CN117110513A - Detection method of three-way catalytic converter of gasoline car based on oxygen concentration - Google Patents
Detection method of three-way catalytic converter of gasoline car based on oxygen concentration Download PDFInfo
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- 229910052760 oxygen Inorganic materials 0.000 title claims abstract description 353
- 239000001301 oxygen Substances 0.000 title claims abstract description 353
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 title claims abstract description 350
- 238000001514 detection method Methods 0.000 title claims abstract description 278
- 230000003197 catalytic effect Effects 0.000 title claims abstract description 117
- SAZUGELZHZOXHB-UHFFFAOYSA-N acecarbromal Chemical compound CCC(Br)(CC)C(=O)NC(=O)NC(C)=O SAZUGELZHZOXHB-UHFFFAOYSA-N 0.000 title claims abstract description 11
- 238000000034 method Methods 0.000 claims abstract description 94
- 230000008569 process Effects 0.000 claims abstract description 25
- 238000013507 mapping Methods 0.000 claims description 14
- DOTMOQHOJINYBL-UHFFFAOYSA-N molecular nitrogen;molecular oxygen Chemical compound N#N.O=O DOTMOQHOJINYBL-UHFFFAOYSA-N 0.000 claims description 12
- 238000007689 inspection Methods 0.000 claims description 8
- 238000012797 qualification Methods 0.000 claims description 6
- 238000004364 calculation method Methods 0.000 claims description 5
- CKUAXEQHGKSLHN-UHFFFAOYSA-N [C].[N] Chemical compound [C].[N] CKUAXEQHGKSLHN-UHFFFAOYSA-N 0.000 claims description 3
- 238000007789 sealing Methods 0.000 claims description 3
- 230000008859 change Effects 0.000 abstract description 11
- 230000010354 integration Effects 0.000 abstract 1
- 239000003054 catalyst Substances 0.000 description 63
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical group [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 26
- 229910002091 carbon monoxide Inorganic materials 0.000 description 26
- 239000007789 gas Substances 0.000 description 16
- 238000002485 combustion reaction Methods 0.000 description 15
- 238000003860 storage Methods 0.000 description 14
- 239000000446 fuel Substances 0.000 description 13
- 238000006243 chemical reaction Methods 0.000 description 11
- 239000011232 storage material Substances 0.000 description 10
- 230000000694 effects Effects 0.000 description 8
- 238000007254 oxidation reaction Methods 0.000 description 8
- 239000011248 coating agent Substances 0.000 description 7
- 238000000576 coating method Methods 0.000 description 7
- 230000001133 acceleration Effects 0.000 description 6
- 238000006555 catalytic reaction Methods 0.000 description 5
- 230000003647 oxidation Effects 0.000 description 5
- 238000005516 engineering process Methods 0.000 description 4
- 238000012544 monitoring process Methods 0.000 description 4
- 230000033228 biological regulation Effects 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 239000003344 environmental pollutant Substances 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 231100000719 pollutant Toxicity 0.000 description 3
- 238000006722 reduction reaction Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 239000000872 buffer Substances 0.000 description 2
- 239000000919 ceramic Substances 0.000 description 2
- 150000002430 hydrocarbons Chemical class 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910000510 noble metal Inorganic materials 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 229910052703 rhodium Inorganic materials 0.000 description 2
- 230000000630 rising effect Effects 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000007809 chemical reaction catalyst Substances 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000003745 diagnosis Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 229910001385 heavy metal Inorganic materials 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 238000013486 operation strategy Methods 0.000 description 1
- 230000033116 oxidation-reduction process Effects 0.000 description 1
- 239000013618 particulate matter Substances 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000011895 specific detection Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
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- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M15/00—Testing of engines
- G01M15/04—Testing internal-combustion engines
- G01M15/10—Testing internal-combustion engines by monitoring exhaust gases or combustion flame
- G01M15/102—Testing internal-combustion engines by monitoring exhaust gases or combustion flame by monitoring exhaust gases
- G01M15/104—Testing internal-combustion engines by monitoring exhaust gases or combustion flame by monitoring exhaust gases using oxygen or lambda-sensors
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- G—PHYSICS
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- 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
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Abstract
The invention discloses a detection method of a three-way catalytic converter of a gasoline car based on oxygen concentration, which comprises the steps of running the car to reach a detection state, performing primary detection according to a steady-state working condition method ASM, and acquiring the front oxygen concentration, the rear oxygen concentration, the car speed and the detection time of the three-way catalytic converter in the primary detection process; if the primary detection oxygen integral difference value is lower than the primary detection threshold value, and the primary detection of the three-way catalytic converter is judged to be unqualified, the NEDC working condition is used for re-detection; and judging whether the difference value of the oxygen integration of the re-detection window is larger than a re-detection threshold value or not. According to the invention, parameters such as the front oxygen concentration and the rear oxygen concentration of the vehicle in the detection window are detected by the steady-state working condition method and the NEDC working condition detection method, and the time integral of the oxygen concentration is performed, so that the front-rear change of the oxygen concentration in the detection window can be more accurately obtained, and the accuracy is higher.
Description
Technical Field
The invention relates to a rapid detection method of a three-way catalytic converter, in particular to a detection method of a three-way catalytic converter of a gasoline car based on oxygen concentration.
Background
The main component of petroleum-based fuel is hydrocarbon compound, and after the internal combustion engine is fully combusted, the theoretical product is CO 2 And water. PeopleA great deal of work is carried out on the efficient combustion, not only the heat-power conversion efficiency is improved, but also the incomplete combustion products such as hydrocarbon H are reduced m C n Total amount of carbon monoxide (CO) and particulate matter produced. On the other hand, since modern in-cylinder combustion technology still cannot achieve complete oxidation of fuel, small amounts of C remain in the engine exhaust m H n And CO, and also because nitrogen in the engine intake inevitably reacts with oxygen in the intake under high temperature combustion in the cylinder to produce oxynitride NOx (NO+NO) 2 ) The emission regulation of gasoline vehicles on H cannot be met by only optimizing the combustion of the engine m C n Emission limits for CO and NOx.
Under such conditions, gasoline vehicle exhaust aftertreatment technologies have evolved. The three-effect catalytic converter for gasoline car uses ceramic honeycomb carrier as basic carrier, and the ceramic honeycomb carrier is loaded with gamma-Al with large specific surface area and high thermal stability 2 O 3 The coating takes noble metal elements Pt, pd and Rh as catalytic active components, can efficiently promote H m C n The oxidation and reduction reactions of three main pollutant emission components of CO and NOx, and harmless water and low-harmful CO are generated 2 。
The main reactions of modern three-way catalysts are:
oxidation reaction:
C m H n +(1+n/4)O 2 →mCO2+(n/2)H 2 O...................................(1)
CO+(1/2)O 2 →CO 2 ....................................(2)
CO+H 2 O→CO 2 +H 2 ......................................(3)
reduction reaction:
NO (or NO) 2 )+CO→(1/2)N 2 +CO 2 ......................................(4)
NO (or NO) 2 )+H 2 →(1/2)N 2 +H 2 O......................................(5)
(2+n/2) NO (or NO 2 )+C m H n →(1+n/4)N 2 +mCO 2 +(n/2)H 2 O........(6)
The catalytic reactions must occur simultaneously and efficiently under appropriate engine exhaust conditions. When the exhaust gas is rich in oxygen, CO and HC oxidation efficiency is high, but NOx is difficult to reduce under oxygen-rich conditions. Conversely, under oxygen-deficient conditions, the oxidation reaction efficiency rapidly decreases.
In view of the important influence of the three-way catalytic converter on the emission of the gasoline vehicle, specific regulations are made on the performance and durability requirements of the catalytic converter and the test method in China. The current emission regulation has the emission durability requirement of 16 ten thousand kilometers when the M1, M2 and N1 type vehicle types of the gasoline engine are used for authentication, and the requirement can ensure that the original catalyst can meet the emission durability requirement of the gasoline vehicle in the whole life cycle under the normal use condition.
In order to prevent the original catalyst from being degraded in advance under special conditions (for example, the exhaust temperature is too high for a short time and the catalyst is deactivated due to the fire of an engine), the current emission standard in China is added with a monitoring method for the failure catalyst by an on-board diagnosis (OBD) system, and the method is based on the principle that:
a wide-range oxygen sensor (front oxygen sensor) is mounted at an engine exhaust port (or a catalyst inlet), the exhaust oxygen concentration of a gasoline engine is monitored in real time, and a switching value oxygen sensor (rear oxygen sensor) is mounted at a catalyst exhaust port. Since a three-way catalytic converter can only achieve C in a relatively narrow window around engine stoichiometric air-fuel ratio m H n CO and NOx are converted simultaneously and efficiently, a large amount of oxygen storage components (such as CexZr1-xO 2) are added into the coating of the modern three-way catalytic converter in order to offset the influence of the fluctuation of the air-fuel ratio at the inlet of the catalytic converter, and the oxygen storage materials are multivalent oxides and can buffer lean and rich oxygen conditions so as to reduce the influence of the fluctuation of the oxygen content of exhaust gas on a reaction system, thereby leading the fluctuation frequency of the oxygen concentration at the outlet of the catalytic converter to be lower than that at the inlet. The OBD monitoring utilizes the characteristic, and the performance of the oxygen storage material (oxygen storage capacity) of the catalyst is qualitatively judged by detecting the switching frequency of the oxygen sensor at the exhaust outlet of the catalyst, so that the activity of the catalyst is judged.
Patent CN2017114284002 discloses a method and apparatus for detecting failure of a three-way catalytic converter; the method comprises the following steps: and acquiring the change frequency of the excessive air coefficient at the upstream and downstream of the three-way catalytic converter in a preset time period, calculating the ratio of the change frequency of the excessive air coefficient at the downstream, judging the relation between the ratio and a preset first threshold value, and if the ratio is larger than the preset first threshold value, indicating the failure of the three-way catalytic converter. Therefore, on the premise of not adding any external equipment, the rapid on-line detection of the failure of the three-way catalytic converter is realized. The above patent is also based on prior art methods that employ frequency variation to determine if a three-way catalytic converter is malfunctioning. The frequency of the change in the excess air ratio of the above patent is expressed in terms of the number of fluctuation periods in a preset time; the period of fluctuation is expressed as: the value of the excess air coefficient is larger than a preset threshold value, or the voltage value representing the excess air coefficient is larger than the preset threshold value; i.e. the frequency value is increased by 1 only if the signal detected by the detection sensor is greater than the threshold value.
The principle of the monitoring method is scientific and the method is simple, but the 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 oxygen storage material in the catalytic coating are in a certain linear relation, so that the reduction of the reaction activity of the catalyst can be indirectly judged according to the attenuation of the oxygen storage capacity of the catalytic coating. The hypothetical relationship of the oxygen storage capacity of the catalytic coating to the catalyst reactivity will be broken when the following occurs, leading to a significant deviation in the monitoring results: (1) When the quality of the original catalyst in mass production is inconsistent with that of the sample authenticated by the model, particularly, the price of noble metals Pt, pd and Rh used by the catalyst is high, and a part of manufacturers steal materials and reduce materials for illegally making a profit, the durability of the actual loading catalyst is insufficient. (2) When the catalyst is not used properly, for example, contaminated with oil impurities, leading to early deterioration of the catalyst, etc.
Therefore, the technology takes the performance of the oxygen storage material in the three-way catalytic coating as an indirect judgment index of the catalyst activity and the degradation degree thereof, and is limited in technology.
The invention aims to bypass the judgment of the performance of the oxygen storage material of the catalyst coating and directly measure and calculate the effect of removing HC and CO of the catalyst so as to accurately judge the catalytic activity of the catalyst.
Disclosure of Invention
The invention aims to provide a detection method of a gasoline car three-way catalytic converter based on oxygen concentration; all technical problems to be solved by the invention include:
(1) In the prior art, the inaccuracy of the catalytic performance of the three-way catalytic converter is judged through the performance of the oxygen storage material, so that errors are easy to generate, and particularly when the performance of the oxygen storage material and the performance of the catalytic converter are asynchronous.
(2) In the prior art, the change frequency of the detected oxygen concentration is realized by judging the switching frequency of the electric signal of the oxygen concentration, namely, a signal is generated once when the detected oxygen concentration reaches a certain limit, and the performance of the catalyst is judged according to the change times of the signal, but a specific concentration value is not obtained, so that the detection error is larger.
(3) In the prior art, the detection window is not clear, and different detection windows have larger influence on the detection effect, so that detection errors are caused.
(4) The NO compound consumes a part of CO and H in the catalytic process, and the concentration of the NO compound has a certain influence on the detection effect, so that errors are generated when different detection windows and the concentrations of the NO compound are different.
To achieve the above object, in one embodiment of the present invention, there is provided a method for detecting a three-way catalytic converter of a gasoline vehicle based on oxygen concentration, comprising the steps of:
step (1) running the vehicle to reach a detection state, performing primary detection according to a steady-state working condition method ASM, setting a data acquisition period t in the primary detection process, acquiring the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter, establishing a mapping relation between the detection time and the vehicle speed and the front oxygen concentration and the rear oxygen concentration, and obtaining a steady-state working condition detection curve;
step (2) setting the vehicle as a primary detection window under a steady-state working condition when the vehicle runs at a second constant speed to obtainTaking the concentration C of the front oxygen of the three-effect catalytic converter in the primary detection window f And post oxygen concentration C b Calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t, and judging whether the primary detection oxygen integral difference value in the primary detection window is larger than a primary detection threshold value or not;
if the primary detection oxygen integral difference value is larger than the primary detection threshold value, judging that the three-way catalytic converter is qualified for primary detection;
if the primary detection oxygen integral difference value is smaller than the primary detection threshold value, judging that the three-way catalytic converter is unqualified for primary detection;
if the three-way catalytic converter is judged to be unqualified in the primary detection, re-detection is carried out by using the NEDC working condition; the NEDC working condition rechecking method comprises the following steps:
the method comprises the steps of enabling a vehicle to run according to NEDC working conditions, setting a data acquisition period, obtaining the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of a three-way catalytic converter, establishing a mapping relation between the detection time and the vehicle speed and between the front oxygen concentration and the rear oxygen concentration, and obtaining a NEDC working condition detection curve;
setting the driving stage of the vehicle in 837 s-1113 s as a reinspection window under the NDEC working condition, and acquiring the front oxygen concentration C of the three-way catalytic converter in the reinspection window f And post oxygen concentration C b Calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t, and judging whether the oxygen integral difference value of the reinspection in the reinspection window is larger than a reinspection threshold value;
if the difference value of the oxygen re-detection integral is larger than the re-detection threshold value during re-detection, judging that the three-way catalytic converter is qualified;
if the difference value of the oxygen re-detection integral is smaller than the re-detection threshold value during re-detection, judging that the three-way catalytic converter is unqualified;
the method for calculating the oxygen integral difference value C comprises the following steps:
C＝C1-C2
wherein t is a data acquisition period, n is the number of data acquisition times in the detection window,
t is the total duration 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.
The detection state is preferably that the vehicle engine and the exhaust system are fully preheated after preheating for a preset time, and the three-way catalytic converter reaches the light-off temperature T80.
In the invention, 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 of the three-way catalytic converter; acquiring corresponding oxygen concentration signals through a front oxygen sensor and a rear oxygen sensor; and 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 acquired from the OBD system during detection.
The invention preferably arranges a wide-area front oxygen sensor at the inlet end of the three-way catalytic converter, and an extension pipe with the diameter of more than 500mm is additionally arranged at the outlet of the vehicle exhaust pipe during detection, the extension pipe is connected in a sealing way without leakage, and the wide-area rear oxygen sensor is arranged at a position close to the outlet of the vehicle exhaust pipe; acquiring corresponding oxygen concentration signals through a front oxygen sensor and a rear oxygen sensor; uploading signals of the front oxygen sensor to an OBD system, and directly acquiring data of the front oxygen sensor from the OBD system during detection; the data of the rear oxygen sensor is read from the field.
In the invention, preferably, the nitrogen-oxygen concentration Q at the inlet of the three-way catalytic converter or at the outlet of the engine is obtained in the detection process, and in the primary detection and the secondary detection processes, if the carbon-nitrogen ratio is lower than the interference threshold value in the detection process, the oxygen integral difference value is corrected: c=k+c1-C2;
the calculation method of the corrected integral value K comprises the following steps:
wherein,
alpha is an adjusting coefficient, and the value range is 0.98-1.05;
beta is the excess air factor;
t is the detected data acquisition period; namely, collecting the nitrogen-oxygen concentration parameter once every interval t;
Q p in order to take the detection time as an order, obtaining a nitrogen-oxygen concentration parameter at each detection time point;
n is the number of times the nitrogen-oxygen concentration parameter is detected within the total duration of the detection window.
Preferably, the total duration of the initial detection window is 70s, the interval from 20s to 90s under the working condition of ASM2540, and the second constant speed of initial detection is 40km/h; the total duration of the re-inspection window is 276s, and the speed of the re-inspection window is 50 km/h-120 km/h.
Preferably, the method for obtaining the data of the initial detection threshold value comprises the following steps:
(1) Taking a new automobile which passes the detection qualification, running the automobile to enable the new automobile to reach a detection state, continuing running according to the detection process of a steady-state working condition method, acquiring 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, and establishing a mapping relation between the detection time and the vehicle speed and the front oxygen concentration and the rear oxygen concentration to acquire a steady-state working condition detection curve;
(2) Setting the vehicle as a primary detection window when the vehicle runs at a second constant speed under a steady-state working condition, and obtaining the front oxygen concentration C of the three-way catalytic converter in the primary detection window f And post oxygen concentration C b And calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t and the total duration of the detection window, wherein the oxygen integral difference value is multiplied by 80 percent to obtain the initial detection threshold value.
Preferably, the method for obtaining the data of the recheck threshold value comprises the following steps:
(1) Taking a new automobile which passes the detection qualification, running the automobile to enable the new automobile to reach a detection state, enabling the automobile to run according to NEDC working conditions, setting a data acquisition period, acquiring the front oxygen concentration, the rear oxygen concentration, the automobile speed and the detection time of the three-way catalytic converter under the NEDC working conditions, establishing a mapping relation between the detection time and the automobile speed and the front oxygen concentration and the rear oxygen concentration, and obtaining a NEDC working condition detection curve;
setting the driving stage of the vehicle in 837 s-1113 s as a reinspection window under the NDEC working condition, and acquiring the front oxygen concentration C of the three-way catalytic converter in the reinspection window f And post oxygen concentration C b And (3) calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t, wherein the oxygen integral difference value is multiplied by 80% to obtain a recheck threshold value.
In summary, the invention has the following advantages:
1. the invention detects parameters such as front oxygen concentration, rear oxygen concentration and the like in the detection window of a specific time period in the running process of the vehicle through the steady-state working condition method ASM and the NEDC working condition detection method, obtains an oxygen integral value through detection for a plurality of times in a preset period, can more accurately obtain the front-rear change of the oxygen concentration in the detection window through time integral of the oxygen concentration, is equivalent to judging based on the total gas passing amount during detection, and is more accurate than the prior art that the number of times of switching of an instantaneous signal is used for replacing the data of the whole detection period.
2. According to the invention, whether the catalyst fails or not is judged without detecting the oxygen storage capacity of the oxygen storage material of the catalyst, and the total integral amount of the oxygen concentration before and after the three-way catalytic converter is directly detected, so that the method is more direct, and the error generated when the effectiveness of the oxygen storage material and the catalyst are inconsistent is avoided; namely, detection errors caused by inconsistent effective degrees of the oxygen storage material and the heavy metal catalyst are avoided;
3. the invention also considers the influence of NOx on the detection result, calculates the integral total amount of NOx in the detection period by adding the NOx sensor, and corrects the detection result so that the detection result is more accurate.
4. According to the characteristics of the vehicle running under the NEDC working condition and the steady-state working condition, the invention selects the specific primary detection window and the specific secondary detection window by considering the engine characteristics and the emission level of the vehicle when the vehicle runs under the NEDC working condition and the steady-state working condition, so that the invention has the advantages of representativeness, avoiding the influence of other interference stages and further improving the accuracy of the detection result. Meanwhile, the invention selects part of time periods or data of detection windows in the steady-state working condition method and the NEDC working condition method for detection, and also considers that the two working condition methods are common working condition methods in the prior art, thereby facilitating the familiarity of operators with operation flows.
5. The invention uses the circulation working condition of the whole vehicle, combines the catalytic reaction mechanism to define the evaluation window of the efficiency of the catalyst, records the front oxygen concentration and the rear oxygen concentration of the three-way catalytic converter in the period of the evaluation window, tests the speed and the detection time of the vehicle, and judges the performance of the catalyst according to the time integral difference value of the exhaust oxygen concentration measured by the front oxygen and the rear oxygen of the catalyst. The method for detecting and calculating the front and rear oxygen concentrations of the catalyst in the detection window of the vehicle can eliminate the influence of the oxygen storage capacity of the catalyst on the front and rear oxygen concentrations of the catalyst, so that the detected oxygen concentration change is directly related to the catalyst performance, and a more convenient, accurate and effective method is provided for detecting the reaction activity of the catalyst.
6. According to the invention, the ASM is subjected to primary detection by the steady-state working condition method, the NEDC working condition method is carried out again when the primary detection is unqualified, the primary detection can be rapidly screened, the re-detection process is more complex and accords with the actual running condition, so that the detection result is more reliable, the primary detection can be confirmed when the primary detection is failed, and the influence of the whole vehicle running problem on the detection result is discharged.
Drawings
FIG. 1 is a graph of CO/NOx ratio versus vehicle speed versus time for various time periods for a vehicle operating according to an NDEC operating regime in accordance with an embodiment of the present invention;
FIG. 2 is a graph showing vehicle speed versus time for a vehicle during steady state operation in accordance with one embodiment of the present invention;
FIG. 3 is a graph illustrating vehicle speed, front oxygen concentration, rear oxygen concentration, and time during operation of a vehicle under NDEC conditions in accordance with an embodiment of the present invention.
Detailed Description
The invention provides a detection method of a gasoline car three-way catalytic converter based on oxygen concentration, which comprises the following steps:
and (1) running the vehicle to a detection state, performing primary detection according to a steady-state working condition method ASM, setting a data acquisition period t in the primary detection process, acquiring the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter, establishing a mapping relation between the detection time and the vehicle speed and the front oxygen concentration and the rear oxygen concentration, and obtaining a steady-state working condition detection curve.
The detection principle of the invention:
the gasoline engine takes the mixed gas of gasoline and air as working medium, and realizes the output of the motor car through the thermal power circulation. From the engine intake inlet to the exhaust gas emission outlet, the following oxygen concentration decreasing equation can be established:
C O2_in ＝C O2_com +C O2_aft +C O2_out
wherein:
C O2_in indicating the total amount of intake oxygen of the engine;
C O2_com indicating the total amount of oxygen consumed in combustion in an engine cylinder;
C O2_aft indicating the total amount of oxygen consumed through the three-way catalytic converter after the cylinder is unconsumed and exhausted;
C O2_out represents the total amount of oxygen in the exhaust gas that is ultimately discharged to the atmosphere via the tailpipe of the automobile;
C O2_in -C O2_com i.e. the total amount of oxygen at the exhaust outlet of the engine; i.e. oxygen at the inlet end of the three-way catalytic converter.
The detection state of the vehicle is that the vehicle engine and the exhaust system are fully preheated after preheating for a preset time, and the three-way catalytic converter reaches the ignition temperature T80. In order to achieve the above detection state, it is generally necessary to preheat the vehicle, and when the vehicle is operated at the relevant speed of the initial detection window or the re-detection window after preheating, the engine air-fuel ratio can reach a preset value, and the bed temperature of the catalyst can also reach the temperature required by T80, so that the catalytic reaction can be performed normally.
The data acquisition period t of the invention is generally 3 s-5 s, and can be set according to specific requirements, the shorter the data acquisition period is, the more data are acquired, and the more oxygen integral difference value obtained after integral of the theoretically obtained parameters is more accurate.
The invention needs to acquire the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter, and an ECU system and an OBD system are arranged in the vehicle, and can read related data. In the existing vehicles, the front oxygen sensor is generally a wide-area front oxygen sensor, but the sensor arranged at the rear end of the three-way catalytic converter is probably a conventional and common sensor, so that the change frequency of the electric signal on the rear oxygen sensor is required to be detected in a plurality of detection methods in the prior art, because the rear oxygen sensor arranged on the existing three-way catalytic converter belongs to a jump-type narrow-area sensor; the signal can be sent only once when the detection condition is reached, and a specific concentration value cannot be obtained, but the cost is low.
The three-way catalytic converter is provided with a narrow-domain oxygen concentration sensor, and the signal of the narrow-domain oxygen concentration sensor can be uploaded to an OBD system, but the signal is the narrow-domain oxygen concentration sensor, so that whether the oxygen concentration exceeds the standard or not can be detected, and specific parameters of the oxygen concentration can not be detected. The embodiment of the invention is to enable the vehicle to use the detection method of the invention, an extension tube is additionally arranged on the exhaust tube, a wide-area type rear oxygen sensor is arranged in the extension tube, and a rear oxygen sensor is additionally arranged to obtain required data. Therefore, in order to acquire the data of the post-oxygen sensor, two modes are designed to acquire the post-oxygen concentration data.
The method comprises the following steps: the inlet end of the three-way catalytic converter is provided with a wide-range front oxygen sensor, and the outlet end of the three-way catalytic converter is provided with a wide-range rear oxygen sensor; acquiring corresponding oxygen concentration signals through a front oxygen sensor and a rear oxygen sensor; and 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 acquired from the OBD system during detection.
The second method is as follows: the inlet end of the three-way catalytic converter is provided with a wide-range front oxygen sensor, an extension pipe with the diameter of more than 500mm is additionally arranged at the outlet of the vehicle exhaust pipe during detection, the extension pipe is connected in a sealing way without leakage, and the wide-range rear oxygen sensor is arranged at a position close to the outlet of the vehicle exhaust pipe; acquiring corresponding oxygen concentration signals through a front oxygen sensor and a rear oxygen sensor; uploading signals of the front oxygen sensor to an OBD system, and directly acquiring data of the front oxygen sensor from the OBD system during detection; the data of the rear oxygen sensor is read from the field.
In the running process of the vehicle, a plurality of parameters can be directly read from the OBD system, so that a coordinate diagram of the vehicle speed, the front oxygen concentration and the rear oxygen concentration and the time can be respectively established by taking the time as an abscissa, and a mapping relation is formed.
And (2) setting the vehicle as a primary inspection window under a steady-state working condition when the vehicle runs at a second constant speed, wherein the ASM2540 stage of the steady-state working condition method corresponds to the vehicle running at the second constant speed. Obtaining the concentration C of the front oxygen of the three-way catalytic converter in the primary detection window f And post oxygen concentration C b And (3) calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t, and judging whether the primary detection oxygen integral difference value in the primary detection window is larger than a primary detection threshold value. The total duration of the initial detection window is 70s, and the second constant vehicle speed of initial detection is 40km/h from 20s to 90s under the working condition of ASM 2540.
The steady state working condition method and the NDEC working condition method are both methods for detecting the content of tail gas emitted by an automobile, and the detection process and the vehicle operation parameters are fixed. In the prior art, the steady-state working condition method and the NDEC working condition method can not directly detect the good and bad catalytic capability of the catalyst, but can acquire the front oxygen concentration and the rear oxygen concentration simultaneously when the two working condition methods are operated, so that the corresponding mapping relation of detection time, vehicle speed, front oxygen concentration and rear oxygen concentration is formed in a matching mode, and a steady-state working condition detection curve is obtained. Namely, the working condition method in the prior art can obtain curves such as detection time, vehicle speed, CO content, NO content and the like, and the invention can be used for increasing the data of the front oxygen concentration and the rear oxygen concentration on the basis.
Two constant vehicle speeds exist in the existing steady-state working condition method, wherein the first constant vehicle speed is 25km/h, and the second constant vehicle speed is 40km/h; the running time of the phase where the two constant vehicle speeds are is 90s. The NEDC working condition is characterized in that: the constant-speed running working condition has large duty ratio, and the acceleration is a constant value when the vehicle accelerates and decelerates. The NEDC working condition method is that the vehicle continuously accelerates and decelerates in the speed range of 0-120km/h, the vehicle is detected in the process, and the vehicle is gradually accelerated to 120km/h in the last period of detection. According to the invention, a second constant speed stage of a steady-state working condition method is selected according to the emission condition of the engine, the speed of the stage is proper, and the lower first constant speed is not suitable for the detection of the catalyst, so that the second constant speed stage is selected as a detection window. Similarly, the NDEC working condition method is gradually accelerated to 120km/h in the final stage, and the invention selects the driving stage of 837 s-1113 s as a rechecking window according to the emission conditions in different time periods, so that the catalytic performance of the catalyst can be well promoted, the average speed of the rest driving stages is lower, or the time of the acceleration and deceleration stages is more, and the detection of the catalytic performance serving as the catalyst has a certain error.
The reason why the inventors select a specific detection window in the primary and secondary detection processes is that: the inventor finds that the gasoline vehicle emission working condition method test comprises 4 working conditions of idling, acceleration, constant speed and deceleration, and the operation strategy of an engine and the catalytic effect of the emitted tail gas and a catalyst under each working condition have correlation, and the specific analysis is as follows:
(1) Constant speed operation phase of vehicle
The catalyst inlet oxygen concentration is the lowest and stable because the air-fuel ratio of the gasoline engine is maintained near the stoichiometric air-fuel ratio under the stable condition, and accurate and stable control can be obtained. For the stoichiometric air-fuel ratio, the incomplete combustion products and the excessive air meet the chemical reaction ratio, and the pollutant removal efficiency (i.e. conversion efficiency) η=100% of the catalyst is calculated, in this case, the inlet oxygen of the catalyst will be completely consumed, and the oxygen concentration detected by the oxygen sensor at the time of theoretical detection is 0. However, since the catalytic reaction efficiency is not 100%, the normal catalyst conversion efficiency η is generally 80% or more when the catalyst operating temperature reaches the light-off temperature T80, and thus the oxygen concentration detected by the rear oxygen sensor is about 0.2% or less under normal conditions during the constant-speed operation phase of the vehicle; the stage can be used for measuring the front oxygen concentration and the rear oxygen concentration, has good catalytic performance of the reaction catalyst, can completely utilize the catalytic efficiency of the catalyst, is not greatly influenced by combustion products and tail gas components, and can be used for detecting the efficiency of the catalyst.
(2) Stage of rapid decrease in vehicle speed
At the moment, the fuel supply quantity of the engine is reduced, the engine is dragged by the vehicle inertia, the oxygen content of the exhaust gas of the engine is rapidly increased, and the concentration value detected by the front oxygen sensor is rapidly increased to generate a peak value. The detection shows that the detection concentration of the front oxygen sensor and the rear oxygen sensor rises simultaneously and the peak appears, but the rear oxygen peak is lower than the front oxygen concentration, and the difference value of the oxygen concentration obtained by the front oxygen detection and the rear oxygen detection under the working condition is the largest. This is because the incomplete combustion products HC, CO are fully oxidized under oxygen-rich exhaust conditions, with the maximum consumption of excess oxygen in the exhaust. However, in this stage, the engine produces less incomplete combustion products than in the rising stage and the idling stage, and the exhaust gas has a high oxygen content, so that the catalytic performance of the catalyst may not be completely released. Therefore, the change in the front-rear oxygen concentration cannot fully react the catalytic ability of the catalyst, so that the detected catalytic efficiency of the catalyst is low, resulting in that the normal catalyst is regarded as a dead catalyst.
(3) Stage of increasing vehicle speed
In contrast to the deceleration process, the engine mixture is maintained at a stoichiometric air-fuel ratio or richer, and accordingly the front oxygen concentration is reduced, more oxygen is consumed inside the engine, and the oxygen content discharged from the engine is relatively reduced, so that the rear oxygen detection value is returned to 0 or lower.
(4) Engine idle stage
The stage is similar to a steady-state working condition, but the combustion quality is relatively poor, and corresponds to the theoretical air-fuel ratio, and the incomplete oxidation products in the combustion process and the oxygen concentration in the exhaust gas are higher than the constant-speed running stage and the vehicle speed rising stage of the vehicle and lower than the rapid vehicle speed falling stage. HC and CO in exhaust gas can be completely oxidized by a catalyst according to the theoretical air-fuel ratio of intake air, the concentration of post oxygen is 0, but the actual detection result is influenced due to the fact that the temperature of exhaust is low under idle working conditions and the concentration of incomplete oxidation products is too high, so that the method is not suitable for working conditions for detecting the catalytic effect of the catalyst in idle stage.
In summary, in combination with the four-stage engine exhaust emission parameters, the inventor finds that if the advantages and disadvantages of the three-way catalytic converter or the catalytic efficiency are judged by the front-rear oxygen concentration difference after experiments, the vehicle engine is required to emit proper incomplete combustion matters and oxygen in the running process, so that the front-rear oxygen concentration can truly react with the catalytic performance without being influenced by excessive oxygen enrichment or incomplete combustion matters. Therefore, the constant speed operation phase of the vehicle should be selected as the optimal detection window, followed by the acceleration phase of the vehicle, the deceleration phase should be avoided as much as possible, and the idle phase should not be allowed to be selected.
In the prior art, when detection is performed, the detected working conditions, namely the running speed and running state of the vehicle are not limited. When the vehicle is at different speeds, the emissions are different, and the emissions are also different greatly when the vehicle is at acceleration and deceleration stage, idling and engine reverse towing. From common knowledge, the time of the vehicle running at a constant speed is longest, and the running mileage is greatest, so that the working condition of the three-way catalytic converter during the detection of the vehicle running at the constant speed is more in line with the actual condition. Meanwhile, the content of gas exhausted by the engine is relatively stable in the steady-state uniform-speed running process of the vehicle, and the detection is easier and more accurate at the moment. Therefore, the invention selects to detect when running under the steady-state working condition, removes the data under the unstable working condition, reduces the detection error as much as possible, and simultaneously obtains the detection efficiency as fast as possible.
After the primary detection oxygen integral difference value is obtained, if the primary detection oxygen integral difference value is larger than a primary detection threshold value, judging that the three-way catalytic converter is qualified for primary detection; if the primary detection oxygen integral difference is smaller than the primary detection threshold, the integral total change of the oxygen concentration is considered to be smaller in the total duration of the detection window, which indicates that the oxygen concentration consumption is small, and thus the tail gas of the whole vehicle can be considered to be unqualified after being treated, in this case, the ASM is a simple working condition due to the steady-state working condition method, and the unqualified condition of the ASM is likely to be a problem of the working state of the whole vehicle of the engine or a problem of the catalyst, so when the primary detection is unqualified, a more accurate detection method is needed to judge whether the ASM is unqualified due to the problem of the whole vehicle or the problem of the catalyst.
The steady-state working condition method is a good state because the vehicle runs at a constant speed, and the vehicle is not always at the constant speed in the high-speed running process in practice, so that the running condition of a detection window of the NDEC working condition method is more prone to be caused, the obtained data under the working condition is more accurate, and meanwhile, the influence of other problems in a single state and the whole vehicle running on the result can be avoided. Therefore, when the primary inspection is unqualified, the NDEC working condition method is needed to be used for rechecking, the total time length of the rechecking window is 276s, and the speed of the rechecking window is 50 km/h-120 km/h. This enables further determination of whether the three-way catalytic converter is effective. If the primary inspection is qualified, the finished automobile can be directly qualified when the finished automobile runs, and the NDEC working condition method can be omitted.
If the three-way catalytic converter is judged to be unqualified in the primary detection, re-detection is carried out by using the NEDC working condition; the NEDC working condition rechecking method comprises the following steps:
the method comprises the steps of enabling a vehicle to run according to NEDC working conditions, setting a data acquisition period, obtaining the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of a three-way catalytic converter, establishing a mapping relation between the detection time and the vehicle speed and between the front oxygen concentration and the rear oxygen concentration, and obtaining a NEDC working condition detection curve;
setting the driving stage of the vehicle in 837 s-1113 s as a reinspection window under the NDEC working condition, and acquiring the front oxygen concentration C of the three-way catalytic converter in the reinspection window f And post oxygen concentration C b Calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t, and judging whether the oxygen integral difference value of the reinspection in the reinspection window is larger than a reinspection threshold value;
if the difference value of the oxygen re-detection integral is larger than the re-detection threshold value during re-detection, judging that the three-way catalytic converter is qualified;
and if the difference value of the oxygen re-detection integral is smaller than the re-detection threshold value during re-detection, judging that the three-way catalytic converter is unqualified.
The calculation method of the oxygen integral difference C comprises the following steps:
C＝C1-C2
wherein t is a data acquisition period, n is the number of data acquisition times in the detection window,
t is the total duration 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.
The primary detection threshold and the secondary detection threshold are preset values, the values are designed according to experience and national requirements, and the data acquisition method of the primary detection threshold comprises the following steps:
(1) Taking a new automobile which passes the detection qualification, running the automobile to enable the new automobile to reach a detection state, continuing running according to the detection process of a steady-state working condition method, acquiring 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, and establishing a mapping relation between the detection time and the vehicle speed and the front oxygen concentration and the rear oxygen concentration to acquire a steady-state working condition detection curve;
(2) Setting the vehicle as a primary detection window when the vehicle runs at a second constant speed under a steady-state working condition, and obtaining the front oxygen concentration C of the three-way catalytic converter in the primary detection window f And post oxygen concentration C b And calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t and the total duration of the detection window, wherein the oxygen integral difference value is multiplied by 80 percent to obtain the initial detection threshold value.
Similarly, the data obtaining method of the recheck threshold value includes the following steps:
(1) Taking a new automobile which passes the detection qualification, running the automobile to enable the new automobile to reach a detection state, enabling the automobile to run according to NEDC working conditions, setting a data acquisition period, acquiring the front oxygen concentration, the rear oxygen concentration, the automobile speed and the detection time of the three-way catalytic converter under the NEDC working conditions, establishing a mapping relation between the detection time and the automobile speed and the front oxygen concentration and the rear oxygen concentration, and obtaining a NEDC working condition detection curve;
setting the driving stage of the vehicle in 837 s-1113 s as a reinspection window under the NDEC working condition, and acquiring the front oxygen concentration C of the three-way catalytic converter in the reinspection window f And post oxygen concentration C b And (3) calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t, wherein the oxygen integral difference value is multiplied by 80% to obtain a recheck threshold value.
When the invention is used for detection, firstly, the full preheating is carried out after more than 10 minutes of whole vehicle working condition circulation; the speed of the whole vehicle and the exhaust temperature are high under two working conditions; the fluctuation of the air-fuel ratio is small in the period of the circulation window, and the exhaust system meets the efficient oxidation-reduction condition; the acceleration and deceleration conditions present in the cycle cause fluctuations in exhaust oxygen content, but since the cycle time 10 mm has exceeded 300s before detection; the oxygen storage and release characteristics of the catalyst cannot influence the overall performance evaluation of the catalyst; the speed of the whole vehicle is high, the airspeed is large, and the detection of the whole conversion efficiency of the catalyst is facilitated.
The catalytic reaction directly consumes oxygen, resulting in a linear decrease in the peak value of the post-oxygen; the oxygen storage capacity of the catalyst can lead the peak of the oxygen concentration of the exhaust outlet to be gentle, and the peak of the rear oxygen sensor is reduced to a certain extent. The difference is that the oxygen storage capacity only buffers the outlet release of oxygen and does not reduce the total amount of oxygen emitted.
At present, the loading and discharging ratio of the gasoline engine is smaller than or equal to 1, the oxygen storage capacity of a fresh catalyst sample is generally not larger than 1000mg/L, and the oxygen storage time is about 9S under the condition of 40kg/h of air inlet flow. The total duration of the detection window provided by the invention is far longer than the oxygen storage and release time by 9s no matter the primary detection window or the secondary detection window, the influence of the oxygen storage and release capacity can be eliminated in the window period, and the pollutant conversion efficiency (namely the catalytic activity) is directly judged according to the front and rear oxygen concentration detection values.
The inventor finds that the content of the exhaust gas of the engine under different working conditions is very different. According to the invention, whether the catalyst works normally is judged by the oxygen integral value, and HC and CO reducing agents are consumed by NOx reaction, so that oxygen required to be consumed is reduced, and the discharged oxygen is increased. Therefore, the ideal test working condition of the invention is that NOx emission is the lowest, HC and CO emission is the highest, and the working condition is relatively continuous and stable.
Referring to FIG. 1, FIG. 1 is a graph of the CO/NOx ratio of a vehicle during various periods of time when the vehicle is operating according to the NDEC operating regime. It can be seen that in the recheck window selected in the invention, the ratio of CO/NOx is the lowest, which indicates that the emission values of HC, CO and NOx at the engine outlet are in the same order of magnitude, and the influence of NOx on the oxidation reaction should be considered; meanwhile, as can be seen from the figure 1, the CO/NOx ratio of the re-detection window is the most stable, so that the stable working condition is maintained, and the detection result is more accurate; therefore, in order to eliminate the influence of NOx at the time of the re-inspection window, the present invention introduces a corrected integrated value.
The invention introduces a method for correcting integral value:
acquiring nitrogen-oxygen concentration Q at the inlet of a three-way catalytic converter or at the outlet of an engine in the detection process, and correcting an oxygen integral difference value when the carbon-nitrogen ratio is lower than an interference threshold value in the detection process of primary detection and secondary detection: c=k+c1-C2;
the calculation method of the corrected integral value K comprises the following steps:
the calculation method of the corrected integrated value K is:
wherein,
alpha is an adjusting coefficient, and the value range is 0.98-1.05;
beta is the excess air factor;
t is the detected data acquisition period; namely, collecting the nitrogen-oxygen concentration parameter once every interval t;
Q p in order to take the detection time as an order, obtaining a nitrogen-oxygen concentration parameter at each detection time point;
n is the number of times the nitrogen-oxygen concentration parameter is detected within the total duration of the detection window.
The lower the interference threshold value of the invention is, the lower the ratio of CO to NOx is, and the higher the content of NOx is; the general interference threshold is set to 20.
Although specific embodiments of the invention have been described in detail with reference to the accompanying drawings, it should not be construed as limiting the scope of protection of the present patent. Various modifications and variations which may be made by those skilled in the art without the creative effort are within the scope of the patent described in the claims.
Claims (8)
1. The detection method of the gasoline vehicle three-way catalytic converter based on the oxygen concentration is characterized by comprising the following steps of:
step (1) running the vehicle to reach a detection state, performing primary detection according to a steady-state working condition method ASM, setting a data acquisition period t in the primary detection process, acquiring the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of the three-way catalytic converter, establishing a mapping relation between the detection time and the vehicle speed and the front oxygen concentration and the rear oxygen concentration, and obtaining a steady-state working condition detection curve;
step (2) setting the vehicle as a primary detection window when the vehicle runs at a second constant speed under a steady-state working condition, and obtaining the front oxygen concentration C of the three-way catalytic converter in the primary detection window f And post oxygen concentration C b Calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t, and judging whether the primary detection oxygen integral difference value in the primary detection window is larger than a primary detection threshold value or not;
if the primary detection oxygen integral difference value is larger than the primary detection threshold value, judging that the three-way catalytic converter is qualified for primary detection;
if the primary detection oxygen integral difference value is smaller than the primary detection threshold value, judging that the three-way catalytic converter is unqualified for primary detection;
if the three-way catalytic converter is judged to be unqualified in the primary detection, re-detection is carried out by using the NEDC working condition; the NEDC working condition rechecking method comprises the following steps:
the method comprises the steps of enabling a vehicle to run according to NEDC working conditions, setting a data acquisition period, obtaining the front oxygen concentration, the rear oxygen concentration, the vehicle speed and the detection time of a three-way catalytic converter, establishing a mapping relation between the detection time and the vehicle speed and between the front oxygen concentration and the rear oxygen concentration, and obtaining a NEDC working condition detection curve;
setting the driving stage of the vehicle in 837 s-1113 s as a reinspection window under the NDEC working condition, and acquiring the front oxygen concentration C of the three-way catalytic converter in the reinspection window f And post oxygen concentration C b Calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t, and judging whether the oxygen integral difference value of the reinspection in the reinspection window is larger than a reinspection threshold value;
if the difference value of the oxygen re-detection integral is larger than the re-detection threshold value during re-detection, judging that the three-way catalytic converter is qualified;
if the difference value of the oxygen re-detection integral is smaller than the re-detection threshold value during re-detection, judging that the three-way catalytic converter is unqualified;
the method for calculating the oxygen integral difference value C comprises the following steps:
C＝C1-C2
wherein t is a data acquisition period, n is the number of data acquisition times in the detection window,
t is the total duration 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.
2. The method for detecting the three-way catalytic converter of the gasoline car based on the oxygen concentration as set forth in claim 1, wherein: the detection state is that the vehicle engine and the exhaust system are fully preheated after preheating for a preset time, and the three-way catalytic converter reaches a light-off temperature T80.
3. The method for detecting the three-way catalytic converter of the gasoline car based on the oxygen concentration as set forth in claim 1, wherein: the inlet end of the three-way catalytic converter is provided with a wide-domain front oxygen sensor, and the outlet end of the three-way catalytic converter is provided with a wide-domain rear oxygen sensor; acquiring corresponding oxygen concentration signals through a front oxygen sensor and a rear oxygen sensor; and 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 acquired from the OBD system during detection.
4. The method for detecting the three-way catalytic converter of the gasoline car based on the oxygen concentration as set forth in claim 1, wherein: the inlet end of the three-way catalytic converter is provided with a wide-range front oxygen sensor, an extension pipe with the diameter of more than 500mm is additionally arranged at the outlet of the vehicle exhaust pipe during detection, the extension pipe is connected in a sealing way without leakage, and the wide-range rear oxygen sensor is arranged at a position close to the outlet of the vehicle exhaust pipe; acquiring corresponding oxygen concentration signals through a front oxygen sensor and a rear oxygen sensor; uploading signals of the front oxygen sensor to an OBD system, and directly acquiring data of the front oxygen sensor from the OBD system during detection; the data of the rear oxygen sensor is read from the field.
5. The method for detecting the three-way catalytic converter of the gasoline car based on the oxygen concentration as set forth in claim 1, wherein: acquiring nitrogen-oxygen concentration Q at the inlet of a three-way catalytic converter or at the outlet of an engine in the detection process, and correcting an oxygen integral difference value when the carbon-nitrogen ratio is lower than an interference threshold value in the detection process of primary detection and secondary detection: c=k+c1-C2;
the calculation method of the corrected integral value K comprises the following steps:
wherein,
alpha is an adjusting coefficient, and the value range is 0.98-1.05;
beta is the excess air factor;
t is the detected data acquisition period; namely, collecting the nitrogen-oxygen concentration parameter once every interval t;
Q p in order to take the detection time as an order, obtaining a nitrogen-oxygen concentration parameter at each detection time point;
n is the number of times the nitrogen-oxygen concentration parameter is detected within the total duration of the detection window.
6. The method for detecting the three-way catalytic converter of the gasoline car based on the oxygen concentration as set forth in claim 1, wherein: the total duration of the initial detection window is 70s, the second constant vehicle speed of initial detection is 40km/h from the 20 th section to the 90 th section under the working condition of ASM 2540; the total duration of the re-inspection window is 276s, and the speed of the re-inspection window is 50 km/h-120 km/h.
7. The method for detecting the three-way catalytic converter of the gasoline car based on the oxygen concentration as set forth in claim 1, wherein: the data acquisition method of the preliminary detection threshold value comprises the following steps:
(1) Taking a new automobile which passes the detection qualification, running the automobile to enable the new automobile to reach a detection state, continuing running according to the detection process of a steady-state working condition method, acquiring 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, and establishing a mapping relation between the detection time and the vehicle speed and the front oxygen concentration and the rear oxygen concentration to acquire a steady-state working condition detection curve;
(2) Setting the vehicle as a primary detection window when the vehicle runs at a second constant speed under a steady-state working condition, and obtaining the front oxygen concentration C of the three-way catalytic converter in the primary detection window f And post oxygen concentration C b And calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t and the total duration of the detection window, wherein the oxygen integral difference value is multiplied by 80 percent to obtain the initial detection threshold value.
8. The method for detecting the three-way catalytic converter of the gasoline car based on the oxygen concentration as set forth in claim 1, wherein: the data obtaining method of the rechecking threshold value comprises the following steps:
(1) Taking a new automobile which passes the detection qualification, running the automobile to enable the new automobile to reach a detection state, enabling the automobile to run according to NEDC working conditions, setting a data acquisition period, acquiring the front oxygen concentration, the rear oxygen concentration, the automobile speed and the detection time of the three-way catalytic converter under the NEDC working conditions, establishing a mapping relation between the detection time and the automobile speed and the front oxygen concentration and the rear oxygen concentration, and obtaining a NEDC working condition detection curve;
setting the driving stage of the vehicle in 837 s-1113 s as a reinspection window under the NDEC working condition, and acquiring the front oxygen concentration C of the three-way catalytic converter in the reinspection window f And post oxygen concentration C b And (3) calculating an oxygen integral difference value of the front oxygen concentration and the rear oxygen concentration by combining the data acquisition period t, wherein the oxygen integral difference value is multiplied by 80% to obtain a recheck threshold value.
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