JP2005120860A - Optimal ignition timing setting method and optimal ignition timing setting device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce measurement steps of data necessary for setting an optimal ignition timing (MBT) of an engine to efficiently set the MBT at a low temperature. <P>SOLUTION: After warming-up the engine, a starting position of a main combustion period (period when the combustion mass percentage is 10 through 90%) in the MBT under all operation conditions is measured in advance. Then, after forcibly cooling the engine, operation conditions are changed in each temperature range and a combustion delay period (period when the combustion mass percentage is 0 through 10%) in a predetermined ignition timing at a low temperature for each operation condition is measured in the course while the cooling water temperature rises during the warm-up operation. A position returning by a length of the combustion delay period in the predetermined ignition timing measured at the low temperature from the starting position of the main combustion period in the measured MBT after the warming-up for each operation condition is calculated, and the position is set as an MBT at the low temperature. In this case, the MBT can be set only by measuring a combustion delay period in one ignition timing for one operation condition. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optimal ignition timing setting method and an optimal ignition timing setting device for an internal combustion engine that sets an optimal ignition timing at which the generated torque of the internal combustion engine is maximized.

  In general, as shown in FIG. 13, the generated torque of the internal combustion engine varies depending on the ignition timing, and the optimum ignition timing at which the generated torque becomes maximum is called MBT (Minimum spark advance for Best Torque). As shown in FIGS. 14A to 14E, the MBT includes a rotation speed, a load (cylinder filling air amount), an air-fuel ratio (A / F), an intake valve timing advance amount (intake VVT advance amount), a cooling water temperature, and the like. Varies depending on the operating condition parameters. This is because the combustion speed of the air-fuel mixture filled in the cylinder changes depending on each operating condition parameter. As described above, since MBT varies depending on operating conditions, in order to efficiently operate by controlling the ignition timing of the internal combustion engine to MBT, all operating conditions (all combinations of operating condition parameters) are developed during the development process of the internal combustion engine. ) For the MBT by measuring the relationship between the ignition timing and the generated torque.

  However, recent internal combustion engines are equipped with various functions such as a variable valve timing mechanism, a variable valve lift mechanism, and an exhaust gas recirculation system in order to meet exhaust gas regulations and fuel efficiency regulations that will become increasingly severe in the future. There is a tendency for the number of condition parameter combinations to be very large, and the task of determining the MBT by measuring the relationship between the ignition timing and the generated torque for all operating conditions has become very troublesome.

  Therefore, for example, using the technique of Patent Document 1 (Japanese Patent Laid-Open No. 11-190681), based on the measurement data and the process of measuring the relationship between the ignition timing and the generated torque by the automatic processing by the measurement program There is one that automatically performs the process of determining the MBT.

Further, when obtaining the MBT at a low temperature of the internal combustion engine, for example, with the internal combustion engine stopped, cooling air is applied to the internal combustion engine, or cooling water or lubricating oil cooled by the cooling device is supplied to the cooling water passage of the internal combustion engine. Or by circulating through the lubricating oil passage, the entire internal combustion engine is forcibly cooled to a predetermined temperature (for example, −20 ° C.). Thereafter, as shown in FIG. 15, the internal combustion engine is operated under predetermined operating conditions, and the ignition timing is changed within a predetermined range within each temperature region in the process of increasing the coolant temperature during the warm-up operation. The process of measuring the relationship between the timing and the generated torque is repeated, and the MBT is obtained based on the measurement data, thereby obtaining the MBT at a low temperature under predetermined operating conditions. By carrying out the above processing for all operating conditions, MBT at low temperatures under all operating conditions is obtained.
Japanese Patent Laid-Open No. 11-190681 (second page, etc.)

  However, in the above-described conventional MBT calculation method, when calculating the MBT under one operating condition, it is necessary to change the ignition timing under the operating condition and measure the ignition timing and torque data at multiple points (for example, 10 points). There is. For this reason, as described above, even if the process of determining the MBT by measuring the ignition timing and the generated torque by the measurement program is automated, the ignition timing is changed at all points by changing the ignition timing for all operating conditions. The situation of measuring data remains the same, and the measurement man-hours of data are extremely increased.

  Further, as described above, when obtaining the MBT at a low temperature, for example, as shown in FIG. 15, the ignition timing is set within a predetermined range within each temperature region in the process of increasing the coolant temperature during the warm-up operation. Since it is necessary to change and measure the relationship between ignition timing and generated torque at multiple points, there is no room for changing operating conditions, and the relationship between ignition timing and generated torque within each temperature range with the operating conditions fixed Is measured to obtain MBT at a low temperature under predetermined operating conditions. For this reason, only one MBT at a low temperature under one operating condition can be obtained during one warm-up operation. To obtain the MBT at a low temperature under all operating conditions, forced cooling of the internal combustion engine and warm-up operation are performed. Must be repeated for the number of all combinations of the operating condition parameters. Usually, since cooling time of about 2 hours is required to cool the internal combustion engine, enormous time is required to obtain MBT at low temperature under all operating conditions.

  The present invention has been made in consideration of such circumstances. Accordingly, a first object of the present invention is to reduce the man-hours for measuring data necessary for setting the optimum ignition timing (MBT). The second object is to make it possible to efficiently set the optimum ignition timing at low temperatures under all operating conditions.

  Generally, a combustion process of an in-cylinder mixture of an internal combustion engine has a combustion delay period and a main combustion period. The combustion delay period is a period in which the combustion mass ratio is, for example, 0 to 10%, and the main combustion period is a period in which the combustion mass ratio is, for example, 10 to 90%. According to recent studies by the present inventors, the first feature is that the start position of the main combustion period at the optimal ignition timing (MBT) is substantially constant with little change depending on the temperature. The length of the delay period varies depending on the temperature, but when the combustion position (intermediate position of the combustion delay period) is within a predetermined range, it is almost constant with little change depending on the ignition timing (or combustion position) at the same temperature. Turned out to be.

  Paying attention to these characteristics, the inventions according to claims 1 and 5 of the present invention measure the combustion delay period at the predetermined ignition timing at the predetermined temperature or data related thereto (hereinafter collectively referred to as “combustion delay period data”). On the basis of the combustion delay period data and the start position of the main combustion period at the optimum ignition timing measured at an appropriate temperature or data correlated therewith (hereinafter collectively referred to as “main combustion period start position data”). The optimum ignition timing at temperature is set.

  From the first feature, the main combustion period start position data at the optimum ignition timing measured at an appropriate temperature becomes substitute information of the start position of the main combustion period at the optimum ignition timing at a predetermined temperature, and from the second feature, Combustion delay period data at a predetermined temperature and a predetermined ignition timing is substitute information for the length of the combustion delay period at the optimal ignition timing at a predetermined temperature. Therefore, by using these data, it is possible to grasp the start position of the main combustion period and the length of the combustion delay period at the optimal ignition timing at the predetermined temperature, so that the optimal ignition timing at the predetermined temperature (that is, the main combustion period of the main combustion period). It is possible to calculate a position obtained from the start position by the length of the combustion delay period. In this way, when setting the optimal ignition timing under one operating condition, it is possible to set the optimal ignition timing simply by measuring the combustion delay period data at one ignition timing under that operating condition. Thus, it is possible to reduce the man-hours for measuring data necessary for setting the optimum ignition timing.

  In this case, as in claim 2, combustion delay period data at a predetermined ignition timing is measured at a low temperature of the internal combustion engine, and the combustion delay period data and the start of the main combustion period at the optimal ignition timing measured after the internal combustion engine is warmed up. The optimum ignition timing at low temperatures may be set based on the position data. The present invention can be set only by measuring combustion delay period data at one ignition timing, so that the optimum ignition timing can be set. In this way, it is possible to measure the combustion delay period data for a plurality of operating conditions in each temperature region in the process of increasing the coolant temperature during the warm-up operation, and it is possible to measure a plurality of operating conditions during one warm-up operation. It is possible to set an optimal ignition timing at a low temperature. For this reason, when determining the optimal ignition timing at low temperatures under all operating conditions, the number of repeated forced cooling and warm-up operations of the internal combustion engine can be reduced compared to the conventional case, and at low temperatures under all operating conditions. The time required for setting the optimal ignition timing can be greatly shortened.

  By the way, as the second feature, the length of the combustion delay period hardly changes depending on the ignition timing (or the combustion position) at the same temperature when the combustion position (intermediate position of the combustion delay period) is within a predetermined range. However, strictly speaking, the length of the combustion delay period varies slightly depending on the combustion position, and in particular, the combustion delay period increases as the combustion position moves away from TDC (top dead center). The amount of change in length tends to increase.

  Therefore, as described in claim 3, when setting the optimal ignition timing, the combustion delay period data at the predetermined ignition timing may be corrected according to the combustion position. In this way, the combustion delay period data can be corrected in response to the change in the length of the combustion delay period depending on the combustion position, and the calculation accuracy of the optimum ignition timing can be improved.

  Further, as in claim 4, when measuring the combustion delay period data at the predetermined ignition timing, the combustion delay period data at the predetermined ignition timing is measured for each operating condition while continuously changing the operating conditions of the internal combustion engine. You may make it do. In this way, it is possible to continuously measure the combustion delay period data at a predetermined ignition timing for a plurality of operating conditions, and continuously set the optimum ignition timing for the plurality of operating conditions.

  Hereinafter, the best mode for carrying out the present invention will be described using the following two Examples 1 and 2.

A first embodiment of the present invention will be described with reference to FIGS.
First, the configuration of an optimum ignition timing (hereinafter referred to as “MBT”) setting system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the MBT setting engine 11 (internal combustion engine), and a throttle valve 14 whose opening degree is adjusted by a DC motor or the like is provided downstream of the air cleaner 13. ing.

  Further, a surge tank 15 is provided on the downstream side of the throttle valve 14, and an intake manifold 16 for introducing air into each cylinder of the engine 11 is provided in the surge tank 15, and intake air of the intake manifold 16 of each cylinder is provided. A fuel injection valve 17 for injecting fuel is attached in the vicinity of the port. A spark plug 18 is attached to each cylinder of the engine 11 for each cylinder, and the air-fuel mixture in the cylinder is ignited by the spark discharge of each spark plug 18. On the other hand, the exhaust pipe 19 of the engine 11 is provided with an exhaust gas sensor 20 (air-fuel ratio sensor, oxygen sensor, etc.) for detecting the air-fuel ratio or rich / lean of the exhaust gas.

  The cylinder block of the engine 11 includes an in-cylinder pressure sensor 21 that detects an in-cylinder pressure, a cooling water temperature sensor (not shown) that detects a cooling water temperature, and a crankshaft of the engine 11 that has a constant crank angle (for example, 30). C) A crank angle sensor 22 that outputs a pulse signal every rotation is attached. Based on the output signal of the crank angle sensor 22, the crank angle and the engine speed are detected. The in-cylinder pressure sensor 21 may be a type built in the spark plug 18 or may be a type provided separately from the spark plug 18.

  The output of the in-cylinder pressure sensor 21 is input to the MBT setting computer 24 via the output conversion amplifier 23. The MBT setting computer 24 functions as optimum ignition timing setting means by executing a low temperature MBT calculation program shown in FIG. 9 to be described later, and all operating conditions (operating conditions such as cylinder charge air amount, intake valve timing, etc.). MBT at low temperature is calculated for all combinations of parameters.

Hereinafter, the MBT calculation method by the MBT setting computer 24 will be described in detail. As shown in FIG. 2, first, the combustion mass ratio X [%] is calculated for each resolution by the following equation based on the in-cylinder pressure data detected by the in-cylinder pressure sensor 21.
X (n) = Q (n) / Qmax × 100 0 ≦ n <datenum
Here, Q is the heat generation amount, Qmax is the maximum heat generation amount, and datenum is the number of data per cycle.

The heat generation amount Q is calculated for each resolution as follows.
The heat generation amount Q before the combustion mass ratio start point (0 ≦ n <Cstart) is calculated by the following equation. Here, Cstart is the combustion mass ratio start point data number.
Q (n) = Q (n-1)

The heat generation amount Q when the combustion mass ratio is within the range (Cstart ≦ n ≦ Cend) is calculated as follows. Here, Cend is the combustion mass ratio end point data number.
When dQ (n)> 0, the following formula is used.

Q (n) = Q (n-1) + dQ (n) × D
dQ (n) = 1 / {K (n) -1}
× {V (n) × dP (n) + K (n) × P (n) × dV (n)}

Here, D is the angular resolution [deg], K (n) is the specific heat ratio at n steps, V (n) is the combustion chamber volume at n steps, and dP (n) is the in-cylinder pressure rise rate at n steps. , P (n) is the in-cylinder pressure at n steps, and dV (n) is the combustion chamber volume change rate at n steps.
When dQ (n) ≦ 0, the following formula is used.
Q (n) = Q (n-1)

The heat generation amount Q after the end point of the combustion mass ratio (n> Cend) is calculated by the following equation.
Q (n) = Q (Cend)

  As described above, after calculating the combustion mass ratio based on the in-cylinder pressure data, the combustion delay period and the main combustion period are calculated based on the combustion mass ratio. Here, the combustion delay period is a period in which a flame is formed around the spark plug 18 and gradually grows, and corresponds to a period in which the combustion mass ratio is, for example, 0 to 10%. On the other hand, the main combustion period is a period in which the temperature of the air-fuel mixture rises and the flame propagates at once and burns in earnest, and corresponds to a period in which the combustion mass ratio is, for example, 10 to 90%. It is during this main combustion period that torque is generated.

  As shown in FIGS. 3 to 6, the inventors changed the ignition timing when the cooling water temperature (engine temperature substitute information) is around −10 ° C. and around 85 ° C. under predetermined operating conditions. Then, the combustion delay period and the main combustion period at each ignition timing were measured, and the combustion delay period and the main combustion period were considered based on the measured data.

  As a result, as shown in FIGS. 3 and 4, as a first feature, it has been found that the start position and the length of the main combustion period in the MBT are substantially constant with almost no change depending on the cooling water temperature. Furthermore, as shown in FIGS. 3, 5, and 6, as a second feature, the length of the combustion delay period varies depending on the coolant temperature, but the combustion position (intermediate position of the combustion delay period) is within a predetermined range ( For example, in the case of MBT range of ± 10 ° C., it has been found that the same temperature hardly changes depending on the ignition timing (or combustion position) and is almost constant (for example, the amount of change is within 2 ° A).

  In the first embodiment, paying attention to these characteristics, as shown in FIG. 7, after the warm-up (for example, when the cooling water temperature is 85 ° C.), the start of the main combustion period in MBT under predetermined operating conditions. After the position is measured and the engine 11 is forcibly cooled, the combustion delay period at the predetermined ignition timing is measured under predetermined operating conditions at a low temperature (for example, when the cooling water temperature is a predetermined temperature lower than 85 ° C.) A position which is obtained by the length of the combustion delay period at the predetermined ignition timing measured at the low temperature from the start position of the main combustion period in the MBT measured after the warm-up is calculated, and the position is defined as the MBT at the low temperature. Thereby, when setting MBT in one driving condition, MBT can be set only by measuring a combustion delay period at one ignition timing in the driving condition.

  When setting the MBT at low temperatures for all operating conditions (all combinations of operating condition parameters such as cylinder charge air amount and intake valve timing), for example, after warming up (cooling water temperature is set to 85 ° C., for example). When the MBT is determined by measuring the relationship between the ignition timing and the generated torque for all operating conditions when the temperature is raised), the start position of the main combustion period in the MBT is measured for all operating conditions.

  Thereafter, with the engine 11 stopped, cooling air is applied to the engine 11 or cooling water or lubricating oil cooled by the cooling device is circulated through the cooling water passage or lubricating oil passage of the engine 11. The whole is forcibly cooled to a predetermined temperature (for example, −20 ° C.). Thereafter, as shown in FIG. 8, the engine 11 is started, and the operating conditions (for example, the combination of the cylinder charge air amount and the intake valve timing) are set in each temperature region in the process of increasing the coolant temperature during the warm-up operation. While continuously changing, the process of measuring the combustion delay period at the predetermined ignition timing at low temperature is repeated for each operating condition.

  In this way, the combustion delay period at the predetermined ignition timing measured at low temperatures for each operating condition and the start position of the main combustion period in MBT measured after warming up under the same operating conditions are used. By calculating MBT (that is, the position obtained by the length of the combustion delay period at the predetermined ignition timing measured at low temperature from the start position of the main combustion period in MBT measured after warm-up), during one warm-up operation The MBT at low temperature under a plurality of operating conditions is obtained. These processes are repeated to obtain MBT at low temperatures under all operating conditions.

  The MBT calculation by the MBT setting computer 24 described above is executed according to the low temperature MBT calculation program shown in FIG. When this program is started, first, in step 101, after the engine 11 is warmed up, MBT is determined by measuring the relationship between ignition timing and generated torque for all operating conditions. At that time, the start position of the main combustion period in MBT is measured for all operating conditions. Thereafter, the process proceeds to step 102, and the start point Ms of the main combustion period in the MBT measured after warm-up is stored for all operating conditions.

  Thereafter, the process proceeds to step 103, where the cooling water temperature rises during the warm-up operation after the engine 11 is forcibly cooled, and the operating conditions are continuously changed within each temperature region, and predetermined ignition is performed for each operating condition. The length N of the combustion delay period at the time is measured.

Thereafter, the routine proceeds to step 104, where a position is obtained that is obtained from the start point MS of the main combustion period in MBT by the length N of the combustion delay period at the predetermined ignition timing for each operating condition, and that position is defined as MBT at low temperature. .
MBT = Ms + N
These steps 103 and 104 are repeated to obtain MBTs at low temperatures under all operating conditions.

  According to the first embodiment described above, when setting the MBT under one operating condition, the MBT can be set only by measuring the combustion delay period data at one ignition timing under the operating condition. In addition, it is possible to reduce the man-hours for measuring data necessary for setting the MBT. In addition, when setting the MBT at low temperature, in the process in which the coolant temperature rises during the warm-up operation, the operating conditions are continuously changed within each temperature region, and the combustion delay period at a predetermined ignition timing for each operating condition Therefore, it is possible to measure the combustion delay period for a plurality of operating conditions in each temperature region, and in a plurality of operating conditions (for example, nine operating conditions) during one warm-up operation. MBT at low temperature can be set. For this reason, when determining the MBT at low temperatures under all operating conditions, the number of repeated forced cooling and warm-up operations of the engine 11 can be reduced as compared with the conventional case, and the MBT at low temperatures under all operating conditions. The time required for setting can be greatly shortened, and the MBT at low temperature can be set efficiently.

  Next, Embodiment 2 of the present invention will be described with reference to FIGS. As the second feature described above, the length of the combustion delay period hardly changes depending on the ignition timing (or combustion position) at the same temperature when the combustion position (intermediate position of the combustion delay period) is within a predetermined range. Although considered to be almost constant, strictly speaking, as shown in FIG. 10, the length of the combustion delay period varies slightly depending on the combustion position, and in particular, the combustion position moves away from TDC (top dead center) toward the advance side. There is a tendency for the amount of change in the length of the combustion delay period to increase.

  Therefore, in the second embodiment, when setting the optimal ignition timing, the length of the combustion delay period at the predetermined ignition timing is corrected according to the combustion position as follows.

As shown in FIG. 11, the relationship between the combustion delay period change amount Y with respect to a reference point (for example, −5 ° C. A ATDC) and the combustion position X can be expressed by the following relational expression.
Y = aX ² + bX

  Using the above relational expression, for example, the amount of change in the combustion delay period in MBT and the amount of change in the combustion delay period in the predetermined ignition timing are obtained based on the combustion position, and the difference in the amount of change is calculated as the combustion delay period in the predetermined ignition timing. The length of the combustion delay period at the predetermined ignition timing is corrected (that is, converted into the length of the combustion delay period in MBT).

  The setting of MBT at low temperature in the second embodiment is executed according to the low temperature MBT calculation program shown in FIG. In this program, after the engine 11 is warmed up, the MBT is determined for all the operating conditions, and the start point Ms of the main combustion period in the MBT measured at that time is stored (steps 201 and 202).

Thereafter, the process proceeds to step 203, and after measuring the length N of the combustion delay period at the predetermined ignition timing for each operating condition at low temperatures, the process proceeds to step 204, and the length N of the combustion delay period is calculated using the above relational expression. Correct according to the combustion position.
Nc ← N

Thereafter, the routine proceeds to step 205, where for each operating condition, a position calculated by the length Nc of the combustion delay period at the corrected predetermined ignition timing is calculated from the start point MS of the main combustion period in MBT, and the position is calculated at a low temperature. MBT.
MBT = Ms + Nc
These steps 203 to 205 are repeated to obtain the MBT at low temperatures under all operating conditions.

  In the second embodiment described above, when the MBT is set, the length of the combustion delay period at the predetermined ignition timing is corrected according to the combustion position, so that the length of the combustion delay period depends on the combustion position. Corresponding to the change, the length of the combustion delay period can be corrected, and the calculation accuracy of MBT can be improved.

  In each of the first and second embodiments, when setting the MBT in one operating condition, the combustion delay period data is measured at one ignition timing in the operating condition. The combustion delay period may be measured at the timing and the average value thereof may be used. Even in this case, the number of measurement steps can be reduced if the number of ignition timing measurement points is made smaller than before. .

  In each of the first and second embodiments, the start position of the main combustion period in MBT measured after warm-up is used. However, the present invention is not limited to this, and the start position of the main combustion period in MBT measured at low temperatures is used. It may be used.

  In each of the first and second embodiments, when the MBT is set, the start position of the main combustion period and the combustion delay period are used. However, the present invention is not limited to this, and data correlating with the start position of the main combustion period ( In-cylinder pressure data, combustion mass ratio data, etc.) and data correlated with the combustion delay period (in-cylinder pressure data, combustion mass ratio data, etc.) may be used.

  Further, in each of the first and second embodiments, when the MBT is set, the start position of the main combustion period is used. However, the present invention is not limited to this, and the start equivalent position of the main combustion period (for example, the start position of the main combustion period) May be used (predetermined position between approximately 50% and approximately 50% position) (see FIG. 7). This is because, from the start position of the main combustion period in MBT to the position of about 50%, it is almost constant with almost no change depending on the temperature.

  Further, in each of the first and second embodiments, the present invention is applied to the setting of MBT at a low temperature. However, the present invention may be applied to the case where MBT is set for different temperatures after warm-up.

It is a schematic block diagram of the MBT setting system in Example 1 of this invention. It is a figure for demonstrating a combustion delay period and the main combustion period. It is a time chart which shows the relationship between ignition timing, a combustion delay period, and the main combustion period in different cooling water temperature. It is a figure which shows the relationship between a combustion position and the length of the main combustion period in different cooling water temperature. It is a figure which shows the relationship between a combustion position and the length of a combustion delay period in different cooling water temperature. It is a figure which shows the relationship between a combustion position and the length of a combustion delay period. It is a time chart for demonstrating the setting method of MBT. It is a time chart for demonstrating the method to measure a combustion delay period, changing an operating condition. 6 is a flowchart illustrating a flow of processing of a low temperature MBT calculation program according to the first embodiment. It is a figure which shows the relationship between a combustion position and the length of a combustion delay period. It is a figure for demonstrating the correction method of a combustion delay period. 12 is a flowchart illustrating a flow of processing of a low temperature MBT calculation program according to the second embodiment. It is a figure which shows the relationship between ignition timing and torque. It is a figure which shows the relationship between a rotational speed and MBT. It is a figure which shows the relationship between cylinder filling air amount and MBT. It is a figure which shows the relationship between A / F and MBT. It is a figure which shows the relationship between intake VVT advance amount and MBT. It is a figure which shows the relationship between cooling water temperature and MBT. It is a time chart for demonstrating the setting method of the MBT at the time of the conventional low temperature.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 14 ... Throttle valve, 17 ... Fuel injection valve, 18 ... Spark plug, 19 ... Exhaust pipe, 20 ... Exhaust gas sensor, 21 ... In-cylinder pressure sensor, 22 ... Crank angle Sensor, 24 ... MBT setting computer (optimum ignition timing setting means)

Claims (5)

In an optimal ignition timing setting method for an internal combustion engine that sets an optimal ignition timing at which the generated torque of the internal combustion engine is maximized,
The combustion delay period at the predetermined ignition timing at the predetermined temperature or the data correlated therewith (hereinafter referred to as “combustion delay period data”) is measured, and this combustion delay period data and the main combustion at the optimal ignition timing measured at an appropriate temperature An optimal ignition timing setting method for an internal combustion engine, wherein the optimal ignition timing at the predetermined temperature is set based on a start position of a period or data correlated therewith (hereinafter collectively referred to as “main combustion period start position data”) .   Combustion delay period data at the predetermined ignition timing is measured at a low temperature of the internal combustion engine, and based on the combustion delay period data and the main combustion period start position data at the optimal ignition timing measured after the internal combustion engine is warmed up. The optimal ignition timing setting method for an internal combustion engine according to claim 1, wherein the optimal ignition timing is set.   3. The method for setting an optimal ignition timing for an internal combustion engine according to claim 1, wherein when setting the optimal ignition timing, the combustion delay period data at the predetermined ignition timing is corrected according to a combustion position.   The combustion delay period data at the predetermined ignition timing is measured for each operating condition while continuously changing the operating conditions of the internal combustion engine when measuring the combustion delay period data at the predetermined ignition timing. Item 5. An optimal ignition timing setting method for an internal combustion engine according to any one of Items 1 to 3. In an optimal ignition timing setting device for an internal combustion engine comprising optimal ignition timing setting means for setting an optimal ignition timing at which the generated torque of the internal combustion engine is maximized,
The optimum ignition timing setting means measures a combustion delay period at a predetermined temperature at a predetermined temperature or data related thereto (hereinafter referred to as “combustion delay period data”), and sets the combustion delay period data at an appropriate temperature. The optimum ignition timing at the predetermined temperature is set based on the start position of the main combustion period at the measured optimum ignition timing or data correlated therewith (hereinafter collectively referred to as “main combustion period start position data”). An optimal ignition timing setting device for an internal combustion engine.

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