JP2007303352A - Misfire determination device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a misfire determination device for an internal combustion engine capable of appropriately determining misfire according to an operating condition, and thereby improving misfire determination accuracy. <P>SOLUTION: This misfire determination device 1 for the internal combustion engine 3 determining misfire of the internal combustion engine 3 according to cylinder inner pressure PCYLF generated in a cylinder 3A is provided with cylinder inner pressure detecting means 20, 2 detecting cylinder inner pressure, a motoring pressure estimating means 2 estimating motoring pressure PCYLMDLK, a determination timing setting means 2 setting determination timing θPmax according to the detected operating condition of the internal combustion engine 3, a threshold setting means 2 setting a threshold PCYLLMT based on the operating condition of the internal combustion engine 3, and a misfire determination means 2 determining whether or not the internal combustion engine 3 is misfired based on the result of a comparison between cylinder inner pressure and motoring pressure PCYLMDLK which are obtained at the set determination timing and the threshold value PCYLLMT. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a misfire determination device for an internal combustion engine that determines misfire of the internal combustion engine in accordance with an in-cylinder pressure generated in the cylinder.

  As a conventional misfire determination device for an internal combustion engine, for example, one disclosed in Patent Document 1 is known. This internal combustion engine is a gasoline engine, and each cylinder is provided with an in-cylinder pressure sensor for detecting the in-cylinder pressure. In this misfire determination device, the lower limit value of the in-cylinder pressure to be obtained at a predetermined crank angle (for example, 40 °) after the top dead center at the start of the expansion stroke is determined based on the rotational speed of the internal combustion engine and the intake air amount. Calculate as a value. When the in-cylinder pressure detected at the predetermined crank angle is smaller than the misfire determination value, it is determined that the internal combustion engine has misfired.

  However, the method of changing the in-cylinder pressure is not necessarily constant, and varies depending on the operating state of the internal combustion engine. For example, in a high load operation state, the in-cylinder pressure increases rapidly due to combustion, reaches a peak at an earlier timing, and then decreases rapidly. On the other hand, in the conventional misfire determination device, the misfire determination is performed based on the in-cylinder pressure detected at a predetermined crank angle. Therefore, in a high load operation state as described above, a predetermined decrease is caused by a rapid decrease in the in-cylinder pressure. As a result of the in-cylinder pressure falling below the misfire determination value at the crank angle, there is a risk of misjudging that misfire has occurred. On the other hand, in the low-load operation state, the peak reaches at a later timing, so that the in-cylinder pressure does not increase by a predetermined crank angle, and there is a possibility that the misfire is erroneously determined.

  The present invention has been made to solve such a problem, and can appropriately determine misfire according to the operating state, thereby improving the misfire determination accuracy. An object of the present invention is to provide a misfire determination apparatus.

Japanese Patent No. 2623921

  To achieve this object, the invention according to claim 1 determines the misfire of the internal combustion engine 3 according to the in-cylinder pressure generated in the cylinder 3a (the final in-cylinder pressure PCYLF in the embodiment (hereinafter, the same applies in this section)). A misfire determination apparatus 1 for an internal combustion engine 3 that performs in-cylinder pressure detection means (in-cylinder pressure sensor 20, ECU 2) for detecting in-cylinder pressure, and in-cylinder pressure generated when combustion is not performed in the cylinder 3a. Motoring pressure estimation means (ECU2) that estimates the motoring pressure PCYLMLDLK, operating state detection means (ECU2) that detects the operating state of the internal combustion engine 3, and determination timing (in accordance with the detected operating state of the internal combustion engine 3) Based on the determination timing setting means (ECU 2, step 2) for setting the maximum in-cylinder pressure angle θPmax) and the operating state of the internal combustion engine 3, the threshold value PCYLLMT is set. The internal combustion engine 3 is misfired based on the threshold value setting means (ECU2, steps 22 to 28) to be determined and the comparison result between the in-cylinder pressure and the motoring pressure PCYLMLDLK and the threshold value PCYLLMT obtained at the set determination timing. Misfire determination means (ECU2, Steps 4 to 6) for determining whether or not the vehicle is operating.

  According to the misfire determination apparatus for an internal combustion engine, the in-cylinder pressure detecting means detects the in-cylinder pressure generated in the cylinder, and the motoring pressure estimating means is configured to detect the in-cylinder pressure generated when combustion is not performed in the cylinder. Is estimated as the motoring pressure. The determination timing setting means sets the determination timing according to the detected operating state of the internal combustion engine, and the threshold value setting means sets the threshold value based on the operating state of the internal combustion engine. The misfire determination means determines misfire of the internal combustion engine based on the comparison result between the in-cylinder pressure and motoring pressure obtained at the determination timing and the threshold value.

  The in-cylinder pressure detected by the in-cylinder pressure detecting means includes a combustion pressure generated by combustion and a motoring pressure. Therefore, by using the motoring pressure as one of the misfire determination parameters, it is possible to appropriately determine the misfire of the internal combustion engine while taking into account the influence of the motoring pressure included in the in-cylinder pressure. Further, as described above, since the manner in which the in-cylinder pressure changes varies depending on the operating state of the internal combustion engine, the misfire detection timing is set according to the operating state of the internal combustion engine, thereby changing the in-cylinder pressure. Misfire can be determined at an appropriate timing. Furthermore, when the operating state of the internal combustion engine changes, the relationship between the in-cylinder pressure and the motoring pressure changes as the magnitude of the combustion pressure changes. For this reason, by setting the threshold value based on the operating state of the internal combustion engine, it is possible to set an appropriate threshold value while taking into account the relationship between the in-cylinder pressure and the motoring pressure. Therefore, the misfire determination can be more appropriately performed according to the operation state, and the misfire determination accuracy can be improved as described above.

  The invention according to claim 2 is characterized in that, in the misfire determination device 1 of the internal combustion engine 3 according to claim 1, the determination timing setting means sets the determination timing to a timing at which a peak of the in-cylinder pressure occurs.

  According to this configuration, the misfire determination timing is set to the timing at which the peak of the in-cylinder pressure at which the combustion state appears most clearly, so the actual peak value of the detected in-cylinder pressure is used to determine the threshold and By comparing, misfire determination can be accurately performed, and the determination accuracy can be further improved.

  According to a third aspect of the present invention, in the misfire determination device 1 for the internal combustion engine 3 according to the first aspect, the determination timing setting means includes a predetermined interval (start angle CAST) including a timing at which the peak of the in-cylinder pressure occurs. To ending angle CAEND).

  According to this configuration, since the misfire determination timing is set to a predetermined section including the timing at which the peak of the in-cylinder pressure occurs, the in-cylinder pressure at which the combustion state clearly appears is used as in the invention according to claim 2. , Misfire can be determined accurately. In addition, by setting the determination timing as a section instead of a point, it is possible to eliminate the influence of temporary fluctuations in the detected in-cylinder pressure caused by noise, etc. Can be improved.

  According to a fourth aspect of the present invention, in the misfire determination device 1 of the internal combustion engine 3 according to the third aspect, the misfire determination means calculates a pressure ratio between the in-cylinder pressure detected in a predetermined section and the motoring pressure PCYLMDLK. An internal combustion engine having a calculation means (ECU2) and an average value calculation means (ECU2, step 46) for calculating an average value of pressure ratio RATPAVR when the average value of pressure ratio RATPAVR is smaller than a threshold value PCYLLMT 3 is determined to be misfired.

  According to this configuration, the average value calculating means calculates the average value of the pressure ratio between the in-cylinder pressure and the motoring pressure detected in the predetermined section, and when the calculated average value is smaller than the threshold value. It is determined that the internal combustion engine has misfired. As the internal combustion engine approaches the misfire state, the pressure ratio between the in-cylinder pressure and the motoring pressure approaches the value 1. Therefore, when the average value of the pressure ratio is smaller than the threshold value, it is appropriate that the internal combustion engine is misfired. Can be determined. Further, by using the average value of the pressure ratio, it is possible to eliminate the influence due to the temporary fluctuation of the in-cylinder pressure caused by noise or the like, and it is possible to further improve the accuracy of misfire determination.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic configuration of a misfire determination apparatus 1 according to an embodiment of the present invention and an internal combustion engine (hereinafter referred to as “engine”) 3 to which the misfire determination apparatus 1 is applied. The engine 3 is, for example, a gasoline engine having four cylinders 3a (only one is shown), and a combustion chamber 3e is formed between the piston 3b and the cylinder head 3c of each cylinder 3a.

  An intake pipe 4 and an exhaust pipe 5 are connected to the cylinder head 3c, an intake valve 4a and an exhaust valve 5a are provided, and a spark plug 6 is attached so as to face the combustion chamber 3e. The spark plug 6 is discharged when a high voltage is applied at a timing corresponding to the ignition timing IGLOG by a drive signal from the ECU 2 to be described later and then shut off, thereby igniting the air-fuel mixture in each cylinder 3a. Is done.

  An in-cylinder pressure sensor 20 is integrally attached to the spark plug 6. The in-cylinder pressure sensor 20 (in-cylinder pressure detecting means) is composed of a ring-shaped piezoelectric element, and is sandwiched between the spark plug 6 and the cylinder head 3c by being screwed into the cylinder head 3c together with the spark plug 6. A detection signal indicating the pressure change amount DPV in the cylinder 3 a of the engine 3 is output to the ECU 2.

  The intake camshaft 7 and the exhaust camshaft 8 of the engine 3 are integrally provided with a plurality of intake cams 7a and exhaust cams 8a (only one is shown). The intake camshaft 7 is connected to the crankshaft 3d via a timing chain (not shown), and rotates once every two rotations of the crankshaft 3d. The intake valve 4a is driven to open and close by the rotation of the intake cam 7a accompanying the rotation of the intake camshaft 7.

  Similarly, the exhaust camshaft 8 is connected to the crankshaft 3d via a timing chain (not shown). The exhaust camshaft 8 rotates once every two rotations of the crankshaft 3d, and the intake cam 8a rotates with this rotation. As a result, the exhaust valve 5a is driven to open and close.

  Further, although not shown, each of the intake cam 7a and the exhaust cam 8a includes a low-speed cam and a high-speed cam having a cam profile higher than that of the low-speed cam. These low-speed cam and high-speed cam are switched by the cam profile switching mechanism 9, whereby the valve timings of the intake valve 4 a and the exhaust valve 5 a are changed between a low-speed valve timing (hereinafter referred to as “LO.VT”) and a high-speed valve timing ( (Hereinafter referred to as “HI.VT”). HI. When VT, LO. As compared with the case of VT, the valve opening period of the intake valve 4a and the exhaust valve 5a and the valve overlap therebetween are increased, and the valve lift amount is increased, so that the charging efficiency is increased. The cam profile switching mechanism 9 is controlled by controlling the electromagnetic control valve 9 a by a drive signal from the ECU 2 and changing the hydraulic pressure supplied to the cam profile switching mechanism 9.

  The crankshaft 3 d of the engine 3 is provided with a cylinder discrimination sensor 21 and a crank angle sensor 22. Each of these sensors 21 and 22 includes a magnet rotor and an MRE pickup, and outputs a pulse signal at each predetermined crank angle position. Specifically, the cylinder discrimination sensor 21 generates a cylinder discrimination signal CYL (hereinafter referred to as “CYL signal”) at a predetermined crank angle position of a specific cylinder 3a.

  The crank angle sensor 22 generates a CRK signal and a TDC signal, which are pulse signals, as the crankshaft 3d rotates. The CRK signal is output every predetermined crank angle (for example, 1 °), and the ECU 2 calculates the engine speed (hereinafter referred to as “engine speed”) NE of the engine 3 based on the CRK signal. The TDC signal is a signal indicating that the piston 3b of each cylinder 3a is at a predetermined crank angle position near the TDC at the start of the intake stroke, and is output at every crank angle of 180 ° in this example of the 4-cylinder type.

  The intake pipe 4 is provided with a throttle valve 10 and a fuel injection valve (hereinafter referred to as “injector”) 11 in order from the upstream side. The throttle valve 10 is connected to an actuator 10a made of, for example, a DC motor. The opening (hereinafter referred to as “throttle opening”) TH of the throttle valve 10 is controlled by controlling the duty ratio of the current supplied to the actuator 10a by the ECU 2. Further, the fuel injection amount and injection timing of the injector 11 are controlled by a drive signal from the ECU 2.

  The exhaust pipe 5 is provided with a catalyst device 12. This catalyst device 12 is a combination of a NOx catalyst and a three-way catalyst. This NOx catalyst is used in the exhaust gas when the air-fuel ratio of the air-fuel mixture supplied to the engine 3 is leaner than the stoichiometric air-fuel ratio. The NOx is purified by being adsorbed, and when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the adsorbed NOx is reduced. The three-way catalyst purifies CO, HC and NOx in the exhaust gas by an oxidation-reduction action.

  The intake pipe 4 is provided with an air flow sensor 23 upstream of the throttle valve 10 and an intake air temperature sensor 24 downstream of the throttle valve 10. The air flow sensor 23 detects the intake air amount QA, the intake air temperature sensor 24 detects the temperature TA (hereinafter referred to as “intake air temperature”) TA in the intake pipe 4, and these detection signals are output to the ECU 2.

  Further, a detection signal representing an operation amount (hereinafter referred to as “accelerator opening”) AP of an accelerator pedal (not shown) is output from the accelerator opening sensor 25 to the ECU 2.

  In the present embodiment, the ECU 2 is constituted by a microcomputer including an I / O interface, a CPU, a RAM, a ROM, and the like. The detection signals from the various sensors 20 to 25 described above are output to the CPU after A / D conversion and shaping by the I / O interface. In this embodiment, the ECU 2 corresponds to in-cylinder pressure detection means, motoring pressure estimation means, operating state detection means, determination timing setting means, threshold setting means, misfire determination means, calculation means, and average value calculation means. To do.

  In accordance with these input signals, the CPU calculates the motoring pressure PCYLMLDLK and the final in-cylinder pressure PCYLF as follows in accordance with a control program stored in the ROM.

  Specifically, the motoring pressure PCYLMLDLK (n) is an in-cylinder pressure that is generated when combustion is not performed in the cylinder 3a, and an intake air amount QA (n), an intake air temperature TA (n), and In accordance with the volume Vc (n) of the cylinder 3a, it is calculated by using a gas state equation. The volume Vc (n) of the cylinder 3a is the volume of the space surrounded by the cylinder head 3c, the cylinder 3a and the piston 3b. The volume of the combustion chamber 3e, the cross-sectional area of the piston 3b, the crank angle CA, the length of the connecting rod. And is calculated according to the crank length of the crankshaft 3d. The symbol n represents the discretized time, and each discrete data with the symbol (n) is calculated or sampled every time a CRK signal is generated. This also applies to the following discrete data (time series data). In the following description, this symbol (n) is omitted as appropriate.

  The final in-cylinder pressure PCYLF is calculated as follows. That is, first, after integrating the output DPV of the in-cylinder pressure sensor 20 by the charge amplifier, the provisional value PCYLT of the in-cylinder pressure is calculated by pyroelectric correction of the integrated value. Next, the final in-cylinder pressure PCYLF is calculated by correcting the calculated provisional value PCYLT as follows.

  This correction is for correcting the deviation of the provisional value PCYLT from the actual in-cylinder pressure due to the deterioration of the in-cylinder pressure sensor 20 with time, and is performed based on the following viewpoint. That is, during the period from the start of the compression stroke to immediately before the ignition timing IGLOG (hereinafter referred to as “non-combustion compression period”), the combustion is not performed, so the motoring pressure PCYLMLDLK becomes equal to the actual in-cylinder pressure. Further, in this non-combustion compression period, the in-cylinder pressure greatly changes due to the compression of the volume Vc in the cylinder 3a by the piston 3b as compared with the intake stroke and the exhaust stroke in which combustion is not performed in the same manner. A deviation of the provisional value PCYLT with respect to the in-cylinder pressure clearly appears. For the above reasons, the provisional value PCYLT is corrected using the provisional value PCYLT and the motoring pressure PCYLMLDLK obtained during the non-combustion compression period.

  The relationship between the provisional value PCYLT (n) and the identification value PCYLT_HAT (n) is defined by the following equation (1). The identification value PCYLT_HAT represents the provisional value PCYLT in which the deviation due to the temporal deterioration of the in-cylinder pressure sensor 20 is corrected. First, in the non-combustion compression period, the model parameter K1 (n) of the equation (1) and the vector θ (n) of C1 (n) are obtained by the sequential least square method represented by the following equations (2) to (8). Identify.

Here, in equation (2), KP (n) is a vector of gain coefficients, and ide (n) is an identification error. In addition, θ (n) ^T in Equation (3) is a transposed matrix of θ (n). In addition, the identification error ide (n) in equation (2) is calculated by equation (4), and ζ (n) in equation (5) is a vector whose transpose matrix is expressed as in equation (6). is there. Further, the gain coefficient vector KP (n) is calculated by Expression (7), and P (n) of Expression (7) is a quadratic square matrix defined by Expression (8). Further, the weight parameters λ ₁ and λ ₂ in the equation (8) are set to a value of 1.

  The vector θ (n) is calculated by the algorithm shown in the above equations (2) to (8) so that the identification error ide (n) is minimized. That is, the vector θ (n) is identified so that the identification value PCYLT_HAT (n) becomes the motoring pressure PCYLMLDLK (n). When the engine 3 is started, a predetermined value is used as the previous value θ (n−1) of the vector used in equation (2) and the like.

  Next, the obtained model parameters K1 (n) and C1 (n) are learned, and the provisional value PCYLT (n) is corrected by the following equation (9) according to the learned K1 (n) and C1 (n). To calculate the final in-cylinder pressure PCYLF.

  Note that, after the end of the current non-combustion compression period, until the next vector θ (n) is identified, the model parameters K1 (n) and C1 ( n) is used to calculate the final in-cylinder pressure PCYLF.

  As described above, in the non-combustion compression period, the motoring pressure PCYLMLDLK is equal to the actual in-cylinder pressure, whereas in the model parameters K1 and C1 of the model represented by the formula (1), the identification value PCYLT_HAT is the PCYLMDLK value. Asking. Therefore, it can be said that K1 and C1 are obtained so that PCYLT_HAT becomes an actual in-cylinder pressure. Therefore, the final in-cylinder pressure PCYLF can be accurately calculated as the in-cylinder pressure by the equation (9) in which PCYLT_HAT in the equation (1) is replaced with the final in-cylinder pressure PCYLF.

  FIG. 2 shows an example of a transition of (a) the provisional value PCYLT and the like (b) a transition of the final in-cylinder pressure PCYLF when the in-cylinder pressure sensor 20 is deteriorated with time. As shown in FIG. 6A, the provisional value PCYLT is the actual in-cylinder pressure PCYLACT because the output DPV is reduced due to deterioration with time and the model parameters K1 and C1 are not corrected. Is much smaller than.

  On the other hand, the final in-cylinder pressure PCYLF substantially coincides with the actual in-cylinder pressure PCYLACT, there is almost no error, and the accuracy is very high.

  Further, the CPU executes the misfire determination of the engine 3 using the calculated final in-cylinder pressure PCYLF. This misfire determination is performed for each cylinder 3a based on the CYL signal. In the following description, the same processing is performed for each cylinder 3a, and therefore, for convenience of description, one cylinder 3a is described.

  FIG. 3 is a flowchart showing misfire determination processing of the engine 3 according to the first embodiment of the present invention. This process is executed in synchronization with the generation of the CRK signal. In this process, first, in step 1 (illustrated as “S1”, the same applies hereinafter), it is determined whether or not the current crank angle CA is not less than the first angle CA1 and not more than the second angle CA2. The first angle CA1 and the second angle CA2 are crank angle (hereinafter referred to as “cylinder pressure maximum angle”) θPmax calculation section (hereinafter referred to as “cylinder pressure maximum angle calculation section”) where the peak of the final cylinder pressure θPmax occurs. It is determined. The first angle CA1 is set to the crank angle corresponding to the ignition timing IGLOG, and the second angle CA2 is set to the crank angle at the end of the expansion stroke. If the determination result of step 1 is NO and CA <CA1 or CA> CA2, this process ends.

  On the other hand, if the determination result in step 1 is YES and the crank angle CA is within the in-cylinder pressure maximum angle calculation section, the in-cylinder pressure maximum angle θPmax is calculated (step 2).

  This in-cylinder pressure maximum angle θPmax is calculated by the calculation process shown in FIG. First, in step 11, as in step 1, it is determined whether or not the crank angle CA is not less than the first angle CA1 and not more than the second angle CA2. When the determination result is NO, this process is terminated. On the other hand, when the determination result in step 11 is YES, it is determined whether or not the crank angle CA is equal to the first angle CA1 (step 12). When the determination result is YES and this time corresponds to the start of the in-cylinder pressure maximum angle calculation section, the final in-cylinder pressure PCYLF (n) at that time is set as a provisional value PCYLFMAXT of the maximum in-cylinder pressure PCYLFMAX (step 13). The first angle CA1, which is the crank angle CA at that time, is set as the provisional value θPmaxt of the in-cylinder pressure maximum angle θPmax (step 14), and then the process proceeds to step 15. When the determination result at step 12 is NO, the steps 13 and 14 are skipped and the process proceeds directly to step 15.

  In step 15, it is determined whether or not the final in-cylinder pressure PCYLF (n) is larger than the provisional value PCYLFMAXT of the maximum in-cylinder pressure. When the determination result is YES and PCYLF (n)> PCYLFMAXT, the provisional value PCYLFMAXT of the maximum in-cylinder pressure is updated to the final in-cylinder pressure PCYLF (n) (step 16), and the provisional value θPmaxt of the in-cylinder pressure maximum angle is After updating to the crank angle CA (n) at that time (step 17), the process proceeds to step 18. On the other hand, when the determination result of step 15 is NO, the process proceeds directly to step 18.

  In step 18, it is determined whether or not the crank angle CA is equal to the second angle CA2. When the determination result is NO, this process is terminated. On the other hand, when the determination result in step 18 is YES and this time corresponds to the end of the in-cylinder pressure maximum angle calculation section, the provisional value PCYLFMAXT obtained up to that time is set as the final maximum in-cylinder pressure PCYLFMAX (step 19). ), The provisional value θPmaxt is set as the final in-cylinder pressure maximum angle θPmax (step 20), and this process is terminated.

  Returning to FIG. 3, in step 3 following step 2, the motoring pressure PCYLMLDLK at the in-cylinder pressure maximum angle θPmax is calculated. Next, it is determined whether or not the pressure ratio (PCYLFMAX / PCYLMLDLK) between the maximum in-cylinder pressure PCYFLMAX set in step 19 and the motoring pressure PCYLMLDLK is greater than or equal to a threshold value PCYLLMT (step 4).

  This threshold value PCYLLMT is calculated by the calculation process shown in FIG. This process is executed in synchronization with the generation of the TDC signal. First, in step 21, it is determined whether or not a timer value TMDL, which will be described later, is 0. When the determination result is YES, it is determined whether or not the engine 3 is idling (step 22). When the determination result is YES, it is determined whether or not the engine 3 is in a warm-up operation of the catalyst device 12 immediately after starting (hereinafter referred to as “catalyst warm-up operation”) (step 23).

  When the determination result is YES and the catalyst warm-up operation of the engine 3 is in the catalyst warm-up operation, the map value PCYLFR for warm-up operation is obtained by searching the map shown in FIG. 6 based on the engine speed NE and the intake air amount QA. Then, this map value PCYLFR is set as a threshold value PCYLLMT (step 24).

  In this map, the map value PCYLFR is set to a larger value as the engine speed NE is lower and as the intake air amount QA is larger. This is due to the following reason. That is, as described above, the in-cylinder pressure sensor 20 is provided in a state of being sandwiched between the spark plug 6 and the cylinder head 3c, so that pressure remains in the in-cylinder pressure sensor 20 when the piston 3b is lowered. Further, the lower the engine speed NE is, the lower the moving speed of the piston 3b is, so that the degree of residual pressure increases, and the final in-cylinder pressure PCYLF is detected accordingly. Further, the smaller the intake air amount QA, the smaller the combustion pressure, so the final in-cylinder pressure PCYLF approaches the motoring pressure PCYLMLDLK. As described above, by setting the map value PCYLFR according to the engine speed NE and the intake air amount QA, the threshold value PCYLLMT can be appropriately set according to the operating state.

  Returning to FIG. 5, when the determination result in step 23 is NO, as in step 24, the map value PCYLID for idle operation is searched from the map based on the engine speed NE and the intake air amount QA, and the threshold value is obtained. Set as PCYLLMT (step 25). Although not shown, also in this map, the map value PCYLID is set to a larger value as the engine speed NE is lower and the intake air amount QA is larger for the reasons described above. The map value PCYLID is set to a value larger than the map value PCYLFR for warm-up operation in the entire region of the engine speed NE and the intake air amount QA. This is because, during the idling operation, the ignition timing IGLOG is controlled to the advance side and during the catalyst warm-up operation, and the final in-cylinder pressure PCYLF becomes larger.

  On the other hand, when the determination result of step 22 is NO and the engine 3 is not in idle operation, the engine 3 is LO. It is determined whether or not the VT operation is being performed (step 26). When the result of this determination is YES, LO. From the map is based on the engine speed NE and the intake air amount QA. The map value PCYLLO for VT operation is retrieved and set as the threshold value PCYLLMT (step 27). Although not shown, also in this map, the map value PCYLLO is set to a larger value as the engine speed NE is lower and the intake air amount QA is larger for the reasons described above. Further, this map value PCYLLO is set to a value larger than the map value PCYLID for idle operation in the entire region of the engine speed NE and the intake air amount QA. This is LO. This is because the load on the engine 3 is higher during the VT operation than during the idle operation, and the final in-cylinder pressure PCYLF becomes higher as a whole.

  On the other hand, when the determination result of step 26 is NO, the HI. Is determined from the map based on the engine speed NE and the intake air amount QA. The map value PCYLHI for VT operation is retrieved and set as a threshold value PCYLLMT (step 28). Although not shown, also in this map, the map value PCYLHI is set to a larger value as the engine speed NE is lower and the intake air amount QA is larger for the reasons described above. In addition, this map value PCYLHI is set to LO.P in all regions of the engine speed NE and the intake air amount QA. It is set to a value larger than the map value PCYLLO for VT operation. This is because HI. During VT operation, LO. This is because the load of the engine 3 is higher than that during the VT operation, and the final in-cylinder pressure PCYLF becomes higher as a whole.

  In step 29 following the step 24, 25, 27 or 28, the operating state of the engine 3 is changed between any two of the four operations described above (idle, catalyst warm-up, LO.VT and HI.VT). It is determined whether or not it is immediately after switching to.

  When the determination result is NO, this process is terminated. On the other hand, when the determination result in step 29 is YES and immediately after the operation state is switched, the timer value TMDL of a down-count timer (not shown) is set to a predetermined time TTM (for example, 0.5 sec) (step) 30). Then, the previous threshold value PCYLLMT (n−1) is set as the threshold value PCYLLMT (step 31), and this process is terminated.

  Further, when the determination result of step 21 is NO, that is, when the predetermined time TTM has not elapsed since the operation state of the engine 3 was switched, this processing is ended as it is. As a result, the previous threshold value PCYLLMT (n−1) is held until the predetermined time TTM has elapsed after the switching of the operating state.

  FIG. 7 shows that the engine 3 is in LO. FIG. 6 shows an operation example obtained by the process of FIG. 5 when switching to the VT operation. As shown in the figure, first, during idle operation before timing t1, the threshold value PCYLLMT is set to the map value PCYLID for idle operation, the throttle opening TH is almost fully closed, and the ignition timing IGLOG. Is set at a predetermined time. At t1, the accelerator pedal is depressed, and the operating state of the engine 3 is LO. When switching to the VT operation, the timer value TMDL is set to a predetermined time TTM and the timer is started. Along with the switching of the operating state, the ignition timing IGLOG and the throttle opening TH are set to LO. It is controlled to gradually change to a value for VT operation. The threshold value PCYLLMT is held at the map value PCYLID for idling operation because the determination result of step 21 is NO until the predetermined time TTM elapses after the operation state of the engine 3 is switched. Thereafter, when the predetermined time TTM has elapsed since the switching of the operation state (t2), the timer value TMDL becomes 0, whereby the threshold value PCYLLMT is set to LO. The map value PCYLLO for VT operation is set. As described above, when the predetermined time TTM has elapsed after the switching of the operating state, the switching to the switching destination threshold value PCYLLMT is performed to wait until the operating state of the switching destination engine 3 is reliably stabilized. The value PCYLLMT can be applied.

  Returning to FIG. 3, when the determination result in step 4 is YES and PCYLFMAX / PCYLMLDLK ≧ PCYLLMT, it is determined that the engine 3 has not misfired because the pressure ratio between the final in-cylinder pressure PCYLF and the motoring pressure PCYLMLDLK is large. Then, the misfire flag F_MF is set to “0” (step 5), and this process is terminated.

  On the other hand, if the determination result in step 4 is NO and PCYLFMAX / PCYLMLDLK <PCYLLMT, it is determined that the engine 3 has misfired, the misfire flag F_MF is set to “1” (step 6), and this process is terminated. .

  As described above, according to the present embodiment, by comparing the pressure ratio (PCYLFMAX / PCYLMLDLK) between the maximum in-cylinder pressure PCYLFMAX and the motoring pressure PCYLMLDLK obtained at the in-cylinder pressure maximum angle θPmax with the threshold value PCYLLMT, Perform 3 misfire determination. As described above, the final in-cylinder pressure PCYLF includes the combustion pressure generated by combustion and the motoring pressure PCYLMLDLK. As the engine 3 approaches the misfire state, the combustion pressure decreases and the pressure ratio approaches value 1. Therefore, the determination method can appropriately determine misfire of the engine 3 while taking into account the influence of the motoring pressure PCYLMDLK.

  In addition, the misfire determination timing is set to the maximum in-cylinder pressure angle θPmax at which the combustion state appears most clearly, and the detected maximum in-cylinder pressure PCYLFMAX is compared with the threshold value PCYLLMT. It can be done with certainty. Furthermore, since the threshold value PCYLLMT is set for each operation state of the engine 3, misfire determination can be performed more appropriately according to the operation state, and thus the misfire determination accuracy can be improved.

  Further, in the embodiment, since the final in-cylinder pressure PCYLF is corrected based on the motoring pressure PCYLMLDLK, it is possible to eliminate the influence due to the shift in output characteristics due to the deterioration of the in-cylinder pressure sensor 20 with time, thereby improving the accuracy of misfire determination. Further improvement can be achieved.

  FIG. 8 is a flowchart showing misfire determination processing of the engine 3 according to the second embodiment of the present invention. In this process, first, in step 41, as in step 1 of FIG. 3, it is determined whether or not the crank angle CA is within the in-cylinder pressure maximum angle calculation section defined by the first angle CA1 and the second angle CA2. When this determination result is NO, this process is terminated as it is.

  On the other hand, if the determination result in step 41 is YES and the cylinder pressure is within the maximum cylinder angle calculation section, the current final cylinder pressure PCYLF is stored as PCYLFi in association with the crank angle CAi at that time (step 42). Next, as in the first embodiment, the in-cylinder pressure maximum angle θPmax is calculated by the process of FIG. 4 (step 43), and the misfire determination section start angle CAST and end angle CAEND are set according to the in-cylinder pressure maximum angle θPmax. Calculate (step 44). As shown in FIG. 9, the start angle CAST and end angle CAEND are set to values on the advance side and the retard side by a predetermined angle centered on the maximum in-cylinder pressure angle θPmax, as shown in FIG. Has been.

  Next, a motoring pressure PCYLMDLKI corresponding to the crank angle CAi (i = CAST to CAEND) in the misfire determination section is calculated (step 45).

  Next, an average value RATPAVR of the pressure ratio between the final in-cylinder pressure PCYLFi and the motoring pressure PCYLMDLKI is calculated (step 46). This average value RATPAVR is calculated by dividing the integrated value of the pressure ratio between the final in-cylinder pressure PCYLFi and the motoring pressure PCYLMDLKI in the misfire determination section by the number of calculations (CAEND-CAST).

  Next, it is determined whether or not the calculated average value RATPAVR is greater than or equal to a threshold value PCYLLMT (step 47). This threshold value PCYLLMT is calculated by the process of FIG. 5 as in the first embodiment.

  When the determination result is YES and the average value RATPAVR is equal to or greater than the threshold value PCYLLMT, it is determined that the pressure ratio between the final in-cylinder pressure PCYLF and the motoring pressure PCYLMLDLK in the misfire determination section is large and the engine 3 has not misfired. The misfire flag F_MF is set to “0” (step 48), and this process is terminated.

  On the other hand, when the determination result in step 47 is NO, it is determined that the pressure ratio between the final in-cylinder pressure PCYLF and the motoring pressure PCYLMLDLK is small and the engine 3 has misfired, and the misfire determination flag F_MF is set to “1”. (Step 49), the process is terminated.

  As described above, according to the present embodiment, the average value RATPAVR and the threshold value PCYLLMT of the pressure ratio between the final in-cylinder pressure PCYLF and the motoring pressure PCYLMLDLK obtained in the misfire determination section centered on the in-cylinder pressure maximum angle θPmax are obtained. By comparing, it is possible to accurately determine misfire as in the first embodiment described above. In the present embodiment, the misfire determination timing is set as a misfire determination section centered on the in-cylinder pressure maximum angle θPmax, and the average value RATPAVR of the pressure ratio obtained in this section is used. For this reason, the influence by the temporary fluctuation | variation of the final in-cylinder pressure PCYLF resulting from noise etc. can be excluded, and the precision of misfire determination can be improved further.

  In addition, this invention can be implemented in a various aspect, without being limited to embodiment described. For example, in the first and second embodiments, the misfire determination angle and interval are set based on the in-cylinder pressure maximum angle θPmax. However, the present invention is not limited to this, and for example, a threshold value PCYLLMT is set for each operating state. It may be set for each of the four operating states. In the embodiment, the misfire determination is performed by using the pressure ratio between the final in-cylinder pressure PCYLF and the motoring pressure PCYLMLDLK. However, the present invention is not limited to this, and a deviation between the two may be used.

  Further, the embodiment is an example in which the present invention is applied to a gasoline engine. However, the present invention is not limited to this, and various engines other than the gasoline engine, for example, a diesel engine or a ship in which a crankshaft is arranged in the vertical direction. It can be applied to an engine for a marine propulsion device such as an external unit. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

It is a figure which shows schematic structure of the internal combustion engine provided with the misfire determination apparatus of this invention. It is a figure which shows an example of transition of (a) provisional value etc., when an in-cylinder pressure sensor has deteriorated with time, (b) an example of transition of final in-cylinder pressure. It is a flowchart which shows the misfire determination process by 1st Embodiment of this invention. It is a flowchart which shows the calculation process of the cylinder pressure maximum angle. It is a flowchart which shows the calculation process of a threshold value. FIG. 6 is a map for calculating a warm-up map value used in the process of FIG. 5. FIG. The engine is idle from idle operation. It is a figure which shows the operation example obtained by the process of FIG. 5 at the time of switching to VT driving | operation. It is a flowchart which shows the misfire determination process by 2nd Embodiment of this invention. It is a figure which shows an example of transition of the final in-cylinder pressure and motoring pressure.

Explanation of symbols

1 Misfire detection device
2 ECU (in-cylinder pressure detection means, motoring pressure estimation means, operating state detection means
Stage, determination timing setting means, threshold setting means, misfire determination means, calculation
Output means and average value calculation means)
3 Internal combustion engine
3a cylinder
20 In-cylinder pressure sensor (in-cylinder pressure detection means)
PCYLF Final cylinder pressure (cylinder pressure)
PCYLMLDLK Motoring pressure PCYLLMT Threshold CAST Start angle (predetermined section)
CAEND end angle (predetermined section)
RATPAVR average value θPmax In-cylinder pressure maximum angle (judgment timing)

Claims (4)

A misfire determination apparatus for an internal combustion engine that determines misfire of the internal combustion engine according to an in-cylinder pressure generated in the cylinder,
In-cylinder pressure detecting means for detecting the in-cylinder pressure;
Motoring pressure estimating means for estimating an in-cylinder pressure generated when combustion is not performed in the cylinder as a motoring pressure;
An operating state detecting means for detecting an operating state of the internal combustion engine;
Determination timing setting means for setting a determination timing according to the detected operating state of the internal combustion engine;
Threshold setting means for setting a threshold based on the operating state of the internal combustion engine;
Misfire determination means for determining whether or not the internal combustion engine has misfired based on a comparison result between the in-cylinder pressure and the motoring pressure obtained at the set determination timing and the threshold value;
A misfire determination device for an internal combustion engine, comprising:   2. The misfire determination apparatus for an internal combustion engine according to claim 1, wherein the determination timing setting means sets the determination timing to a timing at which the peak of the in-cylinder pressure occurs.   2. The misfire determination apparatus for an internal combustion engine according to claim 1, wherein the determination timing setting unit sets the determination timing to a predetermined section including a timing at which the peak of the in-cylinder pressure occurs. The misfire determination means includes
Calculating means for calculating a pressure ratio between the in-cylinder pressure detected in the predetermined section and the motoring pressure;
Average value calculating means for calculating an average value of the pressure ratio,
4. The misfire determination apparatus for an internal combustion engine according to claim 3, wherein the internal combustion engine is determined to have misfired when an average value of the pressure ratio is smaller than the threshold value.

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