JP6357985B2 - Ignition device and ignition method for internal combustion engine - Google Patents

Description

  The present invention relates to an ignition device and an ignition method for an internal combustion engine that generates a discharge voltage between electrodes of an ignition plug using an ignition coil, and more particularly, to an ignition device and an ignition method for estimating a gap length between electrodes. .

  In an ignition device using an ignition coil, a primary current is supplied to the primary coil, and then the primary current is cut off at a predetermined ignition timing, so that a high discharge voltage is generated in the secondary coil and the mixture is insulated. A discharge occurs between the electrodes of the spark plug with destruction. Specifically, a very high voltage capacitive discharge occurs instantaneously, followed by an induction discharge. During the induction discharge, the secondary current flowing between the electrodes decreases relatively abruptly in a triangular wave shape with the passage of time from the start of the discharge.

  The electrode of the spark plug gradually wears with discharge, and therefore the gap length between the electrodes gradually increases. And when this gap length expands to a certain limit, it is necessary to replace the spark plug.

  Patent Documents 1 and 2 propose techniques for monitoring such an increase in gap length during engine operation. Patent Document 1 focuses on the fact that the required voltage required for the discharge of the spark plug increases as the gap increases. The voltage applied to the spark plug is detected, and this voltage is set based on the load. When the reference voltage becomes higher than the reference voltage, an abnormal signal indicating that the gap length has abnormally increased is output.

Patent Document 2 sums up the number of discharges by dividing each discharge voltage and each electrode temperature, and adds the electrode consumption volume based on the discharge voltage and the electrode consumption volume based on the electrode temperature to obtain the total consumption volume. The technique which calculated | required and converted this into gap length is disclosed. And in patent document 2, if the obtained gap length reaches a threshold value, a warning lamp will be lighted and it will alert | report to a driver.

JP-A-8-106970 JP 2009-180157 A

  In the method of Patent Document 1, since a very high voltage applied to the spark plug is handled, it is difficult to apply to an actual internal combustion engine. Further, since the required voltage changes when the ignition timing is different even with the same load, the determination error is large.

  On the other hand, the method of Patent Document 2 is merely a technique for estimating the gap length based on the operation history after replacing the spark plug with a new one, and the gap length is determined only from the actual current operation state. It cannot be estimated.

The present invention relates to an ignition device for an internal combustion engine that generates a discharge voltage between electrodes of an ignition plug connected to a secondary coil by energizing and interrupting a primary current to the primary coil of the ignition coil.
A discharge time detecting means for detecting a discharge time in which a secondary current flows between the electrodes;
Gas density calculating means for obtaining the gas density in the cylinder at the ignition timing;
A gas flow rate calculating means for obtaining a gas flow rate in the cylinder at the ignition timing;
Gap length estimation means for estimating the gap length between the electrodes based on the in-cylinder gas density at the discharge time and the ignition timing and the in-cylinder gas flow velocity at the ignition timing;
It is configured with.

  In-cylinder gas pressure at the ignition timing may be used instead of the in-cylinder gas density at the ignition timing.

That is, the three highly sensitive parameters that affect the discharge time are the in-cylinder gas density (or in-cylinder gas pressure) at the ignition timing, the in-cylinder gas flow rate at the ignition timing, and the discharge gap length. When these three parameters are determined, the discharge time is uniquely determined. Therefore, conversely, it is possible to estimate the gap length during discharge based on the three parameters of the cylinder gas density (or cylinder gas pressure) at the ignition timing, the cylinder gas flow velocity at the ignition timing, and the discharge time. It is.
Furthermore, the invention according to claim 8 is an internal combustion engine ignition device for generating a discharge voltage between electrodes of an ignition plug connected to a secondary coil by energizing and interrupting a primary current to the primary coil of the ignition coil. In
A discharge time detecting means for detecting a discharge time in which a secondary current flows between the electrodes;
A gas density / pressure calculating means for obtaining the gas density or pressure in the cylinder at the ignition timing;
A gas flow rate calculating means for obtaining a gas flow rate in the cylinder at the ignition timing;
Threshold calculating means for obtaining a discharge time threshold corresponding to the limit gap length based on the in-cylinder gas density or pressure at the ignition timing and the in-cylinder gas flow velocity at the ignition timing;
Determining means for determining whether or not the discharge time is equal to or less than the threshold;
It is configured with.
As described above, it is possible to estimate the gap length during discharge based on the three parameters of the cylinder gas density (or cylinder gas pressure) at the ignition timing, the cylinder gas flow velocity at the ignition timing, and the discharge time. If the discharge time is equal to or less than the discharge time threshold corresponding to the limit gap length, the gap length is equal to or greater than the limit gap length.

According to the present invention, it is possible to accurately estimate the gap length during engine operation without requiring detection of the discharge voltage and without depending on the past history , or the gap length is within an allowable range. whether Ru can be accurately determined.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows one Example of the internal combustion engine to which this invention was applied. Structure explanatory drawing which shows the structure of the ignition unit of each cylinder. The wave form diagram of the primary current etc. in an ignition coil. Explanatory drawing of the discharge time of the secondary current used as detection object. The characteristic view which shows the relationship between the in-cylinder gas density and discharge time in an ignition timing. The characteristic view which shows the relationship between the in-cylinder gas flow velocity and discharge time in ignition timing. The characteristic view which shows the relationship between discharge gap length and discharge time. The characteristic view which shows the relationship between the in-cylinder gas pressure and the discharge time at the ignition timing. The flowchart which shows 1st Example of this invention. The characteristic view which shows the characteristic of the cylinder gas flow velocity with respect to ignition timing and rotation speed. The flowchart which shows 2nd Example of this invention. The characteristic view which shows the range of the ignition timing which performs gap length estimation. The flowchart which shows 3rd Example of this invention. The flowchart which shows the prohibition process of gap length estimation accompanying external EGR introduction. The flowchart which shows 4th Example of this invention.

  FIG. 1 shows the system configuration of an automotive internal combustion engine 1 to which the present invention is applied. The internal combustion engine 1 is an in-cylinder direct injection type spark ignition type internal combustion engine with four cylinders, and includes a fuel injection valve 2 for injecting fuel into the cylinder for each cylinder, and is generated. A spark plug 3 for igniting the air-fuel mixture is provided, for example, at the center of the ceiling surface. The spark plug 3 is connected to an ignition unit 4 described later provided for each cylinder. For example, each ignition unit 4 is arranged so that the ignition unit 4 is directly connected to the terminal portion at the upper end of the spark plug 3.

  Each cylinder includes an intake valve 5 and an exhaust valve 7, and the tip of the intake port connected to the intake collector 8 is opened and closed by the intake valve 5 and the tip of the exhaust port connected to the exhaust passage 9. Is opened and closed by the exhaust valve 7. Here, in the present embodiment, the intake valve 5 includes a variable valve gear 6 that can variably control the opening / closing timing (at least the closing timing) of the intake valve 5. In the present invention, the variable valve gear 6 is not necessarily essential.

  An electronically controlled throttle valve 11 whose opening is controlled by a control signal from the engine controller 10 is interposed at the inlet of the intake collector 8.

  The engine controller 10 includes a crank angle sensor 13 for detecting the engine speed, an air flow meter 14 for detecting the intake air amount, a water temperature sensor 15 for detecting the cooling water temperature, and an accelerator pedal depression amount operated by the driver. Detection signals of sensors such as an accelerator opening sensor 16 for detecting the air-fuel ratio and an air-fuel ratio sensor 17 for detecting the exhaust air-fuel ratio are input. Based on these detection signals, the engine controller 10 determines the fuel injection amount and injection timing by the fuel injection valve 2, the ignition timing of the spark plug 3 via the ignition unit 4, the opening and closing timing of the intake valve 5, and the opening of the throttle valve 11. , Etc. are optimally controlled.

  As shown in detail in FIG. 2, the ignition unit 4 includes an ignition coil 21 including a primary coil 21a and a secondary coil 21b, and an igniter 22 that controls energization / interruption of a primary current to the primary coil 21a of the ignition coil 21. The in-vehicle battery 24 is connected to the primary coil 21a of the ignition coil 21, and the ignition plug 3 is connected to the secondary coil 21b. And in order to monitor the secondary current which flows between the electrodes of the spark plug 3 at the time of discharge, the resistance 23 for secondary current detection is provided in series with the secondary coil 21b. A signal indicating the secondary current of each cylinder detected through the secondary current detection resistor 23 is input to the engine controller 10 and monitored by the engine controller 10.

  FIG. 3 shows the operation of the ignition unit 4 using the ignition coil 21 as described above. Based on a control signal (ignition signal) output from the engine controller 10, a primary current is supplied to the primary coil 21 a of the ignition coil 21 through the igniter 22 for an appropriate energization time. This primary current is interrupted at a predetermined ignition timing. Along with the interruption of the primary current, a high discharge voltage (secondary voltage) is generated in the secondary coil 21b, and discharge occurs between the electrodes of the spark plug 3 with dielectric breakdown of the air-fuel mixture. Specifically, a very high voltage capacitive discharge occurs instantaneously, followed by an induction discharge. During the induction discharge, the secondary current flowing between the electrodes decreases relatively abruptly in a triangular wave shape with the passage of time from the start of the discharge.

  As shown in FIG. 4, the engine controller 10 reads a time during which a secondary current exceeding a predetermined threshold flows as a discharge time Tdis. The threshold value is set to an appropriate value so as to avoid erroneous detection, but may be a very small value close to 0. Since the capacity discharge period at the time of dielectric breakdown is very short, the above discharge time Tdis is generally an induction discharge period.

  According to the knowledge of the present inventor, three highly sensitive parameters that affect the discharge time are the in-cylinder gas density (or in-cylinder gas pressure) at the ignition timing, the in-cylinder gas flow velocity at the ignition timing, and the discharge gap length. One. That is, as a result of multiple regression analysis of a large number of data on the discharge time, it has been found that the discharge time can be predicted with high accuracy based on these three parameters having relatively high sensitivity. Therefore, conversely, it is possible to estimate the gap length during discharge based on the three parameters of the cylinder gas density (or cylinder gas pressure) at the ignition timing, the cylinder gas flow velocity at the ignition timing, and the discharge time. It is.

  FIG. 5 shows the result of determining the relationship between the in-cylinder gas density at the ignition timing and the discharge time under the conditions that the in-cylinder gas flow velocity and the gap length at the ignition timing are constant. As shown, the higher the in-cylinder gas density, the shorter the discharge time.

  FIG. 6 shows the results of determining the relationship between the in-cylinder gas flow rate at the ignition timing and the discharge time under the conditions that the in-cylinder gas density and the gap length at the ignition timing are constant. As shown in the figure, the higher the in-cylinder gas flow rate, the shorter the discharge time.

  FIG. 7 shows the result of determining the relationship between the gap length and the discharge time under the condition that the cylinder gas density at the ignition timing and the cylinder gas flow velocity at the ignition timing are constant. As shown in the figure, the larger the gap length, the shorter the discharge time.

  FIG. 8 shows the result of determining the relationship between the in-cylinder gas pressure at the ignition timing and the discharge time under the condition that the in-cylinder gas flow velocity and the gap length at the ignition timing are constant. As shown, the higher the in-cylinder gas pressure, the shorter the discharge time.

  The discharge time Tdis can be expressed by the following equation, where Gp is the gap length, Ng is the in-cylinder gas density at the ignition timing, and Fg is the in-cylinder gas flow rate at the ignition timing.

Tdis = -A * Gp-B * Ng-C * Fg + X
Here, “−A”, “−B”, and “−C” are respective coefficients obtained by multiple regression analysis, and X is a constant obtained by multiple regression analysis.

  Therefore, the gap length Gp can be obtained by the following equation (1).

Gp = (-Tdis-B.Ng-C.Fg + X) / A (1)
The same applies to the case where the in-cylinder gas pressure Pg at the ignition timing is used instead of the in-cylinder gas density Ng at the ignition timing, and the discharge time Tdis can be expressed by the following equation.

Tdis = -A'.Gp-B'.Pg-C'.Fg + Y
Here, “−A ′”, “−B ′”, and “−C ′” are coefficients obtained by multiple regression analysis, and Y is a constant obtained by multiple regression analysis.

  Therefore, the gap length Gp can be obtained by the following equation (2).

Gp = (− Tdis−B ′ · Pg−C ′ · Fg + Y) / A ′ (2)
FIG. 9 shows a specific example of the first embodiment in which the gap length Gp is estimated based on the three parameters of the cylinder gas density Ng at the ignition timing, the cylinder gas flow rate Fg at the ignition timing, and the discharge time Tdis. It is a flowchart which shows the flow of a simple process. The process shown in this flowchart is executed in the engine controller 10 every time each cylinder is ignited, for example.

  In step 1, the rotational speed and load of the internal combustion engine 1 and other necessary environmental conditions are read. In step 2, based on these conditions, the intake pressure P1, the ignition timing ADV, the valve timing of the variable valve gear 6, etc. are determined.

  In step 3, the in-cylinder gas density Ng at the ignition timing is calculated.

  The in-cylinder gas density Ng at the ignition timing can be obtained by the following equation (3) using the in-cylinder gas pressure Pg at the ignition timing and the in-cylinder gas temperature Tg at the ignition timing. C1 is a constant.

Ng = Pg / Tg × C1 (3)
The in-cylinder gas pressure Pg at the ignition timing has the relationship of the following equation (4) with respect to the intake pressure P1, the actual compression ratio εign and the specific heat ratio κ at the ignition timing.

Pg = P1 × εsign ^κ (4)
The in-cylinder gas temperature Tg at the ignition timing has the following equation (5) with respect to the compression start in-cylinder gas temperature T1, the actual compression ratio εign at the ignition timing, and the specific heat ratio κ.

Tg = T1 × εsign ^κ−1 (5)
Here, the intake pressure P1 and the specific heat ratio κ can be obtained, for example, with reference to a map or table created in advance using the engine speed and load or the ignition timing as parameters. The intake pressure P1 can be detected directly by providing an intake pressure sensor in the intake collector 8.

  The compression start in-cylinder gas temperature T1 can be obtained, for example, with reference to a map or table created in advance using the intake air temperature and the oil / water temperature as parameters.

  The actual compression ratio .epsilon.ign at the ignition timing has a relationship of the following equation (6) with respect to the volume Vivc at the intake valve closing timing and the volume Vign at the ignition timing.

εsign = Vivc / Vign (6)
Next, in step 4, the in-cylinder gas flow rate Fg at the ignition timing is calculated. The in-cylinder gas flow rate has a relationship as shown in FIG. 10 with respect to the crank angle and the engine rotation speed. Therefore, if the ignition timing ADV is determined, the in-cylinder gas flow rate Fg at the ignition timing can be obtained from the relationship of FIG. 10 based on the engine speed at that time.

  In step 5, as shown in FIG. 4, the discharge time Tdis is detected based on the secondary current value.

  In step 6, the gap length Gp is calculated from the following equation (1) using the three parameters (Tdis, Ng, Fg) obtained as described above.

Gp = (-Tdis-B.Ng-C.Fg + X) / A (1)
In step 7, the estimated gap length Gp is compared with a predetermined threshold Gp0. If the estimated gap length Gp is greater than or equal to the threshold value Gp0, the process proceeds to step 8 to notify that the spark plug 3 should be replaced by lighting a warning lamp or the like.

  As described above, according to the above embodiment, the gap length Gp is obtained by directly or indirectly obtaining the three parameters of the cylinder gas density Ng at the ignition timing, the cylinder gas flow rate Fg at the ignition timing, and the discharge time Tdis. It can be estimated with high accuracy.

  Next, FIG. 11 shows a second embodiment in which the gap length Gp is estimated based on the three parameters of the cylinder gas pressure Pg at the ignition timing, the cylinder gas flow velocity Fg at the ignition timing, and the discharge time Tdis. It is a flowchart which shows the flow of the specific process of. The process shown in this flowchart is executed in the engine controller 10 every time each cylinder is ignited, for example.

  In step 11, the rotational speed and load of the internal combustion engine 1 and other necessary environmental conditions are read. In step 12, the intake pressure P1, the ignition timing ADV, the valve timing of the variable valve gear 6 and the like are determined based on these conditions.

  In the next step 13, it is determined whether the ignition timing ADV is within a predetermined crank angle range in which the gap length Gp should be estimated. That is, the gap length is estimated on the condition that the ignition timing ADV is on the retard side with respect to the predetermined crank angle ADV1 shown in FIG. As shown in FIG. 12, the crank angle ADV1 is set in a region where the absolute value of the gas flow velocity is small and the gas flow velocity fluctuation is also small. If the ignition timing ADV is more advanced than the predetermined crank angle ADV1, the gap length Gp is not estimated. Thereby, an estimation error can be made small.

  In step 14, the in-cylinder gas pressure Pg at the ignition timing is calculated. The in-cylinder gas pressure Pg at the ignition timing can be obtained from the relationship of the following equation (4) as described above.

Pg = P1 × εsign ^κ (4)
Steps 15 and 16 are the same as Steps 4 and 5 of the above-described embodiment, and the in-cylinder gas flow rate Fg and the discharge time Tdis at the ignition timing are obtained, respectively.

  In step 17, the gap length Gp is calculated from the following equation (2) using the three parameters (Tdis, Pg, Fg) obtained as described above.

Gp = (− Tdis−B ′ · Pg−C ′ · Fg + Y) / A ′ (2)
In step 18, the estimated gap length Gp is compared with a predetermined threshold value Gp0. If the estimated gap length Gp is equal to or greater than the threshold value Gp0, the process proceeds to step 19 where a warning lamp is turned on.

  Next, in the flowchart of FIG. 13, when the gap length Gp is estimated based on the three parameters of the in-cylinder gas pressure Pg at the ignition timing, the in-cylinder gas flow rate Fg at the ignition timing, and the discharge time Tdis, the EGR In the third embodiment, the ratio (R_egr), the air-fuel ratio (AFR), and the battery voltage (Vb) are considered. The process shown in this flowchart is executed in the engine controller 10 every time each cylinder is ignited, for example.

  In step 21, the rotational speed and load of the internal combustion engine 1 and other necessary environmental conditions are read. In step 22, the intake pressure P1, the ignition timing ADV, the valve timing of the variable valve gear 6, the target EGR rate, the target air-fuel ratio, and the like are determined based on these conditions.

  In the next step 23, as in step 13 of the second embodiment described above, it is determined whether or not the ignition timing ADV is on the retard side with respect to a predetermined crank angle ADV1 for which the gap length Gp is to be estimated.

  Steps 24 to 26 are the same as Steps 14 to 16 of the second embodiment described above, and the in-cylinder gas pressure Pg at the ignition timing, the in-cylinder gas flow rate Fg at the ignition timing, and the discharge time Tdis are obtained, respectively.

  In step 27, the EGR rate R_egr, air-fuel ratio AFR, and battery voltage Vb at that time are read.

  In step 28, the gap length Gp is calculated from the following equation (7) using the six parameters (Tdis, Pg, Fg, R_egr, AFR, Vb) obtained as described above.

  That is, the effects of the EGR rate R_egr, the air-fuel ratio AFR, and the battery voltage Vb on the discharge time Tdis can also be obtained by multiple regression analysis as in the above-described equations (1) and (2). Note that the effects of these EGR rates and the like are relatively small compared to the three main factors of the gap length Gp, the cylinder gas pressure Pg at the ignition timing, and the cylinder gas flow velocity Fg at the ignition timing.

  The discharge time Tdis can be expressed by the following equation.

Tdis = -A ", Gp-B", Pg-C ", Fg-D, R_egr-E, AFR + F, Vb + Z
Here, “−A ″”, “−B ″”, “−C ″”, “−D”, “−E”, and “F” are coefficients obtained by multiple regression analysis, and Z is It is the constant similarly calculated | required by multiple regression analysis.

  Therefore, the gap length Gp can be obtained by the following equation (7).

Gp = (-Tdis-B ".Pg-C" .Fg-D.R_egr-E.AFR + F.Vb + Z) / A "(7)
In step 29, the estimated gap length Gp is compared with a predetermined threshold value Gp0, and if the estimated gap length Gp is equal to or greater than the threshold value Gp0, the process proceeds to step 30 where a warning lamp is turned on.

  Thus, in the third embodiment, since the gap length Gp is corrected based on the EGR rate R_egr, the air-fuel ratio AFR, and the battery voltage Vb, the estimation accuracy becomes higher. In the third embodiment, all of the EGR rate R_egr, the air-fuel ratio AFR, and the battery voltage Vb are considered, but one or two of these parameters may be considered. Alternatively, although not shown, correction by the cylinder gas temperature Tg at the ignition timing may be added.

  Next, FIG. 14 is a flowchart showing an embodiment in which the estimation of the gap length Gp is prohibited when the external EGR is introduced. This flowchart is used in combination with the flowcharts of the first to third embodiments, for example.

  In step 41, the rotational speed and load of the internal combustion engine 1 and other necessary environmental conditions are read. In step 42, based on these conditions, the intake pressure P1, the ignition timing ADV, the valve timing of the variable valve gear 6, the target EGR rate, the target air-fuel ratio, and the like are determined.

  In the next step 43, it is determined whether or not the operating condition is that the external EGR is introduced. If it is a condition for introducing the external EGR, the process proceeds to step 44 to prohibit the estimation of the gap length Gp. If the condition is such that the external EGR is not introduced, the process proceeds to step 45, where the estimation of the gap length Gp is permitted.

  In this way, by prohibiting the estimation of the gap length Gp when the external EGR is introduced, erroneous determination due to the external EGR is prevented.

  Next, FIG. 15 shows a discharge time threshold value corresponding to the limit gap length that requires the replacement of the spark plug 3, and when the discharge time Tdis falls below this threshold value, the warning lamp is turned on. The flowchart of 4 Example is shown. The process shown in this flowchart is executed in the engine controller 10 every time each cylinder is ignited, for example.

  In step 51, the rotational speed and load of the internal combustion engine 1 and other necessary environmental conditions are read. In step 52, the intake pressure P1, the ignition timing ADV, the valve timing of the variable valve gear 6 and the like are determined based on these conditions.

  In step 53, the in-cylinder gas density Ng at the ignition timing is calculated by the same process as in step 3 of the first embodiment.

  In step 54, the in-cylinder gas flow rate Fg at the ignition timing is calculated by the same process as in step 4 of the first embodiment.

  In step 55, a discharge time threshold value LMTTd corresponding to the limit gap length Gp_lmt that requires the replacement of the spark plug 3 is obtained. This is because of the relationship of “Tdis = −A · Gp−B · Ng−C · Fg + X” by the multiple regression analysis described above, the critical gap length Gp_lmt, the cylinder gas density Ng at the ignition timing, and the cylinder gas flow velocity at the ignition timing. Fg can be used.

  In step 56, as shown in FIG. 4, the discharge time Tdis is detected based on the secondary current value.

  In step 57, the detected discharge time Tdis is compared with the discharge time threshold value LMTTd. If the discharge time Tdis is less than or equal to the discharge time threshold LMTTd, it means that the gap length Gp is greater than or equal to the limit gap length Gp_lmt. Is notified.

  Thus, according to the fourth embodiment, it is possible to accurately determine whether or not the gap length Gp is within the allowable range from the length of the discharge time Tdis.

  In the fourth embodiment, the in-cylinder gas pressure Pg at the ignition timing can be used instead of the in-cylinder gas density Ng at the ignition timing.

DESCRIPTION OF SYMBOLS 3 ... Spark plug 4 ... Ignition unit 10 ... Engine controller 21 ... Ignition coil 23 ... Resistance for secondary current detection

Claims (10)

In an ignition device for an internal combustion engine that generates a discharge voltage between electrodes of an ignition plug connected to a secondary coil by energizing and interrupting a primary current to the primary coil of the ignition coil,
A discharge time detecting means for detecting a discharge time in which a secondary current flows between the electrodes;
Gas density calculating means for obtaining the gas density in the cylinder at the ignition timing;
A gas flow rate calculating means for obtaining a gas flow rate in the cylinder at the ignition timing;
Gap length estimation means for estimating the gap length between the electrodes based on the in-cylinder gas density at the discharge time and the ignition timing and the in-cylinder gas flow velocity at the ignition timing;
An ignition device for an internal combustion engine comprising: In an ignition device for an internal combustion engine that generates a discharge voltage between electrodes of an ignition plug connected to a secondary coil by energizing and interrupting a primary current to the primary coil of the ignition coil,
A discharge time detecting means for detecting a discharge time in which a secondary current flows between the electrodes;
A gas pressure calculating means for obtaining a gas pressure in the cylinder at the ignition timing;
A gas flow rate calculating means for obtaining a gas flow rate in the cylinder at the ignition timing;
Gap length estimation means for estimating the gap length between the electrodes based on the in-cylinder gas pressure at the ignition time and the in-cylinder gas flow velocity at the ignition timing,
An ignition device for an internal combustion engine comprising:   The ignition device for an internal combustion engine according to claim 2, wherein the estimated gap length is corrected based on the gas temperature in the cylinder at the ignition timing.   The ignition device for an internal combustion engine according to any one of claims 1 to 3, wherein the gas flow velocity calculation means obtains an in-cylinder gas flow velocity at an ignition timing from a rotation speed of the internal combustion engine and an ignition timing.   The ignition device for an internal combustion engine according to any one of claims 1 to 4, wherein the gap length is estimated on the condition that the ignition timing is on the retard side with respect to a predetermined crank angle.   The ignition device for an internal combustion engine according to any one of claims 1 to 5, wherein the estimated gap length is corrected based on at least one of an EGR rate, an air-fuel ratio, and a battery voltage of the internal combustion engine.   The internal combustion engine ignition device according to any one of claims 1 to 6, wherein gap length estimation is prohibited when external EGR is introduced. In an ignition device for an internal combustion engine that generates a discharge voltage between electrodes of an ignition plug connected to a secondary coil by energizing and interrupting a primary current to the primary coil of the ignition coil,
A discharge time detecting means for detecting a discharge time in which a secondary current flows between the electrodes;
A gas density / pressure calculating means for obtaining the gas density or pressure in the cylinder at the ignition timing;
A gas flow rate calculating means for obtaining a gas flow rate in the cylinder at the ignition timing;
Threshold calculating means for obtaining a discharge time threshold corresponding to the limit gap length based on the in-cylinder gas density or pressure at the ignition timing and the in-cylinder gas flow velocity at the ignition timing;
Determining means for determining whether or not the discharge time is equal to or less than the threshold;
An ignition device for an internal combustion engine comprising: In an ignition method for an internal combustion engine that generates a discharge voltage between electrodes of an ignition plug connected to a secondary coil by energizing and interrupting a primary current to the primary coil of the ignition coil,
Detecting the discharge time during which a secondary current flows between the electrodes,
Find the gas density in the cylinder at the ignition timing,
Find the gas flow rate in the cylinder at the ignition timing,
Estimating the gap length between the electrodes based on the in-cylinder gas density at the discharge time and ignition timing and the in-cylinder gas flow velocity at the ignition timing;
Ignition method for internal combustion engine. In an ignition method for an internal combustion engine that generates a discharge voltage between electrodes of an ignition plug connected to a secondary coil by energizing and interrupting a primary current to the primary coil of the ignition coil,
Detecting the discharge time during which a secondary current flows between the electrodes,
Find the gas pressure in the cylinder at the ignition timing,
Find the gas flow rate in the cylinder at the ignition timing,
Estimating the gap length between the electrodes based on the in-cylinder gas pressure at the ignition time and the in-cylinder gas flow velocity at the ignition timing,
Ignition method for internal combustion engine.

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