Misfire detection device for internal combustion engines

Abstract

To provide a misfire detection device for an internal combustion engine, which can calculate a torsional velocity component with high accuracy.SOLUTION: A CPU substitutes a difference between a crank-side speed ωe, which is the rotation speed of a crankshaft, and a rear stage-side speed ωout, which is a speed of a damper on the side opposite to the crankshaft, into a differential speed ωdamp (S46). The CPU calculates a torsion angle θdamp by integration processing of the differential speed ωdamp (S48). The CPU calculates a torsional velocity component ωr, which is the velocity component of the crankshaft due to torsion of the damper, on the basis of multiplication of the torsion angle θdamp and a damper stiffness value K (S58). Based on the torsional speed component ωr, the CPU calculates a time T30 as a variable representing the speed of the crankshaft (S60), which is used for misfire determination. The CPU switches the value of the damper stiffness value K depending on whether or not a vehicle is idling (S50-S54).SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a misfire detection device for an internal combustion engine. [Background technology]

[0002] For example, the following Patent Document 1 describes a misfire detection device applied to an internal combustion engine in which the crankshaft is mechanically connected to the drive wheels via a damper. This device calculates the torsional speed component of the crankshaft rotation speed due to resonance based on a physical model that uses as input the difference between the rotation speed of the crankshaft and the rear-stage speed, which is the rotation speed of the damper on the drive wheels side. This device then determines the presence or absence of misfire based on the value obtained by removing the torsional speed component from the crankshaft rotation speed.

[0003] The physical model uses the fact that the torque applied to the damper is the value obtained by multiplying the torsional angle of the damper by the damper stiffness value. Here, the integrated value of the above difference indicates the torsional angle of the damper. Therefore, the torque applied to the damper can be calculated by multiplying the integrated value by the damper stiffness value. And, since this torque determines the rate of change of the torsional angle, the torsional speed component can be calculated based on this. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-248877 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, since the relationship between the torsion angle and the torque applied to the damper varies, if the damper stiffness value is set to a fixed value, it may not be possible to accurately represent the target characteristics using a physical model. [Means for solving the problem]

[0006] Means for solving the above problems and their effects will be described below. The present invention is applied to an internal combustion engine having a plurality of cylinders, and a crankshaft of the internal combustion engine is connected to a torsional rigid body, and a crank side acquisition process, a rear stage side acquisition process, a torsional speed component calculation process, a judgment fluctuation amount calculation process, and a judgment process are executed, the crank side acquisition process is a process for acquiring a crank side speed variable which is a variable indicating the rotation speed of the crankshaft based on a crank signal, the rear stage side acquisition process is a process for acquiring a rear stage side speed variable which is a variable indicating the rotation speed of the torsional rigid body on the opposite side to the crankshaft, and the torsional speed component calculation process is a process for calculating a difference between the crank side speed variable and the rear stage side speed variable based on a damper stiffness value. A misfire detection device for an internal combustion engine, which is a process for calculating a torsional speed component, which is a speed component caused by torsion of the torsional rigidity body, includes a stiffness value varying process, the judgment fluctuation amount calculation process is a process for calculating a judgment fluctuation amount based on the value of the crank side speed variable from which the torsional speed component has been removed, the judgment fluctuation amount is an amount indicating a rotation fluctuation amount used in determining whether or not a misfire has occurred in the internal combustion engine, and the stiffness value varying process is a process for changing the damper stiffness value based on the magnitude of the load on the internal combustion engine.

[0007] The relationship between the torsion angle of the damper rigid body and the torque is nonlinear. On the other hand, when the load of the internal combustion engine is large, the torque applied to the internal combustion engine is large compared to when the load is small, so the center of variation of the torsion angle tends to deviate from zero. When the center of variation deviates from zero, the angle at which the misfire detection device recognizes the torsion angle as zero may deviate from the actual zero point. Therefore, if the same proportional constant is used as the damper rigidity value when the load is large and when it is small, the physical characteristics of the torsion rigidity body cannot be accurately expressed by the physical model. Therefore, in the above configuration, the damper rigidity value is changed based on the magnitude of the load of the internal combustion engine, so that the physical characteristics of the torsion rigidity body can be expressed with high accuracy regardless of the magnitude of the load of the internal combustion engine. Therefore, in the above configuration, the torsion speed component can be calculated with high accuracy, so that misfire can be detected with high accuracy. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a diagram showing a control device and a drive system according to an embodiment. [Diagram 2] 4 is a flowchart showing a procedure of a process executed by the control device according to the embodiment. [Diagram 3] 4 is a flowchart showing a procedure of a process executed by the control device according to the embodiment. [Figure 4] FIG. 4 is a diagram showing the relationship between the damper torsion angle and torque according to the embodiment. [Diagram 5] FIG. 4 is a cross-sectional view showing a configuration of a portion of the damper. [Figure 6] 13(a) and (b) are cross-sectional views showing the state of the coil spring of the damper. [Figure 7] 4A and 4B are diagrams showing the tendency of a map for calculating a damper stiffness value. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment will be described with reference to the drawings. As shown in Fig. 1, the internal combustion engine 10 is a four-stroke engine having four cylinders #1, #2, #3, and #4. A crank rotor 20 having teeth 22 is coupled to a crankshaft 12 of the internal combustion engine 10. The teeth 22 indicate each of a plurality of rotation angles of the crankshaft 12. The crank rotor 20 is basically provided with teeth 22 at intervals of 10° CA, but is provided with one missing tooth portion 24 where the interval between adjacent teeth 22 is 30° CA. This is for indicating a reference rotation angle of the crankshaft 12.

[0010] A planetary gear mechanism 30 constituting a power split device is mechanically connected to the crankshaft 12 via a damper 14. The damper 14 is provided with a coil spring and exerts elastic force. The planetary gear mechanism 30 splits the power of the internal combustion engine 10, the first motor generator 40, and the second motor generator 50. The crankshaft 12 is mechanically connected to a carrier C of the planetary gear mechanism 30 via the damper 14. A rotating shaft 42 of the first motor generator 40 is mechanically connected to a sun gear S of the planetary gear mechanism 30. A rotating shaft 52 of the second motor generator 50 is mechanically connected to a ring gear R of the planetary gear mechanism 30. The output voltage of the first inverter 44 is applied to the terminals of the first motor generator 40. The output voltage of the second inverter 54 is applied to the terminals of the second motor generator 50.

[0011] In addition to the rotary shaft 52 of the second motor generator 50 , the ring gear R of the planetary gear mechanism 30 is mechanically connected to the drive wheels 34 via the transmission 32 . The control device 60 operates various operating parts of the internal combustion engine 10 to control the torque, exhaust component ratio, and other controlled variables of the internal combustion engine 10 as a controlled object. The control device 60 also operates the first inverter 44 to control the torque, rotation speed, and other controlled variables of the first motor generator 40 as a controlled object. The control device 60 also operates the second inverter 54 to control the torque, rotation speed, and other controlled variables of the second motor generator 50 as a controlled object.

[0012] When controlling the above-mentioned controlled variables, the control device 60 refers to the output signal Scr of the crank angle sensor 70. The control device 60 also refers to the output signal Sm1 of the first rotation angle sensor 72 that detects the rotation angle of the rotating shaft 42 of the first motor-generator 40. The control device 60 also refers to the output signal Sm2 of the second rotation angle sensor 74 that detects the rotation angle of the rotating shaft 52 of the second motor-generator 50.

[0013] The control device 60 includes a CPU 62, a ROM 64, a RAM 66, and a peripheral circuit 68, which are capable of communicating with each other via a local network 69. Here, the peripheral circuit 68 includes a circuit for generating a clock signal that regulates the internal operation, a power supply circuit, a reset circuit, etc. The control device 60 controls the control amount by the CPU 62 executing a program stored in the ROM 64.

[0014] Fig. 2 shows the procedure of the process executed by the control device 60. The process shown in Fig. 2 is realized by the CPU 62 repeatedly executing a program stored in the ROM 64 at a predetermined crank angle period. In the following, the step number of each process is represented by a number preceded by "S".

[0015] In the series of processes shown in Fig. 2, the CPU 62 first obtains the time T30 required for the crankshaft 12 to rotate 30 CA degrees (S10). Next, the CPU 62 executes a process of substituting the time T30[m] into the time T30[m+1] where "m = 0, 1, 2, 3, ..." and a process of substituting the time T30 newly obtained in the process of S10 into the time T30[0] (S12). These processes are performed so that the variable in parentheses after the time T30 has a larger number the earlier it is. If the value of the variable in parentheses is one number larger as a result of these processes, the time T30 becomes 30 CA degrees earlier.

[0016] Next, the CPU 62 determines whether the current rotation angle of the crankshaft 12 is ATDC120° CA based on the compression top dead center of any of the cylinders #1 to #4 (S14). When the CPU 62 determines that the current rotation angle is ATDC120° CA (S14: YES), it assigns the rotation fluctuation amount ΔT30[m] to the rotation fluctuation amount ΔT30[m+1], and assigns the value obtained by subtracting the time T30[4] from the time T30[0] to the rotation fluctuation amount ΔT30[0] (S16). The rotation fluctuation amount ΔT30 is a variable that is negative when no misfire occurs in the cylinder that is the subject of the determination of the presence or absence of misfire, and is positive when a misfire occurs. Here, the cylinder that is the subject of the determination of the presence or absence of misfire is the cylinder that is determined to have passed the compression top dead center by 120° in the process of S14.

[0017] Next, the CPU 62 determines whether or not a value obtained by subtracting the rotation fluctuation amount ΔT30 “2” from the rotation fluctuation amount ΔT30[0] is equal to or greater than a threshold value ΔTth (S18). This process is a process for determining whether or not a misfire has occurred in the cylinder to be determined. In other words, if a misfire has not occurred, the rotational fluctuation amount ΔT30[0] and the rotational fluctuation amount ΔT30[2] are approximately the same value, so the difference between them has a small absolute value. In contrast, if a misfire has occurred in the cylinder to be determined, the rotational fluctuation amount ΔT30[0] is a positive value. On the other hand, if a misfire has not occurred in the cylinder that reached the compression top dead center 360° CA before the cylinder to be determined, the rotational fluctuation amount ΔT30[2] is a negative value. Therefore, if a misfire has occurred in the cylinder to be determined, the value obtained by subtracting the rotational fluctuation amount ΔT30 “2” from the rotational fluctuation amount ΔT30[0] is a positive value with a large absolute value.

[0018] When the CPU 62 determines that the detected misfire is equal to or greater than the threshold value ΔTth (S18: YES), the CPU 62 provisionally determines that a misfire has occurred (S20), and then increments a counter Cn that counts the number of provisional determinations (S22).

[0019] When the CPU 62 completes the process of S22 or when the CPU 62 makes a negative determination in the process of S18, the CPU 62 determines whether a predetermined period of time has elapsed (S24). Here, the start point of the predetermined period is the later of the timing when the process of S18 is first executed and the timing when the process of S32, which will be described later, is last executed. When the CPU 62 determines that the predetermined period of time has elapsed (S24: YES), the CPU 62 determines whether the counter Cn is equal to or greater than the threshold value Cth (S26). The threshold value Cth is set according to a lower limit value of the misfire rate when misfire occurs at a rate that cannot be overlooked within the predetermined period of time. In other words, the length of the predetermined period of time and the threshold value Cth are determined in advance according to the above-mentioned lower limit value.

[0020] When the CPU 62 determines that the misfire rate is equal to or greater than the threshold Cth (S26: YES), the CPU 62 makes a final determination that a misfire has occurred (S28). The CPU 62 then executes a notification process to notify the user that the misfire rate has occurred at a level that cannot be overlooked by operating the warning light 80 shown in Fig. 1 (S30). On the other hand, when the CPU 62 determines that the counter Cn is less than the threshold Cth (S26: NO), the CPU 62 initializes the counter Cn (S32).

[0021] When the processes of S30 and S32 are completed, or when a negative determination is made in the processes of S14 and S24, the CPU 62 temporarily ends the series of processes shown in FIG. Fig. 3 shows a process for calculating the time T30 required for the crankshaft 12 to rotate 30 CA degrees. The process shown in Fig. 3 is realized by the CPU 62 repeatedly executing a program stored in the ROM 64 at a period in which the crankshaft 12 rotates 30 CA degrees. Specifically, the process is repeatedly executed, for example, when the crank angle sensor 70 detects a predetermined tooth portion 22. It is assumed that the predetermined tooth portion 22 is defined every 30 CA degrees.

[0022] In the series of processes shown in Fig. 3, the CPU 62 first calculates the time et3txdh required for the crankshaft 12 to rotate through the most recent rotational angle region of 30 CA (S40). This process is a timing process for measuring the time required from when the crank angle sensor 70 detects one of two teeth portions 22 spaced apart by 30 CA to when it detects the other, as shown in Fig. 1. Next, the CPU 62 divides the angle constant CR corresponding to 30 CA by the time et3txdh to calculate the crank side speed ωe, which is the rotational speed of the crankshaft 12 in the most recent rotational angle region of 30 CA (S42).

[0023] Next, the CPU 62 calculates a downstream side speed ωout, which is the rotational speed of the carrier C side of the damper 14 (S44). The CPU 62 calculates the downstream side speed ωout based on the rotational speed ωm1 in the small rotation angle region of the rotating shaft 42 of the first motor generator 40 and the rotational speed ωm2 in the small rotation angle region of the rotating shaft 52 of the second motor generator 50. At this time, the CPU 62 refers to the gear ratio of the planetary gear mechanism 30. Here, the small rotation angle region is a rotational angle region smaller than one rotation. The rotational speed ωm1 is calculated by the CPU 62 based on the output signal Sm1 of the first rotation angle sensor 72. The rotational speed ωm2 is calculated by the CPU 62 based on the output signal Sm2 of the second rotation angle sensor 74.

[0024] Next, the CPU 62 assigns a value obtained by subtracting the rear stage speed ωout from the crank side speed ωe to the differential speed ωdamp (S46). Next, the CPU 62 calculates the torsion angle θdamp between the crankshaft 12 side and the carrier C side of the damper 14 based on the integration process of the differential speed ωdamp (S48). Here, in order to suppress the accumulation of errors due to the integration process, the CPU 62 regards the average value of the torsion angle θdamp in a predetermined period as the point where the torsion angle θdamp is zero. This can be roughly realized by, for example, the following three processes. The first process is a process of calculating a new torsion angle θdamp by integration process per unit section of the differential speed ωdamp. The second process is a process of updating the average value based on the torsion angle θdamp newly calculated this time. The third process is a process of setting the value obtained by subtracting the updated average value from the newly calculated torsion angle θdamp as the final torsion angle θdamp.

[0025] Next, the CPU 62 determines whether the internal combustion engine 10 is idling (S50). Here, idling refers to an operation state in which the shaft torque of the internal combustion engine 10 is controlled to zero. In other words, it refers to an operation state in which the rotation speed of the crankshaft 12 of the internal combustion engine 10 is maintained only by the combustion control of the internal combustion engine 10.

[0026] When the CPU 62 determines that the engine is not idling (S50: NO), it performs map calculations of the damper stiffness value K using normal map data (S52). On the other hand, when the CPU 62 determines that the engine is idling (S50: YES), it performs map calculations of the damper stiffness value K using idle map data (S54).

[0027] Here, the reason for switching the damper stiffness value depending on whether the engine is idling or not will be described. FIG. 4 shows the relationship between the torsional angle θdamp of the damper 14 and the torsional torque Tdamp that is generated in the damper 14. As shown in FIG. 4, the relationship between the torsional angle θdamp and the torsional torque Tdamp is nonlinear. In more detail, when the torsional angle θdamp changes from zero to positive, a set torque T1 is suddenly applied. Also, when the torsional angle θdamp changes from zero to negative, a set torque "(-1)·T1" is suddenly applied. The set torque is generated because the spring of the damper 14 is arranged to be in a compressed state even when the torsional angle θdamp is zero.

[0028] Fig. 5 shows a cross-sectional configuration of a portion of the damper 14. As shown in Fig. 5, both ends of the coil spring 14a are sandwiched between sheets 14b. Fig. 5 shows the case where the torsion angle θdamp is zero. In this case, the length L1 of the coil spring is shorter than the free length L0 at which the elastic force is zero.

[0029] 4, in the damper 14, the amount of change in the torsional torque Tdamp relative to the amount of change in the torsional angle θdamp changes significantly depending on whether the magnitude of the torsional angle θdamp is smaller or larger than the threshold value θth. This is because the way in which the load of the coil spring 14a is applied to the seat 14b differs depending on the magnitude of the torsional angle θdamp.

[0030] Fig. 6(a) shows a cross section of a portion of the damper 14 when the torsion angle θdamp is less than the threshold value θth. As shown in Fig. 6(a), in this case, the inner peripheral side of the coil spring 14a applies a load to the seat 14b, while the outer peripheral side of the coil spring 14a does not apply a load to the seat 14b.

[0031] Fig. 6(b) shows a cross section of a part of the damper 14 when the torsion angle θdamp is greater than the threshold value θth. As shown in Fig. 6(b), in this case, both the inner and outer circumferential sides of the coil spring 14a apply a load to the seat 14b. Therefore, when the torsion angle θdamp exceeds the threshold value θth, the change in torque with respect to the change in the torsion angle θdamp becomes larger than when the torsion angle θdamp is less than the threshold value θth.

[0032] As described above, the CPU 62 regards the average value of the torsional angle θdamp as the zero point of the torsional angle θdamp. However, when the shaft torque of the internal combustion engine 10 continues to be greater than zero, the torsional angle θdamp recognized by the CPU 62 differs from the actual zero point shown in Fig. 4. Therefore, when the internal combustion engine 10 is not operating at idle, if the damper stiffness value K is set based on the characteristics shown in Fig. 4, the damper stiffness value K will not be a value that represents the correct characteristics of the damper 14.

[0033] In consideration of the above, normal map data and idle map data are stored in the ROM 64. FIG. 7(a) shows the relationship between the absolute value of the torsion angle θdamp indicated by the idle map data and the damper stiffness value K. As shown in FIG. 7(a), when the absolute value of the torsion angle θdamp is equal to or less than the backlash width θ0, the damper stiffness value K is zero. This shows the angle range in which the damper 14 can rotate without causing torsion in the damper 14 even if the crankshaft 12 rotates due to mechanical backlash of the planetary gear mechanism 30. This is because the torsion angle θdamp is not the actual torsion angle of the damper 14 but a calculated torsion angle. Incidentally, FIG. 4 shows the relationship between the actual torsion angle θdamp and torque.

[0034] In the region where the torsional angle θdamp is between the backlash width θ0 and the set width θ1, the damper stiffness value increases rapidly due to the set torque. When the set width θdamp exceeds the set width θ1, the damper stiffness value K becomes an approximately constant value. Note that the idle map data may include data for a portion where the absolute value of the torsional angle θdamp exceeds the threshold value θth. In that case, when the torsional angle θdamp exceeds the threshold value θth, the damper stiffness value may be increased rapidly.

[0035] FIG. 7(b) shows the relationship between the absolute value of the torsional angle θdamp and the damper stiffness value K, which is shown in the normal map data. As shown in FIG. 7(b), the damper stiffness value K is almost constant regardless of the absolute value of the torsional angle θdamp. This is set in consideration of the fact that the actual value of the torsional angle θdamp is assumed to be greater than the threshold value θth during non-idling operation. Note that the normal map data may be data that increases the damper stiffness value K when the torsional angle θdamp is very large. This makes it possible to take into account the case where the change in the torsional torque Tdamp relative to the torsional angle θdamp becomes greater than the gradient shown in FIG. 4 in a region where the actual torsional angle is much greater than the threshold value θth.

[0036] When completing the processes of S52 and S54, the CPU 62 assigns a value obtained by multiplying the torsional angle θdamp by the damper stiffness value K to the torsional torque Tdamp (S56 in FIG. 3). Then, the CPU 62 calculates a torsional speed component ωr, which is a speed component that quantifies the influence of the torque generated by the torsion of the damper 14 on the rotation speed of the crankshaft 12, based on the integration process of the torsional torque Tdamp (S58). Here, a physical model is used that calculates the torsional speed component ωr by integration process of the angular acceleration component of the crankshaft 12 that is proportional to the torsional torque Tdamp. The CPU 62 then assigns a value obtained by dividing the angle constant CR by a value obtained by subtracting the torsional speed component ωr from the crank side speed ωe to the time T30 (S60).

[0037] When the CPU 62 completes the process of S60, the CPU 62 temporarily ends the series of processes shown in FIG. Here, the operation and effects of this embodiment will be described.

[0038] The CPU 62 performs misfire detection processing using a time T30 that is a value obtained by dividing an angle constant CR by a value obtained by subtracting a torsional speed component ωr from the crank side speed ωe. Here, the CPU 62 uses a damper stiffness value K in calculating the torsional speed component ωr. The CPU 62 sets the damper stiffness value K to a different value depending on whether the internal combustion engine 10 is idling or not. This allows the torsional torque Tdamp to be calculated with high accuracy.

[0039] According to the present embodiment described above, the following actions and effects can be obtained. (1) When the absolute value of the torsional angle θdamp is equal to or smaller than the backlash width θ0, the CPU 62 sets the damper stiffness value K to zero. This makes it possible to express a region in which the torsional angle θdamp does not become large despite the rotation of the crankshaft 12 due to mechanical backlash in the power transmission system connected to the crankshaft 12.

[0040] (2) The CPU 62 suddenly increases the damper stiffness value K in the region where the absolute value of the torsional angle θdamp is equal to or larger than the backlash width θ0 and equal to or smaller than the set width θ1. This allows the set torque of the damper 14 to be expressed.

[0041] <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the "Means for solving the problem" section above is as follows: Crank side acquisition processing corresponds to the processing of S40, S42. Rear stage side acquisition processing corresponds to the processing of S44. Torsional velocity component calculation processing corresponds to the processing of S48 to S58. Stiffness value variation processing corresponds to the processing of S50 to S54. Judgment use fluctuation amount calculation processing corresponds to the processing of S16. Judgment processing corresponds to the processing of S18.

[0042] <Other embodiments> This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0043] "About crank side speed variables" In the above embodiment, the crank angle range defining the crank side speed variable, which is a variable indicating the rotational speed of the crankshaft 12 in the crank angle range equal to or less than the interval between the compression top dead centers, is set to 30° CA, but this is not limited thereto. For example, it may be 10° CA, or may be the interval between the compression top dead centers itself.

[0044] The crank speed variable is not limited to a quantity having a time dimension, but may be, for example, a quantity having a speed dimension. "About rotation fluctuation" In the above embodiment, the rotation fluctuation amount ΔT30 is the difference between the crank side speed variables spaced apart by 120° CA, but is not limited to this. For example, it may be the difference between the crank side speed variables spaced apart by 90° CA.

[0045] The amount of rotational fluctuation is not limited to the difference between the crank side speed variables, but may be the ratio between the crank side speed variables. "About provisional judgment processing" The provisional determination process is not limited to using the difference between rotational fluctuation amounts ΔT30 that are spaced apart by 360° CA or 720° CA. In short, by using the difference between rotational fluctuation amounts ΔT30 that are spaced apart by an integer multiple of 360° CA, it is possible to prevent the accuracy of the provisional determination from being reduced due to the tolerance of the teeth 22 of the crank rotor 20.

[0046] The provisional judgment process is not limited to a process of comparing the difference between rotational fluctuation amounts ΔT30 that are spaced apart by an integer multiple of 360° CA with a threshold value, but may also be a process of directly comparing the rotational fluctuation amount of the cylinder to be judged with a threshold value.

[0047] "About the vehicle" The hybrid vehicle is not limited to a series-parallel hybrid vehicle. For example, a parallel hybrid vehicle may be used. However, the present invention is not limited to a hybrid vehicle, and may be a vehicle in which the thrust generating device of the vehicle is only the internal combustion engine 10. [Explanation of symbols]

[0048] 10. Internal combustion engine 12…Crankshaft 14…Damper 14a…coil spring 14b…Sheet 20…Crank rotor 30...Planetary gear mechanism 34…Drive wheel

Claims

[Claim 1] Applied to an internal combustion engine having multiple cylinders, a crankshaft of the internal combustion engine is connected to a torsionally rigid body; Executes a crank side acquisition process, a rear stage side acquisition process, a torsion speed component calculation process, a judgment fluctuation amount calculation process, and a judgment process; the crank side acquisition process is a process of acquiring a crank side speed variable, which is a variable indicating a rotation speed of the crankshaft, based on a crank signal; the downstream side acquisition process is a process of acquiring a downstream side speed variable which is a variable indicating a rotation speed of a portion of the torsional rigid body opposite to the crankshaft, the torsional velocity component calculation process is a process of calculating a torsional velocity component, which is a velocity component caused by torsion of the torsional rigidity body, based on a damper stiffness value using a difference between the crank side speed variable and the rear stage side speed variable as an input, and includes a stiffness value varying process; the determination-use fluctuation amount calculation process is a process of calculating a determination use fluctuation amount based on a value of the crank side speed variable obtained by removing the torsional speed component from the value of the crank side speed variable, The fluctuation amount for determination is an amount indicating a rotation fluctuation amount used for determining a misfire, the rotation fluctuation amount is a change amount of the crank side speed variable, the determination process is a process for determining whether or not a misfire has occurred in the internal combustion engine based on a magnitude of the determination fluctuation amount, The damper stiffness value is calculated by map calculation using map data, The map data is data in which the torsion angle calculated based on the integration process of the difference is an input variable and the damper stiffness value is an output variable, and includes idle map data and normal map data. the stiffness value varying process is a process for performing map calculation of the damper stiffness value using the idle map data when a shaft torque of the internal combustion engine is zero, and for performing map calculation of the damper stiffness value using the normal map data when the shaft torque is not zero, A misfire detection device for an internal combustion engine, wherein the value of the output variable of the idle map data is zero when the absolute value of the torsion angle is equal to or less than a backlash width, and in a region from the backlash width to a set width larger than the backlash width, the increase in the damper stiffness value with respect to an increase in the absolute value of the torsion angle is greater than in a region exceeding the set width.

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