KR102264304B1 - Misfire diagnosis method and device of Multi cylinder four-stroke engine - Google Patents

Abstract

Provided are a method and an apparatus for diagnosing whether a misfire has occurred for each cylinder of an engine using a tooth signal (the time required for an engine crankshaft to rotate at a certain angle) output from a crank angle sensor that recognizes a tooth of a target wheel. The misfire diagnosis method for a multi-cylinder engine according to the present invention includes a linear trend removing step for removing a linear trend from a tooth signal output by the crank angle sensor during one cycle, a step of generating a misfire diagnosis index for each cylinder using the tooth signal from which the linear trend is removed, and a misfire diagnosing step for diagnosing whether a misfire has occurred for each cylinder by comparing the extracted misfire diagnosis index with a set threshold value. Accordingly, the method and the apparatus can simply and accurately diagnose and detect a misfire for each cylinder of the engine from only the output signal of the crank angle sensor without additional sensor or equipment.

Description

Misfire diagnosis method and device of Multi cylinder four-stroke engine

The present invention relates to a method and apparatus for diagnosing a misfire of an engine, and more specifically, engine speed information calculated from a tooth signal (tooth time signal, time required for an engine crankshaft to rotate at a certain angle) measured by a crank angle sensor. It relates to a method and apparatus for diagnosing a misfire of an engine for diagnosing a misfire using

A phenomenon in which fuel injected from an engine using fossil fuels is discharged to the outside air as it is without combustion is called a misfire. When an engine misfire occurs, unburned fuel may be discharged as it is, adversely affecting air pollution, or unburned fuel may be burned in the catalyst to damage the catalyst.

Accordingly, in the case of automobiles, a misfire detection logic is installed in the ECU to diagnose a misfire, thereby preventing air pollution or damage to the catalyst. In the case of general mass-produced vehicles, the engine roughness method for diagnosing misfire by extracting engine speed from a tooth time signal measured by a crank angle sensor is mainly adopted.

The engine roughness method using engine speed variability covers the misfire detection area stipulated by CARB (USA California Air Environment Agency), but the area is limited, so it diagnoses misfire in some areas such as high RPM and low load sections. The disadvantage is that the accuracy is lowered.

A method of diagnosing a misfire by measuring an ionic current generated in a spark plug circuit during an explosion stroke is also known in addition to the method using the variability of the engine speed. Also, a method of diagnosing a misfire by directly measuring the combustion pressure of a cylinder has been known.

However, these methods (a method using an ion current or a method using a combustion pressure characteristic) increase the vehicle price because a new function or a new sensor must be added to the existing vehicle, which makes it difficult to apply to a mass-produced vehicle. There is bound to be a burden in terms of cost.

In order to solve this problem, a frequency analysis method has been proposed that detects whether the engine is misfired using the output signal measured from the crank angle sensor without adding a separate sensor or equipment, but the frequency analysis method has complicated diagnostic logic and , there is a problem that the amount of calculation is large and the memory usage is large, so it may not be used depending on the performance of the ECU.

Korean Patent Registration No. 10-1869324 (Registration Date 2018.06.14)

The technical problem to be solved by the present invention is to provide a method and apparatus for diagnosing misfire of a multi-cylinder engine that can simply and accurately diagnose/detect a misfire by cylinder only with an output signal of a crank angle sensor without adding a separate sensor or equipment would like to

According to one aspect of the present invention as a means of solving the problem,

A method of diagnosing whether a multi-cylinder engine (N-cylinder engine, where N is an even number of 4 or more) misfires using a tooth time signal output from a crank angle sensor that recognizes a tooth of a target wheel,

a) a linear trend removing step of removing a linear trend from the tooth signal output by the crank angle sensor during one cycle;

b) a misfire diagnostic index generating step of generating a misfire diagnostic index for each cylinder using the tooth signal from which the linear trend has been removed;

c) a misfire diagnosis step of diagnosing whether each cylinder has misfired by comparing the misfire diagnosis index extracted in step b) with a set threshold value;

Here, the set threshold is

Plotting the misfire diagnostic index on a three-dimensional graph having engine load and speed (rpm) as factors;

Convert the three-dimensional plotted misfire diagnostic index into a two-dimensional flat graph form viewed from the plane, and extract the representative values of the misfire diagnostic index for each section in the engine speed (rpm) and load (Load) regions. constructing an n*m grid in a dimensional graph;

extracting only the true story diagnostic index values located in each grid of the n*m grid from among the true story diagnostic indexes;

arbitrarily selecting a misfire diagnostic index capable of distinguishing between normal combustion and misfire among the misfire diagnostic indexes extracted from within each grid and setting it as a temporary threshold value, and calculating the misfire diagnostic rate for each grid while changing the set temporary threshold value;

deriving a critical plane by extracting an optimal value of a threshold value selection section in which the true story diagnosis rate calculated for each grid is maintained in a specific range and plotting it on a three-dimensional graph;

It can be extracted through the step of storing the misfire diagnostic index existing on the critical plane in the form of a data map for two factors of engine speed and load.

Preferably, the method may further include; correcting the critical plane based on the floating result so that the derived critical plane represents a smooth plane after the critical plane is derived in the process of extracting the set threshold value.

Here, the misfire diagnosis rate may be defined as any one of a ratio that is diagnosed as an actual misfire among artificially generated misfire signals, a ratio of the number of misfire diagnoses to the number of misfire signals, and a ratio that is a misfire signal among those diagnosed as misfire.

As a preferred example, the misfire diagnostic index is a line (L1) connecting the engine speeds of the initial intake stroke and the end of the exhaust stroke on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed and the engine speed for each cylinder. It may be an angle θ formed by a line L2 connecting the maximum value and the minimum value.

As another preferred example, the misfire diagnostic index is the engine speed on the line L1 connecting the engine speeds at the beginning of the intake stroke and the end of the exhaust stroke on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. It can be defined as the product (D1*D2) of the maximum and the shortest distances (D1, D2) to the minimum value.

_{As another preferred example, the misfire diagnosis index may include a difference between the maximum and minimum engine speed (rpm max} - rpm _min ) or the maximum engine speed on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. and the square of the difference of the minimum value ((rpm _max - rpm _min ) ² ). In some cases, it may be _{the difference (rpm max} ² - rpm _min ² ) between the square of the maximum value of the engine speed and the square of the minimum value for each cylinder.

As another preferred example, the misfire diagnostic index is the slope of the line L1 connecting the engine speeds at the beginning of the intake stroke and the end of the exhaust stroke on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. It may be the inclination of a line connecting two preset points on the engine speed curve (a line connecting engine speeds at two preset positions).

According to another aspect of the present invention as a means of solving the problem,

As a device for diagnosing whether an engine is misfired,

a crank angle sensor disposed around a target wheel of the engine crankshaft to generate a tooth time signal necessary for calculating engine speed;

a controller that analyzes the change in engine speed of one cycle from the tooth signal of the crank angle sensor and diagnoses whether a misfire occurs using the analysis result;

The controller is

a linear trend removing unit for removing a linear trend from the tooth signal output from the crank angle sensor during one cycle;

A misfire diagnostic index generator for generating a misfire diagnostic index for each cylinder using the tooth signal from which the linear trend has been removed;

There is provided a misfire diagnosis apparatus for an engine comprising a misfire diagnosis unit that compares the extracted misfire diagnosis index with a set threshold value to diagnose whether each cylinder is misfired.

The set threshold is plotted on a three-dimensional graph having the engine load and speed (rpm) as factors of the misfire diagnostic index, and the three-dimensional plotted misfire diagnostic index is converted into a two-dimensional flat graph when viewed from a plane. In order to extract a representative value of the misfire diagnostic index for each section in each area of engine speed (rpm) and load (Load), an n*m grid network is constructed in the converted two-dimensional graph, and among the misfire diagnostic indexes, the Extract only the true fire diagnostic index values located in each grid of the n*m grid, and randomly select a misfire diagnostic index that can distinguish between normal combustion and misfire among the extracted misfire diagnostic indexes within each grid and set it as a temporary threshold, Calculating the true story diagnosis rate for each grid while changing the temporary threshold, extracting the optimal value of the threshold value selection section in which the calculated true story diagnosis rate for each grid is maintained in a specific range, and plotting it on a three-dimensional graph to derive a critical plane , it can be extracted through the process of storing the misfire diagnostic index existing on the critical plane in the form of a data map for two factors of engine speed and load.

In addition, the misfire diagnostic index extracted by the misfire diagnostic index generator is a line connecting the engine speeds of the initial intake stroke and the end of the exhaust stroke for each cylinder on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. It may be an angle θ formed between L1 and a line L2 connecting the maximum and minimum engine speed values for each cylinder.

As another preferred example, the misfire diagnostic index is the engine speed on the line L1 connecting the engine speeds at the beginning of the intake stroke and the end of the exhaust stroke on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. It can be defined as the product (D1*D2) of the maximum and the shortest distances (D1, D2) to the minimum value.

_{As another preferred example, the misfire diagnosis index may include a difference between the maximum and minimum engine speed (rpm max} - rpm _min ) or the maximum engine speed on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. and the square of the difference of the minimum value ((rpm _max - rpm _min ) ² ). In some cases, it may be _{the difference (rpm max} ² - rpm _min ² ) between the square of the maximum value of the engine speed and the square of the minimum value for each cylinder.

As another preferred example, the misfire diagnostic index is the slope of the line L1 connecting the engine speeds at the beginning of the intake stroke and the end of the exhaust stroke on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. It may be the inclination of a line connecting two preset points on the engine speed curve (a line connecting engine speeds at two preset positions).

According to an embodiment of the present invention, some information about engine characteristics that can clearly distinguish between normal ignition and misfire (the initial engine speed of each cylinder and the engine speed at the end of the exhaust stroke, which can be known from the signal output from the crank angle sensor) , it is possible to accurately diagnose a misfire with only the maximum and minimum engine speed values for each cylinder.

In other words, by diagnosing/detecting a true story with only the minimum main information that can clearly determine whether a true story is true, it is possible to diagnose/detect the true story with high accuracy while simplifying the process for diagnosing/detecting the true story, without additional hardware configuration. Since it can be implemented only with software, it has the advantage of low development cost.

1 is a conceptual diagram of an engine misfire diagnosis apparatus according to an embodiment of the present invention;
2 is a graph showing engine speed variation according to elapsed time before and after removing the linear trend from the tooth signal data output by the crank angle sensor.
3 is an exemplary diagram for explaining a process of generating a true story diagnostic index.
4 is a view showing another preferred embodiment of a true story diagnostic index generated by a true story diagnostic index generator;
5 is experimental data, (a) of FIG. 5 is an engine speed curve extracted when ignition is normally made in all four cylinders without misfire during one cycle in a four-cylinder engine, and FIG. A graph showing the engine speed curve extracted when a misfire signal is sent to cylinder 4 to artificially cause a misfire.
6 to 10 are diagrams for explaining a process of deriving a threshold, which is a reference for misfire diagnosis.
11 is a flowchart illustrating a method for diagnosing an engine misfire according to an embodiment of the present invention.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings.

In describing the present invention, the terms used in the following specification are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise.

In addition, in this specification, terms such as "comprise" or "have" are intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification exist, but one or more other It is to be understood that this does not preclude the possibility of addition or presence of features or numbers, steps, operations, components, parts, or combinations thereof.

Also, terms such as first and second may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another.

In addition, terms such as “…unit”, “…unit”, “…module”, etc. described in the specification mean a unit that processes at least one function or operation, which may be implemented by hardware or software or a combination of hardware and software. can

In the description with reference to the accompanying drawings, the same reference numerals will be assigned to the same components, and repeated descriptions of the same components will be omitted. In the description of the present invention, when it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Hereinafter, the meaning of key terms used in describing embodiments of the present invention will be briefly reviewed.

Among terms used to describe an embodiment of the present invention, “one cycle” refers to a section in which the engine crankshaft rotates two wheels (720°), and includes intake-compression-explosion (combustion expansion)-exhaust strokes one at a time. means the section

For example, in a 4-stroke single-cylinder engine, when intake-compression-explosion-exhaust occurs one cycle, one cycle ends, and in the case of a 4-stroke 4-cylinder engine, four cylinders are installed in the prescribed order in the order of intake-compression-explosion- When the exhaust occurs once and rotates the crankshaft by two wheels (720°), one cycle is completed.

In addition, among terms used to describe the embodiment of the present invention, “misfire diagnostic index” refers to the initial intake stroke for each cylinder on the engine speed curve for one cycle generated from the tooth time signal output by the crank angle sensor. It means the angle θ formed by the line L1 connecting the engine speed at the end of the exhaust stroke and the line L2 connecting the maximum and minimum engine speed values for each cylinder.

As another example, the “misfire diagnostic index” is a line (L1) connecting the engine speed of each cylinder at the beginning of the intake stroke and the end of the exhaust stroke on the engine speed curve for one cycle generated from the tooth signal from which the linear trend has been removed. It may be the product (D1*D2) of the shortest distance (D1, D2) to the maximum and minimum values of the star engine speed.

As another example, the “misfire diagnostic index” is the difference between the maximum and minimum engine speed values for each cylinder (rpm _max - rpm _min ) or the engine for each cylinder on the engine speed curve for one cycle generated from the tooth signal from which the linear trend has been removed. It may be the square of the difference between the speed maximum value and the minimum value ((rpm _max - rpm _min ) ^{2 ).} In some cases, it may be _{the difference (rpm max} ² - rpm _min ² ) between the square of the maximum value of the engine speed and the square of the minimum value for each cylinder.

Alternatively, the “misfire diagnostic index” is the slope of the line (L1) connecting the engine speed of each cylinder at the beginning of the intake stroke and the end of the exhaust stroke on the engine speed curve for one cycle generated from the tooth signal from which the linear trend has been removed. Alternatively, it may be the inclination of a line connecting two preset points for each cylinder on the engine speed curve (a line connecting the engine speeds at two specific locations preset for each cylinder).

Here, the “maximum and minimum engine speed values” for each cylinder refer to the engine speed generated from the tooth signals at two specific positions among the tooth signals for each cylinder output by the crank angle sensor that detects the rotation angle or rotation position of the crankshaft during the one cycle described above. As a related value, the “two specific positions” may be preset positions as the rotational positions of the target wheels at which the maximum and minimum engine speed values for each cylinder appear.

And the “engine speed at the beginning of the intake stroke and the end of the exhaust stroke” for each cylinder is the engine speed at the beginning of the intake stroke and the end of the exhaust stroke for each cylinder among the tooth signals for each cylinder output by the crank angle sensor that detects the rotation angle or position of the crankshaft during the cycle. It may be a value related to the engine speed calculated from the tooth signal at the rotation position of the target wheel set corresponding to the rotation position of the crankshaft.

For reference, the tooth time signal means the time required for the engine crankshaft to rotate at a certain angle, and is formed at equal intervals around the outer surface of the target wheel concentrically installed at the tip of the crankshaft. It means a signal that the crankshaft position sensor recognizes and outputs a plurality of teeth.

In addition, the "misfire diagnosis rate" may be defined as any one of a ratio of misfire signals diagnosed as real misfire among artificially generated misfire signals, a ratio of the number of misfire diagnoses to misfire signals, and a ratio of misfire signals diagnosed as misfire signals.

1 is a conceptual diagram schematically illustrating an engine misfire diagnosis apparatus according to an embodiment of the present invention. With reference to this, an engine misfire diagnosis apparatus according to an embodiment of the present invention will be described. Hereinafter, a four-cylinder engine will be described as an example. do. However, the present invention is not limited to diagnosing a misfire of a four-cylinder engine, and discloses that it is a technology applicable to a single-cylinder engine as well as a two-cylinder or more multi-cylinder engine.

Referring to FIG. 1 , an engine misfire diagnosis apparatus according to an embodiment of the present invention includes a crank angle sensor 10 and a controller 20 . The controller 20 may be an ECU, and the crank angle sensor 10 is disposed around the target wheel 40 on the engine crankshaft 30, and according to the rotation of the target wheel 40, a tooth signal ( Tooth time signal) signal is generated.

A plurality of teeth are formed on the outer peripheral surface of the target wheel 40 to measure the angular velocity of the crankshaft 30, and when the target wheel 40 rotates, the crank angle sensor 20 The controller 20 calculates the angular velocity of the engine crankshaft 30 by using the tooth detection time information. Then, the engine speed is output from the calculated angular speed.

The controller 20 controls the energization state of the fuel injector 60 and the ignition coil 50 according to the driver's request for acceleration or deceleration through the operation of the accelerator pedal (not shown) to control the engine speed as well as the crank angle. From the tooth time signal of the sensor 10, the engine speed change of one engine cycle, which is the target of misfire analysis, is analyzed. Then, using the analysis results, it is diagnosed whether a misfire has occurred.

As mentioned in the background art, misfire refers to a phenomenon in which fuel injected into an engine cylinder is discharged to the outside air without combustion. When a misfire occurs, the periodicity of the tooth time signal (the time it takes for the engine crankshaft to rotate at a certain angle) is damaged because the energy source that accelerates the engine speed does not occur during the explosion (combustion expansion) stroke.

Misfire is manifested as no fuel combustion in the explosion stroke -> no combustion pressure -> reduction in piston speed -> reduction in crankshaft rotational momentum, which results in a longer tooth time and reduced engine speed. That is, when a misfire occurs, the energy source for driving the engine does not occur, so the engine speed decreases. Therefore, by analyzing the engine speed in one cycle, it is possible to diagnose whether a misfire occurs.

The present invention makes it possible to accurately and quickly diagnose/detect a misfire occurring in a multi-cylinder engine using the characteristic of engine speed change that occurs during a misfire. For this purpose, the controller 20 applied to this embodiment is a linear It includes a trend removing unit 22 and a true story diagnosis indicator generating unit 24 . It also includes a misfire diagnosis unit 29 that compares the extracted misfire diagnosis index with a set threshold value to diagnose whether each cylinder is misfired.

Let's take a closer look at the configuration of each part constituting the controller.

The linear trend removing unit 22 removes a linear trend from the tooth signal output from the crank angle sensor 10 (using linear regression) for one cycle. This is because, if the linear trend is not removed from the signal data output by the crank angle sensor 10, the post oscillation phenomenon that appears immediately after the misfire occurs may affect the engine speed variation for each cylinder.

If the post oscillation phenomenon that appears immediately after a misfire affects the engine speed fluctuation for each start, it may be difficult to accurately and precisely diagnose whether a misfire occurs. Therefore, it is preferable to remove the influence of the post oscillation phenomenon immediately after misfire on the engine speed in advance by removing the linear trend from the output signal data of the crank angle sensor 10 collected during one cycle.

Removing the linear trend from all the tooth signals in one cycle means subtracting these linear trend components from the engine speed calculated from all the tooth signals during one cycle. It is preferable to understand that the speed, that is, the engine speed at the beginning of the intake stroke and the engine speed at the end of the exhaust stroke for each cylinder is approximately the same.

In FIG. 2, (a) is a graph showing the engine speed change over time before removing the linear trend from the tooth signal data output by the crank angle sensor, and (b) is the engine speed change after removing the linear trend. It is a graph.

The misfire diagnostic index generating unit 24 generates a misfire diagnostic index by using a tooth signal at a specific location preset for each cylinder among the tooth signals from which the linear trend has been removed. For example, in the case of a 4-cylinder engine with 4 cylinders, a total of 4 misfire diagnostic indicators are generated for each cylinder during one cycle (while the crankshaft rotates two wheels (720°)). In the case of a 6-cylinder engine, a total of 6 misfire diagnostic indicators are generated for each start during one cycle.

For the process of generating a true story diagnostic index, reference will be made to FIG. 3 below.

3 is an exemplary view for explaining the process of generating a misfire diagnostic index, and there are 4 cylinders, that is, No. 1 (Cyl 1)-3 No. (Cyl 3) No. 4 (Cyl 4) No. 2 (Cyl 2) In a four-cylinder engine where combustion occurs in the order of cylinders (cylinders), the tooth signal output from the crank angle sensor 10 is classified for each cylinder and the engine speed change (y) according to the elapse of time (x-axis direction) after linear trend removal (Detrend) axial direction) are experimental data.

Referring to FIG. 3 , the misfire diagnostic index generated by the misfire diagnostic index generating unit 24 is preferably the initial intake stroke and exhaust for each cylinder on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. It may be an angle θ formed by a line L1 connecting each engine speed at the end of the stroke and a line L2 connecting the maximum and minimum engine speed values for each cylinder.

In the drawing, L1 is a point on the engine speed curve including the engine speed (first tooth)_rpm) component calculated from the tooth signal at the beginning of the intake stroke for each cylinder and the rotational position component of the target wheel 40 (FTH), A line connecting the engine speed (LTH (last tooth)_rpm) component calculated from the tooth signal at the end of the exhaust stroke for each cylinder and another point (LTH) on the engine speed curve including the rotation position component of the target wheel 40 it means.

More specifically, in FIG. 3 , FTH is a point including an engine speed (first tooth (FTH)_rpm) component on the y-axis and a rotational position component of the target wheel 40 on the x-axis, and LTH is also a y-axis Since it is a point that contains the engine speed (LTH(last tooth)_rpm) component on the upper side and the time component on the x-axis, using a simple formula (the equation of a straight line passing through two points), L1 can be derived without difficulty. .

L2 may be a line connecting two specific positions (two preset points) on the engine speed curve generated from the tooth signal. Here, the two specific positions are the rotational positions of the target wheels where the maximum and minimum engine speed values for each cylinder appear among the tooth signals output by the crank angle sensor that detects the rotation angle or rotation position of the crankshaft during one cycle. It may be a preset position. .

Likewise here, the two positions previously designated for extracting the maximum and minimum engine speed values for each cylinder also include engine speed (rpm _max, rpm _min ) components on the y-axis on the engine speed curve of FIG. 3 and time components on the x-axis Since it is a point including , L2 can be derived without difficulty by using a simple calculation process including the equation of a straight line passing through the two points.

4 is a diagram illustrating another preferred embodiment of a true story diagnostic index generated by a true story diagnostic index generator.

Referring to FIG. 4 , the misfire diagnostic index generated by the misfire diagnostic index generating unit 24 is the initial intake stroke and the end of the exhaust stroke for each cylinder on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. It can be defined as the product (D1*D2) of the shortest distances (D1, D2) from the maximum and minimum engine speed values for each cylinder on the line L1 connecting the engine speeds of (see Fig. 4 (a)).

The misfire diagnostic index generated by the misfire diagnostic index generating unit 24 is also shown in FIG. 4(b) , on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed, the engine-by-cylinder engine It may be the difference between the maximum and minimum speed values (rpm _max - rpm _min ) or the square of the difference between the maximum and minimum engine speed values for each cylinder ((rpm _max - rpm _min ) ² ).

In some cases, it may be _{the difference (rpm max} ² - rpm _min ² ) between the square of the maximum value of the engine speed and the square of the minimum value for each cylinder.

The misfire diagnostic index generated by the misfire diagnostic index generating unit 24 also shows the engine speed of each cylinder at the beginning of the intake stroke and at the end of the exhaust stroke on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. It is the slope of the connecting line L1 (see Fig. 4(c)), or a line connecting two preset points for each cylinder on the engine speed curve, although not shown in the drawing (engines at two specific positions preset for each cylinder) It can also be the slope of the line connecting the speed).

Here, the two points set in advance for each cylinder for generating the misfire diagnosis index are clearly differentiated from the engine speed increase pattern in normal ignition on the engine speed curve of FIG. As a possible point, it may be a point obtained through a prior repeated experiment or simulation. That is, the two points may be the points that best express the speed reduction caused by the misfire.

The information on the true story diagnostic index for each cylinder extracted from the true story diagnostic index generating unit 24 is provided to the misfire diagnostic unit 29, which sets the received information (true story diagnostic index) with a set threshold value and Compare and diagnose. More specifically, a misfire is diagnosed by fetching a corresponding threshold value from the recording device according to the current engine state (engine speed and size of load) and comparing it with the misfire diagnosis index.

Preferably, in applying the threshold value, the cylinder may be configured to diagnose a misfire by applying the same threshold value to cylinders having the same tooth section recognized by the crank angle sensor during the explosion stroke. Here, "a cylinder with the same tooth section recognized by the crank angle sensor during the explosion stroke" means a cylinder with the same stroke with a wheel (360°) phase difference based on the rotation of the crankshaft (or target wheel), that is, Administratively means a pair of cylinders.

For example, in the case of a 4-cylinder engine in which combustion occurs in the order of 1 (Cyl 1)-3 (Cyl 3)-4 (Cyl 4)-2 (Cyl 2), the misfire diagnosis unit ( 29) is to apply the same threshold (threshold _1), the cylinder to Executive pair and forms 1 4, and then diagnosing misfire, the second cylinder and the third time, the threshold (threshold ₁₎ and the other identical threshold ( Threshold ₂ ) means that the true story can be diagnosed.

5 is experimental data, (a) of FIG. 5 is an engine speed curve extracted when ignition is normally made in all four cylinders without misfire during one cycle in a four-cylinder engine, and FIG. This is a diagram showing the engine speed curve extracted when a misfire signal is sent to cylinder 4 to artificially cause a misfire. As shown in FIG. 3, the angle (θ) between L1 and L2 is used as a misfire diagnosis index. to be.

In normal ignition, an energy source that accelerates the engine speed is generated in each cylinder's explosion stroke. On the other hand, if a misfire occurs, there is no additional energy to accelerate the engine speed. As a result, as shown in FIG. 5, the misfire diagnostic index has a distinctly different pattern between the misfire and the normal ignition (Cylinders 1 and 3 in (a) where the normal ignition occurred and cylinders 1 and 3 in (b) where the misfire occurred). of the true story diagnostic index (θ)).

The present invention is such that the misfire diagnostic index appears in distinctly different ways depending on whether the misfire occurs (in Fig. 5, cylinders 1 and 3 in (a) where normal ignition occurred and cylinders 1 and 3 in (b) where the misfire occurred) It is to diagnose whether a true story is true by using the point where the true story diagnosis index (θ) is clearly different).

Specifically, the misfire diagnosis unit 29 may diagnose a misfire when the misfire diagnosis index exceeds a threshold value set in correspondence with each cylinder. To this end, when the misfire diagnosis unit 29 applied to this embodiment uses the angle θ between L1 and L2 as a misfire diagnosis index, the misfire diagnosis unit 29 detects a misfire according to whether the boundary of a threshold value set in correspondence with it in advance is exceeded. It may include an algorithm for diagnosing.

The set threshold, which is the standard for judging whether or not a misfire occurs, is a misfire diagnostic index that can distinguish between normal ignition and misfire by engine load and speed (rpm) through simulation or repeated experiments in the same simulated environment. The value may be a value stored in a matrix form for two factors of the engine load and engine speed on a dedicated map.

That is, when the current engine load and speed are input, the dedicated map may be configured to quickly diagnose a misfire by fetching a threshold value corresponding to the current engine load and speed condition and comparing it with a misfire diagnosis index.

A procedure for obtaining a setting threshold value serving as a reference for misfire diagnosis for each cylinder will be described in more detail with reference to FIGS. 6 to 10 .

6 shows the distribution of the misfire diagnosis index generated in the 4-cylinder engine in which combustion occurs in the order of the 1st (Cyl 1)-3 (Cyl 3)-4 (Cyl 4)-2 (Cyl 2) cylinder (cylinder). As a 3D graph showing, it is a graph showing the distribution of misfire diagnostic indicators when a misfire is artificially caused by blocking fuel injection of a preset cylinder (cylinder) at a preset timing while varying the engine load and speed.

In deriving the threshold, first, as shown in FIG. 6, the misfire diagnostic index is plotted on a three-dimensional graph having engine load (Load) and speed (rpm) as factors. For reference, in FIG. 6 , countless gray dots indicate the distribution of misfire diagnostic indicators during normal combustion, and colored dots indicate misfire in a specific cylinder at a preset timing. It shows the distribution of the true story diagnostic index extracted when it occurs.

Looking at the distribution of points indicating the misfire diagnostic index for each cylinder in FIG. 6 , it can be seen that the normal combustion and the misfire are clearly divided and distributed. Therefore, the large frame of the threshold derivation process described below is to create a critical plane that can distinguish between normal combustion and misfire in the middle region between normal combustion and misfire, and use the misfire diagnostic index existing on the critical plane for engine speed and load. Each section is extracted separately and recorded in the form of a map.

Continuing to examine the threshold value derivation process, as shown in FIG. 6 , after 3D plotting the true story diagnostic index, the 3D true story diagnostic index of FIG. 6 is converted into a 2D flat graph form viewed from a plane. And in order to extract the representative value of the misfire diagnostic index for each section (misfire diagnostic index that can distinguish misfire and normal combustion for each section) in each area of engine speed (rpm) and load, on the converted two-dimensional graph A grid of n*m is constructed (refer to FIG. 7).

Then, only the true story diagnostic index values located in each grid of the n*m grid are extracted from among the true story diagnostic indexes. For reference, FIG. 7 shows that the engine speed for forming the grid is ㅁ100 (rpm) width based on 700, 1400, 300, 4000, 5000, and 6000 (unit rpm), and the engine load is 14, 20, 30, Based on 40, 50, 60, 70, 80, 90 (unit %), 14 and 20 are test data showing an example of configuring a 6*9 grid with ㅁ3 and 30~90 with ㅁ5 as the width .

Of course, the width (engine width and load width) of two factors constituting the grid in FIG. 7 can be changed according to test data, and representative engine speeds (700, 1400, 300, 4000, 5000, 6000 ( Since the unit rpm)) can also be changed in the test data, it is not limited to the numerical value illustrated in FIG. 7 .

For example, in the case of a box represented by a blue bold line in FIG. 7 , (rpm, load) = (2900~3100, 55~65), and a representative value is an engine speed of 3000 and an engine load of 60 becomes this For reference, the reason for selecting the grid section as shown in FIG. 7 in a two-dimensional graph state in which the misfire diagnostic index is expressed only by engine speed and load is to ensure maximum homogeneity of the misfire diagnostic index value in the representative value.

Next, among the misfire diagnostic indicators extracted from within each grid, a misfire diagnostic index capable of distinguishing between normal combustion and misfire by section (for each grid) is randomly selected and set as a temporary threshold value, but the misfire diagnosis rate is increased by changing the set temporary threshold value. Calculate. For example, as shown in FIG. 8 , the false story diagnosis rate can be calculated while increasing the threshold value (temporary threshold value) by 10 in the section where the ^{true story diagnosis index is -0.5*10 4} to 0.5*10 ^{4 .}

Here, the misfire diagnosis rate is the ratio that is diagnosed as an actual misfire when artificially generated by blocking the fuel injection of a preset cylinder at a preset timing in the middle while varying the engine speed and load by using the temporary threshold as a standard for misfire determination means That is, when the temporary threshold is used as a criterion for determining a misfire, it means a ratio of artificially generated misfire signals diagnosed as an actual misfire.

For example, when a total of 100 misfires are artificially generated while the engine is running while varying the engine speed and load, and when 100 misfires are actually detected as a result of determining a misfire with the temporary threshold value, the misfire diagnosis rate is 1. The fact that the true story diagnosis rate is 1 means that the true story is accurately diagnosed without misdiagnosis when the temporary threshold is used as a criterion for judging the true story.

In addition to the above-mentioned ratio (the ratio of misfire signals diagnosed as real misfires), the misfire diagnosis rate is the ratio of the number of misfire diagnoses to the number of actual misfire signals (for example, the number of misfire diagnoses is 99 and the number of actual misfire signals is 100). In this case, the misfire diagnosis rate becomes 0.99) or it can be defined as the ratio of misfire signals among those diagnosed as misfires. All of the mentioned diagnosis rates mean that the closer the value is to 1, the higher the diagnosis accuracy.

9 shows the false fire diagnosis rate calculated while changing the temporary threshold value (misfire diagnosis index that can distinguish between normal combustion and misfire) when (rpm, load) = (3000, 50) as plotting test data, and the temporary threshold value This is test data showing the case in which the misfire diagnosis rate maintains 1 when it is set in the range of -4000 ~ -1300.

In the graph shown in FIG. 9, when a 6*9 grid network is configured as shown in FIG. 7, a total of 54 graphs are derived, one for each grid (for each engine load and speed section).

Subsequently, when the misfire diagnosis rate is calculated, the optimum value is extracted from the threshold value selection section (the section indicated by the arrow in Fig. 9) in which the misfire diagnosis rate calculated for each grid (by engine load and speed section) is maintained in a specific range, and then extracted A critical plane is derived by plotting the obtained value (the optimum value of the threshold value selection section) on a three-dimensional graph as shown in FIG. 10 .

Here, the specific range of the misfire diagnosis rate for determining the threshold selection interval may be a range in which the true story diagnosis rate is 0.99 to 1.01. However, the present invention is not limited thereto. Since there may be slight fluctuations depending on the test conditions, it is desirable to make a decision based on the data that varies depending on the test conditions.

And, the optimal value of the true story diagnostic index is preferably the middle value among the misfire diagnostic indexes belonging to the threshold selection section (section indicated by the arrow in FIG. 9), but this may also vary slightly depending on the test conditions, so it depends on the test conditions. It is desirable to make a decision based on different data.

In FIG. 10, gray dots and colored dots represent misfire diagnostic indicators during normal combustion and misfire, respectively, and are flat in the middle region that separates gray dots and colored dots. The figure expressed as an image represents a critical plane (a plane derived using the optimal value of the threshold selection section for each grid).

In FIG. 10 , the black bar in the middle vertical direction represents only the section in which the true fire diagnosis rate is 1 in the diagram ( FIG. 9 ) showing the above-mentioned false fire diagnosis rate for each test condition, and the red inverted triangle indicates that the true fire diagnosis rate is 1 It indicates the position of the optimal value, preferably the median value, of the interval, and it can be seen that the black bar and the critical plane meet in several grids (corresponding to the case where the most ideal threshold value is derived).

On the other hand, when the critical plane is derived as shown in FIG. 10, the threshold value derivation is completed by storing the misfire diagnostic index existing on the derived critical plane in the form of a data map for two factors of engine speed and load, and in some cases After the critical plane is derived, a process of correcting the critical plane may be performed based on the plotting result as shown in FIG. 10 so that the derived critical plane represents a smooth plane.

Hereinafter, a misfire diagnosis process performed by the engine misfire diagnosis apparatus will be described with reference to the flowchart of FIG. 11 .

11 is a flowchart illustrating a method for diagnosing a misfire of an engine according to an embodiment of the present invention. For convenience of description, the configuration shown in FIG. 1 refers to the corresponding reference numerals, and similarly, a four-cylinder engine will be described as an example.

Referring to FIG. 11 , the misfire diagnosis process performed by the engine misfire diagnosis apparatus according to the embodiment of the present invention largely includes a linear trend removal step (S100), a misfire diagnosis index generation step (S200), and a misfire diagnosis step (S300). ) is included. Hereinafter, the calculation or processing process for diagnosing a true story performed in each step will be described in more detail.

In the linear trend removal step ( S100 ), the rotation of the target wheel 40 is detected for one cycle and the linear trend is removed (Linear Detrend) from the tooth signal output by the crank angle sensor 10 . This is because, if the linear trend is not removed from the signal data output by the crank angle sensor, the post oscillation phenomenon that occurs immediately after the misfire may affect the engine speed fluctuation for each cylinder.

In some cases, in order to reduce the amount of signal data to be processed by selecting only the specific tooth signal of the crank angle sensor 10, thereby greatly reducing the computational load that the controller has to bear, only the signals necessary for diagnosing misfire are selected and linear Trends can also be removed. For example, the tooth signal can be collected only at the beginning of the intake stroke and the end of the exhaust stroke for each cylinder, and at the position of the target wheel where the maximum and minimum engine speed values are displayed.

In the true story diagnostic index generation step (S200), a myth diagnostic index for each cylinder is generated by using the tooth signal from which the linear trend is removed. More specifically, the misfire diagnosis index is calculated for each cylinder during one cycle by using the tooth signal output from a predetermined position (rotational position of the target wheel) for each cylinder among the tooth signals from which the linear trend has been removed through the step S100. create one by one

For example, if it is a four-cylinder engine with four cylinders, a total of four misfire diagnostic indicators are generated, one for each cylinder in one cycle.

The misfire diagnostic index generated in the misfire diagnostic index generating step (S200) is preferably the engine speed of each cylinder at the beginning of the intake stroke and at the end of the exhaust stroke on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. It may be an angle θ formed between the connecting line L1 and the line L2 connecting the maximum and minimum engine speed values for each cylinder (see FIG. 3 ).

For reference, a location for collecting a tooth signal for generating a misfire diagnostic index for each cylinder may be a rotational position of a target wheel which is preset and stored 4 for each cylinder. Two are the rotation positions of the target wheel 40 at the beginning of the intake stroke and the end of the exhaust stroke for each cylinder, and the other two are the rotation positions of the target wheel at which the maximum engine speed value (rpm _max ) and minimum value (rpm _min ) for each cylinder appear. can

As another example, the misfire diagnostic index generated in the misfire diagnostic index generating step (S200) is the engine speed of each cylinder at the beginning of the intake stroke and at the end of the exhaust stroke on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. It may be the product (D1*D2) of the shortest distance (D1, D2) between the maximum and minimum engine speed values for each cylinder on the line L1 connecting them (see Fig. 4(a)).

As another example, the misfire diagnostic index generated in the generating step (S200) of the misfire diagnostic index is the difference between the maximum and minimum engine speed values for each cylinder on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. (rpm _max - rpm _min ) or the square of the difference between the maximum and minimum engine speed values for each cylinder ((rpm _max - rpm _min ) ² ) (refer to (b) of FIG. 4 ).

In some cases, the misfire diagnostic index generated in the step of generating the misfire diagnostic index (S200) may be the difference between the square of the maximum value of the engine speed for each cylinder and the square of the minimum value (rpm _max ² - rpm _min ^{2 ).}

As another example, the misfire diagnostic index generated in the step of generating the misfire diagnostic index ( S200 ) includes the initial intake stroke and the end of the exhaust stroke for each cylinder on the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed. The slope of the line L1 connecting the engine speeds of (see Fig. 4(c)) or a line connecting two preset points for each cylinder on the engine speed curve (not shown in the drawing) (two preset points for each cylinder) It may be the slope of the line connecting the engine speed at a specific location).

In the misfire diagnosis step (S300), the misfire diagnosis index for each cylinder is analyzed by the misfire diagnostic index generated in the misfire diagnostic index generation step (S200) to diagnose the misfire for each cylinder. Preferably, the misfire diagnosis index for each cylinder generated in step S200 is compared with a set threshold value recorded in a recording device (eg, a memory storing the above-described dedicated map (threshold value map)) to diagnose whether misfire occurs.

In normal ignition, an energy source that accelerates the engine speed is generated in each cylinder's explosion stroke. On the other hand, if a misfire occurs, there is no additional energy to accelerate the engine speed. Therefore, as exemplified in FIG. 5 above, the misfire diagnostic index is clearly different from the misfire and normal ignition. Therefore, if there is information on the misfire diagnosis index for each maneuver, it is possible to accurately diagnose whether the misfire is issued.

In the misfire diagnosis step (S300), specifically, in applying the set threshold value for misfire diagnosis, the cylinders (cylinders forming a pair in the administration) are paired with the same threshold value by pairing the tooth section recognized by the crank angle sensor during the explosion stroke. can be applied. This is because, in terms of stroke, the paired cylinders have the same tooth section recognized by the crank angle sensor during the explosion stroke, so that the engine speed profile appears almost the same.

Meanwhile, in the misfire diagnosis step (S300), the set threshold value, which is a criterion for misfire determination, is as described above,

Plotting the misfire diagnostic index on a three-dimensional graph having engine load and speed (rpm) as factors;

Convert the three-dimensional plotted misfire diagnostic index into a two-dimensional flat graph form viewed from the plane, and extract the representative values of the misfire diagnostic index for each section in the engine speed (rpm) and load (Load) regions. constructing an n*m grid in a dimensional graph;

extracting only the true story diagnostic index values located in each grid of the n*m grid from among the true story diagnostic indexes;

arbitrarily selecting a misfire diagnostic index capable of distinguishing between normal combustion and misfire among the misfire diagnostic indexes extracted from within each grid and setting it as a temporary threshold value, and calculating the misfire diagnostic rate for each grid while changing the set temporary threshold value;

deriving a critical plane by extracting an optimal value of a threshold value selection section in which the true story diagnosis rate calculated for each grid is maintained in a specific range and plotting it on a three-dimensional graph;

It can be extracted through the step of storing the misfire diagnostic index existing on the critical plane in the form of a data map for two factors of engine speed and load.

According to the embodiment of the present invention discussed above, some information on engine characteristics that can clearly distinguish between normal ignition and misfire (initial engine speed and exhaust stroke for each cylinder, which can be known from the signal output from the crank angle sensor) It is possible to accurately diagnose a misfire with only the end engine speed and the maximum and minimum engine speed values for each cylinder.

In other words, by diagnosing/detecting a true story with only the minimum main information that can clearly determine whether a true story is true, it is possible to diagnose/detect the true story with high accuracy while simplifying the process for diagnosing/detecting the true story, without additional hardware configuration. Since it can be implemented only with software, it has the advantage of low development cost.

In the above detailed description of the present invention, only specific embodiments thereof have been described. However, it is to be understood that the present invention is not limited to the particular form recited in the detailed description, but rather, it is to be understood to cover all modifications and equivalents and substitutions falling within the spirit and scope of the present invention as defined by the appended claims. should be

10: crank angle sensor
20: controller
22: linear trend removal unit
24: true story diagnostic index generation unit
29: true story diagnosis department
30: crankshaft
40: target wheel
50: ignition coil
60: fuel injector

Claims (14)

A method of diagnosing whether an engine is misfired using a tooth time signal output from a crank angle sensor recognizing a tooth of a target wheel,
a) a linear trend removing step of equalizing the starting speed of the engine by subtracting the linear trend component from the engine speed calculated from all the tooth signals output by the crank angle sensor during one cycle;
b) generating a true story diagnostic index using the tooth signal from which the linear trend has been removed;
c) a misfire diagnosis step of diagnosing a misfire by comparing the misfire diagnosis index extracted in step b) with a set threshold value;
The set threshold is,
Plotting the misfire diagnostic index on a three-dimensional graph having engine load and speed (rpm) as factors;
Convert the three-dimensional plotted misfire diagnostic index into a two-dimensional flat graph form viewed from the plane, and extract the representative values of the misfire diagnostic index for each section in the engine speed (rpm) and load (Load) regions. constructing an n*m grid in a dimensional graph;
extracting only the true story diagnostic index values located in each grid of the n*m grid from among the true story diagnostic indexes;
arbitrarily selecting a misfire diagnostic index capable of distinguishing between normal combustion and misfire among the misfire diagnostic indexes extracted from within each grid and setting it as a temporary threshold value, and calculating the misfire diagnostic rate for each grid while changing the set temporary threshold value;
deriving a critical plane by extracting an optimal value of a threshold value selection section in which the true story diagnosis rate calculated for each grid is maintained in a specific range and plotting it on a three-dimensional graph;
A misfire diagnosis method of an engine extracted through; storing the misfire diagnosis index existing on the critical plane in the form of a data map for two factors of engine speed and load.
delete The method of claim 1,
The method of diagnosing misfire of an engine further comprising: correcting the critical plane based on the plotting result so that the derived critical plane represents a smooth plane after the critical plane is derived.
The method of claim 1,
The true diagnosis rate is,
Misfire diagnosis method of an engine, which is any one of the ratio of misfire signals diagnosed as real misfire among artificially generated misfire signals, the ratio of the number of misfire diagnoses to the number of misfire signals, and the ratio of misfire signals among those diagnosed as misfire
5. The method of any one of claims 1, 3 to 4,
The true diagnosis index is,
On the engine speed curve for one cycle generated from the tooth signal from which the linear trend has been removed, the line (L1) connecting the engine speeds of the initial intake stroke and the end of the exhaust stroke for each cylinder and the line connecting the maximum and minimum engine speed values ( A method for diagnosing a misfire of an engine, which is the angle θ formed by L2).
5. The method of any one of claims 1, 3 to 4,
The true diagnosis index is,
On the engine speed curve for one cycle generated from the tooth signal from which the linear trend has been removed, the shortest distance (D1, D1, A method for diagnosing engine misfire, defined as the product (D1*D2) of D2).
5. The method of any one of claims 1, 3 to 4,
The true diagnosis index is,
The linear regression that the engine speed difference between the engine speed maximum value and the minimum value on the curve for one cycle are generated from the tooth signal removal (rpm _max - rpm _min) or the engine speed maximum value and the rpm squared ((the difference between the minimum value _max - rpm _min ) ² ) or the difference between the square of the maximum and the minimum square of the engine speed for each cylinder (rpm _max ² - rpm _min ² ).
5. The method of any one of claims 1, 3 to 4,
The true diagnosis index is,
On the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed, the slope of the line L1 connecting the engine speeds at the beginning of the intake stroke and the end of the exhaust stroke, or two presets for each cylinder on the engine speed curve A method of diagnosing engine misfire, which is the slope of the line connecting the points (the line connecting the engine speeds at two specific preset locations).
A device for diagnosing engine misfire, comprising:
a crank angle sensor disposed around a target wheel of the engine crankshaft to generate a tooth time signal necessary for calculating engine speed;
a controller that analyzes the change in engine speed of one cycle from the tooth signal of the crank angle sensor and diagnoses whether a misfire occurs using the analysis result;
The controller is
a linear trend removing unit that equalizes the starting speed of the engine by subtracting the linear trend component from the engine speed calculated from all the tooth signals output by the crank angle sensor during one cycle;
A misfire diagnostic index generator for generating a misfire diagnostic index for each cylinder using the tooth signal from which the linear trend has been removed;
It is composed of a misfire diagnosis unit that compares the extracted misfire diagnosis index with a set threshold value and diagnoses whether each cylinder is misfired,
The set threshold is,
Plot the misfire diagnostic index on a three-dimensional graph with engine load and speed (rpm) as factors,
Convert the three-dimensional plotted misfire diagnostic index into a two-dimensional flat graph form viewed from the plane, and extract the representative values of the misfire diagnostic index for each section in the engine speed (rpm) and load (Load) regions. Constructs an n*m grid in the dimensional graph,
Extracting only the true story diagnostic index values located in each grid of the n*m grid among the true story diagnostic indexes,
Among the misfire diagnostic indicators extracted from each grid, a misfire diagnostic index capable of distinguishing between normal combustion and misfire is randomly selected and set as a temporary threshold, and the set temporary threshold is changed to calculate the misfire diagnostic rate for each grid.
The critical plane is derived by extracting the optimal value of the threshold selection section in which the false diagnosis rate calculated for each grid is maintained in a specific range and plotting it on a three-dimensional graph,
An engine misfire diagnosis device extracted through the process of storing the misfire diagnosis index existing on the critical plane in the form of a data map for two factors of engine speed and load.
delete 10. The method of claim 9,
The true story diagnostic index extracted by the true story diagnostic index generation unit is,
On the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed, the line (L1) connecting the engine speeds at the beginning of the intake stroke and the end of the exhaust stroke (L2) and the line connecting the maximum and minimum values of the engine speed (L2) The engine misfire diagnosis device, which is the angle θ formed by this.
10. The method of claim 9,
The true story diagnostic index extracted by the true story diagnostic index generation unit is,
On the engine speed curve for one cycle generated from the tooth signal from which the linear trend has been removed, the shortest distance (D1, D1, Engine misfire diagnosis device that is the product of D2) (D1*D2).
10. The method of claim 9,
The true story diagnostic index extracted by the true story diagnostic index generation unit is,
The linear regression that the engine speed difference between the engine speed maximum value and the minimum value on the curve for one cycle are generated from the tooth signal removal (rpm _max - rpm _min) or the engine speed maximum value and the rpm squared ((the difference between the minimum value _max - rpm _min ) ² ) or the difference between the square of the maximum and the minimum square of the engine speed for each cylinder (rpm _max ² - rpm _min ² ).
10. The method of claim 9,
The true story diagnostic index extracted by the true story diagnostic index generation unit is,
On the engine speed curve for one cycle generated from the tooth signal from which the linear trend is removed, the slope of the line L1 connecting the engine speeds at the beginning of the intake stroke and the end of the exhaust stroke, or two preset points on the engine speed curve The engine misfire diagnosis device, which is the slope of the connected line (the line connecting the engine speed at two specific locations preset for each cylinder).

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