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CN119086815B - Failure diagnosis method for NOx sensor downstream of SCR - Google Patents

Failure diagnosis method for NOx sensor downstream of SCR

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Publication number
CN119086815B
CN119086815B CN202411105948.3A CN202411105948A CN119086815B CN 119086815 B CN119086815 B CN 119086815B CN 202411105948 A CN202411105948 A CN 202411105948A CN 119086815 B CN119086815 B CN 119086815B
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scr
nox sensor
data
pems
downstream
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CN119086815A (en
Inventor
袁雨
王善元
董波
郑雪茹
邓基峰
江琳琳
袁梓悦
胡建华
李畅
郑大维
张勃
李楚桥
卢勇
郭璇
孙哲
吴家坤
沈昊
王帅
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Dongfeng Automobile Co Ltd
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Dongfeng Automobile Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/007—Arrangements to check the analyser
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
    • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
    • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
    • G01N33/0037—NOx
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Health & Medical Sciences (AREA)
  • Medicinal Chemistry (AREA)
  • Food Science & Technology (AREA)
  • Combustion & Propulsion (AREA)
  • Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Exhaust Gas After Treatment (AREA)

Abstract

本发明提供了一种SCR下游NOx传感器失效诊断方法，包括以下步骤：1)确认SCR下游NOx传感器、氨传感器与ECU通讯正常；安装PEMS设备，确认PEMS设备测试数据准确无误；2)启动待测车辆，在市区、郊区和高速三种工况下进行PEMS排放试验；3)对PEMS设备进行数据剔除，并对剩余数据分工况进行时间对齐，随后分工况进行对比获得不同工况下的误差，并获得总误差；4)若总误差>所述设定阈值，即所述待测车辆所安装的SCR下游NOx传感器已失效；或者，若总误差≤设定阈值，则所述待测车辆所安装的SCR下游NOx传感器正常。本发明可以准确判断SCR下游NOx传感器失效情况，具有科学合理、可靠性高、应用范围广的优点，可为车辆的正常运行提供理论依据。

This invention provides a method for diagnosing the failure of a downstream NOx sensor in an SCR system, comprising the following steps: 1) Confirming normal communication between the downstream NOx sensor, ammonia sensor, and ECU; installing a PEMS (Pressure Producer Analyzer) device and confirming the accuracy of the PEMS device test data; 2) Starting the vehicle under test and conducting PEMS emission tests under three operating conditions: urban, suburban, and highway; 3) Removing data from the PEMS device and aligning the remaining data according to the operating conditions, then comparing the data under different operating conditions to obtain the error and the total error; 4) If the total error > the set threshold, the downstream NOx sensor installed in the vehicle under test has failed; or, if the total error ≤ the set threshold, the downstream NOx sensor installed in the vehicle under test is normal. This invention can accurately determine the failure status of the downstream NOx sensor in an SCR system, and has the advantages of being scientifically sound, highly reliable, and widely applicable, providing a theoretical basis for the normal operation of vehicles.

Description

SCR downstream NOx sensor failure diagnosis method
Technical Field
The invention relates to the technical field of exhaust gas treatment of internal combustion engines, in particular to a failure diagnosis method of an SCR downstream NOx sensor.
Background
The downstream NO x sensor is used as an important component in the aftertreatment assembly, can detect the value of Nitrogen oxides (NOx) at the SCR outlet, reflects the emission level of the vehicle, can be used for calculating an emission model and SCR efficiency, and has important significance for optimizing calibration parameters and improving the emission level by closed loop correction of urea injection coefficient.
Damage to downstream NOx sensors may cause the diesel engine control system to fall into an open loop condition, failing to accurately feed back emissions data, making it difficult for the engine control unit to accurately regulate emissions. In this case, the emission of the vehicle may exceed the prescribed standard, and the life of the exhaust emission treatment device may be shortened. The downstream NOx sensor is used as an important component of the electronically controlled urea injection system and plays a key role in the normal operation of the engine and the effective control of the exhaust emission. Once the downstream NOx sensor becomes defective, it may cause deterioration of the engine condition, and symptoms such as idle reduction, engine operation misalignment, and power drop occur.
Therefore, a method for accurately judging the failure condition of the NOx sensor is needed, which provides theoretical basis for the normal operation of the vehicle.
Disclosure of Invention
In order to overcome the defects of the technology, the invention aims to provide the failure diagnosis method of the SCR downstream NOx sensor, and the failure condition of the NOx sensor can be accurately judged by combining the comparison of the test data of the SCR downstream NOx sensor and the ammonia sensor with the test data of PEMS equipment, so that a theoretical basis is provided for the normal operation of a vehicle.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
A method for diagnosing failure of an SCR downstream NOx sensor, comprising the steps of:
1) The method comprises the steps of determining that the communication between an SCR downstream NOx sensor and an ammonia sensor is normal, installing PEMS equipment, and checking standard gas before a test to determine that the test data of the PEMS equipment are accurate;
2) Starting a vehicle to be tested, and performing a PEMS emission test to obtain data in the test process, wherein the PEMS emission test is performed under three working conditions of urban area, suburban area and high speed;
3) The PEMS equipment is subjected to data elimination before the SCR downstream NOx sensor passes through the dew point, time alignment is carried out on the remaining data according to working conditions, errors under different working conditions are obtained through comparison of the working conditions, and total errors are obtained based on the errors under different working conditions;
4) And comparing the total error with a set threshold value, and judging whether the SCR downstream NOx sensor fails, wherein if the total error is greater than the set threshold value, the SCR downstream NOx sensor installed on the vehicle to be tested fails, or if the total error is less than or equal to the set threshold value, the SCR downstream NOx sensor installed on the vehicle to be tested is normal.
Preferably, the mounting positions of the downstream NOx sensor and the ammonia sensor of the SCR are the positions of an SCR outlet, and the sampling position of the PEMS equipment is the position of an exhaust pipe outlet.
Preferably, in the step 2), the vehicle to be tested is an N2 type vehicle, in the PEMS emission test process, the test time of different working conditions respectively comprises 45% in urban area, 25% in suburban area and 30% in high speed, the total test duration is not less than 3h, and the vehicle speeds in urban area, suburban area and high speed working conditions are respectively 15-30 km/h, 45-70 km/h and >70km/h.
Preferably, in the step 2), the data comprise the total content of NOx and NH 3 measured by a downstream NOx sensor of the SCR, the content of NH 3 measured by an ammonia sensor and the content of NOx measured by PEMS equipment, and the data of the downstream NOx sensor of the SCR and the ammonia sensor are acquired by the ECU.
Preferably, the step 3) specifically includes:
3.1 Removing NOx data measured by PEMS equipment in a time period before the dew point of a NOx sensor at the downstream of the SCR passes;
3.2 Time alignment is carried out on the residual data after the PEMS equipment is subjected to data rejection and the data measured by the SCR downstream NOx sensor and the ammonia sensor;
3.3 Subtracting the value measured by the ammonia sensor from the value measured by the SCR downstream NOx sensor after time alignment to obtain a difference value, averaging the data measured by PEMS equipment after time alignment, comparing the two averages to obtain an error, calculating the absolute value of the error, and obtaining the total error based on the absolute value.
Preferably, in the step 3.2), the time alignment is performed under the working conditions of urban area, suburban area and high speed, and the time alignment is performed respectively, wherein the specific operation of the time alignment is that the time difference between the peak position of the value measured by the SCR downstream NOx sensor and the peak time of the value measured by the PEMS device is obtained at the starting stage of any working condition, the time alignment is performed according to the time difference, and the data measured by the SCR downstream NOx sensor and the ammonia sensor have no time difference and do not need to be time aligned.
Preferably, in the step 3.3), the calculation of the error is performed under different working conditions to obtain absolute values of the error under different working conditions, and weights are introduced for different working conditions, and weighted average values of the absolute values of the error under different working conditions are obtained to obtain the total error.
Preferably, the weight distribution is as follows, urban 0.2, suburban 0.3, high speed 0.5.
Preferably, the error is a relative error.
Preferably, in the step 4), the threshold is set to 10%.
Compared with the prior art, the invention has the beneficial effects that:
According to the failure diagnosis method for the SCR downstream NOx sensor, the data measured by the SCR downstream NOx sensor and the ammonia sensor are combined, and after time alignment is carried out, the difference between the sensor data and PEMS equipment data is calculated. Particularly, considering that PEMS tests are carried out in urban areas, suburban areas and high-speed working conditions, introducing corresponding weights to different working conditions, calculating the integrated errors of the measured values of the sensor and the measured values of PEMS equipment by using a weighted average method, setting a threshold value, and recognizing that the sensor fails when the integrated errors exceed the set threshold value. The method can accurately judge the failure condition of the SCR downstream NOx sensor, has the advantages of being scientific and reasonable, high in reliability and wide in application range, and can provide theoretical basis for normal operation of the vehicle.
Drawings
FIG. 1 is a flow chart of a method for diagnosing failure of an SCR downstream NOx sensor according to the present invention.
Detailed Description
For a better explanation of the present invention, the main content of the present invention is further elucidated below in conjunction with the specific examples, but the content of the present invention is not limited to the following examples only.
The invention provides a failure diagnosis method of an SCR downstream NOx sensor, which mainly comprises the steps of taking different weights into consideration of different working conditions as evaluation indexes after time alignment of NOx sensor data passing through a dew point, ammonia sensor data and data measured by PEMS equipment, and judging whether the SCR downstream NOx sensor fails or not. As shown in fig. 1, the method specifically comprises the following steps:
1) Before formally developing PEMS test, it is necessary to confirm that the communication between the SCR downstream NOx sensor and the ammonia sensor and the ECU is normal, and the numerical values of NOx and NH 3 can be read from the ECU, and the PEMS equipment is installed and checked for standard gas before the test to ensure that the PEMS equipment is tested accurately.
2) And carrying out one complete road emission test, namely a PEMS test, and carrying out urban area, suburban area and high-speed development according to the requirements of regulations. In the test process, the ECU is used for recording data measured by the SCR downstream NOx sensor and the ammonia sensor, the PEMS equipment is used for recording tail emission data, and the recorded data is processed in the next step. The test vehicle of the specific embodiment is an N2 type vehicle, the time ratio of urban areas, suburban areas and high-speed working conditions is 45%,25% and 30%, and the total test duration is not less than 3h. The urban area, suburban area and high-speed vehicle speed are respectively 15-30 km/h, 45-70 km/h and >70km/h.
3) And (3) carrying out data elimination on PEMS equipment, carrying out time alignment on the remaining data according to working conditions, and then comparing according to the working conditions to obtain relative errors under different working conditions, and obtaining total errors based on the relative errors under different working conditions.
3.1 The PEMS equipment records tail emission data from the beginning of the test, the downstream NOx sensor of the SCR starts to have data after a period of time passes through the dew point, and in actual calculation, the data before the dew point of the downstream NOx sensor recorded in the PEMS equipment passes through is removed, and the data after the dew point passes through is compared with the sensor data.
In the test process, 3 groups of data including data of an SCR downstream NOx sensor, data of an ammonia sensor and data of NOx tested by PEMS equipment are obtained, and in view of the fact that the data can be measured only by the SCR downstream NOx sensor through a dew point, the PEMS equipment starts to measure tail emission concentration from the beginning of the test, the data of NOx measured by the PEMS equipment before the dew point are removed, and the removed data are compared.
3.2 The mounting positions of the NOx sensor and the ammonia sensor at the downstream of the SCR are the positions of the outlet of the SCR, and samples analyzed by PEMS equipment can be obtained only by pumping gas at the tail end of the exhaust pipe through a sampling pipe, and the samples are far delayed from the sensors in time, so that the samples need to be aligned in time before error calculation is carried out. When the vehicle starts, a peak exists in the tail row, the time difference between the peak of NOx measured by the sensor and the peak of PEMS equipment is observed, and the corresponding time difference is obtained, so that time alignment is carried out. The ammonia sensor is mounted close to the downstream NOx sensor of the SCR, is almost in the same cross section in the exhaust flow direction, and can be considered to be consistent with the test data of the downstream NOx sensor of the SCR in time, and can be considered to be consistent with the downstream NOx sensor of the SCR in time alignment with the PEMS equipment. In view of the different conditions, the exhaust flow rates and the time of passage in the exhaust pipe are different, and the PEMS equipment has different lags (largest in urban area, inferior in suburban area and smallest in high speed) relative to the sensor, and can be performed according to the urban area, suburban area and high speed when time alignment is performed.
3.3 The downstream NOx sensor of the SCR cannot distinguish between NOx and NH 3 in the exhaust gas, the data measured by the downstream NOx sensor of the SCR is the sum of the NOx value and the ammonia slip value, and the NOx measured by the PEMS device is a pure nitrogen oxide, so when comparing the data with the data measured by the PEMS device, the data measured by the downstream NOx sensor of the SCR is used to subtract the data measured by the ammonia sensor to obtain a difference value, and the difference value is used to compare the data with the NOx measured by the PEMS device.
And (3) averaging the data measured by the SCR downstream NOx sensor and the ammonia sensor according to the difference working conditions, averaging the PEMS equipment data subjected to dew point removal and time alignment according to the working conditions, averaging the two groups of averages, calculating relative errors, and calculating absolute values of the relative errors to obtain the absolute values of three groups of relative errors under urban, suburban and high-speed working conditions.
The relative error under each working condition is calculated as follows:
relative error = difference of two sets of averages/average of PEMS device data;
Taking urban working conditions as an example, the calculation method of the relative error is that under the urban working conditions, the average value of the data measured by the SCR downstream NOx sensor and the ammonia sensor is A, the average value of the PEMS equipment data is B, the relative error of the urban working conditions is (A-B)/B, and at the moment, the absolute value of the relative error under the urban working conditions is I (A-B)/B I. And calculating other working conditions by referring to urban working conditions.
Different working conditions not only can lead to different exhaust flow rates and influence time alignment, but also can lead to different exhaust flow rates and influence the mixing uniformity of nitrogen oxides in exhaust, the larger the exhaust flow rate is, the better the mixing uniformity of exhaust is, the more accurate the data measured by an SCR downstream NOx sensor, an ammonia sensor and PEMS equipment are, and because different weight factors are introduced for different working conditions, the urban area, suburban area and high speed are respectively 0.2, 0.3 and 0.5, the weighted average is calculated on the absolute values of the three groups of relative errors, so that the total error is obtained, namely:
Total error = 0.2 x absolute value of relative error in urban operating conditions +0.3 x absolute value of relative error in suburban operating conditions +0.5 x absolute value of relative error in high speed operating conditions.
4) And setting a preset threshold value to be 10%, comparing the total error with the preset threshold value, and if the total error is greater than the preset threshold value, considering that the downstream NOx sensor is invalid, otherwise, considering that the sensor is normal.
It should be noted that the above-mentioned embodiments are merely preferred embodiments of the present invention, and the present invention is not limited thereto, but may be modified or substituted for some of the technical features thereof by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention. Other non-illustrated parts are known in the art.

Claims (7)

1.一种SCR下游NOx传感器失效诊断方法，其特征在于：包括以下步骤：1. A method for diagnosing the failure of a NOx sensor downstream of an SCR, characterized by comprising the following steps: 1)确认SCR下游NOx传感器、氨传感器与ECU通讯正常；安装PEMS设备，并进行试验前的标气检查，确认PEMS设备测试数据准确无误；1) Confirm that the NOx sensor and ammonia sensor downstream of the SCR are communicating normally with the ECU; install the PEMS equipment and perform a standard gas check before the test to confirm that the test data of the PEMS equipment is accurate. 2)启动待测车辆，进行PEMS排放试验，获取试验过程中的数据；所述PEMS排放试验在市区、郊区和高速三种工况下进行；2) Start the vehicle under test and conduct the PEMS emission test to obtain data during the test; the PEMS emission test is conducted under three operating conditions: urban area, suburbs, and highway. 3)对PEMS设备进行SCR下游NOx传感器通过露点前的数据剔除，并对剩余数据分工况进行时间对齐，随后分工况进行对比获得不同工况下的误差，并基于不同工况下的误差获得总误差；3) Remove the data from the NOx sensor downstream of the SCR in the PEMS equipment before the dew point, and align the remaining data by time according to different operating conditions. Then compare the data under different operating conditions to obtain the error under different operating conditions, and obtain the total error based on the error under different operating conditions. 所述步骤3)具体包括：Step 3) specifically includes: 3.1)将SCR下游NOx传感器的露点通过之前的时间内PEMS设备所测的NOx数据剔除；3.1) Remove the dew point data from the NOx sensor downstream of the SCR by using NOx data measured by the PEMS device within the previous time period; 3.2)对PEMS设备进行数据剔除后的剩余数据与SCR下游NOx传感器和氨传感器所测的数据进行时间对齐；所述时间对齐分工况进行，分别对市区、郊区和高速三种工况下获得的数据进行时间对齐；所述时间对齐的具体操作为：在任一工况的起步阶段，获取SCR下游NOx传感器所测数值波峰位置与PEMS设备所测NOx数值波峰时间差，依据所述时间差，进行时间对齐；所述SCR下游NOx传感器和氨传感器所测数据无时间差异，无需进行时间对齐；3.2) The remaining data after data removal from the PEMS device is time-aligned with the data measured by the NOx sensor and ammonia sensor downstream of the SCR. The time alignment is performed under different operating conditions, specifically for data obtained under urban, suburban, and highway conditions. The specific operation of the time alignment is as follows: at the start-up stage of any operating condition, the time difference between the peak position of the NOx value measured by the downstream NOx sensor and the peak position of the NOx value measured by the PEMS device is obtained, and time alignment is performed based on the time difference. The data measured by the downstream NOx sensor and ammonia sensor have no time difference and do not require time alignment. 3.3)用时间对齐后的SCR下游NOx传感器所测数值减去氨传感器所测数值获得差值，对所述差值求平均值；对时间对齐后的PEMS设备所测数据求平均值；将两个平均值进行对比，得到误差，并计算误差的绝对值，基于所述绝对值获得总误差；所述误差的计算分工况进行，以获得不同工况下误差的绝对值，并针对不同工况引入权重，对不同工况下误差的绝对值求加权平均值，获得所述总误差；3.3) Subtract the ammonia sensor value from the NOx sensor value measured downstream of the SCR after time alignment to obtain the difference, and calculate the average value of the difference; calculate the average value of the data measured by the PEMS device after time alignment; compare the two average values to obtain the error, and calculate the absolute value of the error, and obtain the total error based on the absolute value; the error calculation is performed under different operating conditions to obtain the absolute value of the error under different operating conditions, and weights are introduced for different operating conditions, and the weighted average value of the absolute value of the error under different operating conditions is calculated to obtain the total error; 4)基于所述总误差与设定阈值进行比较，判断SCR下游NOx传感器是否失效：若总误差>设定阈值，即所述待测车辆所安装的SCR下游NOx传感器已失效；或者，若总误差≤设定阈值，则所述待测车辆所安装的SCR下游NOx传感器正常。4) Based on the comparison between the total error and the set threshold, determine whether the downstream NOx sensor of the SCR is faulty: if the total error > the set threshold, the downstream NOx sensor of the SCR installed in the vehicle under test has failed; or, if the total error ≤ the set threshold, the downstream NOx sensor of the SCR installed in the vehicle under test is normal. 2.根据权利要求1所述的SCR下游NOx传感器失效诊断方法，其特征在于：所述SCR下游NOx传感器和氨传感器的安装位置为SCR出口处，所述PEMS设备的采样位置为排气管出口处。2. The method for diagnosing the failure of the downstream NOx sensor of SCR according to claim 1, characterized in that: the downstream NOx sensor and ammonia sensor of SCR are installed at the SCR outlet, and the sampling position of the PEMS device is at the exhaust pipe outlet. 3.根据权利要求2所述的SCR下游NOx传感器失效诊断方法，其特征在于：所述步骤2)中，待测车辆为N2类车辆，PEMS排放试验过程中，不同工况的试验时间占比分别为：市区45％、郊区25％和高速30％，且总试验时长≥3h，市区、郊区和高速工况下的车速分别为15～30km/h、45～70km/h、>70km/h。3. The method for diagnosing the failure of the downstream NOx sensor of SCR according to claim 2, characterized in that: in step 2), the vehicle under test is an N2 category vehicle, and during the PEMS emission test, the test time proportions for different operating conditions are: 45% in urban areas, 25% in suburban areas and 30% on highways, and the total test time is ≥3h, and the vehicle speeds in urban areas, suburban areas and highways are 15～30km/h, 45～70km/h and >70km/h, respectively. 4.根据权利要求3所述的SCR下游NOx传感器失效诊断方法，其特征在于：所述步骤2)中，数据包括SCR下游NOx传感器所测的NOx和NH3总含量、氨传感器所测的NH3含量、PEMS设备所测的NOx含量；所述SCR下游NOx传感器、氨传感器的数据通过ECU获取。4. The method for diagnosing the failure of the downstream NOx sensor of SCR according to claim 3, characterized in that: in step 2), the data includes the total NOx and NH3 content measured by the downstream NOx sensor of SCR, the NH3 content measured by the ammonia sensor, and the NOx content measured by the PEMS device; the data of the downstream NOx sensor of SCR and the ammonia sensor are obtained through the ECU. 5.根据权利要求1所述的SCR下游NOx传感器失效诊断方法，其特征在于：所述权重的分布如下：市区0.2，郊区0.3，高速0.5。5. The method for diagnosing the failure of a downstream NOx sensor in an SCR according to claim 1, wherein the weights are distributed as follows: 0.2 for urban areas, 0.3 for suburban areas, and 0.5 for highways. 6.根据权利要求1所述的SCR下游NOx传感器失效诊断方法，其特征在于：所述误差为相对误差。6. The method for diagnosing the failure of a downstream NOx sensor in an SCR according to claim 1, wherein the error is a relative error. 7.根据权利要求6所述的SCR下游NOx传感器失效诊断方法，其特征在于：所述步骤4)中，设定阈值为10％。7. The method for diagnosing the failure of a downstream NOx sensor of an SCR according to claim 6, wherein in step 4), the threshold is set to 10%.
CN202411105948.3A 2024-08-13 2024-08-13 Failure diagnosis method for NOx sensor downstream of SCR Active CN119086815B (en)

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