Misfire diagnosis method and structure based on ethanol fuel concentration

Abstract

The invention relates to a misfire diagnosis method and structure based on ethanol fuel concentration. The method comprises the following steps: judging an enabling condition; determining a misfire detection mode; testing and calculating an extreme value of a misfire threshold, respectively using ethanol fuel with the lowest ethanol concentration and ethanol fuel with the highest ethanol concentration, collecting crankshaft rotation time data under the corresponding ethanol concentration, and calculating the misfire threshold; reading the ethanol concentration, calculating a misfire threshold value according to the ethanol concentration, reading the ethanol concentration, and calculating a misfire threshold value corresponding to the target ethanol concentration according to the misfire threshold values corresponding to the lowest ethanol concentration and the highest ethanol concentration respectively and a coefficient obtained according to the ethanol concentration; determining a misfire rate, identifying a misfire cylinder, performing statistics according to the misfire index to obtain the misfire rate, and correspondingly judging the misfire cylinder; determining a detected misfire type; and a misfire test result and a misfire cylinder are reported. Compared with the prior art, the method has the advantage that the fire working conditions under different ethanol concentrations can be accurately identified.

Description

Technical Field

[0001] This invention belongs to the technical field of engine electronic control systems, and relates to a misfire diagnosis method and structure based on ethanol fuel concentration. Background Technology

[0002] Misfire diagnosis, as one of the main diagnostic methods for automotive engines, has crucial comprehensive significance, its value spanning multiple core dimensions including vehicle safety, environmental compliance, performance maintenance, lifespan extension, and regulatory compliance. From a safety perspective, timely diagnosis can prevent sudden power interruption, jerking, or even stalling caused by misfires, reducing the risk of rear-end collisions and loss of control at high speeds. It also prevents unburned fuel from diluting engine oil, causing excessive wear on pistons and crankshafts, and serious mechanical damage such as cylinder scoring and engine failure. In the environmental field, diagnosis can effectively reduce the surge in hydrocarbon (HC) and carbon monoxide (CO) emissions caused by misfires, prevent unburned fuel from damaging the three-way catalytic converter, ensure vehicles comply with major global emission regulations such as China VI, Euro VI, and L8, and reduce atmospheric pollution. From a performance maintenance perspective, repairing misfire problems through diagnosis can restore engine power lost due to interrupted cylinder combustion (e.g., a single-cylinder misfire in a four-cylinder engine results in approximately a 25% power loss). This approach not only prevents the engine from increasing fuel injection to compensate for power loss, thus avoiding artificially high fuel consumption and ensuring both power output and fuel economy, but also extends engine lifespan. Early diagnosis can address low-cost causes such as spark plug aging and ignition coil malfunctions, preventing secondary damage from unburned fuel eroding the cylinder wall lubricating film and accelerating valve carbon buildup. This avoids escalating the problem and incurring high repair costs such as catalytic converter failure and major engine overhauls, extending the engine's entire lifespan. Furthermore, according to mandatory requirements such as OBD-II and L8, engine misfire diagnosis is an essential function of on-board diagnostic systems. It can monitor in real time through the electronic control unit (ECU) and trigger malfunction indicator lamps and store fault codes, ensuring vehicle compliance during annual inspections and protecting legal road rights. In conclusion, engine misfire diagnosis is not only a fault repair method but also a preventative barrier ensuring the safe, environmentally friendly, and economical operation of the vehicle throughout its entire lifespan, playing an irreplaceable role.

[0003] Currently, ethanol fuel is widely used, and users often mix gasoline and ethanol in different proportions to create various concentrations of ethanol gasoline according to their preferences. Different concentrations of ethanol gasoline exhibit different combustion characteristics, which directly affect the crankshaft rotation speed of the engine. Changes in crankshaft rotation speed, in turn, alter the diagnostic threshold of the misfire diagnostic system. This chain reaction leads to practical problems: when a vehicle is filled with ethanol gasoline of different concentrations, the misfire diagnostic system may issue false alarms, incorrectly identifying a misfire, or even failing to diagnose properly or accurately determine whether a misfire has actually occurred, causing difficulties in vehicle fault diagnosis and normal use.

[0004] In the practical application of traditional engine misfire diagnosis technology, its core limitation lies in the single nature of the diagnostic object and the lack of adaptability to operating conditions. When designed, this type of technology often uses a specific type of single fuel (such as traditional gasoline) as a benchmark to build diagnostic models and judgment logic, failing to fully consider the dynamic changes in fuel composition in actual engine operating scenarios—especially in the context of the widespread use of ethanol gasoline. The ethanol concentration in fuel fluctuates significantly due to factors such as fuel quality, refueling scenario, and operating condition requirements; for example, the ethanol concentration may dynamically adjust within the range of 0% to 100%.

[0005] This design limitation directly leads to a significant decrease in the diagnostic accuracy of traditional misfire diagnostic technology when faced with fuels of different ethanol concentrations. On the one hand, its preset diagnostic thresholds, parameter benchmarks, and dynamic compensation mechanisms cannot match the differences in combustion characteristics caused by changes in ethanol concentration. For example, the latent heat of vaporization, octane number, and combustion speed of ethanol fuel are significantly different from those of traditional gasoline, which directly affects key diagnostic signals such as cylinder pressure, exhaust composition, and speed fluctuations when misfire occurs. On the other hand, the technology system lacks a real-time sensing and adaptive adjustment module for dynamic changes in ethanol concentration, making it difficult to optimize the diagnostic algorithm based on real-time changes in fuel composition, and thus unable to accurately identify misfire phenomena under different ethanol fuel concentration conditions.

[0006] Ultimately, traditional technologies not only fail to meet the diagnostic needs under complex fuel conditions, but also exhibit significant shortcomings in adaptability—they cannot effectively detect minor misfires in low-ethanol-concentration fuels, nor can they accurately distinguish between normal combustion fluctuations and actual misfire signals under high-ethanol-concentration fuel conditions. This results in a significant reduction in the reliability and practicality of diagnostic results, failing to provide precise support for the safe operation and troubleshooting of engines.

[0007] Patent CN102116241A discloses a method for diagnosing misfires in gasoline engines. The specific diagnostic steps are as follows: The crankshaft timing deviation is calculated using the following formula: ΔT=(T2-T1)-(T1-T0), where ΔT is the crankshaft timing deviation, T2 is the current ignition timing, T1 is the previous ignition timing, and T0 is calculated accordingly. The engine speed fluctuation value is judged. If the fluctuation value is too large, it is necessary to determine whether it is a bad circuit or a misfire. If it is a misfire, it is necessary to determine whether it is a single-cylinder misfire or a multi-cylinder misfire. If it is a single-cylinder misfire, it is necessary to determine which cylinder misfired. All misfires need to be statistically analyzed to obtain an assessment report on the degree of misfire, and then determine whether it is related to emissions or catalytic converter damage. Finally, the fault is reported and the test is completed, and the fault is stored. However, the misfire detection method used in this patent has limitations in its applicability, and can only be used for misfire diagnosis of engines using a single type of fuel. When the engine has the ability to use multiple fuels, due to the significant differences in the core combustion characteristics of different fuels, such as combustion speed, ignition temperature, and energy release efficiency, the original detection logic and judgment criteria cannot be adapted to the combustion conditions of multiple fuels. This leads to inaccurate misfire diagnosis results, which may result in the failure to report real misfire faults and the false reporting of normal combustion conditions, thus affecting the reliability and practicality of the diagnosis.

[0008] Patent CN119062441A discloses a misfire signal correction method, apparatus, device, and storage medium, comprising: when the engine meets the misfire diagnosis conditions, acquiring the current engine speed and current intake load; obtaining a preset concentration misfire self-learning value based on the current engine speed, the current intake load, and an intake load-engine speed-misfire self-learning value mapping table; obtaining a target misfire self-learning value based on the current misfire self-learning value and the preset concentration misfire self-learning value; and correcting the misfire signal based on the target misfire self-learning value. The patent's technical optimization focuses solely on engine operating conditions. Specifically, its core improvement lies in pre-setting differentiated misfire diagnostic thresholds for different combinations of engine speed and load during operation. This improves the adaptability of misfire diagnosis under different operating conditions to some extent, even in a single fuel-compatible scenario. However, this optimization has significant limitations, failing to consider the impact of fuel type differences on diagnostic results. When the engine is operating at the same speed and load, changes in fuel type can lead to differences in the judgment logic and signal characteristics of misfire due to fundamental differences in key characteristics such as ignition performance, combustion stability, and energy release patterns. The patent does not design corresponding diagnostic calibration mechanisms for different fuel types, relying instead on a unified core judgment standard. Therefore, it cannot accurately adapt to the combustion states of different fuels under the same operating conditions, ultimately making it difficult to accurately diagnose misfires under the same speed and load conditions, and failing to effectively cover the diagnostic needs of multi-fuel usage scenarios. Summary of the Invention

[0009] The purpose of this invention is to overcome at least one of the shortcomings of the prior art, such as insufficient accuracy in diagnosing misfires of ethanol fuels with different concentrations under the same operating conditions, and to provide a misfire diagnosis method and structure based on ethanol fuel concentration. This invention can achieve accurate identification and determination of misfire status for fuels with different ethanol concentrations under the same operating conditions.

[0010] The objective of this invention can be achieved through the following technical solutions:

[0011] One of the technical solutions of the present invention is to provide a misfire diagnosis method based on ethanol fuel concentration, the method comprising the following steps:

[0012] S1. Determine the enabling condition;

[0013] S2. Determine the fire detection mode;

[0014] S3. Experimentally calculate the extreme value of the fire threshold.

[0015] Using ethanol fuel with the lowest and highest ethanol concentrations respectively, crankshaft rotation time data were collected at the corresponding ethanol concentrations and the misfire threshold was calculated.

[0016] S4. Read the ethanol concentration and calculate the fire threshold based on the ethanol concentration.

[0017] Read the ethanol concentration, and calculate the fire threshold corresponding to the target ethanol concentration based on the fire thresholds corresponding to the lowest and highest ethanol concentrations, and the coefficient derived from the ethanol concentration.

[0018] S5. Determine the misfire rate and identify the misfire cylinder.

[0019] The misfire rate is obtained from the misfire index statistics. The misfire rate is the proportion of the number of times the misfire index exceeds the misfire threshold within 100 complete strokes to the total number of ignitions, and the misfired cylinder is determined accordingly.

[0020] S6. Determine the type of fire detected;

[0021] S7. Report the misfire test results and the misfire cylinder.

[0022] Further, in step S1, it is checked whether there is a misfire detection failure. Misfire detection failures include crankshaft signal loss, water temperature sensor short circuit, intake pressure sensor short circuit, and electronic throttle (ETC) module failure.

[0023] Determine whether the diagnostic enabling condition parameters are within the diagnostic range. The diagnostic enabling condition parameters include atmospheric pressure, water temperature, engine speed, and battery voltage.

[0024] Furthermore, in step S2, it is determined whether the engine misfire is a single-cylinder misfire or a cylinder-to-cylinder misfire, which is used to confirm the calculation method of the misfire index.

[0025] Furthermore, the fire index is calculated as follows:

[0026] The misfire index in single-cylinder mode of the engine is calculated by comparing the time difference of a single cylinder's complete stroke when the crankshaft rotates to an independent reference point, which corresponds to a specific tooth position on the crank position signal disk.

[0027] The formula for calculating the misfire index in single-cylinder mode of an engine is as follows:

[0028] Rev index = CST 4-2 CST 2+ CST 0,

[0029] in, Rev index This refers to the misfire index per cylinder. CST 0 represents the moment when the crankshaft sensor scans an independent reference point during the first revolution of the engine. CST 2 represents the moment when the crankshaft sensor scans an independent reference point during the second revolution of the engine. CST 4 represents the moment when the crank position sensor scans an independent reference point after the engine has rotated its second revolution;

[0030] The misfire index of the engine cylinder-matching mode is calculated by comparing the time difference between the two cylinders when the crankshaft rotates to an independent reference point. The independent reference point corresponds to two specific teeth on the crank position signal disk, and the alignment angle between the two teeth of the independent reference point is 180 CA °.

[0031] The formula for calculating the misfire index in cylinder-matching mode of an engine is as follows.

[0032] Cyl index = CST 2-2 CST 1+ CST 0,

[0033] in, Cyl index To determine the cylinder misfire index, CST 0 represents the moment when the crankshaft sensor scans an independent reference point during the first revolution of the engine. CST 1 represents the moment when the crankshaft sensor scans another independent reference point during the first revolution of the engine. CST 2 represents the moment when the crank position sensor scans an independent reference point after the engine has rotated its first revolution;

[0034] If there is a machining error in the curved signal disk, causing the alignment angle between the two teeth of the independent reference point to deviate by 180CA°, it will affect the fire diagnosis result. Taking the time when the curved sensor scans another independent reference point as the reference, the time when the curved sensor scans an independent reference point will produce a time deviation.

[0035] The formula for calculating the misfire index in engine cylinder mode when mechanical error exists in the crank position signal disc is as follows.

[0036] Cyl index '= Cyl index +2 δ ,

[0037] in, Cyl index 'This is the cylinder misfire index when mechanical errors are present.' δ The time deviation for scanning an independent reference point by a curvature sensor is subject to mechanical error.

[0038] Furthermore, in step S3, based on the time difference of crankshaft rotation under fire conditions, the two extreme values ​​of the ethanol concentration detection limit during the fire fault process are calculated by conversion ratio. These are the fire thresholds corresponding to the lowest and highest ethanol concentrations, respectively. The two thresholds serve as the core judgment basis for calculating the target fire threshold corresponding to the ethanol concentration between the two, ensuring the clarity of the detection range and diagnostic criteria. The calculation formulas for the fire thresholds corresponding to the lowest and highest ethanol concentrations are as follows:

[0039] In single-cylinder mode, one cylinder fails to fire, causing the engine to misfire. RevEmin index =0.75 Rev indexmin , RevEmax index =0.75 Rev indexmax ,

[0040] in, RevEmin index Minimum ethanol concentration vmin The corresponding single-cylinder misfire threshold, Rev indexmin Minimum ethanol concentration at the time of fire vmin The corresponding single-cylinder misfire index, RevEmax index The highest ethanol concentration vmax The corresponding single-cylinder misfire threshold, Rev indexmax The highest ethanol concentration at the time of the fire vmax The corresponding single-cylinder misfire index;

[0041] In cylinder deactivation mode, one pair of cylinders fails to ignite, causing the engine to misfire. CylEmin index =0.75 Cyl indexmin , CylEmax index =0.75 Cyl indexmax ,

[0042] in, CylEmin index Minimum ethanol concentration vmin The corresponding misfire threshold for cylinders, Cyl indexmin Minimum ethanol concentration at the time of fire vmin The corresponding misfire index, CylEmax index The highest ethanol concentration vmax The corresponding misfire threshold for cylinders, Cyl indexmax The highest ethanol concentration at the time of the fire vmax The corresponding misfire index.

[0043] Furthermore, in step S3, the minimum and maximum ethanol concentrations corresponding to the fire thresholds are calculated at any speed and load. The extreme values ​​of the fire thresholds at each speed and load are collected to obtain a calibrable table. Subsequently, the extreme values ​​of the fire thresholds can be retrieved from the calibrable table based on the speed and load.

[0044] Furthermore, in step S4, given that switching ethanol concentration may cause deviations in the misfire threshold calculation, a fault suppression strategy needs to be implemented during the ethanol fuel switching process; after refueling is completed and a fixed amount of fuel is injected, the final ethanol concentration is determined, and then the misfire diagnosis function is activated to accurately calculate the misfire threshold based on the final ethanol concentration.

[0045] When the ethanol concentration sensor detects a change in ethanol concentration, the electronic control unit performs diagnostic operations according to the following procedure:

[0046] Ethanol concentration learning involves calculating the amount of fuel needed to fill the low-pressure pipeline based on its length and cross-sectional area. This is the volume of ethanol fuel that needs to be injected. The electronic control unit then controls the injector to inject a fixed volume of ethanol fuel. This process verifies and learns the current actual ethanol concentration, ensuring the accuracy of ethanol concentration detection.

[0047] The diagnostic function is temporarily disabled during the ethanol concentration learning process to avoid misdiagnosis caused by fluctuations in ethanol concentration during the learning process.

[0048] Normal diagnosis and threshold calculation: Once the ethanol concentration is successfully learned, the misfire diagnosis function is immediately activated. At the same time, the electronic control unit calculates the misfire threshold under the corresponding speed and load based on the currently confirmed ethanol concentration, and enters normal operation diagnosis.

[0049] Furthermore, in step S4, for ethanol concentrations between the minimum and maximum ethanol concentrations, the corresponding misfire threshold can be calculated by combining the combustion characteristics of ethanol fuel. The calculation formula for the misfire threshold corresponding to the target ethanol concentration is as follows:

[0050] In single-cylinder mode of the engine, RevEn index = RevEmin index + α ( RevEmax index - RevEmin index ),

[0051] in, RevEn index Ethanol concentration vn The corresponding single-cylinder misfire threshold, RevEmin index Minimum ethanol concentration vmin The corresponding single-cylinder misfire threshold, RevEmax index The highest ethanol concentration vmax The corresponding single-cylinder misfire threshold, α The coefficient is derived from the ethanol concentration, i.e. α =( vn - vmin ) / ( vmax - vmin );

[0052] Engine cylinder deactivation mode, CylEn index = CylEmin index + α ( CylEmax index - CylEmin index ),

[0053] in, CylEn index Ethanol concentration vn The corresponding misfire threshold for cylinders, CylEmin index Minimum ethanol concentration vmin The corresponding misfire threshold for cylinders, CylEmax index The highest ethanol concentration vmax The corresponding misfire threshold for cylinders, αThe coefficient is derived from the ethanol concentration, i.e. α =( vn - vmin ) / ( vmax - vmin ).

[0054] Furthermore, in step S6, the types of misfires include catalyst-damaged misfires and emission-damaged misfires. Catalyst-damaged misfires are those where the misfire causes the catalyst temperature to reach its tolerance limit threshold, leading to physical / chemical failure of the catalyst. Emission-exceeding misfires are those where the misfire causes exhaust pollutants (hydrocarbons HC, carbon monoxide CO, nitrogen oxides NO) to exceed emission standards. x Fire types exceeding statutory standards or set limits;

[0055] Catalyst-damaged misfires occur when the misfire rate reaches or exceeds the critical damage misfire rate, and emission-damaged misfires occur when the misfire rate does not reach the critical damage misfire rate.

[0056] As a preferred technical solution, the misfire rate is gradually increased by controlling the rotation speed and load using a misfire generator until the catalyst temperature reaches its tolerance limit threshold. The misfire rate data at this point is recorded as the critical damage misfire rate, thereby defining the critical conditions for catalyst damage-type misfire.

[0057] One of the technical solutions of the present invention is to provide a misfire diagnosis structure based on ethanol fuel concentration. This structure implements the method described above. The engine is electrically connected to an electronic control unit (ECU), which stores the charts required for calculation. The structure includes a low-pressure section and a high-pressure section.

[0058] In the low-pressure section, the fuel tank is connected to the fuel pump, the fuel pump is connected to the low-pressure pipeline, an ethanol concentration sensor is installed on the low-pressure pipeline, and the fuel pump is electrically connected to the electronic control unit.

[0059] In the high-pressure section, the high-pressure oil pump is connected to the low-pressure pipeline and the high-pressure pipeline, and the high-pressure oil pump is electrically connected to the electronic control unit.

[0060] The high-pressure pipeline is connected to the high-pressure fuel rail. The engine contains cylinders and a crankshaft. The high-pressure fuel rail is connected to the fuel injector. The high-pressure fuel rail injects fuel into the cylinder through the fuel injector. One end of the crankshaft that extends out of the cylinder is connected to the crank position signal disk. A crank position sensor is located next to the crank position signal disk. The fuel injector and the crank position sensor are electrically connected to the electronic control unit.

[0061] As a preferred technical solution, the fuel tank is connected to the fuel pump via a circulation pipeline.

[0062] As a preferred technical solution, the electronic control unit controls the fuel pump to draw fuel from the fuel tank to the low-pressure line, maintains the fuel pressure in the low-pressure line, and returns excess fuel to the fuel tank.

[0063] As a preferred technical solution, the high-pressure oil pump is connected to the drive cam.

[0064] As a preferred technical solution, the drive cam is mounted on the camshaft. One end of the camshaft is connected to the cam signal disk, and the other end is connected to the variable valve timing (VVT) phaser. A cam position sensor is mounted next to the cam signal disk. The variable valve timing phaser and the cam position sensor are electrically connected to the electronic control unit.

[0065] As a preferred technical solution, the driving cam drives the piston of the high-pressure oil pump to move upward, and the electronic control unit controls the high-pressure oil pump to close the execution valve of the high-pressure oil pump at an appropriate time, using the upward energy of the piston to forcibly pump fuel into the high-pressure pipeline.

[0066] The electronic control unit controls the rotational offset of the variable valve timing phaser. The rotational offset of the variable valve timing phaser drives the rotational offset of the camshaft, thereby causing the valve lift to change and realizing continuous variable valve timing.

[0067] The relative rotational offset information of the variable valve timing phaser is characterized by the offset position of the cam signal disk. The cam position sensor captures the offset position information of the cam signal disk and transmits it to the electronic control unit, which then calculates the final variable valve timing phase opening.

[0068] As a preferred technical solution, an oil pressure sensor is installed on the high-pressure oil rail, and the oil pressure sensor is electrically connected to the electronic control unit.

[0069] As a preferred technical solution, the oil pressure sensor measures the pressure information in the high-pressure pipeline in a timely manner and feeds it back to the electronic control unit;

[0070] The electronic control unit outputs a drive signal to the high-pressure oil pump, controls the high-pressure oil pump switch, and injects an appropriate amount of fuel to maintain the theoretical fuel rail pressure.

[0071] The electronic control unit combines the engine's current speed and load information to calculate the amount of fuel injection required by the injectors of each cylinder, and calculates the final injection pulse width and injection phase of each cylinder, and outputs it to the injectors of each cylinder for execution.

[0072] The crank position sensor feeds back the gear signal from the crank position signal disk, which is used to calculate the engine's actual crankshaft position and speed information.

[0073] One of the technical solutions of the present invention is to provide a fire diagnosis device based on ethanol fuel concentration. The device implements the method described above. The device includes an acquisition module, a storage module, a reading module, a calculation module, and a comparison module. The acquisition module acquires the external parameters required for calculation. The storage module stores the charts required for calculation. The reading module reads the indicators required for calculation from the charts based on the external parameters. The calculation module calculates the indicators. The comparison module compares the indicators.

[0074] One of the technical solutions of the present invention is to provide a fire diagnostic device based on ethanol fuel concentration, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method.

[0075] One of the technical solutions of the present invention is to provide a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described.

[0076] One of the technical solutions of the present invention is to provide a computer program product, including a computer program, which, when executed by a processor, implements the steps of the method described.

[0077] Compared with the prior art, the present invention has the following beneficial effects:

[0078] (1) This invention first collects the current ethanol concentration information of ethanol fuel in real time through an ethanol concentration sensor, and constructs a multi-dimensional input matrix by combining engine speed, engine load and other operating parameters. Then, a concentration adaptation correction algorithm is introduced. Since there are differences in fuel combustion speed and ignition energy requirements under different ethanol concentrations, the misfire threshold is dynamically calibrated to establish a mapping relationship between ethanol concentration and misfire threshold, so as to achieve accurate identification of misfire conditions and location of misfire cylinder. This invention can cover the misfire diagnosis needs of ethanol fuel in the range of 0~100% ethanol concentration by adjusting the minimum and maximum ethanol concentration diagnostic misfire thresholds that define the lower and upper limits of detection, as well as the target misfire threshold of dynamic calibration. The diagnostic accuracy is significantly improved compared with the traditional fixed threshold method, and it can effectively avoid misdiagnosis and missed diagnosis caused by concentration changes. It is compatible with flexible fuel supply systems and provides reliable protection for engine safe operation and emission control.

[0079] (2) The present invention optimizes the fire diagnosis method. By deeply combining the characteristics of ethanol fuel and the dynamic diagnosis requirements, it fundamentally solves the above pain points. The core improvement logic is that it no longer relies on a fixed threshold, but takes the real-time signal of the ethanol concentration sensor as the core trigger point. When a change in concentration is detected, a targeted threshold adjustment process is immediately started. The fire threshold boundary corresponding to the lowest and highest ethanol concentration is locked by the preset fire threshold calculation method. Then, combined with the combustion characteristics difference of intermediate ethanol concentration, the exclusive fire threshold under each ethanol concentration is accurately calculated to achieve dynamic matching of ethanol concentration and fire threshold.

[0080] (3) The present invention incorporates a phased control mechanism in the diagnostic process. During the ethanol concentration learning and threshold calculation phase, the misfire diagnosis function is temporarily disabled to avoid the combustion instability during the concentration fluctuation period from interfering with the diagnostic results. After the misfire threshold is accurately determined, the diagnosis is restarted and the misfire phenomenon occurring when fuels with different ethanol concentrations are accurately identified under the same operating conditions based on the misfire threshold corresponding to the current ethanol concentration. At the same time, the minimum and maximum ethanol concentration boundaries are obtained by re-looking up the table under different speed and load conditions, and differentiated monitoring is performed. Whether it is a low-load idling condition or a high-load acceleration condition, the characteristic signals of the misfire fault can be accurately identified based on the misfire threshold adapted to the current combustion characteristics.

[0081] (4) This comprehensive optimization design of the present invention ultimately achieves three core values: First, it eliminates the risk of missed detection, ensuring that misfire faults under any operating condition can be accurately captured within the full concentration range, avoiding the expansion of faults due to diagnostic blind spots; Second, it eliminates false alarms, effectively filtering normal combustion fluctuations caused by changes in ethanol concentration through dynamic matching and phased control of ethanol concentration and misfire threshold, reducing unnecessary alarms and protection actions, and improving the stability of system operation; Third, it improves diagnostic adaptability, ensuring that the system can quickly respond and adjust diagnostic logic regardless of changes in ethanol concentration, maintaining high diagnostic accuracy under complex operating conditions, providing a solid guarantee for engine power performance, fuel economy and emission compliance, while also reducing maintenance costs and user inconvenience caused by false alarms and missed detections. Attached Figure Description

[0082] Figure 1 This is a schematic diagram of a misfire diagnosis structure based on ethanol fuel concentration in an embodiment of the present invention;

[0083] Figure 2 This is a schematic diagram illustrating the timing of fire threshold calculation in an embodiment of the present invention;

[0084] Figure 3 This is a schematic diagram of the diagnostic process when the ethanol concentration changes in an embodiment of the present invention;

[0085] Figure 4 This is a schematic flowchart of the misfire diagnosis method based on ethanol fuel concentration in an embodiment of the present invention.

[0086] Explanation of markings in the diagram:

[0087] 1—Fuel tank, 2—Fuel pump, 3—Low-pressure line, 4—Cam position sensor, 5—Cam signal disc, 6—High-pressure fuel pump, 7—Drive cam, 8—Camshaft, 9—Variable valve timing phaser, 10—Engine, 11—Cylinder, 12—High-pressure line, 13—Fuel pressure sensor, 14—High-pressure fuel rail, 15—Injector, 16—Crankshaft, 17—Crank position signal disc, 18—Crank position sensor, 19—Electronic control unit. Detailed Implementation

[0088] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0089] Example:

[0090] A misfire diagnosis structure based on ethanol fuel concentration, such as Figure 1 As shown, the engine 10 is electrically connected to the electronic control unit (ECU) 19, which stores the graphs required for calculation and has a structure including a low-pressure section and a high-pressure section.

[0091] In the low-pressure section, the fuel tank 1 is connected to the fuel pump 2 through the circulation pipeline, the fuel pump 2 is connected to the low-pressure pipeline 3, the low-pressure pipeline 3 is equipped with an ethanol concentration sensor, and the fuel pump 2 is electrically connected to the electronic control unit 19.

[0092] The electronic control unit 19 controls the fuel pump 2 to draw fuel from the fuel tank 1 to the low-pressure line 3, maintains the fuel pressure in the low-pressure line 3, and returns excess fuel to the fuel tank 1.

[0093] In the high-pressure section, the high-pressure oil pump 6 is connected to the low-pressure pipeline 3 and the high-pressure pipeline 12, the high-pressure oil pump 6 is connected to the drive cam 7, and the high-pressure oil pump 6 is electrically connected to the electronic control unit 19.

[0094] The drive cam 7 drives the piston of the high-pressure oil pump 6 to move upward. The electronic control unit 19 controls the high-pressure oil pump 6 to close the execution valve of the high-pressure oil pump 6 at an appropriate time, and uses the upward energy of the piston to force fuel into the high-pressure pipeline 12.

[0095] The drive cam 7 is mounted on the camshaft 8. One end of the camshaft 8 is connected to the cam signal disk 5, and the other end is connected to the variable valve timing (VVT) phaser 9. A cam position sensor 4 is mounted next to the cam signal disk 5. The variable valve timing phaser 9 and the cam position sensor 4 are electrically connected to the electronic control unit 15.

[0096] The electronic control unit 19 controls the rotational offset of the variable valve timing phaser 9. The rotational offset of the variable valve timing phaser 9 drives the rotational offset of the camshaft 8, thereby causing the valve lift to change and realizing continuous variable valve timing.

[0097] The relative rotational offset information of the variable valve timing phaser 9 is characterized by the offset position of the cam signal disk 5. After the cam position sensor 4 captures the offset position information of the cam signal disk 5, it transmits it to the electronic control unit 19, which calculates the final variable valve timing phase opening amount.

[0098] High-pressure line 12 is connected to high-pressure oil rail 14. Oil pressure sensor 13 is installed on high-pressure oil rail 14. Cylinder 11 and crankshaft 16 are installed inside engine 10. High-pressure oil rail 14 is connected to injector 15. Oil is injected into cylinder 11 through high-pressure oil rail 14 and injector 15. One end of crankshaft 16 extending out of cylinder 11 is connected to crank position signal disk 17. Crank position sensor 18 is installed next to crank position signal disk 17. Oil pressure sensor 13, injector 15 and crank position sensor 18 are electrically connected to electronic control unit 19.

[0099] The oil pressure sensor 13 measures the pressure information in the high-pressure pipeline 12 in a timely manner and feeds it back to the electronic control unit 19;

[0100] The electronic control unit 19 controls the output drive signal to the high-pressure oil pump 6, controls the switch of the high-pressure oil pump 6, and presses in an appropriate amount of fuel to maintain the theoretical fuel rail pressure.

[0101] The electronic control unit 19 calculates the amount of fuel injection required by the injector 15 of each cylinder 11 by combining the current speed and load information of the engine 10, and calculates the final injection pulse width and injection phase of each cylinder 11, and outputs them to the injector 15 of each cylinder 11 for execution.

[0102] The crank position sensor 18 feeds back the gear signal from the crank position signal disk 17 to calculate the actual crankshaft position and speed information of the engine 10.

[0103] A misfire diagnosis method based on ethanol fuel concentration, such as Figure 4 As shown, the specific steps are as follows:

[0104] S1. Determine the enabling condition.

[0105] Check for any misfire suppression detection malfunctions, including crankshaft 16 signal loss, coolant temperature sensor short circuit, intake pressure sensor short circuit, and electronic throttle control (ETC) module malfunction.

[0106] Determine whether the diagnostic enabling condition parameters are within the diagnostic range. The diagnostic enabling condition parameters include atmospheric pressure, water temperature, engine speed, and battery voltage.

[0107] S2. Determine the fire detection mode.

[0108] To determine whether the misfire of engine 10 is a single-cylinder misfire or a cylinder-to-cylinder misfire, and to confirm the calculation method of the misfire index;

[0109] S3. Experimentally calculate the extreme value of the fire threshold.

[0110] Using ethanol fuel with the lowest and highest ethanol concentrations respectively, the crankshaft 16 rotation time data at the corresponding ethanol concentrations were collected and the misfire threshold was calculated.

[0111] The minimum and maximum ethanol concentrations corresponding to the lowest and highest flare thresholds are calculated at any speed and load. The extreme values ​​of the flare thresholds at each speed and load are collected to obtain a calibrable table. The extreme values ​​of the flare thresholds can then be retrieved from the calibrable table based on the speed and load.

[0112] S4. Read the ethanol concentration and calculate the fire threshold based on the ethanol concentration.

[0113] Read the ethanol concentration, and calculate the fire threshold corresponding to the target ethanol concentration based on the fire thresholds corresponding to the lowest and highest ethanol concentrations, and the coefficient derived from the ethanol concentration.

[0114] S5. Determine the misfire rate and identify the misfire cylinder.

[0115] The misfire rate is obtained from the misfire index statistics. The misfire rate is the proportion of the number of times the misfire index exceeds the misfire threshold within 100 complete strokes to the total number of ignitions, and the misfired cylinder is determined accordingly.

[0116] S6. Determine the type of fire detected.

[0117] Misfire types include catalyst-damage misfires and emission-damage misfires. Catalyst-damage misfires occur when the misfire causes the catalyst temperature to reach its tolerance limit, leading to physical / chemical failure of the catalyst. Emission-exceeding misfires occur when the misfire causes exhaust pollutants (hydrocarbons HC, carbon monoxide CO, nitrogen oxides NO) to exceed emission standards. x Fire types exceeding statutory standards or set limits;

[0118] Catalyst-damaged misfires occur when the misfire rate reaches or exceeds the critical damage misfire rate; emission-damaged misfires occur when the misfire rate does not reach the critical damage misfire rate.

[0119] By controlling the rotational speed and load, the misfire rate is gradually increased using a misfire generator until the catalyst temperature reaches its tolerance limit threshold. The misfire rate data at this point is recorded as the critical damage misfire rate, thereby defining the critical conditions for catalyst damage-type misfire.

[0120] S7. Report the misfire test results and the misfire cylinder.

[0121] In this embodiment, the engine 10 is a four-cylinder engine, and the crank position signal disk 17 has a 58 (60-2) tooth structure, wherein the 58 teeth are designed with evenly spaced tooth tips and tooth grooves, and the 2 teeth are designed with missing teeth.

[0122] The crank position sensor 18 measures and inputs a 60-2 tooth signal to the electronic control unit 19. For every revolution of the engine 10, the electronic control unit 19 acquires a complete 60-2 tooth signal, with each tooth representing a 6-degree crankshaft rotation angle (CA °).

[0123] like Figure 2 As shown, the fire index is calculated as follows:

[0124] The misfire index of engine 10 single-cylinder mode is calculated by comparing the time difference of a single cylinder's complete stroke when crankshaft 16 rotates to an independent reference point. The independent reference point corresponds to two specific tooth positions on crank position signal disk 17, and the alignment angle between the two teeth of the independent reference point is 180 CA °.

[0125] In this embodiment, the independent reference points are the 7th tooth and the 37th tooth;

[0126] The formula for calculating the misfire index in engine 10 single-cylinder mode is as follows:

[0127] Rev index =( CST 4- CST 3)-( CST 2- CST 1)+( CST 3- CST 2)-( CST 1- CST 0)= CST 4-2 CST 2+ CST 0,

[0128] in, Rev index This refers to the misfire index per cylinder. CST 0 represents the moment when the crankshaft position sensor 18 scans the 7th tooth during the first revolution of engine 10. CST 1 represents the moment when the crankshaft position sensor 18 scans the 37th tooth during the first revolution of engine 10. CST 2 represents the moment when the crankshaft sensor 18 scans the 7th tooth during the second revolution of engine 10. CST 3 represents the moment when the crankshaft sensor 18 scans the 7th tooth during the second revolution of engine 10. CST 4 is the moment when the crank position sensor 18 scans the 7th tooth after the engine 10 has rotated for the second time;

[0129] Since the time for a complete stroke is 720 CA °, the first and third strokes, and the second and fourth strokes, are compared between a complete stroke.

[0130] The misfire index of the engine 10 cylinder mode is calculated by comparing the time difference between the two cylinders when the crankshaft 16 rotates to the independent reference point. The independent reference point corresponds to two specific tooth positions on the crank position signal disk 17, and the alignment angle between the two teeth of the independent reference point is 180 CA °.

[0131] In this embodiment, the independent reference points are the 7th tooth and the 37th tooth;

[0132] The formula for calculating the misfire index in a 10-cylinder mode engine is as follows:

[0133] Cyl index =( CST 2- CST 1)-( CST 1- CST 0)= CST 2-2 CST 1+ CST 0,

[0134] in, Cyl index To determine the cylinder misfire index, CST 0 represents the moment when the crankshaft position sensor 18 scans the 7th tooth during the first revolution of engine 10. CST 1 represents the moment when the crankshaft position sensor 18 scans the 37th tooth during the first revolution of engine 10. CST 2 is the moment when the crank position sensor 18 scans the 7th tooth after the engine 10 has rotated for the first time;

[0135] If there is a machining error in the curved signal disk 17, causing the alignment angle between the two teeth of the independent reference point to deviate by 180 CA°, it will affect the fire diagnosis result. Taking the time when the curved sensor 18 scans the 37th tooth as the reference, the time when the curved sensor 18 scans the 7th tooth will produce a time deviation.

[0136] The formula for calculating the misfire index of engine cylinder 10 mode when mechanical error exists in the crank position signal disk 17 is as follows.

[0137] Cyl index '=( CST 2'- CST 1)-( CST 1- CST 0')= CST 2'-2 CST 1+ CST 0',

[0138] in, Cyl index 'This is the cylinder misfire index when mechanical errors are present.' CST0' represents the moment when the crankshaft position sensor 18 scans for mechanical error in the 7th tooth during the first revolution of engine 10. CST 1 represents the moment when the crankshaft position sensor 18 scans the 37th tooth during the first revolution of engine 10. CST 2' is the moment when the crank position sensor 18 scans the 7th tooth for mechanical error after the engine 10 has rotated the first revolution;

[0139] therefore, Cyl index '- Cyl index =( CST 2'-2 CST 1+ CST 0')-( CST 2-2 CST 1+ CST 0)= CST 2'- CST 2+ CST 0- CST 0',

[0140] It is deduced that, Cyl index '= Cyl index +2 δ ,

[0141] in, δ The time deviation due to mechanical error in the scanning of the 7th tooth by the position sensor 18 is as follows: δ = CST 2'- CST 2= CST 0- CST 0'.

[0142] In step S3, based on the time difference of crankshaft 16 rotation under fire conditions, the two extreme values ​​of the ethanol concentration detection limit during the fire fault process are calculated by conversion ratio. These are the fire thresholds corresponding to the lowest and highest ethanol concentrations, respectively. The two thresholds serve as the core judgment basis for calculating the target fire threshold corresponding to the ethanol concentration between the two, ensuring the clarity of the detection range and diagnostic criteria. The calculation formulas for the fire thresholds corresponding to the lowest and highest ethanol concentrations are as follows:

[0143] In single-cylinder mode, one cylinder 11 fails to ignite, causing engine 10 to misfire. RevEmin index =0.75 Rev indexmin , RevEmax index =0.75 Rev indexmax ,

[0144] in,RevEmin index Minimum ethanol concentration vmin The corresponding single-cylinder misfire threshold, Rev indexmin Minimum ethanol concentration at the time of fire vmin The corresponding single-cylinder misfire index, RevEmax index The highest ethanol concentration vmax The corresponding single-cylinder misfire threshold, Rev indexmax The highest ethanol concentration at the time of the fire vmax The corresponding single-cylinder misfire index;

[0145] In cylinder deactivation mode, cylinder 11 of a pair of cylinders fails to ignite, causing engine 10 to misfire. CylEmin index =0.75 Cyl indexmin , CylEmax index =0.75 Cyl indexmax ,

[0146] in, CylEmin index Minimum ethanol concentration vmin The corresponding misfire threshold for cylinders, Cyl indexmin Minimum ethanol concentration at the time of fire vmin The corresponding misfire index, CylEmax index The highest ethanol concentration vmax The corresponding misfire threshold for cylinders, Cyl indexmax The highest ethanol concentration at the time of the fire vmax The corresponding misfire index;

[0147] In this embodiment, the minimum ethanol volume fraction of the ethanol gasoline is 27%, corresponding to the code E27, and the maximum ethanol volume fraction is 100%, corresponding to the code E100.

[0148] In this embodiment, the ethanol fuel is replaced, and the ethanol volume fraction of the ethanol gasoline increases from 27% to 61%, corresponding to a change in the code from E27 to E61.

[0149] like Figure 3 As shown, in step S4, since switching ethanol concentration may cause deviations in the misfire threshold calculation, a fault suppression strategy needs to be implemented during the ethanol fuel switching process; after refueling is completed and a fixed amount of fuel is injected, the final ethanol concentration is determined, and then the misfire diagnosis function is activated to accurately calculate the misfire threshold based on the final ethanol concentration.

[0150] When the ethanol concentration sensor detects a change in ethanol concentration, the electronic control unit 19 performs a diagnostic operation according to the following procedure:

[0151] Ethanol concentration learning: The amount of fuel to be injected to fill the low-pressure pipeline 3 is calculated based on the length and cross-sectional area of ​​the low-pressure pipeline 3, that is, the volume of ethanol fuel to be injected. The electronic control unit 19 controls the injector 15 to inject a fixed volume of ethanol fuel, thereby verifying and learning the current actual ethanol concentration and ensuring the accuracy of ethanol concentration detection.

[0152] The diagnostic function is temporarily disabled during the ethanol concentration learning process to avoid misdiagnosis caused by fluctuations in ethanol concentration during the learning process.

[0153] Normal diagnosis and threshold calculation: After the ethanol concentration is successfully learned, the misfire diagnosis function is immediately activated. At the same time, the electronic control unit 19 calculates the misfire threshold under the corresponding speed and load based on the currently confirmed ethanol concentration, and enters normal operation diagnosis.

[0154] In step S4, for ethanol concentrations between the minimum and maximum ethanol concentrations, the corresponding misfire threshold can be calculated by combining the combustion characteristics of ethanol fuel. The calculation formula for the misfire threshold corresponding to the target ethanol concentration is as follows:

[0155] Engine 10 single-cylinder mode, RevEn index = RevEmin index + α ( RevEmax index - RevEmin index ),

[0156] in, RevEn index Ethanol concentration vn The corresponding single-cylinder misfire threshold, RevEmin index Minimum ethanol concentration vmin The corresponding single-cylinder misfire threshold, RevEmax index The highest ethanol concentration vmax The corresponding single-cylinder misfire threshold, α The coefficient is derived from the ethanol concentration, i.e. α =( vn - vmin ) / ( vmax - vmin );

[0157] Engine 10-cylinder mode, CylEn index = CylEmin index +α ( CylEmax index - CylEmin index ),

[0158] in, CylEn index Ethanol concentration vn The corresponding misfire threshold for cylinders, CylEmin index Minimum ethanol concentration vmin The corresponding misfire threshold for cylinders, CylEmax index The highest ethanol concentration vmax The corresponding misfire threshold for cylinders, α The coefficient is derived from the ethanol concentration, i.e. α =( vn - vmin ) / ( vmax - vmin ).

[0159] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A misfire diagnosis method based on ethanol fuel concentration, characterized in that, The method includes the following steps: S1. Determine the enabling condition; S2. Determine the fire detection mode; S3. Experimentally calculate the extreme value of the fire threshold. Using ethanol fuel with the lowest and highest ethanol concentrations respectively, crankshaft rotation time data were collected at the corresponding ethanol concentrations and the misfire threshold was calculated. S4. Read the ethanol concentration and calculate the fire threshold based on the ethanol concentration. Read the ethanol concentration, and calculate the fire threshold corresponding to the target ethanol concentration based on the fire thresholds corresponding to the lowest and highest ethanol concentrations, and the coefficient derived from the ethanol concentration. S5. Determine the misfire rate and identify the misfire cylinder. Based on the fire index statistics, the fire rate is obtained, and the fire cylinder is determined accordingly. S6. Determine the type of fire detected; S7. Report the misfire test results and the misfire cylinder.

2. The misfire diagnosis method based on ethanol fuel concentration according to claim 1, characterized in that, In step S1, check if there is a misfire detection fault. Misfire detection faults include crankshaft signal loss, water temperature sensor short circuit, intake pressure sensor short circuit, and electronic throttle module fault. Determine whether the diagnostic enabling condition parameters are within the diagnostic range. The diagnostic enabling condition parameters include atmospheric pressure, water temperature, engine speed, and battery voltage.

3. The misfire diagnosis method based on ethanol fuel concentration according to claim 1, characterized in that, In step S2, it is determined whether the engine misfire is a single-cylinder misfire or a cylinder-to-cylinder misfire.

4. The misfire diagnosis method based on ethanol fuel concentration according to claim 1, characterized in that, The fire risk index is calculated as follows: The misfire index in single-cylinder mode of the engine is calculated by comparing the time difference of a single cylinder's complete stroke when the crankshaft rotates to an independent reference point. The independent reference point corresponds to a tooth position on the crank position signal disk. The formula for calculating the misfire index in single-cylinder mode of an engine is as follows: Rev index = CST 4-2 CST 2+ CST 0， in, Rev index This refers to the misfire index per cylinder. CST 0 represents the moment when the crankshaft sensor scans an independent reference point during the first revolution of the engine. CST 2 represents the moment when the crankshaft sensor scans an independent reference point during the second revolution of the engine. CST 4 represents the moment when the crank position sensor scans an independent reference point after the engine has rotated its second revolution; The misfire index of the engine cylinder-matching mode is calculated by comparing the time difference between the two cylinders when the crankshaft rotates to an independent reference point. The independent reference point corresponds to two teeth on the crank position signal disk, and the alignment angle between the two teeth of the independent reference point is 180 CA °. The formula for calculating the misfire index in cylinder-matching mode of an engine is as follows. Cyl index = CST 2-2 CST 1+ CST 0， in, Cyl index To determine the cylinder misfire index, CST 0 represents the moment when the crankshaft sensor scans an independent reference point during the first revolution of the engine. CST 1 represents the moment when the crankshaft sensor scans another independent reference point during the first revolution of the engine. CST 2 represents the moment when the crank position sensor scans an independent reference point after the engine has rotated its first revolution; The formula for calculating the misfire index in engine cylinder mode when mechanical error exists in the crank position signal disc is as follows. Cyl index '= Cyl index +2 δ ， in, Cyl index 'This is the cylinder misfire index when mechanical errors are present.' δ The time deviation for scanning an independent reference point by a curvature sensor is subject to mechanical error.

5. The misfire diagnosis method based on ethanol fuel concentration according to claim 1, characterized in that, In step S3, based on the time difference of crankshaft rotation under fire conditions, the two extreme values ​​of the ethanol concentration detection limit during the fire fault process are calculated by conversion ratio, namely the fire thresholds corresponding to the lowest and highest ethanol concentrations, respectively. The calculation formulas for the fire thresholds corresponding to the lowest and highest ethanol concentrations are as follows: In single-cylinder mode, one cylinder fails to fire, causing the engine to misfire. RevEmin index =0.75 Rev indexmin , RevEmax index =0.75 Rev indexmax , in, RevEmin index Minimum ethanol concentration vmin The corresponding single-cylinder misfire threshold, Rev indexmin The minimum ethanol concentration at the time of fire vmin The corresponding single-cylinder misfire index, RevEmax index The highest ethanol concentration vmax The corresponding single-cylinder misfire threshold, Rev indexmax The highest ethanol concentration at the time of the fire vmax The corresponding single-cylinder misfire index; In cylinder deactivation mode, one pair of cylinders fails to ignite, causing the engine to misfire. CylEmin index =0.75 Cyl indexmin , CylEmax index =0.75 Cyl indexmax , in, CylEmin index Minimum ethanol concentration vmin The corresponding misfire threshold for cylinders, Cyl indexmin The minimum ethanol concentration at the time of fire vmin The corresponding misfire index, CylEmax index The highest ethanol concentration vmax The corresponding misfire threshold for cylinders, Cyl indexmax The highest ethanol concentration at the time of the fire vmax The corresponding misfire index.

6. The misfire diagnosis method based on ethanol fuel concentration according to claim 1, characterized in that, In step S3, the minimum and maximum ethanol concentrations corresponding to the fire thresholds are calculated at any speed and load. The extreme values ​​of the fire thresholds at each speed and load are collected to obtain a calibrable table. Subsequently, the extreme values ​​of the fire thresholds can be retrieved from the calibrable table based on the speed and load.

7. The misfire diagnosis method based on ethanol fuel concentration according to claim 1, characterized in that, In step S4, when the ethanol concentration sensor detects a change in ethanol concentration, the diagnostic operation is performed according to the following procedure: Ethanol concentration learning involves controlling the injector to inject a fixed volume of ethanol fuel, thereby verifying and learning the current actual ethanol concentration. The diagnostic function has been temporarily disabled during the ethanol concentration learning process due to temporary adjustments. Normal diagnosis and threshold calculation: After the ethanol concentration is successfully learned, the misfire diagnosis function is activated. At the same time, based on the currently confirmed ethanol concentration, the misfire threshold under the corresponding speed and load is calculated, and normal operation diagnosis is entered.

8. The misfire diagnosis method based on ethanol fuel concentration according to claim 1, characterized in that, In step S4, the formula for calculating the misfire threshold corresponding to the target ethanol concentration is as follows: In single-cylinder mode of the engine, RevEn index = RevEmin index + α ( RevEmax index - RevEmin index ), in, RevEn index Ethanol concentration vn The corresponding single-cylinder misfire threshold, RevEmin index Minimum ethanol concentration vmin The corresponding single-cylinder misfire threshold, RevEmax index The highest ethanol concentration vmax The corresponding single-cylinder misfire threshold, α The coefficient is derived from the ethanol concentration, i.e. α =( vn - vmin ) / ( vmax - vmin ); Engine cylinder deactivation mode, CylEn index = CylEmin index + α ( CylEmax index - CylEmin index ), in, CylEn index Ethanol concentration vn The corresponding misfire threshold for cylinders, CylEmin index Minimum ethanol concentration vmin The corresponding misfire threshold for cylinders, CylEmax index The highest ethanol concentration vmax The corresponding misfire threshold for cylinders, α The coefficient is derived from the ethanol concentration, i.e. α =( vn - vmin ) / ( vmax - vmin ).

9. The misfire diagnosis method based on ethanol fuel concentration according to claim 1, characterized in that, In step S6, the types of misfires include catalyst damage misfires and emission damage misfires. Catalyst damage misfires are misfires that cause the catalyst temperature to reach the tolerance limit threshold, resulting in catalyst performance failure. Emission exceeding the standard misfires are misfires that cause exhaust pollutants to exceed the statutory standards or set limits. Catalyst-damaged misfires occur when the misfire rate reaches or exceeds the critical damage misfire rate, and emission-damaged misfires occur when the misfire rate does not reach the critical damage misfire rate.

10. A misfire diagnosis structure based on ethanol fuel concentration, characterized in that, The structure implements the method as described in any one of claims 1 to 9, wherein the engine (10) is electrically connected to the electronic control unit (19), and the structure includes a low-pressure section and a high-pressure section; In the low-pressure section, the fuel tank (1) is connected to the fuel pump (2), the fuel pump (2) is connected to the low-pressure pipeline (3), an ethanol concentration sensor is installed on the low-pressure pipeline (3), and the fuel pump (2) is electrically connected to the electronic control unit (19). In the high-pressure section, the high-pressure oil pump (6) is connected to the low-pressure pipeline (3) and the high-pressure pipeline (12), and the high-pressure oil pump (6) is electrically connected to the electronic control unit (19). The high-pressure pipeline (12) is connected to the high-pressure oil rail (14). The engine (10) is equipped with a cylinder (11) and a crankshaft (16). The high-pressure oil rail (14) is connected to the injector (15). The high-pressure oil rail (14) injects oil into the cylinder (11) through the injector (15). One end of the crankshaft (16) extending out of the cylinder (11) is connected to the crank position signal disk (17). A crank position sensor (18) is provided next to the crank position signal disk (17). The injector (15) and the crank position sensor (18) are electrically connected to the electronic control unit (19).

Images