JP5062415B2 - Exhaust gas detection system for exhaust purification means - Google Patents

Description

  The present invention relates to an exhaust gas detection system for exhaust purification means, and is particularly useful when applied to the case where the NOx concentration flowing out from an NOx storage catalyst that purifies exhaust gas from an internal combustion engine is detected with high accuracy.

  A NOx storage catalyst (hereinafter abbreviated as NTC) is disposed in the exhaust system to purify NOx in exhaust gas during lean operation in a diesel engine or the like, and a reducing agent is supplied to the NTC through periodic rich operation. Thus, there is an exhaust gas detection system that releases and reduces (NOx purge) NOx stored by NTC. Such a system according to the prior art is shown in FIG. As shown in the figure, the exhaust gas detection system includes an NTC 3 disposed in the middle of an exhaust pipe 2 connected to the engine 1. The NOx amount (NOx concentration) passing through the NTC 3 and reaching the downstream side is detected by the NOx sensor 4 disposed downstream of the NTC 3, and the detection result is monitored by a monitoring means (not shown). By such a monitoring method, the purification performance of the NTC 3 is reduced or a failure is determined, and the NOx purge execution method is changed so as to satisfy the required NOx purification efficiency.

  The following patent documents can be cited as publicly known documents disclosing such an exhaust gas detection system.

Japanese Patent No. 3778118

  In the exhaust gas detection system as described above, it becomes difficult to use the output data of the NOx sensor 4 due to the problem of accuracy in the following cases.

1) The amount of NOx (NOx concentration) leaking from the NTC 3 during the lean period is small, about several to 200 ppm. Therefore, in order to increase the measurement accuracy in such a concentration range, the NOx sensor 4 having a full scale (FS) of about 500 ppm is generally used. On the other hand, when the NOx occlusion amount in NTC3 increases excessively or when the reduction performance of NTC3 decreases, high concentration NOx of about 100 to several thousand ppm may be discharged during the NOx purge period. F. When the NOx sensor 4 having S of 500 ppm is used, it is naturally impossible to measure due to overrange.

  On the other hand, when the NOx sensor 4 capable of measuring up to high concentration NOx is adopted, the detection accuracy in the low concentration NOx region is low this time, so the error in the integrated value of the exhausted NOx concentration at the time of lean operation with high operation frequency is very large. It becomes. As a result, a situation may occur in which the NOx purge execution permission condition cannot be satisfied.

2) The NOx sensor 4 detects not only NOx but also NH ₃ because of its structure. Here, since NH ₃ is generated in the exhaust system during the rich combustion that is the NOx purge period, the NOx sensor 4 shows a numerical value equal to or higher than the actual NOx emission concentration, that is, a measured value in which the concentration of NH ₃ is weighted. This causes a measurement error of the NOx concentration.

  Incidentally, in the prior art including the above-mentioned Patent Document 1, when a range over occurs, a measure is used such that the measured value immediately before the over range occurs is used, and the measured value in the over range portion is not used with a mask. It is dealt with in. However, such a measure is insufficient in terms of detection accuracy particularly when detecting a failure of NTC3.

  In view of the above-described prior art, the present invention provides exhaust gas detection by an exhaust purification means that can accurately detect the amount of a specific component in the exhaust gas that exceeds the measurement range of the sensor. The purpose is to provide a system.

The first aspect of the present invention for achieving the above object is as follows:
A sensor for detecting the amount of a specific component in the exhaust gas downstream of the exhaust purification means disposed in the exhaust system of the internal combustion engine;
Detachment execution means for detaching the specific component occluded by the exhaust purification means for a predetermined period;
Different values of the detected values at the first time point when the detected value of the sensor exceeds the measurable range of the sensor and at the second time point when the detected value of the sensor returns to the measurable range again during the leaving period in which the leaving execution unit operates. Differential value calculating means for calculating
Period detecting means for detecting a range over period from the first time point to the second time point;
Estimation that estimates the detected value in the overrange period based on the differential values calculated at the first time point and the second time point by the differential value calculating means and the overrange period detected by the period detecting means. Means,
Sensor detection value calculation means for calculating the detection value in the separation period using the estimation result of the estimation means;
In the exhaust gas detection system of the exhaust gas purification means.

  According to this aspect, it is possible to accurately estimate the discharge amount of the specific component in the over-range portion, which can contribute to highly accurate estimation of the total amount of the specific component.

According to a second aspect of the present invention, there is provided an exhaust gas detection system for exhaust purification means described in the first aspect,
The estimating means includes estimated value integrating means for calculating an estimated integrated value by integrating the estimated values of the detected values,
The sensor detection value calculating means adds the estimated integrated value calculated by the estimated value integrating means and the measured integrated value obtained by integrating the measured value of the sensor within the measurable range, and An exhaust gas detection system for an exhaust gas purification unit is characterized in that a detection value is calculated.

  According to this aspect, it is possible to accurately estimate the discharge amount of the specific component in the over-range portion, and to estimate the total amount of the specific component released during the separation period with high accuracy. It can be done accurately and can contribute to optimization of the control.

The third aspect of the present invention is:
In the exhaust gas detection system of the exhaust gas purification means described in the first or second aspect,
The estimated integrated value is calculated based on an area of a triangle determined based on the two differential values and the range over period.

  According to this aspect, it is possible to accurately approximate the estimated area of the over-range portion.

The fourth aspect of the present invention is:
In the exhaust gas detection system for the exhaust gas purification means according to any one of the first to third aspects,
The exhaust purification means is a NOx storage catalyst, the specific component is NOx, the sensor is a NOx sensor, and the separation period is a NOx purge period in which the NOx stored in the NOx storage catalyst is released / reduced. In the exhaust gas detection system of the exhaust gas purification means.

  According to this aspect, the functions and effects of the first to third aspects can be exhibited in the processing system for NOx in the exhaust gas.

  According to the present invention, the total discharge amount of the specific component released during the withdrawal period can be detected with high accuracy. Therefore, the exhaust gas purification effect by the exhaust gas purification means can be properly grasped, and the failure determination and the like can be accurately performed. In addition, it becomes easy to optimally control the exhaust gas purification means so as to satisfy the required purification standard.

  On the other hand, the measurable range of the sensor can be set to an optimum region that matches the normal measurement region, so that the normal measurement accuracy within the measurement range is sufficiently high. be able to.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing an exhaust gas detection system according to an embodiment of the present invention. As shown in the figure, the exhaust gas detection system according to the present embodiment includes the NTC 3 disposed in the middle of the exhaust pipe 2 connected to the engine 1, the concentration of NOx flowing into the NTC 3, and the NOx flowing out from the NTC 3. It has NOx sensors 5 and 6 for measuring the concentrations. Each NOx sensor 5, 6 sends output signals SG 1, SG 2 representing the NOx concentration measured by each to an electronic control unit (hereinafter abbreviated as ECU) 7. The ECU 7 processes the output signal SG2 of the NOx sensor 6 to detect the concentration of NOx leaking from the NTC 3 during the lean operation of the engine 1 and also releases the NOx occluded by the NTC 3 in accordance with the regular rich operation. -The concentration of NOx released from the NTC 3 is detected during the NOx purge period to be reduced. Further, the ECU 7 appropriately controls the fuel injection amount for the engine 1 by the output signal SG. That is, the lean operation for storing the NOx in the NTC 3 and the rich operation for releasing the stored NOx from the NTC 3 are performed under the control of the ECU 7.

  The waveforms of the output signals SG1 and SG2 of the NOx sensors 5 and 6 are shown in FIG. As shown in the figure, the output signal SG1 is a predetermined measurement value depending on the operating condition of the engine 1. On the other hand, the output signal SG2 is a measured value that gradually increases until reaching the NOx purge periods PT1 and PT2, and rapidly increases in the NOx purge periods PT1 and PT2. Until the NOx purge periods PT1 and PT2, the NOC is continuously occluded by the NTC3, and what is detected by the NOx sensor 6 is leaked from the NTC3 without being occluded. This is because NOx released from NTC3 is superimposed in periods PT1 and PT2. Therefore, in the NOx purge periods PT1 and PT2, a case where the NOx concentration exceeds the measurement upper limit value FS of the NOx sensor 6 occurs. In this embodiment, when the measurement upper limit value FS is exceeded in the NOx purge periods PT1 and PT2, the range over periods T1, T2 that are the time from when the measurement upper limit value FS is exceeded to when the measurement upper limit value FS is less than or equal to the measurement upper limit value FS. NOx concentration is estimated by calculation processing in the ECU 7.

  A specific aspect of this estimation process will be described with respect to the range over period T2. The integrated value of the NOx concentration in the range over period T2 can be approximated by the estimated integrated value ΣNOre_ro which is a gray portion in FIG. The estimated integrated value ΣNOre_ro is given as an area of a triangle whose base is the range over period T2. The area of the triangle can be calculated by using the range over period T2, the differential value C of the output signal SG2 at the time of range over, and the differential value B of the output signal SG2 at the time of recovery from the range over. That is, the estimated integrated value ΣNOre_ro is given by the following equation (1).

  In the above equation (1), “A” is a predetermined coefficient (<1.0). Incidentally, the measured value of the output signal SG2 in the range over period T2 is generally dull at the apex portion of the approximate triangle. Therefore, considering this point, an appropriate coefficient value is determined based on a measured value or the like measured separately.

  Here, how to obtain the area S of the triangle will be described with reference to FIG. FIG. 3 is a diagram showing a triangle that approximates the estimated integrated value ΣNOre_ro in FIG. 2 extracted and enlarged. As shown in the figure, the area S of the triangle includes an area S1 of a right triangle involving a differential value B divided by a perpendicular line extending from the apex to the base, and an area S2 of a right triangle involving a differential value C. It is calculated as the sum of Here, the area S1 and the area S2 are given by the following equations (2) and (3), respectively.

  In the above equations (2) and (3), T is the base of the triangle of area S (corresponding to the range over period T2), and t is the base of the triangle of area S2.

  Accordingly, the area S is expressed by the following equation (4).

  On the other hand, since the heights of the triangles of the areas S1 and S2 are the same, the relationship of the following equation (5) is established.

  Substituting the above equation (5) into the above equation (4) to eliminate t results in the following equation (6).

  Thus, if the right side of the above equation (6) is multiplied by the coefficient A, the above equation (1) is obtained.

  The above calculation is executed by the ECU 7 based on the output signal SG2. That is, the ECU 7 determines the differential values C and B of the output signal SG2 when the NOx sensor concentration exceeds the measurement upper limit value of the NOx sensor 6 and returns to the measurement upper limit value again during the NOx purge periods PT1 and PT2, and the range. The estimated integrated value ΣNOre_ro is obtained by calculation by estimating the integrated value of the NOx concentration in the range over periods T1, T2 based on the over periods T1, T2. Based on this estimated integrated value ΣNOre_ro, the total amount of NOx released from the NTC 3 during the NOx purge periods PT1 and PT2 can be accurately estimated.

  On the other hand, the measured integrated value ΣNOre_me, which is an integrated value of the NOx concentration released during the NOx purge periods PT1 and PT2 and measured by the NOx sensor 6, is a value obtained by subtracting the NOx concentration flowing into the NTC 3 from the measured value of the NOx sensor 6. The integrated value during the NOx purge periods PT1, PT2 can be obtained. Here, data representing the NOx concentration flowing into the NTC 3 is supplied to the ECU 7 as the output signal SG 1 of the NOx sensor 5. Therefore, by performing predetermined subtraction processing and integration processing based on the output signals SG1 and SG2, a measured integrated value ΣNOre_me that is an integrated value of the NOx concentration that is released during the NOx purge periods PT1 and PT2 and is actually measured by the NOx sensor 6 is obtained. It can be obtained by calculation processing of the ECU 7.

  As a result, the integrated release value ΣNOsens_re representing the total amount of NOx released from the NTC 3 during the NOx purge periods PT1, PT2 is obtained as the sum of the measured integrated value ΣNOre_me and the estimated integrated value ΣNOre_ro by the following equation (7).

By the way, since the NOx sensor 6 has a LAFS + α structure, generally, the air-fuel ratio A / F (∝O ₂ concentration) can be simultaneously measured together with the NOx concentration. Here, as shown in FIG. 4, the concentration of NH ₃ generated during the rich period (NOx purge period) is a function of A / F. Therefore, if this is utilized, the integrated value of the NH ₃ concentration in the NOx purge periods PT1, PT2 can be estimated. That is, the NH ₃ concentration estimated value Cnh3 in this case can be expressed as the following equation (8).

  In the above equation (8), the coefficient D takes into account the deterioration of the NTC 3 and may be appropriately determined based on the NOx occlusion amount, for example.

Thus, if the time during which NH ₃ is generated is known, the integrated value of the NH ₃ concentration estimated value Cnh3 can be estimated, and the NH ₃ concentration estimated integrated value ΣNOsens_re thus determined is subtracted from the measured integrated value ΣNOre_me. By subtracting, the corrected measurement integrated value can be obtained. Here, the corrected measurement integrated value is a more accurate approximation of the true value related to the total amount of NOx released in the NOx purge periods PT1 and PT2.

Details of such correction processing will be described with reference to FIG. FIG. 5 shows the relationship between the indicated value of the NOx sensor and the NH ₃ concentration during the NOx purge period. FIG. 5A shows the relationship between the NOx indicated value by the NOx sensor 6 and the NH ₃ concentration taking the NOx purge period PT2 as an example. (B) is a graph showing the relationship between the NOx instruction value by the NOx sensor 6 and the A / F instruction value in the NOx purge period PT2. As shown in FIG. 9A, when the NOx purge period PT2, the NOx instruction value of the NOx sensor 6 has a characteristic of rapidly rising and then falling. The aforementioned measured integrated value ΣNOre_me is given as the area of the portion surrounded by the output signal SG2 in the NOx purge period PT2 of the NOx sensor 6. However, the area actually includes an area (NH ₃ concentration estimated integrated value ΣNOsens_re) depending on the concentration of NH ₃ shown as a white portion in FIG. To determine the NH ₃ concentration estimated integrated value ΣNOsens_re corresponding to such area, A / F indicated value shown in (b) may be integrated and NH ₃ concentration estimated value Cnh3 a period in the rich side. As shown in FIG. 5 (b), when the flow into the NTC 3 and the flow out from the NTC 3 are different in the timing of shifting to the rich state (the case where the flow out is delayed), the flow into the NTC 3 due to the rich operation. This is because NH ₃ is produced after the components in the exhaust gas have consumed all the O ₂ stored in the NTC ₃ . That is, there is a purge period OPT of O ₂ adsorbed on the NTC 3 at the beginning of the rich period.

As a result, the corrected measurement integrated value is given by (ΣNOre_me−ΣCnh3). Therefore, the corrected release integrated value ΣNOx_re taking into account the NH ₃ concentration estimated integrated value ΣCnh3 is given by the following equation (9).

  When the output signal SG2 of the NOx sensor 6 is not over the range, the second term in the above equation (9) is naturally zero.

The ECU 7 finally detects the corrected release integrated value ΣNOx_re of the above equation (9) as the total release amount of NOx in the NOx purge periods PT1 and PT2. Such a detection value reflects the NOx concentration released from the NTC ₃ in the NOx purge periods PT1 and PT2 with high accuracy by reducing the influence of the NH ₃ concentration detected by the NOx sensor 6 as much as possible. It becomes.

As described above, according to the present embodiment, when the NOx concentration exceeds the measurement upper limit value FS of the NOx sensor 6, the integrated value of the NOx concentration in that period is estimated and the concentration of NH ₃ generated at the same time is subtracted for correction. The integrated discharge value ΣNOx_re is obtained by calculation. However, at this time, it is usually not considered that the corrected release integrated value ΣNOx_re exceeds the NOx occlusion amount in the NTC 3. Therefore, in the ECU 7 in this embodiment, the stored NOx concentration integrated value ΣNOx_ad and the corrected release integrated value stored by the NTC 3 from the end time of the previous (n−1) NOx purge to the start time of the current (n) NOx purge are stored. When ΣNOx_ad <ΣNOx_re, the result is clipped to ΣNOx_ad = ΣNOx_re. Thereby, it is possible to verify whether or not the estimation in the ECU 7 is appropriate.

  Here, the stored NOx concentration integrated value ΣNOx_ad is, for example, a halftone dot portion in FIG. 2, and the difference between the output signal SG1 of the NOx sensor 5 and the output signal SG2 of the NOx sensor 6 is determined from the end point of the NOx purge period PT1. It can be obtained by integrating the time until the start time of the purge period PT2.

FIG. 6 is a flowchart showing a processing procedure in the ECU 7. The processing procedure will be described in time series based on FIG.
1) First, the NOx concentration discharged from the NTC 3 is monitored by the NOx sensor 6 (see step ST1).
2) Next, it is determined whether or not it is a NOx purge period (see step ST2).
3) If it is determined in the process of step ST2 that it is not the NOx purge period, the storage NOx concentration integrated value ΣNOx_ad at the time of lean is obtained (see step ST3).
4) When it is determined in the process of step ST2 that it is the NOx purge period, it is determined whether or not the NOx concentration exceeds the measurement upper limit value of the NOx sensor 6 (see step ST4), and the measurement estimated value ΣNOre_me is calculated. (Refer to step ST5). At the same time, the A / F instruction value obtained by processing the output signal SG2 of the NOx sensor 6 is monitored (see step ST6).
5) If it is determined in step ST4 that the measurement upper limit value of the NOx sensor 6 has not been exceeded, there is no range over portion, so the estimated integrated value ΣNOre_ro is set to zero (see step ST7).
6) When it is determined in step ST4 that the measurement upper limit value of the NOx sensor 6 has been exceeded, that is, when the range is over, the differential value of the output signal SG2 at the time of over-range entry, over-range return The differential value and the range over period of the output signal SG2 at the time are calculated (see step ST8).
7) Next, an estimated integrated value ΣNOre_ro is obtained by calculation based on the calculation result of step ST8 (see step ST9 and the previous equation (1)).
8) Based on the monitoring result of step ST6, the NH ₃ concentration estimated integrated value ΣCnh3 is calculated (see step ST10 and the previous equation (8)).
9) The corrected release integrated value ΣNOx_re is calculated by integrating the calculation results of steps ST5, 7, 9, and 10 (see step ST11 and the previous equation (9)).
10) The stored NOx concentration integrated value ΣNOx_ad and the corrected release integrated value ΣNOx_re are compared, and when ΣNOx_ad <ΣNOx_re, the clip is made to ΣNOx_ad = ΣNOx_re, and when ΣNOx_ad ≧ ΣNOx_re, the process returns to the beginning (step ST12 and (See step ST13).

  In the calculation process, it is desirable to store the output signals SG1 and SG2 for one to several cycles in the memory of the ECU 7. This is because a predetermined process relating to the calculation such as differentiation of the output signal SG2 is facilitated.

In this embodiment, the NOx concentration flowing into the NTC 3 from the upstream of the NTC 3 is measured by the NOx sensor 5, but the present invention is not limited to this configuration. For example, it can be replaced by using the exhausted NOx estimated value of the engine 1 mapped. In the above embodiment, the corrected release integrated value ΣNOx_re is used in the calculation process in the ECU 7, but the present invention is not limited to this. Instead of the corrected release integrated value ΣNOx_re, the release integrated value ΣNOsens_re before correction may be used. Further, the estimation may be performed without setting the stored NOx concentration integrated value ΣNOx_ad as the upper limit value. In the former case, an error corresponding to the measured value due to the NH ₃ concentration occurs. In the latter case, there is a concern that a corrected release integrated value ΣNOx_re exceeding the stored NOx concentration integrated value ΣNOx_ad may be output, but it is still sufficient. This is because the estimation that can be put to practical use becomes possible.

  If the application object of this invention is an internal combustion engine, the kind (diesel engine thru | or gasoline engine) of the engine 1 will not ask | require. Any type of engine can be applied.

  Further, in the above embodiment, the case where the exhaust purification means is NTC3 and the detection gas is NOx has been described. However, the present invention is not limited to this. The present invention can be applied without special limitation to applications that contribute to the quality determination of the exhaust gas purification means through a specific component in the exhaust gas of the exhaust gas purification means.

  The present invention can be used in an industrial field where exhaust gas is processed in an automobile or the like equipped with an internal combustion engine.

It is a block diagram which shows the exhaust gas detection system which detects the leakage NOx density | concentration from NTC which concerns on embodiment of this invention. It is a wave form diagram which shows the waveform of the output signal of the NOx sensor in embodiment shown in FIG. It is explanatory drawing which shows the triangle which approximates the range over part of FIG. It is a graph showing the relationship between the NOx sensor-indicated A / F and a concentration of NH ₃ after NTC. The relationship between the indicated value of the NOx sensor and the NH ₃ concentration during the NOx purge period is shown. (A) is a graph showing the relationship between the NOx indicated value by the NOx sensor and the NH ₃ concentration, and (b) is the NOx by the NOx sensor. It is a graph which shows the relationship between an instruction value and an A / F instruction value. It is a flowchart which shows the process sequence in ECU in embodiment of this invention. It is a block diagram which shows the exhaust system which has NTC which concerns on a prior art.

Explanation of symbols

1 Engine 2 Exhaust pipe 3 NTC (NOx storage catalyst)
5,6 NOx sensor 7 ECU
PT1, PT2 NOx purge period SG, SG1, SG2 Output signal T1, T2 Range over period ΣNOre_ro Estimated integrated value ΣNOre_me Measured integrated value ΣNOsens_re Release integrated value ΣNOsens_re NH ₃ concentration estimated integrated value ΣNOx_re Corrected release integrated value ΣNOx_ad Occluded NOx concentration integrated value

Claims (4)

A sensor for detecting the amount of a specific component in the exhaust gas downstream of the exhaust purification means disposed in the exhaust system of the internal combustion engine;
Detachment execution means for detaching the specific component occluded by the exhaust purification means for a predetermined period;
Different values of the detected values at the first time point when the detected value of the sensor exceeds the measurable range of the sensor and at the second time point when the detected value of the sensor returns to the measurable range again during the leaving period in which the leaving execution unit operates. Differential value calculating means for calculating
Period detecting means for detecting a range over period from the first time point to the second time point;
Estimation that estimates the detected value in the overrange period based on the differential values calculated at the first time point and the second time point by the differential value calculating means and the overrange period detected by the period detecting means. Means,
Sensor detection value calculation means for calculating the detection value in the separation period using the estimation result of the estimation means;
An exhaust gas detection system for exhaust gas purification means. In the exhaust gas detection system of the exhaust gas purification means according to claim 1,
The estimating means includes estimated value integrating means for calculating an estimated integrated value by integrating the estimated values of the detected values,
The sensor detection value calculating means adds the estimated integrated value calculated by the estimated value integrating means and the measured integrated value obtained by integrating the measured value of the sensor within the measurable range, and An exhaust gas detection system for exhaust gas purification means, wherein a detection value is calculated. In the exhaust gas detection system of the exhaust gas purification means according to claim 1 or 2,
The exhaust gas detection system of the exhaust gas purification means, wherein the estimated integrated value is calculated based on a triangular area determined based on the two differential values and the range over period. In the exhaust gas detection system of the exhaust gas purification means according to any one of claims 1 to 3,
The exhaust purification means is a NOx storage catalyst, the specific component is NOx, the sensor is a NOx sensor, and the separation period is a NOx purge period in which the NOx stored in the NOx storage catalyst is released / reduced. An exhaust gas detection system for exhaust purification means.

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