A method for detecting a three-way catalytic converter of a gasoline vehicle based on oxygen concentration

Abstract

The application discloses a kind of based on oxygen concentration's gasoline vehicle three-way catalytic converter detection method, including operating vehicle to reach detection state, according to steady-state operating mode method ASM carries out preliminary inspection, obtains the front oxygen concentration, rear oxygen concentration, vehicle speed and detection time of three-way catalytic converter in preliminary inspection process;If preliminary inspection oxygen integral difference is lower than preliminary inspection threshold value, when determining three-way catalytic converter preliminary inspection unqualified, then using NEDC operating mode carries out re-inspection;It is judged whether the re-inspection oxygen integral difference in re-inspection window is greater than re-inspection threshold value.The application is detected to the front oxygen concentration and rear oxygen concentration etc. parameter of vehicle in detection window by steady-state operating mode method and NEDC operating mode detection method, the time integral of oxygen concentration, can be more accurately obtained the front and rear change of oxygen concentration in detection window, more accurately.

Description

TECHNICAL FIELD

[0001] The present application relates to a rapid detection method of three-way catalytic converter, in particular to a detection method of gasoline vehicle three-way catalytic converter based on oxygen concentration. BACKGROUND

[0002] The main component of petroleum-based fuel is hydrocarbon compounds, and the theoretical product after full combustion in an internal combustion engine is CO2 and water. A lot of work has been done on efficient combustion, which not only improves the thermal power conversion efficiency, but also reduces the incomplete combustion products such as hydrocarbons H m C n , carbon monoxide (CO) and total particulate matter. On the other hand, due to the fact that modern engine in-cylinder combustion technology still cannot achieve complete oxidation of fuel, a small amount of C m H n and CO still exists in the engine exhaust. In addition, due to the fact that nitrogen in the engine intake is inevitably reacted with oxygen in the intake to form nitrogen oxides NOx (NO+NO2) under high temperature combustion in the cylinder, only relying on engine combustion optimization cannot meet the emission limit value requirements of H m C n , CO and NOx of gasoline vehicle emission regulations.

[0003] Under this condition, the gasoline vehicle emission aftertreatment technology emerged as the times require. The gasoline vehicle three-way catalytic converter is based on a ceramic honeycomb carrier as a basic carrier, and the ceramic honeycomb carrier is loaded with a large specific surface area and high thermal stability γ-Al2O3 coating, and the noble metal elements Pt, Pd and Rh are used as catalytic active components, which can efficiently promote the oxidation and reduction reactions of H m C n , CO and NOx, the three main pollutant emission components, to generate harmless water and low-hazard CO2.

[0004] The main reactions of modern three-way catalysts are:

[0005] Oxidation reaction:

[0006] C m H n +(1+n / 4)O2→mCO2+(n / 2)H2O.................(1)

[0007] CO+(1 / 2)O2→CO2................(2)

[0008] CO+H2O→CO2+H2.....................(3)

[0009] Reduction reaction:

[0010] NO (or NO2) + CO → (1 / 2) N2 + CO2 (4)

[0011] NO (or NO2) + H2→ (1 / 2) N2 + H2O (5)

[0012] (2 + n / 2) NO (or NO2) + C m H n → (1 + n / 4) N2 + m CO2 + (n / 2) H2O (6)

[0013] The above catalytic reactions must occur simultaneously and efficiently under appropriate engine exhaust conditions. When the exhaust is oxygen-rich, CO and HC oxidation efficiency is high, but NOx is difficult to reduce under oxygen-rich conditions. Conversely, under lean oxygen conditions, oxidation reaction efficiency decreases rapidly.

[0014] In view of the important influence of three-way catalytic converters on gasoline vehicle emissions, China has made specific provisions for catalytic converter performance, durability requirements, and test methods. The current stage of emission regulations requires 160,000 kilometers of emission durability for M1, M2, and N1 type vehicles using gasoline engines during type approval. This requirement ensures that the original catalytic converter can meet the emission durability requirements throughout the vehicle's life under normal operating conditions.

[0015] To prevent premature degradation of the original catalytic converter in special cases (such as engine misfire leading to short-term excessive exhaust temperature and catalyst deactivation), China's current emission standards have added a method for monitoring failed catalytic converters using the on-board diagnostic (OBD) system. The principle of this method is:

[0016] A wide-range oxygen sensor (front oxygen sensor) is installed at the engine exhaust port (or catalytic converter inlet) to monitor the exhaust oxygen concentration of the gasoline engine in real time, and a switching oxygen sensor (rear oxygen sensor) is installed at the catalytic converter exhaust port. Since three-way catalytic converters can only achieve efficient conversion of C m H n , CO, and NOx in a relatively narrow window around the engine's theoretical air-fuel ratio, a large amount of oxygen storage component (such as CexZr1-xO2) is added to the coating of modern three-way catalytic converters to buffer the effects of fluctuations in the air-fuel ratio at the catalytic converter inlet, reducing the impact of exhaust oxygen content fluctuations on the reaction system, which in turn leads to lower oxygen concentration fluctuations at the catalytic converter outlet. OBD monitoring takes advantage of this feature by detecting the switching frequency of the oxygen sensor at the catalytic converter exhaust outlet to qualitatively judge the performance of the catalyst's oxygen storage material (oxygen storage capacity), and then determine the activity of the catalyst.

[0017] A method and device for detecting faults of a three-way catalytic converter are disclosed in patent CN2017114284002; the method comprises: obtaining the change frequency of the excess air coefficient upstream and downstream of the three-way catalytic converter within a preset time period, calculating the ratio of the change frequency of the excess air coefficient downstream, and judging the relationship between the ratio and a preset first threshold value, if the ratio is greater than the preset first threshold value, it indicates that the three-way catalytic converter is faulty. In this way, without adding any external equipment, the rapid online detection of the three-way catalytic converter fault is realized. The above-mentioned patent is also based on the method in the prior art, and the change frequency of the excess air coefficient is used to judge whether the three-way catalytic converter fails. The change frequency of the excess air coefficient in the above-mentioned patent is represented according to the number of fluctuation periods within a preset time; the fluctuation period is represented as: the value of the excess air coefficient is greater than the preset threshold value, or the voltage value representing the excess air coefficient is greater than the preset threshold value; that is, only when the signal detected by the detection sensor is greater than the threshold value, the frequency value increases by 1.

[0018] The above-mentioned monitoring method is scientific in principle and simple in method, but its principle and the reliability of the detection result are based on an important assumption: the activity of the catalyst and the oxygen storage capacity of the catalytic coating material are in a certain linear relationship, so the decay amount of the oxygen storage capacity of the catalytic coating can be used to indirectly judge the decline of the catalytic activity. When the following situations occur, the assumed relationship between the oxygen storage capacity of the catalytic coating and the catalytic activity will be broken, resulting in a significant deviation in the monitoring result: (1) When the original catalyst produced in batches and the type-identified sample are inconsistent in quality, especially when the prices of precious metals Pt, Pd and Rh used in the catalyst are high, some manufacturers illegally reduce the cost to make profits, resulting in insufficient durability of the actual installed catalyst. (2) When the catalyst is not used correctly, for example, oil impurities pollute the catalyst, causing the catalyst to deteriorate prematurely, etc.

[0019] Therefore, the technology uses the performance of the oxygen storage material in the three-way catalytic coating as an indirect indicator of the catalytic activity and the degree of degradation, which is technically limited.

[0020] The present application aims to bypass the judgment of the performance of the oxygen storage material in the catalytic coating and directly measure and calculate the effect of the catalyst on removing HC and CO to accurately judge the catalytic activity of the catalyst. SUMMARY

[0021] The purpose of the present application is to provide a detection method for a three-way catalytic converter of a gasoline vehicle based on oxygen concentration; all technical problems to be solved by the present application include:

[0022] (1) The existing technology is inaccurate in judging the catalytic performance of the three-way catalytic converter by the performance of the oxygen storage material, which is prone to errors, especially when the oxygen storage material and the catalyst performance are not synchronized.

[0023] (2) In the prior art, the frequency of change of oxygen concentration after detection is realized by the switching frequency of the electrical signal that determines the oxygen concentration. That is, when the oxygen concentration reaches a certain limit, a signal is generated. The performance of the catalyst is judged based on the number of signal changes. However, the specific concentration value is not obtained, which makes the detection error large.

[0024] (3) The existing technology does not clearly define the detection window. Different detection windows have a significant impact on the detection effect, leading to detection errors.

[0025] (4) NO compounds consume some CO and H during the catalytic process. The concentration of NO compounds also has a certain impact on the detection effect, resulting in errors when different detection windows and different concentrations of NO compounds are used.

[0026] To achieve the above objectives, one embodiment of the present invention provides a method for detecting the oxygen concentration of a gasoline vehicle's three-way catalytic converter, comprising the following steps:

[0027] Step (1) Run the vehicle to reach the test state and perform a preliminary test according to the steady-state working condition method (ASM). During the preliminary test, set the data acquisition period t, obtain the pre-oxygen concentration, post-oxygen concentration, vehicle speed and test time of the three-way catalytic converter, establish the mapping relationship between test time-vehicle speed-pre-oxygen concentration and post-oxygen concentration, and obtain the steady-state working condition test curve.

[0028] Step (2) Set the initial inspection window as when the vehicle is traveling at the second constant speed under steady-state conditions, and obtain the pre-oxygen concentration C of the three-way catalytic converter within the initial inspection window. f and post-oxygen concentration C b Combined with the data acquisition period t, the oxygen integral difference between the previous oxygen concentration and the subsequent oxygen concentration is calculated to determine whether the initial oxygen integral difference within the initial detection window is greater than the initial detection threshold.

[0029] If the initial oxygen integral difference is greater than the initial inspection threshold, the three-way catalytic converter is deemed to have passed the initial inspection.

[0030] If the initial oxygen integral difference is less than the initial inspection threshold, the three-way catalytic converter is deemed to have failed the initial inspection.

[0031] Step (3) If the three-way catalytic converter is determined to be unqualified in the initial inspection, a re-inspection shall be performed using the NEDC operating condition; the method for re-inspection under the NEDC operating condition is as follows:

[0032] Run the vehicle according to the NEDC test conditions, set the data acquisition cycle, obtain the pre-oxygen concentration, post-oxygen concentration, vehicle speed and test time of the three-way catalytic converter, establish the mapping relationship between test time, vehicle speed and pre-oxygen concentration and post-oxygen concentration, and obtain the NEDC test curve.

[0033] The vehicle is in the NDEC working condition, the driving stage of the vehicle in 837s~1113s is the re-inspection window, the front oxygen concentration C f and the rear oxygen concentration C b of the three-way catalytic converter in the re-inspection window are obtained, the oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration is calculated combined with the data acquisition period t, whether the re-inspection oxygen integral difference value in the re-inspection window is greater than the re-inspection threshold value is judged;

[0034] If the re-inspection oxygen integral difference value is greater than the re-inspection threshold value when re-inspecting, it is determined that the three-way catalytic converter is qualified;

[0035] If the re-inspection oxygen integral difference value is less than the re-inspection threshold value when re-inspecting, it is determined that the three-way catalytic converter is unqualified;

[0036] The calculation method of the oxygen integral difference value C is:

[0037]

[0038]

[0039] C=C1-C2

[0040] Wherein, t is the data acquisition period, n is the data acquisition number in the detection window,

[0041] t*n is the total length of the detection window;

[0042] C1 is the front oxygen concentration integral, C2 is the rear oxygen concentration integral, and C is the oxygen integral difference value.

[0043] Preferably, the detection state is that the vehicle engine and exhaust system are fully warmed up after preheating for a preset time, and the three-way catalytic converter reaches the light-off temperature T80.

[0044] Preferably, a wide-range front oxygen sensor is arranged at the inlet end of the three-way catalytic converter, and a wide-range rear oxygen sensor is arranged at the outlet end; the corresponding oxygen concentration signals are obtained through the front oxygen sensor and the rear oxygen sensor; the signals of the front oxygen sensor and the rear oxygen sensor are uploaded to the OBD system, and the data of the front oxygen sensor and the rear oxygen sensor is directly obtained from the OBD system during detection.

[0045] Preferably, a wide-range front oxygen sensor is arranged at the inlet end of the three-way catalytic converter, and a 500mm or more extension pipe is additionally arranged at the outlet of the vehicle exhaust pipe during detection, the extension pipe is airtight and leakproof, and a wide-range rear oxygen sensor is installed close to the outlet of the vehicle exhaust pipe; the corresponding oxygen concentration signals are obtained through the front oxygen sensor and the rear oxygen sensor; the signal of the front oxygen sensor is uploaded to the OBD system, and the data of the front oxygen sensor is directly obtained from the OBD system during detection; the data of the rear oxygen sensor is read on site.

[0046] Preferably, in the detection process, the nitrogen oxygen concentration Q at the inlet of the three-way catalytic converter or the engine outlet is obtained, and in the preliminary detection and re-detection processes, the oxygen integral difference value is corrected if the carbon nitrogen ratio is lower than the interference threshold value at the time of detection: C=K+C1-C2.

[0047] The method for calculating the corrected integral value K is:

[0048]

[0049] Wherein,

[0050] α is an adjustment coefficient, and the value range is 0.98-1.05;

[0051] β is the excess air coefficient;

[0052] t is the data collection period of detection; that is, the nitrogen oxygen concentration parameter is collected once every interval t;

[0053] Q p is the nitrogen oxygen concentration parameter obtained at each detection time point in sequence of detection time;

[0054] n is the number of nitrogen oxygen concentration parameters detected in the total duration of the detection window.

[0055] Preferably, the total duration of the preliminary detection window is 70s, the second constant vehicle speed of the preliminary detection is 40km / h in the interval from the 20th s to the 90th s under the ASM2540 working condition, the total duration of the re-detection window is 276s, and the vehicle speed of the re-detection window is 50km / h-120km / h.

[0056] Preferably, the data obtaining method of the preliminary detection threshold value comprises the following steps:

[0057] (1) taking a new vehicle that has passed the detection and qualified, running the vehicle to reach the detection state, continuing to run according to the detection process of the steady state working condition method, obtaining the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter during the continuous running, establishing the mapping relationship of the detection time-vehicle speed-front oxygen concentration-rear oxygen concentration, and obtaining the steady state working condition detection curve;

[0058] (2) setting the vehicle running at the second constant vehicle speed in the steady state working condition as the preliminary detection window, obtaining the front oxygen concentration C f and the rear oxygen concentration C b of the three-way catalytic converter in the preliminary detection window, calculating the oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration combined with the data collection period t and the total duration of the detection window, and multiplying the oxygen integral difference value by 80% to obtain the preliminary detection threshold value.

[0059] The data obtaining method of the retest threshold value preferably comprises the following steps:

[0060] (1) taking a new vehicle that has passed the detection, running the vehicle to reach a detection state, running the vehicle according to the NEDC mode, setting a data collection period, obtaining the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter under the NEDC mode, establishing a mapping relationship of the detection time-vehicle speed-front oxygen concentration-rear oxygen concentration, and obtaining a NEDC mode detection curve;

[0061] setting the vehicle under the NDEC mode, the driving stage of the vehicle at 837s-1113s as a retest window, obtaining the front oxygen concentration C f and the rear oxygen concentration C b of the three-way catalytic converter in the retest window, combining the data collection period t, calculating the oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration, and multiplying the oxygen integral difference value by 80% to obtain the retest threshold value.

[0062] In summary, the present application has the following advantages:

[0063] 1. The present application detects the front oxygen concentration and the rear oxygen concentration and other parameters in the detection window of a specific time period in the driving process of the vehicle through the steady state mode ASM and the NEDC mode detection method, obtains the oxygen integral value through multiple detections in the preset period, and time-integrates the oxygen concentration to more accurately obtain the front and rear changes of the oxygen concentration in the detection window, which is equivalent to judging based on the total amount of gas passing during detection, and is more accurate than using the number of instantaneous signal switching quantities instead of the data in the entire detection period in the prior art.

[0064] 2. The present application does not judge whether the catalyst fails by detecting the oxygen storage capacity of the catalyst storage material, but directly detects the integral total amount of the oxygen concentration before and after the three-way catalytic converter, which is more direct and avoids errors caused by inconsistency between the oxygen storage material and the effectiveness of the catalyst; that is, avoids detection errors caused by inconsistency between the effectiveness of the oxygen storage material and the heavy metal catalyst.

[0065] 3. The present application also considers the influence of NOx on the detection result, increases the NOx sensor to calculate the integral total amount of NOx in the detection period, and corrects the detection result, so that the detection result is more accurate.

[0066] 4. Based on the characteristics of vehicle operation under NEDC and steady-state conditions, this invention considers the engine characteristics and emission levels of the vehicle under these two conditions, and selects specific initial and re-inspection windows. This ensures greater representativeness, avoids the influence of other interference stages, and further improves the accuracy of the test results. Furthermore, this invention selects data from specific time periods or test windows within the steady-state and NEDC methods for testing, taking into account that these two methods are commonly used in existing technologies, making it easier for operators to familiarize themselves with the operating procedures.

[0067] 5. This invention uses a full vehicle operating cycle and, in conjunction with the catalytic reaction mechanism, defines an evaluation window for catalyst performance. It records the pre- and post-catalytic oxygen concentrations of the three-way catalytic converter within the evaluation window, along with the test vehicle speed and detection time. The catalyst performance is judged based on the time-integrated difference between the measured exhaust oxygen concentrations before and after the catalyst. The method for detecting and calculating the pre- and post-catalytic oxygen concentrations within the detection window proposed in this invention eliminates the influence of the catalyst's oxygen storage capacity on the pre- and post-catalytic oxygen concentrations, making the detected oxygen concentration changes directly related to catalyst performance. This provides a more convenient, accurate, and effective method for detecting catalyst reactivity.

[0068] 6. This invention first performs an initial inspection using the steady-state operating condition (ASM) method. If the initial inspection fails, a second inspection is performed using the NEDC operating condition method. The initial inspection allows for rapid screening, while the second inspection process is more complex and conforms to actual operating conditions. Therefore, the test results are more reliable and can be confirmed when the initial inspection fails, thus eliminating the impact of vehicle operation problems on the test results. Attached Figure Description

[0069] Figure 1 This is a graph showing the CO / NOx ratio-vehicle speed-time curve of a vehicle operating according to the NDEC test cycle in one embodiment of the present invention.

[0070] Figure 2 This is a vehicle speed-time comparison diagram under steady-state operating conditions in one embodiment of the present invention;

[0071] Figure 3 This is a graph showing the vehicle speed, initial oxygen concentration, subsequent oxygen concentration, and time during vehicle operation under NDEC conditions, according to one embodiment of the present invention. Detailed Implementation

[0072] This invention provides a method for detecting oxygen concentration in a gasoline vehicle's three-way catalytic converter, comprising the following steps:

[0073] Step (1) running vehicle to reach the detection state, according to steady state method ASM initial detection, initial detection process set data acquisition period t, obtain three effect catalytic converter before oxygen concentration, after oxygen concentration, vehicle speed and detection time, establish detection time-vehicle speed-before oxygen concentration, after oxygen concentration mapping relationship, obtain steady state detection curve.

[0074] The detection principle of the application is as follows:

[0075] Gasoline engine uses gasoline and air mixture as working medium, and realizes vehicle output through heat work cycle. From engine air inlet to tail gas discharge outlet, the following oxygen concentration decreasing formula can be established:

[0076] C O2_in =C O2_com +C O2_aft +C O2_out

[0077] In the formula:

[0078] C O2_in represents total oxygen amount of engine air inlet;

[0079] C O2_com represents total oxygen amount consumed by engine cylinder combustion;

[0080] C O2_aft represents total oxygen amount consumed by three effect catalytic converter after cylinder non-consumption and discharge;

[0081] C O2_out represents total oxygen amount in exhaust gas finally discharged into atmosphere through automobile tail pipe;

[0082] C O2_in -C O2_com namely total oxygen amount of engine exhaust gas outlet; namely oxygen of three effect catalytic converter inlet end.

[0083] The detection state of the vehicle of the application is that the vehicle engine and exhaust system are fully preheated after preheating for a preset time, and the three effect catalytic converter reaches light-off temperature T80. In order to reach the above detection state, the vehicle generally needs to be preheated, and after preheating, the engine air-fuel ratio can reach a preset value, and the bed temperature of the catalyst can reach the required temperature of T80 when running at a related speed in the initial detection window or the re-detection window, so that the catalytic reaction can be normally carried out.

[0084] The data acquisition period t of the application is generally 3s-5s, and can also be set according to specific needs. The shorter the data acquisition period, the more data collected, and the more accurate oxygen integral difference obtained by integrating the obtained parameters in theory.

[0085] The present application must obtain the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter, and the vehicle is internally provided with an ECU system and an OBD system, which can read relevant data. In the existing vehicle, the front oxygen sensor is generally a wide-range front oxygen sensor, but the sensor arranged at the rear end of the three-way catalytic converter may be only a conventional ordinary sensor, so in many detection methods in the prior art, it is disclosed that the frequency of the change of the electric signal on the rear oxygen sensor needs to be detected, because the rear oxygen sensor installed on many three-way catalytic converters in the prior art belongs to a jump type narrow-range sensor; only one signal can be sent when the detection condition is reached, and the specific concentration value cannot be obtained, but the price is low.

[0086] The narrow-range oxygen concentration sensor is installed on the three-way catalytic converter, the signal of the narrow-range oxygen concentration sensor can be uploaded to the OBD system, but since it is a narrow-range oxygen concentration sensor, it can only detect whether the oxygen concentration exceeds the standard, and cannot detect the specific parameters of the oxygen concentration. The embodiment of the present application is to enable such vehicles to also use the detection method of the present application, and an extension pipe is additionally arranged on the exhaust pipe, and a wide-range rear oxygen sensor is arranged in the extension pipe, and an additional rear oxygen sensor is arranged to obtain the required data. Therefore, in order to obtain the data of the rear oxygen sensor, two ways are designed to obtain the rear oxygen concentration data.

[0087] Method one: a wide-range front oxygen sensor is arranged at the inlet end of the three-way catalytic converter, and a wide-range rear oxygen sensor is arranged at the outlet end; the corresponding oxygen concentration signals are obtained through the front oxygen sensor and the rear oxygen sensor; the signals of the front oxygen sensor and the rear oxygen sensor are uploaded to the OBD system, and the data of the front oxygen sensor and the rear oxygen sensor is directly obtained from the OBD system during detection.

[0088] Method two: a wide-range front oxygen sensor is arranged at the inlet end of the three-way catalytic converter, and a 500mm or more extension pipe is additionally arranged at the outlet of the vehicle exhaust pipe during detection, the extension pipe is tightly coupled without leakage, and a wide-range rear oxygen sensor is installed close to the outlet of the vehicle exhaust pipe; the corresponding oxygen concentration signals are obtained through the front oxygen sensor and the rear oxygen sensor; the signal of the front oxygen sensor is uploaded to the OBD system, and the data of the front oxygen sensor is directly obtained from the OBD system during detection; and the data of the rear oxygen sensor is read from the field.

[0089] During the driving of the vehicle, multiple parameters can be directly read from the OBD system, so that the coordinate graphs of the vehicle speed, the front oxygen concentration, the rear oxygen concentration and the time can be respectively established with the time as the horizontal coordinate, so as to form a mapping relationship.

[0090] Step (2) sets the vehicle in the steady state operating condition, the vehicle travels at a second constant speed as the initial detection window, and the vehicle travels at a second constant speed, which corresponds to the ASM2540 stage of the steady state operating condition method. The front oxygen concentration C f and the rear oxygen concentration C b of the three-way catalytic converter in the initial detection window are obtained, and the oxygen integral difference between the front oxygen concentration and the rear oxygen concentration is calculated combined with the data acquisition period t, to determine whether the initial detection oxygen integral difference in the initial detection window is greater than the initial detection threshold. The total duration of the initial detection window is 70s, from the 20s to the 90s interval of the ASM2540 operating condition, and the second constant speed of the initial detection is 40km / h.

[0091] The steady state operating condition method and the NDEC operating condition method are both methods for detecting the content of automobile exhaust emissions disclosed in the prior art, and the detection process and vehicle operating parameters have been fixed. The steady state operating condition method and the NDEC operating condition method in the prior art do not directly detect the catalytic ability of the catalyst, but when operating according to the above two operating condition methods, the front oxygen concentration and the rear oxygen concentration can be collected simultaneously, and then the corresponding detection time-vehicle speed-front oxygen concentration, rear oxygen concentration mapping relationship is matched to obtain the steady state operating condition detection curve. That is, the operating condition method of the prior art can obtain the detection time-vehicle speed-CO content-NO content curve, and the data of the front oxygen concentration and the rear oxygen concentration can be added on this basis.

[0092] The existing steady state operating condition method has two constant speeds, the first constant speed is 25km / h, and the second constant speed is 40km / h; the running time of the two constant speed stages is 90s. The characteristic of NEDC operating condition is that the uniform speed driving condition accounts for a large proportion, and the acceleration is constant when the vehicle accelerates and decelerates. The NEDC operating condition method is a process of continuously accelerating and decelerating the vehicle in the speed range of 0-120km / h, and detection is performed during this process. In the last period of detection, gradually accelerate to 120km / h. According to the emission situation of the engine, the second constant speed stage of the steady state operating condition method is selected, which is suitable for the detection of the catalyst. The first constant speed is too low, so the second constant speed stage is selected as the detection window. Similarly, the NDEC operating condition method gradually accelerates to 120km / h in the last stage. According to the emission situation in different time periods, the driving stage of 837s-1113s is selected as the re-detection window, which can well reflect the catalytic performance of the catalyst. The average speed of the remaining driving stages is low, or the time of the acceleration and deceleration stage is long, which has certain error for the detection of the catalytic performance of the catalyst.

[0093] The reason why the present inventors select the specific detection window in the first detection and the re-detection is that the present inventors find that the gasoline vehicle emission test method includes four working conditions, i.e., idle, acceleration, constant speed and deceleration, and the engine operation strategy, the exhaust emission and the catalytic effect of the catalyst under each working condition are correlated, and the specific analysis is as follows.

[0094] (1) Vehicle constant speed running stage

[0095] The catalyst inlet oxygen concentration is the lowest and stable, because the air-fuel ratio of the gasoline engine is maintained near the theoretical air-fuel ratio under the stable working condition, and can be accurately and stably controlled. For the theoretical air-fuel ratio, the incomplete combustion products and the excess air meet the chemical reaction ratio, and according to the catalyst pollutant removal efficiency (i.e., conversion efficiency) η = 100%, the catalyst inlet oxygen will be completely consumed in this case, and the oxygen concentration detected by the rear oxygen sensor is theoretically 0. However, since the catalytic reaction efficiency is not 100%, when the catalyst working temperature reaches the light-off temperature T80, the normal catalyst conversion efficiency η is generally above 80%, and thus the oxygen concentration detected by the rear oxygen sensor is about 0.2% or below under the normal condition during the vehicle constant speed running stage; when the front oxygen concentration and the rear oxygen concentration are measured at this stage, the catalytic performance of the catalyst can be well reflected, the catalytic efficiency of the catalyst is fully utilized, and the combustion products and the exhaust composition have little effect, and the efficiency of the catalyst can be detected.

[0096] (2) Vehicle speed sharply decreasing stage

[0097] At this time, the engine oil supply is reduced, the vehicle inertia drags the engine, the engine exhaust oxygen content rapidly rises, and the front oxygen sensor detects the concentration value rapidly rising and appearing a peak. The detection shows that the detection concentrations of the front and rear oxygen sensors simultaneously rise and appear peaks, but the rear oxygen peak is lower than the front oxygen concentration, and the oxygen concentration difference obtained by the front and rear oxygen detection is the largest under this working condition. This is because the incomplete combustion products HC and CO are completely oxidized under the condition of rich oxygen exhaust, and the excess oxygen in the exhaust is consumed to the maximum extent. However, the engine produces less incomplete combustion products at this stage than at the rising stage and the idle stage, and the oxygen content in the exhaust gas is high, so the catalytic ability of the catalyst may not be fully released. Therefore, the change of the front and rear oxygen concentrations cannot fully reflect the catalytic ability of the catalyst, the catalytic efficiency of the detected catalyst is low, and the normal catalyst is identified as a failed catalyst.

[0098] (3) Vehicle speed rising stage

[0099] This stage is opposite to the deceleration process, the engine mixture maintains the theoretical air-fuel ratio or is slightly rich, and accordingly the front oxygen concentration decreases, and more oxygen is consumed in the engine, so that the oxygen content discharged from the engine is relatively reduced, and thus the rear oxygen detection value returns to 0 or a lower value.

[0100] (4) Engine idle stage

[0101] This stage is also a steady state condition, but the combustion quality is relatively poor, corresponding to the theoretical air-fuel ratio, the incomplete oxidation products in the combustion process and the oxygen concentration in the exhaust gas are higher than those in the vehicle constant speed running stage and the vehicle speed rising stage, but lower than those in the vehicle speed sharply declining stage. According to the calculation of the theoretical air-fuel ratio of the intake air, the HC and CO in the exhaust gas can be completely oxidized by the catalyst, and the post-oxygen concentration is 0. However, due to the low exhaust temperature of the idle condition, the concentration of incomplete oxidation products is too high, which will affect the actual test results, therefore, the idle stage is not suitable for detecting the catalytic effect of the catalyst.

[0102] In summary, combined with the engine exhaust emission parameters of the four stages, the present inventors found through experiments that if the pre-post oxygen concentration difference is used to judge the advantages and disadvantages of the three-way catalytic converter or the catalytic efficiency, the vehicle engine needs to emit appropriate incomplete combustion products and oxygen during operation, so that the pre-post oxygen concentration can truly reflect the catalytic performance, and will not be affected by excessive oxygen or excessive incomplete combustion products. Therefore, the vehicle constant speed running stage should be selected as the optimal detection window, followed by the vehicle acceleration stage, and the deceleration stage should be avoided as much as possible, and the idle stage is not allowed.

[0103] In the prior art, the detection condition is not limited, that is, the vehicle speed and the running state of the vehicle. When the vehicle is running at different speeds, the emissions are different, and when the vehicle is accelerating, decelerating, idling and engine reverse dragging, the content of the emissions is also quite different. As known from common sense, the vehicle runs at a constant speed for the longest time and has the largest mileage, so detecting the working condition of the three-way catalytic converter during constant speed running is more in line with the actual situation. At the same time, during the steady state constant speed running of the vehicle, the content of the engine exhaust gas is relatively stable, and detection at this time is also easier and more accurate. Therefore, the present application selects to detect first during steady state running, removes the data under unstable conditions, reduces the detection error as much as possible, and obtains the fastest detection efficiency.

[0104] After the initial oxygen integral difference value is obtained, if the initial oxygen integral difference value is greater than the initial threshold value, it is determined that the three-way catalytic converter is initial inspection qualified; if the initial oxygen integral difference value is less than the initial threshold value, it is considered that the total amount of oxygen concentration integral changes little within the total length of the detection window, indicating that the oxygen concentration consumption is small, and then it can be considered that the exhaust treatment of the whole vehicle is unqualified, so in this case, since the steady state condition method ASM is a simple condition, the unqualified condition may be due to the problem of the engine of the whole vehicle or the problem of the catalyst, therefore, when the initial inspection is unqualified, a more accurate detection method is needed to determine whether the unqualified condition is caused by the problem of the whole vehicle or the problem of the catalyst.

[0105] Since the steady state condition method is driven at a constant speed, it is a relatively good state, since in fact the vehicle will not always run at a constant speed during high speed operation, and is more inclined to the driving condition of the detection window of the NDEC condition method, the data obtained under this condition is more accurate, and at the same time, the influence of single state and other problems of the whole vehicle on the result can be avoided. Therefore, when the initial inspection is unqualified, NDEC condition method is needed for re-inspection, the total length of the re-inspection window is 276s, and the speed of the re-inspection window is 50km / h~120km / h. In this way, whether the three-way catalytic converter is effective can be further determined. If the initial inspection is qualified, it can be directly determined that the whole vehicle is qualified when running, and the detection of the NDEC condition method can be omitted.

[0106] Step (3) if it is determined that the three-way catalytic converter is unqualified in the initial inspection, then the NEDC condition is used for re-inspection; the method of NEDC condition re-inspection is:

[0107] The vehicle is driven according to the NEDC condition, the data acquisition period is set, the front oxygen concentration, the rear oxygen concentration, the speed and the detection time of the three-way catalytic converter are obtained, the mapping relationship of the detection time-speed-front oxygen concentration, rear oxygen concentration is established, and the NEDC condition detection curve is obtained;

[0108] The vehicle is driven according to the NEDC condition, the vehicle is driven according to the NEDC condition, the driving stage of the vehicle in 837s~1113s is the re-inspection window, the front oxygen concentration C f and the rear oxygen concentration C b of the three-way catalytic converter in the re-inspection window are obtained, the data acquisition period t is combined, the oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration is calculated, and whether the re-inspection oxygen integral difference value in the re-inspection window is greater than the re-inspection threshold value is judged;

[0109] If the re-inspection oxygen integral difference value is greater than the re-inspection threshold value when the re-inspection is carried out, it is determined that the three-way catalytic converter is qualified;

[0110] If the re-inspection oxygen integral difference value is less than the re-inspection threshold value when the re-inspection is carried out, it is determined that the three-way catalytic converter is unqualified.

[0111] The calculation method of the oxygen integral difference value C is as follows:

[0112]

[0113]

[0114] C=C1-C2

[0115] Wherein, t is the data acquisition period, n is the data acquisition times in the detection window,

[0116] t*n is the total duration of the detection window;

[0117] C1 is the front oxygen concentration integral, C2 is the rear oxygen concentration integral, and C is the oxygen integral difference value.

[0118] The preliminary detection threshold and the re-detection threshold are preset values, which are designed according to experience and national requirements. The data acquisition method of the preliminary detection threshold comprises the following steps:

[0119] (1) Take a new vehicle that has passed the detection, run the vehicle to reach the detection state, continue to run according to the steady state working condition method, during the continuous running, obtain the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter, establish the mapping relationship of the detection time-vehicle speed-front oxygen concentration, rear oxygen concentration, and obtain the steady state working condition detection curve;

[0120] (2) Set the vehicle to run at a second constant speed as the preliminary detection window under the steady state working condition, obtain the front oxygen concentration C f and the rear oxygen concentration C b of the three-way catalytic converter in the preliminary detection window, combine the data acquisition period t and the total duration of the detection window, calculate the oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration, and the oxygen integral difference value multiplied by 80% is the preliminary detection threshold.

[0121] Similarly, the data acquisition method of the re-detection threshold comprises the following steps:

[0122] (1) Take a new vehicle that has passed the detection, run the vehicle to reach the detection state, let the vehicle run according to the NEDC working condition, set the data acquisition period, obtain the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter of the vehicle under the NEDC working condition, establish the mapping relationship of the detection time-vehicle speed-front oxygen concentration, rear oxygen concentration, and obtain the NEDC working condition detection curve;

[0123] Set the vehicle to run in the running stage of 837s-1113s as the re-detection window under the NDEC working condition, obtain the front oxygen concentration C f and the rear oxygen concentration Cb , combined with the data acquisition cycle t, the oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration is calculated, and the oxygen integral difference value multiplied by 80% is the re-inspection threshold.

[0124] When the present application is detected, first, it is fully preheated through more than 10 minutes of vehicle working condition cycle; the vehicle speed and the exhaust temperature are high at two working conditions; the air-fuel ratio fluctuation is small within the cycle window period, and the exhaust system meets the high-efficiency oxidation reduction condition; the acceleration and deceleration conditions existing in the cycle lead to the fluctuation of the exhaust oxygen content, but since the cycle time of 10 minutes before detection has exceeded 300s, the catalyst oxygen storage characteristic will not affect the overall performance evaluation of the catalyst; the high vehicle speed and the large air speed are helpful for detecting the overall conversion efficiency of the catalyst.

[0125] The catalytic reaction directly consumes oxygen, resulting in a linear decrease in the post-oxygen peak value; the oxygen storage capacity of the catalyst can make the oxygen concentration wave peak at the exhaust outlet become flat, and the performance is also a certain degree of decrease in the post-oxygen sensor peak value. The difference between the two is that the oxygen storage capacity only buffers the outlet release of oxygen, and does not reduce the total amount of oxygen emission.

[0126] At present, the installation and discharge ratio of a gasoline engine is less than or equal to 1, and the oxygen storage capacity of a fresh catalyst sample is generally not greater than 1000mg / L, and under the condition of an intake air flow of 40kg / h, the oxygen storage time is about 9s. The detection window given by the present application, whether it is the initial detection window or the re-detection window, the total time is much longer than the oxygen storage time of 9s, and the influence of the oxygen storage capacity can be eliminated within the window period, and the pollutant conversion efficiency (i.e. catalytic activity) is directly judged according to the front and rear oxygen concentration detection values.

[0127] The present inventor has found that the content of engine exhaust gas under different working conditions has a very big difference. The present application judges whether the catalyst is working normally by the oxygen integral value, since the NOx reaction consumes HC and CO reducing agent, and then reduces the oxygen consumption, and increases the oxygen emission. Therefore, the ideal test condition of the present application is that the NOx emission is the lowest, the HC and CO emission is the highest, and the working condition is relatively stable.

[0128] Reference Figure 1 , Figure 1 is the CO / NOx ratio curve of the vehicle at each time period when the vehicle is operated according to the NDEC working condition method. It can be seen that in the re-detection window selected by the present application, the CO / NOx ratio is the lowest, indicating that the HC, CO and NOx emission values at the engine outlet at this time are in the same order of magnitude, and the influence of NOx on the oxidation reaction should be considered; at the same time, from Figure 1It can also be seen that the CO / NOx ratio of the re-check window is the most stable, which is also conducive to maintaining stable working conditions, so that the detection result is more accurate. Therefore, in order to eliminate the influence of NOx in the re-check window, the application introduces a correction integral value.

[0129] The application introduces a correction integral value method:

[0130] In the detection process, the nitrogen oxygen concentration Q at the inlet of the three-way catalytic converter or the outlet of the engine is obtained. In the initial detection and re-detection processes, if the carbon-nitrogen ratio is lower than the interference threshold value during detection, the oxygen integral difference value is corrected: C=K+C1-C2.

[0131] The calculation method of the correction integral value K is:

[0132] The calculation method of the correction integral value K is:

[0133]

[0134] Wherein,

[0135] Alpha is an adjustment coefficient, and the value range is 0.98-1.05;

[0136] Beta is an excess air coefficient;

[0137] T is the data acquisition period of detection, that is, the nitrogen oxygen concentration parameter is collected every interval t;

[0138] Q p is the nitrogen oxygen concentration parameter obtained at each detection time point in sequence of detection time;

[0139] N is the number of nitrogen oxygen concentration parameters detected within the total duration of the detection window.

[0140] The lower the interference threshold value of the application, the lower the ratio of CO and NOx, and the higher the content of NOx. Generally, the interference threshold value is set to 20.

[0141] Although the specific embodiments of the application are described in detail with reference to the accompanying drawings, it should not be understood as limiting the protection scope of the patent. Various modifications and variations made by those skilled in the art within the scope described in the claims are still within the protection scope of the patent.

Claims

1. A method for detecting a gasoline vehicle three-way catalytic converter based on oxygen concentration, characterized in that, The method comprises the following steps: Step (1) running the vehicle to reach a detection state, performing preliminary detection according to the steady state method (ASM), setting a data acquisition period t during the preliminary detection, obtaining the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter, establishing a mapping relationship of the detection time-vehicle speed-front oxygen concentration-rear oxygen concentration, and obtaining a steady state detection curve; Step (2) sets the vehicle in a steady state, the vehicle at a second constant speed when traveling as the initial detection window, and obtains the front oxygen concentration C f and the rear oxygen concentration C b of the three-way catalytic converter in the initial detection window, combines the data acquisition period t, calculates the oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration, and judges whether the initial detection oxygen integral difference value in the initial detection window is greater than the initial detection threshold value; If the preliminary oxygen integral difference is greater than the preliminary detection threshold, it is determined that the three-way catalytic converter is preliminarily qualified; If the preliminary oxygen integral difference is less than the preliminary detection threshold, it is determined that the three-way catalytic converter is preliminarily unqualified; Step (3) if the three-way catalytic converter is determined to be preliminarily unqualified, NEDC condition is used for re-detection; the method of NEDC condition re-detection is as follows: The vehicle is run according to the NEDC condition, a data acquisition period is set, the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter are obtained, a mapping relationship of the detection time-vehicle speed-front oxygen concentration-rear oxygen concentration is established, and a NEDC condition detection curve is obtained; The vehicle is set in the NDEC working condition, the driving stage of the vehicle from 837s to 1113s is a re-check window, the front oxygen concentration C of the three-way catalytic converter in the re-check window is acquired f and the rear oxygen concentration C b , the oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration is calculated combined with a data acquisition period t, whether the re-check oxygen integral difference value in the re-check window is greater than a re-check threshold value is judged. If the re-detection oxygen integral difference is greater than the re-detection threshold, it is determined that the three-way catalytic converter is qualified; If the re-detection oxygen integral difference is less than the re-detection threshold, it is determined that the three-way catalytic converter is unqualified; The calculation method of the oxygen integral difference C is as follows: Wherein, t is the data acquisition period, n is the number of data acquisition in the detection window, t*n is the total length of the detection window; C1 is the front oxygen concentration integral, C2 is the rear oxygen concentration integral, and C is the oxygen integral difference; Wherein, the data acquisition method of the front oxygen sensor and the rear oxygen sensor is any one of the following methods: The wide-range front oxygen sensor is arranged at the inlet end of the three-way catalytic converter, and the wide-range rear oxygen sensor is arranged at the outlet end; the corresponding oxygen concentration signals are obtained through the front oxygen sensor and the rear oxygen sensor; the signals of the front oxygen sensor and the rear oxygen sensor are uploaded to the OBD system, and the data of the front oxygen sensor and the rear oxygen sensor are directly obtained from the OBD system during detection; Or: the wide-range front oxygen sensor is arranged at the inlet end of the three-way catalytic converter, and a lengthened pipe of more than 500 mm is additionally arranged at the outlet of the vehicle exhaust pipe during detection, the lengthened pipe is tightly connected without leakage, and the wide-range rear oxygen sensor is installed close to the outlet of the vehicle exhaust pipe; the corresponding oxygen concentration signals are obtained through the front oxygen sensor and the rear oxygen sensor; the signal of the front oxygen sensor is uploaded to the OBD system, and the data of the front oxygen sensor is directly obtained from the OBD system during detection; the data of the rear oxygen sensor is read from the field.

2. The method for detecting an oxygen concentration-based gasoline vehicle three-way catalytic converter according to claim 1, characterized by: The detection state is that the vehicle engine and exhaust system are fully preheated after preheating for a preset time, and the three-way catalytic converter reaches the light-off temperature T80.

3. The method for detecting an oxygen concentration-based gasoline vehicle three-way catalytic converter according to claim 1, characterized by: During the detection process, the nitrogen oxygen concentration Q at the inlet of the three-way catalytic converter or the outlet of the engine is obtained; during the preliminary detection and the re-detection, if the carbon nitrogen ratio is lower than the interference threshold during the detection, the oxygen integral difference is corrected: C=K+C1-C2; The calculation method of the corrected integral value K is as follows: Wherein, α is the adjustment coefficient, and the value range is 0.98-1.05; β is the excess air coefficient; t is the data acquisition period of the detection; that is, the nitrogen oxygen concentration parameter is collected every t. Q p a nitrogen oxide concentration parameter acquired at each detection time point in chronological order of the detection time; n is the number of nitrogen oxygen concentration parameters detected within the total duration of the detection window.

4. The method for detecting an oxygen concentration-based gasoline vehicle three-way catalytic converter according to claim 1, characterized by: The total duration of the initial detection window is 70 s, the initial detection second constant vehicle speed is 40 km / h from the 20th s to the 90th s interval under the ASM2540 working condition, and the total duration of the re-detection window is 276 s, and the vehicle speed of the re-detection window is 50 km / h-120 km / h.

5. The method of claim 1, wherein the method is based on oxygen concentration of a gasoline vehicle three-way catalytic converter. The data obtaining method of the initial detection threshold value comprises the following steps: (1) Take a new vehicle that has passed the detection and make it reach the detection state, continue to run according to the detection process of the steady state working condition method, obtain the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter during the continuous running, establish the mapping relationship of the detection time-vehicle speed-front oxygen concentration, rear oxygen concentration, and obtain the steady state working condition detection curve; (2) Set the vehicle in a steady state, the vehicle at a second constant speed for the initial detection window, to obtain the initial detection window before the three-way catalytic converter oxygen concentration C f And the oxygen concentration C b After, combined with the data acquisition cycle t and the total length of the detection window, calculate the oxygen integral difference value of the oxygen concentration before and after, which is multiplied by 80% to obtain the initial detection threshold.

6. The method for detecting an oxygen concentration-based gasoline vehicle three-way catalytic converter according to claim 1, characterized by: The data obtaining method of the re-detection threshold value comprises the following steps: (1) Take a new vehicle that has passed the detection and make it reach the detection state, let the vehicle run according to the NEDC working condition, set the data acquisition period, obtain the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter of the vehicle under the NEDC working condition, establish the mapping relationship of the detection time-vehicle speed-front oxygen concentration, rear oxygen concentration, and obtain the NEDC working condition detection curve; The vehicle is set in the NDEC mode, and the driving stage of the vehicle from 837s to 1113s is the recheck window, and the front oxygen concentration C of the three-way catalytic converter in the recheck window is obtained f and the rear oxygen concentration C b , combined with the data acquisition period t, the oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration is calculated, and the oxygen integral difference value multiplied by 80% is the recheck threshold value.

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