JP2010209835A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of learning a deposit ratio and an evaporation rate, and more appropriately adding fuel according to the geometric machine difference of a vehicle and fuel property. <P>SOLUTION: The exhaust emission control device for the internal combustion engine includes: a NOx storage reduction catalyst 34 provided in an exhaust flow passage 26 from the internal combustion engine 1 to purify exhaust gas and also regenerating an emission control function; and a fuel adding valve 21 adding fuel to the exhaust flow passage 26 upstream of the NOx storage reduction catalyst 34. An air-fuel ratio sensor 58 is provided for detecting an air-fuel ratio in the exhaust flow passage 26 downstream of the NOx storage reduction catalyst 34. The evaporation rate is calculated based on a reaching fuel estimated mode using two pairs of displacement, air-fuel ratio and cylinder injection quantity detected at time intervals after the fuel is added, and also the deposit ratio is calculated based on the minimum peak value of the air-fuel ratio by the air-fuel ratio sensor 58 after the fuel is added, displacement at that time, and a cylinder injection quantity (S170-S210). The amount of fuel added from the fuel adding valve 21 to the exhaust flow passage 26 is calculated based on the calculated deposit ratio and evaporation rate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine provided with a fuel addition valve for adding fuel to an exhaust passage.

  2. Description of the Related Art Conventionally, in an internal combustion engine that performs lean combustion in which the air is in excess of the stoichiometric air-fuel ratio, such as a lean burn gasoline engine or a diesel engine, for example, a NOx occlusion reduction type catalyst is used for purifying nitrogen oxide (NOx) in exhaust gas. In the NOx occlusion reduction type catalyst, NOx is occluded in a lean atmosphere, and the NOx occluded is reduced by being switched to the rich atmosphere and is discharged as harmless nitrogen, whereby the NOx occlusion reduction type catalyst is regenerated. In order to create this rich atmosphere, a fuel addition valve for directly adding fuel to the exhaust is provided, and the fuel is added to the exhaust passage.

  Further, a particulate filter is provided in the exhaust flow path of the internal combustion engine so that particulate matter contained in the exhaust gas of the internal combustion engine is not released to the atmosphere. The particulate matter in the exhaust gas is once collected by this filter, but if the amount of the particulate matter collected in the filter increases, the pressure of the exhaust gas upstream of the filter will rise, so that the output of the internal combustion engine and fuel consumption will be reduced. Induces deterioration. In such a case, the fuel is added to the exhaust gas from the fuel addition valve to raise the temperature of the filter, and the particulate matter deposited on the filter is oxidized to regenerate the filter that removes the particulate matter.

  In order to perform this fuel addition appropriately, for example, Patent Document 1 discloses that fuel is added from a preset map based on the exhaust flow rate, the exhaust temperature, and the temperature of the inner wall of the exhaust passage when adding fuel to the exhaust system. An exhaust purification device is described that estimates the amount of evaporation and calculates the amount of fuel added from the fuel addition valve in consideration of the amount of evaporation.

  Further, Patent Document 2 describes an exhaust purification device that prohibits fuel addition when the fuel accumulation amount in the exhaust system becomes larger than a reference accumulation amount by adding fuel from a fuel addition valve, and prevents white smoke generation. Has been. At that time, the rate of fuel adhering to the exhaust system among the added fuel and the evaporation rate of vapor from the added fuel and adhering fuel are calculated from a preset map based on the intake air amount and the exhaust temperature. The fuel accumulation amount is calculated from the adhesion rate, evaporation rate, and fuel addition amount.

JP 2002-038939 A JP 2005-180290 A

  Such a conventional apparatus is an open control that calculates the fuel addition amount based on a preset map, and is based on the exhaust flow rate, the intake air amount, the exhaust temperature, etc., irrespective of the geometrical difference of the vehicle and the fuel properties. Thus, the evaporation amount, the adhesion rate, and the evaporation rate are calculated. However, in actuality, there is a problem that the control performance according to the target cannot be obtained because the degree of adhesion varies depending on the geometrical difference of the vehicle, or the evaporation speed varies depending on the fuel properties.

  An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that learns the adhesion rate and the evaporation rate and can perform more appropriate fuel addition according to the geometrical difference of the vehicle and the fuel properties. .

In order to achieve this problem, the present invention has taken the following measures in order to solve the problem. That is,
An exhaust purification member provided in an exhaust passage from the internal combustion engine to purify exhaust and regenerate the purification function;
A fuel addition valve for adding fuel to the exhaust passage upstream of the exhaust purification member;
An arrival fuel estimation model for estimating the fuel reaching the exhaust purification member based on an addition pattern of the fuel addition valve, an adhesion rate of the added fuel to the exhaust passage, and an evaporation rate of the attached fuel from the exhaust passage; An exhaust gas purification apparatus for an internal combustion engine that regenerates the exhaust gas purification member with the added fuel,
Air-fuel ratio detection means for detecting an air-fuel ratio of the exhaust flow path downstream from the exhaust purification member;
Learning means for calculating the adhesion rate and the evaporation rate based on the arrived fuel estimation model using the air-fuel ratio detected by the air-fuel ratio detection means after the fuel addition, the exhaust amount at that time, and the in-cylinder injection amount. This is an exhaust emission control device for an internal combustion engine.

  The learning of the adhesion rate may be performed after the learning of the evaporation rate is completed. Further, the learning means for calculating the evaporation rate uses the at least two sets of exhaust amount, air-fuel ratio, and in-cylinder injection amount detected at intervals after the fuel addition, based on the reached fuel estimation model. The rate may be calculated. Alternatively, the learning means for calculating the adhesion rate uses the minimum peak value of the air-fuel ratio detected by the air-fuel ratio detection means after the fuel addition and the exhaust amount, air-fuel ratio, and in-cylinder injection amount at that time. The adhesion rate may be calculated based on the reached fuel estimation model. Further, the learning means may store the calculated adhesion rate and evaporation rate in association with the exhaust amount and the exhaust temperature at that time. The exhaust purification member may be configured to be at least one of a NOx catalyst that stores nitrogen oxides and a filter that collects particulate matter.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention learns the evaporation rate and the adhesion rate, so that the evaporation rate and the adhesion rate for each vehicle can be obtained, and the evaporation rate and the adhesion rate corresponding to the geometrical difference of the vehicle can be obtained. Moreover, since the evaporation rate and the adhesion rate according to the fuel properties are learned, there is an effect that appropriate fuel addition can be performed.

1 is a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine as one embodiment of the present invention. It is explanatory drawing of the estimation model of the fuel which reaches | attains the exhaust gas purification member of this embodiment. It is a graph which shows the relationship between the addition signal and adhesion fuel of this embodiment. It is a flowchart which shows an example of the adhesion rate / evaporation rate learning process performed in the electronic control circuit of this embodiment. It is a flowchart which shows an example of the addition control process performed in the electronic control circuit of this embodiment. It is a graph which shows the relationship between the addition signal of this embodiment, a counter value, and an air fuel ratio sensor output. It is a graph which shows the relationship between the addition signal of this embodiment, and the average value of attached fuel. It is a graph which shows the relationship between the catalyst arrival fuel amount and addition interval of this embodiment. It is a graph which shows the relationship between the addition signal of this embodiment, an air fuel ratio, and the amount of adhesion fuel.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine as one embodiment of the present invention. As shown in FIG. 1, the internal combustion engine 1 is a multi-cylinder, for example, a four-cylinder diesel engine in this embodiment, and a combustion chamber 8 is formed from a cylinder 2, a piston 4, and a cylinder head 6.

  The intake system of the internal combustion engine 1 is provided with an intake port 14 that communicates with the combustion chamber 8 via an intake valve 12, an intake passage 16, and a throttle valve 20 that adjusts the intake air amount. A fuel injection valve 21 that injects fuel into each combustion chamber 8 for each cylinder of the internal combustion engine 1 is provided in the cylinder head 6. The internal combustion engine 1 is not limited to a diesel engine, and may be a gasoline engine.

  The exhaust system of the internal combustion engine 1 is provided with an exhaust port 24 and an exhaust passage 26 that communicate with the combustion chamber 8 via an exhaust valve 22. A recirculation flow path 28 that connects the intake flow path 16 and the exhaust flow path 26 is provided, and a control valve 30 is interposed on the intake flow path 16 side of the recirculation flow path 28.

  The exhaust passage 26 is provided with an exhaust purification device 32 in which an exhaust purification member is internally provided. In this embodiment, a NOx occlusion reduction type catalyst (hereinafter referred to as LNT) 34 as an exhaust purification member is provided in the interior. Has been. The LNT 34 occludes NOx when the air-fuel ratio of the exhaust is lean, the air-fuel ratio in the exhaust becomes small (or the oxygen concentration becomes low), and a reducing agent such as HC or CO exists in the exhaust. In this case, the stored NOx is removed and reduced and purified.

  By utilizing this action, NOx in the exhaust is stored in the NOx storage agent when the air-fuel ratio of the exhaust is in a lean state, and when the storage efficiency of the NOx storage agent decreases after a certain period of use, the upstream of the NOx storage agent The NOx occluded in the NOx occlusion agent is removed by adding fuel or the like on the side, and NOx is further reduced by reacting with HC or CO in the exhaust gas and discharged as harmless nitrogen. By reducing NOx, HC and CO themselves are oxidized to water and carbon dioxide, and the LNT 34 is regenerated.

  Further, the exhaust purification member installed in the exhaust purification device 32 may be a diesel particulate filter (hereinafter referred to as DPF). Exhaust gas contains a large amount of particulates (particulate matter) mainly composed of carbon, and causes exhaust black smoke. The DPF is, for example, a honeycomb filter made of porous ceramic or the like, and has a large number of passages formed along the longitudinal direction. The DPF takes in oxygen and retains oxygen when excess oxygen is present in the surroundings, and An active oxygen release agent that releases retained oxygen in the form of active oxygen when the surrounding oxygen concentration is lowered is supported.

  The DPF is a well-known one that collects and burns such particulates. The collected particulates are burned, but the impurities contained in the particulates (additives contained in oil, fuel, etc.) adhere as ash-like burning residue, causing clogging when used for a long time, There is a risk of adversely affecting the operating state of the internal combustion engine 1.

  Therefore, for example, when the exhaust pressure difference between both sides of the DPF becomes a predetermined value or more, the fuel is supplied to the DPF, the fuel burns in the DPF, the DPF becomes high temperature, the deposit is burned, and the DPF Can be played. The exhaust purification member may be LNT34 or DPF, and at least one may be provided, but both LNT34 and DPF may be provided.

  The fuel system of the internal combustion engine 1 is provided with a common rail 36 that stores high-pressure fuel, and a high-pressure fuel supply pump 38 that pressurizes fuel from the fuel tank 37 and supplies the pressurized fuel to the common rail 36. The common rail 36 has a target pressure set based on the operating state and the like, and accumulates the high-pressure fuel supplied from the high-pressure fuel supply pump 38 to the target pressure. The fuel injection valve 21 injects high-pressure fuel supplied from the common rail 36 into the combustion chamber 8 in the cylinder of the internal combustion engine 1.

  Further, a fuel addition valve 41 for adding fuel from the high-pressure fuel supply pump 38 is provided in the exhaust passage 26 upstream of the LNT 34. The fuel addition valve 41 adjusts the air-fuel ratio of the exhaust passage 26 by changing an addition period T, an addition interval INT, the number n of additions, and the like, which will be described later, in accordance with an input addition signal.

  The detection system of the internal combustion engine 1 includes a throttle sensor 46 that detects the opening of the throttle valve 20, a rotation speed sensor 48 that detects the rotation speed of the internal combustion engine 1, and intake air that detects the amount of intake air into the intake passage 16. The air-fuel ratio is detected based on the oxygen concentration of the exhaust gas downstream of the amount sensor 50, the accelerator opening sensor 54 that detects the depression amount of the accelerator pedal 52, the exhaust gas temperature sensor 56 that detects the exhaust gas temperature upstream of the LNT 34, and the LNT 34. An air-fuel ratio sensor 58 is disposed.

  In the present embodiment, the exhaust amount described later of the exhaust passage 26 is calculated based on the intake air amount detected by the intake air amount sensor 50. However, the exhaust amount sensor that detects the exhaust amount in the exhaust passage 26 is calculated. May be provided. Further, the oxygen concentration of the air-fuel mixture used for combustion is reflected on the oxygen concentration in the exhaust gas by subtracting the oxygen supplied for combustion as it is. If the oxygen concentration (air-fuel ratio) in the air-fuel mixture is high, The oxygen concentration (air / fuel ratio) basically increases as well. Although the exhaust temperature sensor 56 is provided on the upstream side of the LNT 34, the exhaust temperature may be estimated from the operating state without being limited to this, and the exhaust temperature is estimated from a sensor that detects the temperature of the LNT 34. You may make it do.

  Each of the sensors is connected to an electronic control circuit 60. The electronic control circuit 60 is configured as a logical operation circuit centering on a well-known CPU 62, ROM 64, RAM 66, etc., and an input / output circuit 68 for inputting / outputting from / to the outside. They are connected to each other via a common bus 70.

  The CPU 62 inputs input signals from the throttle sensor 46, the rotational speed sensor 48, the intake air amount sensor 50, the accelerator opening sensor 54, the exhaust temperature sensor 56, the air-fuel ratio sensor 58, etc. via the input / output circuit 68, and these The CPU 62 outputs a signal to the fuel injection valve 21, the fuel addition valve 41, and the like via the input / output circuit 68 based on the above signal, data in the ROM 64 and RAM 66 and a control program stored in advance.

  In order to add an appropriate amount of fuel to the LNT 34, the amount of fuel flowing into the LNT 34 is estimated. The fuel that flows into the exhaust purification device 32 at the time of fuel addition evaporates and atomizes the fuel added from the fuel addition valve 41, and the fuel once attached to the wall surface of the exhaust passage 26 evaporates. There is a minute to reach. At the time of fuel addition, an appropriate amount of fuel is added by estimating the amount of fuel flowing into the LNT 34 in consideration of both the amount that directly reaches and the amount that the attached fuel evaporates and reaches.

  FIG. 2 shows an estimation model of fuel that is added from the fuel addition valve 41 into the exhaust passage 26 and reaches the LNT 34. As shown in FIG. 2, when fuel is added from the fuel addition valve 41 into the exhaust flow path 26, the evaporated or atomized fuel of the added fuel reaches the LNT 34 as it is, and the other one is added. Part of the fuel adheres to the wall surface of the exhaust passage 26. The evaporated fuel from the fuel once attached to the wall surface also reaches the LNT 34 after that.

  Here, if the amount of fuel adhering to the wall surface is Qa, the adhesion rate is α, the evaporation rate is β, and the addition amount from the fuel addition valve 41 is q, the amount of change in the fuel adhering to the wall surface is (1) It is shown by the formula. The attached fuel amount Qa and the added amount q are an amount per unit time and an amount per one period (fixed time) in performing a process described later.

dQa / dt = αq-βQa (1)
In addition, when fuel is added from the fuel addition valve 41, the fuel that reaches the LNT 34 includes the amount that the added fuel directly reaches after evaporation and atomization, and the fuel that has adhered to the wall surface of the exhaust passage 26. There is a part to evaporate. When the fuel is not added from the fuel addition valve 41, the fuel that reaches the LNT 34 has the amount that the fuel attached to the wall surface of the exhaust passage 26 evaporates. From this, the fuel amount Q reaching the LNT 34 at the time of addition is expressed by the following equation (2), and the fuel amount Q reaching the LNT 34 at the time of non-addition is expressed by the following equation (3).

Q = (1−α) q + βQa (2)
Q = βQa (3)
FIG. 3 shows the relationship between the addition signal to the fuel addition valve 41 and the adhered fuel in this ultimate fuel estimation model. As shown in FIG. 3A, a signal in which the addition period T and the addition interval INT are repeated at the time of one addition is input as the addition signal. As shown in FIG. 3 (b), when the fuel is added from the fuel addition valve 41 according to the addition period T and fuel is added, the amount Qa of fuel adhering to the wall surface of the exhaust passage 26 increases exponentially. During the addition interval INT, the fuel evaporates and the attached fuel amount Qa decreases exponentially. The adhering fuel amount Qa increases when the addition period T ends, and the adhering fuel amount Qa decreases when the addition interval INT ends.

  From the addition time T, the addition interval INT, the number n of additions, etc., the adhered fuel amount Qa # max (n) at the end of the nth addition period T can be calculated by the following equation (4). The attached fuel amount Qa # min (n-1) at the end of the interval INT can be calculated by the following equation (5).

次に、前述した電子制御回路６０において行われる付着率・蒸発率学習処理について、図４のフローチャートによって説明する。

Next, the adhesion rate / evaporation rate learning process performed in the electronic control circuit 60 will be described with reference to the flowchart of FIG.

  An injection amount command value is calculated from a previously stored map or the like based on the throttle opening detected by the throttle sensor 46 and the rotation speed detected by the rotation speed sensor 48 as the operating state of the internal combustion engine 1. Based on this injection amount command value, fuel is injected from the fuel injection valve 21 and the internal combustion engine 1 is operated.

  As described above, the LNT 34 has a characteristic of absorbing NOx if the oxygen concentration in the exhaust gas is high and reducing NOx to NO2 or NO if the oxygen concentration is low. Therefore, as long as the oxygen in the exhaust gas is in a high concentration state, the LNT 34 has NOx. Will be absorbed. However, there is a limit amount in the NOx absorption amount of the LNT 34, and when the LNT 34 absorbs the limit amount of NOx, NOx in the exhaust gas is not absorbed by the catalyst and passes through the LNT 34.

The fuel addition is performed, for example, when all of the following conditions (1) to (3) are satisfied.
(1) It is determined that the operation state of the internal combustion engine 1 is suitable for fuel addition from the relationship between the engine speed Ne and the accelerator depression amount. This corresponds to a condition in which the operating state of the internal combustion engine 1 is in a region where trouble such as torque fluctuation does not occur even when fuel addition is executed. For example, this condition is satisfied when decelerating.
(2) The exhaust temperature Tex is higher than a predetermined temperature (for example, 250 ° C.). This corresponds to a condition that the NOx catalyst is sufficiently activated.
(3) The NOx absorption amount of the NOx catalyst exceeds a predetermined amount. This means that the amount of NOx absorbed by the NOx catalyst has approached its limit value to some extent. This absorption amount may be estimated based on the elapsed time from the end of the previous fuel addition, the history of the air-fuel ratio and the exhaust temperature, and the like.

The electronic control circuit 60 determines that fuel addition should be executed when all of the conditions (1) to (3) are satisfied.
The adherence rate / evaporation rate learning process is performed by interruption every predetermined time with the regeneration process of the exhaust purification device 32. First, whether or not the fuel addition valve 41 has just started the addition of fuel to the exhaust passage 26 is determined. (Step 100, hereinafter referred to as S100, and so on).

  If it is immediately after the start of addition by the fuel addition valve 41 (S100: YES), first, the counter C_OFF is cleared (S110), and this control process is once ended and executed repeatedly at regular intervals. Next, when it is determined by the fuel addition valve 41 that it is not immediately after the start of addition (S100: NO), it is determined whether or not the counter C_OFF is equal to or less than the threshold value DELY_AF (S120).

  When the counter C_OFF is equal to or less than the set threshold value DELY_AF (S120: YES), the air-fuel ratio of the exhaust passage 26 detected by the air-fuel ratio sensor 58 is updated to the peak value (S130). That is, when the air-fuel ratio detected by the current process is smaller than the air-fuel ratio detected by the previous process, the air-fuel ratio is updated.

  Next, it is determined whether or not fuel is being added by the fuel addition valve 41 (S140). When fuel is being added by the fuel addition valve 41 (S140: YES), this control process is once ended. This control process is repeatedly executed, and when it is determined that the fuel is not being added by the process of S140 (S140: NO), it is determined whether or not the counter C_OFF is equal to or less than a preset upper limit value Te (S150). The upper limit value Te is a value sufficiently larger than the threshold value DELY_AF. The counter C_OFF continues to be counted up (S160) until the counter C_OFF exceeds the upper limit value Te (S150: YES).

  By repeatedly executing the processing from S100 to S160, as shown in FIG. 6A, immediately after the addition of fuel from the fuel addition valve 41 is started (S100: YES), it is shown in FIG. 6B. As described above, the counter C_OFF is cleared (S110).

  Then, by repeatedly executing this control process, the peak value of the air-fuel ratio is updated as shown in FIG. 6C until the counter C_OFF exceeds the threshold value DELY_AF. When fuel is added to the exhaust passage 26 by the opening / closing drive of n times from the fuel addition valve 41, a rich state is established and the LNT 34 is regenerated. FIG. 9 shows the relationship among the addition signal, the air-fuel ratio, and the amount of attached fuel.

  The output of the air-fuel ratio sensor 58 becomes a rich air-fuel ratio with a delay time according to the addition of fuel. The peak value AFpeak at which the air-fuel ratio is minimum is updated after the delay time after the fuel addition valve 41 finishes adding fuel. At the same time, the in-cylinder injection amount Qe from the fuel injection valve 21 when the air-fuel ratio takes the peak value AFpeak and the intake air amount detected by the intake air amount sensor 50 when the air-fuel ratio takes the peak value AFpeak are calculated. The displacement Ga is stored.

  After the air-fuel ratio updates the peak value AFpeak, the threshold value DELY_AF is set so that the counter C_OFF exceeds the threshold value DELY_AF. In this embodiment, the threshold value DELY_AF is set from a map (not shown) according to the exhaust amount. Yes.

  If it is determined by the process of S120 that the counter C_OFF has exceeded the threshold value DELY_AF (S120: NO), it is determined whether or not the counter C_OFF is the first set value T0 or the second set value T1 (S170). As shown in FIG. 6 (c), the first set value T0 and the second set value T1 are set in advance by experiments or the like in the middle of the air-fuel ratio returning from the rich state to the lean state after fuel addition. The value is larger than the threshold value DELY_AF and smaller than the upper limit value Te. The first set value T0 and the second set value T1 are set with a predetermined time interval Δt.

  When the counter C_OFF is the first set value T0 or the second set value T1 (S170: YES), a sample of evaporation rate estimation data is acquired (S180). In the present embodiment, when the counter C_OFF is the first set value T0 or the second set value T1, the air-fuel ratios AF0 and AF1 detected by the air-fuel ratio sensor 58 and the intake air amount detected by the intake air amount sensor 50 are used. The exhaust amounts Ga0 and Ga1 calculated based on the above and the fuel injection amounts Qe0 and Qe1 into the cylinder by the fuel injection valve 21 are acquired as data.

  Next, it is determined whether or not the air-fuel ratio peak value AFpeak and the evaporation ratio estimation air-fuel ratios AF0 and AF1 have been updated (S190). When updated (S190: YES), the evaporation rate β is calculated (S200), and the adhesion rate α is calculated (S210).

  The evaporation rate β is calculated from the fuel amounts Q0 and Q1 reaching the LNT 34 at the respective times of the first set value T0 and the second set value T1 based on the estimation model of the fuel reaching the LNT 34 described above (6 ) Is calculated by the following equation (7) derived from the equation.

また、到達燃料量Ｑ0 ，Ｑ1 は、空燃比の定義から、下記（８）（９）式により算出される。

Further, the reached fuel amounts Q0 and Q1 are calculated by the following equations (8) and (9) from the definition of the air-fuel ratio.

ここで、Ｑｅ0 ，Ｑｅ1 は、前述した第１設定値Ｔ0 または第２設定値Ｔ1 のときの燃料噴射弁２１による筒内への燃料噴射量である。Ｇａ0 ，Ｇａ1 は、前述した第１設定値Ｔ0 または第２設定値Ｔ1 のときの吸入空気量センサ５０により検出される吸入空気量に基づいて算出される排気量である。

Here, Qe0 and Qe1 are the amounts of fuel injected into the cylinder by the fuel injection valve 21 at the first set value T0 or the second set value T1 described above. Ga0 and Ga1 are exhaust amounts calculated based on the intake air amount detected by the intake air amount sensor 50 at the first set value T0 or the second set value T1 described above.

  In the calculation of the adhesion rate α, as shown in FIG. 7, the average value QT of the addition period of the adhered fuel amount is expressed by the following equation (10) for the sake of simplification regarding the nth fuel addition, outside the addition period of the adhered fuel amount. The average value QINT of is considered as the following equation (11).

このとき、ｎ回目の添加によるＬＮＴ３４への到達燃料量は、添加期間Ｔと非添加期間ＩＮＴの時間比から求まると考えると、付着率αは下記（１２）式から導かれる下記（１３）式により算出される。

At this time, assuming that the amount of fuel reaching the LNT 34 by the n-th addition is obtained from the time ratio between the addition period T and the non-addition period INT, the adhesion rate α is derived from the following expression (12), the following expression (13) Is calculated by

この最大到達燃料量Ｑmax が空燃比センサ５８により検出される空燃比が最小となるときのＬＮＴ３４に到達する燃料量であると考えれば、下記（１４）式から、空燃比のピーク値ＡＦpeakから最大到達燃料量Ｑmax を算出できる。よって、付着率αは下記（１４）を前記（１３）式に代入して算出できる。

Assuming that this maximum fuel amount Qmax is the amount of fuel that reaches the LNT 34 when the air-fuel ratio detected by the air-fuel ratio sensor 58 is minimum, the maximum value from the peak value AFpeak of the air-fuel ratio is obtained from the following equation (14). The reached fuel amount Qmax can be calculated. Therefore, the adhesion rate α can be calculated by substituting the following (14) into the equation (13).

ここで、Ｑｅは空燃比がピーク値ＡＦpeakをとるときの燃料噴射弁２１からの筒内噴射量、Ｇａは空燃比がピーク値ＡＦpeakをとるときの吸入空気量センサ５０により検出される吸入空気量に基づいて算出される排気量である。

Here, Qe is the in-cylinder injection amount from the fuel injection valve 21 when the air-fuel ratio takes the peak value AFpeak, and Ga is the intake air amount detected by the intake air amount sensor 50 when the air-fuel ratio takes the peak value AFpeak. The exhaust amount calculated based on

  The calculated evaporation rate β and adhesion rate α are stored as two-dimensional maps of the exhaust amount Ga and the exhaust temperature, respectively. By repeatedly performing this adhesion rate / evaporation rate learning process, the evaporation rate β and the adhesion rate α for each exhaust amount Ga and the exhaust temperature are obtained, so that the evaporation rate β and the adhesion rate α for each vehicle are obtained. The evaporation rate β and the deposition rate α corresponding to the geometric machine difference are obtained. Further, an evaporation rate β and an adhesion rate α corresponding to the properties of the fuel supplied are obtained.

  If it is determined in the process of S170 that the counter C_OFF is not the first set value T0 or the second set value T1 (S170: NO), no sample is acquired and the air-fuel ratio is not updated (S190). : NO), this control process is repeatedly executed without calculating the evaporation rate β and the adhesion rate α.

Next, an addition control process in which the fuel addition valve 41 is controlled using the evaporation rate β and the adhesion rate α to add fuel to the exhaust passage 26 will be described with reference to the flowchart of FIG.
First, the required catalyst reaching fuel amount Qreq to be supplied to the LNT 34 is calculated from the following equation (15) based on the exhaust state based on the current air-fuel ratio AF and the exhaust amount Ga and the target air-fuel ratio AF_TRG. The target air-fuel ratio AF_TRG is an air-fuel ratio that is brought into a rich state in order to process and regenerate NOx stored in the LNT 34, and the required catalyst arrival fuel amount Qreq is a fuel amount that is required for regeneration of the LNT 34 at that time .

次に、要求触媒到達燃料量Ｑreq に基づいて、基本添加パラメータを算出する（Ｓ３１０）。基本添加パラメータとして、燃料添加弁４１を駆動する際の添加期間Ｔと添加回数ｎとを算出する。これらの基本添加パラメータは、例えば、内燃機関の回転数とアクセル開度の２次元マップにより補間計算する。

Next, a basic addition parameter is calculated based on the required catalyst reaching fuel amount Qreq (S310). As basic addition parameters, an addition period T and the number n of additions when the fuel addition valve 41 is driven are calculated. These basic addition parameters are calculated by interpolation using, for example, a two-dimensional map of the rotational speed of the internal combustion engine and the accelerator opening.

  Next, the maximum value INT_MAX and the minimum value INT_MIN of the addition interval INT are calculated (S320). The maximum value INT_MAX and the minimum value INT_MIN are preset values, and are values indicating the control allowable range of the fuel addition valve 41.

  Then, the catalyst reaching fuel amount Q # min when the addition interval INT is the maximum value INT_MAX and the catalyst reaching fuel amount Q # max when the addition interval INT is the minimum value INT_MIN are calculated from the above-described equation (12).

  That is, the evaporation rate β and the adhesion rate α are read from the map of the evaporation rate β and the adhesion rate α calculated by the adhesion rate / evaporation rate learning process according to the exhaust amount Ga and the exhaust temperature at that time. Then, the amount of fuel reaching the catalyst Q # min when the addition period T and the addition interval INT calculated in S310 are the maximum value INT_MAX is calculated from the equation (12). Similarly, the catalyst reaching fuel amount Q # max when the addition interval INT is the minimum value INT_MIN is calculated from the equation (12).

  Then, as shown in FIG. 8, the maximum value INT_MAX and the minimum value INT_MIN of the addition interval INT are calculated by interpolating the catalyst arrival fuel amount Q # max and the catalyst arrival fuel amount Q # min with the required catalyst arrival fuel amount Qreq. Then, the corrected addition interval INTF is calculated (S340). Next, based on the addition period T, the number n of additions, and the corrected addition interval INTF, the fuel addition valve 41 is driven to add fuel to the exhaust passage 26 (S350).

  By repeatedly executing this adhesion rate / evaporation rate learning process, the calculated evaporation rate β and adhesion rate α are stored as two-dimensional maps of the exhaust amount Ga and the exhaust temperature, respectively. Therefore, since the evaporation rate β and the adhesion rate α are learned by the adhesion rate / evaporation rate learning process, the evaporation rate β and the adhesion rate α for each vehicle are obtained, and the evaporation rate β and the adhesion corresponding to the geometrical difference of the vehicle are obtained. The rate α is obtained.

  In addition, a plurality of components having different boiling points are mixed in the fuel, and the ratio may be slightly different depending on the fuel to be supplied. When the ratio is different, the evaporation rate β and the adhesion rate α are different, but the evaporation rate β and the adhesion rate α are learned by the adhesion rate / evaporation rate learning process, so an appropriate amount of fuel is added according to the fuel properties. It is possible to prevent the NOx reduction rate from decreasing and the generation of white smoke.

  The present invention is not limited to such embodiments as described above, and can be implemented in various modes without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 4 ... Piston 6 ... Cylinder head 8 ... Combustion chamber 16 ... Intake flow path 20 ... Throttle valve 21 ... Fuel injection valve 26 ... Exhaust flow path 28 ... Recirculation flow path 30 ... Control valve 32 ... Exhaust Purification device 34 ... NOx storage reduction catalyst (LNT)
36 ... Common rail 37 ... Fuel tank 38 ... High pressure fuel supply pump 41 ... Fuel addition valve 46 ... Throttle sensor 48 ... Revolution sensor 50 ... Intake air amount sensor 52 ... Accelerator pedal 54 ... Accelerator opening sensor 56 ... Exhaust temperature sensor 58 ... Air-fuel ratio sensor 60 ... Electronic control circuit

Claims (6)

An exhaust purification member provided in an exhaust passage from the internal combustion engine to purify exhaust and regenerate the purification function;
A fuel addition valve for adding fuel to the exhaust passage upstream of the exhaust purification member;
An arrival fuel estimation model for estimating the fuel reaching the exhaust purification member based on an addition pattern of the fuel addition valve, an adhesion rate of the added fuel to the exhaust passage, and an evaporation rate of the attached fuel from the exhaust passage; An exhaust gas purification apparatus for an internal combustion engine that regenerates the exhaust gas purification member with the added fuel,
Air-fuel ratio detection means for detecting an air-fuel ratio of the exhaust flow path downstream from the exhaust purification member;
Learning means for calculating the adhesion rate and the evaporation rate based on the arrived fuel estimation model using the air-fuel ratio detected by the air-fuel ratio detection means after the fuel addition, the exhaust amount at that time, and the in-cylinder injection amount. An exhaust emission control device for an internal combustion engine, characterized by comprising: The exhaust purification device for an internal combustion engine according to claim 1, wherein the learning of the adhesion rate is executed after the learning of the evaporation rate is completed. The learning means for calculating the evaporation rate uses the at least two sets of exhaust amount, air-fuel ratio, and in-cylinder injection amount detected at intervals after the fuel addition to calculate the evaporation rate based on the reached fuel estimation model. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is calculated. The learning means for calculating the adhesion rate uses the minimum peak value of the air-fuel ratio detected by the air-fuel ratio detection means after the addition of fuel and the exhaust amount, air-fuel ratio, and in-cylinder injection amount at that time to reach the reached fuel. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the adhesion rate is calculated based on an estimation model. The said learning means memorize | stores the calculated said adhesion rate and the said evaporation rate in correlation with the exhaust_gas | exhaustion amount and exhaust_gas | exhaustion temperature at that time, The said any one of Claim 3 or Claim 4 characterized by the above-mentioned. Exhaust gas purification device for internal combustion engine. 6. The exhaust purification member according to claim 1, wherein the exhaust purification member is at least one of a NOx catalyst that stores nitrogen oxides and a filter that collects particulate matter. An exhaust purification device for an internal combustion engine.

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