excess air ratio required for NOx purge rich control.

_Further, by using the fuel injection amount Q _{fnl_corrd} after learning correction as the fuel injection amount of each in-cylinder injector 11, the target injection amount instruction value Q _{NPR_Trgt} can be set by feedforward control, and each in-cylinder injector 11 It is possible to effectively eliminate the influence of aging deterioration and characteristic changes.

  The NOx purge control unit 60 monitors the output from the NOx / lambda sensor 45 after the execution of the rich control of the first half, and the late rich control (an example of the second rich control of the present invention) on condition that the output is reversed. To start. In the late rich control, fuel is injected at an injection amount determined based on the amount of NOx stored in the NOx storage reduction catalyst 32 and the catalyst temperature.

FIG. 5A is a block diagram showing a setting process of the target injection amount instruction value Q _{NPR_Trgt_NOX} (injection amount per unit time) of exhaust pipe injection or post injection in the late rich control. The third target excess air ratio setting map 65C is a map that is referred to based on the NOx occlusion amount estimated by the occlusion amount estimation unit 80, which will be described in detail later, and the catalyst temperature estimated by the catalyst temperature estimation unit 70. Thus, the excess air ratio target value λ _{NPR_Trgt_NOX} at the time of NOx purge rich control corresponding to the NOx occlusion amount and the catalyst temperature is set in advance based on experiments or the like.

In the example shown in FIG. 5B, the third target excess air ratio setting map 65C has two levels of “low” or “high” for the NOx occlusion amount, and two levels of “low” or “high” for the catalyst temperature. It consists of 4 conditions (areas). The excess air ratio target value λ _{NPR_Trgt_NOX} is set for each of the four conditions. For example, the excess air ratio target value λ _{NPR_Trgt_NOX} is determined in the range of 0.8 to _{0.9 under} the conditions of the NOx occlusion amount “high” and the catalyst temperature “high”. Excess air ratio target value lambda _{NPR_Trgt_NOX} in this condition may be less than the excess air ratio target value lambda _{NPR_Trgt} in year rich control. For example, a large amount of NOx stored in the NOx occlusion-reduction catalyst 32, and, when the catalyst temperature is sufficiently high, the excess air ratio target value lambda _{NPR_Trgt_NOX} is smaller than the excess air ratio target value λ _{NPR_Trgt.} On the other hand, in the other three conditions, the excess air ratio target value λ _{NPR_Trgt_NOX} is determined in the range of 0.9 to 1.0. The read excess air ratio target value λ _{NPR_Trgt_NOX} is input to the injection amount target value calculation unit 66.

The injection amount target value calculation unit 66 shown in FIG. 5A calculates the target injection amount instruction value Q _{NPR_Trgt_NOX} (an example of the second injection amount of the present invention) based on the excess air ratio target value λ _{NPR_Trgt_NOX} . Specifically, the target injection amount instruction value _{Q NPR_Trgt_NOX} is the excess air ratio target value lambda _{NPR_Trgt} in the above equation (2), is calculated by replacing the air excess ratio target value λ _{NPR_Trgt_NOX.} This target injection amount instruction value Q _{NPR_Trgt_NOX} is immediately transmitted to the exhaust injector 34 or each in-cylinder injector 11 as an injection instruction signal.

  Accordingly, as shown in FIG. 5B, in the late rich control, the excess air ratio (λ) is about 0.8 to 0.9 under the conditions of the NOx occlusion amount “high” and the catalyst temperature “high”. Deep rich control is performed. On the other hand, under the other three conditions, shallow rich control with an excess air ratio of about 0.9 to 1.0 is performed.

Thus, in this embodiment, the NOx occlusion amount and the catalyst temperature at the time when oxygen is released from the NOx occlusion reduction type catalyst 32 are referred to. The excess air ratio target value λ _{NPR_Trgt_NOX} is determined based on the referenced NOx occlusion amount and the catalyst temperature, and fuel is injected so as to reach this target value. For this reason, NOx occluded in the NOx occlusion reduction type catalyst 32 can be efficiently reduced and purified with a necessary and sufficient amount of fuel injection.

  For example, when a large amount of NOx is occluded in the NOx occlusion reduction type catalyst 32 and the catalyst temperature is sufficiently high, the late rich control becomes deep rich control with a target excess air ratio smaller than that of the previous rich control. Thereby, excessive NOx desorption in the initial stage of catalyst regeneration is suppressed, and NOx occluded in the NOx occlusion reduction catalyst 32 can be efficiently reduced and purified with a necessary and sufficient amount of fuel injection.

  In the third target excess air ratio setting map 65C in FIG. 5B, the NOx occlusion amount and the catalyst temperature are two levels, respectively, but the present invention is not limited to this. You may set more than 3 levels.

[Catalyst temperature estimation]
FIG. 6 is a block diagram showing an estimation process of the oxidation catalyst temperature and the NOx catalyst temperature by the catalyst temperature estimation unit 70. The catalyst temperature estimation unit 70 estimates the catalyst temperature based on the amount of unburned fuel contained in the exhaust and the heat generation amount of the oxidation catalyst 31 and the NOx storage reduction catalyst 32.

The lean HC map 71A is a map that is referred to based on the operating state of the engine 10, and the amount of HC discharged from the engine 10 during lean operation (hereinafter referred to as lean HC discharge amount) is set in advance through experiments or the like. Has been. When both the filter forced regeneration flag F _DPF and the NOx purge flag F _NP are off (F _DPF = 0, F _NP = 0), reading is performed from the lean HC map 71A based on the engine speed Ne and the accelerator opening Q. The lean HC emission amount is transmitted to each of the heat generation amount estimation units 76A and 76B.

The lean CO map 71B is a map that is referred to based on the operating state of the engine 10, and the amount of CO discharged from the engine 10 during lean operation (hereinafter referred to as lean CO emission) is set in advance through experiments or the like. Has been. When both the filter forced regeneration flag F _DPF and the NOx purge flag F _NP are off (F _DPF = 0, F _NP = 0), reading is performed from the lean CO map 71B based on the engine speed Ne and the accelerator opening Q. The lean CO emission amount is transmitted to each of the heat generation amount estimation units 76A and 76B.

The filter forced regeneration HC map 72A is a map that is referred to based on the operating state of the engine 10, and is the amount of HC discharged from the engine 10 when filter forced regeneration control is performed (hereinafter referred to as HC exhaust during filter regeneration). (Referred to as “quantity”) is set in advance by experiments or the like. When the filter forced regeneration flag F _DPF is on (F _DPF = 1), the engine regeneration amount HC emission amount read from the filter forced regeneration HC map 72A based on the engine speed Ne and the accelerator opening Q is A predetermined correction coefficient corresponding to the ten operating states is multiplied and transmitted to each of the heat generation amount estimation units 76A and 76B.

The filter forced regeneration CO map 72B is a map that is referred to based on the operating state of the engine 10, and is the amount of CO discharged from the engine 10 when filter forced regeneration control is performed (hereinafter referred to as CO exhaust during filter regeneration). (Referred to as “quantity”) is set in advance by experiments or the like. When the filter forced regeneration flag F _DPF is ON (F _DPF = 1), the engine regeneration amount CO emission amount read from the filter forced regeneration CO map 72B based on the engine speed Ne and the accelerator opening Q is A predetermined correction coefficient corresponding to the ten operating states is multiplied and transmitted to each of the heat generation amount estimation units 76A and 76B.

The NOx purge HC map 73A is a map that is referred to based on the operating state of the engine 10, and is the amount of HC discharged from the engine 10 when the NOx purge control is performed (hereinafter referred to as NOx purge HC discharge amount). ) Is set in advance by experiments or the like. When the NOx purge flag F _NP is ON (F _NP = 1), the operation of the engine 10 is performed based on the NOx purge HC discharge amount read from the NOx purge HC map 73A based on the engine speed Ne and the accelerator opening Q. A predetermined correction coefficient corresponding to the state is multiplied and transmitted to each of the heat generation amount estimation units 76A and 76B.

The NOx purge CO map 73B is a map that is referred to based on the operating state of the engine 10, and is the amount of CO discharged from the engine 10 when the NOx purge control is performed (hereinafter referred to as NOx purge CO emission). ) Is set in advance by experiments or the like. When the NOx purge flag F _NP is on (F _NP = 1), the engine 10 is operated based on the NOx purge CO emission amount read from the NOx purge CO map 73B based on the engine speed Ne and the accelerator opening Q. A predetermined correction coefficient corresponding to the state is multiplied and transmitted to each of the heat generation amount estimation units 76A and 76B.

  The post-injection amount instruction value correcting unit 75, when NOx purge rich control or filter forced regeneration control is performed by post-injection, uses a post-injection amount instruction value used for estimating the catalyst heat generation amount, which will be described later. The post-injection amount instruction value correction that is corrected by the learning correction coefficient input from is executed.

More specifically, when the NOx purge flag F _NP is turned on and the NOx purge rich control is performed by post-injection, the NOx purge rich value input from the injection amount target value calculation unit 66 (NOx purge control unit 60). post injection amount instruction value _{Q NPR_Post_Trgt} the learning correction coefficient _{F Corr} post injection amount instruction value _{Q NPR_Post_Corr} corrected by multiplying _{(= Q NPR_Post_Trgt} × _{F Corr)} are each heating value estimating unit 76A, so as to be transmitted to 76B ing.

Further, when the filter forced regeneration flag F _DPF is turned on and the forced filter regeneration control is performed by post injection, the learning correction coefficient is _added to the filter regeneration post injection amount instruction value Q _{DPF_Post_Trgt} input from the filter regeneration control unit 51. post injection amount instruction value after correction obtained by multiplying _{F Corr Q DPF_Post_Corr (= Q DPF_Post_Trgt} × F Corr) are each heating value estimating unit 76A, is adapted to be sent to 76B.

The oxidation catalyst heat generation amount estimation unit 76A performs the HC / CO emission amount input from each of the maps 71A to 73B in accordance with ON / OFF of the NOx purge flag F _NP and the filter forced regeneration flag F _DPF and the exhaust pipe injection / post injection. Based on the post-injection amount instruction value after correction input from the post-injection amount instruction value correction unit 75 according to the selection, etc., the HC / CO heat generation amount in the oxidation catalyst 31 (hereinafter referred to as the oxidation catalyst HC / CO heat generation amount). Estimated). The oxidation catalyst HC / CO heat generation amount is estimated and calculated based on, for example, a model formula or map including the HC / CO emission amount and the corrected post-injection amount instruction value as input values.

The NOx catalyst heat generation amount estimation unit 76B performs the HC / CO emission amount input from each map 71A to 73B and the exhaust pipe injection / post injection according to ON / OFF of the NOx purge flag F _NP and the filter forced regeneration flag F _DPF . Based on the post-injection amount instruction value after correction input from the post-injection amount instruction value correction unit 75 according to the selection, etc., the HC / CO heat generation amount (hereinafter referred to as the NOx catalyst HC / CO) inside the NOx storage reduction type catalyst 32. Estimated calorific value). The NOx catalyst HC / CO heat generation amount is estimated and calculated based on, for example, a model formula or map including the HC / CO emission amount and the corrected post injection amount instruction value as input values.

  The oxidation catalyst temperature estimation unit 77A includes an oxidation catalyst inlet temperature detected by the first exhaust temperature sensor 43, an oxidation catalyst HC / CO heating value input from the oxidation catalyst heating value estimation unit 76A, a sensor value of the MAF sensor 40, and outside air. The catalyst temperature of the oxidation catalyst 31 is estimated and calculated based on a model equation or map including, as an input value, the amount of heat released to the outside air estimated from the sensor value of the temperature sensor 47 or the intake air temperature sensor 48.

  The NOx catalyst temperature estimation unit 77B is an oxidation catalyst temperature (hereinafter also referred to as NOx catalyst inlet temperature) input from the oxidation catalyst temperature estimation unit 77A, and a NOx catalyst HC / CO heating value input from the NOx catalyst heating value estimation unit 76B. The catalyst temperature of the NOx occlusion reduction type catalyst 32 is estimated and calculated based on a model formula or map including, as an input value, the amount of heat released to the outside air estimated from the sensor value of the outside air temperature sensor 47 or the intake air temperature sensor 48.

  As described above in detail, in the present embodiment, when the NOx purge control and the forced filter regeneration control are performed by the post injection, the corrected correction in which the learning correction value is reflected in the calorific value estimation calculation of each of the catalysts 31 and 32. The post injection amount instruction value is used. As a result, it is possible to calculate the heat generation amount of the catalyst in consideration of the influence of the aging deterioration of the in-cylinder injector 11 with high accuracy, and the temperature estimation accuracy of each of the catalysts 31 and 32 can be reliably improved.

  In addition, by switching the HC / CO maps 71A to 73B and the like appropriately according to each operation state such as normal lean operation with different HC / CO emissions, filter forced regeneration, NOx purge, etc., these operation states are obtained. It is possible to calculate the HC / CO heat generation amount in the corresponding catalyst accurately, and the temperature estimation accuracy of each of the catalysts 31 and 32 can be effectively improved.

[FB control reference temperature selection]
The reference temperature selection unit 78 shown in FIG. 6 selects a reference temperature used for the temperature feedback control of the filter forced regeneration described above.

  In the exhaust gas purification system including the oxidation catalyst 31 and the NOx occlusion reduction type catalyst 32, the HC / CO heat generation amount in each of the catalysts 31, 32 varies depending on the heat generation characteristics of the catalyst. For this reason, it is preferable to select the catalyst temperature with the larger calorific value as the reference temperature for the temperature feedback control in order to improve the controllability.

  The reference temperature selection unit 78 selects one of the oxidation catalyst temperature and the NOx catalyst temperature that has a larger calorific value estimated from the operating state of the engine 10 at that time, and the filter regeneration control unit 51. The NOx purge control unit 60 and the occlusion amount estimation unit 80 are configured to transmit the reference temperature for the temperature feedback control. As described above, in this embodiment, the controllability can be effectively improved by selecting the catalyst temperature with the larger HC / CO heat generation amount as the reference temperature for the temperature feedback control.

[NOx / SOx occlusion estimation]
As shown in FIG. 7, the storage amount estimation unit 80 includes an SOx storage amount calculation unit 81 and a NOx storage amount calculation unit 82. The SOx occlusion amount calculation unit 81 is based on the following mathematical formula (3), and the total SOx occlusion amount when it is assumed that the entire amount is generated in the exhaust and is occluded in the occlusion material of the NOx occlusion reduction type catalyst 32. _{SOx_TTL} (g) is calculated.

数式（３）で示すように、総ＳＯｘ吸蔵量ＳＯｘ__ＴＴＬは、燃料由来のＳＯｘ量ＳＯｘ_{＿Ｆｕｅｌ}（ｇ／ｓ）とエンジンオイル由来のＳＯｘ量ＳＯｘ_＿ｏｉｌ（ｇ／ｓ）とＳＯｘ放出量ＳＯｘ_{_ｏｕｔ}（ｇ／ｓ）との総和を積分したものである。ここで、燃料由来のＳＯｘ量ＳＯｘ_{＿Ｆｕｅｌ}とエンジンオイル由来のＳＯｘ量ＳＯｘ_＿ｏｉｌとは、内燃機関の運転状態に基づいて演算される。ＳＯｘ放出量ＳＯｘ_{_ｏｕｔ}は、ＮＯｘ吸蔵還元型触媒３２の触媒温度等に基づいて演算される。触媒温度は、上述した触媒温度推定部７０によって推定される。ＳＯｘ放出量ＳＯｘ_{_ｏｕｔ}は負の値で表現されている。

As shown in Equation (3), the total amount of SOx occlusion SOx_ _TTL, the fuel from the SOx amount _{SOx _Fuel} (g / s) and the engine oil from the SOx amount _{SOx _oil} (g / s) and SOx emissions SOx _{_out} ( g / s) and the sum total. Here, the amount of SOx _{SOx _Oil} from SOx amount _{SOx _Fuel} and engine oil derived fuels, is calculated on the basis of the operating state of the internal combustion engine. The SOx release amount _{SOx_out} is calculated based on the catalyst temperature of the NOx storage reduction catalyst 32 and the like. The catalyst temperature is estimated by the catalyst temperature estimation unit 70 described above. The SOx release amount _{SOx_out} is expressed as a negative value.

Storage Here, the total amount of SOx occurring in the exhaust (i.e., the total amount of SOx occlusion SOx_ _TTL) is not necessarily occluded in the occlusion material of the NOx occlusion-reduction catalyst 32, the other materials and precious metals other than occlusion material Has been.

Therefore, in the present embodiment, SOx occlusion amount calculation unit 67, taking into account the amount of SOx occlusion of the non-absorbing material, the total amount of SOx occlusion SOx_ _TTL, predetermined storage rate coefficient C2 (0 <C2 <1 ) _Is estimated as the SOx occlusion amount _{SOx_STR} (g) in the occlusion material of the NOx occlusion reduction type catalyst 32. Here, the storage ratio coefficient C2 may be a constant obtained in advance by experiments or the like, or may be a variable read from a map that is referred to by the catalyst temperature and the heat history.

As described above, the SOx occlusion amount _{SOx_STR} in the occlusion material of the NOx occlusion reduction catalyst 32 is estimated in consideration of the SOx adsorption amount to other than the occlusion material, so that the NOx occlusion reduction catalyst 32 of the NOx occlusion reduction catalyst 32 can be estimated with higher accuracy. The SOx occlusion amount in the occlusion material can be estimated.

NOx storage amount calculation unit 82, based on the NOx & SOx occlusion level NOx & SOx_ _LEV following equation (4), calculates the NOx adsorption amount _NOx _ADS to be trapped by the occluding material of the NOx occlusion reduction type catalyst 32 (g / s) .

数式（４）で示すように、ＮＯｘ＆ＳＯｘ吸蔵量レベルＮＯｘ＆ＳＯｘ__ＬＥＶは、ＮＯｘ吸蔵量ＮＯｘ__ＳＴＲ（ｇ）と、ＳＯｘ吸蔵量演算部８１により算出されるＳＯｘ吸蔵量ＳＯｘ__ＳＴＲ（ｇ）との和をＮＯｘ吸蔵還元型触媒３２のＮＯｘ吸蔵容量ＬＮＴ_＿ＮＯｘ__{ＳＴＲ_ＣＡＰ}（ｇ）で除算した値である。ＮＯｘ吸蔵量ＮＯｘ__ＳＴＲ（ｇ）は、後述するＮＯｘ吸着量ＮＯｘ__ＡＤＳ（ｇ／ｓ）と、ＮＯｘ還元量ＮＯｘ__ＲＥＤ（ｇ／ｓ）とを逐次積算して得られる。

As shown in Equation (4), NOx & SOx occlusion amount level NOx & SOx_ _LEV is, NOx and NOx storage amount NOx_ _STR (g), the sum of the amount of SOx occlusion SOx_ _STR calculated (g) by SOx occlusion amount calculation unit 81 is a value obtained by dividing the NOx storage capacity _LNT _ _{NOx_ STR_CAP} the occlusion-reduction catalyst 32 (g). NOx occlusion amount NOx_ _STR (g) includes a later-described NOx adsorption amount NOx_ _ADS (g / s), is obtained by sequentially multiplying the NOx reduction amount NOx_ _RED (g / s).

The NOx occlusion amount calculation unit 82 calculates the NOx adsorption _{amount_ADS} (g / s) by taking the product of the NOx amount (engine exit NOx amount) discharged from the engine 10 and the occlusion efficiency of the NOx occlusion reduction type catalyst 32. ) Is calculated. The engine outlet NOx amount is estimated from the operating state of the engine 10 based on the engine speed Ne and the fuel injection amount Q. Storage efficiency of the NOx occlusion-reduction catalyst 32, the catalyst temperature of the NOx occlusion-reduction catalyst 32, gas flow rate (MAF value) is determined from the model formula or a map or the like including a NOx & SOx occlusion level NOx & SOx_ _LEV as an input value.

Reduced NOx amount _NOx _RED (g / s) is calculated based on the NOx & SOx occlusion level NOx & SOx_ _LEV of the equation (4). Specifically, the NOx occlusion amount calculation unit 77 calculates the NOx reduction amount NOx_ by taking the product of MAF (g / s) and the NOx occlusion efficiency of the NOx occlusion catalyst of the NOx occlusion reduction type catalyst 32. _RED (g / s) is calculated.

In this embodiment, rather than the total amount of SOx occlusion SOx_ _TTL, and calculates the NOx & SOx occlusion amount level NOx & SOx_ _LEV with the amount of SOx occlusion SOx_ _STR which is estimated to be occluded by the occluding material of the NOx occlusion-reduction catalyst 32 Therefore, the NOx & SOx occlusion amount level can be made more accurate.

Further, by using the NOx & SOx occlusion amount level NOx & SOx_ _LEV, since to calculate the storage efficiency of the NOx storage catalyst can be estimated more accurately NOx adsorption amount _{_} ADS (g / s). For this reason, the NOx occlusion amount _{NOx_STR} of the NOx occlusion reduction type catalyst 32 can be estimated with high accuracy.

[MAF tracking control]
The MAF follow-up control unit 85 includes (1) a switching period from the lean state of the normal operation to the rich state by the NOx purge control, and (2) a switching period from the rich state to the lean state of the normal operation by the NOx purge control. MAF follow-up control for correcting the fuel injection timing and the fuel injection amount of the in-cylinder injector 11 according to the MAF change is executed.

[Injection amount learning correction]
As shown in FIG. 8, the injection amount learning correction unit 90 includes a learning correction coefficient calculation unit 91 and an injection amount correction unit 92.

The learning correction coefficient calculation unit 91 is based on the error Δλ between the actual lambda value λ _Act detected by the NOx / lambda sensor 45 during the lean operation of the engine 10 and the estimated lambda value λ _Est, and the learning correction coefficient F for the fuel injection amount. Calculate _Corr . When the exhaust is in a lean state, the HC concentration in the exhaust is very low, so that the change in the exhaust lambda value due to the oxidation reaction of HC at the oxidation catalyst 31 is negligibly small. Therefore, the actual lambda value λ _Act in the exhaust gas that passes through the oxidation catalyst 31 and is detected by the downstream NOx / lambda sensor 45 matches the estimated lambda value λ _Est in the exhaust gas discharged from the engine 10. Conceivable. That is, when an error Δλ occurs between the actual lambda value λ _Act and the estimated lambda value λ _Est , it can be assumed that the difference is between the instructed injection amount for each in-cylinder injector 11 and the actual injection amount. Hereinafter, the learning correction coefficient calculation processing by the learning correction coefficient calculation unit 91 using the error Δλ will be described with reference to the flowchart of FIG. 9.

  In step S300, based on the engine speed Ne and the accelerator opening Q, it is determined whether or not the engine 10 is in a lean operation state. If it is in the lean operation state, the process proceeds to step S310 to start the calculation of the learning correction coefficient.

In step S310, an error Δλ obtained by subtracting the actual lambda value λ _Act detected by the NOx / lambda sensor 45 from the estimated lambda value λ _Est is multiplied by the learning value gain K ₁ and the correction sensitivity coefficient K ₂ to thereby obtain the learning value F _CorrAdpt is calculated (F _CorrAdpt = (λ _Est −λ _Act ) × K ₁ × K ₂ ). The estimated lambda value λ _Est is estimated and calculated from the operating state of the engine 10 according to the engine speed Ne and the accelerator opening Q. Further, the correction sensitivity coefficient _{K 2} is read the actual lambda value lambda _Act detected by the NOx / lambda sensor 45 from the correction sensitivity coefficient map 91A shown in FIG. 8 as an input signal.

In step S320, it is determined whether or not the absolute value | F _CorrAdpt | of the learning value F _CorrAdpt is within the range of the predetermined correction limit value A. If the absolute value | F _CorrAdpt | exceeds the correction limit value A, the present control is returned to stop the current learning.

In step S330, it is determined whether the learning prohibition flag _FPro is off. The learning prohibition flag F _Pro corresponds to, for example, a transient operation of the engine 10 or a NOx purge control (F _NP = 1). This is because when these conditions are satisfied, the error Δλ increases due to a change in the actual lambda value λ _Act , and accurate learning cannot be performed. Whether or not the engine 10 is in a transient operation state is determined based on, for example, the time change amount of the actual lambda value λ _Act detected by the NOx / lambda sensor 45 when the time change amount is larger than a predetermined threshold value. What is necessary is just to determine with a transient operation state.

In step S340, the learning value map 91B (see FIG. 8) referred to based on the engine speed Ne and the accelerator opening Q is updated to the learning value F _CorrAdpt calculated in step S310. More specifically, on the learning value map 91B, a plurality of learning areas divided according to the engine speed Ne and the accelerator opening Q are set. These learning regions are preferably set to have a narrower range as the region is used more frequently and to be wider as a region is used less frequently. As a result, learning accuracy is improved in regions where the usage frequency is high, and unlearning can be effectively prevented in regions where the usage frequency is low.

In step S350, the learning correction coefficient F _Corr is calculated by adding “1” to the learned value read from the learned value map 91B using the engine speed Ne and the accelerator opening Q as input signals (F _Corr = 1 + F). _CorrAdpt ). The learning correction coefficient F _Corr is input to the injection amount correction unit 92 shown in FIG.

The injection amount correction unit 92 multiplies each basic injection amount of pilot injection Q _Pilot , pre-injection Q _Pre , main injection Q _Main , after-injection Q _After , and post-injection Q _{Post by} a learning correction coefficient F _Corr. The injection amount is corrected.

In this way, by correcting the fuel injection amount to each in-cylinder injector 11 with a learning value corresponding to the error Δλ between the estimated lambda value λ _Est and the actual lambda value λ _Act , the aging deterioration and characteristics of each in-cylinder injector 11 are corrected. Variations such as changes and individual differences can be effectively eliminated.

[MAF correction coefficient]
MAF correction coefficient calculating unit 95 calculates the MAF correction coefficient _{Maf _Corr} used to set the MAF target value _{MAF NPL_Trgt} and the target injection amount _{Q NPR_Trgt} during NOx purge control.

In the present embodiment, the fuel injection amount of each in-cylinder injector 11 is corrected based on the error Δλ between the actual lambda value λ _Act detected by the NOx / lambda sensor 45 and the estimated lambda value λ _Est . However, since lambda is the ratio of air and fuel, the factor of error Δλ is not necessarily the only effect of the difference between the commanded injection amount and the actual injection amount for each in-cylinder injector 11. That is, there is a possibility that the error of the MAF sensor 40 as well as the in-cylinder injectors 11 affects the lambda error Δλ.

FIG. 10 is a block diagram showing the setting process of the MAF correction coefficient _{Maf_corr} by the MAF correction coefficient calculation unit 95. The correction coefficient setting map 96 is a map that is referred to based on the engine speed Ne and the accelerator opening Q. The MAF indicating the sensor characteristics of the MAF sensor 40 corresponding to the engine speed Ne and the accelerator opening Q is shown in FIG. The correction coefficient _{Maf_corr} is set in advance based on experiments or the like.

The MAF correction coefficient calculation unit 95 reads the MAF correction coefficient _{Maf_corr} from the correction coefficient setting map 96 using the engine speed Ne and the accelerator opening Q as input signals, and _{uses the} MAF correction coefficient _{Maf_corr} as the MAF target value calculation unit 62 and It transmits to the injection quantity target value calculating part 66. As a result, the sensor characteristics of the MAF sensor 40 can be effectively reflected in the settings of the MAF target value MAF _{NPL_Trgt} and the target injection amount Q _{NPR_Trgt} during the NOx purge control.

[Others]
In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

DESCRIPTION OF SYMBOLS 10 Engine 11 In-cylinder injector 12 Intake passage 13 Exhaust passage 16 Intake throttle valve 24 EGR valve 31 Oxidation catalyst 32 NOx occlusion reduction type catalyst 33 Filter 34 Exhaust injector 40 MAF sensor 45 NOx / lambda sensor 50 ECU

Claims (4)

An NOx reduction type catalyst that reduces and purifies NOx in the exhaust gas provided in the exhaust passage of the internal combustion engine, and an excess air ratio of the exhaust gas that is provided downstream of the NOx reduction type catalyst and flows through the exhaust passage. By switching the exhaust air-fuel ratio from the lean state to the rich state by using both the sensor for detecting the amount of air and the air system control for decreasing the intake air amount and the injection system control for increasing the fuel injection amount, An exhaust purification system comprising: a control unit that executes a regeneration process for recovering the purification capability;
The controller is
Fuel is injected at a first injection amount obtained by adding an injection amount commensurate with the amount of oxygen released from the NOx storage reduction catalyst to an injection amount necessary for reducing NOx released from the NOx storage reduction catalyst. First rich control;
A second rich control for injecting fuel at a second injection amount determined based on the amount of NOx stored in the NOx storage reduction catalyst and the temperature of the NOx storage reduction catalyst after the execution of the first rich control; , Do the exhaust purification system. The exhaust purification system according to claim 1, wherein the second rich control includes a control region in which a target excess air ratio is smaller than a target excess air ratio of the first rich control. 3. The exhaust gas according to claim 1, wherein the control unit performs the second rich control on condition that an excess air ratio detected by the sensor has reached a predetermined value after the first rich control is performed. Purification system. The sensor outputs one of positive and negative when the excess air ratio of the exhaust is equal to or greater than the predetermined value, and the other of positive and negative when the excess air ratio of the exhaust is less than the predetermined value. The exhaust gas purification system according to any one of claims 1 to 3, wherein an output is provided.

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