JP2010106718A - Exhaust gas estimation device of internal combustion engine - Google Patents

Abstract

The present invention relates to an exhaust gas estimation device for an internal combustion engine, and an object thereof is to ensure good estimation accuracy of exhaust gas information in consideration of catalyst deterioration while avoiding an increase in calculation load.
A catalyst model 60 is provided that receives information on a gas containing a catalyst flowing into a catalyst 40 disposed in an exhaust passage 22 of an internal combustion engine 10 and outputs information on a catalyst output gas. Using the catalyst model 60, the catalyst bed temperature Tw (i) and the purification amount X (i) are calculated for each part of the catalyst 40 virtually divided into a plurality of parts. When the calculated catalyst bed temperature Tw (i) is higher than a predetermined threshold, the calculation of the purification amount X (i) related to the corresponding divided part is skipped.
[Selection] Figure 2

Description

  The present invention relates to an exhaust gas estimation device for an internal combustion engine.

  Conventionally, for example, Patent Document 1 discloses an exhaust gas estimation device used for an internal combustion engine. This conventional estimation device uses a catalyst-containing gas model that estimates the characteristics of gas flowing into the catalyst based on the operating state of the internal combustion engine, and a gas that flows into the catalyst using a preliminarily constructed general formula for the catalytic reaction. A catalyst model for estimating the characteristics of the gas discharged from the catalyst based on the characteristics of the catalyst, and a catalyst deterioration model for obtaining a correction term for correcting the general formula based on the thermal load applied to the catalyst. .

JP 2002-195080 A JP 2007-327475 A Japanese National Patent Publication No. 10-512647 JP 2007-239472 A

  According to the above-described conventional estimation device, by correcting the general formula based on the thermal load applied to the catalyst, the characteristics of the gas discharged from the catalyst can be improved in consideration of the deterioration of the catalyst due to the thermal load. It is possible to estimate with accuracy. However, when correcting the general expression as described above, it may be necessary to perform a complicated calculation, and there is a concern that the calculation load increases.

  The present invention has been made to solve the above-described problems, and is an internal combustion engine that can ensure good estimation accuracy of exhaust gas information in consideration of catalyst deterioration while avoiding an increase in calculation load. An object is to provide an exhaust gas estimation device.

A first invention is an exhaust gas estimation device for an internal combustion engine,
A catalyst disposed in the exhaust passage of the internal combustion engine;
Temperature acquisition means for dividing the catalyst into a plurality of parts, and obtaining the catalyst bed temperature for each part or the inlet gas temperature for each part;
Purification index calculating means for calculating an estimated value of the purification rate or amount of unpurified components contained in the exhaust gas for each part, and
When the catalyst bed temperature or the inlet gas temperature acquired by the temperature acquisition unit is higher than a predetermined threshold, the purification index calculation unit omits calculation of the estimated value for the corresponding part. Including omission means.

The second invention is the first invention, wherein
The plurality of portions of the catalyst are divided more finely on the upstream side of the exhaust gas flow than on the downstream side of the flow.

The third invention is the first or second invention, wherein
Inlet gas flow rate acquisition means for acquiring the flow rate of the inlet gas flowing into the catalyst;
A dividing number variable means for reducing the dividing number of the plurality of portions in the flow direction of the exhaust gas when the inlet gas flow rate of the catalyst is small and the fluctuation of the inlet gas temperature of the catalyst is small;
Is further provided.

  According to the first aspect of the invention, the catalyst bed temperature or the inlet gas temperature is considered to have deteriorated at the divided portion, and the calculation of the purification rate or the estimated amount of purification is omitted. Catalyst degradation can be easily taken into account without adding a new model to consider degradation. As a result, it is possible to ensure good estimation accuracy of the exhaust gas information in consideration of catalyst deterioration while reducing the calculation load.

  According to the second invention, it is possible to effectively improve the estimation accuracy even when the number of divisions is the same as in the case of division at equal intervals.

  When the flow rate (flow velocity) of the inlet gas flowing into the catalyst is small and the fluctuation of the inlet gas temperature is small, the estimation accuracy of the exhaust gas becomes relatively good even if the number of divisions in the flow direction of the exhaust gas is small. For this reason, according to the third invention, by reducing the number of divisions under such circumstances as compared with other situations, it is possible to satisfactorily reduce the calculation load and optimize the estimation accuracy of the exhaust gas. it can.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a configuration of an internal combustion engine system to which an exhaust gas estimation device for an internal combustion engine according to Embodiment 1 of the present invention is applied. The system of this embodiment includes an internal combustion engine 10. Here, it is assumed that the internal combustion engine 10 is an in-line four-cylinder engine. A piston 12 is provided in the cylinder of the internal combustion engine 10. The piston 12 is connected to the crankshaft 16 via a connecting rod 14. A combustion chamber 18 is formed in the cylinder of the internal combustion engine 10 on the top side of the piston 12. An intake passage 20 and an exhaust passage 22 communicate with the combustion chamber 18.

  An air flow meter 24 for detecting the intake air amount Ga is disposed near the inlet of the intake passage 20. In addition, a throttle valve 26 is provided in the intake passage 20. The throttle valve 26 is an electronically controlled throttle valve that can control the throttle opening independently of the accelerator opening. In the vicinity of the throttle valve 26, a throttle position sensor 28 for detecting the throttle opening degree TA is disposed. A fuel injection valve 30 for injecting fuel into the intake port of the internal combustion engine 10 is disposed downstream of the throttle valve 26.

  Further, a spark plug 32 is attached to each cylinder head of the internal combustion engine so as to protrude from the top of the combustion chamber 18 into the combustion chamber 18 for each cylinder. The intake port and the exhaust port are respectively provided with an intake valve 34 and an exhaust valve 36 for bringing the combustion chamber 18 and the intake passage 20 or the combustion chamber 18 and the exhaust passage 22 into a conductive state or a cut-off state. The intake valve 34 and the exhaust valve 36 are driven by an intake variable valve operating (VVT) mechanism 38 and an exhaust variable valve operating (VVT) mechanism 40, respectively. The variable valve mechanisms 38 and 40 are mechanisms that can change the valve timings of the intake valve 34 and the exhaust valve 36.

  A catalyst 42 for purifying exhaust gas is disposed in the exhaust passage 22 of the internal combustion engine 10. Further, an air-fuel ratio sensor 44 for detecting the exhaust air-fuel ratio at that position is arranged upstream of the catalyst 42, and the air-fuel ratio at that position is rich or lean downstream of the catalyst 42. An oxygen sensor 46 that generates a signal according to whether or not there is disposed.

  The system shown in FIG. 1 includes an ECU (Electronic Control Unit) 50. In addition to the various sensors described above, the ECU 50 includes a crank angle sensor 52 for detecting the engine speed Ne, a cam angle sensor 54 for detecting the rotational position (advance amount) of the intake camshaft, and an internal combustion engine. A water temperature sensor 56 for detecting the cooling water temperature of 10 is connected. In addition, a signal indicating shift position information of the transmission is input to the ECU 50. The ECU 50 is connected to the various actuators described above. The ECU 50 can control the operation state of the internal combustion engine 10 based on the sensor output and the calculation result using a catalyst model 60 described later virtually built in the ECU 50.

[Overview of catalyst model]
FIG. 2 is a diagram for explaining the outline of the catalyst model 60 in the first embodiment of the present invention.
The catalyst model 60 receives as input information (composition (HC, CO, NOx), temperature Tg, flow rate (= Ga), etc.) of gas flowing into the catalyst 42 (hereinafter sometimes referred to as “entry gas”). This is a model that outputs information (composition, temperature) of the gas discharged from the catalyst 42 (hereinafter sometimes referred to as “outgas”) and the catalyst bed temperature Tw according to a general expression that models the catalytic reaction. This is a model for estimating the exhaust gas purification amount X by the catalyst 42 from the input / output values.

  In the catalyst model 60 of the present embodiment, in order to improve the estimation accuracy of the model, the catalyst 42 is virtually divided into a plurality of parts with respect to the flow direction of the exhaust gas, and the catalyst bed temperature Tw (i) for each part. ), The purification amount X (i) is calculated. In addition, in this embodiment, as shown in FIG. 2, the gas amount Cin (i) of the calculation target component (unpurified component (such as CO)) in the incoming gas flowing into the i-th divided portion and the i-th divided portion. As a difference from the purification amount X (i) of the calculation target component at, the emission amount Cout (i) of the calculation target component in the output gas discharged from the i-th divided portion is calculated. By performing such calculation for all the divided portions, the emission amount Cout in the gas finally discharged from the catalyst 42 is changed from the gas amount Cin in the gas discharged from the cylinder to all the divided portions. The difference is calculated as the difference from the total sum ΣX (i) of the purification amounts at the site.

  Further, in the present embodiment, as shown in FIG. 2, when the catalyst 42 is divided into a plurality of parts with respect to the direction of the exhaust gas flow, the upstream part of the exhaust gas flow is changed to the downstream part. It is divided more finely at unjust intervals, and more specifically, it is divided so as to become coarser toward the downstream side.

  FIG. 3 is a schematic diagram showing in more detail the relationship between the catalyst model 60 and the surrounding configuration in the first embodiment of the present invention. The configuration in FIG. 3 is a model of the configuration of the catalyst 42 provided in the exhaust passage 22 of the actual internal combustion engine system and the surrounding configuration.

  As shown in FIG. 3, the catalyst model 60 is connected to a catalyst-containing gas model 62 and a catalyst deterioration model 64. The catalyst-containing gas model 62 is based on the input values of the operating conditions such as the engine speed Ne of the internal combustion engine 10, the load factor KL, the air-fuel ratio A / F, the ignition timing SA, the valve timing VT, This is a model for calculating temperature Tg, flow rate Ga, and the like.

  The catalyst model 60 is configured to use the information (composition, temperature Tg, flow rate Ga, etc.) of the catalyst-containing gas calculated by the catalyst-containing gas model 62 as an input. In addition, you may make it provide not only such a structure but the various sensors for detecting the said information of the gas containing a catalyst.

  The catalyst model 60 is obtained by modeling a reaction performed in the actual catalyst 42 by a general reaction of a ternary reaction and oxygen adsorption / desorption. As described above, the catalyst model 60 can calculate the catalyst bed temperature Tw (i) and the purification amount X (i) of each divided portion based on the information on the catalyst-containing gas and the information on the catalyst outgas. The total emission amount Cout (Cin−ΣX (i)) in the exhaust gas finally discharged from the catalyst 42 can be calculated. Therefore, according to the catalyst model 60, the emission value can be obtained by model calculation without actually measuring the exhaust gas component.

  As shown in FIG. 3, the catalyst model 60 is inputted with physical values of the catalyst shape. Examples of the physical property value of the catalyst shape include the opening area of the cell of the catalyst 42, the number of cells, and the heat transfer coefficient. The catalyst model 60 outputs the composition and temperature of the catalyst output gas in consideration of these characteristic values.

In the catalyst 42 of the actual system, a plurality of reactions such as a reaction between carbon monoxide CO and nitrogen monoxide NO, a reaction between carbon monoxide CO and oxygen O _2, and a reaction between hydrocarbon HC and oxygen O ₂ are performed. Is called. In the catalyst model 60, all these reactions are modeled. The catalyst model 60 calculates the composition and temperature of the catalyst output gas from the composition of the gas containing the catalyst, the temperature Tg, and the flow rate Ga based on the gas purification rate of the catalyst 42 for each of these reactions.

Hereinafter, the reaction between carbon monoxide CO and oxygen O ₂ will be described as an example. Within the catalyst 42, carbon monoxide CO reacts with oxygen O ₂ to become carbon dioxide CO ₂ . FIG. 4 is a characteristic diagram showing the purification rate of carbon monoxide CO by this reaction (the reaction efficiency of the catalyst). As shown in FIG. 4, the purification rate of carbon monoxide CO varies according to the air-fuel ratio A / F of the exhaust gas flowing into the catalyst 42. The purification rate can be expressed by the following equation (1).
(Equation 1)
Purification rate = ([CO] _input- [CO] _output ) / [CO] _input (1)
In the above formula (1), [CO] _input is the concentration of carbon monoxide CO in the catalyst-containing gas. [CO] _output is the concentration of carbon monoxide CO in the catalyst output gas.

  As shown in FIG. 4, when the air-fuel ratio A / F is rich, the amount of oxygen contained in the exhaust gas is small, so the purification rate of carbon monoxide CO decreases. When the air-fuel ratio A / F becomes lean, the amount of oxygen contained in the exhaust gas increases, and the purification rate of carbon monoxide CO increases.

In the catalyst model 60, in the reaction of carbon monoxide CO and oxygen O _2, by identifying the reaction rate constant K, characteristic of FIG. 4 is modeled in advance. Therefore, according to the catalyst model 60, the carbon monoxide concentration in the catalyst output gas is calculated based on the carbon monoxide concentration in the catalyst-containing gas input from the catalyst-containing gas model 62 by using the characteristics of FIG. Can be calculated.

Hereinafter, a method for modeling the characteristics of FIG. 4 in the catalyst model 60 will be described. The rate at which carbon monoxide CO and oxygen O ₂ react is represented by the reaction rate R. The reaction rate R is determined by the reaction rate constant K. Here, the relationship of the following equation (2) is established between the reaction rate R and the reaction rate constant K.
(Equation 2)
R = K * [CO] _input (2)

The reaction rate constant K is usually calculated from the following equation (3).
(Equation 3)
K = (a / G) * exp (−E / RTw) (3)
In the above equation (3), a represents a frequency factor, G represents a suppression term, and E represents activation energy. R is a gas constant, and Tw is a catalyst bed temperature as described above. Here, the frequency factor a is a parameter representing the number of active points in the catalyst 42. Since the number of active points increases as the value of the frequency factor a increases, the reaction in the catalyst 42 is promoted. Therefore, the value of the reaction rate constant K increases as the value of the frequency factor a increases. Further, the activation energy E indicates energy necessary for the reaction to occur. As the activation energy E decreases, the reaction is more likely to occur, so the reaction rate constant K decreases. Instead of the catalyst bed temperature Tw, a catalyst-containing gas temperature Tg may be used.

  According to the above equation (3), the characteristics shown in FIG. 4 can be identified by setting the frequency factor a, the suppression term G, and the activation energy E to appropriate values. The catalyst model 60 outputs the composition and temperature in the catalyst output gas based on the composition and temperature in the catalyst-containing gas by modeling the catalytic reaction using the above equation (3) as a general expression.

  When modeling the characteristics of FIG. 4, a process for identifying the reaction rate constant K is performed based on the actual value of the purification rate obtained from the actual catalyst 42. Hereinafter, a method for obtaining the relationship between the purification rate and the air-fuel ratio A / F and a method for identifying the reaction rate constant K will be described with reference to FIGS. FIG. 5 is a schematic diagram showing a method of actually measuring the relationship between the air-fuel ratio A / F and the purification rate. FIG. 5A shows the measured values of the concentration of carbon monoxide in the catalyst-containing gas and the catalyst output gas. In FIG. 5A, the characteristic indicated by the broken line indicates the carbon monoxide concentration in the gas containing the catalyst, and the characteristic indicated by the solid line indicates the carbon monoxide concentration in the catalyst output gas. FIG. 5B shows the air-fuel ratio A / F of the catalyst-containing gas sent to the actual catalyst 42.

  As shown in FIG. 5B, when the reaction rate constant K is identified, the mixture supplied to the internal combustion engine 10 so that the air-fuel ratio A / F of the gas containing the catalyst changes between rich and lean. The air-fuel ratio A / F is controlled. In the example of FIG. 5B, the control is performed so that the air-fuel ratio A / F changes between 14 and 15 with the time T as a period. Note that before the time t0 shown in FIG. 5B, the air-fuel ratio A / F of the catalyst-containing gas is set to lean.

  The carbon monoxide concentration shown in FIG. 5 (A) is actually measured when the air-fuel ratio A / F of the gas containing the catalyst is varied with the characteristics shown in FIG. 5 (B). As indicated by a broken line in FIG. 5B, when the air-fuel ratio A / F is set to 14 (rich) at time t0, the carbon monoxide concentration in the catalyst-containing gas becomes a relatively high value, and time t1 When the air-fuel ratio A / F is set to 15 (lean), the concentration of carbon monoxide in the catalyst-containing gas decreases.

  As shown by the solid line in FIG. 5A, immediately after the air-fuel ratio A / F is set to 14 (rich) at time t0, the air-fuel ratio A / F before time t0 is lean, so The concentration of carbon monoxide in the gas is decreasing. Thereafter, the carbon monoxide concentration in the catalyst output gas increases with the passage of time, and becomes a value similar to the carbon monoxide concentration in the catalyst-containing gas.

  When the air-fuel ratio A / F is set to 15 at time t1, the carbon monoxide concentration in the catalyst-containing gas decreases, and the carbon monoxide contained in the catalyst-containing gas is almost purified when passing through the catalyst 42. The Accordingly, the carbon monoxide concentration in the catalyst output gas is substantially zero between time t1 and time t2 when the air-fuel ratio A / F is set to 15.

  As shown in FIG. 5, when the air-fuel ratio A / F is rich and lean, the carbon monoxide concentration in the catalyst-containing gas and the carbon monoxide concentration in the catalyst exit gas are obtained. ) Based on the equation, the actual measured value of the carbon monoxide purification rate can be obtained for each of the cases where the air-fuel ratio A / F is rich and lean.

  The reaction rate constant k is identified based on the purification rate when the air-fuel ratio A / F is rich and the purification rate when the air-fuel ratio A / F is lean. At this time, the concentration of carbon monoxide is in a stable state at time t3 immediately before time t1 and time t4 immediately before time t2, and therefore is based on the purification rate measured at the timings of time t3 and time t4. Thus, by identifying the reaction rate constant k, the influence of the oxygen adsorption / desorption reaction can be suppressed, and the identification can be performed with high accuracy.

  As described above, the purification rates at time t3 and time t4 can be calculated from the above equation (1). Further, the air-fuel ratio A / F of the catalyst-containing gas at time t3 is 14, and the air-fuel ratio A / F of the catalyst output gas at time t4 is 15. Therefore, the purification rate when the air-fuel ratio A / F is 14 and 15 can be calculated.

  FIG. 6 is a schematic diagram showing a method for identifying the reaction rate constant K based on the relationship between the air-fuel ratio A / F calculated by the method of FIG. 5 and the purification rate. As shown in FIG. 6, the purification rate when the air-fuel ratio A / F is 14 and the purification rate when the air-fuel ratio A / F is 15 are plotted with black circles in FIG. The calculation of the purification rate by the method of FIG. 5 is also performed when the air-fuel ratio A / F of the catalyst-containing gas is changed between, for example, 14.2 and 14.8. Accordingly, as shown in FIG. 6, the purification rate when the air-fuel ratio A / F is 14.2 and the purification rate when the air-fuel ratio A / F is 14.8 are plotted with white circles in FIG. . Therefore, by changing the air-fuel ratio A / F of the catalyst-containing gas and repeating such processing, the relationship between the purification rate and the air-fuel ratio A / F can be obtained as shown in FIG.

  Then, the reaction rate constant K is identified so as to meet the purification rate characteristic thus obtained. Specifically, among the parameters for determining the reaction rate constant K, the values of the frequency factor a, the suppression term G, and the activation energy E are determined so as to match the purification rate characteristics of FIG. According to the identified reaction rate constant K, the characteristics of FIG. 4 can be reproduced. Thereby, according to the catalyst model 60, it becomes possible to calculate the carbon monoxide concentration of the catalyst output gas based on the carbon monoxide concentration of the catalyst-containing gas.

  Next, the catalyst deterioration model 64 will be described. The actual catalyst 42 becomes a high temperature state due to the exhaust gas, and deteriorates due to factors such as the catalyst bed temperature Tw and oxygen concentration (air-fuel ratio). When the catalyst 42 deteriorates due to the influence of the heat load, the purification rate of each component contained in the exhaust gas changes. The catalyst deterioration model 64 receives the input of a thermal load such as the catalyst temperature Tw and oxygen concentration from the catalyst model 60, and changes the characteristic values such as the catalytic reaction rate constant K and the maximum oxygen storage amount according to the thermal load. It has become.

  An input value representing the amount of change in these characteristic values is sent from the catalyst deterioration model 64 to the catalyst model 60. Therefore, the catalyst model 60 is based on the above-described purification rate model obtained by identifying the reaction rate constant K and the parameter representing the change amount of the reaction rate constant K input from the catalyst deterioration model 64. The emission of catalyst outgas can be accurately output in consideration of catalyst deterioration.

The details of the catalyst deterioration model 64 as described above are described in detail in, for example, Japanese Patent Application Laid-Open No. 2007-239723, and thus detailed description thereof is omitted here. However, the amount of deviation between the actual value of the purification rate and the purification rate obtained by modeling is the air-fuel ratio A / F of the catalyst-containing gas or the catalyst bed temperature Tw (or the temperature Tg of the catalyst-containing gas). It may change depending on the situation. Therefore, for example, a correction term f (A / F, Tw) that changes according to the air-fuel ratio A / F and the catalyst bed temperature Tw may be added to the right side of the above equation (3). The following expression (4) is an expression obtained by multiplying the right side of expression (3) by the correction term f (A / F, Tw).
(Equation 4)
K = f (A / F, Tw) * (a / G) * exp (−E / RTw) (4)
Here, the correction term f (A / F, Tw) is assumed to be previously mapped in relation to the air-fuel ratio A / F and the catalyst bed temperature Tw.

  The catalyst deterioration model 64 obtains values such as the catalyst bed temperature Tw and oxygen concentration from the catalyst model 60, calculates a correction coefficient f (A / F, Tw) corresponding to the heat load applied to the catalyst 42, and calculates it. The corrected coefficient f (A / F, W) is input to the catalyst model 60. In the catalyst model 60, the right side of the equation (3) is multiplied by the correction coefficient f (A / F, Tw) to construct the equation (4). According to such a method, in the catalyst model 60, it is possible to calculate the emission value of the catalyst output gas with high accuracy in consideration of the catalyst deterioration due to the heat load.

  However, when the above-described catalyst deterioration model 64 is additionally used and the method is always relied on a method that considers the influence of the catalyst deterioration due to the heat load, a complicated calculation is additionally performed. There is a concern that the calculation load will increase.

[Characteristics of Embodiment 1]
Therefore, in the present embodiment, in order to ensure the calculation accuracy of the catalyst model 60 in consideration of deterioration of the catalyst 42 due to the heat load while avoiding an increase in calculation load, the following processing is performed. I made it.

  That is, it is assumed that the catalyst 42 deteriorates when the bed temperature of the catalyst 42 is high. Therefore, in the present embodiment, it is determined that degradation has occurred in the divided portion where the catalyst bed temperature Tw (i) is assumed to be deteriorated when the catalyst bed temperature Tw (i) is higher than a predetermined threshold. did. Then, the calculation of the purification amount X (i) at the divided part is skipped, and the purification amount X (i) at the divided part is regarded as zero.

FIG. 7 is a flowchart of a routine executed by the ECU 50 in the first embodiment to realize the above function.
In the routine shown in FIG. 7, first, information (composition, temperature, flow rate, air-fuel ratio A / F, etc.) of the gas entering the catalyst 42 is acquired using the catalyst-containing gas model 62 and the air-fuel ratio sensor 44 described above. (Step 100). Note that the various types of information on the input gas may be actually measured by various sensors instead of using the catalyst-containing gas model 62.

上記（５）式において、σは触媒セルの開口率、ρｇはガス密度、ρｗは触媒密度、Ｃｐｇはガス比熱、Ｃｐｗは触媒比熱、ｈｚは熱伝達率、λｗは熱伝導率、Ｓｇｅｏは幾何学的表面積、およびνｇはガス流速である。 Next, for each divided portion, the catalyst bed temperature Tw (i) is calculated according to the following equation (5) in consideration of heat transfer between the catalyst wall and the gas, heat conduction at the catalyst wall, and generated heat ( Step 102). Note that a method of actually measuring the catalyst bed temperature Tw (i) with a temperature sensor can also be used.

In the above equation (5), σ is the opening ratio of the catalyst cell, ρg is the gas density, ρw is the catalyst density, Cpg is the specific heat of the gas, Cpw is the specific heat of the catalyst, hz is the heat transfer coefficient, λw is the thermal conductivity, and Sgeo is the geometric The chemical surface area, and νg is the gas flow rate.

  Next, it is determined whether or not the deterioration condition of each divided portion of the catalyst 42 is satisfied, more specifically, whether or not the catalyst bed temperature Tw (i) is higher than a predetermined threshold ( Step 104). The threshold value in this step 104 is a value determined in advance by experiment or simulation as a temperature at which the purification rate of the catalyst 42 deteriorates due to deterioration due to heat load.

  If it is determined in step 104 that the catalyst bed temperature Tw (i) at a certain divided portion is not higher than the threshold value, it is determined that the divided portion has not deteriorated, and the purification amount X at the divided portion is determined. (I) is calculated (step 106). More specifically, the purification rate of each component in the divided part can be obtained in relation to the air-fuel ratio A / F by the method described above with reference to FIGS. The purification amount X (i) can be calculated based on the purification rate thus obtained and the gas amount Cin (i) of the calculation target component flowing into the divided part.

  On the other hand, when it is determined in step 104 that the catalyst bed temperature Tw (i) at a certain divided portion is higher than the threshold value, it is determined that the divided portion is deteriorated. In this case, the deterioration flag is set to ON for the divided part, the purification amount X (i) at the divided part is set to zero, and the purification amount calculation is skipped.

  When the calculation of the purification amount X (i) (including the case where it is regarded as zero) is completed for all the divided parts by the processing of steps 106 and 108, the emission contained in the exhaust gas discharged from the catalyst 42 is then performed. The amount is calculated as a total emission amount Cout for each target component (NOx, etc.) (step 110). Specifically, as described above, if the amount of gas entering the catalyst 42 of a certain component is Cin, the amount of gas emitted from the catalyst 42 of the component (total emission amount) Cout is (Cin−ΣX (i)). ).

  According to the routine shown in FIG. 7 described above, the catalyst model 60 determines that the catalyst bed temperature Tw (i) has deteriorated at the divided portion where the catalyst bed temperature Tw (i) exceeds the threshold value, and skips the purification amount calculation. Catalyst degradation can be easily taken into account without requiring a new model for considering degradation. As a result, in a configuration including a catalyst model that sequentially estimates the emission value discharged behind the catalyst 42, the estimation accuracy of the emission can be easily secured in consideration of catalyst deterioration while reducing the calculation load. Is possible.

  Further, in the present embodiment, as shown in FIG. 2, when the catalyst 42 is divided into a plurality of parts in the direction of the exhaust gas flow, the upstream part of the exhaust gas flow is changed to the downstream part. It is divided more finely at unjust intervals, and more specifically, it is divided so as to become coarser toward the downstream side. In general, the upstream portion of the catalyst has a higher heat transfer rate than the downstream portion because high-temperature exhaust gas flows in and the gas is more turbulent. For this reason, temperature changes very much in the upstream part. In order to utilize this characteristic in the warm-up process, a catalyst having an increased amount of noble metal supported on the upstream side is also known. On the other hand, the portion that is easily deteriorated is also upstream.

  In the catalyst model 60, the estimation accuracy is improved as the number of divisions in the exhaust gas flow direction is increased, and the calculation load is reduced if the number of divisions is reduced. Therefore, in the catalyst model 60, the estimation accuracy of the emission by the catalyst model 60 can be improved by finely dividing the upstream portion that has a large influence on the estimation accuracy of the catalyst model 60 due to a large temperature change. In addition, an increase in calculation load can be prevented by roughly dividing the downstream portion that has a small influence on the estimation accuracy of the catalyst model 60 because the temperature change is relatively small. As described above, according to the division method of the present embodiment, the estimation accuracy of the catalyst model 60 can be effectively improved even when the number of divisions is the same as in the case of division at equal intervals.

  By the way, in the first embodiment described above, the catalyst bed temperature Tw (i) is compared with a predetermined threshold value for each divided portion to determine whether or not each divided portion is deteriorated. However, the parameter used for such determination is not limited to the catalyst bed temperature Tw (i), and may be, for example, the inlet gas temperature Tg (i) flowing into each divided portion.

  In the first embodiment described above, the ECU 50 executes the process of step 102 or 100, so that the “temperature acquisition means” in the first invention executes the process of step 106. The “purification index calculating means” in the first invention and the “estimated value calculation omitting means” in the first invention are realized by executing the processing of steps 104 and 108, respectively.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG.
The system of the present embodiment uses the hardware configuration shown in FIG. 1 and the configuration of the catalyst model 60 shown in FIGS. 2 and 3 to cause the ECU 50 to execute a routine shown in FIG. 8 described later instead of the routine shown in FIG. Can be realized.

  The system of the present embodiment is characterized in that the number of divisions of the catalyst model 60 is changed based on the operating conditions of the internal combustion engine 10, the catalyst-containing gas flow rate Ga, and the catalyst-containing gas temperature Tg. More specifically, in the present embodiment, for example, under the operating conditions where it can be determined that the internal combustion engine 10 is in a steady state, such as during idling after warm-up, the catalyst-containing gas flow rate Ga and the catalyst-containing gas temperature Tg Are both stable, the number of divisions of the catalyst model 60 is made smaller than the number of divisions under other operating conditions.

FIG. 8 is a flowchart of a routine executed by the ECU 50 in the second embodiment to realize the above function.
In the routine shown in FIG. 8, first, the catalyst-containing gas flow rate Ga and the catalyst-containing gas temperature Tg are respectively acquired using the catalyst-containing gas model 62 (or sensor) (step 200).

  Next, the current vehicle shift position information is acquired (step 202). Next, it is determined whether or not the acquired shift position is in an N (neutral) range (step 204).

  As a result, if it is determined in step 204 that the current shift position is not in the N range, the emission amount Cout is calculated by the catalyst model 60 using the normal division number setting (step 206).

  On the other hand, if it is determined in step 204 that the current shift position is in the N range, that is, if it can be determined that the internal combustion engine 10 is in a steady state, then the catalyst-containing gas flow rate Ga and the catalyst-containing gas are determined. It is determined whether or not a stable condition that both temperatures Tg are stable is established (step 208).

  As a result, if it is determined in step 208 that the stability condition is not satisfied, the emission amount Cout is calculated using the normal setting of the number of divisions (step 206). On the other hand, if it is determined that the stability condition is satisfied, the emission amount Cout is calculated using the catalyst model 60 using the setting of the division number smaller than the normal division number (step 210). ).

  According to the routine shown in FIG. 8 described above, when it can be determined that the internal combustion engine 10 is in a steady state and the catalyst-containing gas flow rate Ga and the catalyst-containing gas temperature Tg are both stable, The number of divisions of the catalyst model 60 is set to be smaller than usual. When the catalyst-containing gas flow rate Ga (flow velocity) is small and the fluctuation of the catalyst-containing gas temperature Tg is small, the estimation accuracy of the catalyst bed temperature Tw and the purification amount X is relatively high even if the number of divisions in the exhaust gas flow direction is small. Get better. Therefore, by reducing the number of divisions under such circumstances as compared with other situations, the calculation load can be reduced and the model estimation accuracy can be optimized.

  By the way, in the second embodiment described above, it is determined whether or not the operating state of the internal combustion engine 10 is in a steady state by the processing of the above steps 202 and 204. However, the condition for determining whether or not the internal combustion engine 10 is in a steady state is not limited to the above determination method.

  In the second embodiment described above, the catalyst model can be determined when it can be determined that the internal combustion engine 10 is in a steady state and both the catalyst-containing gas flow rate Ga and the catalyst-containing gas temperature Tg are stable. The number of divisions of 60 is set to be smaller than usual. However, the optimization of the emission estimation accuracy and the calculation load reduction is not limited to such a method. For example, the catalyst model 60 can be used under conditions in which the operating state of the internal combustion engine 10 changes suddenly, such as during sudden acceleration. The number of divisions may be increased over other operating conditions, and emission estimation accuracy may be prioritized over calculation load reduction.

  In the second embodiment described above, the ECU 50 executes the process of step 200, whereby the “inlet gas flow rate acquisition means” in the third invention executes the processes of steps 204 to 210. As a result, the “division number variable means” in the third aspect of the present invention is realized.

It is a figure for demonstrating the structure of the internal combustion engine system to which the exhaust-gas estimation apparatus of the internal combustion engine of Embodiment 1 of this invention was applied. It is a figure for demonstrating the outline | summary of the catalyst model in Embodiment 1 of this invention. It is a schematic diagram which shows the relationship between the catalyst model in Embodiment 1 of this invention and the structure of the periphery in detail. It is a characteristic diagram showing the purification of carbon monoxide CO by reaction with carbon monoxide CO and oxygen O ₂ (reaction efficiency of the catalyst). It is a schematic diagram which shows the method of actually measuring the relationship between an air fuel ratio A / F and a purification rate. FIG. 6 is a schematic diagram showing a method for identifying a reaction rate constant K based on the relationship between the air-fuel ratio A / F calculated by the method of FIG. 5 and the purification rate. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a flowchart of the routine performed in Embodiment 2 of this invention.

Explanation of symbols

10 Internal combustion engine 20 Intake passage 22 Exhaust passage 24 Air flow meter 42 Catalyst 44 Air-fuel ratio sensor 46 Oxygen sensor 50 ECU (Electronic Control Unit)
52 Crank angle sensor 60 Catalyst model 62 Gas model with catalyst 64 Catalyst degradation model

Claims (3)

A catalyst disposed in the exhaust passage of the internal combustion engine;
Temperature acquisition means for dividing the catalyst into a plurality of parts, and obtaining the catalyst bed temperature for each part or the inlet gas temperature for each part;
Purification index calculating means for calculating an estimated value of the purification rate or amount of unpurified components contained in the exhaust gas for each part, and
When the catalyst bed temperature or the inlet gas temperature acquired by the temperature acquisition unit is higher than a predetermined threshold, the purification index calculation unit omits calculation of the estimated value for the corresponding part. An exhaust gas estimation device for an internal combustion engine, characterized in that the exhaust gas estimation device includes an omission unit.   The exhaust gas estimation device for an internal combustion engine according to claim 1, wherein the plurality of portions of the catalyst are divided more finely on the upstream side of the flow of exhaust gas than on the downstream side of the flow. Inlet gas flow rate acquisition means for acquiring the flow rate of the inlet gas flowing into the catalyst;
A dividing number variable means for reducing the dividing number of the plurality of portions in the flow direction of the exhaust gas when the inlet gas flow rate of the catalyst is small and the fluctuation of the inlet gas temperature of the catalyst is small;
The exhaust gas estimation device for an internal combustion engine according to claim 1 or 2, further comprising:

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