JP2007056727A - Ignition timing control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To previously predict operation stability after adjusting ignition timing when adjusting ignition timing in an ignition timing control device for an internal combustion engine. <P>SOLUTION: Supposed ignition timing SAi advanced more than the present ignition timing SAc is assumed (step 118). Cylinder pressure history data under the supposed ignition timing SAi are created by a significant number of cycles (step 120). Based on the cylinder pressure history data, knocking cycle frequencies under the supposed ignition timing SAi are predicted (step 134). Based on the predicted knocking cycle frequencies, ignition timing is set to approximate MBT (minimum advance for best torque) within a range not causing knocking (steps 150-158). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ignition timing control device for an internal combustion engine.

  In a spark ignition internal combustion engine, the ignition timing greatly affects the operating state. In normal operation and steady state, it can be said that the ignition timing at which the output torque is maximized in a range where knocking does not occur is the optimum ignition timing.

  The optimal ignition timing varies depending on parameters such as engine speed, load factor (intake pressure), and coolant temperature. Therefore, it has been conventionally performed to create a map that defines the relationship between these parameters and the optimum ignition timing, and to control the ignition timing with reference to the map.

  The optimum ignition timing further varies depending on machine difference variation and secular change. For this reason, the true optimum ignition timing cannot be obtained only by referring to the map prepared in advance. Therefore, knocking feedback control using a knock sensor that detects knocking has been conventionally performed. In this control, when knocking is detected by the knock sensor, the ignition timing is gradually retarded until knocking is no longer detected. When knocking is no longer detected, the ignition timing is gradually advanced, and when knocking reoccurs, the ignition timing is retarded again.

  Japanese Patent Laid-Open No. 9-250435 discloses a technique for detecting an actual combustion rate up to a predetermined crank angle and performing feedback control of the ignition timing so that the combustion rate becomes a target value.

JP-A-9-250435 JP-A-9-317522 Japanese Patent Application Laid-Open No. 64-87874 Japanese Patent Laid-Open No. 10-110638

  However, the knocking feedback control is based on the assumption that knocking is detected as described above. That is, the optimum ignition timing cannot be found unless knocking is once generated. For this reason, damage and noise to the internal combustion engine due to knocking cannot be completely prevented. Similar problems remain in the technique disclosed in Japanese Patent Laid-Open No. 9-250435.

  The present invention has been made in view of the above points. An ignition timing control device for an internal combustion engine capable of predicting in advance the operational stability after adjusting the ignition timing when adjusting the ignition timing. The purpose is to provide.

In order to achieve the above object, a first invention is an ignition timing control device for an internal combustion engine,
Simulated in-cylinder pressure history data generating means for generating simulated in-cylinder pressure history data simulating in-cylinder pressure history with respect to the crank angle, assuming that the ignition timing of the internal combustion engine has been changed from the current value;
Based on the simulated in-cylinder pressure history data for a large number of cycles, driving stability prediction means for predicting driving stability after changing the ignition timing in advance;
Ignition timing setting means for setting an actual ignition timing based on the prediction result of the driving stability prediction means;
It is characterized by providing.

The second invention is the first invention, wherein
The simulated in-cylinder pressure history data generating means includes:
Combustion model means for simulating the combustion state based on predetermined combustion parameters;
A standard deviation predicting means for predicting a standard deviation of the distribution of the combustion parameter after the ignition timing is changed;
Combustion parameter extraction means for randomly extracting the value of the combustion parameter from a normal distribution having the standard deviation prediction means as a standard deviation;
In-cylinder pressure history calculating means for calculating the simulated in-cylinder pressure history data based on a simulated combustion state obtained by inputting the value extracted by the combustion parameter extracting means to the combustion model means;
It is characterized by including.

The third invention is the second invention, wherein
The combustion parameter includes a value related to combustion efficiency, a value related to a crank angle at which a predetermined combustion ratio is obtained, and a value related to a combustion period until the first combustion ratio changes to the second combustion ratio. To do.

Moreover, 4th invention is 2nd or 3rd invention,
The standard deviation predicting means includes
Average value acquisition means for acquiring an average value of the actual values of the combustion parameters in the current operating state;
Means for storing an arithmetic expression for deriving a standard deviation predicted value of the combustion parameter based on the average value acquired by the average value acquisition means and a predetermined operating parameter representing the current operating state;
Driving parameter acquisition means for acquiring the actual value of the driving parameter in the current driving state;
It is characterized by including.

The fifth invention is the fourth invention, wherein
The average value acquisition means includes
An in-cylinder pressure sensor for detecting an actual in-cylinder pressure;
Combustion parameter calculation means for calculating the actual value of the combustion parameter in the current operating state for each cycle based on the history of the actual in-cylinder pressure with respect to the crank angle;
Arithmetic average means for calculating an arithmetic average for each type of calculated values of the combustion parameter calculating means;
It is characterized by including.

The sixth invention is the fifth invention, wherein
An actual standard deviation calculating means for calculating an actual standard deviation of the combustion parameter from a distribution of actual values of the combustion parameter calculated by the combustion parameter calculating means;
It further comprises calibration means for calibrating the coefficient in the arithmetic expression by inputting the actual standard deviation and the actual value of the operation parameter into the arithmetic expression for deriving the standard deviation predicted value. And

According to a seventh invention, in any one of the first to sixth inventions,
The driving stability prediction means includes
Knock cycle determination means for determining whether or not the cycle is a knock cycle that causes knock for each simulated in-cylinder pressure history data;
Knocking judging means for judging whether or not the occurrence frequency of the knock cycle is below an allowable level;
It is characterized by including.

The eighth invention is the seventh invention, wherein
The knock cycle determination means includes
Self-ignition prediction means for predicting the self-ignition time of the cycle based on the simulated in-cylinder pressure history data;
A combustion ratio calculation determination means for determining that the cycle is a knock cycle when the predicted combustion ratio at the time of self-ignition is equal to or less than a determination value;
It is characterized by including.

According to a ninth invention, in any one of the first to sixth inventions,
The driving stability prediction means includes
For each simulated in-cylinder pressure history data, an indicated torque calculating means for calculating an indicated torque of the cycle;
A variation degree calculating means for calculating a variation degree of the distribution of the indicated torque;
Torque fluctuation determining means for determining whether or not the degree of variation is below an allowable level;
It is characterized by including.

  According to the first invention, simulated in-cylinder pressure history data simulating the in-cylinder pressure history with respect to the crank angle after changing the ignition timing can be generated in a predictive manner. By collecting the simulated in-cylinder pressure history data for many cycles, it is possible to express the state of combustion fluctuation predicted after the ignition timing is changed. Operational stability is closely related to combustion fluctuations. According to the present invention, the operational stability after changing the ignition timing can be accurately predicted in advance based on the state of combustion fluctuation. According to the present invention, the ignition timing can be adjusted to the optimum timing based on the prediction result of the driving stability so as not to cause a situation that the driving stability is impaired. In addition, the above-described effects can be reliably achieved without being affected by machine difference variation or secular change.

  According to the second invention, it is possible to predict the standard deviation of the combustion parameter to be input to the combustion model means for simulating the combustion state after changing the ignition timing. Then, by inputting the combustion parameter value randomly extracted from the normal distribution having the predicted value as the standard deviation to the combustion model means, highly accurate simulated in-cylinder pressure history data can be generated. Therefore, according to this invention, the driving stability after changing the ignition timing can be predicted with better accuracy.

  According to the third invention, the combustion model means relates to a value related to the combustion efficiency, a value related to the crank angle at which the predetermined combustion ratio is obtained, and a combustion period until the first combustion ratio changes to the second combustion ratio. The combustion state can be simulated based on the value. For this reason, the combustion state can be simulated more closely to the actual situation. Therefore, according to the present invention, the operation stability after changing the ignition timing can be predicted with better accuracy.

  According to the fourth aspect, the standard deviation of the combustion parameter after changing the ignition timing can be predicted with better accuracy. Therefore, according to the present invention, the simulated in-cylinder pressure history data can be generated with higher accuracy, and thus the operational stability after changing the ignition timing can be predicted with better accuracy.

  According to the fifth aspect, based on the output of the in-cylinder pressure sensor that detects the actual in-cylinder pressure, the average value of the actual values of the combustion parameters in the current operating state can be actually measured. Since the standard deviation of the combustion parameter after changing the ignition timing is predicted based on the actually measured average value, the prediction accuracy can be further improved.

  According to the sixth aspect, the actual standard deviation of the combustion parameter can be acquired from the distribution of the actual value of the actually measured combustion parameter. According to the present invention, the coefficient in the arithmetic expression for deriving the standard deviation predicted value can be calibrated using the actual standard deviation value. Therefore, the calculation formula for deriving the standard deviation prediction value of the combustion parameter can reflect the influence of machine difference variation and secular change. For this reason, since the influence of machine difference variation and secular change can be more accurately incorporated, the state of combustion fluctuation can be predicted with better accuracy.

  According to the seventh aspect, it is possible to predict whether or not knocking will occur as driving stability. For this reason, according to the present invention, the ignition timing can be adjusted to the optimum timing without causing knocking even once.

  According to the eighth aspect, whether or not knocking occurs can be predicted with better accuracy.

  According to the ninth aspect of the invention, it is possible to predict whether or not the magnitude of torque fluctuation falls within an allowable level as driving stability. For this reason, according to the present invention, the ignition timing can be adjusted to the optimum timing without causing any adverse effects due to torque fluctuations.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. As shown in FIG. 1, the system of this embodiment includes a spark ignition type internal combustion engine 10. The internal combustion engine 10 incorporates a crank angle sensor 12 that detects a crank angle. The crank angle sensor 12 is a sensor that reverses the Hi output and the Lo output each time the crankshaft rotates by a predetermined rotation angle. According to the output of the crank angle sensor 12, the crank angle (rotational position of the crankshaft), the engine speed NE, and the like can be detected.

  Further, the internal combustion engine 10 includes a water temperature sensor 16 for detecting the cooling water temperature THW and an in-cylinder pressure sensor 18. The in-cylinder pressure sensor 18 can detect the pressure generated in the cylinder (combustion chamber).

  A surge tank 20 is provided in the intake passage 19 of the internal combustion engine 10. The surge tank 20 is provided with an intake pressure sensor 21 for detecting the internal pressure, that is, the intake pipe pressure. The intake pipe pressure is proportional to the amount of intake air per stroke of the internal combustion engine 10. Therefore, according to the output of the intake pressure sensor 21, the load factor KL [%] of the internal combustion engine 10 can be detected. The load factor KL is a percentage of the mass of fresh air sucked into the cylinder with respect to the mass of fresh air that occupies the total stroke volume in the standard state.

  In addition, an air flow meter 22 for detecting an intake air amount GA flowing through the inside of the intake passage 19 is disposed. A throttle valve 24 is disposed downstream of the air flow meter 22. In the vicinity of the throttle valve 24, a throttle opening sensor 26 for detecting the throttle opening TA is assembled.

  A fuel injection valve 28 for injecting fuel such as gasoline is disposed in the intake port of the internal combustion engine 10. The internal combustion engine 10 is provided with a spark plug 30 for igniting the air-fuel mixture in the combustion chamber. Further, an exhaust pressure sensor 33 is installed in the exhaust passage 32 of the internal combustion engine 10 to detect its internal pressure, that is, the exhaust pipe pressure. A catalyst 34 for purifying exhaust gas is incorporated in the exhaust passage 32.

  The internal combustion engine 10 includes a variable valve mechanism 36. According to the variable valve mechanism 36, the valve timing of the intake valve 38 can be advanced or retarded. A cam angle sensor 40 that detects the rotational position of the intake camshaft is provided in the vicinity of the variable valve mechanism 36. According to the output of the cam angle sensor 40, the actual advance amount of the valve timing of the intake valve 38 can be detected. Hereinafter, the actual advance amount of the valve timing of the intake valve 38 is referred to as “VVT advance amount” and is represented by the symbol VT [degCA]. The VVT advance amount VT is set to 0 degCA when the valve timing of the intake valve 38 is in the most retarded state.

  The system of this embodiment includes an ECU (Electronic Control Unit) 50. Sensor signals are supplied to the ECU 50 from the various sensors described above. The ECU 50 can control various actuators such as the fuel injection valve 28, the spark plug 30, and the variable valve mechanism 36 based on the sensor signals.

[Basic idea of Embodiment 1]
In the present embodiment, the ECU 50 controls the ignition timing to be an optimal timing when the internal combustion engine 10 is in a normal operation state and a steady state. The optimum ignition timing in this case is an ignition timing at which the torque of the internal combustion engine 10 becomes maximum within a range where knocking does not occur. The normal operation means an operation state in which special control such as catalyst warm-up control is not performed. Hereinafter, the normal operation and the steady state may be simply referred to as “steady operation”.

  Generally, there is an ignition timing that maximizes the torque of the internal combustion engine 10 under constant operating conditions other than the ignition timing. The ignition timing is referred to as MBT (Minimum spark advance for Best Torque). On the other hand, knocking is more likely to occur as the ignition timing is advanced.

  In general, the knock ignition timing at which knocking starts to occur and the MBT are close to each other. The knock ignition timing and MBT change depending on the operating conditions and also change over time. Furthermore, there are machine difference variations (individual differences) in knock ignition timing and MBT. Also, the order in which the knock ignition timing or MBT exists on the advance side is not fixed.

  The conventional idea of knock feedback control has been to obtain the optimum ignition timing by gradually advancing the ignition timing until knocking is detected by a knock sensor. However, with this method, knocking inevitably occurs once before the optimum ignition timing is adjusted. For this reason, noise and engine damage due to knocking could not be completely eliminated.

  Therefore, in the present embodiment, prior to actually advancing the ignition timing, whether or not knocking occurs after the ignition timing advance is predicted in advance. The ignition timing is actually advanced only when the prediction result that knocking does not occur even if the ignition timing is advanced is obtained. Thereby, when adjusting the ignition timing to the optimal timing, it is possible to prevent knocking from occurring.

[Combustion fluctuation]
In operation of the internal combustion engine 10, combustion fluctuations generally occur. Combustion fluctuation means that the state of combustion of the air-fuel mixture in the cylinder changes from cycle to cycle. The combustion fluctuation occurs not only in the transient operation state but also in the steady operation state. The cause of combustion fluctuation is considered to be that the mixing ratio of air and fuel, the remaining amount of burned gas in the previous cycle, the flow state (turbulence) of the air-fuel mixture in the cylinder, etc. change from cycle to cycle. It has been.

  FIG. 2 is a graph showing measured data of the in-cylinder pressure history with respect to the crank angle. In FIG. 2, the compression top dead center is set to 0 degCA. In the graph of FIG. 2, the in-cylinder pressure histories of a large number of cycles measured during steady operation with the engine speed NE, the load factor KL, etc. kept constant are drawn in an overlapping manner. According to FIG. 2, it can be seen that the waveform indicating the in-cylinder pressure history (combustion pressure history) during the combustion period varies from cycle to cycle due to combustion fluctuations even in the steady operation state. Hereinafter, in-cylinder pressure history data with respect to the crank angle is referred to as “in-cylinder pressure history data”.

[knocking]
Combustion in the spark ignition engine proceeds as the flame generated by ignition by the spark plug 30 propagates to the surroundings. Knocking is a phenomenon caused by a pressure wave generated by self-ignition of an air-fuel mixture where a flame has not yet reached.

  Due to the combustion fluctuation described above, the combustion state changes from cycle to cycle. For this reason, even when knocking occurs, there are a cycle in which knocking occurs and a cycle in which knocking does not occur in each cycle. And it is thought that the strength of knocking increases as the frequency of occurrence of knocking cycles (hereinafter referred to as “knock cycles”) increases.

  Thus, whether knocking occurs or not is closely related to the state of combustion fluctuation. Therefore, if it is possible to predict the state of combustion fluctuation when it is assumed that the ignition timing is advanced from the current value, the basis for predicting whether knocking will occur after the ignition timing is advanced will be laid. . The state of combustion fluctuation can be expressed by collecting in-cylinder pressure history data for many cycles as shown in FIG.

  Therefore, in this embodiment, simulated in-cylinder pressure history data is created under the condition that the ignition timing is changed from the current value. This data is hereinafter referred to as “simulated in-cylinder pressure history data”. By collecting the simulated in-cylinder pressure history data for many cycles, it is possible to predict in advance the state of combustion fluctuation after the ignition timing is changed. The simulated in-cylinder pressure history data can be generated by a combustion fluctuation prediction model described below.

[Combustion fluctuation prediction model]
In this combustion fluctuation prediction model, a combustion state in a cylinder is simulated using a Wiebe function known as an approximate function of a heat generation pattern. The Wiebe function is expressed by the following equation.

The above equation (1) is established during the combustion period. The meaning of each symbol in this formula is as follows.
Q: Cumulative heating rate [J]
θ: Crank angle [deg]
k: Combustion efficiency
Qf: Calorific value of fuel used for combustion (fuel drawn into the cylinder) [J]
a = −ln (1−0.999)
m: Shape parameter θ ₀ : Combustion start point [degCA]
θ _0-100 : 0-100% combustion period [degCA]

The fuel heating value Qf is determined by the type of fuel. In this model, the fuel heating value Qf is a default value. The combustion efficiency k is expressed by k = Qmax / Qf using the maximum value Qmax of the cumulative heating rate Q and the fuel heating value Qf. That is, the combustion efficiency k is a value indicating how close the combustion of the cycle is to complete combustion. The 0-100% combustion period θ _0-100 represents the period until the combustion ratio Xb changes from 0% to 100% in terms of crank angle. The combustion ratio Xb is an amount that represents the progress of combustion. That is, the 0-100% combustion period θ _0-100 is the crank angle representing the entire combustion period from the combustion start point θ ₀ to the combustion end point.

The 0-100% combustion period θ _0-100 and the combustion start point θ ₀ in the above equation (1) are further expressed by the following equations.

In the above equation (2), θ _10-70 means a 10-70% combustion period [degCA]. The 10-70% combustion period θ _10-70 represents the period until the combustion ratio Xb changes from 10% to 70% in terms of crank angle. In the above formula (3), θ ₅₀ means a 50% combustion point [degCA]. The 50% combustion point θ ₅₀ is the crank angle at which the combustion ratio Xb reaches 50%.

  The Wiebe function can be converted into an in-cylinder pressure history during the combustion period of the cycle by a known method, that is, a method combined with a thermodynamic energy conservation law. This method will be described later.

When the above equations (2) and (3) are used, parameters to be substituted into the Wiebe function are combustion efficiency k, shape parameter m, 50% combustion point θ ₅₀ , and 10-70% combustion period θ _{10−. It} becomes four of ₇₀ . The combustion fluctuation is considered to correspond to the fact that these four parameters vary from cycle to cycle. In other words, it is considered that the combustion fluctuation can be expressed (simulated) by changing the Wiebe function for each cycle.

However, according to the research of the inventors of the present invention, it has been clarified that the shape parameter m among the four parameters does not significantly affect the combustion fluctuation. For this reason, in this embodiment, the shape parameter m is a default value. Then, the degree of variation for each cycle of the three parameters of the remaining combustion efficiency k, 50% combustion point θ ₅₀ , and 10-70% combustion period θ _10-70 was taken into consideration. Hereinafter, the above three parameters are referred to as “combustion parameters”.

The bar graph in FIG. 3 shows measured data of the distribution of the combustion efficiency k for each cycle in the steady operation state. The actual measurement data substantially matches the normal distribution indicated by the solid line in FIG.
Further, the bar graph in FIG. 4 shows measured data of the distribution of the 50% combustion point θ ₅₀ for each cycle in the steady operation state. The actual measurement data substantially matches the normal distribution indicated by the solid line in FIG.
And the bar graph in FIG. 5 has shown the actual measurement data of distribution of 10-70% combustion period (theta) _10-70 for every cycle in a steady operation state. The actual measurement data substantially matches the normal distribution indicated by the solid line in FIG.

FIG. 6 is a correlation diagram of measured values of 50% combustion point θ ₅₀ and 10-70% combustion period θ _10-70 in a steady operation state. FIG. 7 is a correlation diagram between the combustion efficiency k and the measured value of the 50% combustion point θ ₅₀ in the steady operation state. FIG. 8 is a correlation diagram _between the measured values of the combustion efficiency k and the 10-70% combustion period θ _10-70 in the steady operation state.

It can be seen from FIG. 6 that the 50% combustion point θ ₅₀ and the 10-70% combustion period θ _10-70 have a correlation. On the other hand, FIG. 7 shows that there is almost no correlation between the combustion efficiency k and the 50% combustion point θ _50, and FIG. 8 shows that the combustion efficiency k and the 10-70% combustion period θ _10−. It can be seen that there is almost no correlation with ₇₀ .

  In order to create simulated in-cylinder pressure history data for a large number of cycles, it is necessary to generate a large number of Wiebe functions that express combustion fluctuations when the ignition timing is changed. For that purpose, it is necessary to predict the cycle-by-cycle variation of the three combustion parameters to be substituted into the Wiebe function.

On the other hand, from the measured data shown in FIGS. 3 to 8, it is clear that the variation of the three combustion parameters for each cycle almost follows a multivariable normal distribution taking into account the correlation between θ ₅₀ and θ _10-70. is there. Therefore, in this embodiment, a set of combustion parameters k, θ ₅₀ , θ _10-70 is randomly extracted from this multivariable normal distribution, and these values are substituted into the Wiebe function. A large number of such Wiebe functions are generated and converted into in-cylinder pressure history, thereby generating simulated in-cylinder pressure history data for many cycles.

  In the present embodiment, by combining the simulated in-cylinder pressure history data for a large number of cycles thus obtained and a self-ignition prediction formula described later, whether or not knocking will occur after the ignition timing is changed is predicted in advance. It was.

[Specific Processing in Embodiment 1]
FIG. 9 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is executed for each cycle in synchronization with the crank angle. According to the routine shown in FIG. 9, first, various parameters representing the current operating state are measured and stored (step 100). Specifically, the engine speed NE, the load factor KL, and the VVT advance amount VT are measured and stored.

  Next, it is determined whether or not the current operation state is a normal operation and a steady state (step 102). An object of the present embodiment is to control the ignition timing during normal operation in which special control such as catalyst warm-up control is not performed. For this reason, when it is not in the normal operation state, the data stored in step 100 is reset (step 104), and then the current processing cycle is promptly terminated.

  In the present embodiment, it is also assumed that the internal combustion engine 10 is in a steady state. In step 102, whether or not the engine is in a steady state depends on whether the measured values of the engine speed NE, the load factor KL, and the VVT advance amount VT acquired in step 100 are the same as the measured values in the previous processing cycle. It is determined by whether or not. As a result of the determination, if it is not a steady state, the data stored in step 100 and step 110 described later is reset (step 104), and then the current processing cycle is immediately terminated.

On the other hand, if it is determined in step 102 that the vehicle is in normal operation and in a steady state, the count value cyc is incremented by one. In the present embodiment, the average value of the combustion parameters k, θ ₅₀ , and θ _10-70 in 50 consecutive cycles is calculated. The count value cyc is a value for counting the 50 cycles, and its initial value is 0.

  Next, the history of the actual in-cylinder pressure with respect to the crank angle in the current cycle is measured (step 108). Specifically, the output of the in-cylinder pressure sensor 18 is sampled for each predetermined crank angle Δθ, and the obtained actual in-cylinder pressure value is stored. The Δθ is, for example, about 1 to 3 degCA. Here, the actual in-cylinder pressure may not be measured over the entire range of 720 deg CA, and may be measured, for example, in the crank angle range from when the intake valve is closed to when the exhaust valve is opened.

Next, actual values of the three combustion parameters k, θ ₅₀ , and θ _10-70 in this cycle are calculated based on the history of the actual in-cylinder pressure measured in step 108 (step 110). Hereinafter, this calculation process will be described. For this calculation process, the following equation is used.

In the above formulas (4) and (5), P represents the in-cylinder pressure [Pa], V represents the in-cylinder volume [m ³ ], and κ represents the specific heat ratio. Both of these equations correspond to a thermodynamic energy conservation law expressed as a cumulative heating rate Q, an in-cylinder pressure P, an in-cylinder volume V, and a crank angle θ. Further, the above equation (5) corresponds to an integral of both sides of the above equation (4) with the crank angle θ.

  V and dV / dθ in both the above equations are geometrically determined according to the crank angle θ. That is, V and dV / dθ are functions of the crank angle θ. Using that relationship, V can be eliminated from both equations. The ECU 50 performs the calculation using both the above equations in a state where the V is deleted. In the calculation, the specific heat ratio κ is set to a constant default value.

  The integration on the right side of the above equation (5) starts from the crank angle at the time of ignition. A value obtained by calculating this integration up to a certain crank angle θ is hereinafter expressed as Q (θ). Here, θ is defined between the ignition time and the exhaust valve closing time.

  In step 110, first, the value of Q (θ) for the actual in-cylinder pressure history measured in step 108 is approximately calculated by numerical calculation for each predetermined crank angle. That is, the values obtained by substituting the in-cylinder pressure value at each point and the rate of change thereof into P and dP / dθ on the right side of the above equation (5) are integrated.

  The cumulative heating rate Q (θ) calculated in this way continues to increase due to the heat of combustion while combustion continues. After the combustion is completed, the cumulative heating rate Q (θ) starts to decrease due to the loss of heat escaping to the combustion chamber inner wall and the cylinder inner wall. Therefore, the cumulative heating rate Q (θ) takes a maximum value Qmax at a certain crank angle between the ignition time and the exhaust valve closing time. In step 110, the maximum value Qmax is obtained from Q (θ) calculated for each predetermined crank angle.

  As described above, the combustion efficiency k can be expressed as k = Qmax / Qf. The actual value of the combustion efficiency k of the current cycle is calculated according to this equation. The fuel heat generation amount Qf can be calculated based on the fuel characteristic value, which is a predetermined value, the current air-fuel ratio, and the in-cylinder intake fresh air amount.

The combustion ratio Xb at the crank angle θ can be calculated as Xb = Q (θ) / Qmax × 100. Therefore, the actual value of the 50% combustion point θ ₅₀ of the current cycle can be obtained as a crank angle that satisfies Q (θ) /Qmax=0.5. The actual value of the 10-70% combustion period θ _10-70 can be obtained as the crank angle range until Q (θ) / Qmax changes from 0.1 to 0.7.

In step 110, the actual values of the three combustion parameters k, θ ₅₀ , and θ _10-70 are calculated as described above, and the calculated values are stored. Next, it is determined whether or not the count value cyc exceeds 50 (step 112). This determination corresponds to determination of whether or not the combustion parameter actual value data calculated in step 110 has been accumulated for 50 cycles.

  If the result of determination in step 112 is that the count value cyc has not reached 50, the current processing cycle is immediately terminated. In this case, the routine shown in FIG. 9 is executed again in synchronization with the next operation cycle of the internal combustion engine 10. At that time, if the steady operation is continued, the processing of steps 106 to 108 is performed again, and the measured value data of the combustion parameter is accumulated. On the other hand, when the operating condition has changed, the actual measurement value data of the combustion parameter accumulated up to the previous time is reset in step 104, and the count value cyc is also reset to zero.

If the steady operation continues for 50 cycles or more, it is recognized in step 112 that cyc> 50 is established. In this case, measured value data of combustion parameters for 50 cycles is accumulated. In this case, next, an average value (arithmetic average) of actually measured value data of the combustion parameters k, θ ₅₀ , θ _{10-70 for} the 50 cycles is calculated (step 114). The average value of the combustion efficiency k calculated here is expressed as kc, the average value of the 50% combustion point θ ₅₀ is expressed as BPc, and the average value of the 10-70% combustion period θ _10-70 is expressed as BDc.

In the present embodiment, a virtual ignition timing that is a target for predicting whether knocking will occur is referred to as an assumed ignition timing SAi. Further, the predicted value of the average value of the 50% combustion point θ ₅₀ when the assumed ignition timing SAi is realized is represented as an assumed 50% combustion point average value BPi.

  When the processing of step 114 is completed, the current values are then substituted as reference values for the assumed ignition timing SAi and the assumed 50% combustion point average value BPi (step 116). That is, the current value SAc of the ignition timing is substituted for the assumed ignition timing SAi. The ignition timing current value SAc is the ignition timing value currently set by the ECU 50. Further, the average value BPc of the actually measured values for 50 cycles calculated in step 114 is substituted for the assumed 50% combustion point average value BPi.

Next, the assumed ignition timing SAi and the assumed 50% combustion point average value BPi are each updated to a value smaller by 2 degCA (step 118). The processing in step 118 corresponds to advancing the assumed ignition timing SAi by 2 deg CA. According to the knowledge of the present inventors, when the ignition timing is moved, the average value of the 50% combustion point θ ₅₀ is also moved by substantially the same amount. Therefore, when the ignition timing is advanced by 2 deg CA, the average value of the 50% combustion point θ ₅₀ is also predicted to be advanced by 2 deg CA. In order to express this phenomenon, in step 118, not only the assumed ignition timing SAi but also the assumed 50% combustion point average value BPi is updated to a value smaller by 2 degCA.

  When the process of step 118 is performed for the first time, after that process, the assumed ignition timing SAi and the assumed 50% combustion point average value BPi each represent a value on the advance side of 2 deg CA from the current value.

  Next, the cycle fluctuation of the in-cylinder pressure history at the assumed ignition timing SAi is predicted (step 120). Specifically, simulated in-cylinder pressure history data at the assumed ignition timing SAi is generated for 100 cycles. FIG. 10 is a flowchart of a subroutine executed by the ECU 50 to perform the process of step 120.

In the subroutine shown in FIG. 10, first, the standard deviation of the distribution of each combustion parameter k, θ ₅₀ , θ _10-70 and the 50% combustion point θ ₅₀ and 10-70% combustion period θ _{10− at the} assumed ignition timing SAi. The covariance with ₇₀ is predicted (step 122). Specifically, those values are calculated based on the following functions func _{1 to} func ₄ .

σ ₁ / μ ₁ = func ₁ (NE, KL, KL ² ) (6)
σ ₂ / μ ₃ = func ₂ (NE, KL, KL ² , VT ² ) (7)
σ ₃ / μ ₃ = func ₃ (NE, NE ² , KL, KL ² , VT) (8)
σ ₂₃ / μ ₃ ² = func ₄ (NE, NE ² , KL, KL ² , VT) (9)

In the above equations (6) to (9), σ ₁ is the standard deviation of the combustion efficiency k, σ ₂ is the standard deviation of the 50% combustion point θ ₅₀ , and σ ₃ is the standard deviation of the 10-70% combustion period θ _10-70 . , Σ ₂₃ is the covariance between the 50% combustion point θ ₅₀ and the 10-70% combustion period θ _10-70 , μ ₁ is the average value of the combustion efficiency k, and μ ₃ is the 10-70% combustion period θ _10-70 . Average value, NE represents engine speed, KL represents load factor, and VT represents VVT advance amount.

The above equations (6) to (9) are the multiple regression equations obtained from the measurement data obtained by experiments performed in advance. That is, the standard deviations σ ₁ , σ ₂ , σ ₃ and covariance σ ₂₃ are measured under various operating conditions in which the engine speed NE, the load factor KL, and the VVT advance amount VT are different in the internal combustion engine 10. By regressing from the actual measurement data, the above equations (6) to (9) can be obtained. The right side of the above equations (6) to (9) is a polynomial of variables in parentheses.

In step 122, the standard deviations σ ₁ , σ ₂ , σ ₃ and covariance are obtained by substituting the values of NE, KL, VT, μ ₁ , and μ _{3 into} the equations (6) to (9). σ ₂₃ is calculated. At this time, the values of the engine speed NE, the load factor KL, and the VVT advance amount VT measured in step 100 are substituted into NE, KL, and VT. The mu _1, the value of kc calculated in step 114 is substituted. The mu _3, the value of BDc calculated in step 114 is substituted.

As described above, the average value of the 50% combustion point θ ₅₀ under the assumed ignition timing SAi is predicted to be the assumed 50% combustion point average value BPi. Further, the standard deviation of the variation of the 50% combustion point θ ₅₀ under the assumed ignition timing SAi is predicted to be σ ₂ calculated in step 122 above. Therefore, the variation of the 50% combustion point θ ₅₀ under the assumed ignition timing SAi is predicted to follow a normal distribution having an average value BPi and a standard deviation σ ₂ , that is, a normal distribution shown in FIG.

On the other hand, variations in the combustion efficiency k and the 10-70% combustion period θ _10-70 under the assumed ignition timing SAi are predicted as follows. According to the knowledge of the present inventors, even when the ignition timing is moved, the average value of the combustion efficiency k hardly changes. In addition, the average value of the 10-70% combustion period θ _10-70 has sensitivity to the ignition timing, but may hardly change by changing the ignition timing by about 2 deg CA. Therefore, the average value of the combustion efficiency k and the average value of the 10-70% combustion period θ _10-70 under the assumed ignition timing SAi are predicted to be equal to the current values kc and BDc calculated in step 114, respectively. Is done. _Further , the standard deviations of the variations in the combustion efficiency k and the 10-70% combustion period θ _10-70 under the assumed ignition timing _SAi are predicted to be σ ₁ and σ ₃ calculated in step 122, respectively. The

Thus, variations in the combustion efficiency k under the assumption ignition timing SAi is an average value kc, the normal distribution of the standard deviation and sigma _1, i.e. is expected to follow a normal distribution shown in FIG. 12. _Further , the variation of the 10-70% combustion period θ _10-70 under the assumed ignition timing SAi is predicted to follow a normal distribution having an average value BDc and a standard deviation σ ₃ , that is, a normal distribution shown in FIG. The

Next to step 122, a set of three combustion parameters k, θ ₅₀ , and θ _10-70 is randomly extracted from the normal distribution (multivariate normal distribution) shown in FIGS. 11 to 13 described above. (Step 124). However, as described above, the 50% combustion point θ ₅₀ and the 10-70% combustion period θ _10-70 have a correlation. The degree of correlation between the two under the assumed ignition timing SAi is predicted by the covariance σ ₂₃ calculated at step 122. Therefore, in the extraction of the 50% combustion point θ ₅₀ and the 10-70% combustion period θ _10-70 in step 124, the covariance σ _{23 of} both is incorporated. Note that the method of randomly extracting values from the normal distribution in step 124 is not particularly limited. For example, a method of using random numbers can be used.

By the processing in step 124, a set of values of k, θ ₅₀ , and θ _10-70 that can occur probabilistically under the assumed ignition timing _SAi can be generated. Next, the values of k, θ ₅₀ , θ _10-70 are substituted into the Wiebe function of the above equation (1) via the above equations (2) and (3) (step 126). It can be said that the Wiebe function obtained by the process of step 126 simulates combustion of a certain cycle that can occur stochastically under the assumed ignition timing SAi.

  Next, based on the Wiebe function obtained in step 126, a simulated in-cylinder pressure history during the combustion period, that is, a simulated in-cylinder pressure history from the time of ignition to the end of combustion is calculated (step 128). Specifically, the following processing is performed. First, it is assumed that the Wiebe function corresponding to the right side of the above equation (1) is equal to the right side of the above equation (4). Thereby, a differential equation of the in-cylinder pressure P is obtained. The ECU 50 approximates this differential equation by numerical calculation, whereby a simulated in-cylinder pressure history during the combustion period is calculated.

  FIG. 14 is a graph showing an example of simulated in-cylinder pressure history data created by the subroutine processing shown in FIG. In FIG. 14, the compression top dead center is set to 0 degCA. As described above, the simulated in-cylinder pressure history during the combustion period calculated in step 128 corresponds to the simulated in-cylinder pressure history during the period (3) in FIG.

  Following step 128, a simulated in-cylinder pressure history other than during the combustion period (3) in FIG. 14 is calculated (step 130). In this step 130, the simulated in-cylinder pressure history during the period from the end of combustion to the time when the exhaust valve is opened (EVO) (period (4) in FIG. 14) is calculated from the equation of heat loss by the Woschini heat transfer model, It is calculated based on the equation (4). Since this method is publicly known, further explanation is omitted here. Then, the simulated in-cylinder pressure history during the period from intake valve closing (IVC) to ignition (period (2) in FIG. 14) is calculated by approximating the polytropic change with the polytropic index as the cycle average value. The Since this method is publicly known, further explanation is omitted here. Further, the simulated in-cylinder pressure history data in the intake stroke period (period (1) in FIG. 14) is a constant value equal to the average value of the surge tank pressure detected by the intake pressure sensor 21. Further, the simulated in-cylinder pressure history data in the exhaust stroke period (period (5) in FIG. 14) is a constant value equal to the average value of the exhaust pipe pressure detected by the exhaust pressure sensor 33 at that time.

  By the processes in steps 124 to 130, simulated in-cylinder pressure history data for one cycle as illustrated in FIG. 14 is generated. In the present embodiment, such simulated in-cylinder pressure history data is collected for a large number of cycles (here, 100 cycles) to obtain data as shown in FIG. 2, so that the state of combustion fluctuations under the assumed ignition timing SAi is obtained. Expressed.

  After step 130, it is determined whether or not the created simulated in-cylinder pressure history data has reached 100 cycles (step 132). Then, the processes in steps 124 to 130 are repeated until the created simulated in-cylinder pressure history data reaches 100 cycles, and then the subroutine process shown in FIG. 10 is terminated.

  After the simulated in-cylinder pressure history data for 100 cycles is created by the processing of the subroutine shown in FIG. 10, the number of knock cycles that cause knocking out of the 100 cycles is investigated (in FIG. 9). Step 134). FIG. 15 is a flowchart of a subroutine executed by the ECU 50 for performing the process of step 134.

  In the subroutine shown in FIG. 15, the loop 1 process indicated by the loop start end 136 and the loop end 138 is performed for each simulated in-cylinder pressure history data. That is, the processing in the loop 1 is repeated 100 times (for 100 cycles). In the process of loop 1, first, the self-ignition time is calculated for the target simulated in-cylinder pressure history data (step 140). In the process of step 140, a self-ignition prediction formula expressed by the following formula is used.

The meaning of each symbol in the formula (10) is as follows.
t: time
P (t): In-cylinder pressure [kgf / cm ² ]
Tu (t): Unburned gas temperature [K]
Φ: Equivalent ratio
ON: Fuel octane number
A, B, C, F, Ea: Conformance constant (default)

  According to the self-ignition prediction formula, the point in time when the unburned gas in the cylinder self-ignites can be predicted as follows. The integration of the left side of the above equation (10) starts from the time when the intake valve is closed, and when the value becomes 1, that is, when the above equation (10) is established, it is predicted that self-ignition will occur.

  In step 140, the integration of the left side of the above equation (10) is numerically calculated, and the time when the above equation (10) is established is calculated. In this calculation, the value to be substituted in the above equation (10) can be obtained as follows. The in-cylinder pressure P (t) is a history of the in-cylinder pressure with respect to time. The simulated in-cylinder pressure history data that is the history of the in-cylinder pressure P with respect to the crank angle can be converted into P (t) using the engine speed NE measured in step 100. P (t) obtained by this conversion is substituted into the above equation (10). Further, the unburned gas temperature Tu (t) is obtained by substituting the above-described P (t) and the in-cylinder volume V determined from the crank angle θ into the gas state equation. Further, the equivalent ratio Φ can be obtained by conversion from the target air-fuel ratio currently set by the ECU 50 or by conversion from an actual air-fuel ratio detected by an air-fuel ratio sensor (not shown). The fuel octane number ON and the compatible constants A, B, C, F, and Ea are predetermined constants.

  Here, a method for determining a knock cycle in the present embodiment will be described. FIG. 16 is a graph showing the history of the combustion ratio Xb with respect to the crank angle. In the present embodiment, when the combustion ratio Xb at the time of self-ignition is equal to or less than a determination value (here, 90%), it is determined that it is a knock cycle.

  For example, when the crank angle is point A in FIG. 16 at the time of self-ignition, the combustion ratio Xb has not reached 90%. In such a case, a relatively large amount of unburned gas still remains at the time of self-ignition. For this reason, when self-ignition occurs, a large pressure wave is generated due to abnormal combustion of a large amount of unburned gas. Thus, such a cycle can be predicted to cause knock.

  On the other hand, when the crank angle is a point B in FIG. 16 at the time of self-ignition, the combustion ratio Xb exceeds 90%. In such a case, almost no unburned gas remains at the time of self-ignition. For this reason, even if self-ignition occurs, the generated pressure wave is weak. Thus, such a cycle can be predicted not to cause knock.

  After the self-ignition time is calculated in step 140, the following processing is executed to perform the knock cycle determination as described above. First, the cumulative heating rate Qs at the time of self-ignition is calculated (step 142). Specifically, first, the value at the time of self-ignition is converted into the crank angle θs at the time of self-ignition using the value of the engine speed NE. Next, the integral of the above equation (5) is calculated to calculate the integral up to the crank angle θs, that is, Q (θs). This calculation process is similar to the calculation process in step 110 described above. However, in this case, P in the simulated in-cylinder pressure history data and the rate of change thereof are substituted for P and dP / dθ in the above equation (5), respectively. Q (θs) calculated in this way corresponds to the cumulative heating rate Qs at the time of self-ignition.

  Next, the maximum value Qmax of the cumulative heating rate is calculated based on the simulated in-cylinder pressure history data (step 144). Specifically, the cumulative heating rate Q (θ) is calculated for each predetermined crank angle until the exhaust valve is closed, exceeding the crank angle θs. This calculation process can be calculated in the same manner as in step 142 described above. The maximum value of Q (θ) for each crank angle calculated in this way corresponds to the calculated Qmax.

  Next, it is determined whether or not the value of Qs / Qmax is 0.9 or less (step 146). The establishment of Qs / Qmax ≦ 0.9 means that the combustion ratio Xb at the time of self-ignition has not reached 90%. In this case, it can be determined that this cycle is a knock cycle based on the above-described concept of the knock cycle determination method. In this case, the count value KNC is incremented by one (step 148), and then the loop 1 is terminated. The count value KNC is a value representing the number of knock cycles. The initial value of the count value KNC is 0.

  On the other hand, when Qs / Qmax ≦ 0.9 is not established, it means that the combustion ratio Xb at the time of self-ignition exceeds 90%. Therefore, it can be determined that this cycle is not a knock cycle. Therefore, in this case, the increment processing of the count value KNC is skipped and the loop 1 is ended.

  After the processing of loop 1 as described above is repeatedly performed on the simulated in-cylinder pressure history data for 100 cycles, the processing of the subroutine shown in FIG. 15 is ended. At that time, the count value KNC is a value representing the number of knock cycles of the 100 cycles. That is, the count value KNC is a value representing the frequency of occurrence of knock cycles in 100 cycles.

  After the processing of the subroutine shown in FIG. 15 is completed, it is next determined whether or not the count value KNC is less than or equal to the allowable value α (step 150 in FIG. 9). As described above, the higher the frequency of the knock cycle, the stronger the knocking strength. On the other hand, if the frequency of the knock cycle is below a certain level, the knocking strength is at a level where no damage to the engine or harm such as noise actually occurs. The allowable value α is set in advance as a value with which it can be determined that the knocking strength is within a range where there is no actual harm.

  Hereinafter, for convenience of explanation, a case where the knocking strength is at a level causing actual damage is defined as “knocking”. According to this definition, if the count value KNC exceeds the allowable value α, knocking is predicted to occur, and if the count value KNC is equal to or less than the allowable value α, knocking does not occur. It will be predicted.

  If it is determined in step 150 that KNC ≦ α is not established, it is predicted that knocking will occur when the assumed ignition timing SAi is realized. In this case, the assumed ignition timing SAi is updated to a value delayed by 2 degCA (step 152). That is, 2 deg CA is added to the assumed ignition timing SAi. Thereafter, the updated assumed ignition timing SAi is set as the actual ignition timing SAm (step 154). That is, after the processing of step 154, the internal combustion engine 10 is operated at the ignition timing SAm (= SAi).

  If the determination in step 150 is performed only once, the assumed ignition timing SAi is returned to a value equal to the current ignition timing SAc by the processing in step 152. That is, in this case, the actual ignition timing is not changed, and the operation of the internal combustion engine 10 is continued with the current ignition timing SAc. Therefore, in this case, knocking does not actually occur.

  On the other hand, if it is determined in step 150 that KNC ≦ α is established, it is next determined whether or not the assumed ignition timing SAi is on the more advanced side than MBT, that is, whether or not SAi> MBT. (Step 156). The relationship between the MBT, the engine speed NE, and the load factor KL has been studied in advance and is already known. The ECU 50 stores a map that defines the relationship. In step 156, the MBT value calculated with reference to the map is used.

  In the present embodiment, there is no actual benefit of advancing the actual ignition timing with respect to the MBT. Therefore, if it is determined in step 156 that the assumed ignition timing SAi is on the advance side of the MBT, the assumed ignition timing SAi is updated to the MBT value (step 158), and then the assumed ignition timing SAi is changed. The actual ignition timing SAm is set (step 154). That is, in this case, after the processing of step 154, the internal combustion engine 10 is operated at the ignition timing SAm equal to MBT. In this case, in the processing of step 150, it is predicted that knocking will not occur even if the ignition timing is on the advance side of the MBT. Therefore, in this case, knocking does not actually occur even when the internal combustion engine 10 is operated by MBT.

  On the other hand, if it is determined in step 156 that the assumed ignition timing SAi is behind the MBT, the ignition timing is advanced more than the current assumed ignition timing SAi from the viewpoint of torque improvement. Is preferable. Therefore, in this case, the process from step 118 is executed again in order to predict whether knocking will occur when the ignition timing is advanced further than the current assumed ignition timing SAi. Specifically, in step 118, the assumed ignition timing SAi and the assumed 50% combustion point average value BPi are updated to values further advanced by 2 degCA. Then, whether or not knocking occurs under the updated assumed ignition timing SAi is predicted again (steps 120 to 150).

  Thus, by providing the loop returning from step 156 to step 118, it is possible to find an ignition timing as close as possible to the MBT among the ignition timings predicted not to cause knocking. In the case of passing through a loop returning from step 156 to step 118, the determination in step 150 is performed a plurality of times. When it is determined that KNC ≦ α is not satisfied in the plurality of times of step 150, that is, when it is predicted that knocking will occur, in step 152, the assumed ignition timing SAi is updated to a value delayed by 2 degCA, and thereafter The updated assumed ignition timing SAi is set as the actual ignition timing SAm in step 154. In this case, the value set as the actual ignition timing SAm is equal to the value of the ignition timing predicted not to cause knocking in the processing of step 150 one time before. Therefore, in this case, knocking does not actually occur.

  As described above, according to this embodiment, when the ignition timing is advanced, it is possible to predict in advance whether knocking will occur after the ignition timing advance. When the prediction that knocking will not occur is obtained, the ignition timing is actually advanced. Therefore, the ignition timing can be controlled to the optimum value without causing actual knocking even for a moment. Therefore, damage and noise to the internal combustion engine 10 due to knocking can be further reduced as compared with the conventional case.

  In the present embodiment, simulated in-cylinder pressure history data is generated based on the combustion parameters actually measured using the in-cylinder pressure sensor 18. The combustion parameter measured using the in-cylinder pressure sensor 18 reflects the current state of the internal combustion engine 10 that is affected by machine difference variation and aging. For this reason, the simulated in-cylinder pressure history data also reflects the influence of machine difference of the internal combustion engine 10 and aging. Therefore, according to the present embodiment, it is possible to accurately predict the state of combustion fluctuation after changing the ignition timing according to the machine difference variation and the secular change. For this reason, the effect mentioned above can be show | played irrespective of machine difference variation and a secular change.

  In the first embodiment described above, the internal combustion engine that injects fuel into the port has been described. However, the present embodiment can also be applied to a control device for an internal combustion engine that directly injects fuel into the cylinder.

  Further, in the first embodiment described above, the assumed ignition timing SAi is updated to a value obtained by advancing 2 deg CA in step 118, but the value advanced here is not limited to 2 deg CA. Further, the value to be advanced here is not a fixed value, but may be a value that changes in accordance with operating conditions such as the engine speed NE.

  In the first embodiment described above, the self-ignition time is predicted using the above equation (10), but the method of predicting the self-ignition time is not limited to this. For example, the self-ignition time may be predicted by a method described in International Publication No. 2002/079629 pamphlet.

In the first embodiment described above, simulated in-cylinder pressure history data over the entire crank angle range (720 deg CA) of one cycle is created. However, the simulated in-cylinder pressure history data in the present invention is in the entire crank angle range. It is not limited to what passes. For example, the simulated in-cylinder pressure history data may represent the in-cylinder pressure history only during the combustion period.
It should be noted that each modification as described above can be similarly applied to each embodiment described later.

  In the first embodiment described above, the occurrence frequency of the knock cycle corresponds to the “driving stability” in the first invention. Further, when the ECU 50 executes the processing of the steps 100 to 132, the “simulated in-cylinder pressure history data generating means” in the first aspect of the invention executes the processing of the steps 134 to 150. The “driving timing setting means” according to the first aspect of the present invention is realized by executing the processing of steps 152 to 158 by the “driving stability prediction means” according to the present invention.

  In the first embodiment described above, the ECU 50 executes the processes of steps 126 and 128, so that the “combustion model means” in the second invention executes the processes of steps 100 to 118 and 122. By doing so, the “standard deviation predicting means” in the second aspect of the invention executes the processing of step 124, so that the “combustion parameter extracting means” of the second aspect of the invention executes the processing of steps 126 and 128. Thus, the “in-cylinder pressure history calculating means” in the second aspect of the present invention is realized.

In the first embodiment described above, the combustion efficiency k is the “value relating to the combustion efficiency” in the third invention, and the 50% combustion point θ ₅₀ is the “predetermined combustion ratio” in the third invention. The 10-70% combustion period θ _10-70 corresponds to the “value relating to the angle”, and the “value relating to the combustion period until the first combustion rate changes to the second combustion rate” in the third aspect of the invention. ing.

  In the first embodiment described above, the engine speed NE, the load factor KL, and the VVT advance amount VT are the “predetermined operating parameters” in the fourth invention, and the ECU 50 is the “memory” in the fourth invention. Respectively. Further, when the ECU 50 executes the processing of the above steps 108 to 114, the “average value acquisition means” in the fourth invention executes the processing of the above step 100 to thereby execute the “operating parameter” in the fourth invention. "Acquisition means" is realized respectively.

  Further, in the first embodiment described above, the ECU 50 executes the process of step 110, so that the “combustion parameter calculating means” in the fifth aspect of the invention executes the process of step 114. The “arithmetic averaging means” in the fifth invention is realized.

  In the first embodiment described above, the ECU 50 executes the processes of steps 140 to 146, so that the “knock cycle determination means” in the seventh invention executes the processes of steps 148 and 150. Thus, the “knocking determination means” in the seventh aspect of the present invention is realized.

  In the first embodiment described above, the ECU 50 executes the process of step 140, so that the “self-ignition predicting means” in the eighth invention executes the processes of steps 142 to 146. The “combustion ratio calculation determination means” in the eighth aspect of the invention is realized.

Embodiment 2. FIG.
Next, the second embodiment of the present invention will be described, focusing on the differences from the above-described first embodiment, and description of similar matters will be omitted or simplified. The system of the present embodiment is realized by causing the ECU 50 to execute the routine shown in FIGS. 17 and 18 described later and the routine shown in FIG. 10 described above using the hardware configuration shown in FIG. Can do.

[Features of Embodiment 2]
In the first embodiment described above, the case where the present invention is applied to the control for obtaining the optimal ignition timing in the normal operation state has been described. In contrast, the present embodiment is directed to control for obtaining an optimal ignition timing in the catalyst warm-up operation at the cold start.

  The catalyst 34 provided in the exhaust passage 32 of the internal combustion engine 10 exhibits a good exhaust purification action when heated to the activation temperature. The catalyst 34 is warmed by the heat of the exhaust gas. In order to reduce the exhaust emission, it is necessary to raise the temperature of the catalyst 34 to the activation temperature as soon as possible after the cold start. For this reason, conventionally, catalyst warm-up control for retarding the ignition timing after cold start has been performed. When the ignition timing is retarded, the exhaust gas temperature rises as much as the work of the combustion gas on the piston decreases. For this reason, the catalyst 34 can be warmed up early.

  The exhaust gas temperature increases as the ignition timing is retarded. For this reason, from the viewpoint of warming up the catalyst 34 earlier, it is preferable to set the ignition timing to a more retarded side. However, the later the ignition timing, the more unstable the combustion, and the greater the fluctuation in combustion. As the combustion fluctuation increases, the torque fluctuation tends to increase. In the conventional catalyst warm-up control, the ignition timing is excessively retarded, resulting in excessive torque fluctuations that impair the comfort of the vehicle, or the time required for catalyst warm-up because the ignition retard width is not sufficient. It was easy to get long.

  In view of the above problems, the present embodiment predicts the magnitude of torque fluctuation when it is assumed that the ignition timing is retarded from the current value. Then, when the predicted magnitude of the torque fluctuation is an allowable level, the ignition timing is actually retarded.

  The magnitude of torque fluctuation when the ignition timing is retarded can be predicted based on simulated in-cylinder pressure history data for many cycles. That is, by calculating the indicated torque for each simulated in-cylinder pressure history data, the torque fluctuation for each cycle can be predicted.

[Specific Processing in Second Embodiment]
FIG. 17 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. In FIG. 17, the same steps as those shown in FIG. 9 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  According to the routine shown in FIG. 17, first, various parameters representing the current operating state are measured and stored (step 100). Next, it is determined whether or not the current operation state is during catalyst warm-up control and is in a steady state (step 160). In the present embodiment, it is assumed that the internal combustion engine 10 is under catalyst warm-up control and is in a steady state. For this reason, when the condition of step 160 is denied, the data is reset (step 104), and then the current processing cycle is immediately terminated. Steps 106 to 116 are the same processes as those in the first embodiment, and a description thereof will be omitted.

  Next, the assumed ignition timing SAi and the assumed 50% combustion point average value BPi are each updated to a value larger by 2 degCA (step 162). The assumed ignition timing SAi in the present embodiment is a hypothetical ignition timing that is a target for predicting whether or not the torque fluctuation falls within an allowable range. The processing in step 162 corresponds to retarding the assumed ignition timing SAi by 2 degCA. When the process of step 162 is performed for the first time, after that process, the assumed ignition timing SAi and the assumed 50% combustion point average value BPi each represent a value on the retard side of 2 deg CA from the current value.

  In the next step 120, as in the first embodiment, the subroutine processing shown in FIG. 10 is executed. By this processing, simulated in-cylinder pressure history data for 100 cycles under the assumed ignition timing SAi is created.

  Next, the standard deviation of the indicated torque is calculated based on the simulated in-cylinder pressure history data for 100 cycles (step 164 in FIG. 17). FIG. 18 is a flowchart of a subroutine executed by the ECU 50 for performing the processing of step 164.

  In the subroutine shown in FIG. 18, in order to calculate the indicated torque for each simulated in-cylinder pressure history data, the process for calculating the indicated torque (step 166) is repeated 100 times (for 100 cycles). In step 166, the indicated torque can be calculated by integrating (integrating) the in-cylinder pressure P of the simulated in-cylinder pressure history data over a range of 720 deg CA. Through the above processing, the indicated torque for each cycle under the assumed ignition timing SAi is calculated.

Next, based on the indicated torque data for 100 cycles, a process for calculating a standard deviation σ _T indicating the degree of variation is performed (step 168). Thereafter, the subroutine processing shown in FIG. 18 ends.

Next, it is determined whether or not the standard deviation σ _T of the indicated torque is equal to or less than the allowable value β (step 170 in FIG. 17). It is considered that the greater the standard deviation σ _T is, the greater the degree of variation in the indicated torque for each cycle, and thus the greater the torque fluctuation. The allowable value β is set in advance as a value capable of determining that the magnitude of torque fluctuation falls within a range that does not actually cause a problem.

If it is determined in step 170 that σ _T ≦ β is not established, it is predicted that the torque fluctuation becomes too large when the assumed ignition timing SAi is realized. In this case, the assumed ignition timing SAi is updated to a value advanced by 2 degCA (step 172). That is, 2 degCA is subtracted from the assumed ignition timing SAi. Thereafter, the updated assumed ignition timing SAi is set as the actual ignition timing SAm (step 154).

  If the determination in step 150 is performed only once, the assumed ignition timing SAi is returned to a value equal to the current ignition timing SAc by the processing in step 152. That is, in this case, the actual ignition timing is not changed, and the operation of the internal combustion engine 10 is continued with the current ignition timing SAc. Therefore, in this case, the torque fluctuation does not actually become too large.

On the other hand, if the establishment of σ _T ≦ β is recognized in step 170, it is predicted that the torque fluctuation will be at an acceptable level even if the assumed ignition timing SAi is realized. However, from the viewpoint of early warm-up of the catalyst, the later the ignition timing, the better. Therefore, in this case, the processing after step 162 is executed again in order to predict whether or not the torque fluctuation falls within the allowable level when the ignition timing is further retarded from the current assumed ignition timing SAi. Specifically, in step 162, the assumed ignition timing SAi and the assumed 50% combustion point average value BPi are updated to values further delayed by 2 degCA. Then, it is predicted again whether the torque fluctuation falls within the allowable level under the updated assumed ignition timing SAi (steps 120 to 170).

Thus, by providing a loop that returns from step 170 to step 162, it is possible to find an ignition timing that is as late as possible among the ignition timings at which torque fluctuations are predicted to fall within an allowable level. In the case of passing through a loop returning from step 170 to step 162, the determination in step 170 is performed a plurality of times. If it is determined that σ _T ≦ β is not satisfied in step 170 for the second time, that is, if it is predicted that the torque fluctuation will be too large, in step 172, the assumed ignition timing SAi is advanced by 2 deg CA. Then, the updated assumed ignition timing SAi is set as the actual ignition timing SAm in step 154. In this case, the value set as the actual ignition timing SAm is equal to the value of the ignition timing predicted that the torque fluctuation falls within the allowable level in the processing of step 170 immediately before. Therefore, in this case, the torque fluctuation does not actually become excessively large.

  As described above, according to the present embodiment, when the ignition timing is to be retarded, it is possible to predict in advance whether the magnitude of torque fluctuation after the ignition timing retardation does not exceed the allowable level. it can. Then, when it is predicted that the magnitude of torque fluctuation will be below the allowable level, the ignition timing is actually retarded. For this reason, it is possible to control the ignition timing as late as possible without causing any adverse effects due to torque fluctuations. Therefore, both early catalyst warm-up and prevention of adverse effects of torque fluctuations can be achieved.

In the second embodiment described above, the standard deviation σ _T is calculated as a value indicating the degree of variation in the indicated torque. However, the value indicating the degree of variation in the indicated torque is not limited to this. For example, the indicated torque distribution may be used instead.

  In the second embodiment described above, the ECU 50 executes the process of step 166, so that the “illustrated torque calculation means” in the ninth invention executes the process of step 168. The “variation degree calculating means” according to the ninth aspect of the invention implements the “torque fluctuation determining means” according to the ninth aspect of the invention by executing the processing of step 170.

  In the second embodiment described above, the magnitude of the torque fluctuation corresponds to the “driving stability” in the first invention. Further, when the ECU 50 executes the processes of the above steps 134 to 170, the “driving stability predicting means” in the first invention executes the processes of the above steps 172 and 154. "Ignition timing setting means" is realized respectively.

Embodiment 3 FIG.
Next, a third embodiment of the present invention will be described. The difference from the above-described first embodiment will be mainly described, and the description of the same matters will be omitted or simplified. The system of the present embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 19 described later using the hardware configuration shown in FIG.

[Features of Embodiment 3]
The present embodiment is characterized in that, in addition to the process of the first embodiment described above, a process of calibrating the above equations (6) to (9) based on actually measured data is further performed. As described above, in the first embodiment, the combustion parameter k, theta _50, the standard deviation sigma _{1 θ 10-70, σ 2, σ 3} , and theta covariance sigma ₂₃ and ₅₀ and theta _10-70, The prediction is made based on the regression equation represented by the above equations (6) to (9).

In the above formulas (6) to (9), a plurality of coefficients are included. In the present embodiment, these coefficients are calibrated based on actual measurement data in order to further improve the prediction accuracy of the standard deviations σ ₁ , σ ₂ , σ ₃ , and covariance σ ₂₃ .

[Specific Processing in Embodiment 3]
FIG. 19 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is executed in synchronization with the processing of step 114 in the routine shown in FIG. In the following, in order to simplify the description, a process for calibrating the above equation (6) will be representatively described.

The right side of the above equation (6) includes four coefficients. The following equation is an equation in which the four coefficients are replaced with undetermined coefficients X ₁ , X ₂ , X ₃ , and X ₄ .
σ ₁ / μ ₁ = X ₁ NE + X ₂ KL + X ₃ KL ² + X ₄ (11)
The routine shown in FIG. 19 calibrates the equation (6) by calculating back the undetermined coefficients X ₁ , X ₂ , X ₃ , and X ₄ in the equation (11) from the measured data.

In the process of step 114 in FIG. 9, as described above, the average values kc, BPc, and BDc are calculated based on the actual measurement data of the combustion parameters k, θ ₅₀ , θ _10-70 for 50 cycles. Is done. At this time, the routine shown in FIG. 19 is executed.

In the routine shown in FIG. 19, first, the actual standard deviation σ _k is calculated from the actually measured value of the combustion efficiency k for 50 cycles (step 174). Next, the actual standard deviation σ _k , the measured average value kc of the combustion efficiency k calculated at step 114 in FIG. 9, the engine speed NE and the load factor KL measured at step 100 in FIG. The value is substituted into the above (11) (step 176). At this time, σ _k is substituted for σ ₁ in the above equation (11), and kc is substituted for μ ₁ . Thereby, one calibration formula that defines the relationship among the undetermined coefficients X ₁ , X ₂ , X ₃ , X ₄ is obtained.

In order to obtain the values of the undetermined coefficients X ₁ , X ₂ , X ₃ , and X ₄ , the above-described calibration formula is required for the number of the undetermined coefficients X ₁ , X ₂ , X ₃ , and X ₄ (here, 4). Therefore, after step 176, it is determined whether or not four calibration equations have been prepared. If there are not four calibration equations, the current processing cycle is terminated.

  As described above, the routine shown in FIG. 9 is completed by executing the processing after step 114 only when the steady operation state continues for 50 cycles or more. When the process of step 114 is executed, the routine shown in FIG. 19 is executed, and one calibration equation can be created by the process of step 176 described above. Therefore, when the routine shown in FIG. 9 is completed four times, the above four calibration equations are prepared.

When it is recognized that the above four calibration equations are prepared, the values of the undetermined coefficients X ₁ , X ₂ , X ₃ , and X ₄ are calculated by solving the four calibration equations as simultaneous equations. (Step 180). Subsequently, the coefficients in the equation (6) are updated to the values of X ₁ , X ₂ , X ₃ , and X ₄ calculated in step 180 (step 182). By this processing, the regression equation of the above equation (6) is calibrated.

  As described above, the case where the above equation (6) is calibrated has been described as a representative. However, the above equations (7) to (9) can be similarly calibrated. However, the equation (7) has 5 coefficients, and the equations (8) and (9) have 6 coefficients. When calibrating each equation, it is only necessary to prepare calibration equations for the number of coefficients.

As described above, in the present embodiment, processing for calibrating the regression equations (6) to (9) based on the actual measurement data is performed. For this reason, in _predicting the standard deviations σ ₁ , σ ₂ , σ _{3 of} the combustion parameters k, θ ₅₀ , θ _10-70 and the covariance σ ₂₃ between θ ₅₀ and θ _10-70 , It is possible to more accurately reflect the effects of machine differences and aging. Accordingly, the prediction accuracy can be further increased. For this reason, the state of the combustion fluctuation after the ignition timing change can be predicted with higher accuracy. As a result, it is possible to predict the driving stability such as whether or not knocking occurs after the ignition timing is changed with higher accuracy.

  In the third embodiment described above, the ECU 50 executes the process of step 174, so that the “actual standard deviation calculating means” in the sixth aspect of the invention executes the processes of steps 176 to 182. Thus, the “calibration means” according to the sixth aspect of the present invention is realized.

  In the third embodiment described above, the process for calibrating the regression equations (6) to (9) is incorporated in the first embodiment, but the present invention is not limited to this. Absent. That is, the above-described processing unique to the present embodiment may be incorporated in the second embodiment.

Embodiment 4 FIG.
Next, the fourth embodiment of the present invention will be described, focusing on the differences from the above-described first embodiment, and description of similar matters will be omitted or simplified. The system of the present embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 20 described later instead of the routine shown in FIG. 9 using the hardware configuration shown in FIG.

[Features of Embodiment 4]
In the first embodiment described above, the values of the combustion parameters k, θ ₅₀ , and θ _10-70 are measured for each cycle based on the output of the in-cylinder pressure sensor 18 over 50 cycles. Based on the actual measurement data, the average values kc, BPc, and BDc of the actual values of the combustion parameters k, θ ₅₀ , and θ _10-70 in the current operating state are acquired. In contrast, in this embodiment, it is used, so that the mathematical model, a combustion parameter k, theta _50, the average value kc real value of theta _10-70, BPc, was to get the BDc. Thereby, in this embodiment, the cylinder pressure sensor 18 can be made unnecessary.

[Specific Processing in Embodiment 4]
FIG. 20 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. In FIG. 20, the same steps as those shown in FIG. 9 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

According to the routine shown in FIG. 20, first, the current engine speed NE, load factor KL, and VVT advance amount VT are measured and stored (step 100). Next, average values kc, BPc, BDc of actual values of the combustion parameters k, θ ₅₀ , θ _10-70 in the current operating state are calculated based on the function of the following equation (step 184).
Kc = f ₁ (NE, KL, VT, SAc, A / F) (12)
BPc = f ₂ (NE, KL, VT, SAc, A / F) (13)
BDc = f ₃ (NE, KL, VT, SAc, A / F) (14)

The above equations (12) to (14) are respectively expressed as average values kc, BPc, with engine speed NE, load factor KL, VVT advance amount VT, current ignition timing SAc, and current air-fuel ratio A / F as variables. This is a function for obtaining BDc. The above equations (12) to (14) are multivariable multiple regression equations created based on experiments performed in advance at the design stage. That is, the above equations (12) to (14) are obtained by _calculating the average value data of the combustion parameters k, θ ₅₀ , θ _10-70 measured under various operating conditions with different NE, KL, VT, SAc, and A / F. This is a predetermined function obtained by regressing from. The ECU 50 stores the expressions (12) to (14) in advance.

  In step 184, the values of NE, KL, and VT measured in step 100 are substituted into the equations (12) to (14). Also, the value of the ignition timing currently set by the ECU 50 is substituted for SAc in the above equations (12) to (14), and the value of the target air-fuel ratio currently set by the ECU 50 is substituted for A / F. Alternatively, the actual air-fuel ratio value detected by an air-fuel ratio sensor (not shown) is substituted.

  After step 184, the processing after step 116 is the same as in the first embodiment. According to the present embodiment, since the in-cylinder pressure sensor 18 is unnecessary, the present invention can be applied to a system that does not include the in-cylinder pressure sensor 18. Further, the present embodiment does not assume that the internal combustion engine 10 is in a steady operation state, and therefore can be applied to the ignition timing control in a transient operation state.

  In the above-described fourth embodiment, the “average value acquisition means” according to the fourth aspect of the present invention is implemented when the ECU 50 executes the processing of step 184.

Further, in the above-described fourth embodiment, the process for calculating the average values kc, BPc, and BDc of the actual values of the combustion parameters k, θ ₅₀ , θ _10-70 using a mathematical model is incorporated in the first embodiment. However, the present invention is not limited to this. That is, the above-described processing unique to the present embodiment may be incorporated in the second embodiment.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a graph which shows the actual measurement data of the cylinder pressure history with respect to a crank angle. It is a figure which shows the actual measurement data of distribution of the combustion efficiency k for every cycle in a steady operation state. It is a figure which shows the actual measurement data of distribution of 50% combustion point (theta) ₅₀ for every cycle in a steady operation state. It is a figure which shows the actual measurement data of distribution of 10-70% combustion period (theta) _10-70 for every cycle in a steady operation state. FIG. 6 is a correlation diagram of actual measurement values of a 50% combustion point θ ₅₀ and a 10-70% combustion period θ _{10-70 in} a steady operation state. It is a correlation diagram of the measured values of combustion efficiency k and 50% burn point theta ₅₀ in a steady operating state. It is a correlation diagram of the measured value of the combustion efficiency k in a steady operation state, and 10-70% combustion period (theta) _10-70 . It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a normal distribution showing variation in 50% combustion point θ ₅₀ under the assumed ignition timing SAi. It is a normal distribution indicating variation in combustion efficiency k under the assumed ignition timing SAi. It is normal distribution which shows the dispersion _| variation in 10-70% combustion period (theta) _10-70 under assumption ignition timing SAi. It is a figure which graphs and shows an example of simulated in-cylinder pressure history data. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a graph which shows the log | history of the combustion ratio Xb with respect to a crank angle. It is a flowchart of the routine performed in Embodiment 2 of this invention. It is a flowchart of the routine performed in Embodiment 2 of this invention. It is a flowchart of the routine performed in Embodiment 3 of the present invention. It is a flowchart of the routine performed in Embodiment 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Crank angle sensor 18 In-cylinder pressure sensor 21 Intake pressure sensor 30 Spark plug 33 Exhaust pressure sensor 34 Catalyst 36 Variable valve mechanism 40 Cam angle sensor 50 ECU (Electronic Control Unit)

Claims (9)

Simulated in-cylinder pressure history data generating means for generating simulated in-cylinder pressure history data simulating in-cylinder pressure history with respect to the crank angle, assuming that the ignition timing of the internal combustion engine has been changed from the current value;
Based on the simulated in-cylinder pressure history data for a large number of cycles, driving stability prediction means for predicting driving stability after changing the ignition timing in advance;
Ignition timing setting means for setting an actual ignition timing based on the prediction result of the driving stability prediction means;
An ignition timing control device for an internal combustion engine, comprising: The simulated in-cylinder pressure history data generating means includes:
Combustion model means for simulating the combustion state based on predetermined combustion parameters;
A standard deviation predicting means for predicting a standard deviation of the distribution of the combustion parameter after the ignition timing is changed;
Combustion parameter extraction means for randomly extracting the value of the combustion parameter from a normal distribution having the standard deviation prediction means as a standard deviation;
In-cylinder pressure history calculating means for calculating the simulated in-cylinder pressure history data based on a simulated combustion state obtained by inputting the value extracted by the combustion parameter extracting means to the combustion model means;
The ignition timing control device for an internal combustion engine according to claim 1, comprising:   The combustion parameter includes a value related to combustion efficiency, a value related to a crank angle at which a predetermined combustion ratio is obtained, and a value related to a combustion period until the first combustion ratio changes to the second combustion ratio. The ignition timing control device for an internal combustion engine according to claim 2. The standard deviation predicting means includes
Average value acquisition means for acquiring an average value of the actual values of the combustion parameters in the current operating state;
Means for storing an arithmetic expression for deriving a standard deviation predicted value of the combustion parameter based on the average value acquired by the average value acquisition means and a predetermined operating parameter representing the current operating state;
Driving parameter acquisition means for acquiring the actual value of the driving parameter in the current driving state;
The ignition timing control device for an internal combustion engine according to claim 2 or 3, characterized by comprising: The average value acquisition means includes
An in-cylinder pressure sensor for detecting an actual in-cylinder pressure;
Combustion parameter calculation means for calculating the actual value of the combustion parameter in the current operating state for each cycle based on the history of the actual in-cylinder pressure with respect to the crank angle;
Arithmetic average means for calculating an arithmetic average for each type of calculated values of the combustion parameter calculating means;
The ignition timing control device for an internal combustion engine according to claim 4, comprising: An actual standard deviation calculating means for calculating an actual standard deviation of the combustion parameter from a distribution of actual values of the combustion parameter calculated by the combustion parameter calculating means;
It further comprises calibration means for calibrating the coefficient in the arithmetic expression by inputting the actual standard deviation and the actual value of the operation parameter into the arithmetic expression for deriving the standard deviation predicted value. An ignition timing control device for an internal combustion engine according to claim 5. The driving stability prediction means includes
Knock cycle determination means for determining whether or not the cycle is a knock cycle that causes knock for each simulated in-cylinder pressure history data;
Knocking judging means for judging whether or not the occurrence frequency of the knock cycle is below an allowable level;
The ignition timing control device for an internal combustion engine according to any one of claims 1 to 6, further comprising: The knock cycle determination means includes
Self-ignition prediction means for predicting the self-ignition time of the cycle based on the simulated in-cylinder pressure history data;
A combustion ratio calculation determination means for determining that the cycle is a knock cycle when the predicted combustion ratio at the time of self-ignition is equal to or less than a determination value;
The ignition timing control device for an internal combustion engine according to claim 7, comprising: The driving stability prediction means includes
For each simulated in-cylinder pressure history data, an indicated torque calculating means for calculating an indicated torque of the cycle;
A variation degree calculating means for calculating a variation degree of the distribution of the indicated torque;
Torque fluctuation determining means for determining whether or not the degree of variation is below an allowable level;
The ignition timing control device for an internal combustion engine according to any one of claims 1 to 6, further comprising:

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