JP2016098690A - Internal combustion engine misfire determination apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the determination (main determination) as to whether a misfire occurs without missing an opportunity.SOLUTION: An internal combustion engine misfire determination apparatus comprises: a misfire correlation acquisition unit; a rotation variation acquisition unit that acquires a differential amount between a misfire correlation value of one cylinder and a misfire correlation value of the other cylinder having a specific relation with one cylinder in an ignition order as a rotation variation of the one cylinder; and a misfire determination unit that determines that there is a probability that a misfire occurred in a specific cylinder that is a cylinder of which the rotation variation exceeding a predetermined threshold is acquired when the acquired rotation variation exceeded the predetermined threshold, the misfire determination unit being configured to select the cylinder corresponding to a larger rotation variation out of rotation variations of the two cylinders as the specific cylinder when the rotation variations of the two cylinders adjacent in the ignition order continuously exceed the predetermined threshold.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a misfire determination apparatus for an internal combustion engine that determines the presence or absence of misfire based on the amount of change in engine rotation speed.

  Focusing on the fact that the rotational speed of the internal combustion engine fluctuates when a misfire occurs, a misfire determination apparatus has been proposed that determines whether misfire has occurred based on this rotational fluctuation. As one of them, a “rotational fluctuation amount” correlated with the engine rotational speed is acquired in the expansion stroke of each cylinder, and misfiring is performed based on the magnitude of this rotational fluctuation amount and the temporal variation pattern (change pattern) of the rotational fluctuation amount. There has been proposed a misfire determination apparatus that performs the above determination (see, for example, Patent Document 1).

  Hereinafter, it is a four-cylinder internal combustion engine, and the ignition sequence is the first cylinder # 1, the third cylinder # 3, the fourth cylinder # 4, and the second cylinder # 2 (# 1 → # 3 → # 4 → # 2). The operation of this conventional determination device (hereinafter referred to as “conventional device”) will be described in more detail using an example in order.

  In the conventional apparatus, as shown in FIGS. 7A and 7B, the time required for the crankshaft to rotate in the range from the compression top dead center TDC (0 ° CA) to 30 ° CA of each cylinder. (Required rotation time) Tpre and a required rotation time Tmid in the range from 90 ° CA to 120 ° CA after the compression top dead center TDC are acquired. Each of the required rotation times Tpre and Tmid is inversely proportional to the “crank angular velocity”, and increases as the crank angular velocity decreases. In the present specification, “CA” represents a crank angle.

  Further, the conventional apparatus acquires the difference D (= Tmid−Tpre) between the required rotation times Tpre and Tmid. When the normal combustion state continues in the internal combustion engine (no misfire has occurred), the required rotation time Tpre at the beginning of the expansion stroke is longer than the required rotation time Tmid at the middle of the expansion stroke. Therefore, in this case, the difference D is a negative value. On the other hand, when misfire has occurred, the crank angular speed decreases from the initial stage to the middle stage of the expansion stroke, so that the required rotation time Tmid is longer than the required rotation time Tpre. Therefore, in this case, the difference D is a positive value.

Next, in the conventional device, the latest difference D (= Dnow) and the cylinder having the compression top dead center TDC at 360 ° CA before the compression top dead center TDC of the cylinder from which the latest difference D was obtained. The difference D (= Dold) obtained in the expansion stroke is applied to the following equation (1) to obtain the rotational fluctuation amount ΔNE. In the present specification, the cylinder having the latest difference D is referred to as “current cylinder”, and the cylinder that has reached the compression top dead center TDC 360 ° CA before the compression top dead center TDC of the current cylinder is It is called “reference cylinder”.

ΔNE = Dnow−Dold (1)

For example, as shown in FIG. 7B, when the current cylinder is the third cylinder # 3, the difference Dnow is T4-T3. At this time, the reference cylinder is the second cylinder # 2, and therefore the difference Dold is T2-T1 as shown in FIG. Therefore, the rotational fluctuation amount ΔNE (= ΔNE (# 3)) for the current cylinder (third cylinder # 3) is obtained by the following equation (2).

ΔNE (# 3) = Dnow−Dold = (T4−T3) − (T2−T1) (2)

  Assuming that a misfire has occurred in the current cylinder (for example, the third cylinder # 3), the difference Dnow (= T4−T3) is a positive value as described above. On the other hand, if normal combustion is performed in the reference cylinder (in this case, the second cylinder # 2) (that is, if there is no misfire), the difference Dold (= T2−T1) is negative as described above. Value. Accordingly, in this case, as shown in FIG. 8A, the rotational fluctuation amount ΔNE (= ΔNE (# 3)) for the current cylinder (in this case, the third cylinder # 3) is a large positive value.

  The cylinder that reaches the expansion stroke next to the third cylinder # 3 is the fourth cylinder # 4. When the fourth cylinder # 4 is the current cylinder, the reference cylinder is the first cylinder # 1. Since no misfire has occurred in these cylinders, the difference Dnow (difference D in the fourth cylinder # 4) and the difference Dold (difference D in the first cylinder # 1) are both negative values and their magnitudes. Are substantially equal to each other. Accordingly, the rotational fluctuation amount ΔNE (= ΔNE (# 4)) for the fourth cylinder # 4 is substantially “0”.

  Furthermore, the cylinder that reaches the expansion stroke next to the fourth cylinder # 4 is the second cylinder # 2. When the second cylinder # 2 is the current cylinder, the reference cylinder is the third cylinder # 3 in which misfire has occurred. Therefore, the difference Dnow (difference D in the second cylinder # 2) is a negative value, but the difference Dold (difference D in the third cylinder # 3) is a large positive value. As a result, the rotational fluctuation amount ΔNE (= ΔNE (# 2)) for the second cylinder # 2 becomes a negative value having a large absolute value. The magnitude (absolute value) of the rotational fluctuation amount ΔNE (# 2) for the second cylinder # 2 is substantially equal to the magnitude of the rotational fluctuation amount ΔNE (# 3) for the third cylinder # 3.

  The cylinder that reaches the expansion stroke next to the second cylinder # 2 is the first cylinder # 1. When the first cylinder # 1 is the current cylinder, the reference cylinder is the fourth cylinder # 4. Since no misfire has occurred in these cylinders, the difference Dnow (difference D in the first cylinder # 1) and the difference Dold (difference D in the fourth cylinder # 4) are both negative values and their magnitudes. Are substantially equal to each other. Accordingly, the rotational fluctuation amount ΔNE (= ΔNE (# 1)) for the first cylinder # 1 is substantially “0”.

  As understood from the above description, the rotational fluctuation amount ΔNE of the cylinder in which misfire has occurred (third cylinder # 3 in the example shown in FIG. 8A) is the rotational fluctuation amount of the cylinder in which misfire has not occurred. It is a very large positive value compared to ΔNE. Therefore, it is considered that it can be determined that a misfire has occurred when the rotational fluctuation amount ΔNE exceeds the “predetermined threshold value Nth”.

  By the way, even when misfire does not occur, the engine rotational speed fluctuates due to disturbances caused by vehicle travel, misfires that occurred in the past, and the like, and the rotational fluctuation amount ΔNE of a certain cylinder exceeds a predetermined threshold Nth There is. Therefore, it cannot be determined that a misfire has occurred only when the rotational fluctuation amount ΔNE exceeds the “predetermined threshold value Nth”. On the other hand, when the engine rotational speed fluctuates due to disturbance caused by vehicle travel, misfires, etc. that occurred in the past, the change pattern of the rotational fluctuation amount ΔNE indicated by the solid line in FIG. There was found. Here, the change pattern is a rotation fluctuation amount ΔNE of a cylinder that reaches a compression top dead center TDC 360 ° CA after the compression top dead center TDC of the cylinder after the rotation fluctuation amount ΔNE of a cylinder exceeds a predetermined threshold Nth. Refers to a pattern that falls greatly.

  Therefore, the conventional apparatus first determines that there is a possibility that misfire has occurred (temporary determination) when the rotational fluctuation amount ΔNE exceeds the predetermined threshold value Nth.

  Further, after the provisional determination, the conventional apparatus is the cylinder that has been provisionally determined that misfire may have occurred (the third cylinder # 3 in the example of FIG. 8A). The cylinder that reaches the compression top dead center TDC after 360 ° CA from the compression top dead center TDC (referred to as the second cylinder # 2 in the example of FIG. 8A, hereinafter referred to as the “next cylinder”). The magnitude | ΔNE (# 2) | In addition, the conventional device is the cylinder (first cylinder # 1 in the example of FIG. 8A) that reaches the compression top dead center TDC after 540 ° CA from the compression top dead center TDC of the provisionally determined cylinder. The magnitude of rotation fluctuation amount | ΔNE (# 1) | is acquired. The conventional apparatus finally determines that misfire has occurred in the provisionally determined cylinder when the ratio (| ΔNE (# 2) | / | ΔNE (# 1) |) is equal to or greater than a predetermined ratio (this determination). To do.

JP 2006-152971 A

  In the conventional apparatus, when the rotational fluctuation amount ΔNE of a certain cylinder exceeds a predetermined threshold value Nth (that is, when a temporary determination is made that a misfire may have occurred), the rotational fluctuation amount of the next cylinder and the subsequent cylinders In order to obtain ΔNE, the counter C shown in FIG. 8B is used.

  In other words, the conventional device, first, when the obtained rotational fluctuation amount ΔNE exceeds a predetermined threshold Nth, the time when the rotational fluctuation amount ΔNE is obtained (for example, 120 ° CA from the compression top dead center TDC of the provisionally determined cylinder). After), the value of the counter C is set to “0” (counter C is reset). Then, the value of the counter C is incremented by “1” 120 ° CA after the expansion (exhaust) bottom dead center of the provisional determination cylinder (that is, 180 ° CA after the counter C is reset). Thereafter, the conventional device counts up the value of the counter C by “1” every time 180 ° CA elapses. Then, the conventional device acquires the rotation fluctuation amount ΔNE newly obtained when the value of the counter C is “2” as the rotation fluctuation amount ΔNE of the next cylinder (rotation fluctuation amount ΔNE (# 2) in FIG. 8). In addition, the rotational fluctuation amount ΔNE newly obtained when the value of the counter C is “3” is acquired as the rotational fluctuation amount ΔNE of the cylinders one after another (the rotational fluctuation amount ΔNE (# 1) in FIG. 8). Then, as described above, the conventional apparatus performs the main determination as to whether or not misfire has occurred using the rotation fluctuation amount ΔNE of the next cylinder and the subsequent cylinder.

  However, in practice, as shown in FIG. 9A, the rotational fluctuation amount ΔNE (= ΔNE (# 3)) in a certain cylinder (third cylinder # 3 in FIG. 9A) is a predetermined threshold value due to misfire. In some cases, the rotational fluctuation amount ΔNE (= ΔNE (# 4)) in the cylinder immediately after that (fourth cylinder # 4 in FIG. 9A) exceeds the predetermined threshold Nth for some reason. In this case, the conventional device resets the counter C again. As a result, the conventional device makes this determination as to whether or not misfire has occurred in the cylinder that has not misfired (fourth cylinder # 4 in FIG. 9A). Therefore, the conventional device cannot make a main determination as to whether or not a misfire has occurred in a cylinder in which a misfire has actually occurred, and may miss the occurrence of a misfire.

  The present invention has been made to address the above problems. That is, one of the objects of the present invention is that misfiring has occurred in a highly probable cylinder in which misfiring has occurred when the rotational fluctuation amount continuously exceeds a predetermined threshold in two cylinders whose ignition order is adjacent. It is an object of the present invention to provide a misfire determination device that can reliably perform the determination without missing the opportunity of determination of whether or not a misfire has occurred (main determination).

  An internal combustion engine misfire determination apparatus (hereinafter referred to as “the present invention apparatus”) of the present invention includes a misfire correlation value acquisition unit, a rotation fluctuation amount acquisition unit, and a misfire determination unit.

  The misfire correlation value acquisition unit is a value having a correlation with a crank angular velocity in an expansion stroke of an arbitrary cylinder, and is larger when a misfire occurs than when normal combustion is performed in the arbitrary cylinder. Get the value as a misfire correlation value.

  For example, the misfire correlation value acquisition unit first acquires a value (required rotation time) that is inversely proportional to the crank angular velocity in each of the initial expansion stroke and the intermediate expansion stroke of each cylinder. Next, the misfire correlation value acquisition unit acquires, for example, a difference (Tmid−Tpre) between the required rotation time Tpre in the initial stage of the expansion stroke and the required rotation time Tmid in the middle of the expansion stroke as a misfire correlation value. The misfire correlation value is a negative value when normal combustion is performed in an arbitrary cylinder, and is a positive value when a misfire occurs. Alternatively, the misfire correlation value may be a time Tmid required for the crankshaft to rotate by a predetermined crank angle in the middle of the expansion stroke of each cylinder. Even in this case, the misfire correlation value (time Tmid) is small when normal combustion is performed in an arbitrary cylinder, and is large when misfire occurs.

  The rotation fluctuation amount acquisition unit calculates a difference amount between a misfire correlation value in one cylinder and a misfire correlation value in another cylinder having a specific relationship with the one cylinder in an ignition order, and calculates a rotation amount of the one cylinder. Obtained as a variation. For example, the rotation fluctuation amount acquisition unit may select a cylinder that has reached the compression top dead center TDC 360 ° CA before the compression top dead center TDC of the one cylinder as the other cylinder.

  When the acquired rotational fluctuation amount exceeds a predetermined threshold, the misfire determination unit may have misfired in a “specific cylinder” that is a cylinder from which the rotational fluctuation amount exceeding the predetermined threshold is acquired. Is determined.

  If this rotational fluctuation amount exceeds a predetermined threshold in the “specific cylinder”, there is a possibility that misfire has occurred in the specific cylinder. However, it cannot be denied that the engine rotational speed fluctuates due to disturbances caused by vehicle travel, misfires that occurred in the past, and the like, and the rotational fluctuation amount of a certain cylinder exceeds a predetermined threshold. Therefore, the device of the present invention determines (temporary determination) that there is a possibility that misfire has occurred in the specific cylinder.

  Further, the misfire determination unit generates misfire in the specific cylinder based on the change pattern of the rotational fluctuation amount acquired for each expansion stroke of each cylinder in a “predetermined period” after the expansion stroke of the “specific cylinder”. Determine whether or not.

  The misfire determination unit determines that a misfire has occurred in the specific cylinder when the obtained change pattern of the rotational fluctuation amount satisfies a predetermined relationship. For example, according to the above-described example, the rotational fluctuation amount becomes a large negative value in the cylinder (next cylinder) after 360 ° CA from the cylinder (provisional determination cylinder) determined to have the possibility of misfire. . Further, the rotational fluctuation amount has a small absolute value in the cylinder after 540 ° CA from the cylinder determined to have the possibility of misfiring (second cylinder).

  Therefore, the misfire determination unit, for example, the magnitude of rotation variation of the cylinder (next cylinder) after 360 ° CA from the specific cylinder (temporary determination cylinder) | ΔNE360 | and 540 ° CA from the specific cylinder (temporary determination cylinder). If the ratio (| ΔNE360 | / | ΔNE540 |) of the magnitude of rotation fluctuation of the subsequent cylinders (subsequent cylinders) | ΔNE540 | is equal to or greater than a predetermined value, it is determined that misfire has occurred in the specific cylinder. In this case, the end time of the predetermined period is the time when the rotational fluctuation amount for the cylinders is acquired one after another and the determination as to whether or not misfire has occurred in the specific cylinder is completed. In addition, the misfire determination method based on the change pattern of the rotational fluctuation amount is not limited to this example.

  When the result of the provisional determination is correct (a misfire has occurred in the specific cylinder), the obtained change pattern of the rotational fluctuation amount satisfies the predetermined relationship. On the other hand, if the result of the tentative determination is incorrect (no misfire has occurred in the specific cylinder), the change pattern does not satisfy the predetermined relationship. Therefore, the misfire determination unit can determine whether or not misfire has occurred in the specific cylinder.

  In addition, the misfire determination unit responds to a larger rotation fluctuation amount among the rotation fluctuation amounts of the two cylinders when the rotation fluctuation amount continuously exceeds the predetermined threshold in two cylinders whose ignition order is adjacent to each other. A cylinder to be selected is selected as the specific cylinder.

  According to the inventor's study, even if the rotation fluctuation amount exceeds a predetermined threshold value due to disturbances caused by vehicle travel and misfires that occurred in the past, the rotation fluctuation amount is the rotation fluctuation amount due to misfire. Is unlikely to be larger. Therefore, when the rotational fluctuation amount continuously exceeds a predetermined threshold value in two cylinders adjacent to each other in the ignition sequence, the present invention device has a highly probable cylinder that misfires a cylinder having a larger rotational fluctuation amount among these cylinders. to decide.

  That is, for example, when the rotational fluctuation amount exceeds a predetermined threshold value for two consecutive times, the determination apparatus determines that the rotational fluctuation amount for the cylinder (previous cylinder) that first exceeds the predetermined threshold value is for the cylinder immediately after that (immediate cylinder). When it is larger than the rotational fluctuation amount, it is determined that there is a high probability of misfire in the front cylinder. The device of the present invention selects the front cylinder as the specific cylinder. On the other hand, when the rotational fluctuation amount with respect to the preceding cylinder is equal to or less than the rotational fluctuation amount with respect to the immediately following cylinder, the present invention device determines that there is a high probability of misfire in the immediately following cylinder, and selects the immediately following cylinder as the specific cylinder.

  As a result, the present determination apparatus can reliably determine whether or not misfire has occurred without missing the opportunity for determination of whether or not misfire has occurred (main determination).

  Other objects, other features, and attendant advantages of the present invention will be readily understood from the description of each embodiment of the present invention described with reference to the following drawings.

FIG. 1 is a schematic configuration diagram of an internal combustion engine to which a “misfire determination device” according to an embodiment of the present invention is applied. FIG. 2 is a time chart showing the cylinder number, the crank angle, the required rotation time, the difference, and the rotation fluctuation amount in the same cylinder continuous misfire. 3 (A) and 3 (B) are time charts showing changes in the rotational fluctuation amount with respect to the crank angle (FIG. 3 (A) is when a misfire occurs, and FIG. 3 (B) is the occurrence of a swingback after the misfire. Time). FIG. 4 is a time chart showing the variation of the rotational variation with respect to the crank angle and the change of the determination timing counter when the rotational variation for the cylinders adjacent to each other in the ignition order exceeds a predetermined threshold (the rotation with respect to the previous cylinder). When the fluctuation amount is equal to or greater than the rotation fluctuation amount for the subsequent cylinder). FIG. 5 is a time chart showing the variation of the rotational variation with respect to the crank angle and the change in the determination timing counter when the rotational variation for the cylinders whose ignition order is adjacent exceeds the predetermined threshold value (the rotation with respect to the previous cylinder). When the fluctuation amount is less than the rotation fluctuation amount for the subsequent cylinder). FIG. 6 is a flowchart showing a “misfire determination routine” executed by the CPU shown in FIG. FIG. 7 is a diagram for explaining the difference between the required rotation time and the required rotation time. FIG. 8 is a time chart showing the amount of change in rotation with respect to the crank angle and the change in the counter used by the conventional apparatus when misfire occurs (when the amount of change in rotation exceeds a predetermined threshold value only once). FIG. 9 is a time chart showing the amount of change in rotation with respect to the crank angle and the change in the counter used by the conventional apparatus when misfire occurs (when the amount of change in rotation exceeds a predetermined threshold value twice in succession).

<Embodiment>
Hereinafter, a misfire determination apparatus (hereinafter also referred to as “the determination apparatus”) according to an embodiment of the present invention will be described with reference to the drawings.

(Constitution)
This determination apparatus is applied to the internal combustion engine 10 shown in FIG. The engine 10 is a spark ignition type four-cycle piston reciprocating type in-line four-cylinder gasoline internal combustion engine. The engine 10 includes an engine body 20 and an intake / exhaust system 40.

  The engine body 20 includes a cylinder head 21, a cylinder block 22, a fuel injection valve 23, an ignition device 24, an intake valve 25, an exhaust valve 26, a piston 27, a connecting rod 28, a crankshaft 29, a timing rotor 31, a crankcase 32, An intake cam 33 and an exhaust cam 34 are included.

  A combustion chamber 35 is formed in the engine body 20 by the cylinder head 21, the cylinder block 22, and the piston 27. An intake port 36 is formed in the engine body 20 on the intake side of the cylinder head 21. The intake port 36 communicates with the combustion chamber 35. An exhaust port 37 is formed in the engine body 20 on the exhaust side of the cylinder head 21. The exhaust port 37 communicates with the combustion chamber 35.

  The fuel injection valve 23 is configured to inject fuel into the intake port 36. The ignition device 24 is disposed in the cylinder head 21 so that the spark generating part is exposed in the combustion chamber 35. The ignition device 24 includes an igniter, an ignition coil, and a spark plug. When the intake cam 33 rotates, the intake valve 25 follows the cam nose of the intake cam 33 and reciprocates so as to open or shut off the communication portion between the combustion chamber 35 and the intake port 36. When the exhaust cam 34 rotates, the exhaust valve 26 reciprocates so as to open or shut off the communication portion between the combustion chamber 35 and the exhaust port 37 following the cam nose of the exhaust cam 34.

  The crankshaft 29 is connected to the piston 27 via a connection rod 28 accommodated in the crankcase 32, and rotates according to the reciprocating motion of the piston 27. The timing rotor 31 is disposed at the end of the crankshaft 29 and is rotated integrally with the crankshaft 29.

  The intake / exhaust system 40 includes an intake passage portion 41 that forms an intake passage inside, a throttle valve 42, and an exhaust passage portion 43 that forms an exhaust passage inside. The intake passage 41 communicates with the intake port 36. The exhaust passage portion 43 communicates with the exhaust port 37.

  The throttle valve 42 is disposed in the intake passage 41 and is driven by a throttle motor (not shown). The opening of the throttle valve 42 is changed in accordance with a motor control amount calculated by an electronic control device 50 described later and output to the throttle motor. The amount of intake air introduced into the intake passage portion 41 is adjusted according to the opening of the throttle valve 42.

  The fuel injected from the fuel injection valve 23 into the intake port 36 forms an air-fuel mixture together with the intake air in the intake passage portion 41. When the intake valve 25 is opened during the intake stroke of the engine 10, the air-fuel mixture is introduced into the combustion chamber 35. The air-fuel mixture introduced into the combustion chamber 35 is compressed in the compression stroke, and then ignited by the ignition device 24 at a predetermined timing to burn and explode. That is, the expansion stroke starts. The exhaust gas after combustion is discharged to the exhaust passage portion 43 when the exhaust valve 26 is opened in the exhaust stroke. Since a series of these strokes (combustion cycle including intake, compression, expansion, and exhaust) is sequentially performed in the four cylinders, the crankshaft 29 rotates continuously. The ignition of the engine 10 is performed in the order of the first cylinder # 1, the third cylinder # 3, the fourth cylinder # 4, and the second cylinder # 2.

  The electronic control unit (ECU) 50 is an electronic circuit including a known microcomputer, and includes a CPU, ROM, RAM, backup RAM (static RAM or nonvolatile memory), an interface, and the like. The electronic control device 50 is electrically connected to the fuel injection valve 23, the ignition device 24, the throttle motor, and the like.

  The electronic control unit 50 sends an instruction (drive) signal to actuators such as the fuel injection valve 23 and the ignition device 24 in accordance with an instruction from the CPU. Further, the electronic control unit 50 is electrically connected to the crank position sensor 51, the air flow meter 52, the operation state quantity detection sensor 53, and the like, and receives (inputs) signals from the respective sensors.

  The crank position sensor 51 is a sensor for detecting the rotational position of the crankshaft 29. More specifically, the crankshaft 29 includes a timing rotor 31 that rotates integrally with the crankshaft 29. The timing rotor 31 includes external teeth formed on the outer peripheral surface every 30 °. The crank position sensor 51 faces the external teeth of the timing rotor 31. When the external teeth of the timing rotor 31 pass in the vicinity of the crank position sensor 51 as the crankshaft 29 rotates, the crank position sensor 51 outputs a pulse signal synchronized with the passage of the external teeth. In addition, as the timing rotor 31, what the outer tooth was formed every 10 degrees may be applied. In this case, the pulse signal output of the crank position sensor 51 is frequency-divided by the electronic control unit 50 and converted into a pulse output every 30 ° CA.

  The air flow meter 52 is the intake passage portion 41 and is disposed at a position upstream of the intake side of the throttle valve 42. The air flow meter 52 detects the amount of intake air flowing through the intake passage portion 41. The electronic control unit 50 calculates the intake air amount Ga per unit time based on the output signal of the air flow meter 52.

  The operating state amount detection sensor 53 is an accelerator pedal operation amount sensor that detects an accelerator pedal operation amount Accp, an intake pressure sensor that detects an intake pressure Pm in the intake passage portion 41 and downstream of the throttle valve 42, and an engine 10 It includes an air conditioner sensor that detects the operation / non-operation state of the air conditioner of the mounted vehicle, a shift lever sensor that detects whether or not the shift lever of the vehicle on which the engine 10 is mounted is operated, and the like.

(Operation)
Next, the operation of this determination apparatus will be described. This determination apparatus determines whether or not misfire has occurred based on the “rotational fluctuation amount” that is an index amount indicating the degree of change in the engine rotational speed NE. First, the definition of the “rotational fluctuation amount” will be described.

  This “rotational fluctuation amount” is the same as the rotational fluctuation amount in Patent Document 1 described above. That is, as shown in FIGS. 7A and 7B, the determination apparatus first determines the same rotation required time Tpre from the compression top dead center TDC to 30 ° CA in the expansion stroke of each cylinder. The rotation required time Tpre from 90 ° CA to 120 ° CA after the compression top dead center TDC is acquired. The required rotation times Tpre and Tmid indicate the maximum value and the minimum value, respectively, of the time required for the crankshaft to rotate 30 ° CA when the cylinder is normally combusting and exploding.

  Next, the determination apparatus acquires a difference D (= Tmid−Tpre) between the required rotation times Tpre and Tmid. Further, the present determination apparatus applies the difference D (= Dnow) with respect to the current cylinder and the difference D (= Dold) with respect to the reference cylinder to the above equation (1) (ΔNE = Dnow−Dold), and the rotational fluctuation amount ΔNE. To get. If the required rotation times Tpre and Tmid for the current cylinder are T3 and T4, respectively, and the required rotation times Tpre and Tmid for the reference cylinder are T1 and T2, respectively, the rotational fluctuation amount ΔNE for the current cylinder is expressed by the above equation (2) (ΔNE = (T4-T3)-(T2-T1)).

  The difference D (that is, each of Dold and Dnow) is negative when normal combustion / explosion occurs due to the rotation angle from the compression top dead center TDC and the acceleration of the piston 27 due to combustion / explosion of the engine 10. It is a positive value if a misfire has occurred. Accordingly, the rotational fluctuation amount ΔNE is a value near “0” when the current cylinder is normally combusting and exploding, and is “a relatively large positive value” when misfire occurs in the current cylinder. Become.

In the following description, the rotational fluctuation amount ΔNE acquired as described above is distinguished and called as follows.
Rotational fluctuation amount ΔNE0: The rotational fluctuation amount ΔNE acquired for the current cylinder.
Rotational fluctuation amount ΔNE1: A rotational fluctuation amount ΔNE acquired for a cylinder that is ignited about 180 ° CA before the current cylinder (hereinafter also simply referred to as “a cylinder before one cylinder”).
Rotational fluctuation amount ΔNE2: A rotational fluctuation amount ΔNE acquired for a cylinder that is ignited about 360 ° CA before the current cylinder (hereinafter also simply referred to as “cylinder before two cylinders”).
Rotational fluctuation amount ΔNE3: The rotational fluctuation amount ΔNE acquired for a cylinder that is ignited about 540 ° CA before the current cylinder (hereinafter also simply referred to as “a cylinder before three cylinders”).
Rotational fluctuation amount ΔNE4: The rotational fluctuation amount ΔNE acquired for a cylinder that is ignited about 720 ° CA before the current cylinder (hereinafter also simply referred to as “cylinder before four cylinders”). Note that the cylinder before four cylinders is the same cylinder as the current cylinder.

  The determination device determines whether or not misfire has occurred by determining a change pattern of the rotation fluctuation amount based on these rotation fluctuation amounts. This specific determination operation will be described later.

  By the way, as described above, the determination apparatus obtains the rotational fluctuation amount ΔNE from the difference Dnow with respect to the current cylinder and the difference Dold with respect to the reference cylinder 360 ° CA before the current cylinder. That is, the determination device acquires the difference Dnow and the difference Dold using the same external teeth of the timing rotor 31, and acquires the rotation fluctuation amount ΔNE based on the difference therebetween. Therefore, for example, even if the pitch of the external teeth of the timing rotor 31 is not exactly equal due to a manufacturing error, the calculated rotational fluctuation amount ΔNE is not affected by the manufacturing error of the timing rotor 31. As a result, the determination apparatus can accurately acquire the rotation fluctuation amount ΔNE.

  Next, the change in the rotational fluctuation amount ΔNE will be specifically described with reference to FIG. FIG. 2 is a time chart showing the relationship among the cylinder number, the crank angle CA, the time required for the crankshaft to rotate 30 ° CA (required rotation time), the difference D, and the rotation fluctuation amount ΔNE. FIG. 2 shows a state in which misfire continues in the third cylinder # 3 (so-called one-cylinder continuous misfire).

  As can be understood from FIG. 2, the required rotation time starts to decrease from the vicinity of the compression top dead center TDC in the expansion stroke of the cylinder in which no misfire has occurred, and increases in the middle to late stages of the expansion stroke (for example, at time t1). -T2, time t2-t3, time t5-t6, etc.). On the other hand, the required rotation time increases relatively rapidly from the vicinity of the compression top dead center TDC in the expansion stroke of the cylinder in which misfire occurs (in this example, the third cylinder # 3). , Continues until the compression top dead center of the fourth cylinder # 4) (see times t3 to t4). The required rotation time decreases relatively rapidly from the vicinity of the compression top dead center TDC of the fourth cylinder # 4 in the expansion stroke of the fourth cylinder # 4 where no misfire has occurred (see times t4 to t5).

  Therefore, the difference D becomes a large positive value when a misfire occurs in the third cylinder # 3 ((T4-T3) in FIG. 2), but the difference D is a negative value for a cylinder that normally explodes and burns. (In FIG. 2, (T2-T1), (Tb-Ta), (Td-Tc), (Tf-te), etc.).

  As described above, the rotational fluctuation amount ΔNE includes the difference Dnow with respect to the current cylinder and the reference cylinder (a cylinder having reached the compression top dead center TDC 360 ° CA before the compression top dead center TDC of the current cylinder, that is, two cylinders). The difference (Dnow−Dold) from the difference Dold with respect to the previous cylinder).

  On the other hand, if the current cylinder is the third cylinder # 3 and a misfire occurs in the third cylinder # 3, the difference Dnow of the current cylinder becomes a large positive value (T4-T3), and the reference where no misfire has occurred. The difference Dold between the second cylinders serving as cylinders is a negative value (T2−T1). Therefore, the rotational fluctuation amount ΔNE for the third cylinder # 3 which is the current cylinder is a large positive value. That is, as shown in the period corresponding to the crank angles C1 to C2 in FIG. 3A, the rotational fluctuation amount ΔNE for the misfire cylinder (cylinder in which misfire occurs) is a large positive value (from a predetermined threshold value Nth described later). Is also a large value).

  On the other hand, when the cylinder after the misfire cylinder is “normal cylinder (cylinder in which no misfire has occurred) and is the current cylinder (second cylinder # 2 in the example of FIG. 2)”, the reference cylinder of that cylinder Is a misfire cylinder (third cylinder # 3 in the example of FIG. 2). Therefore, the difference Dnow of the current cylinder is a negative value (Tf−Te), and the difference Dold of the reference cylinder is a large positive value (T4−T3). As a result, as shown in the period corresponding to the crank angles C3 to C4 in FIG. 3A, the rotational fluctuation amount ΔNE of the cylinder after the second cylinder becomes a large negative value. Further, as shown in the period corresponding to the crank angles C2 to C3 and the crank angles C4 to C5 in FIG. 3A, the rotational fluctuation with respect to the normal cylinders other than the “normal cylinder after the misfire cylinder and the two cylinders of the misfire cylinder”. The quantity ΔNE is a value having a relatively small absolute value.

  By the way, when a misfire occurs in a cylinder with a misfire, there may be a phenomenon in which the amount of rotation fluctuation thereafter increases due to the misfire. This phenomenon is also called “swing back”. The reason for the occurrence of this swing back is presumed as follows.

  When the engine speed NE decreases due to the occurrence of misfire, the engine 10 is forcibly rotated by the inertial force of the power train and the force of the damper spring of the clutch disk. For this reason, the engine rotational speed NE increases rapidly due to the reaction that the engine rotational speed NE decreases. Thereafter, the engine rotational speed NE decreases again, for example, when the power train side acts as a rotational resistance (due to the suddenly increased reaction).

FIG. 3B shows the rotational fluctuation amount ΔNE when the swing back occurs. As can be understood from FIGS. 3A and 3B, the change pattern of the rotational fluctuation amount at the time of misfire is similar to the change pattern of the rotational fluctuation amount at the time of swingback. However, when both are compared in detail, the change pattern of the rotational fluctuation amount ΔNE is different between when a misfire occurs and when a swingback after a misfire occurs. More specifically, the following formula (3) is satisfied when a misfire occurs, but the formula (3) is not satisfied when swinging back. The value K is a positive constant predetermined by experiment.

K · | ΔNE1 | ≧ | ΔNE0 | (3)

Therefore, the present determination device determines whether or not misfire has occurred by identifying the change pattern of the rotation fluctuation amount ΔNE using the above-described equation (3) (performs this determination). That is, this determination apparatus determines whether misfire has occurred as follows.
Step 1: This determination apparatus determines whether or not the rotational fluctuation amount ΔNE exceeds a threshold value Nth. In other words, provisional determination is performed.
Step 2: When the rotational fluctuation amount ΔNE exceeds the threshold value Nth, the determination device determines that the cylinder is a provisional misfire cylinder.
Step 3: This determination device uses the rotational fluctuation amount ΔNE as a reference rotational fluctuation with respect to the cylinder 2 cylinders after the temporary misfire cylinder (a cylinder that reaches the compression top dead center TDC 360 ° CA after the compression top dead center TDC of the temporary misfire cylinder) Acquired as a quantity ΔNEb.
Step 4: This determination device compares the rotational fluctuation amount ΔNE with respect to the cylinder after the three cylinders of the temporary misfire cylinder (the cylinder that reaches the compression top dead center TDC after 540 ° CA from the compression top dead center TDC of the temporary misfire cylinder). Obtained as the quantity ΔNEc.
Step 5: This determination apparatus determines whether or not the following expression (4) corresponding to the above expression (3) is satisfied, and if satisfied, determines that misfire has occurred in the temporary misfire cylinder.

K · | ΔNEb | ≧ | ΔNEc | (4)

  However, as shown in FIGS. 4 and 5, it has been found that there are cases where the rotational fluctuation amount ΔNE continuously exceeds the predetermined threshold value Nth in two cylinders whose ignition order is adjacent. In this case, according to the inventor's examination, it has been found that the probability that the cylinder having the larger rotational fluctuation amount ΔNE among these two cylinders misfires is high. This is because even if the rotational fluctuation amount ΔNE increases due to a cause other than misfire, the rotational fluctuation amount ΔNE at that time is rarely larger than the rotational fluctuation amount ΔNE during misfire. Therefore, the inventor adopts the cylinder having the larger rotational fluctuation amount ΔNE as the “temporary misfiring cylinder” and monitors the fluctuation pattern of the rotational fluctuation amount ΔNE with respect to the temporary misfiring cylinder (that is, the above steps 3 to 5 are performed). We obtained knowledge that it was desirable to carry out.

  Therefore, in the example of FIG. 4, the determination device resets the determination timing counter Ctmg when the rotational fluctuation amount ΔNE (ΔNE3) of the third cylinder # 3 exceeds the predetermined threshold Nth. Next, the rotational fluctuation amount ΔNE (ΔNE2) of the fourth cylinder # 4 exceeds the predetermined threshold Nth, but the rotational fluctuation amount ΔNE (ΔNE2) of the fourth cylinder # 4 is the rotational fluctuation amount ΔNE (ΔNE3) of the third cylinder # 3. The determination apparatus does not reset the determination timing counter Ctmg again. That is, the present determination apparatus determines that the third cylinder # 3 of the third cylinder # 3 and the fourth cylinder # 4 is a temporary misfire cylinder, and thereafter every time a new rotational fluctuation amount ΔNE is obtained (that is, 180 Each time CA elapses), the value of the counter Ctmg is increased by “1”.

  Further, this determination apparatus adopts the rotation fluctuation amount ΔNE (ΔNE1 in FIG. 4) when the value of the counter Ctmg is “2” as the reference rotation fluctuation amount ΔNEb, and the value of the counter Ctmg is “3”. The rotational fluctuation amount ΔNE at that time (ΔNE0 in FIG. 4) is adopted as the comparative rotational fluctuation amount ΔNEc. And this determination apparatus implements this determination by determining whether said (4) Formula is materialized.

  On the other hand, in the example of FIG. 5, this determination apparatus resets the determination timing counter Ctmg at the time when the rotational fluctuation amount ΔNE (ΔNE4) of the third cylinder # 3 exceeds the predetermined threshold Nth, and the fourth cylinder # 4 The determination timing counter Ctmg is reset again when the rotational fluctuation amount ΔNE (ΔNE3) exceeds the predetermined threshold value Nth. That is, in this determination apparatus, since the rotational fluctuation amount ΔNE (ΔNE3) of the fourth cylinder # 4 is larger than the rotational fluctuation amount ΔNE (ΔNE4) of the third cylinder # 3, the third cylinder # 3 and the fourth cylinder # 4 Of these, the fourth cylinder # 4 is determined to be a temporary misfire cylinder. The subsequent operation is the same as that described above. That is, this determination device increases the value of the counter Ctmg by “1” every time a new rotation fluctuation amount ΔNE is obtained, and the rotation fluctuation amount ΔNE when the value of the counter Ctmg is “2” (FIG. 5). ΔNE1) is adopted as the reference rotational fluctuation amount ΔNEb, and the rotational fluctuation amount ΔNE (ΔNE0 in FIG. 5) when the value of the counter Ctmg is “3” is adopted as the comparative rotational fluctuation amount ΔNEc. And this determination apparatus implements this determination by determining whether said (4) Formula is materialized.

(Actual concrete operation)
Next, a specific operation of the determination apparatus will be described. The CPU of the electronic control unit 50 performs the “misfire determination routine” shown by the flowchart in FIG. 6 when the crank angle CA of any cylinder of the engine 10 reaches 120 ° CA after the compression top dead center TDC. Run against.

  Therefore, when the crank angle CA of any cylinder reaches 120 ° CA after the compression top dead center TDC of the cylinder, the CPU starts the process from step 600 in FIG. Accordingly, the rotational fluctuation amount ΔNE (n) for the current cylinder is acquired. The CPU stores the obtained rotation fluctuation amount ΔNE (n) in the RAM while associating it with the cylinder number of the current cylinder. The required rotation time Tpre and the required rotation time Tpre for each cylinder are separately acquired by a routine (not shown) and stored in the RAM. Further, in the following, the rotational fluctuation amount ΔNE (n−1) is for a cylinder one cylinder before the current cylinder (a cylinder that has reached the compression top dead center TDC 180 ° CA before the compression top dead center TDC of the current cylinder). This represents the rotational fluctuation amount ΔNE.

  Next, the CPU proceeds to step 610 to determine whether or not a “determination execution condition” for determining whether or not misfire has occurred. In misfire determination, it is desirable that the engine speed NE be relatively stable. Accordingly, the determination execution conditions include, for example, that a predetermined time has elapsed since the air conditioner was switched on / off, and that a predetermined time had elapsed since the shift lever was operated. It is done.

  If the determination execution condition is not satisfied, the CPU makes a “No” determination at step 610 to directly proceed to step 695 to end the present routine tentatively. On the other hand, if the determination execution condition is satisfied, the CPU executes the following process. Hereinafter, it is assumed that the determination execution condition continues to be satisfied and the description will be continued while dividing the case.

(Case 1) When the rotational fluctuation amount ΔNE (n) is equal to or less than a predetermined threshold value Nth.
The CPU makes a “Yes” determination at step 610 to proceed to step 615 to increment the total determination number counter Ctotal. The total determination number counter Ctotal is set to “0” in an initial routine (not shown) executed when the ignition key switch is changed from OFF to ON. The total determination number counter Ctotal indicates the number of times that processing for determining the presence or absence of misfire by this routine has been performed.

  Next, the CPU proceeds to step 620 and determines whether or not the rotation fluctuation amount ΔNE (n) is larger than a predetermined threshold value Nth. According to the assumption described above, the rotational fluctuation amount ΔNE (n) is equal to or less than the predetermined threshold value Nth. Therefore, the CPU makes a “No” determination at step 620 to proceed to step 635 to increment the value of the determination timing counter Ctmg (increase by “1”). Note that the value of the counter Ctmg is set to “255” in the above-described initial routine. Further, the value of the counter Ctmg is limited so as not to exceed “255”.

  Next, the CPU proceeds to step 640 to determine whether or not the value of the counter Ctmg is “3”. At this time, since the value of the counter Ctmg is “255”, the CPU makes a “No” determination at step 640 to directly proceed to step 695 to end the present routine tentatively.

(Case 2) The rotational fluctuation amount ΔNE (n) exceeds the predetermined threshold value Nth, but the rotational fluctuation amount ΔNE (n−1) does not exceed the predetermined threshold value Nth (that is, rotational fluctuations in two cylinders adjacent in the ignition order). The amount does not continuously exceed the predetermined threshold Nth).

  In this case, the CPU increments the total determination number counter Ctotal at step 615, determines “Yes” at step 620, and proceeds to step 625. In step 625, the CPU determines that the rotation fluctuation amount ΔNE (n−1) for the “counter 1” cylinder is “the counter Ctmg value is“ 0 ”and the rotation fluctuation amount ΔNE ( n) or more ".

  At present, the value of the counter Ctmg is “255”. Therefore, the CPU makes a “No” determination at step 625 to proceed to step 630, sets the value of the counter Ctmg to “0” (resets the counter Ctmg), and proceeds to step 640.

  As a result, the value of the counter Ctmg is “0”, so the CPU makes a “No” determination at step 640 to directly proceed to step 695 to end the present routine tentatively.

  Thereafter, when this routine is executed, the rotational fluctuation amount ΔNE (n) acquired in step 605 is equal to or less than a predetermined threshold value Nth. Accordingly, when the CPU proceeds to step 620, the CPU makes a “No” determination at step 620 to proceed to step 635 to execute the processing of step 635. As a result, the value of the counter Ctmg is “1”. Therefore, the CPU makes a “No” determination at step 640 to directly proceed to step 695 to end the present routine tentatively. Such processing is repeated until the value of the counter Ctmg becomes “3”.

  Thereafter, when the value of the counter Ctmg becomes “3” by the process of step 635, the CPU determines “Yes” in step 640 and proceeds to step 645, which is equivalent to the relationship of the above expressions (3) and (4). It is determined whether or not the following relationship is satisfied (that is, K · ΔNE (n−1) ≧ ΔNE (n)). At this time, if no misfire has occurred, the relationship between the above equations (3) and (4) is not established. Therefore, in this case, the CPU makes a “No” determination at step 645 to directly proceed to step 655.

  On the other hand, if misfire has occurred, the relationship of the above formulas (3) and (4) is established. Therefore, in this case, the CPU makes a “Yes” determination at step 645 to proceed to step 650 to increment the misfire frequency counter Cmis. The misfire frequency counter Cmis is set to “0” in the above-described initial routine. Therefore, every time it is determined as “Yes” in step 645, the value of the misfire number counter Cmis increases by “1” from “0”. Thereafter, the CPU proceeds to step 655.

  In step 655, the CPU determines whether or not the value of the total determination number counter Ctotal has exceeded “2000”. At this time, if the value of the total determination number counter Ctotal is less than “2000”, the CPU makes a “No” determination at step 655 to directly proceed to step 695 to end the present routine tentatively. As described above, when the case 2 is established, the value of the total determination number counter Ctotal is increased, and a misfire has occurred in the temporary misfire cylinder (the relations of the above expressions (3) and (4) are satisfied). If established), the value of the misfire number counter Cmis is increased.

(Case 3) When the rotational fluctuation amount ΔNE (n) exceeds the predetermined threshold value Nth and the rotational fluctuation amount ΔNE (n−1) also exceeds the predetermined threshold value Nth. That is, a case where the rotational fluctuation amount continuously exceeds the predetermined threshold value Nth in two cylinders adjacent in the ignition order.

  When the CPU proceeds to step 625 at the time when the rotational fluctuation amount ΔNE (n) with respect to the previous cylinder exceeds the predetermined threshold value Nth, the CPU operates in the same manner as in case 2 above. That is, the CPU proceeds to step 630, step 640, and step 695.

  On the other hand, when the CPU proceeds to step 625 when the rotational fluctuation amount ΔNE (n) for the subsequent cylinder exceeds the predetermined threshold value Nth, the CPU executes the routine once before. Since the value of the counter Ctmg is set to “0”, if the rotational fluctuation amount ΔNE (n−1) is equal to or larger than the rotational fluctuation amount ΔNE (n), “Yes” is determined in step 625 and step 635 is performed. Proceed to the following. That is, the CPU determines that the cylinder (cylinder before one cylinder) from which the rotation fluctuation amount ΔNE (n−1) is obtained is a temporary misfire cylinder. As a result, the value of the counter Ctmg is increased by “1” at step 635 to “1”.

  On the other hand, if the rotational fluctuation amount ΔNE (n−1) is less than the rotational fluctuation amount ΔNE (n) for the current cylinder, the CPU makes a “No” determination at step 625 to proceed to step 630 to determine the counter Ctmg. The value is set to “0” (the value of the counter Ctmg is reset again). That is, the CPU determines that the cylinder (current cylinder) from which the rotation fluctuation amount ΔNE (n) is obtained is a provisional misfire cylinder. Thereafter, the CPU proceeds to step 640 and subsequent steps.

  Thereafter, since the CPU makes a “No” determination at step 620, the value of the counter Ctmg gradually increases. Then, when the value of the counter Ctmg becomes “3”, the CPU performs the processing from step 645 onward. Therefore, when the relationship of the above equations (3) and (4) is established, the value of the misfire frequency counter Cmis is increased.

  As described above, even when the case 3 is established, the value of the total determination number counter Ctotal is increased, and when a misfire has occurred in the temporary misfire cylinder, the value of the misfire number counter Cmis is increased. It is done.

  When the processing as described above is repeatedly performed, the value of the total determination number counter Ctotal reaches “2000”. In this case, when the CPU proceeds to step 655, the CPU makes a “Yes” determination at step 655 to proceed to step 660, where the value of the misfire number counter Cmis is equal to or greater than a specified abnormal number (eg, “30”). It is determined whether or not.

  If the value of the misfire count counter Cmis is equal to or greater than the specified abnormal count, the CPU makes a “Yes” determination at step 660 to proceed to step 665 to determine “misfire failure (misfire occurrence)”. At this time, the CPU turns on a warning lamp in the passenger compartment and writes that a misfire has occurred in the backup RAM. Subsequently, the CPU proceeds to step 670, sets the values of the total determination number counter Ctotal and the misfire number counter Cmis to “0”, sets the value of the determination timing counter Ctmg to “255”, and proceeds to step 695. This routine is finished once.

  On the other hand, if the value of the misfire count counter Cmis is less than the specified abnormal count, the CPU makes a “No” determination at step 660 to directly proceed to step 670, and then proceeds to step 695 to end the present routine tentatively. . At this time, the CPU may write “notifying that no misfire has occurred” in the backup RAM.

As described above, this determination apparatus is
A value that correlates with the crank angular velocity in the expansion stroke of an arbitrary cylinder and that is greater when misfiring occurs than when normal combustion is performed in the arbitrary cylinder (rotation required time Tpre and rotation A misfire correlation value acquisition unit that acquires a difference D (= Tmid−Tpre) from the required time Tpre as a misfire correlation value;
The difference amount (Dnow) between the misfire correlation value (difference Dnow) in one cylinder and the misfire correlation value (difference Dold) in another cylinder having a specific relationship (before 360 ° CA) with the one cylinder. -Dold) as a rotational fluctuation amount ΔNE of the one cylinder;
When the acquired rotational fluctuation amount exceeds a predetermined threshold value Nth, it is determined (temporary determination) that there is a possibility that misfire has occurred in a specific cylinder that is a cylinder from which the rotational fluctuation amount exceeding the predetermined threshold value has been acquired. At the same time (determined as “Yes” in step 620 in FIG. 6), the identification based on the change pattern of the rotational fluctuation amount acquired for each expansion stroke of each cylinder in a predetermined period after the expansion stroke of the specific cylinder. Determining whether or not misfire has occurred in the cylinder (this determination) (see FIGS. 3 to 5 and step 645 in FIG. 6);
Is provided.
And the misfire determination unit
When the rotational fluctuation amount exceeds the predetermined threshold value continuously in two cylinders whose ignition order is adjacent, the cylinder corresponding to the largest rotational fluctuation amount among the rotational fluctuation amounts of the two cylinders is selected as the specific cylinder (See step 625 in FIGS. 4, 5 and 6).

  Therefore, the present determination apparatus can monitor the change pattern of the rotational fluctuation amount with respect to the cylinder having a high probability of misfire, so that misfire determination can be more reliably performed.

  The present invention is not limited to the above embodiment, and various modifications can be employed within the scope of the present invention.

For example, in step 625 of FIG. 6 described above, this determination apparatus determines whether the determination timing counter in step 635 satisfies the relationship of the following expression (5) with respect to the rotational fluctuation amount for three cylinders adjacent in the ignition order. Ctmg is counted up, and if the relationship of the following expression (5) is not established, the determination timing counter Ctmg may be reset at step 630. The rotational fluctuation amounts for the current cylinder, the cylinder one cylinder before the current cylinder, and the cylinder two cylinders before the current cylinder are ΔNE (n), ΔNE (n−1), and ΔNE (n−2), respectively.

Ctmg = 0 and ΔNE (n−1) ≧ ΔNE (n)> ΔNE (n−2) (5)

  According to this, as shown in FIG. 4, for example, when the rotational fluctuation amount ΔNE exceeds the predetermined threshold Nth three times in succession (see ΔNE4 ′, ΔNE3, and ΔNE2 in FIG. 4), these rotations. It can be avoided that the cylinder corresponding to the largest rotation fluctuation amount ΔNE among the fluctuation amounts ΔNE is selected as the temporary misfire cylinder (specific cylinder). In such a case, even if the rotation fluctuation amount ΔNE is the largest, the probability that misfire has occurred in the cylinder is low.

  Furthermore, this determination apparatus can also be applied to an internal combustion engine of an engine other than 4 cylinders (for example, 8 cylinders, 12 cylinders, etc.).

  In addition, in the present embodiment, the rotational fluctuation amount ΔNE is calculated from the misfire correlation value (difference D) for the cylinder having a crank angle phase difference of 360 ° CA. However, the present invention is not limited to this. is not. In the present embodiment, the time required for calculating the misfire correlation value is obtained as the time required for the crankshaft to rotate 30 ° (Tpre, Tmid). May be obtained as the time (Tpre, Tmid) required for rotation of the angle by “an angle other than 30 °”. Further, the misfire correlation value is, for example, the time required for the crankshaft to rotate from “X ° CA to Y ° CA after compression top dead center (X and Y are both 0 to 180 ° CA)”. May be. That is, the misfire correlation value is a value that has a correlation with the crank angular velocity in the expansion stroke of an arbitrary cylinder, and is a value that is greater when misfire occurs than when normal combustion is performed in the same cylinder. If it is. Further, the rotational fluctuation amount may be calculated based on an expression other than the expression (2).

  Further, the predetermined threshold value Nth may be a constant value, and changes based on at least one of the engine speed NE and the engine load (for example, intake pressure Pm, accelerator pedal operation amount Accp, intake air amount Ga, etc.). It may be a value.

  DESCRIPTION OF SYMBOLS 20 ... Engine main-body part, 23 ... Fuel injection valve, 24 ... Ignition device, 27 ... Piston, 29 ... Crankshaft, 31 ... Timing rotor, 35 ... Combustion chamber, 41 ... Intake passage part, 42 ... Throttle valve, 43 ... Exhaust A passage part, 50 ... an electronic control unit, 51 ... a crank position sensor.

Claims (1)

A value that correlates with the crank angular velocity in the expansion stroke of an arbitrary cylinder and that is larger when misfire occurs than when normal combustion is performed in the same cylinder is acquired as a misfire correlation value. A misfire correlation value acquisition unit;
Rotation fluctuation amount for acquiring a difference amount between a misfire correlation value in one cylinder and a misfire correlation value in another cylinder having a specific relationship in the ignition order with the one cylinder as a rotation fluctuation amount of the one cylinder An acquisition unit;
When the acquired rotational fluctuation amount exceeds a predetermined threshold value, it is determined that there is a possibility that misfire has occurred in the specific cylinder that is the cylinder from which the rotational fluctuation amount exceeding the predetermined threshold value is acquired, and the specific cylinder A misfire determination unit that determines whether misfire has occurred in the specific cylinder based on a change pattern of the rotational fluctuation amount acquired for each expansion stroke of each cylinder in a predetermined period after the expansion stroke of
In a misfire determination device for an internal combustion engine comprising:
The misfire determination unit
When the rotation fluctuation amount exceeds the predetermined threshold value continuously in two cylinders whose ignition order is adjacent, a cylinder corresponding to a larger rotation fluctuation amount among the rotation fluctuation amounts of the two cylinders is selected as the specific cylinder Configured to
Misfire detection device.

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