JP2007263053A - NOx STORAGE QUANTITY ESTIMATING METHOD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an NOx storage quantity estimating method for highly accurately estimating an NOx storage quantity, while using a polynomial of always modeling the newest catalyst state. <P>SOLUTION: This method estimates the NOx storage quantity of an NOx storage catalyst interposed in an exhaust passage of an engine, and comprises a process 12 of estimating the NOx storage quantity by using the polynomial of reflecting an NOx storage characteristic of the NOx storage catalyst. This process comprises a process 18 of successively correcting respective factors of the polynomial by adaptation estimating logic, and changes a value of a weighting factor of a point of not changing a value of the NOx conversion rate in response to a deterioration characteristic of the NOx storage catalyst, even if a catalyst characteristic of the NOx storage catalyst in the adaptation estimating logic changes. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for estimating a NOx occlusion amount for a NOx occlusion-type reduction catalyst (hereinafter referred to as a NOx occlusion catalyst) interposed in an exhaust passage.

  In general, the NOx occlusion catalyst occludes NOx (nitrogen oxide) in exhaust gas when the exhaust air-fuel ratio is lean, and releases and reduces NOx occluded when the exhaust air-fuel ratio is rich. Specifically, this catalyst has a characteristic of storing NOx in exhaust gas as nitrate in an oxygen excess state (oxidation atmosphere) and reducing the stored NOx to nitrogen in a carbon monoxide excess state (reduction atmosphere). ing.

And in the engine equipped with this catalyst, before the NOx occlusion amount reaches saturation, a rich spike that is intermittently switched to the rich operation is performed, and the performance degradation of the catalyst accompanying the increase in the NOx occlusion amount is suppressed. Thereby, the catalyst is regenerated and the exhaust gas is well purified.
Here, in order to perform this rich spike, it is necessary to accurately estimate or detect the NOx occlusion amount. Therefore, a technique for estimating the NOx occlusion amount using a mathematical catalyst model based on the chemical / physical reaction of the catalyst and using this model equation is disclosed (for example, Patent Document 1).
Japanese Patent Laid-Open No. 9-72235

  By the way, this technology is mainly applied to air-fuel ratio control of a three-way catalyst. That is, the model structure is different from the NOx storage catalyst, and it is difficult to apply to the NOx storage catalyst. In addition, when the NOx occlusion amount is estimated using another catalyst model, the model formula must be changed sequentially. This is because the characteristic value differs for each catalyst type. In addition, more detailed modeling is required to cope with catalyst degradation and the like. As described above, in the above-described technique, even if the NOx occlusion amount can be estimated, there is still a problem regarding the point of estimating the NOx occlusion amount with high accuracy.

  Here, in order to estimate the NOx occlusion amount with high accuracy, a polynomial that reflects the NOx occlusion characteristic is used, and the latest state is always modeled based on data collected by actual measurement, and the NOx occlusion amount is calculated. An estimation method can be considered. However, it should be noted that when using this method, it should not be limited only to the collected data. When data for a narrow region of the engine operating range is collected and the catalyst model is updated and estimated based only on this data, the catalyst model is subject to the fitting to this collected specific operating range, and in other operating ranges. This is because there is a concern that the estimation accuracy of the catalyst model is lowered.

Furthermore, when considering data in other areas other than the collected data, it is necessary to pay attention to the contribution of each data. This is because if the contribution degree of each data is set uniformly, the correction accuracy of the polynomial is lowered.
The present invention has been made in view of such problems, and provides a NOx occlusion amount estimation method that estimates the NOx occlusion amount with high accuracy while always using a polynomial modeled on the latest catalyst state. Objective.

  In order to achieve the above object, the NOx occlusion amount estimation method according to claim 1 is a method for estimating the NOx occlusion amount of the NOx occlusion catalyst interposed in the exhaust passage of the engine, the NOx occlusion catalyst NOx occlusion catalyst. A step of estimating the NOx occlusion amount using a polynomial reflecting the occlusion characteristic, and this step is performed even if the NOx purification rate measured in the exhaust passage and the catalyst characteristic of the NOx occlusion catalyst change. A step of sequentially correcting each coefficient of the polynomial based on the NOx purification rate at a specified point where the value of the NOx purification rate does not change, and performing the successive correction of each coefficient by the following adaptive estimation logic; The weighting coefficient value of the specified point data in the adaptive estimation logic is changed according to the deterioration characteristic of the NOx storage catalyst.

_{k new = k old + δ {} α 0 (r 0 -k old p 0 T) p 0 + α 1 (r 1 -k old p 1 T) p 1 + ··· + α N (r N -k old p N T ) P _N }
Here, k _new is a vector of updated values of coefficients of polynomial terms, k _old is a vector of previously calculated values of coefficients of polynomial terms, r _i is a NOx purification rate, p _i is a NOx occlusion ratio x and exhaust gas. A vector of each input value such as temperature y and SV value z, T is a transposed matrix, δ is a gain, α _i is a weighting coefficient of data collected by actual measurement or data of N specified points.

In the invention according to claim 2, the value of the weighting coefficient of the data of the point specified in the region where the NOx storage catalyst is likely to deteriorate is greater than the weighting coefficient of the data of the point specified in the region where deterioration is difficult. Is also set to be small.
Furthermore, in the invention according to claim 3, the points include points specified before the catalyst deteriorates, and the value of the weighting coefficient of the data at the points increases as the degree of deterioration of the NOx storage catalyst increases. It is characterized by being set to be small.

  Furthermore, in the invention according to claim 4, the points include points specified on the assumption that the catalyst is deteriorated, and the value of the weighting coefficient of the data of the point is large in the degree of deterioration of the NOx storage catalyst. It is characterized by being set so as to increase as the time goes.

  Therefore, according to the estimation method of the NOx storage amount of the present invention described in claim 1, when estimating the NOx storage amount using the polynomial reflecting the NOx storage characteristic, each coefficient of this polynomial is successively calculated by the adaptive estimation logic. It has been corrected. The first term on the right side of this logic is the previous coefficient, and the portion indicated by the subscript 0 in the second term corresponds to data collected by actual measurement. And the part shown with the subscripts 1-N in the same term is equivalent to the data of N specified points in other areas other than the actual measurement area. Therefore, even if the measured data is concentrated in a narrow area, it is possible to identify each coefficient of the polynomial taking into account the data of other areas away from this narrow area. The value is based on correct data.

In addition, since the value of the weighting coefficient of the data of the point in this logic is changed according to the deterioration characteristic of the NOx storage catalyst, the correction accuracy of the above-described polynomial is improved. As a result, this contributes to improvement in the estimation accuracy of the NOx occlusion amount.
According to the second aspect of the present invention, the value of the weighting coefficient of the point data is set to be small in a region where the NOx storage catalyst is likely to deteriorate, and is set to be large in a region where the NOx storage catalyst is difficult to deteriorate. Since the weighting coefficient is optimized, the polynomial is appropriately corrected according to the change in the catalyst characteristics, and the correction accuracy is further improved.

  Furthermore, according to the invention described in claim 3, the value of the weighting coefficient of the data of the point specified on the assumption that the catalyst is not deteriorated is set to be large when the deterioration progress of the NOx storage catalyst is small. And attach importance. On the other hand, when the degree of progress of deterioration of the NOx storage catalyst is large, it is set small and is not regarded as important. As described above, since the weighting coefficient of the data at the point is scheduled in accordance with the change in the catalyst characteristics, the polynomial is appropriately corrected in accordance with the change in the catalyst characteristics, and the correction accuracy is further improved.

  Furthermore, according to the invention of claim 4, the value of the weighting coefficient of the data at the point specified assuming that the catalyst has deteriorated is set to be small when the degree of deterioration of the NOx storage catalyst is small. I do not attach importance. On the other hand, when the degree of progress of deterioration of the NOx storage catalyst is large, it is important to set it small. As described above, since the weighting coefficient of the data at the point is scheduled in accordance with the change in the catalyst characteristics, the polynomial is appropriately corrected in accordance with the change in the catalyst characteristics, and the correction accuracy is further improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration diagram of a vehicle exhaust system to which the present invention is applied. As shown in the figure, a NOx storage catalyst 4 is interposed in the exhaust passage 2. This catalyst 4 occludes NOx in the exhaust gas when the exhaust air-fuel ratio is leaner than stoichiometric, and unburned fuel (HC) or carbon monoxide as a reducing agent in the exhaust gas when the exhaust air-fuel ratio is rich. When (CO) is present, the stored NOx is released and reduced. The catalyst 4 has a known structure.

A NOx sensor 6 for detecting the NOx concentration on the catalyst outlet side is provided downstream of the catalyst 4. Although not shown, the exhaust passage 2 is provided with an O ₂ sensor, a temperature sensor, an air flow sensor (AFS), and the like. These sensors each have an oxygen concentration [O ₂ ] in the exhaust passage ₂ . The exhaust gas temperature [y] and the SV value (or exhaust gas flow velocity) [z] are detected.

  Each sensor described above is electrically connected to an ECU (electronic control unit) 10. The ECU 10 includes an input / output device, a storage device (ROM, RAM, non-volatile RAM, etc.), a calculation device (CPU), a timer counter, and the like. Control is implemented. Further, the ECU 10 is provided with various maps. For example, the NOx concentration [NOx], the CO concentration [CO], and the HC concentration [HC] on the catalyst inlet side are read from the map using the accelerator opening and the engine speed as parameters, respectively. These values may be detected directly from various sensors provided in the exhaust passage 2 instead of the map.

Here, the ECU 10 of the present embodiment includes an occlusion amount estimation unit 12, and the NOx occlusion amount is calculated by a four-dimensional linear polynomial reflecting the NOx occlusion characteristic of the catalyst 4.
More specifically, as shown in FIG. 2, the occlusion amount estimation unit 12 has an estimated NOx purification rate calculation unit 14, and the calculation unit 14 stores a polynomial represented by Expression (1). Then, when each coefficient k _i (i = 0, 1, 2,...) Of the polynomial identified by the coefficient identification unit 18 is used and the NOx occlusion ratio [x] in the catalyst 4 is specified, a known exhaust gas is obtained. The NOx purification rate [r _E ] is calculated from the temperature [y] and the SV value [z].

r _E = f (x, y, z)
= K ₀ + k ₁ x + k ₂ y + k ₃ z + k ₄ xy + k ₅ yz
+ K ₆ zx + k ₇ x ² y + k ₈ xy ² +... (1)
As described above, the NOx storage characteristic of the catalyst 4 can be known in advance by experiments or the like, and can be approximated by a polynomial expression. In addition, the order of Formula (1) can be set arbitrarily.

Next, the occlusion amount estimation unit 12 has an occlusion amount calculation unit 20, in which the equation (2) obtained by modifying the equation (1) is stored, and each coefficient identified by the coefficient identification unit 18 is stored. When the coefficient k _i and the exhaust gas temperature [y] and SV value [z] is input, NOx occlusion ratio in the catalyst 4 [x] that is, the current storage amount / maximum storage amount is calculated.
x = _{[r E - (k 0 + k} 2 y + k 3 z + ··) ] _{/ (k 1 + k 4 y} + ··) ··· (2)
The NOx occlusion ratio [x] specified by the equation (2) is an instantaneous NOx occlusion amount in the calculation cycle in the initial stage, but as shown in FIG. 2, this NOx occlusion ratio [x] Returning to the equation (1) of the calculation unit 14, this NOx occlusion ratio [x] is used in the calculation of the NOx purification rate [r _E ] in the next calculation cycle. In other words, in Formula (1), using the NOx occlusion ratio [x] obtained last time, the exhaust gas temperature [y] and the SV value [z] newly detected in the current calculation cycle, NOx purification rate [r _E ] is calculated. As described above, the storage amount estimation unit 12 calculates the NOx purification rate [r _E ] by repeatedly returning the NOx storage ratio [x] to Equation (1).

On the other hand, the occlusion amount estimation unit 12 has an actual NOx purification rate calculating unit 16, and the NOx purification rate [r _R ] is obtained by using the equation (3).
r _R = ([NOx] −NOx concentration on the catalyst outlet side) / [NOx] (3)
The NOx concentration on the catalyst outlet side is a value detected by the NOx sensor 6, and [NOx] is a value obtained from the map. The NOx purification rate [r _E ] obtained by equation (1) is defined as an estimated value (calculated value), whereas the NOx purification rate [r _R ] obtained by equation (3) is It is defined as a sensor value (actual value).

By the way, the polynomial in the equation (1) is configured as an equation in which each coefficient k _i is sequentially corrected during lean operation based on the detected value of the NOx sensor 6 and the latest catalyst state is always modeled.
More specifically, in view of the fact that each coefficient k _i is an accurate value, the NOx purification rate [r _E ] in Equation (1) matches the NOx purification rate [r _R ] in Equation (3). The coefficient identification unit 18 compares the estimated value [r _E ] of the NOx purification rate with the actually measured value [r _R ], and finds a difference between the estimated value [r _E ] and the actually measured value [r _R ]. If present, each coefficient k _i is corrected so that the estimated value [r _E ] becomes the actually measured value [r _R ]. This correction is performed every time the NOx occlusion ratio [x] is returned to the equation (1) to calculate the NOx purification rate [r _E ]. In other words, the characteristics of the catalyst 4 change depending on the use situation, aging deterioration, etc., but each coefficient k _i is corrected over and over again, so that the polynomial in the equation (1) changes the state of the catalyst 4. The expression has been corrected to be accurate.

Moreover, in the coefficient identification unit 18 of the present embodiment, p is an input value vector [1, x, y, z, xy, yz, etc.] such as the NOx occlusion ratio [x], exhaust gas temperature [y], and SV value [z]. ..], Where T is a transposed matrix, δ is a gain, and α is a weighting coefficient for data, each coefficient k _i is corrected using the adaptive estimation logic of Equation (4).

・・・（４）
ここで、左辺のｋ_ｎｅｗは各係数ｋ_ｉの今回の値のベクトル、右辺第１項のｋ_ｏｌｄは各係数ｋ_ｉの前回の値のベクトル、右辺第２項中のｉ＝０で示される部分は実測によって収集された収集データに相当する。そして、右辺第２項中のｉ＝１〜Ｎで示される部分は、実測によって収集された領域以外の他の領域にＮ個の特定されたポイントの基準データに相当する。

... (4)
Here, the left side of the k _{new new} is indicated in this vector of values, the right-hand side vector of the previous value of k _old the first term each coefficient k _i, i = 0 on the right side in the second term of the coefficient k _i The portion corresponds to the collected data collected by actual measurement. The portion indicated by i = 1 to N in the second term on the right side corresponds to the reference data of N points specified in other regions other than the region collected by actual measurement.

  The other region of the present embodiment is a point where the value does not change even when the catalyst characteristics of the catalyst 4 change (for example, deterioration) (for example, when the exhaust gas temperature [y] is low or high). The NOx purification rate at this point is substantially zero when the exhaust gas temperature [y] is low or high. Therefore, the coefficient identification unit 18 obtains an invariable NOx purification rate based on the above points.

In addition, in this embodiment, when correcting each coefficient k _i , the value of the weighting coefficient of the reference data is changed according to the deterioration characteristic of the catalyst 4, and the weighting coefficient is optimized and scheduled.
Specifically, first, in FIG. 3, with respect to the exhaust gas temperature range corresponding to the operating state of the engine, the measured value of the NOx purification rate before deterioration of the catalyst 4 (indicated by a solid line in the figure: true value), The measured values of the NOx purification rate after deterioration (shown by dotted lines in the figure: true values) are respectively shown, and as indicated by the arrows in the figure, the shape of the mountain shape is shown as the catalyst 4 deteriorates. It turns out that it becomes small toward the inside.

Here, in the catalyst 4 in the figure, assuming that a catalyst having a property of small change on the low temperature side of the exhaust gas temperature [y] is used, among the reference data, the exhaust gas temperature [y] is at the lowest temperature. (Indicated by ● in the figure) is a point where the NOx purification rate is substantially zero and is an invariable value and is difficult to move inward. Therefore, in this embodiment, the value of the weighting coefficient of the reference data is set large as a point that places particular importance on the point. On the other hand, at the highest temperature of the exhaust gas temperature [y], even if the NOx purification rate is substantially zero and an invariable value, it is a point that is easily moved inward as shown in the figure. The value of the weighting coefficient is set small. In other words, the coefficient identification unit 18 sets, for example, α ₁ and α _{N in} Expression (4) to different values in one system, and changes the value of the weighting coefficient for each point. It is.

In addition, when the value of the weighting coefficient of the reference data at a point that is particularly important is set to be large, the value of the weighting coefficient value for each point may be changed for each separate system.
Specifically, although there are separate systems depending on the engine, catalyst, vehicle type, and destination, for example, as shown in FIG. 4, the normal temperature range (indicated by a one-dot chain line in the figure) is the exhaust gas temperature [y]. For vehicle models that are on the low temperature side (for example, dumps), set the weighting factor of the reference data to a large value as a point that places special emphasis on the lowest temperature (indicated by ● in the figure) of the exhaust gas temperature [y] in the normal temperature range. . On the other hand, in a vehicle type (for example, cargo) in which the normal temperature range (indicated by a two-dot chain line in the figure) is on the high temperature side of the exhaust gas temperature [y], the exhaust gas temperature [y] is highest in the normal temperature range (FIG. It is possible to set a large value for the weighting coefficient of the reference data as a point that places emphasis on (indicated by middle circles).

Next, in any of the systems described above, optimal weighting factor scheduling may be performed according to the current operation status, the progress of deterioration of the catalyst 4, and the like.
For example, as indicated by point A in FIG. 5 (indicated by ● in the figure), the NOx purification rate rises from substantially zero before the catalyst deteriorates, or the NOx purification rate falls and falls to substantially zero. In this case, the degree of importance is high as a reference point of the catalyst characteristic curve when the degree of deterioration of the NOx storage catalyst is small. When the degree of progress of deterioration of the NOx storage catalyst increases, point A is far from the point where the NOx purification rate rises from substantially zero or the point where the NOx purification rate falls and falls to substantially zero. Is low. Therefore, as shown in FIG. 6, the value of the weighting coefficient of the data at point A is set to be large when the deterioration progress of the NOx storage catalyst is small, and is set to be small when the deterioration progress of the NOx storage catalyst is large. Is done.

  On the other hand, as shown by point B in FIG. 5 (indicated by a circle in the figure), the point at which the NOx purification rate rises from substantially zero or the point at which the NOx purification rate falls and falls to substantially zero after the catalyst has deteriorated. In this case, the degree of importance is high as a reference point of the catalyst characteristic curve when the degree of deterioration of the NOx storage catalyst is large. When the deterioration degree of the NOx storage catalyst is small, the point B is away from the point where the NOx purification rate rises from substantially zero or the point where the NOx purification rate falls and falls to substantially zero. Less important. Therefore, as shown in FIG. 6, the value of the weighting coefficient of the data at point B is set to be large when the deterioration progress degree of the NOx storage catalyst is large, and is set to be small when the deterioration progress degree of the NOx storage catalyst is small. Is done.

Subsequently, each coefficient k _i identified by the coefficient identification unit 18 described above is output to the estimated NOx purification rate calculation part 14 and the storage amount calculation unit 20, and the calculation unit 20 calculates the NOx storage ratio [x]. Is done. Next, the NOx occlusion ratio [x] is repeatedly returned to the equation (1) to calculate the NOx purification rate [r _E ], whereby the integrated value of NOx occluded in the catalyst 4 (NOx occlusion amount) is highly accurate. It can be calculated.

On the other hand, storage amount estimating section 12 has a discharge amount calculating unit 24, in the arithmetic unit 24, wherein during the rich operation (5), to calculate the NOx emission amount q _d using Equation (6) Yes. This is because NOx is released from the catalyst 4 during the rich operation, so that the NOx release amount is accurately estimated or detected and the initial value of the NOx occlusion amount at the next lean operation is accurately calculated. Incidentally, when switched to rich operation from the lean operation, the coefficients k _i lean the coefficient identification unit 18 operating end is retained, NOx occlusion percentage of lean operation end in storage amount calculating unit 20 [x], i.e., The NOx occlusion amount is stored.

q _d = ∫ ([CO], [HC] concentration × [r ′] − 0.5 × [O ₂ ]) × [z] (5)
[R ′] = f (y, z) (6)
Here, [r ′] is the reducing agent utilization rate, and a map (not shown) is provided. This map stores the characteristics of the reducing agent utilization rate [r ′] based on the exhaust gas temperature [y] and the SV value [z], and the reducing agent utilization rate is calculated from the exhaust gas temperature [y] and the SV value [z]. [R ′] is set.

Next, the occlusion amount estimation unit 12 includes a final occlusion amount calculation unit 22. In the arithmetic unit 22, when switched back to lean operation from rich operation, subtracts the NOx emission amount q _d from the NOx occlusion amount of lean operation end, NOx storage remaining in the catalyst 4 at the rich operation at the end The amount Q _a , that is, the initial value of the NOx occlusion amount at the next lean operation is calculated.

Further, in the arithmetic unit 22, the estimated value of the NOx purification rate of the rich operation at the end _{[r E]} and the measured value is compared with _{[r R]} and the estimated value _{[r E]} and the measured value _{[r R]} and the When the difference exceeds the threshold A, it is determined that the NOx occlusion amount remaining in the catalyst 4 at the end of the rich operation is not accurate, and the estimated value [r _E ] is the measured value [r _R ], The initial value of the NOx occlusion amount during the lean operation is corrected based on the equation (2).

As described above, according to the present invention, when the NOx occlusion amount is estimated using the polynomial of the equation (1) reflecting the NOx occlusion characteristic, each coefficient k _{i of} this polynomial is the adaptive estimation of the equation (4). It is sequentially corrected by logic. Therefore, even if the measurement is data concentrated in a narrow area, it is possible to identify each coefficient k _{i of the} polynomial considering the data of other areas away from this narrow area. It becomes a global value based on the data.

  In addition, the value of the weighting coefficient of the reference data of this logic is changed according to the deterioration characteristics of the catalyst 4, and more specifically, as shown in FIG. 3 and FIG. 4 is set large in the region where deterioration is difficult, and the weighting coefficient is optimized. Thus, the polynomial model is appropriately corrected according to changes in the catalyst characteristics, and the correction accuracy is further improved.

  Further, as shown in FIG. 6, at the point A specified on the assumption that the catalyst 4 is not deteriorated, when the degree of deterioration of the catalyst 4 is small, it is compared with the value of the weighting coefficient when the degree of deterioration is large. It is important to be set large. On the other hand, when the degree of deterioration progress of the catalyst 4 is large, it is set to be smaller than the value of the weighting coefficient when the degree of deterioration progress is small and is not regarded as important. Further, at the point B specified by assuming that the catalyst has been deteriorated, when the degree of deterioration of the catalyst 4 is small, it is important to be set smaller than the weighting coefficient when the degree of deterioration is large. Don't look. On the other hand, when the degree of progress of deterioration of the NOx storage catalyst is large, it is important that the NOx storage catalyst is set larger than the weighting coefficient when the degree of progress of deterioration is small. In this way, since the scheduling of the weighting coefficient of the reference data is performed in accordance with the change in the catalyst characteristics, the model based on the polynomial is appropriately corrected according to the change in the catalyst characteristics, and the correction accuracy is further improved.

As a result, this contributes to improvement in the estimation accuracy of the NOx occlusion amount. As a result, since the execution time of the rich spike is determined based on the NOx occlusion amount, the interval between the rich spikes can be optimized, and the NOx purification rate can be improved and the fuel consumption can be suppressed.
In addition, since the accuracy of monitoring the state of the catalyst 4 is improved, the vehicle can be provided with a function for determining the timing of the S purge, a function for warning the driver of catalyst deterioration, and the like.

  The description of one embodiment of the present invention is finished above, but the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

It is a schematic block diagram of the exhaust system explaining the estimation method of the NOx occlusion amount which concerns on one Embodiment of this invention. It is a block diagram of the occlusion amount estimation part comprised by ECU of FIG. FIG. 2 is a relationship diagram between a NOx purification rate and exhaust gas temperature by the estimation method of FIG. 1. FIG. 2 is a relationship diagram between a NOx purification rate and exhaust gas temperature by the estimation method of FIG. 1. FIG. 2 is a relationship diagram between a NOx purification rate and exhaust gas temperature by the estimation method of FIG. 1. FIG. 2 is a relationship diagram between a logic weighting coefficient and a catalyst deterioration progress degree according to the estimation method of FIG. 1.

Explanation of symbols

2 Exhaust passage 4 NOx storage catalyst 10 ECU (electronic control unit)
12 Occupation Amount Estimation Unit 18 Coefficient Identification Unit

Claims (4)

A method for estimating a NOx occlusion amount of a NOx occlusion catalyst interposed in an exhaust passage of an engine,
The NOx occlusion amount is estimated using a polynomial reflecting the NOx occlusion characteristics of the NOx occlusion catalyst,
The step is based on the NOx purification rate measured in the exhaust passage and the NOx purification rate at a specified point where the value of the NOx purification rate does not change even if the catalyst characteristics of the NOx storage catalyst change. A step of sequentially correcting each coefficient of the polynomial, the correction of each coefficient is performed by the following adaptive estimation logic, and the weighting coefficient value of the data of the specified point in the adaptive estimation logic is the NOx A NOx occlusion amount estimation method, wherein the NOx occlusion amount is changed according to the deterioration characteristics of the occlusion catalyst.
_{k new = k old + δ {} α 0 (r 0 -k old p 0 T) p 0 + α 1 (r 1 -k old p 1 T) p 1 + ··· + α N (r N -k old p N T ) P _N }
Here, k _new is a vector of updated values of coefficients of polynomial terms, k _old is a vector of previously calculated values of coefficients of polynomial terms, r _i is a NOx purification rate, p _i is a NOx occlusion ratio x and exhaust gas. A vector of each input value such as temperature y and SV value z, T is a transposed matrix, δ is a gain, α _i is a weighting coefficient of data collected by actual measurement or data of N specified points.   The value of the weighting coefficient of the point data specified in the easily deteriorated region of the NOx storage catalyst is set smaller than the weighting coefficient of the point data specified in the hardly deteriorated region. The NOx occlusion amount estimation method according to claim 1.   The point includes a point specified before the catalyst deteriorates, and the weighting coefficient value of the data of the point is set so as to decrease as the deterioration progress degree of the NOx storage catalyst increases. The NOx occlusion amount estimation method according to claim 1, wherein the NOx occlusion amount is an estimation method.   The points include the points specified on the assumption that the catalyst has deteriorated, and the value of the weighting coefficient of the data at the points is set to increase as the degree of deterioration of the NOx storage catalyst increases. The NOx occlusion amount estimation method according to claim 1.

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