JP5998904B2 - Misfire detection device for internal combustion engine - Google Patents

Description

  The present invention relates to a misfire determination device for an internal combustion engine.

  Conventionally, for example, Patent Document 1 discloses a combustion control device for an internal combustion engine. This conventional combustion control device includes an in-cylinder pressure sensor for detecting the in-cylinder pressure. The combustion control device calculates the generated heat quantity Q by integrating the heat generation rate q after ignition based on the in-cylinder pressure detected by the in-cylinder pressure sensor. In addition, the combustion control device calculates a change amount (that is, a change rate) ΔQ of the generated heat quantity Q in a predetermined crank angle period, and if the calculated change rate ΔQ of the generated heat quantity is equal to or less than a predetermined determination level ΔQ0, Judge that complete combustion has occurred.

JP 2002-310049 A JP 2012-82712 A JP 2010-48171 A JP-A-4-301158 JP 2010-144484 A JP 2009-197672 A

  Noise may be superimposed on the detection value (output value) of the in-cylinder pressure sensor. If noise is superimposed on the in-cylinder pressure waveform, a correction error may occur when performing absolute pressure correction on the detected value of the in-cylinder pressure, which is a relative pressure. As a result, the in-cylinder pressure waveform includes an offset component. The influence of this offset component also affects the amount of change in the amount of heat generated in the cylinder calculated based on the in-cylinder pressure. Therefore, it is difficult to distinguish between combustion and misfire simply by using the amount of change in heat generation. This is particularly noticeable at the time of slow combustion (for example, at the time of retarded combustion) in which the in-cylinder pressure is not so high as compared with normal combustion.

  The present invention was made to solve the above-described problems, and satisfactorily improves the accuracy of misfire determination using the calorific value calculated based on the in-cylinder pressure detected by the in-cylinder pressure sensor. It is an object of the present invention to provide a misfire determination device for an internal combustion engine capable of performing the same.

1st invention is a misfire determination apparatus of an internal combustion engine,
An in-cylinder pressure sensor for detecting the in-cylinder pressure;
A plurality of changes in the amount of heat generated in the cylinder during a predetermined crank angle period are calculated during one cycle using the detection value of the cylinder pressure sensor, and the maximum value of the plurality of changes in the amount of generated heat calculated during one cycle is calculated. When the first difference between the maximum value and the minimum value is less than or equal to the first predetermined value and the absolute value of the first ratio of the maximum value to the minimum value is less than or equal to the second predetermined value In addition, misfire determination means for determining that misfire has occurred in the cycle in which the amount of change in the heat generation amount is calculated,
It is characterized by providing.

The second invention is the first invention, wherein
The misfire determination means determines that the amount of change in the heat generation amount is the maximum value when noise of a predetermined value or more is superimposed on at least one of the maximum value and the minimum value of the amount of change in the heat generation amount. The second difference between the next largest value and the amount of change in the amount of generated heat is the second smallest value next to the minimum value, and is less than the first predetermined value, and the maximum difference with respect to the next smallest value after the minimum value When the second ratio of the second largest value becomes the second predetermined value, it is determined that a misfire has occurred in the cycle in which the amount of change in the heat generation amount is calculated.

The third invention is the second invention, wherein
When the difference between the first difference and the second difference is greater than a third predetermined value, the misfire determination means determines that at least one of the maximum value and the minimum value of the change amount of the heat generation amount It is determined that noise of a predetermined value or more is superimposed.

  According to the first invention, the cylinder is determined by performing the determination using the first difference between the maximum value and the minimum value of the change amount of the calorific value calculated using the detection value of the in-cylinder pressure sensor and the first ratio. Even when noise is superimposed on the internal pressure waveform, it is possible to accurately distinguish between combustion and misfire.

  According to the second aspect of the present invention, when noise of a predetermined value or more is superimposed on at least one of the maximum value and the minimum value of the amount of change in the heat generation amount, the noise is compared with the first difference and the second ratio. By performing the determination using the second difference and the second ratio that are not easily affected by the above, it is possible to ensure the accuracy of the misfire determination.

  According to the third invention, it is possible to accurately determine a situation in which noise of a predetermined value or more is superimposed on at least one of the maximum value and the minimum value of the amount of change in the heat generation amount.

It is a figure for demonstrating the system configuration | structure of the internal combustion engine in Embodiment 1 of this invention. The form of the offset component included in the waveform of the calorific value Q, and the waveform of the calorific value Q at the time of misfire, retarded combustion, and normal combustion due to the occurrence of the offset component and the difference in the mode of the offset component It is a figure showing (a pattern of heat generation). It is a figure for demonstrating the calculation method of the inclination of the emitted-heat amount Q in Embodiment 1 of this invention. It is the figure showing the misfire determination area | region and the combustion determination area | region by the relationship between the difference s1 of the inclination of the emitted-heat amount Q, and ratio h1. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure showing the waveform of the calorific value Q at the time of misfire in which a negative offset component is included and noise in which the calorific value Q fluctuates in small increments is superimposed. It is a figure showing the waveform of the emitted-heat amount Q at the time of misfire in which the minus offset component is contained and the noise which includes a single and big noise is superimposed. It is a flowchart of the routine performed in Embodiment 2 of this invention. It is a flowchart of the routine which implement | achieves other misfire determination methods.

Embodiment 1 FIG.
[System Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining a system configuration of an internal combustion engine 10 according to Embodiment 1 of the present invention.
The system shown in FIG. 1 includes an internal combustion engine 10. The internal combustion engine 10 is configured as a spark ignition type internal combustion engine (as an example, a gasoline engine). A piston 12 is provided in the cylinder of the internal combustion engine 10. A combustion chamber 14 is formed on the top side of the piston 12 in the cylinder. An intake passage 16 and an exhaust passage 18 communicate with the combustion chamber 14.

  The intake port of the intake passage 16 is provided with an intake valve 20 that opens and closes the intake port, and the exhaust port of the exhaust passage 18 is provided with an exhaust valve 22 that opens and closes the exhaust port. The intake passage 16 is provided with an electronically controlled throttle valve 24.

  Each cylinder of the internal combustion engine 10 is provided with a fuel injection valve 26 for directly injecting fuel into the combustion chamber 14 (inside the cylinder) and an ignition plug 28 for igniting the air-fuel mixture. Further, an in-cylinder pressure sensor 30 for detecting the in-cylinder pressure P is incorporated in each cylinder.

  Furthermore, the system of this embodiment includes an ECU (Electronic Control Unit) 40. In addition to the in-cylinder pressure sensor 30 described above, various sensors for detecting the operating state of the internal combustion engine 10 such as a crank angle sensor 42 for detecting the engine speed are connected to the input portion of the ECU 40. Various actuators such as the throttle valve 24, the fuel injection valve 26, and the spark plug 28 described above are connected to the output portion of the ECU 40. The ECU 40 performs predetermined engine control such as fuel injection control and ignition control by driving the various actuators based on the sensor output and a predetermined program. Further, the ECU 40 is equipped with a process for acquiring an output signal of the in-cylinder pressure sensor 30 by performing AD conversion in synchronization with the crank angle θ. Thereby, the in-cylinder pressure P at an arbitrary timing can be detected within a range allowed by the resolution of AD conversion. Further, the ECU 40 is equipped with a process for calculating the value of the in-cylinder volume V determined by the position of the crank angle θ according to the crank angle θ.

[Misfire Determination Method Using In-Cylinder Pressure Sensor in Embodiment 1]
The in-cylinder heat generation amount Q can be calculated using the detection value of the in-cylinder pressure sensor 30 by using the following method. That is, the heat generation rate dQ / dθ in the cylinder can be calculated according to the following equation (1). The heat generation amount Q can be calculated by integrating the heat generation rate dQ / dθ calculated by the equation (1) with the crank angle θ.
dQ / dθ = 1 / (κ−1) × (VdP / dθ + PκdV / dθ) (1)
However, in the above equation (1), κ is a specific heat ratio, V is an in-cylinder volume, and P is a detected value of the in-cylinder pressure sensor 30.

In general, since the detection value (output value) of the in-cylinder pressure sensor is a relative pressure, correction (absolute pressure correction) is performed to make it an absolute pressure. As a method of performing absolute pressure correction using the detection value of the in-cylinder pressure sensor 30, for example, a method using the following equation (2) is known. This method uses the Poisson's relational expression (PV ^κ = constant) established in the compression stroke regarded as an adiabatic process, and uses the in-cylinder pressure and the cylinder volume at two points during the adiabatic compression stroke. The correction amount (error) is calculated.
Absolute pressure correction amount = (P ₂ V ₂ ^κ− P ₁ V ₁ ^κ ) / (V ₁ ^κ− V ₂ ^κ ) (2)
However, in the above formula (2), P ₁ and P ₂ are detection values of an arbitrary in-cylinder pressure sensor 30 in the adiabatic compression stroke before the start of combustion in the cylinder after the intake valve 20 is closed, and V ₁ , V ₂ is the in-cylinder volume when P ₁ and P _{2 are} detected.

Noise may be superimposed on the detection value (output value) of the in-cylinder pressure sensor 30. When noise is superimposed on the in-cylinder pressure waveform, the pressure values (P ₁ , P ₂ ) at the crank angle used for the absolute pressure correction as described above change, and an error occurs in the absolute pressure correction amount. More specifically, when the correction error in the absolute pressure correction for the true in-cylinder pressure value P is α, the heat generation rate dQ / dθ reflecting the influence of the correction error α is expressed by the following equation (3). It can be expressed as
dQ / dθ = 1 / (κ−1) × (VdP / dθ + (P + α) κdV / dθ) (3)

  FIG. 2 shows the form of the offset component included in the waveform of the calorific value Q, and the respective heat generation during misfire, retarded combustion, and normal combustion due to the presence or absence of the offset component and the difference in the form of the offset component. It is a figure showing the waveform (pattern of heat generation) of quantity Q. Note that FIG. 2 shows the change in the calorific value Q in a simplified and linear manner in order to easily express the difference in the tendency of each pattern of heat generation.

  Waveforms A to C in FIG. 2 respectively show aspects of offset components included in the waveform of the calorific value Q. A waveform A shows a case where the absolute pressure correction error α due to noise superposition does not occur (that is, when there is no offset component). On the other hand, when a negative noise is superimposed on the detection value of the in-cylinder pressure sensor 30 and the absolute pressure correction amount is insufficient, a positive offset component as shown in the waveform B is generated. When noise is superimposed, a minus offset component as shown in waveform C is generated. This can be explained from the process of calculating the calorific value Q using the above equation (3).

  That is, as shown in the above equation (3), the term (κ / (κ−1) × (P + α) dV / dθ) is affected by the absolute pressure correction error. Here, the waveform of the in-cylinder volume V is symmetric with respect to the compression top dead center. Therefore, when the in-cylinder pressure P includes the absolute pressure correction error α, the waveform of the calorific value Q obtained by integrating the equation (3) with the crank angle θ has the following offset: Ingredients will be included. That is, the offset component of the waveform of the calorific value Q is a symmetrical waveform with the compression top dead center as the apex, and the apex is shifted in the vertical direction by the offset due to the influence of the correction error α. In addition, the waveform has different waveforms depending on the sign of the correction error α. As a result, when the absolute pressure correction error α occurs, an offset component having a form as shown by the waveforms B and C in FIG. 2 is included in the waveform of the calorific value Q.

  Next, the waveforms D to L of the calorific value Q at the time of misfire, retarded combustion, and normal combustion in FIG. 2 will be described in consideration of the presence of an offset component and the difference in its form. The retarded combustion is an example of slow combustion in which the in-cylinder pressure P is not so high as compared to normal combustion.

  A waveform D shown in FIG. 2 shows a waveform of the calorific value Q at the time of misfire in a state where no offset component is included. At the time of misfire, if the offset component is not included, the crank angle θ decreases substantially uniformly as the crank angle θ advances before and after the compression top dead center. On the other hand, the waveform E and the waveform F at the time of misfire are obtained by combining the waveform D with a plus offset component (waveform B) and a minus offset component (waveform C), respectively. It becomes a trend waveform.

  A waveform G shown in FIG. 2 shows a waveform of the calorific value Q at the time of retarded combustion in a state where no offset component is included. The timing θ1 after the compression top dead center in the waveform G is the timing at which the retarded combustion starts. As described above, the combustion start timing θ1 at the time of retarded combustion is delayed from the timing θ2 at the time of normal combustion described later. The waveform G before the timing θ1 is the same as the waveform D at the time of misfire, but when the combustion starts at the timing θ1, the calorific value Q starts to increase (the slope changes). On the other hand, the waveform H and the waveform I at the time of misfire are obtained by combining the waveform G with a plus offset component (waveform B) and a minus offset component (waveform C), respectively, and therefore, as shown in FIG. It becomes a trend waveform. That is, a change in the slope of the calorific value Q due to the influence of the start of the retarded angle combustion also appears for these waveforms H and I.

  Further, a waveform J shown in FIG. 2 shows a waveform of the calorific value Q during normal combustion in a state where no offset component is included. The timing θ2 immediately before the compression top dead center in the waveform J is the timing at which normal combustion starts, and the timing θ3 after the compression top dead center is the timing at which normal combustion ends. The waveform J before the timing θ2 is the same as the waveform D at the time of misfire, but when the combustion starts at the timing θ2, a change in the slope of the heat generation amount Q due to the heat generation amount Q starting to increase greatly occurs. Further, at the timing θ3 when the combustion ends thereafter, the change in the calorific value Q is settled, so that the slope of the calorific value Q changes again. On the other hand, the waveform K and the waveform K at the time of misfire are obtained by combining the waveform J with a plus offset component (waveform B) and a minus offset component (waveform C), respectively. It becomes a trend waveform. That is, changes in the slope of the calorific value Q due to the influence of the start and end of normal combustion also appear for these waveforms K and L.

  If an absolute pressure correction amount error of the in-cylinder pressure P occurs due to noise superimposition, the in-cylinder pressure P is not corrected correctly. As described above with reference to FIG. 2, the in-cylinder pressure P after the absolute pressure correction is used. Thus, an error (offset component) also occurs in the waveform of the calorific value Q calculated as described above. Therefore, it is difficult to distinguish between combustion and misfire by simply using the amount of change in the heat generation amount Q during the predetermined crank angle period. This is particularly noticeable in combustion in which the in-cylinder pressure P during combustion does not increase so much, such as retarded combustion. Therefore, in the present embodiment, in order to be able to accurately discriminate between combustion and misfire using the calorific value Q calculated based on the in-cylinder pressure P detected by the in-cylinder pressure sensor 30, The following judgment process was performed.

FIG. 3 is a diagram for explaining a method for calculating the gradient of the calorific value Q in the first embodiment of the present invention.
In the present embodiment, first, the amount of change in the amount of heat generation Q in the cylinder at a predetermined crank angle interval (here, 30 ° CA as an example) (hereinafter referred to as “the slope of the amount of heat generation Q”) during one cycle. Multiple calculations were made. More specifically, as shown in FIG. 3, a predetermined crank angle period (here, as an example, a period from 60 ° CA before compression top dead center to 120 ° CA after compression top dead center, The inclination of the heat generation amount Q is calculated every 5 ° CA in the crank angle during the combustion period in which the change in the heat generation amount Q according to the presence or absence of the combustion and the change in the combustion state and a predetermined period before and after that. As a result, in the example shown in FIG. 3, the gradient of the calorific value Q at 31 points is calculated as a total.

  In addition, in the present embodiment, the maximum value and the minimum value of the slopes (change amounts) of the plurality of calorific values Q calculated in one cycle are calculated, and the difference s1 between the calculated maximum value and minimum value is a threshold value. When the absolute value of the ratio h1 of the maximum value with respect to the minimum value is equal to or less than the threshold value h, a misfire has occurred in the current cycle in which the slope (change amount) of the heat generation amount Q is calculated. Judgment was made.

  The difference s1 in the slope of the heat generation amount Q is a value obtained by subtracting the minimum value from the maximum value of the slope of the heat generation amount Q within the predetermined crank angle period in which the heat generation amount Q is calculated as described above. Therefore, the difference s1 is always a positive value regardless of the sign of the maximum value and the minimum value. On the other hand, the slope ratio h1 of the calorific value Q may be negative because it is assumed that the sign of the maximum value is positive and the sign of the minimum value is negative.

  Even in the case of a misfire, if a negative offset component or a positive offset component is included in the waveform of the calorific value Q, a change appears in the slope of the calorific value Q as shown by waveforms E and F in FIG. . However, during normal combustion, as shown by waveforms J to L in FIG. 2, a change in the slope of the calorific value Q that is sufficiently larger than that at the time of misfiring appears in the vicinity of the compression top dead center. Therefore, by calculating the difference s1 between the maximum value and the minimum value of the slope of the calorific value Q and comparing it with the threshold value s, it can be determined whether or not the calorific value Q in a certain cycle is at the level during combustion. Become.

  On the other hand, during retarded combustion, a change appears in the slope of the calorific value Q after compression top dead center at a timing (θ1) delayed from that during normal combustion, but the change is more gradual than during normal combustion. It becomes. For this reason, if only the difference s1 between the maximum value and the minimum value of the gradient of the calorific value Q is used, it may be difficult to accurately determine retarded combustion and misfire. For this reason, in this embodiment, in addition to the difference s1, the ratio h1 between the maximum value and the minimum value of the gradient of the calorific value Q is used for misfire determination.

  At the time of misfire, if the offset component is not included in the waveform of the calorific value Q, the slope of the calorific value Q does not change roughly as shown by the waveform D in FIG. h1 is approximately 1. Further, even if a negative offset component or a positive offset component is included in the calorific value Q waveform at the time of misfire, the calorific value Q waveform in this case is shown as waveforms E and F in FIG. It is close to left-right symmetry with the compression top dead center as the apex. That is, at the time of misfire, since the calorific value Q does not increase except for the offset effect, the slope of the calorific value Q does not change after the compression top dead center. As a result, in the case of misfire, the maximum value and the minimum value of the gradient of the calorific value Q substantially coincide with each other in absolute value, and the absolute value of the ratio h1 is approximately 1. More specifically, if the sign of the maximum value and the minimum value of the slope is the same, the ratio h1 is approximately 1, and if the maximum value is positive and the minimum value is negative, the ratio h1 is approximately − 1

  On the other hand, since heat is generated during the retarded combustion, the slope of the calorific value Q once again changes (rises) after compression top dead center. As a result, the absolute value of the slope ratio h1 is larger than 1. More specifically, if the sign of the maximum value and the minimum value of the slope are the same, the ratio h1 is greater than 1, and if the maximum value is positive and the minimum value is negative, the ratio h1 is Less than -1. Therefore, by calculating the absolute value of the ratio h1 of the maximum value to the minimum value of the gradient of the calorific value Q and comparing it with the threshold value h, it becomes possible to distinguish between retarded combustion and misfire.

FIG. 4 is a diagram showing the misfire determination region and the combustion determination region in relation to the difference s1 in the gradient of the heat generation amount Q and the ratio h1.
Using the relationship between the difference s1 in the slope of the calorific value Q and the ratio h1, the determination region according to the method of the present embodiment described above is illustrated, and the combustion determination region as shown in FIG. It can be expressed as a misfire determination area.

  FIG. 5 is a flowchart showing a routine executed by the ECU 40 in order to realize the misfire determination in the first embodiment of the present invention. Note that this routine is repeatedly executed for each cylinder in each cycle of the internal combustion engine 10.

  In the routine shown in FIG. 5, the ECU 40 first determines whether or not a predetermined misfire detection condition as a precondition is satisfied (step 100). The misfire detection conditions here are, for example, that fuel cut is not being executed and that the engine speed is equal to or higher than a predetermined engine speed.

  If the ECU 40 determines in step 100 that the misfire detection condition is satisfied, the ECU 40 then performs the predetermined crank angle period in the current cycle (for example, from 60 ° CA before compression top dead center to 120 after compression top dead center. In-cylinder pressure waveform (period in which the vertical axis is the in-cylinder pressure P and the horizontal axis is the crank angle θ) in the period up to ° CA is acquired (step 102). More specifically, in step 102, the in-cylinder pressure P in the predetermined crank angle period is acquired as being related to the crank angle θ every 5 ° CA (an example) in the crank angle θ.

  Next, the ECU 40 performs absolute pressure correction on the in-cylinder pressure P acquired as described above using the method described above (step 104). Next, the ECU 40 uses the in-cylinder pressure P after the absolute pressure correction to calculate the in-cylinder heat generation amount Q by the method described above (step 106).

  Next, the ECU 40 determines the predetermined value for the calorific value Q during the predetermined crank angle period (for example, the period from 60 ° CA before compression top dead center to 120 ° CA after compression top dead center). A plurality of inclinations of the calorific value Q corresponding to the amount of change in the calorific value Q at the crank angle interval (for example, 30 ° CA) are calculated while shifting the in-cylinder pressure value used for the calculation by 5 ° CA by the crank angle (step 108). . The predetermined crank angle interval when calculating the gradient of the calorific value Q is the magnitude of noise superimposed on the acquired in-cylinder pressure data interval (in the above, 5 ° CA) and the detected value of the in-cylinder pressure P. Accordingly, the interval is set so as to be less susceptible to noise.

  Next, the ECU 40 selects the maximum value and the minimum value from the slopes of the plurality of calorific values Q calculated as described above, and subtracts the minimum value from the maximum value to obtain the difference s1 in the slope of the calorific value Q. Calculate (step 110). Next, the ECU 40 determines whether or not the difference s1 of the calculated gradient of the calorific value Q is equal to or less than a predetermined threshold value s (step 112).

  If the ECU 40 determines in step 112 that the difference s1 in the gradient of the heat generation amount Q is greater than the threshold value s, the ECU 40 determines that the heat generation amount Q in the current cycle is at the level during combustion, and combustion is performed in the current cycle. It is determined that it has been performed (step 114). On the other hand, when the ECU 40 determines that the difference s1 in the slope of the heat generation amount Q is equal to or less than the threshold s in step 112, the ECU 40 calculates a ratio h1 of the maximum value to the minimum value of the slope of the heat generation amount Q (step 116). ).

  Next, the ECU 40 determines whether or not the absolute value of the calculated slope ratio h1 of the calorific value Q is equal to or less than a predetermined threshold value h (step 118). As a result, if the ECU 40 determines that the absolute value of the ratio h1 of the calorific value Q is greater than the threshold value h, it determines that heat is generated by combustion, and combustion is performed in the current cycle. (Step 114). On the other hand, if the ECU 40 determines that the absolute value of the ratio h1 of the calorific value Q is equal to or less than the threshold value h, it determines that a misfire has occurred in the current cycle for the reason described above (step 120). .

  According to the routine shown in FIG. 5 described above, noise is superimposed on the in-cylinder pressure waveform by using the difference s1 and the ratio h1 between the maximum value and the minimum value of the gradient (change amount) of the calorific value Q. Even if it is, it becomes possible to accurately distinguish between combustion and misfire.

  Further, in the present embodiment, the gradient (change amount) of the heat generation amount Q is not simply a difference between two in-cylinder pressure values close to the crank angle θ, but an appropriate crank angle interval (the predetermined crank angle such as 30 ° CA). It is calculated as the difference in the in-cylinder pressure value at the angular interval). As a result, the influence of a sharp change in the amount of heat generation Q caused by noise can be excluded.

FIG. 6 is a diagram showing a waveform of the calorific value Q at the time of misfire in which a negative offset component is included and noise in which the calorific value Q fluctuates in small increments is superimposed.
In the waveform of the calorific value Q on which noise is superimposed, the calorific value Q may change in several places after the compression top dead center as shown by circles in FIG. In the case where such noise is superimposed on the waveform of the calorific value Q, the method of detecting misfire based on the heat generation pattern described later with reference to FIG. There is a possibility of misjudging that it is combustion. On the other hand, in the method of the present embodiment, the difference s1 between the maximum value and the minimum value of the gradient (change amount) of the heat generation amount Q and the magnitude of the ratio h1 are determined. Even if is superimposed, it is possible to avoid misjudging misfire as combustion.

  In the above-described first embodiment, the difference s1 is the “first difference” in the first invention, the threshold s is the “first predetermined value” in the first invention, and the ratio h1 is the first The threshold value h corresponds to the “second predetermined value” in the first aspect of the present invention. Further, the “misfire determination means” according to the first aspect of the present invention is realized by the ECU 40 executing a series of processes of the routine shown in FIG.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. 7 and FIG.
The system of the present embodiment can be realized by causing the ECU 40 to execute a routine shown in FIG. 8 described later instead of the routine shown in FIG. 5 using the hardware configuration shown in FIG.

FIG. 7 is a diagram showing a waveform of the calorific value Q at the time of misfire in which a negative offset component is included and noise that includes a single and large noise is superimposed.
As shown in FIG. 7, there is a possibility that single and large noise may be superimposed on the waveform of the calorific value Q. When such single and large noise is superimposed on the waveform of the calorific value Q, the calorific value Q may be calculated to be large or small due to the influence as shown by a circled part in FIG. As a result, when the noise is superimposed as described above, the influence of noise is also included in the maximum value and the minimum value of the slope calculated using the calorific value Q, and the above-described slope difference s1 and h1 are used. There is a concern that the accuracy of misfire determination by the method of the first embodiment will be reduced.

  Therefore, in the present embodiment, in order to avoid the influence of large noise such as single noise, noise that is equal to or larger than a predetermined value is at least one of the maximum value and the minimum value of the gradient (change amount) of the heat generation amount Q. Are determined using the second largest value and the second smallest value instead of the maximum value and the minimum value of the inclination, the inclination difference s2 and the ratio h2 are calculated. I did it. In this case, when the difference s2 is equal to or smaller than the threshold value s and the absolute value of the ratio h2 is equal to or smaller than the threshold value h, it is determined that a misfire has occurred in the current cycle. .

  FIG. 8 is a flowchart showing a routine executed by the ECU 40 in order to realize the misfire determination in the second embodiment of the present invention. In FIG. 8, the same steps as those shown in FIG. 5 in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 8, the ECU 40 calculates the difference s1 in the slope of the heat generation amount Q in step 110, and then calculates the difference s2 between the second largest value and the second smallest value in the heat generation amount Q slope. Calculate (step 200).

  Next, the ECU 40 determines whether or not the difference (s1−s2) between the difference s1 and the difference s2 is equal to or less than a predetermined threshold value a (step 202). The threshold value a used in this step 202 is the influence of noise in which the difference s1 in the slope of the calorific value Q (more specifically, at least one of the maximum value and the minimum value of the slope constituting the difference s1) is a predetermined value or more. It is a value set in advance as a value for determining whether or not it is received.

  If the determination in step 202 is satisfied, that is, if the difference (s1−s2) is equal to or less than the threshold value a, large noise is superimposed on both the maximum value and the minimum value of the gradient of the calorific value Q. If it can be determined that the processing has not been performed, a series of processing in steps 112 to 120 is executed.

  On the other hand, if the determination in step 202 is not satisfied, that is, the difference (s1−s2) is larger than the threshold value a, it is larger than at least one of the maximum value and the minimum value of the gradient of the calorific value Q. If it can be determined that noise is superimposed, the ECU 40 then determines whether or not the calculated difference s2 in the gradient of the calorific value Q is equal to or less than the threshold value s (step 204).

  If the ECU 40 determines in step 204 that the difference s2 in the slope of the heat generation amount Q is greater than the threshold value s, the ECU 40 determines that the heat generation amount Q in the current cycle is at the level during combustion, and combustion is performed in the current cycle. It is determined that it has been performed (step 206). On the other hand, if the ECU 40 determines in step 204 that the difference s2 in the slope of the heat generation amount Q is equal to or less than the threshold value s, the ratio between the second largest value and the second smallest value in the slope of the heat generation amount Q. h2 is calculated (step 208).

  Next, the ECU 40 determines whether or not the absolute value of the calculated slope ratio h2 of the calorific value Q is equal to or less than the threshold value h (step 210). As a result, when the ECU 40 determines that the absolute value of the ratio h2 of the gradient of the calorific value Q is larger than the threshold value h, it determines that heat is generated due to combustion, and combustion is performed in the current cycle. (Step 206). On the other hand, if the ECU 40 determines that the absolute value of the slope ratio h2 of the calorific value Q is equal to or less than the threshold value h, it determines that a misfire has occurred in the current cycle for the same reason as the determination in step 118. (Step 212).

  According to the routine shown in FIG. 8 described above, it is determined that a large noise is superimposed on the maximum value or the minimum value of the slope because the difference (s1−s2) between the difference s1 and the difference s2 is larger than the threshold value a. If possible, a misfire determination using the difference s2 and the ratio h2 based on the second largest value and the second smallest value of the gradient of the calorific value Q is executed. If a large amount of noise is generated only once, the influence of the noise is less likely to be affected by the second value of the magnitude and smallness of the slope of the calorific value Q than the maximum and minimum values. . For this reason, by performing the misfire determination using the difference s2 and the ratio h2 in such a case, the accuracy of the misfire determination can be ensured.

  By the way, in Embodiment 2 mentioned above, since the difference (s1-s2) of the difference s1 and the difference s2 is larger than the threshold value a, it can be judged that big noise has superimposed on the maximum value and minimum value of inclination. In this case, misfire determination using the difference s2 and the ratio h2 based on the second largest value and the second smallest value of the gradient of the calorific value Q is performed. However, it is also conceivable that large noise is superimposed at a plurality of locations. In such a case, the following misfire determination may be performed by applying the method of the second embodiment described above. That is, the difference (s2−s3) between the second difference s2 and the third difference s3 is compared with a predetermined threshold value a in the magnitude and smallness of the gradient of the calorific value Q. As a result, when this difference is larger than the threshold value a, it is determined that a large noise is superimposed on the second value for the magnitude or smallness of the gradient of the calorific value Q, and the difference based on the third value Misfire determination using s3 and ratio h3 is performed.

In the second embodiment, the difference s2 corresponds to the “second difference” in the second invention, and the ratio h2 corresponds to the “second ratio” in the first invention.
In the second embodiment described above, the threshold value a corresponds to the “third predetermined value” in the third aspect of the invention.

Other misfire detection methods.
As a method for accurately determining misfire using the calorific value Q calculated based on the in-cylinder pressure P detected by the in-cylinder pressure sensor, in addition to the method described in the first and second embodiments, The following methods can be considered. Here, the determination method using the configuration of the internal combustion engine 10 shown in FIG. 1 will be described.

  The waveform pattern (heat generation pattern) of the calorific value Q during misfire, retarded combustion, and normal combustion is shown in FIG. 2 depending on whether or not an offset component is generated due to noise superposition and the difference in the mode of the offset component. It can be expressed as described above with reference. Therefore, misfire and combustion may be separated and determined by capturing such a difference in heat generation pattern.

  FIG. 9 is a flowchart showing a routine executed by the ECU 40 in order to realize another misfire determination method. In FIG. 9, the same steps as those shown in FIG. 5 in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 9, after calculating the heat generation amount Q in step 106, the ECU 40 then determines whether or not the calculated maximum value of the heat generation amount Q is equal to or greater than a predetermined value (step 300). The maximum value of the heat generation amount Q at the time of combustion is sufficiently larger than the shift amount of the heat generation amount Q due to the influence of the offset component. For this reason, when the calculated maximum value of the calorific value Q is equal to or greater than a predetermined value, it can be determined that combustion has been performed in the current cycle. Therefore, when the determination in step 300 is established, the ECU 40 determines that combustion has been performed in the current cycle (step 302).

  On the other hand, if the determination in step 300 is not satisfied, the ECU 40 calculates a plurality of inclinations (change amounts) of the heat generation amount Q in step 108 and then calculates a plurality of changes (differences) H in the inclination of the heat generation amount Q. Calculate (step 304). More specifically, in the present step 304, the predetermined crank angle period (for example, the period from 60 ° CA before compression top dead center to 120 ° CA after compression top dead center) is plural (in the example of FIG. (31 points in total) With respect to the calculated inclination of the heat generation amount Q, two inclination changes H near the crank angle θ are calculated while shifting the crank angle θ by 5 ° CA. Illustratively, the slope calculated using the calorific value Q at 60 ° CA before compression top dead center and the calorific value Q at 30 ° CA before compression top dead center, and at 55 ° CA before compression top dead center An amount of change H between the calorific value Q and the slope calculated using the calorific value Q at 25 ° CA before compression top dead center is calculated. Next, the slope calculated using the calorific value Q at 55 ° CA before compression top dead center and the calorific value Q at 25 ° CA before compression top dead center, and the heat generated at 50 ° CA before compression top dead center The amount of change H between the amount Q and the slope calculated using the calorific value Q at 20 ° CA before compression top dead center is calculated, and so on.

  Next, the ECU 40 determines whether or not the change amount H that is equal to or greater than a predetermined threshold among the change amounts H of the slope of the calorific value Q calculated in step 304 is less than two (step 306). ). As a result, when the determination in step 306 is not established, the ECU 40 determines that combustion has been performed in the current cycle (step 302). On the other hand, if the determination in step 306 is satisfied, the ECU 40 then determines whether or not the timing at which the change amount H that is equal to or greater than the threshold is calculated is within a predetermined range near the compression top dead center. (Step 304). As a result, if the determination in this step 308 is not established, the ECU 40 determines that combustion has been performed in the current cycle (step 302). Conversely, if the determination in this step 308 is established, It is determined that a misfire has occurred in the current cycle (step 310).

  As shown in each pattern of heat generation in FIG. 2, when combustion (including retarded angle combustion) occurs, the waveform of the calorific value Q shows the calorific value twice or more near the compression top dead center. A change in Q appears. On the other hand, at the time of misfire, since the calorific value Q does not change due to the influence other than the offset component, the calorific value Q changes at most once near the compression top dead center, and after the compression top dead center The slope never changes. For example, as shown as a waveform F in FIG. 2, when the waveform of the calorific value Q at the time of misfire includes a minus offset component, the slope of the calorific value Q is a negative value near the compression top dead center. After the value becomes positive value from, it becomes constant, and the change amount H of the inclination becomes minute. On the other hand, heat generation occurs during retarded combustion, so that the gradient of the calorific value Q once again changes after leaving the compression top dead center. For example, when a negative offset component is included in the waveform of the calorific value Q at the time of retarded combustion, the slope of the calorific value Q changes from a negative value to a positive value near the compression top dead center. It changes to a larger positive value. Therefore, when both the determinations in steps 306 and 308 are established, the occurrence of misfire can be determined separately from combustion.

  According to the misfire determination method described above, even when noise is superimposed on the detection value of the in-cylinder pressure sensor 30 during slow combustion in which the in-cylinder pressure P does not become too high, the accuracy is determined based on the heat generation pattern. A good misfire judgment can be made.

  When the misfire determination is performed by the routine method shown in FIG. 9, in order to reduce the processing load of the ECU 40, with reference to the heat generation pattern as shown in FIG. It is also possible to reduce the number of calculation points of the amount of change H of the slope of. In other words, the transition of the change in the slope of the calorific value Q at several points before and after the compression top dead center and the heat generation timing according to the retard amount are grasped in advance, and the section carefully selected based on the grasp result The change amount H of the slope of the heat generation amount Q is calculated on the actual machine. As a result, it is possible to determine whether an offset component is generated due to the influence of noise, and to distinguish between misfire and combustion.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Piston 14 Combustion chamber 16 Intake passage 18 Exhaust passage 20 Intake valve 22 Exhaust valve 24 Throttle valve 26 Fuel injection valve 28 Spark plug 30 In-cylinder pressure sensor 40 ECU (Electronic Control Unit)
42 Crank angle sensor

Claims (3)

An in-cylinder pressure sensor for detecting the in-cylinder pressure;
A plurality of changes in the amount of heat generated in the cylinder during a predetermined crank angle period are calculated during one cycle using the detection value of the cylinder pressure sensor, and the maximum value of the plurality of changes in the amount of generated heat calculated during one cycle is calculated. When the first difference between the maximum value and the minimum value is less than or equal to the first predetermined value and the absolute value of the first ratio of the maximum value to the minimum value is less than or equal to the second predetermined value In addition, misfire determination means for determining that misfire has occurred in the cycle in which the amount of change in the heat generation amount is calculated,
A misfire determination device for an internal combustion engine, comprising:   The misfire determination means determines that the amount of change in the heat generation amount is the maximum value when noise of a predetermined value or more is superimposed on at least one of the maximum value and the minimum value of the amount of change in the heat generation amount. The second difference between the next largest value and the amount of change in the amount of generated heat is the second smallest value next to the minimum value, and is less than the first predetermined value, and the maximum difference with respect to the next smallest value after the minimum value 2. The method according to claim 1, wherein when the second ratio of the second largest value is the second predetermined value, it is determined that a misfire has occurred in a cycle in which the amount of change in the heat generation amount is calculated. The misfire determination apparatus of the internal combustion engine of description.   When the difference between the first difference and the second difference is greater than a third predetermined value, the misfire determination means determines that at least one of the maximum value and the minimum value of the change amount of the heat generation amount The misfire determination apparatus for an internal combustion engine according to claim 2, wherein it is determined that noise of a predetermined value or more is superimposed.

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