A Diagnostic Method and Device for the Aging State of a Three-Way Catalytic Converter

Abstract

The present application relates to a method for diagnosing the aging state of a three-way catalytic converter, including: at the first moment t0, starting from the first moment t0, obtaining a sequence of Nernst voltage values of the front oxygen sensor; at the second moment t1 after the first moment t0, starting from the second moment t1, obtaining a sequence of Nernst voltage values of the rear oxygen sensor; the sequence of Nernst voltage values of the rear oxygen sensor corresponds one-to-one with the sequence of Nernst voltage values of the front oxygen sensor; obtaining a difference sequence of the Nernst voltage values of the front and rear oxygen sensors according to the sequence of Nernst voltage values of the front oxygen sensor and the sequence of Nernst voltage values of the rear oxygen sensor; calculating the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors; judging the aging state of the three-way catalytic converter according to the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors. The present application can more accurately describe the working state of the three-way catalytic converter, reduce the occurrence of false alarms, and make the diagnosis result of its aging state more accurate.

Description

Technical Field

[0001] The present application relates to the technical field of vehicles, and particularly to a method and device for diagnosing the aging state of a three-way catalytic converter. Background Art

[0002] Currently, with the increasingly serious environmental problems caused by automobile exhaust, the three-way catalytic converter has become a standard configuration of the exhaust after-treatment system. Once the three-way catalytic converter fails, it will affect the normal operation of the engine and reduce the emission performance of the vehicle. Most of the current diagnoses of the aging state of the three-way catalytic converter extract features through the average voltage value and pressure difference value of the post-oxygen sensor, and the matching accuracy is relatively low. Summary of the Invention

[0003] In view of the problems existing in the background art, the present application provides a method for diagnosing the aging state of a three-way catalytic converter, which can more accurately describe the working state of the three-way catalytic converter, reduce the occurrence of false alarm problems, and make the diagnosis result of the aging state of the three-way catalytic converter more accurate.

[0004] According to one aspect of the present invention, a method for diagnosing the aging state of a three-way catalytic converter is provided, including: at a first moment t0, starting from the first moment t0, obtaining a sequence of Nernst voltage values of a pre-oxygen sensor; at a second moment t1 after the first moment t0, starting from the second moment t1, obtaining a sequence of Nernst voltage values of a post-oxygen sensor; the sequence of Nernst voltage values of the post-oxygen sensor corresponds one by one to the sequence of Nernst voltage values of the pre-oxygen sensor; obtaining a difference sequence of the Nernst voltage values of the pre-oxygen sensor and the post-oxygen sensor according to the sequence of Nernst voltage values of the pre-oxygen sensor and the sequence of Nernst voltage values of the post-oxygen sensor; calculating the variance of the difference sequence of the Nernst voltage values of the pre-oxygen sensor and the post-oxygen sensor; and judging the aging state of the three-way catalytic converter according to the variance of the difference sequence of the Nernst voltage values of the pre-oxygen sensor and the post-oxygen sensor.

[0005] By using the method for diagnosing the aging state of the three-way catalytic converter in the present technical solution, for a healthy three-way catalytic converter, an aging three-way catalytic converter, and a failed three-way catalytic converter, the Nernst voltage collected by the post-oxygen sensor shows stable, small-amplitude fluctuations, and large-amplitude fluctuations in sequence. As a result, the variances of the difference sequences of the Nernst voltage values of the pre-oxygen sensor and the post-oxygen sensor will be distributed from large to small in sequence. Therefore, according to the magnitude of the variance of the difference sequence of the Nernst voltage values of the pre-oxygen sensor and the post-oxygen sensor, the working state of the three-way catalytic converter can be more accurately described, the occurrence of false alarm problems can be reduced, and the diagnosis result of the aging state of the three-way catalytic converter can be made more accurate.

[0006] In some embodiments of the present invention, the first moment t0 is when the crankshaft and / or camshaft angle is consistent with the injection phase.

[0007] In some embodiments of the present invention, the acquisition of the first moment t0 includes: collecting the crankshaft and / or camshaft angles in real time. When the crankshaft and / or camshaft angles are consistent with the injection phase, the fuel injector or the air injection valve starts to perform the injection action; when the crankshaft and / or camshaft angles are inconsistent with the injection phase, the crankshaft and / or camshaft angles are repeatedly collected and the injection phase is matched until the crankshaft and / or camshaft angles are consistent with the injection phase, and the fuel injector or the air injection valve starts to perform the injection action.

[0008] In some embodiments of the present invention, for the second moment t1, t1 = t0 + L / V; where L is the distance between the front oxygen sensor and the rear oxygen sensor, and V is the gas flow rate.

[0009] In some embodiments of the present invention, the slopes of the respective voltages of the Nernst voltage value sequence of the front oxygen sensor and the respective voltages of the Nernst voltage value sequence of the rear oxygen sensor are obtained. According to the slope, it is judged whether there is data abnormality in the corresponding voltage. When the corresponding data is abnormal, filtering is performed before calculating the variance of the Nernst voltage difference, and the filtering step size is the data abnormality point and several data points before and after it.

[0010] In some embodiments of the present invention, the filtering step size is the data abnormality point and five data points before and after it.

[0011] In some embodiments of the present invention, it is set that when the variance of the difference sequence of the Nernst voltage values of the current and rear oxygen sensors is within [a, b), the three-way catalytic converter is in a failure state; when the variance is within [b, c), the three-way catalytic converter is in an aging state; when the variance is within [c, d], the three-way catalytic converter is in a healthy state; where a < b < c < d.

[0012] In some embodiments of the present invention, a, b, c, and d can be obtained by training using a machine learning method.

[0013] In some embodiments of the present invention, the acquisition of the variances a, b, c, and d includes: respectively selecting three-way catalytic converters in the first, second, third, and fourth usage states with gradually increasing usage time, and obtaining the variances of the difference sequences of the Nernst voltage values of the front and rear oxygen sensors corresponding to each three-way catalytic converter multiple times and calculating the average value. Among them, the average values of the variances of the difference sequences of the Nernst voltage values of the front and rear oxygen sensors of the three-way catalytic converters in the first, second, third, and fourth usage states correspond to d, c, b, and a respectively.

[0014] According to another aspect of the present invention, a method for diagnosing the aging state of a three-way catalytic converter is provided, including: a front oxygen sensor voltage data acquisition module, which is used to execute collecting the Nernst voltage data of the front oxygen sensor within a set time length when the crankshaft and / or camshaft angles are consistent with the injection phase, and continuously collecting for a target number of times;

[0015] The post-oxygen sensor voltage data acquisition module is used to execute the acquisition of the Nernst voltage data of the post-oxygen sensor within a set time length and continuously acquire the target number of times when the crankshaft and / or camshaft angle is consistent with the injection phase and after a certain duration is extended.

[0016] The diagnosis module calculates the difference sequence of the Nernst voltage values of the front and rear oxygen sensors according to the Nernst voltage value sequences of the front and rear oxygen sensors, and then calculates the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors; and judges the aging state of the three-way catalytic converter according to the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors.

[0017] As can be seen from the above technical solutions, the embodiments of the present application have the following advantages:

[0018] The embodiments of the present application provide a method for diagnosing the aging state of a three-way catalytic converter. The method obtains the Nernst voltage value sequence of the front oxygen sensor starting from the first moment t0 when the crankshaft and / or camshaft angle is consistent with the injection phase; extends the duration for the gas to flow from the front oxygen sensor to the rear oxygen sensor, that is, the second moment t1, and starts to obtain the Nernst voltage value sequence of the rear oxygen sensor, obtaining the Nernst voltage value sequences of the front and rear oxygen sensors without time delay, and then obtains the difference sequence of the Nernst voltage values of the front and rear oxygen sensors according to the Nernst voltage value sequences of the front and rear oxygen sensors, and calculates the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors. According to the magnitude of the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors, the working state of the three-way catalytic converter can be described more accurately, the generation of false alarms can be reduced, and the diagnosis result of the aging state of the three-way catalytic converter is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present application. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0020] Figure 1 is a flowchart of the method for diagnosing the aging state of the three-way catalytic converter in the embodiments of the present application;

[0021] Figure 2 is a comparison diagram of the front and rear oxygen sensor signals of a healthy three-way catalytic converter;

[0022] Figure 3 is a comparison diagram of the front and rear oxygen sensor signals of an aging three-way catalytic converter;

[0023] Figure 4 It is a comparison chart of the front and rear oxygen sensor signals of a failed three-way catalytic converter;

[0024] Figure 5 It is a schematic structural diagram of a diagnostic device for the aging state of a three-way catalytic converter according to an embodiment of the present application. Specific embodiments

[0025] It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts belong to the scope of protection of the present application.

[0026] When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are only examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0027] In the description of the present application, it should be understood that the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances. In addition, in the description of the present application, unless otherwise specified, "a plurality of" means two or more. "And / or" describes the association relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0028] Three-way catalysis is the most important part of the exhaust gas after-treatment system. Because it mainly targets three harmful gases, namely carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), during the treatment process, it is called the "three-way catalytic system".

[0029] Under normal operating conditions, when the fuel injector or gas injector starts to perform the injection action, the fuel / gas is atomized through the nozzle and enters the cylinder. At the same time, the piston makes the oxygen-containing air enter the cylinder through alternating motion and mix with the atomized fuel / gas; then, the ignition coil is driven to generate a spark to ignite the mixed gas, generating harmful gases such as carbon monoxide, hydrocarbons, and nitrogen oxides; finally, the harmful gas products generated by combustion enter the three-way catalytic system for exhaust gas after-treatment, and after the chemical reaction of the three-way catalytic converter, they are discharged.

[0030] The component that plays an oxidizing role in the three-way catalytic system is called the three-way catalytic converter. The oxygen sensor is an essential component for the three-way catalytic converter to reduce exhaust pollution; the oxygen sensors located upstream and downstream of the three-way catalytic converter are respectively called the front oxygen sensor and the rear oxygen sensor.

[0031] The Nernst voltage is a potential difference formed on both sides of the electrode of the oxygen sensor due to different ambient oxygen concentrations. Ideally, the Nernst voltage of the oxygen sensor is 0.45V (i.e., the excess air coefficient is equal to 1). The front oxygen sensor is used to detect the oxygen concentration in the combustion products after the combustion reaction of the cylinder mixture. Generally speaking, the higher the oxygen concentration, the leaner the mixture gas. The front oxygen sensor collects the oxygen concentration and converts it into an electrical signal and transmits it to the ECU (Electronic Control Unit). Thus, the ECU can configure the mixture gas according to this signal. The rear oxygen sensor is used to detect the conversion of harmful gases generated by the combustion reaction.

[0032] Therefore, in the three-way catalytic system, the front oxygen sensor and the rear oxygen sensor are essentially in a control relationship. The front oxygen sensor is the environmental acquisition before the three-way catalytic converter works, and the rear oxygen sensor is the environmental acquisition after the three-way catalytic converter works.

[0033] The following will describe the diagnostic method and device for the aging state of the three-way catalytic converter provided by the embodiments of the present application with reference to the accompanying drawings.

[0034] The embodiments of the present application disclose a diagnostic method for the aging state of a three-way catalytic converter. The diagnostic method for the aging state of the three-way catalytic converter can be executed by the ECU. The diagnostic method for the aging state of the three-way catalytic converter includes:

[0035] 1) Comparing the crankshaft and / or camshaft angle with the injection action phase of the engine

[0036] When the vehicle engine does not perform the injection action, the three-way catalytic converter hardly needs to work. At this time, the Nernst voltage of the rear oxygen sensor is the same as the environment, so the aging state of the three-way catalytic converter cannot be accurately detected.

[0037] Therefore, considering the detection timing of the front and rear oxygen sensors, in this embodiment, the ECU real-time collects the crankshaft and / or camshaft angle and compares it with the injection action phase matched by the engine. When the crankshaft and / or camshaft angle is consistent with the injection phase, the fuel injector or air injector starts to perform the injection action; when the crankshaft and / or camshaft angle is inconsistent with the injection phase, the crankshaft and / or camshaft angle is repeatedly collected and the injection phase is matched until the crankshaft and / or camshaft angle is consistent with the injection phase, and the fuel injector or air injector starts to perform the injection action.

[0038] 2) Obtaining the Nernst voltage of the front oxygen sensor

[0039] At the first moment t0 when the crankshaft and / or camshaft angle is consistent with the injection phase, the ECU starts to continuously obtain the sequence of Nernst voltage values V(f)1, V(f)2, V(f)3, V(f)4, …, V(f) of the front oxygen sensor n , continuing until the injection action is completed.

[0040] 3) Obtain the Nernst voltage of the rear oxygen sensor

[0041] Due to the position limitation of the front and rear oxygen sensors in the three-way catalytic system and the conversion rate of the three-way catalytic converter, there will be a certain time difference in the Nernst voltage values collected by the front and rear oxygen sensors for the same gas before and after treatment. Therefore, in this embodiment, for the second moment t1 after the first moment t0, starting from the second moment t1, the ECU continuously obtains the sequence of Nernst voltage values V(b)1, V(b)2, V(b)3, V(b)4, …, V(b) of the rear oxygen sensor n , continuing until the injection action is completed and extended for a certain duration, and the extended duration is the time difference between the second moment t1 and the first moment t0. The sequence of Nernst voltage values of the rear oxygen sensor corresponds one-to-one with the sequence of Nernst voltage values of the front oxygen sensor; where

[0042] t1 = t0 + L / V (1)

[0043] In the formula, L is the distance between the front oxygen sensor and the rear oxygen sensor, and V is the gas flow rate. Therefore, the ECU needs to continuously collect the sequence of Nernst voltage values of the front oxygen sensor starting from the first moment t0 and continuously collect the sequence of Nernst voltage values of the rear oxygen sensor starting from the second moment t1, so that the waveform of the sequence of Nernst voltage values of the rear oxygen sensor is in phase with the waveform of the sequence of Nernst voltage values of the front oxygen sensor.

[0044] 4) Processing of abnormal Nernst voltage data

[0045] In this embodiment, the system also designs a filtering function, which is specifically: the ECU obtains the slopes of the respective voltages of the sequence of Nernst voltage values of the front oxygen sensor and the respective voltages of the sequence of Nernst voltage values of the rear oxygen sensor, and judges whether there is data abnormality according to the slope. When the change slope of the Nernst voltage at the front and rear two angles reaches a certain theoretical value or preset value, it is considered that there is data abnormality. Before calculating the variance of the Nernst voltage difference, filter the abnormal data, and the filtering step size is the data abnormality point and several data points before and after it; specifically, in this embodiment, the filtering step size is preferably the data abnormality point and five data points before and after it; this is to prevent the Nernst voltage of the front oxygen sensor from mutating at a certain angle due to certain special working conditions or reasons, which may cause deviation in subsequent calculations and judgments.

[0046] Thus, the Nernst voltage value sequences of the front and rear oxygen sensors without time-delay can be obtained.

[0047] 5) Obtain the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors

[0048] According to the Nernst voltage value sequence V(f)1, V(f)2, V(f)3, V(f)4, …, V(f) of the front oxygen sensor n and the Nernst voltage value sequence V(b)1, V(b)2, V(b)3, V(b)4, …, V(b) of the rear oxygen sensor n , calculate the difference sequence X1, X2, X3, X4, …, X of the Nernst voltage values between the front oxygen sensor and the rear oxygen sensor n , where

[0049] X = |V(b) - V(f)| (2)

[0050] Then calculate the mean value of the difference sequence of the Nernst voltage values between the front oxygen sensor and the rear oxygen sensor.

[0051]

[0052] Finally, calculate the variance of the difference sequence of the Nernst voltage values between the front oxygen sensor and the rear oxygen sensor.

[0053]

[0054] After that, it is possible to judge whether the three-way catalytic converter is aging according to the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors; as Figure 2 shown, for a healthy three-way catalytic converter, since the Nernst voltage collected by the rear oxygen sensor is the most stable, the difference sequence of the Nernst voltage values of its front and rear oxygen sensors fluctuates most violently and the variance is large; as Figure 3 shown, for an aging three-way catalytic converter, since the Nernst voltage collected by the rear oxygen sensor has small fluctuations, the difference sequence of the Nernst voltage values of its front and rear oxygen sensors has small fluctuations and the variance is moderate; as Figure 4 shown, for a failed three-way catalytic converter, since the Nernst voltage collected by the rear oxygen sensor is almost the same as that of the front oxygen sensor, the difference sequence of the Nernst voltage values of its front and rear oxygen sensors has almost no fluctuations and the variance is small; thus, according to the magnitude of the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors, the working state of the three-way catalytic converter can be described more accurately, the generation of false alarms can be reduced, and the diagnosis result of the aging state of the three-way catalytic converter can be made more precise.

[0055] Specifically, in this embodiment, when the variance of the difference sequence of the Nernst voltage values of the current and post-oxygen sensors is within [a, b), the three-way catalytic converter is in a failure state; when the variance is within [b, c), the three-way catalytic converter is in an aging state; when the variance is within [c, d], the three-way catalytic converter is in a healthy state; where a < b < c < d; the specific values of a, b, c, and d can be obtained by training using machine learning methods.

[0056] For example, the three-way catalytic converter can be divided into four stages, including: the first unused state in a brand-new condition, the second used state in which it starts to age after being used for a period of time, the third used state in which it starts to fail after being used for a relatively long time, and the fourth used state in which it is completely failed after being used for a long time. Then, the three-way catalytic converters in the first, second, third, and fourth used states are selected respectively, and the variance of the difference sequence of the Nernst voltage values of the pre- and post-oxygen sensors corresponding to each three-way catalytic converter is obtained multiple times according to the above process, such as 2 times, 3 times, 4 times, etc., and the average value is calculated. Thus, the average variance d in the first used state, the average variance c in the second used state, the average variance b in the third used state, and the average variance a in the fourth used state are obtained.

[0057] When the ECU collects data in real time and calculates that the variance of the difference sequence of the Nernst voltage values of the pre- and post-oxygen sensors is within [a, b), within [b, c), or within [c, d], according to the setting, the working state of the three-way catalytic converter can be accurately and conveniently described, facilitating the user to judge the aging state of the three-way catalytic converter in real time.

[0058] This application also proposes a diagnostic device, which corresponds to the above method embodiment and uses the above diagnostic method to diagnose the aging state of the three-way catalytic converter, such as Figure 5 As shown, the diagnostic device 100 includes:

[0059] A pre-oxygen sensor voltage data acquisition module 101, configured to collect the Nernst voltage data of the pre-oxygen sensor within a set time length when the crankshaft and / or camshaft angle is consistent with the injection phase, and continuously collect the target number of times;

[0060] A post-oxygen sensor voltage data acquisition module 102, configured to collect the Nernst voltage data of the post-oxygen sensor within a set time length when the crankshaft and / or camshaft angle is consistent with the injection phase and after extending a certain duration, and continuously collect the target number of times;

[0061] The diagnostic module 103 calculates the difference sequence of the Nernst voltage values of the front and rear oxygen sensors based on the Nernst voltage value sequences of the front and rear oxygen sensors, and then calculates the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors; and determines the aging state of the three-way catalytic converter based on the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors.

[0062] As described above, only the preferred specific embodiments of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A diagnostic method for the aging state of a three-way catalytic converter, characterized in that, Including: For the first moment t0, starting from the first moment t0, obtain the Nernst voltage value sequence of the front oxygen sensor. The first moment t0 is when the crankshaft and / or camshaft angle is consistent with the injection phase. The acquisition of the first moment t0 includes: real-time collecting the crankshaft and / or camshaft angle. When the crankshaft and / or camshaft angle is consistent with the injection phase, the fuel injector or air injection valve starts to perform the injection action; when the crankshaft and / or camshaft angle is inconsistent with the injection phase, repeatedly collect the crankshaft and / or camshaft angle and match the injection phase until the crankshaft and / or camshaft angle is consistent with the injection phase, and the fuel injector or air injection valve starts to perform the injection action; For the second moment t1 after the first moment t0, starting from the second moment t1, obtain the Nernst voltage value sequence of the rear oxygen sensor; the Nernst voltage value sequence of the rear oxygen sensor corresponds one by one to the Nernst voltage value sequence of the front oxygen sensor; for the second moment t1, t1 = t0 + L / V; where L is the distance between the front oxygen sensor and the rear oxygen sensor, and V is the gas flow rate; Obtain the difference sequence of the Nernst voltage values of the front and rear oxygen sensors according to the Nernst voltage value sequences of the front and rear oxygen sensors; Calculate the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors; Judge the aging state of the three-way catalytic converter according to the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors.

2. The diagnostic method for the aging state of the three-way catalyst according to claim 1, wherein Obtain the slopes of the respective voltages of the Nernst voltage value sequence of the front oxygen sensor and the respective voltages of the Nernst voltage value sequence of the rear oxygen sensor, and judge whether there is data abnormality for the corresponding voltage according to the slope. When the corresponding data is abnormal, perform filtering before calculating the variance of the Nernst voltage difference, and the filtering step size is the data abnormality point and several data points before and after it.

3. The diagnostic method for the aging state of the three-way catalytic converter according to claim 2, characterized in that, The filtering step size is the data abnormality point and five data points before and after it.

4. The diagnostic method for the aging state of the three-way catalytic converter according to claim 1, characterized in that, It is set that when the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors is within [a, b), the three-way catalytic converter is in a failure state; when the variance is within [b, c), the three-way catalytic converter is in an aging state; when the variance is within [c, d], the three-way catalytic converter is in a healthy state; where a < b < c < d.

5. The diagnostic method for the aging state of the three-way catalytic converter according to claim 4, characterized in that, The a, b, c, and d can be obtained by training using a machine learning method.

6. The diagnostic method for the aging state of the three-way catalytic converter according to claim 4 or 5, characterized in that, The acquisition of the variances a, b, c, and d includes: respectively selecting three-way catalytic converters in the first, second, third, and fourth usage states with gradually increasing usage time, obtaining the variances of the difference sequences of the Nernst voltage values of the front and rear oxygen sensors corresponding to each three-way catalytic converter multiple times and calculating the average value. Among them, the average values of the variances of the difference sequences of the Nernst voltage values of the front and rear oxygen sensors of the three-way catalytic converters in the first, second, third, and fourth usage states correspond to d, c, b, and a respectively.

7. A diagnostic device for the aging state of a three-way catalytic converter, characterized in that The diagnostic device adopts the diagnostic method according to any one of claims 1 to 5, and the diagnostic device includes: A front oxygen sensor voltage data acquisition module, configured to collect the Nernst voltage data of the front oxygen sensor within a set time length when the crankshaft and / or camshaft angle is consistent with the injection phase, and continuously collect the target number of times; The post-oxygen sensor voltage data acquisition module is used to execute the acquisition of the Nernst voltage data of the post-oxygen sensor within a set time length and continuously acquire the target number of times when the crankshaft and / or camshaft angle is consistent with the injection phase and extended for a certain duration. The diagnosis module calculates the difference sequence of the Nernst voltage values of the front and rear oxygen sensors according to the Nernst voltage value sequences of the front and rear oxygen sensors, and then calculates the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors; and judges the aging state of the three-way catalytic converter according to the variance of the difference sequence of the Nernst voltage values of the front and rear oxygen sensors.

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