JP2005127285A - Catalyst typical temperature estimating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst typical temperature estimating method capable of highly accurately estimating temperature of whole catalyst subjected to various temperature variation factors. <P>SOLUTION: The catalyst typical temperature estimating method of the present invention is provided with an inlet exhaust gas temperature sensor 3 for detecting the temperature of exhaust gas to be flowed into an exhaust emission control catalyst 2, and an outlet exhaust gas temperature sensor 4 for detecting the temperature of exhaust gas flowed out from the exhaust emission control catalyst 2. A weighted average of a sensor value from the inlet exhaust gas temperature sensor 3 and a sensor value from the outlet exhaust gas temperature sensor 4 is calculated with the weighting of the sensor value from the outlet exhaust gas temperature sensor 4 increased to calculate an instant catalyst typical temperature Tcat'. Subsequently, a weighted average of the calculated instant catalyst typical temperature Tcat'and an instant catalyst typical temperature Tcat<SB>n-1</SB>from one step earlier is calculated to estimate a current catalyst typical temperature Tcat. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a catalyst representative temperature estimation method for estimating a representative temperature of an exhaust gas purifying catalyst provided in an exhaust passage of an internal combustion engine.

  In an engine (internal combustion engine) mounted on an automobile, as an exhaust gas countermeasure, an exhaust gas purification catalyst is provided in the exhaust passage of the engine to purify harmful components contained in the exhaust gas.

  Control of the exhaust gas using the catalyst temperature is indispensable in order to promote the purification of the exhaust gas in accordance with the engine operating state and the catalyst state. In particular, the NOx storage catalyst requires a temperature representative of the entire catalyst in order to manage the amount of NOx stored and the degree of reduction (estimation of the NOx storage amount, etc.).

The catalyst temperature used to control such a catalyst has conventionally been a. A temperature sensor is inserted into the catalyst to detect the catalyst temperature, b. The temperature sensor is used to indirectly calculate or directly detect the inlet side temperature and the outlet side temperature of the catalyst individually (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 10-196433

  However, the temperature of each part of the catalyst varies depending on the progress of the chemical reaction.

  For this reason, the a. Even if the temperature sensor detects the temperature, the detected temperature only represents the local temperature of the catalyst itself, that is, the temperature of a part of the temperature distribution of the entire catalyst. Absent. For this reason, it is not suitable for the temperature value required for control of NOx occlusion amount (such as estimation of NOx occlusion amount) with high accuracy such as a NOx occlusion catalyst. B. Even if the catalyst inlet side temperature or the catalyst outlet side temperature is obtained as described above, it is a local temperature value before and after the catalyst. Similarly, the temperature value representative of the entire catalyst is poor, and NOx occlusion amount management that requires high accuracy is also required. Not suitable for temperature values required for control.

  Accordingly, an object of the present invention is to provide a catalyst representative temperature estimation method capable of estimating the representative temperature of the entire catalyst that receives various factors of temperature change with high accuracy.

  In order to achieve the above-mentioned object, the invention according to claim 1 provides an inlet exhaust gas temperature sensor for detecting the temperature of exhaust gas flowing into the exhaust gas purification catalyst, and the temperature of the exhaust gas flowing out from the catalyst. An outlet exhaust gas temperature sensor is provided, and the sensor value from the inlet exhaust gas temperature sensor and the sensor value from the outlet exhaust gas temperature sensor are sequentially weighted and averaged by increasing the weight of the sensor value of the outlet exhaust gas sensor. The result was used as the representative temperature of the exhaust gas purifying catalyst.

  In addition to the above object, the invention described in claim 2 is currently obtained after the weighted average of claim 1 in order to obtain a highly accurate catalyst representative temperature that takes into account the heat capacity of the exhaust gas purifying catalyst. The weighted average sensor value and the previously obtained weighted average sensor value were weighted averaged, and the result was used as the representative temperature of the exhaust gas purifying catalyst.

  In addition to the above-mentioned object, the invention according to claim 3 further provides an output when the exhaust gas temperature cannot be detected by the inlet exhaust gas temperature sensor in order to make the inlet exhaust gas temperature sensor fail safe. Only the sensor value of the exhaust gas temperature sensor is used for estimating the representative temperature of the exhaust gas purifying catalyst.

  According to the first aspect of the present invention, information on the rapid temperature change of the exhaust gas temperature accompanying the engine load fluctuation caused by the behavior of the exhaust gas temperature flowing into the catalyst inlet, and the exhaust gas temperature flowing out from the catalyst outlet The overall weight of the exhaust gas purification catalyst is calculated by a weighted weighted average that takes into account the effects of the chemical reaction heat of the exhaust gas purification catalyst caused by Can be estimated.

  Therefore, it is possible to estimate the temperature of the entire catalyst subjected to various temperature change factors with high accuracy. This is particularly effective for use in control under high accuracy, for example, management control of the amount of NOx stored in the NOx storage catalyst.

  According to the second aspect of the present invention, the heat capacity of the exhaust gas purifying catalyst (for example, whether the catalyst is easy to cool) is further obtained by performing weighted averaging of the currently obtained weighted average sensor value and the previously obtained weighted average sensor value. Therefore, the catalyst representative temperature can be estimated with higher accuracy.

  According to the invention described in claim 3, in addition to the above effect, even if the inlet exhaust gas temperature sensor fails, the outlet exhaust gas temperature sensor including information on the most important chemical reaction is inferior in accuracy. By using only the output from the engine temporarily to estimate the representative temperature of the exhaust gas purifying catalyst, high fail-safety can be achieved.

[First Embodiment]
Hereinafter, the present invention will be described based on the first embodiment shown in FIG. 1 and FIG.

  In FIG. 1, 1 is an exhaust passage connected to an exhaust manifold (not shown) of an internal combustion engine mounted on an automobile (vehicle), 2 is an exhaust gas purifying catalyst interposed in the middle of the exhaust passage 1, For example, a NOx storage catalyst. The NOx storage catalyst 2 stores NOx in the exhaust when the air-fuel ratio of the inflowing exhaust gas is lean, and the unburned HC, CO, etc. in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is rich. Has the function of reducing by reaction.

  An inlet exhaust gas temperature sensor 3 for detecting the temperature of the exhaust gas flowing into the catalyst 2 is provided on the inlet side of the NOx storage catalyst 2, and the NOx storage catalyst 2 is discharged from the catalyst 2 on the outlet side. An exhaust gas temperature sensor 4 for detecting the temperature of the exhaust gas is provided. Then, the catalyst representative temperature estimation unit 5 configured by the arithmetic processing unit estimates the temperature representative of the entire NOx storage catalyst 2 from the temperature value of the exhaust gas output from both the temperature sensors 3 and 4, and The result is output to a rich operation control system for reducing the stored NOx, for example, and used for estimating the stored NOx amount.

  And the catalyst representative temperature estimation method of this embodiment is applied to the process which estimates the temperature representative of the whole catalyst.

  Here, normally, when exhaust gas from the engine flows into the catalyst, harmful components contained in the exhaust gas chemically react on the catalyst to purify (NOx storage catalyst 2 stores NOx when lean, and when rich, Reduced). At this time, the behavior of the change in the catalyst temperature is influenced by a sudden change in the temperature of the inlet exhaust gas due to the engine load fluctuation, or by the chemical reaction heat on the catalyst and the exhaust gas flow rate. Moreover, the influence of heat of chemical reaction is the greatest.

  In consideration of the factors of such temperature change, in this embodiment, the catalyst representative temperature estimation unit 5 detects the following equation (1), that is, the inlet exhaust gas temperature sensor 3 in order to obtain a temperature representative of the entire catalyst. An equation for weighted averaging of the measured temperature (sensor value) and the temperature (sensor value) detected by the outlet exhaust gas temperature sensor 4 by sequentially increasing the weight of the sensor value of the outlet exhaust gas temperature sensor 4 is set. It is. The calculation result is output to the rich operation control system as the instantaneous representative temperature of the catalyst.

Tcat '= (1-n) .Tgin + n.Tgout (1)
Where Tcat ′: instantaneous catalyst representative temperature estimated value, Tgin: catalyst inlet exhaust gas temperature sensor value, Tgout: catalyst outlet exhaust gas temperature sensor value, n: constant (0.5 <n ≦ 1).

  A method of estimating the instantaneous catalyst representative temperature is shown in the flowchart of FIG. The method for estimating the catalyst representative temperature will be described with reference to this flowchart and the given equation (1). When the exhaust gas of, for example, lean exhausted from the engine 1 passes through the NO storage catalyst 2, the NOx storage catalyst. 2, it is assumed that NOx contained in the exhaust gas is occluded and removed by a chemical reaction.

  Here, the overall temperature of the NOx storage catalyst 2 is a result of various factors causing temperature changes. Factors that cause catalyst temperature changes include abrupt changes in exhaust gas temperature due to load fluctuations caused by engine operation as described above, heat of chemical reaction on the catalyst, and changes in the flow rate of exhaust gas passing through the catalyst. It is done.

  At this time, the temperature change of the exhaust gas due to the load fluctuation is known from the temperature of the exhaust gas flowing into the NOx storage catalyst 2. Further, the temperature change of the catalyst caused by the chemical reaction heat on the catalyst, the change of the exhaust gas flow rate, etc. can be understood from the temperature of the exhaust gas flowing out from the NOx storage catalyst 2.

  Based on such grounds, step S1 in FIG. 2 detects the temperature of the exhaust gas flowing into the NOx occlusion catalyst 2 from the inlet exhaust gas temperature sensor 3, and flows out from the NOx occlusion catalyst 2 from the outlet exhaust gas temperature sensor 4. The content of the exhaust gas is detected.

  Here, the reaction heat generated by the chemical reaction on the catalyst is the largest factor among the temperature change factors. Therefore, simply averaging the inlet / outlet exhaust gas temperature cannot be recognized as the temperature of the entire catalyst.

  Therefore, as shown in step S2 in FIG. 2 and the given equation (1), in order to consider such influence, weighting of the exhaust gas temperature on the outlet side rather than the exhaust gas temperature on the inlet side (0.5 <n ≦ 1) is increased so that the inlet exhaust gas temperature and the outlet exhaust gas temperature are weighted averaged. Then, the representative catalyst temperature at the time of detection, that is, the instantaneous catalyst representative temperature value is estimated from the obtained temperature value. The weighting constant n varies depending on the engine model, the type of catalyst, the arrangement, the size, and the like.

  By estimating the catalyst representative temperature performed in consideration of these various temperature change factors, the temperature of the entire catalyst can be estimated with high accuracy. In particular, the temperature representative of the entire catalyst is effective for control with high accuracy, for example, for controlling the amount of NOx stored in the NOx storage catalyst 2. Moreover, the representative temperature of the entire catalyst may be calculated by a simple equation as shown in the equation (1), and the burden on the control system (ECU, etc.) is small.

[Second Embodiment]
3 to 5 show a second embodiment of the present invention.

  The second embodiment is a modification of the first embodiment, and estimates the catalyst representative temperature in consideration of the heat capacity of the catalyst so that the temperature of the entire catalyst can be estimated with higher accuracy, or two temperature sensors. Among these, even if the inlet exhaust gas temperature sensor 3 fails, the estimation function of the catalyst representative temperature is ensured.

  That is, to devise a technique for ensuring a highly accurate catalyst representative temperature, after sequentially calculating the weighted average (step S2) of the inlet exhaust gas temperature and the outlet gas temperature, the calculation using the following equation (2) and FIG. As shown in the calculation processing contents of step S3 in the middle, the instantaneous catalyst representative temperature estimated value obtained this time and the catalyst representative temperature estimated value obtained one step before (previous) are weighted and averaged, so that The catalyst representative temperature can be estimated with higher accuracy in consideration of the heat capacity of the catalyst (for example, whether or not the catalyst is easy to cool).

Tcat = (1−m) · Tcat _n−1 + m · Tcat ′ (2)
However, Tcat: catalyst representative temperature estimated value, Tcat _n−1 : catalyst representative temperature estimated value before one step, Tcat ′: instantaneous catalyst representative temperature estimated value, m: constant (0 <m ≦ 1).

  When the catalyst representative temperature is estimated in this way, the behavior of the outlet exhaust gas temperature and the catalyst affected by the abrupt temperature change of the inlet exhaust gas and the reaction heat as shown by the thick dashed line in the diagram of FIG. It is possible to obtain a highly accurate temperature value that follows the characteristics in consideration of the heat capacity. The constant m varies depending on the engine model, the type of catalyst, the arrangement, the size, and the like.

  On the other hand, for fail-safe when the inlet exhaust gas temperature sensor 3 among the temperature sensors fails, if it is determined that the inlet exhaust gas temperature sensor 3 has failed as shown in step S4 in FIG. 4, the line of FIG. As shown in the figure, using the fact that the behavior of the outlet exhaust gas temperature follows a history similar to the behavior of the catalyst representative temperature estimated value, that is, the information of the chemical reaction is inferior in accuracy, As shown in S5, only the outlet exhaust gas temperature value is used for estimating the catalyst representative temperature. Specifically, in order to use only the outlet exhaust gas temperature value for estimation of the catalyst representative temperature, in Step S5, using the constants n = 1 and m = m ′, the given expressions (1) and (2) are used. A routine is used to calculate and estimate a temperature representative of the entire catalyst only from the outlet exhaust gas temperature.

  The exhaust gas temperature that can be used for estimation of the representative temperature of the catalyst temporarily contains a lot of information on the heat of chemical reaction of the most important catalyst. As a result, the fail-safe property can be improved.

  In addition, this invention is not limited to each embodiment mentioned above, You may implement in various changes within the range which does not deviate from the main point of this invention. For example, in the above-described embodiment, an example in which the NOx storage catalyst is used has been described. However, the present invention is not limited thereto, and other catalysts may be used.

The figure which shows the structure of the catalyst periphery of the exhaust gas purification apparatus which concerns on the 1st Embodiment of this invention. The flowchart for demonstrating the procedure which estimates the temperature which represents the whole catalyst. The figure which shows the structure of the catalyst periphery of the exhaust gas purification apparatus which concerns on the 2nd Embodiment of this invention. The flowchart for demonstrating the fail safe when the procedure which estimates the temperature which represents the whole catalyst, and an inlet exhaust gas temperature sensor fail. The diagram which compares and shows an inlet exhaust gas temperature, an outlet exhaust gas temperature, and a catalyst representative estimated temperature.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Exhaust passage, 2 ... Catalyst, 3 ... Inlet exhaust gas temperature sensor, 4 ... Outlet exhaust gas temperature sensor, 5 ... Catalyst representative temperature estimation part.

Claims (3)

  An inlet exhaust gas temperature sensor for detecting the temperature of the exhaust gas flowing into the catalyst is provided on the inlet side of the exhaust gas purification catalyst provided in the exhaust passage of the internal combustion engine, and the outlet side of the exhaust gas purification catalyst is provided with the An outlet exhaust gas temperature sensor for detecting the temperature of the exhaust gas flowing out from the catalyst is provided, and the sensor value detected by the inlet exhaust gas temperature sensor and the sensor value detected by the outlet exhaust gas sensor are sequentially output to the outlet exhaust. A catalyst representative temperature estimation method characterized by increasing a weighted average of sensor values of a gas sensor and averaging the result to obtain a representative temperature of an exhaust gas purifying catalyst.   Further, after the weighted average, the weighted average sensor value obtained at present and the weighted average sensor value obtained last time are weighted average, and the result is used as a representative temperature of the catalyst. The method for estimating a catalyst representative temperature described in 1.   Furthermore, when the exhaust gas temperature cannot be detected by the inlet exhaust gas temperature sensor, only the sensor value of the outlet exhaust gas temperature sensor is used for estimating the representative temperature of the exhaust gas purification catalyst. The catalyst representative temperature estimation method according to claim 2.

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