Repair method for hot idle misfire fault of variable valve lift engine

Abstract

The present invention relates to the technical field of automobile fault repair methods, and specifically to a method for repairing a variable valve lift engine hot idle misfire fault. The method is carried out in the following steps: S1. The vehicle to be diagnosed is operated according to the fault diagnosis working condition, and then it is determined whether any cylinder of the engine has a hot idle misfire problem; S2. It is determined whether the cause of the hot idle misfire problem is due to the variable valve lift mechanism; S3. After determining that the cause of the fault is the variable valve lift mechanism, the type of fault is determined; S4. If it is a Class A fault, the angle of the torsion spring of the variable valve lift mechanism is adjusted according to the number of faults; if it is a Class B fault, the cam of the intermediate camshaft of the variable valve lift mechanism is repaired or replaced. The present application can accurately diagnose the engine hot idle misfire fault, accurately determine the cause of the hot idle misfire of the faulty cylinder, and perform corresponding repairs according to the specific cause, so that the engine hot idle misfire problem can be quickly repaired.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile fault repair methods, in particular to a method for repairing a hot idle misfire fault of a variable valve lift engine. Background Art

[0002] Typically, the valve lift of an engine is fixed, and the engine's air intake is regulated by controlling the throttle opening. However, this control method results in significant pumping losses, particularly under high load conditions, which can negatively impact fuel consumption. Continuously variable valve lift technology adjusts the valve lift according to the engine's operating conditions, thereby controlling air intake. This allows the throttle to remain at its maximum opening, effectively reducing fuel consumption and emissions while improving engine efficiency.

[0003] like Figure 1 The figure shows a continuously variable valve lift mechanism (VVL system) comprising a torsion spring 1, a stopper 2, a valve mechanism 5, a valve rocker arm 8, a worm gear 4, and a hydraulic tappet 9. One end of the valve rocker arm 8 is pressed against the valve mechanism 5, and the other end is connected to the hydraulic tappet 9 by a ball socket. The system also includes an intermediate camshaft 3 and a cam rocker arm 7. The cam rocker arm 7 includes a cam rocker arm end face at the lower end of the cam rocker arm 7, and first and second cam rocker arm rollers connected to the cam rocker arm 7. The cam rocker arm 7 end face contacts the valve rocker arm 8, the first cam rocker arm roller contacts the intermediate camshaft 3, and the second cam rocker arm roller contacts the cam 6. The torsion spring 1 is secured to the stopper 2 by bolt fasteners 10. An engine with this variable valve lift mechanism is continuously variable within the maximum valve lift range. However, engines currently equipped with this variable valve lift mechanism occasionally experience slight jitter at idle. While this won't cause a serious accident, it does affect the driver's comfort. The jitter disappears immediately when the accelerator is lightly pressed to increase the engine speed. Inspection revealed that the problem is a hot idle misfire, a subtle issue that can occur only occasionally. Furthermore, this variable valve lift mechanism, or VVL, system involves numerous components, and the multiple factors that can cause this hot idle misfire make it extremely difficult to diagnose and repair. Summary of the Invention

[0004] The purpose of the present invention is to solve the shortcomings of the above-mentioned background technology and provide a method for repairing the hot idle misfire fault of a variable valve lift engine.

[0005] The technical solution of the present invention is: a method for repairing a hot idle misfire fault in a variable valve lift engine, which is performed according to the following steps:

[0006] S1. Operating the vehicle to be diagnosed according to a fault diagnosis operating condition, recording the number of misfires in each cylinder when the engine reaches a first set speed and then returns to idle after releasing the throttle. If the number of misfires in a cylinder exceeds a first set value, the vehicle is determined to have a hot idle misfire fault. The cylinder with the misfire number exceeding the first set value is designated as the faulty cylinder, and the number of misfires in the faulty cylinder is designated as the fault number.

[0007] S2. Continue to operate the faulty vehicle according to the fault diagnosis operating condition, increase the engine speed to a second set speed while idling, and record the number of misfires of each cylinder of the engine after the speed reaches the second set speed; if the number of misfires of the faulty cylinder is less than the first set value, determine that the fault of the faulty cylinder is caused by the variable valve lift mechanism; if the number of misfires of the faulty cylinder is greater than or equal to the first set value, determine that the fault of the faulty cylinder is not caused by the variable valve lift mechanism, and the second set speed is greater than the first set speed;

[0008] S3. If it is determined that the fault of the faulty cylinder originates from the variable valve lift mechanism, the number of faults is compared with a second set value. If the number of faults is less than the second set value, the faulty cylinder is determined to be a Class A fault. If the number of faults is greater than or equal to the second set value, the faulty cylinder is determined to be a Class B fault, and the first set value is less than the second set value.

[0009] S4. If the faulty cylinder is a Class A fault, adjust the angle of the torsion spring of the variable valve lift mechanism according to the number of faults to repair the misfire fault of the faulty cylinder; if the faulty cylinder is a Class B fault, repair the intermediate camshaft of the variable valve lift mechanism to achieve the purpose of repairing the faulty cylinder.

[0010] According to a variable valve lift engine hot idle misfire fault repair method provided by the present application, in step S1, the method of operating the vehicle to be diagnosed according to the fault diagnosis working condition includes: connecting the ICNA software for diagnosing engine faults to the control system of the vehicle to be diagnosed, starting the engine of the vehicle to be diagnosed and preheating it to a water tank temperature not lower than a set temperature, shifting the gear of the vehicle to be diagnosed into neutral, turning off the air conditioner and fan, stepping on the accelerator, and increasing the speed to a first set speed.

[0011] According to a variable valve lift engine hot idle misfire fault repair method provided by the present application, in step S2, if the number of misfires of the faulty cylinder is greater than or equal to a first set value, it is determined that the fault of the faulty cylinder is caused by the fuel injector or ignition coil, and the fuel injector or ignition coil of the faulty cylinder is inspected and repaired.

[0012] According to a variable valve lift engine hot idle misfire fault repair method provided by the present application, in step S4, the method of adjusting the angle of the torsion spring of the variable valve lift mechanism according to the number of faults to repair the misfire fault of the faulty cylinder includes: obtaining the clockwise deflection angle a of the torsion spring of the variable valve lift mechanism corresponding to the current faulty cylinder, if the number of faults is less than a third set value, deflecting the torsion spring a / 2 in the counterclockwise direction; if the number of faults is greater than or equal to the third set value, deflecting the torsion spring a in the counterclockwise direction; the first set value is less than the third set value and less than the second set value.

[0013] According to a variable valve lift engine hot idle misfire fault repair method provided by the present application, in step S4, the method of repairing the intermediate camshaft of the variable valve lift mechanism includes: adjusting the base circle tolerance of the intermediate camshaft of the variable valve lift mechanism so that the base circle tolerance is smaller than the standard tolerance; or replacing the intermediate camshaft whose base circle tolerance is smaller than the standard tolerance.

[0014] According to a variable valve lift engine hot idle misfire fault repair method provided by the present application, the first set value is 36 to 40 times.

[0015] According to a variable valve lift engine hot idle misfire fault repair method provided by the present application, the second set value is 56 to 60 times.

[0016] According to a variable valve lift engine hot idle misfire fault repair method provided by the present application, the third set value is 40 to 48 times.

[0017] According to a variable valve lift engine hot idle misfire fault repair method provided by the present application, the first set speed is 1500 rpm; the second set speed is 2000 rpm.

[0018] According to a variable valve lift engine hot idle misfire fault repair method provided by the present application, the standard tolerance is ±0.025mm.

[0019] The advantages of this application are as follows: 1. This application performs fault diagnosis on the vehicle to be diagnosed to determine whether the vehicle has a hot idle misfire problem, and makes targeted adjustments based on the vehicle with the hot idle misfire problem. The hot idle misfire problem is divided into three situations: non-VVL factors, clockwise offset of the torsion spring, and increased tolerance of the intermediate camshaft base circle. Different fault situations have different definition methods and different repair methods. This application can effectively solve the problem of vehicle hot idle misfire, accurately define the specific situation of the vehicle hot idle misfire fault, provide great convenience for vehicle repair, and has great promotion value.

[0020] 2. This application detects the engine operation of the vehicle to be diagnosed at idle speed. When the vehicle to be diagnosed is in the diagnostic working condition, it can simulate the idle state of the vehicle to be diagnosed under actual use, providing a simulation basis for accurately determining whether the vehicle to be diagnosed has a fault, and the diagnostic judgment mode is extremely simple;

[0021] 3. The misfire frequency of the faulty cylinder in the present application may decrease after the speed exceeds a second set speed. By comparing the misfire frequency of the faulty cylinder after the speed exceeds the second set speed with the first set value, it is possible to accurately determine whether the fault of the current faulty cylinder is caused by the variable valve lift mechanism. This determination method is simple and efficient.

[0022] 4. After determining that the faulty cylinder belongs to fault type A, the present application can perform corresponding repair adjustments based on the deflection angle of the torsion spring of the variable valve lift mechanism. If the faulty cylinder has a low frequency of failure, the clockwise deflected torsion spring can be directly adjusted in the counterclockwise direction by half the deflection angle. If the faulty cylinder has a high frequency of failure, the torsion spring can be adjusted to be aligned to solve the idle misfire problem. The adjustment of the present application fully considers the frequency of failure and the elasticity of the torsion spring, ensuring that the faulty cylinder can be repaired without damaging the elasticity of the torsion spring.

[0023] 5. After determining that the faulty cylinder is a Class B fault, the present application can determine that the idle misfire problem of the current faulty cylinder is caused by the excessive base circle tolerance of the intermediate camshaft of the variable valve lift mechanism. Therefore, the base circle tolerance of the intermediate camshaft can be adjusted to resolve the idle misfire problem. The entire repair and adjustment method is simple and the fault definition is accurate.

[0024] 6. The first set value of this application is 36 to 40 times. The reason for setting the first set value is that it can accurately determine whether an idle misfire fault occurs based on the first set value. The above number of misfires is also the minimum limit that can be felt by the driver, providing a good basis for accurately defining the engine hot idle misfire fault;

[0025] 7. The second set value of the present application is 56 to 60 times. The second set value is used to distinguish the fault type of the faulty cylinder. By comparing the second set value with the number of faults, the fault type of the faulty cylinder can be accurately determined. The determination method is simple and accurate.

[0026] 8. The third setting value of the present application is to subdivide the cylinder fault when the faulty cylinder is a Class A fault, thereby determining the angle of the torsion spring deflection repair of the faulty cylinder, so as to repair the hot idle misfire fault without damaging the torsion spring elastic force as much as possible;

[0027] 9. This application sets a first set speed and a second set speed. The purpose of the first set speed is to simulate the vehicle's daily use, such as idling while waiting at a traffic light, to provide a good simulation state for subsequent determination of whether hot idle misfire problems occur. The second set speed is to eliminate problems other than the vehicle's fuel injector, ignition coil, and variable valve lift mechanism.

[0028] 10. This application defines the base circle tolerance of the intermediate camshaft. By redefining the standard tolerance of the base circle, it ensures that after determining that the fault type of the faulty cylinder is Class B, the hot idle misfire problem of the faulty cylinder can be accurately repaired.

[0029] This application can accurately diagnose engine hot idle misfire faults, accurately determine the cause of the faulty cylinder idle misfire, and perform corresponding repairs based on the specific cause. It can quickly repair the engine hot idle misfire problem. The diagnostic and repair method is simple and efficient, and has great promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 : Schematic diagram of the variable valve lift mechanism structure;

[0031] Figure 2 : Schematic diagram of the torsion spring deflection structure;

[0032] Figure 3 : Flowchart of the fault repair method of this application;

[0033] Among them: 1—torsion spring; 2—limit block; 3—intermediate camshaft; 4—worm gear; 5—valve mechanism; 6—cam; 7—cam rocker arm; 8—valve rocker arm; 9—hydraulic tappet; 10—bolt fastener. DETAILED DESCRIPTION

[0034] The embodiments of the present invention are described in detail below, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but are not to be construed as limiting the present invention.

[0035] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0036] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] The present application relates to a method for repairing a hot idle misfire in a variable valve lift engine. The repair method of the present application is mainly aimed at repairing the misfire problem of a car when idling. In daily use of a car, especially when waiting for a traffic light, when the engine enters the hot idle state, the engine cylinder may experience a hot idle misfire problem, causing the vehicle to shake. The key is that this shaking or hot idle misfire problem is relatively hidden and not easy to find. The occasional vibration does not affect the normal use of the vehicle, but it will affect the driver's perception. The present application proposes a fault repair method for this hot idle misfire problem, which can accurately determine the type of fault and perform corresponding repair operations according to the specific fault type, thereby repairing the engine's hot idle misfire fault.

[0039] Specifically, such as Figure 3 As shown, follow these steps:

[0040] S1. Operating the vehicle to be diagnosed according to a fault diagnosis operating condition, counting the number of misfires in each cylinder when the engine reaches a first set speed and then returns to idle after releasing the throttle. If the number of misfires in a cylinder exceeds a first set value, the vehicle is determined to have a hot idle misfire fault. The cylinder with the misfire number exceeding the first set value is designated as the faulty cylinder, and the number of misfires in the faulty cylinder is designated as the fault number.

[0041] When a vehicle has a hot idle misfire fault, the driver can only make a subjective judgment and cannot be sure that the engine has a hot idle misfire fault problem. Therefore, it is necessary to perform a fault diagnosis on the vehicle to be diagnosed to determine whether the vehicle to be diagnosed has a hot idle misfire fault problem. If the hot idle misfire problem does not exist, then there is no need to perform subsequent operations to avoid false alarms.

[0042] When conducting preliminary fault diagnosis on a vehicle to be diagnosed, a fault diagnosis operating condition is constructed and the vehicle to be diagnosed is operated according to the fault diagnosis operating condition. The fault diagnosis operating condition simulates the normal daily use of the vehicle. By simulating the daily use of the vehicle and recording the number of misfires when the vehicle returns to the idle state, it is possible to accurately determine whether the current engine has a hot idle misfire problem. This judgment method is close to the actual application of the vehicle, the judgment result is more accurate, and the problem of false alarms is eliminated.

[0043] S2. The faulty vehicle is operated continuously according to the fault diagnosis operating condition. After increasing the engine speed to a second set speed at idle, the number of misfires of each cylinder of the engine after the speed reaches the second set speed is counted; if the number of misfires of the faulty cylinder is less than the first set value, it is determined that the fault of the faulty cylinder is caused by the variable valve lift mechanism; if the number of misfires of the faulty cylinder is greater than or equal to the first set value, it is determined that the fault of the faulty cylinder is not caused by the variable valve lift mechanism, and the second set speed is greater than the first set speed;

[0044] The faulty vehicle with hot idle misfire fault also needs to analyze the fault cause. The purpose of this step is mainly to rule out some faults caused by non-variable valve lift mechanism. There may be many reasons for hot idle misfire fault, but the main reason is caused by variable valve lift mechanism. Eliminating the problem caused by non-variable valve lift mechanism can provide a good foundation for subsequent fault repair.

[0045] The problem of automobile hot idle misfire is mainly manifested in the idling process. When the speed of the automobile engine gradually increases from the idle state, the number of misfires may gradually decrease and disappear (because in the medium and high speed stages, the first cam rocker arm roller of the cam rocker arm 7 no longer contacts the cam base circle segment of the intermediate camshaft 3, but instead contacts the lobe segment of the cam, and the valve lift becomes larger). At this time, it can be judged that the cause of the vehicle's hot idle misfire is caused by the variable valve lift mechanism; if the number of misfires of the faulty cylinder does not decrease during the process of increasing speed, and the hot idle misfire fault does not improve, it proves that the cause of the fault is not caused by the variable valve lift mechanism.

[0046] S3. If it is determined that the fault of the faulty cylinder originates from the variable valve lift mechanism, the number of faults is compared with a second set value. If the number of faults is less than the second set value, the faulty cylinder is determined to be a Class A fault. If the number of faults is greater than or equal to the second set value, the faulty cylinder is determined to be a Class B fault, and the first set value is less than the second set value.

[0047] After determining that the cause of the faulty cylinder is from the variable valve lift mechanism, it is necessary to further distinguish the fault type of the faulty cylinder and analyze the specific cause of the faulty cylinder. Repairs will be carried out according to the specific cause of the fault later.

[0048] For faulty cylinders with a fault frequency less than the second set value, this type of fault is a relatively minor hot idle misfire fault, and the number of misfires is relatively small; for faults with a fault frequency greater than or equal to the second set value, the hot idle misfire fault is more serious, and the number of misfires is greater.

[0049] S4. If the faulty cylinder is a Class A fault, adjust the angle of the variable valve lift mechanism's torsion spring based on the fault frequency to correct the misfire in the faulty cylinder. If the faulty cylinder is a Class B fault, repair or replace the intermediate camshaft in the variable valve lift mechanism to correct the misfire in the faulty cylinder.

[0050] The main reason for hot idle misfire is that there are many misfires in the cylinder and insufficient combustion pressure at idle and low speeds. This means that either the intake valve lift is too far off at this stage, causing too much or too little air to be injected and ignition to fail, or the actual valve closing time is delayed relative to the start of ignition, causing the gas in the cylinder to be discharged prematurely.

[0051] Class A faults are relatively minor faults. After checking the vehicles with such faults, it was found that the torsion springs of the variable valve lift mechanisms of such vehicles are all rotated clockwise (clockwise in this application refers to observing the torsion spring from the side of the middle camshaft, such as Figure 1 Observe the torsion spring from left to right in the figure. The direction perpendicular to the paper is clockwise, and the direction perpendicular to the paper is counterclockwise). By adjusting the deflection direction and angle of the torsion spring, this type of fault can be eliminated. Therefore, this type of fault can be repaired by adjusting the deflection angle of the torsion spring.

[0052] Type B faults are more serious. At this time, simply adjusting the torsion spring deflection angle cannot completely repair the hot idle misfire fault. After checking vehicles with such faults, it was found that the intermediate camshaft of the variable valve lift mechanism of such vehicles has a large deviation in the base circle. At idle and low speeds, the cam base circle segment of the intermediate camshaft contacts the cam rocker arm roller. The intermediate camshaft with a large base circle deviation will cause this misfire problem. In order to repair Type B faults, it is necessary to adjust the base circle of the intermediate camshaft or replace the intermediate camshaft with a smaller base circle tolerance.

[0053] The above are the main methods for repairing engine hot idle misfire faults. The method of this application has been verified, and it has been proved that the above method is feasible and can effectively solve the problem of hot idle misfire faults of automobile engines.

[0054] In some embodiments of the present application, this embodiment optimizes the above-mentioned step S1. Specifically, in the above-mentioned step S1, the method for operating the vehicle to be diagnosed according to the fault diagnosis working condition is: connecting the ICNA software for diagnosing engine faults to the control system of the vehicle to be diagnosed, starting the engine of the vehicle to be diagnosed and preheating it to a water tank temperature not lower than a set temperature, shifting the gear of the vehicle to be diagnosed into neutral, turning off the air conditioner and fan, stepping on the accelerator, increasing the speed to a first set speed, then releasing the accelerator to return to idle speed, and starting to record the misfire count of each cylinder.

[0055] ICNA software is used to record the number of misfires in each cylinder of the engine during the diagnostic process. The set temperature in this embodiment is 80°C, which is the water tank temperature in most daily vehicle conditions. The vehicle is in neutral position to facilitate diagnostic operations, and turning off the air conditioner and fan reduces interference factors and avoids misdiagnosis. In this embodiment, the fault diagnosis and maintenance personnel can lightly step on the accelerator pedal to slowly increase the engine speed to the first set speed, and then release the accelerator to allow the engine to enter the idle state. This process actually simulates the process of the engine entering the idle state while waiting at a traffic light.

[0056] During this process, the number of misfires in each cylinder of the engine from the first set speed to the idle speed is recorded separately. If the number of misfires in all cylinders is equal or has little difference, and is lower than a certain threshold value (which can be obtained through calibration test), then each cylinder is running smoothly without misfire. If the number of misfires in a cylinder exceeds this threshold value, then there is an abnormality in the cylinder. Further testing with a cylinder pressure tester reveals that the combustion pressure of the faulty cylinder is significantly lower than that of other normal cylinders.

[0057] This embodiment primarily discusses the issue of hot idle misfire in a single cylinder. If two or more cylinders in an engine experience hot idle misfire simultaneously, it represents a more serious engine failure. This type of failure is highly noticeable, with either severe vibration or a direct alarm from the control system. It is not a hidden, difficult-to-find fault. In the event of such a severe problem, the driver will promptly discover it and initiate repairs. Therefore, this embodiment primarily addresses the issue of hot idle misfire in a single cylinder.

[0058] In a further embodiment of the present application, this embodiment optimizes the above-mentioned step S2. Specifically, in the above-mentioned step S2, if the number of misfires of the faulty cylinder is greater than or equal to a first set value, it is determined that the fault of the faulty cylinder is caused by the fuel injector or the ignition coil, and the fuel injector or the ignition coil of the faulty cylinder is repaired or replaced.

[0059] In a preferred embodiment of the present application, this embodiment optimizes the above-mentioned step S4. Specifically, in the above-mentioned step S4, the method for adjusting the angle of the torsion spring of the variable valve lift mechanism according to the number of faults to repair the misfire fault of the faulty cylinder includes: obtaining the clockwise deflection angle a of the torsion spring of the variable valve lift mechanism corresponding to the current faulty cylinder (the clockwise deflection angle of the present application is not an arbitrary angle, generally a is less than or equal to 30°), if the number of faults is less than the third set value, deflecting the torsion spring a / 2 in the counterclockwise direction; if the number of faults is greater than or equal to the third set value, deflecting the torsion spring a in the counterclockwise direction, the first set value is less than the third set value and less than the second set value.

[0060] For slight vibration, when the number of faults is less than the second set value, the engine with such faults is investigated and it is found that the misfiring cylinders with such faults have common characteristics. Figure 2 The figure shows the front view of the torsion spring of the faulty cylinder. The torsion spring is fixed on the limit block. The torsion spring includes two torsion spring legs. The limit block is located between the two torsion spring legs. The gap between the leg on one side of the torsion spring and the right side of the limit block is R. Figure 2 As shown, the clearance between the other leg of the torsion spring and the left side of the stop block is L. However, when the aforementioned misfire occurs, it is found that R is less than L. Normally, R should be equal to L. When R is less than L, the torsion spring deflects clockwise. Therefore, when the torsion spring deflects clockwise, hot idle misfire may occur.

[0061] In response to this problem, the cause was analyzed. The torsion spring force is proportional to the deformation amount. The clockwise deviation of the torsion spring causes the deformation stroke of the torsion spring leg of the even valve to be reduced due to the pressure of the middle rocker arm, resulting in insufficient rebound force. In order to improve combustion efficiency, the variable valve lift engine makes the valve lift of the even valve greater than that of the odd valve in the idle and low-speed stages. This structure requires more torsion spring leg force for the even valve. The clockwise deviation of the torsion spring causes the valve closing of the even valve to be delayed. The greater the clockwise deviation, the greater the valve closing delay of the even valve, which will cause the gas in the cylinder to be discharged, resulting in insufficient combustion pressure in the faulty cylinder.

[0062] Adjust the deflection angle of the torsion spring and deflect it counterclockwise to resolve the issue of insufficient rebound force. However, different repair methods can be used for different fault frequency. If the fault frequency is less than the third set value, the misfire is relatively minor, and deflecting the torsion spring counterclockwise by a factor of 2 will effectively resolve the misfire. If the fault frequency is greater than or equal to the third set value, the situation is more serious, and the torsion spring needs to be fully deflected counterclockwise to restore the torsion spring to its centered state.

[0063] The reason why the torsion spring is not completely restored to the centered state when the number of faults is less than the third set value is mainly because the misfire fault is relatively minor and the torsion spring itself has been running for a long time in a misaligned state. If the adjustment amplitude is too large, the elastic force of the legs on both sides of the torsion spring may change significantly, which may drastically change the original balance state. Although it may solve the misfire problem, it will bring other problems. Therefore, for this minor misfire fault, it can be adjusted by deflecting half the angle counterclockwise.

[0064] For the case where the number of faults is greater than or equal to the third set value, this type of fire fault is more serious. Simply adjusting the deflection angle of the torsion spring in half counterclockwise is not enough to eliminate the fire fault. The torsion spring needs to be adjusted to the center state. If the problem of improper elastic force of the legs on both sides of the torsion spring still occurs, a new torsion spring needs to be replaced to repair the fault.

[0065] In some other embodiments of the present application, this embodiment optimizes the above-mentioned step S4. Specifically, in the above-mentioned step S4, the method for repairing the intermediate camshaft of the variable valve lift mechanism includes: adjusting the base circle tolerance of the intermediate camshaft of the variable valve lift mechanism so that the base circle tolerance is smaller than the standard tolerance; or replacing the intermediate camshaft whose base circle tolerance is smaller than the standard tolerance.

[0066] When the number of faults exceeds the second set value, the hot idle misfire in the faulty cylinder is more severe. Even after centering the torsion spring, the misfire in the faulty cylinder is not fully resolved. Investigation revealed that the base circle deviation of the intermediate camshaft in the variable valve lift mechanism is significant due to long-term use or machining precision issues. Since the intermediate cam's operating area is near the base circle at idle and low speeds, and at engine speeds exceeding 2000 rpm, the cam's operating area is in the cam lobe. Therefore, the large dimensional deviation near the base circle of the intermediate cam can cause differences in actual valve lift at idle and low speeds, resulting in abnormal air injection or valve closing timing. This in turn causes a drop in combustion pressure in the cylinder, leading to hot idle misfire in the faulty cylinder.

[0067] After checking the faulty cylinders with a fault frequency greater than or equal to the second set value, it was found that the intermediate camshaft base circle portion of the variable valve lift mechanism corresponding to the faulty cylinder had a large deviation. The base circle deviation of the intermediate camshaft was redefined and the standard tolerance of the base circle was set. The standard tolerance of this embodiment is ±0.025mm. The standard tolerance of this embodiment refers to the difference between the actual polar diameter of the intermediate camshaft base circle portion and the designed radius of the intermediate camshaft base circle portion (the designed base circle radius of this embodiment is 12.285mm). By testing a large number of engines with and without misfire faults, the following situations were found:

[0068] Table 1: Measurement of base circle tolerance of intermediate camshafts of faulty and non-faulty parts

[0069]

[0070] This indicates that the base circle tolerance of the intermediate camshaft in the variable valve lift mechanism corresponding to the cylinder experiencing the misfire problem is greater than the standard tolerance. Adjusting the base circle tolerance of the intermediate camshaft can effectively eliminate this problem. Adjusting the base circle tolerance of the intermediate camshaft can be done by removing the faulty intermediate camshaft and grinding the base circle (this adjustment method only applies when the base circle of the faulty intermediate camshaft is larger than the design radius), or by simply replacing the intermediate camshaft with one that meets the standard base circle tolerance. For the faults described in Table 1, replacing the intermediate camshaft with one that meets the standard base circle tolerance significantly reduces the number of misfires in the faulty cylinder, and the hot idle misfire problem in the faulty cylinder is resolved.

[0071] In some other embodiments of the present application, the above-mentioned set values ​​are set by conducting a large number of experiments. The first set value is 36 to 40 times, preferably 36 times; the second set value is 56 to 60, preferably 56 times; and the third set value is 40 to 48, preferably 48 times.

[0072] The first set speed is 1500 rpm, and the second set speed is 2000 rpm.

[0073] The engine idle speed in this application refers to the state where the engine is running in neutral gear, and the engine idle speed is 800 rpm.

[0074] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for repairing a hot idle misfire fault in a variable valve lift engine, characterized by: Follow these steps: S1. Operating the vehicle to be diagnosed according to a fault diagnosis operating condition, recording the number of misfires in each cylinder when the engine reaches a first set speed and then returns to idle after releasing the throttle. If the number of misfires in a cylinder exceeds a first set value, the vehicle is determined to have a hot idle misfire fault. The cylinder with the misfire number exceeding the first set value is designated as the faulty cylinder, and the number of misfires in the faulty cylinder in this step is designated as the fault number. S2. Continue to operate the faulty vehicle according to the fault diagnosis operating condition, increase the engine speed to a second set speed while idling, and count the number of misfires of each cylinder of the engine after the speed reaches the second set speed; if the number of misfires of the faulty cylinder is less than the first set value, determine that the fault of the faulty cylinder is caused by the variable valve lift mechanism; if the number of misfires of the faulty cylinder is greater than or equal to the first set value, determine that the fault of the faulty cylinder is not caused by the variable valve lift mechanism, and the second set speed is greater than the first set speed; S3. If it is determined that the fault of the faulty cylinder originates from the variable valve lift mechanism, the number of faults is compared with a second set value. If the number of faults is less than the second set value, the faulty cylinder is determined to be a Class A fault. If the number of faults is greater than or equal to the second set value, the faulty cylinder is determined to be a Class B fault, and the first set value is less than the second set value. S4. If the faulty cylinder is a Class A fault, adjust the angle of the torsion spring of the variable valve lift mechanism according to the number of faults to repair the misfire fault of the faulty cylinder; if the faulty cylinder is a Class B fault, repair the intermediate camshaft of the variable valve lift mechanism to achieve the purpose of repairing the faulty cylinder.

2. The method for repairing a hot idle misfire fault in a variable valve lift engine according to claim 1, characterized in that: In step S1, the method of operating the vehicle to be diagnosed according to the fault diagnosis working condition includes: connecting ICNA software for diagnosing engine faults to the control system of the vehicle to be diagnosed, starting the engine of the vehicle to be diagnosed and preheating it to a water tank temperature not lower than a set temperature, shifting the gear of the vehicle to be diagnosed into neutral, turning off the air conditioner and fan, and stepping on the accelerator to increase the speed to a first set speed.

3. The method for repairing a hot idle misfire fault in a variable valve lift engine according to claim 1, characterized in that: In step S2, if the misfire count of the faulty cylinder is greater than or equal to a first set value, it is determined that the fault of the faulty cylinder is caused by the fuel injector or the ignition coil, and the fuel injector or the ignition coil of the faulty cylinder is inspected and repaired.

4. The method for repairing a hot idle misfire fault in a variable valve lift engine according to claim 1, wherein: In step S4, the method for adjusting the angle of the torsion spring of the variable valve lift mechanism according to the number of faults to repair the misfire fault of the faulty cylinder includes: obtaining the clockwise deflection angle a of the torsion spring of the variable valve lift mechanism corresponding to the current faulty cylinder, if the number of faults is less than a third set value, deflecting the torsion spring a / 2 in the counterclockwise direction; if the number of faults is greater than or equal to the third set value, deflecting the torsion spring a in the counterclockwise direction; the first set value is less than the third set value and less than the second set value.

5. The method for repairing a hot idle misfire fault in a variable valve lift engine according to claim 1, characterized in that: In step S4, the method for repairing the intermediate camshaft of the variable valve lift mechanism includes: adjusting the base circle tolerance of the intermediate camshaft of the variable valve lift mechanism to make the base circle tolerance smaller than the standard tolerance; or replacing the intermediate camshaft whose base circle tolerance is smaller than the standard tolerance.

6. The method for repairing a hot idle misfire fault in a variable valve lift engine according to claim 1, characterized in that: The first set value is 36 to 40 times.

7. The method for repairing a hot idle misfire fault in a variable valve lift engine according to claim 1, characterized in that: The second set value is 56 to 60 times.

8. The method for repairing a hot idle misfire fault in a variable valve lift engine according to claim 4, characterized in that: The third set value is 40 to 48 times.

9. The method for repairing a hot idle misfire fault in a variable valve lift engine according to claim 1, characterized in that: The first set speed is 1500 rpm; the second set speed is 2000 rpm.

10. The method for repairing a hot idle misfire fault in a variable valve lift engine according to claim 5, characterized in that: The standard tolerance is ±0.025 mm.

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