Rear oxygen sensor fault diagnosis method, computer readable storage medium and controller
The method improves rear oxygen sensor fault diagnosis by identifying suspected faults through exhaust flow integral and voltage monitoring, using passive conditions to reduce false alarms and emissions, thus enhancing diagnostic efficiency and accuracy.
Patent Information
- Application Number
- CN202411305641.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-19
- Publication Date
- 2024-12-10
AI Technical Summary
Current methods for diagnosing rear oxygen sensor faults suffer from low diagnostic efficiency and high false alarm rates, particularly due to the reliance on direct voltage monitoring and active leaning conditions that increase NOx emissions and risk non-compliance with emission regulations.
A method that first identifies suspected faults by monitoring exhaust flow integral and rear oxygen sensor voltage, then performs targeted diagnostics under passive conditions like lean reduction or fuel cut-off to reduce false alarms and emissions, using specific threshold comparisons and self-learning strategies to improve accuracy.
Enhances diagnostic efficiency and accuracy while avoiding increased NOx emissions, maintaining a good driving experience, and ensuring compliance with emission regulations.
Smart Images
Figure CN119102847A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of sensor fault diagnosis, and in particular relates to a rear oxygen sensor fault diagnosis method, a computer-readable storage medium and a controller. Background Art
[0002] The rear oxygen sensor is usually installed after the main catalyst in the exhaust system. The signal of the rear oxygen sensor is used to monitor the catalyst failure. The signal feedback of the rear oxygen sensor can also be used to further correct the deviation of the closed-loop regulation of the front oxygen sensor to ensure that the concentration of the mixed gas is always within the optimal conversion window of the catalyst for pollutants in the exhaust. The concentration of the mixed gas is characterized by the excess air coefficient. The excess air coefficient λ is the ratio of the actual air mass supplied by the combustion of 1 kg of fuel to the theoretical air mass required for the complete combustion of 1 kg of fuel. When λ<1, the mixed gas is a rich mixed gas, and when λ>1, the mixed gas is a lean mixed gas.
[0003] The voltage of the rear oxygen sensor will change with the concentration of the mixed gas. Currently, the voltage of the rear oxygen sensor is monitored to diagnose whether the rear oxygen sensor is faulty, but this has the defects of low diagnostic efficiency and high false alarm rate. Summary of the invention
[0004] The prior art directly performs a diagnosis of a certain fault type, and only performs a diagnosis of another fault type after the diagnosis of one fault type is completed, resulting in low diagnostic efficiency.
[0005] In order to improve the diagnostic efficiency, the present invention provides a rear oxygen sensor fault diagnosis method, comprising the following steps:
[0006] When the exhaust flow integral exceeds the first integral threshold, judging whether there is a suspected fault and the type of the suspected fault according to the voltage value of the rear oxygen sensor currently collected;
[0007] When there is a suspected fault, the corresponding fault diagnosis strategy is used to perform fault diagnosis according to the suspected fault type.
[0008] The present invention first diagnoses the suspected fault type, and then performs targeted diagnosis based on the suspected fault type, thereby eliminating unnecessary fault diagnosis and improving diagnostic efficiency. The suspected fault is diagnosed when the exhaust flow integral exceeds a first integral threshold. Exceeding the first integral threshold means that the basic diagnostic conditions are met and the mixed gas has continued to act on the rear oxygen sensor for a certain period of time under certain working conditions, thereby ensuring the reliability of the suspected fault diagnosis results.
[0009] Furthermore, the steps of determining the suspected fault type include:
[0010] The minimum voltage value of the rear oxygen sensor is compared with the lean edge threshold value. If the current minimum voltage value is greater than or equal to the lean edge threshold value, it is diagnosed as a suspected continuous high voltage fault.
[0011] On the excess air coefficient-rear oxygen sensor voltage curve, with the voltage when the excess air coefficient λ is equal to 1 as the boundary, the lean edge threshold represents the maximum voltage value of the lean mixture, and the rich edge threshold represents the minimum voltage value of the rich mixture.
[0012] The minimum voltage value of the rear oxygen sensor is collected in real time and is the minimum value within the sampling period; the lower the mixture concentration, the smaller the voltage value of the rear oxygen sensor. If after a certain operating condition, the minimum voltage value is still greater than or equal to the lean edge threshold, it may be caused by the insensitivity of the rear oxygen sensor to the lean mixture. Therefore, it is diagnosed as a suspected continuous high voltage fault.
[0013] Furthermore, a fault diagnosis strategy for a continuously high voltage is included, and the fault diagnosis strategy for a continuously high voltage includes the following steps: under a passive lean reduction condition or a passive fuel cut-off condition, collecting the minimum voltage value of the rear oxygen sensor, and determining whether the current minimum voltage value is less than a lean edge threshold; if so, diagnosing that there is no fault; if not, diagnosing that there is a continuously high voltage fault.
[0014] The prior art performs continuous high voltage fault diagnosis under active leaning conditions. Although active leaning conditions can reduce the concentration of the mixed gas, they also cause a significant increase in NOx emissions, which is not conducive to environmental protection and faces the risk of not complying with emission regulations. The present invention performs continuous high voltage fault diagnosis under passive leaning conditions or passive fuel cut-off conditions. Passive leaning conditions and passive fuel cut-off conditions refer to performing continuous high voltage fault diagnosis without actively performing leaning and fuel cut-off, thereby avoiding additional increase in NOx emissions.
[0015] Furthermore, after the duration of the passive leaning condition reaches the first time threshold, the minimum voltage value of the rear oxygen sensor is collected. It is more accurate to collect the minimum voltage value after the passive leaning condition lasts for a certain period of time.
[0016] Furthermore, the passive de-leaning condition includes at least one of a particulate matter trap active regeneration condition and a catalyst heating condition.
[0017] Furthermore, under the active regeneration condition of the particulate matter trap, the larger the target excess air coefficient λ is, the smaller the first time threshold is.
[0018] The larger the target excess air coefficient λ is, the greater the lean range is. Accordingly, by reducing the first time threshold, the required judgment time can be reduced, thereby improving the diagnostic efficiency.
[0019] Furthermore, under the passive fuel cut-off condition, the minimum voltage value of the rear oxygen sensor is collected after one of the following conditions is met: the duration of the passive fuel cut-off condition reaches the second time threshold, or the exhaust flow integral after fuel cut-off reaches the second integral threshold, which is conducive to more accurate collection of the minimum voltage value.
[0020] Furthermore, if the engine running time exceeds the third time threshold and there is no passive lean reduction condition and passive fuel cut-off condition, a suspected voltage continuously high fault diagnosis is performed under the active fuel cut-off condition.
[0021] Under the fuel cut-off condition, the engine takes in air, but the injector does not spray fuel and the engine does not burn, so there is no additional increase in NOx emissions, and the concentration of the mixed gas is naturally reduced. Before the passive de-leaning condition and passive fuel cut-off condition are reached, the system switches to the active fuel cut-off condition to avoid frequent active fuel cut-offs that affect the driving experience.
[0022] Furthermore, under the active fuel cut-off condition, after the duration of the active fuel cut-off condition reaches the fourth time threshold, the minimum voltage value of the rear oxygen sensor is collected, and it is determined whether the current minimum voltage value is less than the lean edge threshold. If so, it is diagnosed as no fault, if not, it is diagnosed as a continuously high voltage fault.
[0023] Furthermore, the steps of determining the suspected fault type include:
[0024] The maximum voltage of the rear oxygen sensor is compared with the rich edge threshold. If the current maximum voltage is less than or equal to the rich edge threshold, it is diagnosed as a suspected voltage continuously low fault.
[0025] On the excess air coefficient-rear oxygen sensor voltage curve, with the voltage when the excess air coefficient λ is equal to 1 as the boundary, the lean edge threshold represents the maximum voltage value of the lean mixture, and the rich edge threshold represents the minimum voltage value of the rich mixture.
[0026] The minimum voltage value of the rear oxygen sensor is collected in real time and is the minimum value within the sampling period; the higher the concentration of the mixture, the higher the voltage value of the rear oxygen sensor. If after a certain operating condition, the maximum voltage is still less than or equal to the lean edge threshold, it may be caused by the insensitivity of the rear oxygen sensor to the rich mixture. Therefore, it is diagnosed as a suspected continuous low voltage fault.
[0027] Furthermore, a voltage continuously low fault diagnosis strategy is included, and the voltage continuously low fault diagnosis strategy includes the following steps:
[0028] Under active enrichment conditions, the maximum voltage of the rear oxygen sensor is collected, and it is determined whether the current maximum voltage is greater than the rich edge threshold. If so, it is diagnosed as no fault. If not, wait for the target excess air coefficient to be self-learned and updated, and then diagnose again based on the maximum voltage of the rear oxygen sensor under active enrichment conditions.
[0029] A quick judgment is made through the first active enrichment condition to improve the diagnostic efficiency; after the target excess air coefficient is updated through self-learning, a judgment is made again through the active enrichment condition to eliminate the continuous low voltage caused by incomplete self-learning, thereby improving the accuracy of the diagnostic results.
[0030] Furthermore, the active enrichment condition includes:
[0031] If the current operating condition is not the active regeneration condition of the particulate matter trap, the mixture is enriched according to the first corrected excess air coefficient λ1;
[0032] If the current operating condition is the active regeneration condition of the particulate matter trap, the mixture is enriched according to the second corrected excess air coefficient λ2;
[0033] The second corrected excess air coefficient λ2 is smaller than the first corrected excess air coefficient λ1, and both the second corrected excess air coefficient λ2 and the first corrected excess air coefficient λ1 are reduced on the basis of a target excess air coefficient of an active regeneration condition of the particulate matter trap.
[0034] The present invention takes into account that the active regeneration condition of the particle trap will cause the concentration of the mixed gas to decrease. Therefore, when the current operating condition is not the active regeneration condition of the particle trap, a smaller excess air coefficient is used for active enrichment, which can compensate for the decrease in the concentration of the mixed gas caused by the active regeneration condition of the particle trap, eliminate the low voltage caused by the active regeneration condition of the particle trap, and make the diagnostic result more accurate.
[0035] Furthermore, after the duration of the active enrichment condition reaches a fourth time threshold, the maximum voltage of the rear oxygen sensor is collected, which is conducive to more accurate collection of the maximum voltage.
[0036] Furthermore, before entering the active enrichment condition for the first time, when the exhaust flow integral reaches the second integral threshold, the maximum voltage of the rear oxygen sensor is collected, and it is determined whether the current maximum voltage is greater than the rich edge threshold. If so, it is diagnosed as no fault; if not, the active enrichment condition is entered.
[0037] Before making a judgment through the active enrichment condition, judging again through the exhaust flow integral can avoid frequent entering the active enrichment condition and affecting the driving experience.
[0038] The present invention also provides a computer-readable storage medium, wherein at least one instruction is stored in the storage medium, and the instruction is loaded and executed by a processor to implement the above-mentioned rear oxygen sensor fault diagnosis method.
[0039] The present invention also provides a controller, including a suspected fault diagnosis unit, a voltage continuously high fault diagnosis unit and a voltage continuously low fault diagnosis unit;
[0040] The suspected fault diagnosis unit is used to determine whether there is a suspected fault and the suspected fault type according to the voltage value of the rear oxygen sensor currently collected when the exhaust flow integral exceeds the first integral threshold, and when a suspected fault exists, start the corresponding fault diagnosis unit according to the suspected fault type to perform fault diagnosis;
[0041] The voltage continuously high fault diagnosis unit is used to diagnose the voltage continuously high fault according to the minimum voltage value of the rear oxygen sensor under the passive lean reduction working condition;
[0042] The voltage continuously low fault diagnosis unit is used to diagnose the voltage continuously low fault according to the maximum voltage of the rear oxygen sensor under the active enrichment condition.
[0043] The present invention can improve the diagnostic efficiency and diagnostic accuracy, and does not generate NOx emissions during the fault diagnosis process of continuously high voltage, which is beneficial to environmental protection; the present invention can also reduce interference with the normal driving process and maintain a good driving experience. BRIEF DESCRIPTION OF THE DRAWINGS
[0044] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0045] Figure 1 This is a schematic diagram of the installation location of the rear oxygen sensor;
[0046] Figure 2 It is the excess air coefficient-rear oxygen sensor voltage curve;
[0047] Figure 3 is a flow chart of a method for diagnosing a rear oxygen sensor fault in this specific implementation manner;
[0048] Figure 4 Is NO under active dilution conditions x Emission curve diagram;
[0049] Figure 5 This is a false alarm diagram of voltage being continuously high after active thinning;
[0050] Figure 6 is a flow chart of the voltage continuously high fault diagnosis strategy in Example 2;
[0051] Figure 7 is a flow chart of the voltage continuously high fault diagnosis strategy in Example 3;
[0052] Figure 8 is a flow chart of a fault diagnosis strategy for a voltage that is continuously too high in Example 4;
[0053] Fig. 9 This is a false alarm diagram of a continuous low rear oxygen voltage fault caused by active regeneration conditions;
[0054] Fig.10 This is a false alarm diagram of the failure of self-learning to update the rear oxygen voltage to be continuously low;
[0055] Fig.11 It is a flow chart of the fault diagnosis strategy for continuous low voltage in Example 6. DETAILED DESCRIPTION
[0056] refer to Figure 1 As shown, the rear oxygen sensor 1 is generally installed after the main catalyst 2 in the exhaust system. The functions of the rear oxygen sensor include: 1) realizing fault monitoring of the catalyst 2 through the signal of the rear oxygen sensor 1; 2) further correcting the deviation of the closed-loop regulation of the front oxygen sensor 3 through the signal feedback of the rear oxygen sensor 1, ensuring that the concentration of the mixed gas is always within the optimal conversion window of the catalyst for pollutants in the exhaust gas.
[0057] The concentration of the mixture is characterized by the excess air coefficient, which is the ratio of the actual air mass supplied to burn 1 kg of fuel to the theoretical air mass required to completely burn 1 kg of fuel. When λ < 1, the mixture is a rich mixture, and when λ > 1, the mixture is a lean mixture.
[0058] refer to Figure 2 As shown, on the excess air coefficient-rear oxygen sensor voltage curve, the voltage when the excess air coefficient λ is equal to 1 is used as the boundary, and the lean edge threshold represents the maximum voltage value of the lean mixture, for example, Figure 2 The medium lean threshold is 0.2V; the rich threshold represents the minimum voltage value of the rich mixture, for example, Figure 2 The mid-rich edge threshold is 0.8V.
[0059] The voltage of the rear oxygen sensor will change with the concentration of the mixed gas. Currently, the voltage of the rear oxygen sensor is monitored to diagnose whether the rear oxygen sensor is faulty, but this has the defects of low diagnostic efficiency and high false alarm rate.
[0060] In order to improve the diagnostic efficiency, refer to Figure 3 As shown, the present invention provides a method for diagnosing a rear oxygen sensor fault, comprising the following steps:
[0061] When the exhaust flow integral exceeds the first integral threshold M1, judging whether there is a suspected fault and the type of the suspected fault according to the voltage value of the rear oxygen sensor currently collected;
[0062] When there is a suspected fault, the corresponding fault diagnosis strategy is used to perform fault diagnosis according to the suspected fault type.
[0063] The present invention first diagnoses the suspected fault type, and then performs targeted diagnosis based on the suspected fault type, thereby eliminating unnecessary fault diagnosis and improving diagnostic efficiency. The suspected fault is diagnosed when the exhaust flow integral exceeds a first integral threshold. Exceeding the first integral threshold means that the basic diagnostic conditions are met and the mixed gas has continued to act on the rear oxygen sensor for a certain period of time under certain working conditions, thereby ensuring the reliability of the suspected fault diagnosis results.
[0064] Basic conditions for diagnosis include:
[0065] 1) Preheat the rear oxygen sensor: Confirm that the rear oxygen sensor has reached the operating temperature (usually needs to be heated to above 400°C), which is the basis for its function.
[0066] 2) Exhaust system preheating status: The exhaust system experiences sufficient exhaust flow to complete sufficient preheating to ensure the reliability of the measurement results.
[0067] 3) Appropriate load conditions: Diagnosis should be performed within a specific load range, when the engine operating conditions are stable, facilitating accurate judgment.
[0068] The first integral threshold M1 is obtained by calibration. For example, a certain exhaust flow integral is added to the exhaust flow integral corresponding to the basic diagnosis condition to serve as the first integral threshold M1.
[0069] Example 1
[0070] This embodiment describes how to determine the type of suspected fault.
[0071] refer to Figure 3 As shown, the steps of determining the suspected fault type in this example include:
[0072] The minimum voltage value of the rear oxygen sensor U min and the rare edge threshold U 稀 Comparison is performed, and if the current minimum voltage value is greater than or equal to the thin edge threshold, a suspected voltage continuously high fault is diagnosed;
[0073] The maximum voltage of the rear oxygen sensor U max and thick edge threshold U 浓 After comparison, if the current maximum voltage is less than or equal to the rich edge threshold, it is diagnosed as a suspected voltage continuously low fault.
[0074] The minimum voltage and maximum voltage of the rear oxygen sensor are collected in real time and are the minimum and maximum values within the sampling period.
[0075] The lower the mixture concentration, the smaller the voltage value of the rear oxygen sensor. If after a certain operating condition, the minimum voltage is still greater than or equal to the lean edge threshold, it may be caused by the insensitivity of the rear oxygen sensor to the lean mixture. Therefore, it is diagnosed as a suspected continuous high voltage fault.
[0076] The higher the mixture concentration, the higher the voltage value of the rear oxygen sensor. If after a certain operating condition, the maximum voltage is still less than or equal to the lean edge threshold, it may be caused by the insensitivity of the rear oxygen sensor to the rich mixture. Therefore, it is diagnosed as a suspected continuous low voltage fault.
[0077] The diagnosis of a suspected continuously high voltage fault and a suspected continuously low voltage fault may be performed simultaneously or successively.
[0078] There are only three possible diagnostic results for suspected faults: (1) There is no suspected fault and the diagnosis is no fault; (2) The diagnosis is a suspected voltage continuously high fault; (3) The diagnosis is a suspected voltage continuously low fault.
[0079] Example 2
[0080] This embodiment describes the diagnosis of a continuously high voltage fault.
[0081] Existing technology uses active lean working conditions to diagnose the fault of continuous high voltage: the system will actively instruct the engine to use a larger excess air coefficient, aiming to reduce the voltage of the rear oxygen sensor to below the lean edge threshold (such as 0.2V), and this adjustment process lasts about 2 to 4 seconds. However, the potential consequence of adopting this strategy is that NOX emissions will increase significantly in a high temperature and oxygen-rich working environment, thereby facing the risk of not meeting emission regulations.
[0082] refer to Figure 4 As shown in the figure, during the active lean reduction process, the instability of the excess air coefficient caused by load fluctuations or the operation to a condition with a rich mixture (the excess air coefficient deviation self-learning value is not corrected in time) may lead to poor lean reduction effect and the voltage may not drop below the lean edge threshold, which may erroneously trigger a fault alarm.
[0083] refer to Figure 5 As shown in the figure, when the rear oxygen voltage is continuously high, the excess air coefficient fluctuates greatly during the leaning process (probably caused by load fluctuations). Finally, after the leaning is completed, the rear oxygen voltage has not dropped below 0.2V, and the rear oxygen sensor voltage fault is immediately reported. If this false alarm problem is to be solved under the current strategy, the leaning range will inevitably be increased or the leaning time will be extended. xTherefore, how to optimize the diagnostic logic and prevent unnecessary fault false alarms has become an urgent problem to be solved.
[0084] Figure 5 In the figure, the rose-red line indicates the voltage signal of the rear oxygen sensor; the blue line indicates the measured excess air coefficient signal; the red line indicates the target excess air coefficient signal; the black line indicates that the voltage of the rear oxygen sensor is continuously high, and 251 is a fault report.
[0085] In order to solve the problem of false alarm and increased NOx emissions during the voltage continuous high fault diagnosis process, this embodiment provides the following voltage continuous high fault diagnosis strategy, refer to Figure 6 As shown, the voltage continuously high fault diagnosis strategy includes the following steps:
[0086] Under the passive lean condition, the minimum voltage value of the rear oxygen sensor is collected, and it is determined whether the current minimum voltage value is less than the lean edge threshold. If so, it is diagnosed as no fault, if not, it is diagnosed as a continuously high voltage fault.
[0087] After the duration of the passive leaning condition reaches the first time threshold t1, the minimum voltage value of the rear oxygen sensor is collected. It is more accurate to collect the minimum voltage value after the passive leaning condition lasts for a certain period of time.
[0088] Preferably, the passive leaning condition includes at least one of a PM trap active regeneration condition and a catalyst heating condition. In this embodiment, if the current condition is a passive leaning condition, which is one of a PM trap active regeneration condition and a catalyst heating condition, the voltage continuously high fault diagnosis process can be entered.
[0089] Preferably, under the active regeneration condition of the particulate matter trap, the larger the target excess air coefficient λ is, the smaller the first time threshold is. The larger the target excess air coefficient λ is, the greater the leaning range is. Accordingly, by reducing the first time threshold, the required judgment time can be reduced, thereby improving the diagnostic efficiency.
[0090] The following Table 1 is a mapping table of the target excess air ratio and the first time threshold t1.
[0091] Table 1
[0092] Target excess air factor 1.02 1.04 1.06 1.08 1.1 First time threshold (s) 25 20 15 10 5
[0093] The prior art performs continuous high voltage fault diagnosis under active leaning conditions. Although active leaning conditions can reduce the concentration of the mixed gas, they also cause a significant increase in NOx emissions, which is not conducive to environmental protection and faces the risk of not complying with emission regulations. This embodiment performs continuous high voltage fault diagnosis under passive leaning conditions. Passive leaning conditions refer to performing continuous high voltage fault diagnosis without active leaning, thereby avoiding additional increase in NOx emissions.
[0094] Example 3
[0095] In order to solve the problem of false alarm and increased NOx emissions during the voltage continuous high fault diagnosis process, this embodiment provides the following voltage continuous high fault diagnosis strategy, refer to Figure 7 As shown, the voltage continuously high fault diagnosis strategy includes the following steps:
[0096] Under the passive fuel cut-off condition, the minimum voltage value of the rear oxygen sensor is collected, and it is determined whether the current minimum voltage value is less than the lean edge threshold. If so, it is diagnosed as no fault, if not, it is diagnosed as a continuously high voltage fault.
[0097] Under the passive fuel cut-off condition, the minimum voltage value of the rear oxygen sensor is collected after one of the following conditions is met: the duration of the passive fuel cut-off condition reaches the second time threshold, or the exhaust flow integral after fuel cut-off reaches the second integral threshold. This is conducive to more accurate collection of the minimum voltage value.
[0098] The prior art performs fault diagnosis of continuously high voltage under active leaning conditions. Although active leaning conditions can reduce the concentration of the mixed gas, they also cause a significant increase in NOx emissions, which is not conducive to environmental protection and faces the risk of not complying with emission regulations. The present invention performs fault diagnosis of continuously high voltage under passive fuel cut-off conditions. Passive fuel cut-off conditions refer to performing fault diagnosis of continuously high voltage without actively cutting off fuel, thereby avoiding additional increase in NOx emissions. Performing fault diagnosis under passive fuel cut-off conditions reduces interference with the normal driving process and maintains a good driving experience.
[0099] Example 4
[0100] In order to ensure the smooth completion of the voltage continuously high fault diagnosis before the passive lean reduction condition and the passive fuel cut-off condition are reached, the present embodiment will perform the voltage continuously high fault diagnosis under the active fuel cut-off condition.
[0101] refer to Figure 8 As shown, if the engine running time exceeds the third time threshold t3, and there is no passive lean reduction condition and passive fuel cut-off condition, then under the active fuel cut-off condition, a suspected voltage continuously high fault diagnosis is performed.
[0102] Under the fuel cut-off condition, the engine takes in air, but the injector does not spray fuel and the engine does not burn, so there is no additional increase in NOx emissions, and the concentration of the mixed gas is naturally reduced. Before the passive de-leaning condition and passive fuel cut-off condition are reached, the system switches to the active fuel cut-off condition to avoid frequent active fuel cut-offs that affect the driving experience.
[0103] Under the active fuel cut-off condition, after the duration of the active fuel cut-off condition reaches the fourth time threshold t4, the minimum voltage value of the rear oxygen sensor is collected, and it is determined whether the current minimum voltage value is less than the lean edge threshold. If so, it is diagnosed as no fault, if not, it is diagnosed as a continuous high voltage fault.
[0104] Example 5
[0105] This embodiment describes the diagnosis of a voltage failure that is continuously low.
[0106] The prior art ignores the influence of the active regeneration condition of the particulate matter trap and the self-learning of the excess air coefficient when diagnosing the fault of continuously low voltage.
[0107] Active regeneration of the particulate matter trap is when the ECU uses a lean air-fuel ratio (corresponding to a high excess air coefficient) and pushes the ignition angle to put the particulate matter trap in a high-temperature, oxygen-rich state to burn off carbon deposits. It is known that the lean air-fuel ratio during active regeneration of the particulate matter trap will affect the diagnosis of a continuous low rear oxygen voltage, that is, when the particulate matter trap actively regenerates, the mixture is diluted, and the rear oxygen voltage will continue to be low. At this time, setting a predetermined air-fuel ratio target value to enrich the mixture is not effective, and the rear oxygen voltage cannot rise to cross the high-side threshold, resulting in a false alarm of a continuous low rear oxygen voltage fault, such as Fig. 9 As shown, the red line is the excess air coefficient signal, and the blue line shows that the rear oxygen sensor power supply signal is continuously low.
[0108] The purpose of closed-loop control is to accurately control the actual excess air coefficient to be near the target excess air coefficient and meet the mandatory requirements of emission regulations for certain emissions. Closed-loop control of the actual excess air coefficient to be near the target excess air coefficient allows the catalyst to accurately store and release oxygen to achieve the best conversion efficiency and reduce emissions. Closed-loop control must also quickly and accurately correct the deviation when the target excess air coefficient deviates from 1. However, if the excess air coefficient has not been fully self-learned, the mixture is lean at this time, and the self-learning has not been updated, it is impossible to correct the lean mixture. If the self-learning deviation is large at this time, then the diagnosis of continued low rear oxygen voltage under this operating condition may lead to a false alarm of continued low rear oxygen voltage fault, such as Fig.10 shown.
[0109] Fig.10In the figure, the green line is the self-learning value of the mixture, which is 1, indicating that self-learning has not been performed; the red line is the engine speed; the brown line shows that the oxygen sensor voltage continues to be low after the fault is reported.
[0110] In order to more accurately diagnose the voltage continuously low fault, this embodiment provides the following voltage continuously low fault diagnosis strategy, refer to Fig.11 As shown, the voltage continuously low fault diagnosis strategy includes the following steps:
[0111] Under active enrichment conditions, the maximum voltage of the rear oxygen sensor is collected, and it is determined whether the current maximum voltage is greater than the rich edge threshold. If so, it is diagnosed as no fault. If not, wait for the target excess air coefficient to be self-learned and updated, and then diagnose again based on the maximum voltage of the rear oxygen sensor under active enrichment conditions.
[0112] A quick judgment is made through the first active enrichment condition to improve the diagnostic efficiency; after the target excess air coefficient is updated through self-learning, a judgment is made again through the active enrichment condition to eliminate the continuous low voltage caused by incomplete self-learning, thereby improving the accuracy of the diagnostic results.
[0113] In this embodiment, the active enrichment condition includes:
[0114] If the current operating condition is not the active regeneration condition of the particulate matter trap, the mixture is enriched according to the first corrected excess air coefficient λ1;
[0115] If the current operating condition is the active regeneration condition of the particulate matter trap, the mixture is enriched according to the second corrected excess air coefficient λ2;
[0116] The second corrected excess air coefficient λ2 is smaller than the first corrected excess air coefficient λ1, and both the second corrected excess air coefficient λ2 and the first corrected excess air coefficient λ1 are reduced on the basis of a target excess air coefficient of an active regeneration condition of the particulate matter trap.
[0117] Taking into account that the active regeneration condition of the particulate matter trap will cause the concentration of the mixed gas to decrease, therefore, when the current operating condition is not the active regeneration condition of the particulate matter trap, using a smaller excess air coefficient for active enrichment can compensate for the decrease in the concentration of the mixed gas caused by the active regeneration condition of the particulate matter trap, eliminate the low voltage caused by the active regeneration condition of the particulate matter trap, and make the diagnostic result more accurate.
[0118] Preferably, after the duration of the active enrichment condition reaches the fourth time threshold, the maximum voltage of the rear oxygen sensor is collected, which is conducive to more accurate collection of the maximum voltage.
[0119] Preferably, before entering the active enrichment condition for the first time, when the exhaust flow integral reaches the second integral threshold, the maximum voltage of the rear oxygen sensor is collected, and it is determined whether the current maximum voltage is greater than the rich edge threshold. If so, it is diagnosed as no fault; if not, the active enrichment condition is entered.
[0120] Before making a judgment through the active enrichment condition, judging again through the exhaust flow integral can avoid frequent entering the active enrichment condition and affecting the driving experience.
[0121] Example 6
[0122] This embodiment provides a computer-readable storage medium, in which at least one instruction is stored. The instruction is loaded and executed by a processor to implement the rear oxygen sensor fault diagnosis method described in any one of Embodiments 1 to 5.
[0123] This embodiment also provides a controller, including a suspected fault diagnosis unit, a voltage continuously high fault diagnosis unit, and a voltage continuously low fault diagnosis unit;
[0124] The suspected fault diagnosis unit is used to determine whether there is a suspected fault and the suspected fault type according to the voltage value of the rear oxygen sensor currently collected when the exhaust flow integral exceeds the first integral threshold, and when a suspected fault exists, start the corresponding fault diagnosis unit according to the suspected fault type to perform fault diagnosis;
[0125] The voltage continuously high fault diagnosis unit is used to diagnose the voltage continuously high fault according to the minimum voltage value of the rear oxygen sensor under the passive lean reduction working condition;
[0126] The voltage continuously low fault diagnosis unit is used to diagnose the voltage continuously low fault according to the maximum voltage of the rear oxygen sensor under the active enrichment condition.
[0127] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection created by this application.
Claims
1. A method for diagnosing a rear oxygen sensor fault. It is characterized in that The following steps are involved: When the exhaust flow integral exceeds the first integral threshold, judging whether there is a suspected fault and the type of the suspected fault according to the voltage value of the rear oxygen sensor currently collected; When there is a suspected fault, the corresponding fault diagnosis strategy is used to perform fault diagnosis according to the suspected fault type.
2. The rear oxygen sensor fault diagnosis method according to claim 1, It is characterized in that The steps to determine the type of suspected fault include: The minimum voltage value of the rear oxygen sensor is compared with the lean edge threshold value. If the current minimum voltage value is greater than or equal to the lean edge threshold value, it is diagnosed as a suspected continuous high voltage fault.
3. The rear oxygen sensor fault diagnosis method according to claim 1, It is characterized in that It includes a fault diagnosis strategy for continuously high voltage, which includes the following steps: under passive leaning conditions or passive fuel cut-off conditions, collecting the minimum voltage value of the rear oxygen sensor, and determining whether the current minimum voltage value is less than the lean edge threshold; if so, diagnosing as no fault; if not, diagnosing as a continuously high voltage fault.
4. The rear oxygen sensor fault diagnosis method according to claim 3, It is characterized in that After the duration of the passive lean reduction condition reaches a first time threshold, a minimum voltage value of the rear oxygen sensor is collected.
5. The rear oxygen sensor fault diagnosis method according to claim 4, It is characterized in that The passive de-leaning condition includes at least one of a particulate matter trap active regeneration condition and a catalyst heating condition.
6. The rear oxygen sensor fault diagnosis method according to claim 5, It is characterized in that In the active regeneration condition of the particulate matter trap, the larger the target excess air coefficient λ is, the smaller the first time threshold is.
7. The rear oxygen sensor fault diagnosis method according to claim 3, It is characterized in that Under the passive fuel cut-off condition, the minimum voltage value of the rear oxygen sensor is collected after one of the following conditions is met: the duration of the passive fuel cut-off condition reaches the second time threshold, or the exhaust flow integral after fuel cut-off reaches the second integral threshold.
8. The rear oxygen sensor fault diagnosis method according to claim 1, It is characterized in that If the engine running time exceeds the third time threshold and there is no passive lean reduction condition and passive fuel cut-off condition, then under the active fuel cut-off condition, a suspected continuous high voltage fault diagnosis is performed.
9. The rear oxygen sensor fault diagnosis method according to claim 8, It is characterized in that Under the active fuel cut-off condition, after the duration of the active fuel cut-off condition reaches the fourth time threshold, the minimum voltage value of the rear oxygen sensor is collected, and it is determined whether the current minimum voltage value is less than the lean edge threshold. If so, it is diagnosed as no fault, if not, it is diagnosed as a continuous high voltage fault.
10. The rear oxygen sensor fault diagnosis method according to claim 1, It is characterized in that The steps to determine the type of suspected fault include: The maximum voltage of the rear oxygen sensor is compared with the rich edge threshold. If the current maximum voltage is less than or equal to the rich edge threshold, it is diagnosed as a suspected voltage continuously low fault.
11. The rear oxygen sensor fault diagnosis method according to claim 1, It is characterized in that The method includes a voltage continuously low fault diagnosis strategy, wherein the voltage continuously low fault diagnosis strategy includes the following steps: Under active enrichment conditions, the maximum voltage of the rear oxygen sensor is collected, and it is determined whether the current maximum voltage is greater than the rich edge threshold. If so, it is diagnosed as no fault. If not, wait for the target excess air coefficient to be self-learned and updated, and then diagnose again based on the maximum voltage of the rear oxygen sensor under active enrichment conditions.
12. The rear oxygen sensor fault diagnosis method according to claim 11, It is characterized in that The active enrichment condition includes: If the current operating condition is not the active regeneration condition of the particulate matter trap, the mixture is enriched according to the first corrected excess air coefficient λ1; If the current operating condition is the active regeneration condition of the particulate matter trap, the mixture is enriched according to the second corrected excess air coefficient λ2; The second corrected excess air coefficient λ2 is smaller than the first corrected excess air coefficient λ1, and both the second corrected excess air coefficient λ2 and the first corrected excess air coefficient λ1 are reduced on the basis of a target excess air coefficient of an active regeneration condition of the particulate matter trap.
13. The rear oxygen sensor fault diagnosis method according to claim 11, It is characterized in that After the duration of the active enrichment condition reaches a fourth time threshold, a maximum voltage of the rear oxygen sensor is acquired.
14. The rear oxygen sensor fault diagnosis method according to claim 11, It is characterized in that Before entering the active enrichment condition for the first time, when the exhaust flow integral reaches the second integral threshold, the maximum voltage of the rear oxygen sensor is collected, and it is determined whether the current maximum voltage is greater than the rich edge threshold. If so, it is diagnosed as no fault; if not, the active enrichment condition is entered.
15. A computer-readable storage medium, It is characterized in that The storage medium stores at least one instruction, and the instruction is loaded and executed by the processor to implement the rear oxygen sensor fault diagnosis method according to any one of claims 1 to 14.
16. A controller, It is characterized in that Including suspected fault diagnosis unit, continuous high voltage fault diagnosis unit and continuous low voltage fault diagnosis unit; The suspected fault diagnosis unit is used to determine whether there is a suspected fault and the suspected fault type according to the voltage value of the rear oxygen sensor currently collected when the exhaust flow integral exceeds the first integral threshold, and when a suspected fault exists, start the corresponding fault diagnosis unit according to the suspected fault type to perform fault diagnosis; The voltage continuously high fault diagnosis unit is used to diagnose the voltage continuously high fault according to the minimum voltage value of the rear oxygen sensor under the passive lean reduction working condition or the passive fuel cut-off working condition; The voltage continuously low fault diagnosis unit is used to diagnose the voltage continuously low fault according to the maximum voltage of the rear oxygen sensor under the active enrichment condition.