Misfire detection device for internal combustion engine

Abstract

To provide an accidental fire determination device for an internal combustion engine capable of excellently determining the presence / absence of accidental fire in an internal combustion engine even when accidental fire occurs in a plurality of cylinders.SOLUTION: An accidental fire determination device 10 for an internal combustion engine comprises: a parameter calculation unit 40 that calculates an accidental fire parameter that has a correlation with an amount of change in rotational speed during a combustion stroke of each of a plurality of cylinders, based on a rotational speed detected by a crank angle sensor 21; and a determination unit 50 that when a comparison circuit 51 determines that the accidental fire parameter is less than a threshold value A1, determines that single cylinder accidental fire has occurred, and when the comparison circuit 55 determines that the accidental fire parameter is less than a threshold value A2, determines that single-cylinder accidental fire or multi-cylinder accidental fire has occurred.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a misfire detection device for an internal combustion engine that detects the presence or absence of a misfire in an internal combustion engine. [Background technology]

[0002] Efforts aimed at mitigating or reducing the impact of climate change have been ongoing for some time now, and research and development into improving emissions has been conducted to achieve this. In this regard, a device has been known that, in an engine equipped with a catalytic converter in an exhaust pipe, integrates the difference between the rotation speed of the internal combustion engine detected at each predetermined crank angle and a reference rotation speed over the entire combustion stroke to calculate a misfire determination parameter, and determines whether or not the misfire determination parameter is smaller than a predetermined threshold value to determine whether or not a misfire has occurred (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-198368 A Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, in an internal combustion engine having multiple cylinders, the rate of decrease in rotation speed when multiple cylinders misfire is smaller than the rate of decrease when a single cylinder misfires. Therefore, simply determining whether the misfire determination parameter is smaller than a predetermined threshold value as in the device described in Patent Document 1 above may not be able to accurately determine whether the internal combustion engine is misfiring when multiple cylinders misfire. [Means for solving the problem]

[0005] One embodiment of the present invention provides a misfire detection device for an internal combustion engine, the misfire detection device comprising: a speed detection unit that detects the rotational speed of an output shaft of an internal combustion engine having a plurality of cylinders; a parameter calculation unit that calculates a misfire parameter based on the rotational speed detected by the speed detection unit, the misfire parameter being correlated with the amount of change in rotational speed in the combustion stroke of each of the plurality of cylinders, the misfire parameter increasing as the increase in rotational speed increases; a first judgment unit that judges whether the misfire parameter calculated by the parameter calculation unit is less than a first threshold value; and a second judgment unit that judges whether the misfire parameter is less than a second threshold value that is greater than the first threshold value, and is equipped with a misfire judgment unit that judges whether or not a misfire has occurred in the internal combustion engine depending on the judgment results of the first judgment unit and the second judgment unit. The parameter calculation unit calculates a misfire parameter based on a relative rotation speed based on a rotation speed detected at a compression top dead center of each of the plurality of cylinders; The misfire determination unit is Identifying a target cylinder that is a cylinder in the middle of a combustion stroke among the plurality of cylinders; When the first determination unit determines that the misfire parameter is less than the first threshold, a single one of the multiple cylinders is subject A single-cylinder misfire, which is a misfire in a cylinder, is determined to have occurred, and a misfire parameter is calculated by a second determination unit. First threshold or more and If it is determined that the value is less than the second threshold value, , multiple Of the several cylinders Including the target cylinder It is determined that a multi-cylinder misfire, which is a misfire in two or more cylinders, has occurred. Effect of the Invention

[0006] According to the present invention, the presence or absence of a misfire in an internal combustion engine can be accurately determined even when multiple cylinders misfire. [Brief description of the drawings]

[0007] [Figure 1] 1 is a diagram showing a schematic configuration of a main part of an engine to which a misfire detection device according to an embodiment of the present invention is applied; [Diagram 2] FIG. 2 is a block diagram showing a control configuration of the engine in FIG. 1. [Figure 3A] 4 is a diagram showing changes in relative rotation speed based on the rotation speed detected near the compression top dead center of each cylinder of the engine; FIG. [Figure 3B] FIG. 3B is a diagram showing misfire parameters corresponding to the relative rotation speeds of FIG. 3A; [Figure 4]4 is a diagram showing changes in misfire parameters for each of a number of misfire patterns of an engine. [Diagram 5] 1 is a block diagram showing a configuration of a main part of an internal combustion engine misfire detection device according to an embodiment of the present invention; [Figure 6] FIG. 4 is a diagram showing an example of a normal cycle misfire parameter and a misfire cycle misfire parameter side by side; [Figure 7] FIG. 6 is a diagram showing the relationship between a flag signal output from the block diagram of FIG. 5 and a misfire pattern. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] An embodiment of the present invention will be described below with reference to Figs. 1 to 7. A misfire determination device for an internal combustion engine according to an embodiment of the present invention is configured to determine the presence or absence of a misfire in an internal combustion engine having a plurality of cylinders. First, a configuration of a gasoline engine as an internal combustion engine to which this embodiment is applied will be described. The engine is mounted in a vehicle and used as a driving source for traveling. The vehicle may be either an engine vehicle that runs using only the engine as a driving source, or a hybrid vehicle that runs using the engine and a motor as driving sources.

[0009] FIG. 1 is a diagram showing a schematic configuration of a main part of an engine 1 to which a misfire determination device according to an embodiment of the present invention is applied. The engine 1 is a four-stroke engine that undergoes four strokes, namely, intake, expansion, compression, and exhaust, during an operating period. A period from the start of the intake stroke to the end of the exhaust stroke is called one cycle of combustion of the engine 1, or simply one cycle. The expansion stroke is a stroke in which the mixture is burned, and is also called a combustion stroke. The engine 1 is a four-cylinder engine having four cylinders. Note that the number of cylinders of the engine 1 is not limited to this, and it may be a six-cylinder engine or an eight-cylinder engine, as long as it has a plurality of cylinders. FIG. 1 shows the configuration of a single cylinder. The configurations of the cylinders are the same as each other.

[0010] As shown in Fig. 1, the engine 1 has a cylinder 102 formed in a cylinder block 101, a piston 103 slidably disposed inside the cylinder 102, and a combustion chamber 105 formed between a crown surface (piston crown surface) 103a of the piston 103 and a cylinder head 104. A recess 103b is formed in the piston crown surface 103a so as to follow, for example, a tumble flow in the cylinder. The piston 103 is connected to a crankshaft 107 via a connecting rod 106, and the crankshaft 107 rotates as the piston 103 reciprocates along the inner wall of the cylinder 102. The crankshaft 107 corresponds to an output shaft of the engine 1.

[0011] The cylinder head 104 is provided with an intake port 111 and an exhaust port 112. An intake passage 113 communicates with the combustion chamber 105 via the intake port 111, and an exhaust passage 114 communicates with the combustion chamber 105 via the exhaust port 112. The intake port 111 is opened and closed by an intake valve 115, and the exhaust port 112 is opened and closed by an exhaust valve 116. A throttle valve 119 is provided in the intake passage 113 upstream of the intake valve 115. The throttle valve 119 is formed of, for example, a butterfly valve, and the amount of intake air to the combustion chamber 105 is adjusted by the throttle valve 119. The intake valve 115 and the exhaust valve 116 are driven to open and close by a valve mechanism 120.

[0012] An ignition plug 11 and an injector 12 are attached to the cylinder head 104 so as to face the combustion chamber 105. The ignition plug 11 is disposed between an intake port 111 and an exhaust port 112, and generates a spark at a predetermined timing using electrical energy to ignite the mixture of fuel and air in the combustion chamber 105.

[0013] Injector 12 is disposed near intake valve 115 and is driven by electrical energy to inject fuel. More specifically, injector 12 is supplied with high-pressure fuel from a fuel tank via a fuel pump. Injector 12 atomizes the fuel and injects the fuel diagonally downward into combustion chamber 105 at a predetermined timing. Note that, although injector 12 is shown in FIG. 1 as an in-cylinder injection type fuel injection valve, the arrangement of injector 12 is not limited thereto, and injector 12 may be disposed facing intake port 111, for example, to configure as a port injection type fuel injection valve.

[0014] The valve mechanism 120 has an intake camshaft 121 and an exhaust camshaft 122. The intake camshaft 121 has an intake cam 121a corresponding to each cylinder (cylinder 102) formed thereon, and the exhaust camshaft 122 has an exhaust cam 122a corresponding to each cylinder. The intake camshaft 121 and the exhaust camshaft 122 are connected to the crankshaft 107 via a timing belt (not shown), and each rotates once for every two rotations of the crankshaft 107.

[0015] Intake valve 115 opens and closes at a predetermined timing according to the profile of intake cam 121a via an intake rocker arm (not shown) as intake camshaft 121 rotates. Exhaust valve 116 opens and closes at a predetermined timing according to the profile of exhaust cam 122a via an exhaust rocker arm (not shown) as exhaust camshaft 122 rotates.

[0016] A catalytic device 13 for purifying exhaust gas is installed in the exhaust passage 114. The catalytic device 13 is a three-way catalyst that has the function of removing and purifying HC, CO, and NOx contained in the exhaust gas by oxidation and reduction. Other catalytic devices, such as an oxidation catalyst that oxidizes CO and HC in the exhaust gas, can also be used. When the temperature of the catalyst contained in the catalytic device 13 increases, the catalyst becomes more active, and the exhaust gas purification effect of the catalytic device 13 increases. For this reason, when the temperature of the catalyst is low, such as when the engine 1 is started, the mixture is after-burned, accelerating the rise in catalyst temperature.

[0017] A crank angle sensor 21 is provided near the crankshaft 107. The crank angle sensor 21 is configured to output a pulse signal (crank signal) in accordance with the rotation of the crankshaft 107. That is, the crank signal is output every time the crankshaft 107 rotates a predetermined angle (for example, 6°). Furthermore, the crank angle sensor 21 outputs a cylinder signal for identifying a cylinder of the engine 1 at a predetermined crank angle position of a specific cylinder, and outputs a top dead center signal when the piston 103 is at a predetermined crank angle position slightly before the top dead center in any cylinder.

[0018] Fig. 2 is a block diagram showing a schematic control configuration of the engine 1. As shown in Fig. 2, signals from a crank angle sensor 21 and other sensors 22 (for convenience, referred to as a sensor group) are input to a controller 20. Based on the signal from the crank angle sensor 21, the controller 20 determines the rotation angle (crank angle) of the crankshaft 107 based on the position of the top dead center TDC of the piston 103, and calculates the engine speed. The sensor group 22 includes an accelerator opening sensor that detects the amount of operation of the accelerator pedal, a water temperature sensor that detects the temperature of the engine coolant, an intake amount sensor that detects the amount of intake air of the engine 1, an AF sensor that detects the air-fuel ratio of the exhaust gas, and the like.

[0019] The controller 20 is an electronic control unit (ECU) for engine control, and is configured to include a computer having a calculation unit such as a CPU, storage units such as a ROM and a RAM, and other peripheral circuits. The controller 20 executes a predetermined process based on signals from the crank angle sensor 21 and the sensor group 22, and outputs control signals to the spark plug 11 and the injector 12 according to the driving mode. That is, the controller 20 controls the operation of the spark plug 11 and the injector 12 according to maps and characteristics according to the driving state, such as a catalyst warm-up mode that promotes warm-up of the catalytic converter 13 to realize early activation of the catalyst, a homogeneity improvement mode that optimizes fuel economy, and a knock suppression mode that suppresses the occurrence of knocking.

[0020] More specifically, the controller 20 outputs a control signal to the spark plug 11 so that the ignition timing is retarded from the optimal ignition timing MBT in the catalyst warm-up mode, so that the ignition timing is the optimal ignition timing or retarded to suppress the occurrence of knocking in the homogeneity improvement mode after the catalyst warm-up is completed, and so that the ignition timing is advanced from retarded to the MBT side in the knock suppression mode. The controller 20 also calculates a target injection amount per cycle according to the intake air amount detected by the intake air amount sensor while performing feedback control so that the actual air-fuel ratio detected by the AF sensor becomes the target air-fuel ratio (e.g., the theoretical air-fuel ratio). Then, the controller 20 calculates a target injection amount per cycle (unit target injection amount) taking into account the number of injections by the injector 12 per cycle, and outputs a control signal to the injector 12 so that the injector 12 injects this unit target injection amount at a predetermined timing.

[0021] When controlling the spark plug 11 and the injector 2, the controller 20 executes a misfire determination process to determine whether or not the engine 1 has misfired. In the misfire determination process, a misfire parameter is calculated for each cylinder in the combustion stroke (expansion stroke), and the misfire parameter is used to determine whether or not the engine 1 has misfired. The misfire parameter is calculated as follows based on a signal from the crank angle sensor 21. In the following, the four cylinders of the engine 1 are referred to as #1 cylinder, #2 cylinder, #3 cylinder, and #4 cylinder in the order of ignition. Misfires are likely to occur during weak combustion when the combustion torque is small, and are also likely to occur when the ignition timing is retarded in a catalyst warm-up mode or the like.

[0022] Fig. 3A is a diagram showing a change in relative rotation speed RV1 based on a rotation speed (referred to as a reference rotation speed RV0) detected near the compression top dead center of each cylinder in one cycle of the engine 1. The relative rotation speed RV1 is calculated by subtracting the reference rotation speed RV0 from the rotation speed RV calculated based on the time interval between crank signals. In Fig. 3A, cylinder #1 is in the combustion stroke when the crank angle θ is in the range from 0 to θ1 (180°), cylinder #2 is in the combustion stroke when the crank angle θ is in the range from θ1 to θ2 (360°), cylinder #3 is in the combustion stroke when the crank angle θ is in the range from θ2 to θ3, and cylinder #4 is in the combustion stroke when the crank angle θ is in the range from θ3 to θ4 (720°).

[0023] In the example of FIG. 3A, the relative rotation speed RV1 of the #1 cylinder, the #2 cylinder, and the #4 cylinder is faster than the relative rotation speed RV1 of the #3 cylinder. big During the combustion stroke (expansion stroke) after the compression top dead center, if a misfire occurs, the relative rotation speed RV1 becomes smaller than when there is no misfire. Therefore, it is estimated that combustion is normal in cylinders #1, #2, and #4, but a misfire is occurring in cylinder #3.

[0024] The controller 20 stores data (crank angle data) of the time intervals of crank signals outputted at every predetermined crank angle (6°) in the most recent cycle. The controller 20 integrates the relative rotation speed RV1 at every predetermined crank angle calculated from the crank angle data over the combustion stroke of each cylinder, and calculates the integral value as the misfire parameter α of each cylinder. The controller 20 may perform a filtering process on the relative rotation speed RV1 to cancel a linear change in one cycle period (720°), and then use the filtered relative rotation speed RV1 to calculate the misfire parameter α. The controller 20 may perform a correction on the relative rotation speed RV1 to compensate for an inertial force rotation speed component caused by the inertial force of the moving parts of the engine 1, and then use the corrected relative rotation speed RV1 to calculate the misfire parameter α.

[0025] Fig. 3B is a diagram showing the misfire parameter α corresponding to the relative rotation speed RV1 in Fig. 3A. As shown in Fig. 3B, the misfire parameters α for the #1, #2 and #4 cylinders are smaller than the misfire parameter α for the #3 cylinder. big Therefore, by setting a threshold value A1 to distinguish between these misfire parameters α and comparing the magnitude of the misfire parameter α with the threshold value A1, it is possible to determine whether or not a misfire occurs in each cylinder.

[0026] As shown in FIG. 3B, in the case of a single cylinder misfire, where a single cylinder #3 misfires, the difference in the misfire parameter α between that cylinder (called the misfiring cylinder) #3 and the cylinders #1, #2, and #4 that are burning normally (called normal cylinders) is large. However, in the case of a multi-cylinder misfire, where multiple cylinders misfire, the decrease in the relative rotation speed RV1 for the misfiring cylinder is smaller than in the case of a single misfiring cylinder. For this reason, it is difficult to accurately determine whether or not a misfire has occurred simply by comparing the magnitude of the misfire parameter α with a single threshold value A1. In particular, during weak combustion when the combustion torque is small, the misfire parameter α for the normal cylinder becomes small, and the difference with the misfire parameter α for the misfiring cylinder decreases, making it even more difficult to accurately determine whether or not a misfire has occurred. This point will be further explained.

[0027] 4 is a diagram showing the change in misfire parameter α for one cycle (720°) for each of a plurality of misfire patterns of the engine 1. In the following, for convenience, a cylinder in the middle of a combustion stroke or immediately after the completion of the combustion stroke, i.e., a cylinder from which the latest misfire parameter α can be obtained, is called the target cylinder a, the cylinder in the combustion stroke immediately before that is called the first reference cylinder a1, the cylinder in the combustion stroke immediately before the first reference cylinder a1 is called the second reference cylinder a2, and the cylinder in the combustion stroke immediately before the second reference cylinder a2 is called the third reference cylinder a3. The target cylinder a is a cylinder that is the subject of the misfire judgment, and the reference cylinders a1 to a3 are cylinders different from the target cylinder a.

[0028] The first reference cylinder a1 is a cylinder that had a combustion stroke one cylinder before the target cylinder a (here, the crank angle is 180° before), the second reference cylinder a2 is a cylinder that had a combustion stroke two cylinders before the target cylinder a (here, the crank angle is 360° before), and the third reference cylinder a3 is a cylinder that had a combustion stroke three cylinders before the target cylinder a (here, the crank angle is 540° before). For example, when the #1 cylinder is the target cylinder a, the #4 cylinder is the first reference cylinder a1, the #3 cylinder is the second reference cylinder a2, and the #2 cylinder is the third reference cylinder a3. When the #3 cylinder is the target cylinder a, the #2 cylinder is the first reference cylinder a1, the #1 cylinder is the second reference cylinder a2, and the #4 cylinder is the third reference cylinder a3. The target cylinder a is switched in sequence every time the crank angle changes by 180°.

[0029] The circles in Figure 4 indicate the change in the misfire parameter α when no misfire occurs in any of the cylinders a, a1 to a3, i.e., in a normal cycle where all of the cylinders a, a1 to a3 are normal cylinders. The crosses indicate the change in the misfire parameter α when a misfire occurs in some of the cylinders, i.e., in a misfire cycle where a misfiring cylinder is included. Note that the misfire parameter α varies to a certain extent from cycle to cycle, and the circles and crosses indicate the average or median value of the misfire parameter α that takes this variation into account.

[0030] Misfire patterns include single-cylinder misfires, where only the target cylinder a misfires, and multi-cylinder misfires, where the target cylinder a misfires and any of the first reference cylinder a1, the second reference cylinder a2, and the third reference cylinder a3. Multi-cylinder misfires are classified into opposed misfires, subsequent consecutive misfires, and preceding consecutive misfires. In opposed misfires, a misfire occurs between the target cylinder a and the second reference cylinder a2, whose combustion stroke is not consecutive to the target cylinder a. In subsequent consecutive misfires, a misfire occurs between the target cylinder a and the third reference cylinder a3, whose combustion stroke is consecutive to the target cylinder a and whose combustion stroke is subsequent to the target cylinder a. In preceding consecutive misfires, a misfire occurs between the target cylinder and the first reference cylinder a1, whose combustion stroke is consecutive to the target cylinder a and whose combustion stroke is prior to the target cylinder a.

[0031] In FIG. 4, cylinders with small combustion torque, i.e., cylinders with weak combustion, are shown by hatching. The misfire patterns in FIG. 4 are steadily repeated. For this reason, for example, in the case of a subsequent consecutive misfire, misfire occurs in the target cylinder a and the third reference cylinder a3 next to the target cylinder a. If the target cylinder at the present time is cylinder #3 and a subsequent consecutive misfire occurs, misfires will occur repeatedly in cylinders #3 and #4 in the combustion cycle of engine 1. In FIG. 4, the target cylinder a is a cylinder with weak combustion, and in all misfire patterns, misfires occur in the cylinders with weak combustion, including the target cylinder a (hatched area).

[0032] When a misfire occurs in the target cylinder a, the reference rotation speed RV0 when calculating the misfire parameter of the third reference cylinder a3, which is the next target cylinder, becomes smaller. Therefore, as shown in FIG. 4, the misfire parameter α of the third reference cylinder a3 becomes larger than the misfire parameter α of the target cylinder a in any misfire pattern. Also, the misfire parameter α (marked with an x) when a misfire occurs in the target cylinder a is smaller than the misfire parameter α (marked with a circle) during normal combustion for the target cylinder a. However, in the case of a multi-cylinder misfire, the misfire parameter α of the target cylinder a is affected by the misfires of the other cylinders a1 to a3, so the decrease in the misfire parameter α is smaller than in the case of a single-cylinder misfire. In particular, in the case of previous consecutive misfires, the reference rotation speed RV0 at the start of the combustion stroke in the target cylinder a becomes smaller due to the strong influence of the misfire in the immediately preceding first reference cylinder a1, so the relative rotation speed RV1 becomes larger, and the misfire parameter α of the target cylinder a tends to become larger.

[0033] Focusing on the difference Δα between the misfire parameter α of the target cylinder a in a normal cycle and the misfire parameter α of the target cylinder a in a misfire cycle, the magnitude of the difference Δα varies depending on the misfire pattern, and the difference Δα is the smallest in the case of previous consecutive misfires. As a result, there is a risk that misfire cannot be accurately determined by simply comparing the magnitude of the misfire parameter α with the threshold value A1 (FIG. 3B). In other words, if the threshold value A1 is set too small, there is a risk that normal combustion is erroneously determined to be occurring even when a misfire has occurred, and if the threshold value A1 is set too large, there is a risk that normal combustion is erroneously determined to be occurring even when a misfire has occurred. Therefore, in order to accurately determine the presence or absence of a misfire even during weak combustion, the misfire determination device of this embodiment is configured as follows.

[0034] Fig. 5 is a block diagram showing the configuration of the main parts of the misfire detection device 10 according to this embodiment. As shown in Fig. 5, the misfire detection device 10 has a crank angle sensor 21, a storage unit 30, a parameter calculation unit 40, and a determination unit 50. The storage unit 30, the parameter calculation unit 40, and the determination unit 50 are functional components of the controller 20. Therefore, in terms of hardware, the misfire detection device 10 is composed of the crank angle sensor 21 and the controller 20.

[0035] The storage unit 30 is a buffer memory that temporarily stores the crank signal from the crank angle sensor 21. The storage unit 30 stores data on the time intervals at which the crank signal occurs within a range from the current crank angle to a crank angle at least one cycle (720°) back, that is, the latest crank angle data for one cycle. In other words, the storage unit 30 stores crank angle data that allows the calculation of the misfire parameter α for each of the target cylinder a, the first reference cylinder a1, the second reference cylinder a2, and the third reference cylinder a3 as shown in FIG. 4.

[0036] The parameter calculation unit 40 includes a reference parameter calculation unit 41 and a combined parameter calculation unit 42. Based on the crank angle data stored in the storage unit 30, the reference parameter calculation unit 41 calculates the relative rotation speed RV1 of each cylinder in the combustion stroke of the engine 1, as described above, and integrates the relative rotation speed RV1 over the combustion stroke (expansion stroke) of each cylinder to calculate the misfire parameter α of each cylinder. That is, the misfire parameters α of the target cylinder a, the first reference cylinder a1, the second reference cylinder a2, and the third reference cylinder a3 are calculated. In FIG. 5, the misfire parameters α of the target cylinder a, the first reference cylinder a1, the second reference cylinder a2, and the third reference cylinder a3 are represented by α0, α1, α2, and α3, respectively.

[0037] Each time the reference parameter calculation unit 41 calculates the misfire parameter α0 of the target cylinder a, the misfire parameter α0 may be stored in the storage unit 30, and each time the cylinder moves in the combustion stroke, the misfire parameters α0, α1, α2 may be changed to α1, α2, α3, respectively. In this way, when the misfire parameter α of the target cylinder a is calculated, the misfire parameters α of the first reference cylinder a1, the second reference cylinder a2, and the third reference cylinder a3 are already stored in the storage unit 30, so that the reference parameter calculation unit 41 needs to calculate only the misfire parameter α0 of the target cylinder a, which reduces the processing load.

[0038] The combined parameter calculation unit 42 has addition circuits 43-45 that perform an addition process of the misfire parameter α. The addition circuit 43 adds the misfire parameter α0 of the target cylinder a and the misfire parameter α1 of the first reference cylinder a1 to calculate a combined parameter α11. The addition circuit 44 adds the misfire parameter α0 of the target cylinder a and the misfire parameter α2 of the second reference cylinder a2 to calculate a combined parameter α12. The addition circuit 45 adds the misfire parameter α0 of the target cylinder a and the misfire parameter α3 of the third reference cylinder a3 to calculate a combined parameter α13.

[0039] The judgment unit 50 has comparison circuits 51-55 for comparing the misfire parameter α with threshold values ​​A1-A4, an OR circuit 56, and an AND circuit 57. In FIG. 5, the cylinders that are the targets of misfire judgment among the multiple cylinders a, a1, a2, and a3 are indicated by hatching between the parameter calculation unit 40 and the judgment unit 50. The comparison circuit 51 judges whether the misfire parameter α0 of the target cylinder a is larger or smaller than a predetermined threshold value A1. The threshold value A1 (FIG. 3B) is set in consideration of the amount of decrease in the misfire parameter α when a single cylinder misfires. In other words, it is set in correspondence with the change in the misfire parameter α when each of the multiple cylinders misfires.

[0040] FIG. 6 is a diagram showing an example of the misfire parameter α (marked with a circle) in a normal cycle and the misfire parameter α (marked with a cross) in a misfire cycle. As shown in FIG. 6, the misfire parameter α in a misfire cycle when a single cylinder misfire occurs is smaller than the misfire parameter α in a multi-cylinder misfire. The threshold value A1 is set to a value that is larger than the misfire parameter α assumed when a single cylinder misfire occurs and smaller than the misfire parameter α assumed when a multi-cylinder misfire occurs, taking into consideration the amount of decrease in the misfire parameter α assumed when a single cylinder misfire occurs due to weak combustion and the amount of decrease in the misfire parameter α assumed when a multi-cylinder misfire occurs. If the comparison circuit 51 in FIG. 5 determines that the misfire parameter α0 of the target cylinder a is less than the threshold value A1, there is a possibility that a single-cylinder misfire occurs in the target cylinder a. In this case, the comparison circuit 51 outputs a flag signal f0 indicating the possibility of a single-cylinder misfire.

[0041] The comparison circuit 55 determines the magnitude relationship between the misfire parameter α0 of the target cylinder a and a predetermined threshold value A2. The threshold value A2 is set in consideration of the decrease in the misfire parameter α0 assumed during multi-cylinder misfire due to weak combustion. That is, it is set in association with the change in the misfire parameter α0 of the target cylinder a when each of all combinations (a, a1), (a, a2), (a, a3) of the target cylinder a and the other cylinders a1 to a3 among the plurality of cylinders misfires (multi-cylinder misfire). As shown in FIG. 6, the threshold value A2 is set to a value larger than the threshold value A1. More specifically, considering the decrease in the misfire parameter α assumed during multi-cylinder misfire and the fluctuation amount of the misfire parameter α assumed during normal combustion, it is set to a value larger than the misfire parameter α0 assumed during multi-cylinder misfire and smaller than the misfire parameter α assumed during normal combustion.

[0042] In the comparison circuit 55 of FIG. 5, when it is determined that the misfire parameter α0 is less than the threshold value A2, single-cylinder misfire may have occurred in the target cylinder a (α < A1 < A2), or multi-cylinder misfire may have occurred between the target cylinder a and the other cylinders a1 to a3 (A1 < α < A2). In this case, the comparison circuit 55 outputs a flag signal f4 indicating the possibility of single-cylinder misfire or multi-cylinder misfire. Thus, the condition for determining that misfire has occurred in the target cylinder a is at least that the flag signal f4 is output. When the flag signal f4 is not output, it is determined that misfire has not occurred in the target cylinder a.

[0043] The comparison circuit 52 determines the magnitude relationship between the combined parameter α11 and a predetermined threshold value A3. The comparison circuit 53 determines the magnitude relationship between the combined parameter α12 and a predetermined threshold value A4. The comparison circuit 54 determines the magnitude relationship between the combined parameter α13 and a predetermined threshold value A3. The threshold value A3 is set corresponding to continuous misfire, and the threshold value A4 is set corresponding to opposed misfire.

[0044] More specifically, the threshold A3 is set in consideration of the decrease in the misfire parameters α assumed during consecutive misfires due to weak combustion. That is, the threshold A3 is set in correspondence with the change in the combined parameters α11 and α13, which are the sum of the misfire parameters α0 and α1 or α0 and α3, assumed when a multi-cylinder misfire occurs in the combination (a, a1) of the target cylinder a and the first reference cylinder a1 among the multiple cylinders, and in the combination (a, a3) of the target cylinder a and the third reference cylinder a3. The threshold A4 is set in consideration of the decrease in the misfire parameters α assumed during opposed misfires due to weak combustion. That is, the threshold A4 is set in correspondence with the change in the combined parameter α12, which is the sum of the misfire parameters α0 and α2, assumed when a multi-cylinder misfire occurs in the combination (a, a2) of the target cylinder a and the second reference cylinder a2 among the multiple cylinders.

[0045] More specifically, if the sum of the misfire parameters α (circles in FIG. 4) of the cylinders in a normal cycle corresponding to the sum parameters α11, α12, α13 is taken as the sum parameter in the normal cycle, the thresholds A3 and A4 are set to values ​​greater than the sum parameters α11, α12, α13 in the misfire cycle and smaller than the sum parameter in the normal cycle. Note that the sum parameter in the normal cycle may be a value obtained by multiplying the misfire parameter α in a normal cycle (misfire parameter α in the target cylinder a) assumed during weak combustion. The thresholds A3 and A4 may be set to the same value. The threshold A3 may be set to different values ​​for the preceding consecutive misfires and the following consecutive misfires.

[0046] The difference between the sum parameters α11, α12, α13 in a misfire cycle and the sum parameters in a normal cycle is larger than the difference Δα (FIG. 4) between the misfire parameter α0 in a misfire cycle and the misfire parameter α in a normal cycle. This makes it easy to set the thresholds A3, A4 so that they are larger than the sum parameters α11, α12, α13 in a misfire cycle and smaller than the sum parameters in a normal cycle. When the comparison circuit 52 determines that the sum parameter α11 is less than the threshold A3, it outputs a flag signal f1 indicating the possibility of a preceding consecutive misfire. When the comparison circuit 53 determines that the sum parameter α12 is less than the threshold A4, it outputs a flag signal f2 indicating the possibility of an opposing misfire. When the comparison circuit 54 determines that the sum parameter α13 is less than the threshold A3, it outputs a flag signal f3 indicating the possibility of a following consecutive misfire.

[0047] When any one of the flag signals f0 to f3 is input, the OR circuit 56 outputs the flag signal f0 to f3, and when none of the flag signals f0 to f3 is input, the OR circuit 56 outputs an OFF signal.

[0048] The AND circuit 57 functions as a determination circuit that determines whether or not a misfire has occurred in the engine 1. When the OR circuit 56 outputs flag signals f0 to f3 and the comparison circuit 55 outputs flag signal f4, the AND circuit 57 determines that a misfire has occurred in the engine 1, that is, that the engine 1 is operating in a misfire cycle. On the other hand, when the OR circuit 56 outputs an off signal or the comparison circuit 55 does not output flag signal f4, the AND circuit 57 determines that a misfire has not occurred in the engine 1, that is, that the engine 1 is operating in a normal cycle.

[0049] When the AND circuit 57 determines that the engine 1 is operating in a misfire cycle, it further identifies a misfire pattern according to the flag signals f0 to f3. That is, when the flag signal f0 is output and none of the flag signals f1 to f3 are output, the AND circuit 57 determines that a single-cylinder misfire has occurred in the target cylinder a. When the flag signal f1 is output and the flag signal f0 is not output, the AND circuit 57 determines that a multi-cylinder misfire (preceding consecutive misfire) has occurred between the target cylinder a and the first reference cylinder a1. When the flag signal f2 is output and the flag signal f0 is not output, the AND circuit 57 determines that a multi-cylinder misfire (opposed misfire) has occurred between the target cylinder a and the second reference cylinder a2. When the flag signal f3 is output and the flag signal f0 is not output, the AND circuit 57 determines that a multi-cylinder misfire (postced consecutive misfire) has occurred between the target cylinder a and the third reference cylinder a3. When flag signal f0 is output and any one of flag signals f1 to f3 is output, it is determined that a single-cylinder misfire is occurring in target cylinder a, or that multiple-cylinder misfire is occurring in multiple cylinders including the target cylinder.

[0050] When the AND circuit 57 determines that a misfire is occurring in the engine 1, the controller 20 (FIG. 2) executes a process to suppress the misfire. For example, when the ignition timing is retarded, a control signal is output to the spark plug 11 so as to advance the ignition timing. Alternatively, a control signal is output to the injector 12 so as to change the injection pattern or injection timing.

[0051] Fig. 7 is a diagram showing the relationship between the flag signals f0 to f4 and misfire patterns. In Fig. 7, a circle indicates when the flag signals f0 to f4 are output, and an x ​​indicates when they are not output. The flag signals f1 to f3 are collectively indicated by a circle when any of the flag signals f1 to f3 is output, and an x ​​indicates when none of the flag signals are output. When the flag signals f0 to f4 are output, it means that at least the target cylinder a is misfiring; cases where normal combustion occurs in the target cylinder a and misfires occur in the other cylinders are not considered here.

[0052] As shown in FIG. 7, when the flag signal f0 and the flag signal f4 are output and the flag signals f1 to f3 are not output, the misfire parameter α0 is less than the threshold value A1 (FIG. 6), and it is determined that single-cylinder misfire has occurred in the target cylinder a. When none of the flag signals f0 to f4 are output, the engine 1 is determined to be burning in a normal cycle.

[0053] Even when the flag signal f4 is output and the flag signals f0 to f3 are not output, the engine 1 is determined to be burning in a normal cycle. In this case, although there is no misfire in the target cylinder a, it is considered that the flag signal f4 is output because the misfire parameter α0 has become smaller than the threshold value A2 due to weak combustion. That is, since the threshold value A2 is larger than the threshold value A1, the misfire parameter α0 may become smaller than the threshold value A2 even though no misfire has occurred. However, in the present embodiment, not only the flag signal f4 is output, but also the occurrence of multi-cylinder misfire is surely determined separately from normal combustion by setting the output of any one of the flag signals f1 to f3 as a condition for multi-cylinder misfire even when α0 < A2 is satisfied.

[0054] When the flag signal f0 and the flag signal f4 are output and further any one of the flag signals f1 to f3 is output, it is determined that single-cylinder misfire has occurred in the target cylinder a or multi-cylinder misfire has occurred in a plurality of cylinders including the target cylinder a. When any one of the flag signals f1 to f3 is output and neither the flag signals f0 nor f4 are output, although there is no misfire in the target cylinder a, it is considered that any one of the flag signals f1 to f3 is output because any one of the combined parameters α11 to α13 has become smaller than the threshold values A3 and A4 due to weak combustion. For this reason, the engine 1 is determined to be burning in a normal cycle.

[0055] When any one of flag signals f1 to f3 and flag signal f4 are output, but flag signal f0 is not output, it is determined that multiple cylinder misfires are occurring in multiple cylinders including target cylinder a. If the condition for determining multiple cylinder misfires were to be the output of flag signal f4 without the output of flag signal f0, there is a risk that it would be erroneously determined that a misfire has occurred even when normal combustion is occurring in engine 1. In contrast, by adding the output of any one of flag signals f1 to f3 to the conditions for determining multiple cylinder misfires, it is possible to reliably determine whether multiple cylinder misfires have occurred.

[0056] According to this embodiment, the following advantageous effects can be obtained. (1) The misfire detection device 10 for an internal combustion engine includes a crank angle sensor 21 that detects the rotation speed of a crankshaft 107 of an engine 1 having a plurality of cylinders, a parameter calculation unit 40 that calculates a misfire parameter α that is correlated with the amount of change in the rotation speed in the combustion stroke of each of the plurality of cylinders based on the rotation speed detected by the crank angle sensor 21, that is, a misfire parameter α that increases as the increase in the rotation speed increases, a comparison circuit 51 that determines whether the misfire parameter α0 calculated by the parameter calculation unit 40 (reference parameter calculation unit 41) is less than a threshold value A1 (first threshold value), and a comparison circuit 55 that determines whether the misfire parameter α0 is less than a threshold value A2 (second threshold value) that is greater than the threshold value A1, and a determination unit 50 that determines whether or not a misfire occurs in the engine 1 based on the determination results of the comparison circuits 51 and 55 (FIG. 5). When the comparison circuit 51 determines that the misfire parameter α0 is less than the threshold value A1, the judgment unit 50 determines that a single-cylinder misfire, which is a misfire in one of the multiple cylinders, has occurred, and when the comparison circuit 55 determines that the misfire parameter α0 is less than the threshold value A2, the judgment unit 50 determines that a single-cylinder misfire or a multi-cylinder misfire, which is a misfire in two or more of the multiple cylinders, has occurred (Figure 5).

[0057] This configuration makes it possible to accurately determine whether or not a multi-cylinder misfire has occurred in the engine 1. That is, because the amount of decrease in the misfire parameter α0 differs between single-cylinder misfire and multi-cylinder misfire, it is difficult to accurately determine whether or not a misfire has occurred simply by comparing the misfire parameter α0 with a single threshold value A1 or A2, but by comparing the misfire parameter α0 with two different threshold values ​​A1, A2, it is possible to accurately determine whether or not a single-cylinder misfire and multi-cylinder misfire has occurred.

[0058] (2) The determination unit 50 identifies a target cylinder a among the multiple cylinders that is in the combustion stroke or has just completed the combustion stroke, and determines that a single-cylinder misfire has occurred in the target cylinder a if the comparison circuit 51 determines that the misfire parameter α0 is less than the threshold value A1, and determines that a multi-cylinder misfire has occurred in two cylinders including the target cylinder a if the misfire parameter α0 is equal to or greater than the threshold value A1 and less than the threshold value A2 (FIG. 6). This makes it possible to identify the cylinder in which a misfire has occurred and to distinguish between single-cylinder misfire and multi-cylinder misfire.

[0059] (3) The parameter calculation unit 40 calculates a misfire parameter α0 that is correlated with the amount of change in the rotation speed in the combustion stroke of the target cylinder a, and misfire parameters α1 to α3 that are correlated with the amount of change in the rotation speed in the combustion stroke of the reference cylinders a1 to a3 within a crank angle range going back one cycle of the engine 1 from the combustion stroke of the target cylinder a, based on the rotation speed detected by the crank angle sensor 21, and calculates a combined parameter (combined misfire parameter) α11 to α13 that is the sum of the misfire parameter α0 and any one of the misfire parameters α1 to α3 (FIG. 5). The determination unit 50 further includes comparison circuits 52 to 54 that determine whether the combined parameters α11 to α13 calculated by the parameter calculation unit 40 are less than thresholds A3 and A4 (third thresholds) (FIG. 5). The determination unit 50 determines that a misfire has occurred in the target cylinder a when the comparison circuit 51 determines that the misfire parameter α0 is less than the threshold A1, and / or the comparison circuits 52-54 determine that the combined parameters α11-α13 are less than the thresholds A3, A4, and the comparison circuit 55 determines that the misfire parameter α0 is less than the threshold A2, and determines that a misfire has not occurred in the target cylinder a even if the comparison circuit 55 determines that the misfire parameter α0 is less than the threshold A2 when the comparison circuit 51 determines that the misfire parameter α0 is equal to or greater than the threshold A1 and the comparison circuits 52-54 determine that the combined parameters α11-α13 are equal to or greater than the thresholds A3, A4 (FIGS. 5 and 7). The characteristics of the misfire parameter α when multiple cylinders misfire can be well reflected by the combined parameters α11-α13. Therefore, the combined parameters α11-α13 can be used to accurately determine the presence or absence of multiple cylinder misfire.

[0060] (4) When the comparison circuit 51 determines that the misfire parameter α0 is less than the threshold A1 and the comparison circuits 52-54 determine that the combined parameters α11-α13 are equal to or greater than the thresholds A3 and A4, the determination unit 50 determines that a single-cylinder misfire has occurred in the target cylinder a. In other words, when the misfire parameter α0 is less than the threshold A1, the condition that the misfire parameter α0 is less than the threshold A2 is satisfied, so the determination unit 50 determines that a single-cylinder misfire has occurred in the target cylinder a without comparing the magnitude of the misfire parameter α0 with the threshold A2 (FIG. 5). This makes it possible to accurately determine whether a single-cylinder misfire has occurred.

[0061] (5) When the comparison circuit 51 determines that the misfire parameter α0 is equal to or greater than the threshold A1, the comparison circuit 55 determines that the misfire parameter α0 is less than the threshold A2, and the comparison circuits 52-54 determine that the combined parameters α11-α13 are less than the thresholds A3 and A4, the determination unit 50 determines that multi-cylinder misfire is occurring in two cylinders including the target cylinder a. This makes it possible to accurately determine whether or not multi-cylinder misfire is occurring.

[0062] (6) The threshold value A1 is set in advance in correspondence with the change in the misfire parameter α0 when a single-cylinder misfire occurs in each of the multiple cylinders ( FIG. 6 ). By setting the threshold value A1 in this manner, single-cylinder misfires and multi-cylinder misfires can be clearly distinguished, and the occurrence of a single-cylinder misfire can be detected with high accuracy.

[0063] (7) The threshold value A2 is set in advance in correspondence with the change in the misfire parameter α0 when multiple cylinder misfires occur when two cylinders in all combinations of the multiple cylinders occur (FIG. 6). By setting the threshold value A2 in this manner, single-cylinder misfires and multiple-cylinder misfires can be clearly distinguished, and the occurrence of multiple-cylinder misfires can be detected with high accuracy.

[0064] (8) The thresholds A3 and A4 are set in advance in correspondence with the changes in the combined parameters α13-α14 when multiple cylinder misfires occur in all combinations of two cylinders. By setting the thresholds A3 and A4 in this manner, multiple cylinder misfires can be clearly distinguished from normal combustion, and the occurrence of multiple cylinder misfires can be detected with high accuracy.

[0065] In the above embodiment, the engine 1 has been described as having four cylinders. However, as long as the engine 1 has a plurality of cylinders, the number of cylinders is not limited to four and may be five or more. In the case of an engine 1 having, for example, six cylinders, a combustion stroke is started in a different cylinder in sequence every time the crank angle θ changes by 120°. In this case, the parameter calculation unit 40 may calculate the misfire parameter α for the target cylinder a based on the crank angle data detected by the crank angle sensor 21 from when the combustion stroke starts in the target cylinder a until when the combustion stroke starts in the next cylinder (another cylinder) (until the crank angle θ changes by 120°). This allows the presence or absence of a misfire in the engine 1 to be accurately determined even if the number of cylinders is five or more.

[0066] In the above embodiment, the misfire determination device 10 is applied to an engine vehicle that runs on the power of the engine 1, but the misfire determination device can also be applied to a hybrid vehicle having the engine 1 and a traveling motor. In this case, the misfire determination device 10 further includes a rotation speed detector such as a resolver that detects the rotation speed of the traveling motor, and the parameter calculation unit 40 calculates the misfire parameter α based on the crank angle data detected by the crank angle sensor 21 (first speed detection unit) and the rotation speed of the traveling motor detected by the rotation speed detector (second speed detection unit). This makes it possible to accurately determine the presence or absence of misfire in the engine 1 by excluding the influence of the rotation of the traveling motor on the rotation speed of the engine 1. Note that the electric device that is rotationally driven by the power of the engine 1 may be another electric device such as a generator instead of the traveling motor, and the rotation speed detector may detect the rotation speed of the generator or the like. A sensor that detects a load acting on the electric device may be provided, and the parameter calculation unit 40 may calculate the misfire parameter α based on the load detected by this sensor and the crank angle data.

[0067] In the above embodiment, a case where two cylinders misfire in one combustion cycle of the engine 1 among a plurality of cylinders of the engine 1 as an internal combustion engine has been described as an example of a multi-cylinder misfire, but the number of cylinders misfiring in a multi-cylinder misfire is not limited to two and may be three or more. In the above embodiment, the crank angle sensor 21 detects the rotation speed of the crankshaft (output shaft) 107 of the engine 1, but the configuration of the speed detection unit is not limited to the above. In the above embodiment, the parameter calculation unit 40 calculates the misfire parameter α for each combustion stroke of the plurality of cylinders over one cycle of the engine 1 based on the crank angle data stored in the storage unit 30. That is, based on the crank angle data, the parameter calculation unit 40 calculates misfire parameter α0 (first misfire parameter) which is correlated with the amount of change in rotational speed during the combustion stroke of the target cylinder a, and misfire parameters α1 to α3 (second misfire parameters) which are correlated with the amount of change in rotational speed during the combustion stroke of the reference cylinders a1 to a3 within a crank angle range going back one cycle from the combustion stroke of the target cylinder a, and calculates combined parameters α11 to α13 which are the sum of the misfire parameter α0 and the misfire parameters α1 to α3. However, the parameter calculation unit may be configured in any way as long as it calculates a misfire parameter which is correlated with the amount of change in rotational speed during the combustion stroke and which increases as the increase in rotational speed increases.

[0068] In the above-described embodiment, the comparison circuit 51 as the first determination unit determines whether α0 < A1, the comparison circuit 55 as the second determination unit determines whether α0 < A2, and further, the comparison circuits 52 to 54 as the third determination unit determine whether α11 < A3, α12 < A4, and α13 < A3, and the presence or absence of misfire in the engine 1 is determined according to the determination results. However, the configuration of the misfire determination unit is not limited to this. For example, the third determination unit may be excluded from the misfire determination unit, and the presence or absence of misfire in the target cylinder a may be determined according to the determination results of the first determination unit and the second determination unit without passing through the AND circuit 57 in FIG. 5. In the above-described embodiment, various threshold values A1 (first threshold value), threshold value A2 (second threshold value), and threshold values A3 and A4 (third threshold value) are stored in the storage unit 30 in advance. In this regard, as long as the value of the threshold A1 is set to a value that can determine whether single-cylinder misfire has occurred corresponding to the misfire parameter, the value of the threshold A1 may be any value. As long as the value of the threshold A2 is set to a value that can determine whether single-cylinder misfire or multi-cylinder misfire has occurred corresponding to the misfire parameter, the value of the threshold A2 may be any value. As long as the settings of the threshold values A3 and A4 are set to values that can determine whether multi-cylinder misfire has occurred corresponding to the combined parameter, the settings of the threshold values A3 and A4 may be any values. Note that the threshold values A1 to A4 change according to the operating conditions of the engine 1. Therefore, the threshold values A1 to A4 may be stored in the memory in advance by a map or the like according to the operating conditions.

[0069] In the above embodiment, when the misfire parameter α0 of the target cylinder a is less than the threshold value A1, it is determined that a single-cylinder misfire has occurred, but the misfire parameter α0 may also be less than the threshold value A1 in the case of multiple cylinder misfires. For example, under limited engine conditions, when a misfire occurs, resonance occurs in the power plant, and an opposing misfire and a subsequent consecutive misfire occur (when a preceding consecutive misfire is not occurring) due to a reaction from the transmission provided in the torque transmission path between the engine and the axle, and the misfire parameter α0 may be less than the threshold value A1. Taking this into consideration, when the first judgment unit determines that the misfire parameter α0 is less than the threshold value A1, the misfire judgment unit may determine that a single-cylinder misfire has occurred, which is a misfire in the target cylinder a, or that a multi-cylinder misfire has occurred, which is a misfire in two or more cylinders (a, a2) or (a, a3) that include the target cylinder a and do not include the cylinder (first reference cylinder a1) that entered the combustion stroke immediately before the target cylinder a (this is referred to as a first multi-cylinder misfire), and when the second judgment unit determines that the misfire parameter α0 is less than the threshold value A2, it may determine that a single-cylinder misfire has occurred, or that a multi-cylinder misfire has occurred, which is a misfire in two or more cylinders (a, a1), (a, a2) or (a, a3) including the target cylinder a (this is referred to as a second multi-cylinder misfire).

[0070] The above description is merely an example, and the present invention is not limited to the above-mentioned embodiment and modifications, as long as the features of the present invention are not impaired. The above-mentioned embodiment and one or more modifications can be arbitrarily combined, and modifications can be combined with each other. [Explanation of symbols]

[0071] 1 engine, 21 crank angle sensor, 40 parameter calculation unit, 50 judgment unit, 51 to 55 comparison circuit, 56 OR circuit, 57 AND circuit, α0 to α4 misfire parameters, α11 to α13 combined parameters, A1 to A4 threshold values

Claims

1. a speed detection unit that detects a rotation speed of an output shaft of an internal combustion engine having a plurality of cylinders; a parameter calculation unit that calculates a misfire parameter that is correlated with an amount of change in the rotation speed in a combustion stroke of each of the plurality of cylinders based on the rotation speed detected by the speed detection unit, the misfire parameter increasing as an increase in the rotation speed increases; a misfire determination unit that has a first determination unit that determines whether the misfire parameter calculated by the parameter calculation unit is less than a first threshold value, and a second determination unit that determines whether the misfire parameter is less than a second threshold value that is greater than the first threshold value, and that determines whether or not there is a misfire in the internal combustion engine depending on determination results of the first determination unit and the second determination unit, the parameter calculation unit calculates the misfire parameter based on a relative rotation speed based on a rotation speed detected at a compression top dead center of each of the plurality of cylinders; The misfire judgment unit identifies a target cylinder among the multiple cylinders which is in the middle of a combustion stroke, and when the first judgment unit judges that the misfire parameter is less than the first threshold value, judges that a single-cylinder misfire has occurred, which is a misfire in the single target cylinder among the multiple cylinders, and when the second judgment unit judges that the misfire parameter is equal to or greater than the first threshold value and less than the second threshold value, judges that a multi-cylinder misfire has occurred, which is a misfire in two or more cylinders including the target cylinder among the multiple cylinders.

2. The misfire detection device for an internal combustion engine according to claim 1, the plurality of cylinders includes the target cylinder and a reference cylinder different from the target cylinder, the parameter calculation unit calculates, based on the rotation speed detected by the speed detection unit, a first misfire parameter that is correlated with an amount of change in the rotation speed during a combustion stroke of the target cylinder and corresponds to the misfire parameter, and a second misfire parameter that is correlated with an amount of change in the rotation speed during a combustion stroke of the reference cylinder within a range going back one cycle of combustion in the internal combustion engine from the combustion stroke of the target cylinder as a starting point, and calculates a combined misfire parameter that is the sum of the first misfire parameter and the second misfire parameter; The misfire determination unit is A misfire detection device for an internal combustion engine further comprising a third judgment unit which judges whether the combined misfire parameter calculated by the parameter calculation unit is less than a third threshold value, and when the first judgment unit judges that the first misfire parameter is equal to or greater than the first threshold value and the third judgment unit judges that the combined misfire parameter is equal to or greater than the third threshold value, the device judges that the multi-cylinder misfire has not occurred in two or more cylinders including the target cylinder, even if the second judgment unit judges that the first misfire parameter is less than the second threshold value.

3. The misfire detection device for an internal combustion engine according to claim 2, A misfire detection device for an internal combustion engine, characterized in that when the third judgment unit judges that the combined misfire parameter is less than the third threshold, the misfire detection unit judges that the multi-cylinder misfire has occurred in two or more cylinders including the target cylinder, even if the first judgment unit judges that the first misfire parameter is less than the first threshold.

4. The misfire detection device for an internal combustion engine according to any one of claims 1 to 3, A misfire determination device for an internal combustion engine, wherein the first threshold value is set in advance in correspondence with a change in the misfire parameter when a single-cylinder misfire occurs in each of the plurality of cylinders.

5. The misfire detection device for an internal combustion engine according to claim 2 or 3, A misfire detection device for an internal combustion engine, characterized in that the second threshold value is set in advance in correspondence with a change in the first misfire parameter when two or more cylinders consisting of all combinations of the plurality of cylinders experience the multi-cylinder misfire.

6. The misfire detection device for an internal combustion engine according to claim 2 or 3, A misfire detection device for an internal combustion engine, characterized in that the third threshold value is set in advance in correspondence with a change in the combined misfire parameter when two or more cylinders consisting of all combinations of the plurality of cylinders misfire.

7. The misfire detection device for an internal combustion engine according to any one of claims 1 to 3, The internal combustion engine has five or more cylinders, a misfire detection device for an internal combustion engine, characterized in that the parameter calculation unit calculates the misfire parameter for the target cylinder based on the rotational speed detected by the speed detection unit from the start of a combustion stroke in the target cylinder to the start of a combustion stroke in another cylinder.

8. The misfire detection device for an internal combustion engine according to any one of claims 1 to 3, the parameter calculation unit calculates the relative rotational speed for each predetermined crank angle of the internal combustion engine by subtracting a rotational speed detected at the compression top dead center immediately before the combustion stroke from the rotational speed in the combustion stroke of each of the plurality of cylinders, integrates the relative rotational speed for each predetermined crank angle over the combustion stroke of each of the plurality of cylinders, and calculates the integrated value as the misfire parameter.

9. A speed detection unit that detects the rotational speed of an output shaft of an internal combustion engine having a plurality of cylinders; a parameter calculation unit that calculates a misfire parameter that is correlated with an amount of change in the rotation speed in a combustion stroke of each of the plurality of cylinders based on the rotation speed detected by the speed detection unit, the misfire parameter increasing as an increase in the rotation speed increases; a misfire determination unit that has a first determination unit that determines whether the misfire parameter calculated by the parameter calculation unit is less than a first threshold value, and a second determination unit that determines whether the misfire parameter is less than a second threshold value that is greater than the first threshold value, and that determines whether or not there is a misfire in the internal combustion engine depending on determination results of the first determination unit and the second determination unit, the misfire determination unit identifies a target cylinder among the plurality of cylinders which is a cylinder in the middle of a combustion stroke, and, when the first determination unit determines that the misfire parameter is less than the first threshold value, determines that a single-cylinder misfire has occurred which is a misfire in the single target cylinder among the plurality of cylinders, and, when the second determination unit determines that the misfire parameter is equal to or greater than the first threshold value and less than the second threshold value, determines that a multi-cylinder misfire has occurred which is a misfire in two or more cylinders including the target cylinder among the plurality of cylinders, the plurality of cylinders includes the target cylinder and a reference cylinder different from the target cylinder, the parameter calculation unit calculates, based on the rotation speed detected by the speed detection unit, a first misfire parameter that is correlated with an amount of change in the rotation speed during a combustion stroke of the target cylinder and corresponds to the misfire parameter, and a second misfire parameter that is correlated with an amount of change in the rotation speed during a combustion stroke of the reference cylinder within a range going back one cycle of combustion in the internal combustion engine from the combustion stroke of the target cylinder as a starting point, and calculates a combined misfire parameter that is the sum of the first misfire parameter and the second misfire parameter; The misfire judgment unit further has a third judgment unit that judges whether the combined misfire parameter calculated by the parameter calculation unit is less than a third threshold, and when the first judgment unit judges that the first misfire parameter is equal to or greater than the first threshold and the third judgment unit judges that the combined misfire parameter is equal to or greater than the third threshold, the misfire judgment unit judges that the multi-cylinder misfire has not occurred in two or more cylinders including the target cylinder, even if the second judgment unit judges that the first misfire parameter is less than the second threshold.

Images